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Evaluating Generator Mechanical and Electrical Specifications | Electric Generator | Insulator (Electricity)
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Generators Evaluating Generator Mechanical and Elec tr ic al Spec if ic ations
INTRODUCTION ............................................................................................................. 6 FACTORS AFFECTING GENERATOR SELECTION ..................................................... 8 Standards ............................................................................................................. 8 NEMA MG-1............................................................................................... 8 17-SAMSS-510 .......................................................................................... 8 SAES-P-114, Chapter 5 ............................................................................. 9 ANSI/IEEE Standard C37.101-1985 ........................................................ 10 ANSI/IEEE Guide C37.102-1987 ............................................................. 10 Types of Systems ............................................................................................... 10 Standby Systems ..................................................................................... 10 Primary Supply......................................................................................... 12 Operational Parameters...................................................................................... 13 Rated Voltage .......................................................................................... 13 Rated Frequency...................................................................................... 14 Rated Speed ............................................................................................ 15 Voltage and Frequency Variations During Operation.............................. 17 Overspeed Rating .................................................................................... 18 Overload Capability.................................................................................. 19 Short Circuit Withstand ............................................................................ 19 Unbalanced Capabilities .......................................................................... 21 Site and Environmental Conditions..................................................................... 22 Dirt ........................................................................................................... 22 Ambient Temperature .............................................................................. 23 Humidity ................................................................................................... 24 Elevation .................................................................................................. 24
SELECTING GENERATOR TECHNICAL CONSTRUCTION REQUIREMENTS ......... 25 Environmental Protection and Enclosure Types ................................................. 25 Open, Drip-Proof, Weather-Protected Types I & II ................................. 25 Totally Enclosed....................................................................................... 27 Stator .................................................................................................................. 33 Mush Wound............................................................................................ 33 Form Wound ............................................................................................ 35 Rotor ................................................................................................................... 37 Laminated-Type ....................................................................................... 37 Solid-Type................................................................................................ 38 Bearings.............................................................................................................. 40 Sleeve ...................................................................................................... 40 Anti-Friction .............................................................................................. 42 Insulation Class and Temperature Rise.............................................................. 45 Exciter Types ...................................................................................................... 47 Direct Current........................................................................................... 47 Alternating Current ................................................................................... 47 Automatic Voltage Regulator .............................................................................. 49 Field Excitation for Exciters...................................................................... 49 Direct alternator excitation ....................................................................... 51 GENERATOR MINIMUM PROTECTION REQUIREMENTS ........................................ 53 Introduction ......................................................................................................... 53 Electrical Protection ............................................................................................ 53 Overload Protection ................................................................................. 53 Phase Fault Protection............................................................................. 57 Ground Fault Protection ........................................................................... 59
Instrumentation and Alarms................................................................................ 61 Small Generators ..................................................................................... 61 Large Generators..................................................................................... 62 WORK AID 1: RESOURCES USED TO DETERMINE IF GENERATOR TECHNICAL CONSTRUCTION SPECIFICATIONS ARE CORRECT............................................................................................. 63 Work Aid 1A: NEMA MG-1 ................................................................................ 63 Work Aid 1B: 17-SAMSS-510............................................................................ 67 Work Aid 1C: Applicable Evaluation Procedures............................................... 67 WORK AID 2: RESOURCES USED TO SELECT GENERATOR MINIMUM PROTECTION REQUIREMENTS................ 71 Work Aid 2A: ANSI/IEEE Standard C37.101-1985............................................ 71 Work Aid 2B: ANSI/IEEE Standard C37.102-1987............................................ 73 Work Aid 2C: SAES-P-114 (25 APR 94), Chapter 5.......................................... 75 Work Aid 2D: 17-SAMSS-510............................................................................ 75 Work Aid 2E: Applicable Selection Procedures ................................................. 75 GLOSSARY................................................................................................................... 85
Figure 1. Single Unit Stand-by Generator.....................................................................11 Figure 2. Multi- Unit Stand-by Generators ....................................................................11 Figure 3. Synchronous Generator Voltage Ratings ......................................................14 Figure 4. Speed Ratings for 60 Hertz Generators ........................................................16 Figure 5. Overspeed Capabilities ..................................................................................18 Figure 6. Maximum Overload Current Capabilities........................................................19
....................................................37 Figure 19.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Elec tr ic al Spec if ic ations Figure 7.....35 Figure 18.............................21 Figure 9...................................33 Figure 16...................................................................................... Form Wound Coil ..34 Figure 17......... Mush Wound Generator Stator Core..... Brush and Slip Ring Excitation .. Automatic Voltage Regulator (Rotating Exciter) .........................................................................................................52 Figure 30..................................................... Round Rotor Retaining Ring and End Turns ...................................39 Figure 21............ Single-Shielded and Double-Shielded Anti-Friction Bearings............ Laminated Salient Pole Rotor...... Static Excitation System .... Hydrogen Seal Rings........ Anti-Friction Bearings ......26 Figure 10.............................................. Air-Cooled Generator Labyrinth Seals............................. Maximum Short Circuit Capabilities....................... Mush Wound Stator Wiring Schematic .. Maximum Unbalanced Capabilities .....44 Figure 25........................................................46 Figure 26.....41 Figure 23............................................................31 Figure 14..............38 Figure 20...........40 Figure 22................................................ Self-Contained Recirculating Generator Cooling System.........................................20 Figure 8...... Cylindrical Sleeve Bearing (Single Insulated)............................................................................................................................................28 Figure 12...............................................47 Figure 27 Brushless Excitation ........43 Figure 24...........50 Figure 29................................ Shaft-Mounted Blowers ................................................................................................................. Air-Cooled Generator...... Hydrogen-Cooled Generator ........................................................................... NEMA MG-1 Insulation Class Temperature Ratings ... Medium Direct-Connected Generator Protection Scheme ................................................... 3600 RPM Open....29 Figure 13.......32 Figure 15.......................48 Figure 28.............................. Spherical-Seat Bearing (Double Insulated) ..................................................55 Saudi Aramco DeskTop Standards iv ............27 Figure 11............. Round Rotor Forging...........................................
..................................................80 Figure 48. IEEE Supplementary Sensitive Ground Fault Protection Scheme ..84 Saudi Aramco DeskTop Standards v .............................................72 Figure 41.............. Emergency Generator One-Line Diagram.......................... Low Resistance Grounding Scheme ............78 Figure 46............... Direct-Connected Generator Protection Scheme .56 Figure 32..................................................................63 Figure 35.........65 Figure 37......................................... High Resistance Grounding.........................82 Figure 49................ Direct-Connected Generators ..................................60 Figure 34............... Temperature Rise for Synchronous Generators....................................77 Figure 45...............Engineering Encyclopedia Generators Evaluating Generator Mechanical and Elec tr ic al Spec if ic ations Figure 31..........................................64 Figure 36... Kilovolt-Ampere and Kilowatt Ratings for Synchronous Generators .......73 Figure 42.............................. Voltage Ratings for Synchronous Generators ...................................... IEEE Ground Fault Protection Scheme 16.............................71 Figure 39............. Large........... Speed Ratings for Synchronous Generators........... Standard MCCB Ampacity Ratings (NEC Article 240-6) ............................ MCCB Interrupting Ratings......66 Figure 38......72 Figure 40..... LVPCB Frame and Sensor Ratings..........79 Figure 47.......................................76 Figure 44.............................................. Large Direct-Connected Generator Protection Scheme........................57 Figure 33......... IEEE Ground Fault Protection Scheme 10.......................... Direct-Connected Generator Protection Scheme..........74 Figure 43.......................... Small Standby/Emergency Generator Phase Fault Protection.......... LVPCB Interrupting Ratings ................ Medium.....
Saudi Aramco DeskTop Standards 6 . The type of system for which the generator is being selected. Generators that are to be used as base load equipment will have economy of operation and low maintenance requirements as primary factors affecting selection. Generators can be divided into two categories based on the type of service for which they will be used. Generators that are to be used as stand-by equipment must have auxiliary systems and a prime mover that have fast start capabilities and a high degree of short term reliability. The service conditions and type of loading under which the generator will operate. The parameters for which the generator is designed to operate. the principle factors that affect the selection are: • • • • The standards to which the generator selection must adhere.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Elec tr ic al Spec if ic ations INTRODUCTION When selecting generators. Generators are also selected on the basis of the service conditions under which they will be operating. These are divided into two categories. usual and unusual. depending on the environmental and operating conditions to which they will be subjected.
a generator that will not see much reactive loading can be designed with a PF close to unity. like all other types of electrical equipment. which will make the generator less expensive. it is usually preferable to initiate an alarm on many different abnormal conditions rather than remove the generator from service. overvoltages. and ground fault protection for the following classes of generators: • • • Small standby/emergency generators Medium size direct-connected generators Large size direct-connected generators Note: Selecting protection for unit-transformer connected generators is beyond the scope of this Module. also called reactive load. The type of loading will affect the power factor (PF) rating of the generator. Saudi Aramco (SAES-P-114) specifies protection requirements based on the size and/or application of the generator in the plant electrical system. Saudi Aramco DeskTop Standards 7 . for example. etc. must be protected against many different types of abnormal conditions. Each generator protective scheme will depend on the desired objectives (alarm or shutdown) to be achieved. A generator that will be used where there is a large inductive or capacitive component in the load requirements. they must be protected against all possible damaging conditions. generators. must be designed to operate under these conditions. With regard to protection. This Module will also explain the factors and develop the procedures for selecting overload. unbalance. overcurrents.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Elec tr ic al Spec if ic ations A pertinent factor in the selection of a generator for either of the above-mentioned purposes is the type of loading to which the generator will be applied. Designing a generator with the capability to operate under these conditions can greatly increase the initial cost. On the other hand. The excitation system selected for a generator that is going to be applied to a high reactive load must also be designed with a higher rating. In those installations where an operator is always on site. phase. Where generators are in unattended installations.
• • Section II. packaged generating set. Each of these parts contain descriptions of the applicable synchronous generators in terms of kilovolt-ampere (kVA) and kilowatts (kW) available at the terminals at 0.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Elec tr ic al Spec if ic ations FACTORS AFFECTING GENERATOR SELECTION Standards NEMA MG-1 Two parts in the NEMA MG-1 Standards Publication contain information on the factors applicable to the selection of synchronous generators. Section III. Part 16 defines General Purpose Synchronous Generators (6. three phase. The specification sets minimum requirements for the field experience of these synchronous generators and describes the reference material needed for verification of that field experience. Part 22 in Section III contains tables on frequency and excitation voltage standards for large synchronous generators in addition to the abovementioned factors. manufacturing. and application data. 60 hertz for further incorporation into a skidmounted. These descriptions are given in tabular form along with voltage ratings and speed ratings. 17-SAMSS-510 also lists the modifications (additions or exceptions) required to be used together with NEMA MG-1 and additional requirements for bearings. packaged generating set.25 to 500 kVA). Both Parts 16 and 22 contain standards for tests and performance.25 to 75000 kVA). lubrication and voltage regulators that Saudi Aramco includes in the specifications for synchronous generators that are to be used in a skid-mounted. 17-SAMSS-510 Saudi Aramco Materials System Specification 17-SAMSS-510 defines the minimum technical requirements for synchronous generators rated 125 kVA (100 kW) through 1250 kVA (1000 kW). Part 22 defines Large Synchronous Generators (1. Saudi Aramco DeskTop Standards 8 .8-power factor lagging (overexcited).
diesel-engine driven generators rated at 480 volts.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Elec tr ic al Spec if ic ations SAES-P-114. Chapter 5 defines four categories of generator protection: • Section 5.5000 kVA.4. Chapter 5 Saudi Aramco Engineering Standard (SAES)-P-114 is the mandatory standard that explains the system and equipment protection requirements for the electrical power systems in Saudi Aramco installations.500 kVA. Small Standby/Emergency Generators: Small standby/emergency.5.8000 volts and kVA ratings greater than 1000 but not exceeding 12.5000 kVA. which are part of the Supplements Manual to SAES-P-114. Large Direct-Connected Synchronous Generators: Direct-connected synchronous generators with a voltage rating of 13. The key difference between the two revisions is that the latest revision now specifies the use of solid-state relays versus electromechanical relays. Section 5. Chapter 5 of SAES-P114 explains the protection requirements for generators.3. Section 5. and 5.8 kV or above and a kVA rating greater than 12.1.8 kV or above and a kVA rating greater than 12. Large Unit-Transformer-Connected Synchronous Generators: Large unit-transformerconnected synchronous generators with a voltage rating of 13. In particular. Medium Size Direct-Connected Synchronous Generators: Medium size direct-connected synchronous generators with a voltage rating of 600 to 13. Saudi Aramco DeskTop Standards 9 .2. • • • Figures 5.3.2. are one-line diagrams of the protection schemes for the synchronous generator protection requirements explained in Chapter 5. SAES-P-114. Section 5. Note: The current revision of SAES-P-114 dated 25 April 94 replaces the latest revision dated 1 July 91. 5.
IEEE Guide for Generator Ground Protection.102. presents a review of the generally accepted forms of protection for the synchronous generator and its excitation system. it is a guide. these generators are sometimes assigned a stand-by rating allowing temperature rises up to 25°C above the rating of a continuous-duty operation generator.Single unit. Many critical primary supply auxiliary systems such as the lube-oil system or generator cooling system are dependent on a backup source of AC power. explanation.102 be consulted for additional guidance.101-1985 ANSI/IEEE Standard C37.102 is not a standard.101-1985. When used as a back-up power source. stand-by generator systems are used primarily for emergency back-up systems where the generator will automatically start on a loss of AC power. Figure 1 shows a schematic diagram of a power system utilizing a 500 kVA generator as a single unit. ANSI/IEEE Guide C37. Types of Systems Standby Systems Single Unit Installation .102-1987 ANSI/IEEE Guide C37.101 be consulted for additional guidance. The guide is primarily concerned with protection against faults and abnormal operating conditions for large hydraulic. steam. emergency back-up power source. It also summarizes the use of relays and devices and serves as a guide for the selection of equipment to obtain adequate protection. and definition.1 of SAES-P-114 also specifies that ANSI/IEEE Guide C37. Section 5. specifies the application of relays and relaying schemes for the protection of synchronous generators for single phase-to-ground faults in the stator winding. The guide is not intended for the selection of generator or ground connection schemes. Saudi Aramco DeskTop Standards 10 . explanation. Note: Although often referred to as a standard. and definition of protection schemes.1 of SAES-P-114 specifically requires that ANSI/IEEE Standard C37. and combustion-turbine generators. IEEE Guide for AC Generator Protection. Section 5.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Elec tr ic al Spec if ic ations ANSI/IEEE Standard C37. C37.
Multi-Unit Installation Figure 2.Unit Stand-by Generators Saudi Aramco DeskTop Standards 11 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Title: 21504-1.EPS from CorelDRAW! Creator: CorelDRAW! CreationDate: Mon Jun 19 09:24:09 1995 Figure 1. Multi. where the load requirements may dictate that more than one generator be operated in parallel to meet the demand.Stand-by systems can require a multi-unit installation in situations where redundancy is required to ensure the reliability of the back-up system or. as shown in Figure 2. Single Unit Stand-by Generator .
couplings. the generator manufacturer must furnish the Wk2. The torque requirements of various synchronous motor applications can vary depending on the design of the particular machine and its operating conditions. The moment of inertia (Wk2 ) of the generator rotor is a factor that could affect the torsional vibration of the generator. The P r of the generator should match the load characteristics to which it is connected. and any other information that may be required to allow the correct design of the combined unit. and other rotating parts. Saudi Aramco DeskTop Standards 12 . Lower values may be adequate or higher values may be required. the weight of the generator rotor. Excessive torsional vibration may result in over stressed shafts. Synchronous kilowatts is the power corresponding to the product of torque and synchronous speed. Factors that affect successful parallel operation are: • • Synchronizing torque coefficient (P r) Moment of inertia (Wk2 ) of the generator rotor The synchronizing torque coefficient (P r) is defined as the change in shaft power expressed in synchronous kilowatts per electrical radian of change in displacement angle. when requested. while electrical radians are defined as: Electrical radians = Electrical degrees X (2π /360) Synchronizing torque coefficient (P r) should correspond to a pulsation frequency of one-half the generator's synchronous speed unless otherwise specified.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Primary Supply A generator that is to be used for primary supply must be of such a design that it functions well in parallel operation with other generators. While factors that affect torsional vibration are primarily contained in the design of the prime mover.
the prime mover. Many generators come equipped with variable tap transformers that provide some flexibility in matching the generator to different voltage requirements. and the system to which they are connected. and T3.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Operational Parameters The following operational parameters are factors that must be considered when selecting a generator for service on a particular power system. Saudi Aramco DeskTop Standards 13 . • • • • • • • • Rated Voltage Rated Voltage Rated Frequency Rated Speed Voltage and Frequency Variations During Operation Overspeed Rating Overload Capability Short Circuit Withstand Capability Unbalanced Capabilities Rated voltage on all three-phase. The neutral leads are normally tied together in the lead box of the generator. These are called the line leads and are the high voltage ends of each of the three phases of the generator's stator winding. T5. Failure to give careful consideration to each of these factors will result in unsatisfactory operation and could cause damage to the generator. and T6 respectively. The generator's rated voltage must be matched to the transformer or the power system that it is to supply. Generators are normally connected to a delta-delta or wye-delta step-up transformer for moderate voltages and to a delta-wye step-up and wye-delta step-down transformer for high voltage transmission systems. The opposite end of each phase is called the neutral lead. T2. wye-connected generators is measured from phase to phase at the output terminals T1. and these are designated T4.
Synchronous Generator Voltage Ratings Rated Frequency With regard to the selection of rated frequency of the generator. NEMA MG-1 Standards Publication Part 22. Figure 3. Saudi Aramco DeskTop Standards 14 .14 states that all frequencies shall be 50 or 60 hertz.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 3 shows information from Table 22-3 of Part 22 of the NEMA MG-1 Standards Publication for Large Synchronous Generators that lists generator voltage ratings. Section MG 1-22.
Critical speeds. This rating will determine what type of prime mover will be used to drive the generator. The factor that will determine the speed at which a generator will operate is primarily the size or kVA rating of the generator. including the foundation and by internal and external damping. Saudi Aramco DeskTop Standards 15 . It is preferable that the operating speed be at least 20% away from the nearest critical speed. Torsional critical speed relates to the response of the shaft system to torsional forces. The speed at which a prime mover is most efficient is usually the most important factor in determining a generator's rated speed. Both lateral and torsional critical speeds must be considered. Torsional critical speeds are excited by external forces such as sudden load changes or a short circuit on the system.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Rated Speed The rated speed of the generator and the number of poles on the rotating field determine the frequency at which a synchronous generator will operate. are affected by shaft support. especially lateral. This speed is defined as its synchronous speed. Figure 4 shows information from the NEMA MG-1 Standards Publication for Large Synchronous Generators that lists the speed ratings for 60 hertz generators based on the number of poles on the rotating field. The shaft system of the entire unit for both the generator and prime mover must be designed with the unit's critical speed in mind. Low speed rotors usually operate below the first critical speed. Lateral critical speed is the speed corresponding to the natural frequency of the shaft system in response to lateral or transverse forces such as a residual unbalance. High speed rotors such as two and four pole rotors often operate above the first critical speed. It is important that these rotors be carefully balanced so that the stresses on them are not excessive while passing through the critical speeds on start-up and shutdown.
Speed Ratings for 60 Hertz Generators Saudi Aramco DeskTop Standards 16 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 4.
frequency. the more expensive the governor and. As previously mentioned. These factors include: • • • • Generator size Type of service Load range Type of load These factors influence the cost of the governor. As the load is increased or decreased on the generator.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Voltage and Frequency Variations During Operation The NEMA MG-1 Standards Publication for Large Synchronous Generators states on Page 6 of Part 22 that "Synchronous generators shall operate successfully at rated kVA. The degree of sophistication of the governor supplied with the prime mover is dependent on a number of factors. the amount of fuel being fed to the prime mover must be increased or decreased by the same amount. Saudi Aramco DeskTop Standards 17 . The more sophisticated the system requirements. The purpose of the governor is to provide speed regulation." The publication gives no allowed margin for frequency variation because this can have an adverse affect on frequency-sensitive equipment to which the generator is supplying power. the more expensive the entire generator set . thereby keeping the generator frequency constant. therefore. the kVA rating and type of service for which the generator is being ordered will determine the type of prime mover best suited for the application. The prime mover must have a governor capable of maintaining it at a constant synchronous speed over the entire load range of the generator. This form of control is called speed regulation. and power factor at any voltage not more than 5 percent above or below the rated voltage of the generator.
All rotating components must be designed to withstand the centrifugal forces created by this overspeed to prevent damage to the unit. Figure 5 shows the percent overspeed required by the NEMA standard based on the synchronous speed of the generator. and the rotating exciter (if one is used to supply the generator) to rapidly increase until the governor can reduce the flow of fuel or steam to the prime mover and slow the unit down.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Overspeed Rating When a generator is operating at or close to its rated capacity (commonly called full load). If something on the system should cause the generator to trip off-line. Overspeed Capabilities Saudi Aramco DeskTop Standards 18 . This action causes the rotational speed of the prime mover. the generator. The NEMA MG-1 Standards Publication for Large Synchronous Generators. Part 22. the load on the prime mover is instantly removed. Synchronous Speed (RPM) 1801 and over 1800 and below % Overspeed of Synchronous Speed 20 25 Figure 5. Page 6 specifies that synchronous generators shall be constructed in such a manner as to be able to withstand an overspeed of not greater than one minute duration without mechanical damage. the generator's prime mover is at full throttle.
relays are used to trip the generator in extreme cases. This type of short circuit could result during generator operation from a conductive coating contaminating the main lead bushings of the generator or from a catastrophic failure in a three-phase transformer connected directly to the generator main leads.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Overload Capability When a generator is on-line. In addition. Page 4 specifies that synchronous generators shall be capable of carrying a one minute overload with the field set for normal rated load excitation in accordance with the information shown in Figure 6. and excitation system. a shop test employing this type of short circuit is used to determine generator parameters. Maximum Overload Current Capabilities Short Circuit Withstand A short circuit occurring directly at the terminals of a generator will place maximum stress on the generator's stator winding. a fault such as a short circuit anywhere in the system will cause an overload on the generator. To protect against this condition. This overload can cause the current in one phase or all three phases. The NEMA MG-1 Standards Publication for Large Synchronous Generators. Synchronous Speed (RPM) 1801 and over 1800 and below Armature Current % of Normal Rated Current 130 150 Figure 6. Under controlled conditions. depending on the system to which it is connected. Part 22. to increase above the generator's rated capacity. field winding. NEMA standards specify the capability to which generators must be built to withstand such overloads and not incur damage to any of their components. Saudi Aramco DeskTop Standards 19 .
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications With regard to this type of short circuit. Maximum Short Circuit Capabilities Saudi Aramco DeskTop Standards 20 . without injury. provided: • The machine phase currents under fault conditions are such that the negative phase sequence current (I2). a thirty second. any other short circuit at its terminals of thirty seconds or less. and • The maximum phase current is limited by external means to a value which does not exceed the maximum phase current obtained from a three-phase fault. three-phase short circuit at its terminals when operating at rated kVA and power factor at five percent over-voltage with fixed excitation. Type of Generator Permissible [(I2)2t] Product 40 Salient Pole Machines Air-Cooled Cylindrical Rotor Machines 30 Figure 7. The generator shall also be capable of withstanding. and the duration of the fault in seconds (t) are limited to the values which give an integrated product [(I2)2t] equal to or less than the values shown in Figure 7. the NEMA MG-1 Standard states that a synchronous generator shall be capable of withstanding. expressed in per-unit of stator current at rated kVA. without injury.
providing the rated kVA is not exceeded and the maximum current does not exceed 105 percent of the generator's rated stator current in any phase.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Unbalanced Capabilities A three-phase generator is designed to operate with equal current flow in each phase of the stator winding. which in turn would produce pulsating air gap torques that could eventually fatigue the mechanical components of the generator and prime mover. Note: The negative-phase-sequence currents shown in Figure 8 are expressed as a percentage of rated stator current. If the impedance of one phase was to change. Type of Generator Permissible (I2) Percent 10 Salient Pole with Connected Amortisseuir Winding Salient Pole with Non-Connected Amortisseuir Winding Air-Cooled Cylindrical Rotor 5 10 Figure 8. the effects of a continuous current unbalance corresponding to a negativephase-sequence current (I2) of the values shown in Figure 8. This unbalance would induce double frequency currents on the rotor surface and field windings. The NEMA MG-1 Standard states that a synchronous generator shall be capable of withstanding. an unbalanced current flow would result. without injury. Maximum Unbalanced Capabilities Saudi Aramco DeskTop Standards 21 .
Machines conforming to NEMA MG-1 Part 22 are designed for operation in accordance with their ratings under usual service conditions. Site and Environmental Conditions Synchronous generators should be properly selected with regard to the site and environmental conditions. causing the conducting components of the stator and rotor to be covered with this contamination. called service conditions in NEMA MG-1. The following factors can constitute unusual service conditions. Continuous performance with non-connected amortisseur windings is not readily predictable. usual or unusual. This contamination can. under which they will be operating. Therefore.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications The values shown in Figure 8 also express the negative-phasesequence current capability at reduced generator kVA capabilities as a percentage of the stator current corresponding to the reduced capability. requiring the utilization of a generator designed for operation in these conditions: • • • • Dirt Dirt Ambient Temperature Humidity Elevation Dirt or other forms of airborne contamination can be drawn into an open. These service conditions are divided into two categories. become conductive. air-cooled generator by the machine's ventilation system. causing a breakdown of the generator's insulating components that could cause significant damage to the generator. machines with connected amortisseur windings should be specified. if unbalanced conditions are anticipated. thereby decreasing the cooling efficiency of the ventilation system. under certain circumstances. Saudi Aramco DeskTop Standards 22 .
Generators Evaluating Generator Mechanical and Electrical Specifications
In many applications where airborne contamination is present, filters are used at the intakes of the ventilation system to remove dirt and contaminants. When filters are employed for this purpose, care must be taken that the filters do not become clogged, causing a reduction in the flow of cooling air that will result in the generator overheating.
In applications where there is the possibility of the generator having to operate in a high ambient temperature environment, three systems require special attention: • • • The generator's cooling or ventilation system The generator's lube-oil system The generator's electrical insulation system
High ambient temperatures require a cooling system with oversized capacity and a greater than normal volume of cooling air to compensate for the higher inlet air temperatures. Oil flow to the bearings may need to be increased to keep the bearings within normal operating temperatures, and the generator's lube-oil system may need extra cooling to keep the oil temperature within normal operating limits. The third system that may require special attention in a high ambient temperature environment is the electrical insulation system. Material Specification 17-SAMSS-510 specifies that Class F insulation, which is rated for a temperature rise of over 100°C, be used on generators being manufactured for Saudi Aramco. If a generator is consistently operated at temperatures above that of its insulation rating, the useful life of that insulation will be greatly decreased.
Synchronous generators that operate in areas of high humidity should be equipped with space heaters to keep the temperature of the stator and rotor windings above the dew point when the unit is not in operation. Moisture forming on these components could cause low insulation resistance values resulting in a flashover on either the rotor or stator winding that could cause a forced outage of the unit.
Air-cooled synchronous generators operating in the reduced air density of higher altitudes would require a more efficient, higher volume cooling system to compensate for the reduced cooling capacity of the thinner air.
SELECTING GENERATOR TECHNICAL CONSTRUCTION REQUIREMENTS Environmental Protection and Enclosure Types
Open, Drip-Proof, Weather-Protected Types I & II
Open, drip-proof, weather-protected generators, also called guarded generators, are defined as machines that are constructed in such a way that all openings giving direct access to live metal or rotating parts (except smooth rotating surfaces) are limited in size by the structural parts or by screens, baffles, grills, expanded metal, or other means to prevent accidental contact with hazardous parts. Openings giving direct access to such live or rotating parts shall not permit the passage of a cylindrical rod 0.75 inches or greater in diameter. weather-protected generators are open machines with ventilating pas-sages constructed to minimize the entrance of rain, snow, and air-borne particles to the electric parts.
Type l ll weather-protected generators have their ventilating passages at both intake and discharge arranged so that high velocity air and air-borne particles blown into the machine by storms or high winds can be discharged without entering the internal ventilating passages leading directly to the electric parts of the machine itself. Type II generators also use the same weatherprotected enclosures as Type I generators. As shown in Figure 9, the normal path of the ventilating air which enters the electric parts of the Type II machine is diverted by baffling or separate housings to provide at least three abrupt changes in direction, none of which are less than 90 degrees. In addition, an area of low velocity not exceeding 600 feet per minute is provided at the intake air path to minimize the possibility of moisture or dirt being carried into the electric parts of the machine. Type
Title: 21504-9.EPS from CorelDRAW! Creator: CorelDRAW! CreationDate: Mon Jun 19 11:15:17 1995
Figure 9. 3600 RPM Open, Air-Cooled Generator
Labyrinth seals with extremely close clearances shown in Figure 11 are commonly used between the rotating and the stationary components to prevent oil vapors from the bearing housings from entering the stator frame and to minimize the exchange of internal cooling air and outside ambient air. but not sufficiently enclosed to be termed air-tight. Figure 10.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Totally Enclosed A totally-enclosed machine as shown in Figure 10 is a generator constructed to prevent the free exchange of air between the inside and the outside of the frame. Self-Contained Recirculating Generator Cooling System Saudi Aramco DeskTop Standards 27 .
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 11. Air-Cooled Generator Labyrinth Seals Saudi Aramco DeskTop Standards 28 .
air-to-air-cooled generator is cooled by circulating the generator's internal air through a heat exchanger that. integral with the rotor shaft as shown in Figure 12.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications A totally-enclosed. is cooled by circulating external air. A fan or fans. The generator's internal air is circulated across the finned tubes by a fan or fans. circulate the internal air within the enclosed generator and through the heat exchanger. is cooled by water that is pumped through finned tubes in the heat exchanger. integral with the rotor shaft or separate. Air-to-Air - Figure 12. or separate from the shaft. air-to-water-cooled generator is cooled by circulating the generator's internal air through a heat exchanger that. and a fan or fans external to the generator frame and integral with the rotor shaft or separate. in turn. Air-to-Water - Saudi Aramco DeskTop Standards 29 . in turn. circulate external air through the heat exchanger. Shaft-Mounted Blowers A totally-enclosed.
the former requires no supplementary cooling system. The open-type is obviously the most economical generator in terms of initial cost. A totally-enclosed system. with its recirculated internal cooling air eliminates the problem of airborne contamination. H2-cooling requires a sophisticated seal oil system. aircooled generator.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications In contrasting an open-type generator to a totally-enclosed. However. H2 has the following disadvantages: • H2 is explosive when mixed with air in a ratio of 5 to 70 percent air. this type of system costs more due to the heat exchanger and external air circulating equipment. to keep the gas from escaping around the openings in the frame for the rotor. causing less friction and less energy expended to circulate it through the generator. but the likelihood of increased maintenance is much greater with an open cooling system. H2 readily picks up heat in the generator and gives up heat in the heat exchangers or coolers. A gas-cooled generator as shown in Figure 13 uses hydrogen gas (H2) for its internal cooling medium. H2 has two advantages over air that makes it a more efficient internal cooling medium in synchronous generators: Gas-Cooled - • H2 is lighter than air. • Saudi Aramco DeskTop Standards 30 . especially if it is operating in an area prone to airborne contamination that can be ingested by the cooling system and deposited on the components of the generator. but is prone to pick up dirt and contamination from the cooling air passing through the components of the generator. • Conversely. shown in Figure 14. This system also limits the mobility of the generator and requires more space dedicated to the machine and its auxiliaries.
Hydrogen-Cooled Generator Saudi Aramco DeskTop Standards 31 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Title: 21504-13.EPS from CorelDRAW! Creator: CorelDRAW! CreationDate: Mon Jun 19 11:16:23 1995 Figure 13.
EPS from CorelDRAW! Creator: CorelDRAW! CreationDate: Mon Jun 19 11:17:05 1995 Figure 14. Hydrogen Seal Rings Saudi Aramco DeskTop Standards 32 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Title: 21504-14.
The conductors are insulated from each other and from the core. Many coils will be wound in the same manner and then connected together to make the stator winding. 17-SAMSS-510 contains an addition to the NEMA MG1 Standard for Synchronous Generators.40.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Stator Mush Wound Figure 15 shows a schematic wiring diagram of a mush wound stator. specifying that Class F insulation be used in applications where the NEMA standard allows insulation with a lower temperature rating and that limits be placed on the temperature rise to which these machines can be subjected in normal operation. Section 22. The core is normally at ground potential. The mush wound stator is composed of a series of wire conductors wrapped into an iron core. Figure 16 shows a typical mush wound coil being placed in the slots of the laminated core of a small generator stator. Mush Wound Stator Wiring Schematic Saudi Aramco DeskTop Standards 33 . The insulation is of relatively low dielectric strength. Figure 15.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 16. Mush Wound Generator Stator Core Saudi Aramco DeskTop Standards 34 .
or as half coils and consist of a number of individually insulated copper strands that are then separated and insulated into groups in the case of multi-turn coils or coils with transposition connections on one end. Form wound coils can be manufactured as full coils as shown in Figure 17. The groups of strands are then insulated from the generator core by ground wall insulation. Figure 17. Form Wound Coil Saudi Aramco DeskTop Standards 35 . The ground wall insulation is of very high dielectric strength.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Form Wound Form wound coils are generally used in stators with higher voltage and power ratings.
Mush wound stators are more prone to be adversely affected by dirt and contamination deposited on them by the cooling air. An example frame designation is 8-75. Some manufacturers provide a unique frame designation number for each stator as a form of identification. The third number indicates the length of the stator core in inches from finger plate to finger plate (64 inches). Westinghouse gives each stator that it manufacturers a frame designation that consists of three sets of numbers. but they have the disadvantage of being limited in their power capabilities. Form wound stators have the disadvantage of being heavier in construction and are more expensive than mush wound stators. the first number indicates the number of poles on the rotating field (8 poles). These points of reference are indicated on the cross-section drawing of the hydrogen-cooled generator shown in Figure 13. Saudi Aramco DeskTop Standards 36 . The frame designation number gives pertinent information about the stator. For example.5X64.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications The advantage of mush wound stators is that they are smaller and lighter than form wound stators. In this example.5 inches). The second number indicates the diameter of the stator core in inches from through bolt to through bolt (75. but they have the advantage of much greater voltage and power capabilities and will withstand abuse much better than mush wound stators.
This style of rotor. is typically found on smaller. a problem that can manifest itself in the slower speed machines that have a large number of poles and a relatively small air gap. Laminated Salient Pole Rotor Saudi Aramco DeskTop Standards 37 . the poles of which are made of laminated steel to improve the flux pattern emanating from the field winding that is wound around the laminated pole. Figure 18. shown in Figure 18. slow speed generators. The advantage of a salient pole rotor is that the laminated poles reduce the eddy-current losses at the pole faces.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Rotor Laminated-Type A laminated-type rotor is a salient pole rotor.
This design provides a more rigid support for the longer. The round design of the rotor also has the advantage of creating less friction at higher speeds. Figure 19. The endturns of the field winding are supported by the use of retaining rings shrunk onto each end of the rotor. heavier copper conductors used in the field winding of larger generators. Generators with solid-type rotors are normally horizontal as shown in Figures 13 and 20.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Solid-Type Solid-type rotors. This type of rotor construction is shown in Figure 20. Generators with solid-type rotors also have a larger air gap that reduces the problem of eddy-current losses on the pole faces. high speed generators with synchronous speeds of 1500 or 3000 rpm for 50 hertz machines and 1800 or 3600 rpm for 60 hertz machines. are used on larger. Round Rotor Forging Saudi Aramco DeskTop Standards 38 . also called round rotors. The solid rotor is designed to have the field windings wound into slots that are machined into the rotor body as shown in Figure 19.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 20. Round Rotor Retaining Ring and End Turns Saudi Aramco DeskTop Standards 39 .
In a sleeve bearing the shaft rides on a film of oil approximately .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Bearings Sleeve Sleeve bearings are generally used on generators that have heavier.003 inches thick. which is a soft. porous metal alloy that retains the bearing lubricating oil. Cylindrical bearings are the most common type of sleeve bearing. larger diameter rotors. eliminating any metal-to-metal contact. Figure 21 shows a cylindrical bearing consisting of a cast iron shell lined with babbitt. There are two types of sleeve bearings: cylindrical and spherical-seat type. Figure 21. Cylindrical Sleeve Bearing (Single Insulated) Saudi Aramco DeskTop Standards 40 .
Figure 22. they differ from sleeve bearings in that the rotor rides on two babbitted shoes and not on a continuous sleeve. The babbitted surfaces of both of these sleeve-type bearings are oil-lubricated by either a self-lubrication or forced-flood lubrication system. As shown in Figure 22.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Spherical-seat bearings are self-aligning and are commonly used in smaller. Spherical-Seat Bearing (Double Insulated) Saudi Aramco DeskTop Standards 41 . single-bearing generators.
used on smaller generators. Ball bearings. This condition prevents testing of the insulation when a single-insulated bearing is used. the ball bearings will roll in the raceways with little or no friction when the shaft rotates. Both bearings rest on insulated bearing seats. Roller bearings are cylindrical in shape as shown in Figure 23B. the generator rotor and the frame are both at ground potential. If kept clean and properly lubricated. This pressure can be supplied by a shaft-driven oil pump or by a separate motor-driven oil pump. as the name implies. ball bearings and roller bearings. Figure 21 shows a cross-section view of the cylindrical bearing resting on a singleinsulated bearing seat. The rings have grooves called raceways machined into them in which the ball bearings roll. Anti-Friction Anti-friction bearings. The housing has an oil gauge to monitor the level of the oil. rotate through an oil bath in the bottom of the bearing housing. are constructed and function in the same manner as ball bearings.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Self-lubrication systems rely on oil rings that are fitted loosely around the shaft journals and. Double insulation allows the bearing insulation to be tested while the generator rotor is coupled to the prime mover. Saudi Aramco DeskTop Standards 42 . Forced-flood lubrication systems have the oil supplied under pressure to the bearing surfaces. usually mounted on an oil reservoir. Figure 22 shows the spherical seat bearing resting on a double-insulated seat. The inner ring is pressed onto the rotating shaft. deep groove ball bearing shown in Figure 23A will sustain a substantial thrust load in either direction in addition to the radial load. come in two varieties. steel balls contained in circular guides called rings. and the outer ring is pressed into the frame of the generator. The rings pick up the oil and deposit it on the journal to lubricate the bearing. They are generally used in heavier radial loading applications. but other than that. are composed of round. When the generator and prime mover are coupled. The single row. due to the rotation of the shaft.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 23. Anti-Friction Bearings Saudi Aramco DeskTop Standards 43 .
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Anti-friction bearings are usually lubricated with grease applied by a grease gun directly to the bearing through a grease fitting on the housing. Note: 17-SAMSS-510 requires anti-friction bearings to be of the double shielded type. Many styles of anti-friction bearing housings are supplied with shields to prevent foreign matter from contaminating the bearing and to retain bearing lubrication. This procedure should be performed only when the unit is not running. Figure 24. Sealed bearings should be specified for applications where there is the possibility of airborne contaminants getting into the bearings. Figure 24 shows an example of an anti-friction bearing with various shield combinations that are available. Single-Shielded and Double-Shielded Anti-Friction Bearings Saudi Aramco DeskTop Standards 44 .
continuous duty basis.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications When comparing the advantages and disadvantages of sleevetype bearings to anti-friction bearings. sleeve-type bearings are able to withstand more loading and punishment than anti-friction bearings if kept properly lubricated. The insulation class determines the temperature rise that an insulation system can withstand on a normal. sleeve-type bearings require a more sophisticated and costly lubrication system than anti-friction bearings. Standards Publication for Synchronous Generators. The 17-SAMSS-510 specification also places limitations on generator temperature rise for normal operation that are more stringent than the NEMA Standard limitations. Saudi Aramco DeskTop Standards 45 . 17-SAMSS-510 supersedes the NEMA standard by specifying that Class F insulation will be used in all applications. Insulation Class and Temperature Rise There are four standard classes of insulation listed in the NEMA MG-1. Figure 25 lists these temperature rise ratings along with the component on which the temperature is being measured and cautions that should be observed. Due to the high ambient temperatures likely to be encountered by Saudi Aramco. However.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Class of Insulation System (See MG 1-1. The temperatures attained by cores. Degrees C 1. Note 3: Temperature rises in the above table are based upon generators rated on a prime power continuous duty basis. brushes.9 (Tc . 90°C. recommended values of ambient temperature are 50°C. etc.85).Ta) where Ta = ambient temperature Tc = 105°C for Class A insulation system 130°C for Class B insulation system 155°C for Class F insulation system 180°C for Class H insulation system When a higher ambient temperature than 40°C is required. Suggested Standard for Future Design 11-12-1981. NEMA MG-1 Insulation Class Temperature Ratings Saudi Aramco DeskTop Standards 46 . Generators intended for use in higher ambient temperatures should have temperature rises not exceeding the value calculated from the formula below. NEMA Standard 11-20-1986. amortisseur windings.) shall not injure the insulation or the machine in any respect. Armature windings-resistance 60 80 105 125 2. and 115°C. In such cases. collector rings. Authorized Engineering Information 11-12-1981. see MG 1-14-04. Field windings-resistance 60 80 105 125 3. revised 11-20-1986. Note 2: The temperature rises given in the above table are based upon a reference ambient temperature of 40°C. special considerations should be given to bearing temperatures. rounded off to the nearest 5 degrees: temperature rise = 0. etc. 65°C. and miscellaneous parts (such as brushholders.65) A B F* H* Time Rating-Continuous Temperature Rise. Note 1: The foregoing values of temperature rise are based upon operation at altitudes of 3300 feet (1000 meters) or less. *Where a Class F or H insulation system is used. Figure 25. For temperature rises for generators intended for operation at altitudes above 3300 feet (1000 meters). lubrication. Synchronous generators may be rated on a standby duty basis (see MG 1-16. it is recommended that temperature rises not exceed those in the foregoing table by more than 25°C under continuous operation at the standby rating.
carbon dust-producing device that limits the power that can be obtained from an excitation system. One style. The DC current is then supplied to the generator rotor through carbon brushes and collector rings. Alternating Current Alternating current exciters are available in two styles. as shown in Figure 26. Figure 26. The commutator is a high maintenance.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Exciter Types Direct Current Direct current exciters use a mechanical rectifier called a commutator to convert the AC voltage developed on the rotating armature to usable DC field current for the generator rotor. Brush and Slip Ring Excitation Saudi Aramco DeskTop Standards 47 . DC exciters are no longer manufactured. For this reason. uses slip rings to put DC current on the rotating field of the exciter and then uses a stationary solid state rectifier to convert the AC voltage induced into the stationary armature to DC.
this exciter uses a rotating rectifier to convert the AC voltage developed on the rotating armature to usable DC field current for the generator rotor. Figure 27 Brushless Excitation Saudi Aramco DeskTop Standards 48 . This style of exciter eliminates the need for slip rings on the exciter armature or collector rings on the generator rotor. As shown in Figure 27.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications The second style of AC exciter is called brushless.
controls the field current in the generator rotor.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Automatic Voltage Regulator Field Excitation for Exciters The AC voltage produced on a generator stator is a function of the number of kilolines of flux emanating from the field winding on the rotor and crossing the stator winding as the rotating field is spun by the prime mover. This function can be performed in either a manual or an automatic mode. Saudi Aramco DeskTop Standards 49 . which in turn. in turn. The voltage regulator also contains limiters and other protective devices to trip the generator to prevent it from being damaged by a fault on the power system to which it is connected. controls the amount of current flowing through the generator field winding. control the voltage on the rotating armature. This flux density is proportional to the amount of field current flowing in the field windings of the rotor. The function of the voltage regulator is to provide the operator with a means of control and regulation of the current in the exciter's stationary field poles. and the voltage. The stationary field poles on the exciter. as illustrated in Figure 28.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 28. Automatic Voltage Regulator (Rotating Exciter) Saudi Aramco DeskTop Standards 50 .
60 hertz. also called static excitation. uses power fed back from the output of the main generator through an excitation transformer to the voltage regulator as shown in Figure 29. is rectified to DC and regulated to meet the voltage demands on the generator. The voltage is then fed to the generator's rotating field windings through carbon brushes and collector rings that are mounted on the end of the generator rotor.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Direct alternator excitation Direct alternator excitation. the voltage which is typically 600 volts. In the voltage regulator. Saudi Aramco DeskTop Standards 51 . 3 phase.
Static Excitation System Saudi Aramco DeskTop Standards 52 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Title: 21504-29.EPS from CorelDRAW! Creator: CorelDRAW! CreationDate: Mon Jun 19 11:24:36 1995 Figure 29.
. The operator then has a choice to shed load or initiate shutdown.RTDs) that may be used in a bridge circuit to provide sensing intelligence to an indicator or a relay (e.500 kVA). for example. medium size directconnected generators (600 . which subsequently trips an alarm circuit.500 kVA). regardless of generator size. and large size directconnected generators (greater than 13. Protection of large unit-transformer-connected generators are beyond the scope of this Module. indicating low machine temperature. 130°C for Class B insulated machines at 50°C.800 V. This Module will describe specific ANSI/IEEE Standard C37 and SAES-P-114 protection schemes for small standby/emergency generators (480 V. an ABB DT-3 relay).01 explained each of the various generator electrical protection requirements in detail. the bridge becomes unbalanced and the contact closes. kVA greater than 1000 kVA but less than or equal to 12. Introduction EEX 215. The relay has contact-opening torque when the resistance is low.800 V and 12.g.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications GENERATOR MINIMUM PROTECTION REQUIREMENTS Note: Refer to Work Aid 2 for the procedures to select minimum generator protection requirements. Electrical Protection This section will describe the following protection requirements for generators: • • • Overload Protection Overload Protection Phase Fault Protection Ground Fault Protection Most generators are equipped with embedded detectors (resistance temperature detectors . 1000 kVA or less). When the temperature of the machine exceeds.13. Saudi Aramco DeskTop Standards 53 .
.e. and an alarm is activated. The same specification also requires that the RTDs shall be platinum. See Figure 30. and when the winding temperature exceeds the specified limits. 100 Ω at 0°C. The RTDs shall also be platinum similar to the RTDs specified for small standby/emergency generators. NEMA MG-1 requires. 130°C in a 50°C ambient environment. should be built-in and provided by the generator manufacturer. i.. not just overload protection. as a minimum. Saudi Aramco DeskTop Standards 54 . Medium Size Generators Large Size Generators. similar to medium size generators. Small Standby/Emergency Generators - 17-SAMSS-510 requires 2 RTDs per phase for generators rated above 500 kVA (400 kW at 0. All medium size generators require two RTDs per phase for overload protection. an alarm is activated. i. When the temperature of the generator exceeds the specified limit. See Figure 31. the contacts close on the relay. SAES-P-114 implies that all protection for small standby/emergency generators.e.80 PF). The RTDs protect the stator winding of the generator.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications RTDs are built into the generator during construction at points which are inaccessible after the generator is built. require two platinum RTDs per phase. three detectors for a three-phase machine. one RTD per phase.
Medium Direct-Connected Generator Protection Scheme Saudi Aramco DeskTop Standards 55 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 30.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Title: 21504-31.EPS from CorelDRAW! Creator: CorelDRAW! CreationDate: Mon Jun 19 11:26:55 1995 Figure 31. Large Direct-Connected Generator Protection Scheme Saudi Aramco DeskTop Standards 56 .
or low voltage power circuit breakers (LVPCB) rated at 100% of the generator’s fullload amperes. See Figure 32.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Phase Fault Protection Small Standby/Emergency Generator phase fault protection is provided by molded case circuit breakers (MCCB) rated at 125% of the generator’s rated full-load amperes. Figure 32. Small Standby/Emergency Generator Phase Fault Protection Saudi Aramco DeskTop Standards 57 .
Large Size Generator Saudi Aramco DeskTop Standards 58 . that simultaneously trips the same devices as the ANSI Device 86G1 relay except for CO2 fire protection. In some applications the differential relay also trips the throttle and admits CO2 to the generator for fire protection. See Figure 30. the relay would not respond at all for sustained fault currents under “stuck regulator” conditions. and neutral breakers (if used) simultaneously using a manually reset lockout auxiliary relay (ANSI Device 86G1). If set high. Ordinary relays cannot be used because if set low to protect the generator for sustained fault currents (possibly less than FLA). See Figure 30. See Figure 31. The overcurrent relay also make use of a manually reset lockout relay (ANSI Device 86G2). field circuit. the generator would trip on normal loads or small overloads. phase fault protection is identical to the protection provided for medium size generators except that an additional level of protection is provided by an overall differential protection relay (ANSI Device 87U). Generator differential relays are usually arranged to trip the generator. Medium Size Generator Overcurrent relays (ANSI Device 51V) that are used for backup phase fault protection are specifically constructed to make the operating characteristics a function of voltage as well as current.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications internal phase fault protection is provided by differential relays (ANSI Device 87G) (Figure 30).
17-SAMSS-510 does specify that solid-state trip (SST) ground units should be provided when zone-selective interlocking is installed on the feeder circuits supplied by the generator. the phase fault protective device. Low Resistance-Grounded Generators - Medium size direct-connected generators use a simple overcurrent relay (ANSI Device 51N) installed in the neutral of the generator (Figure 30). Unless separate ground fault protection is provided by the generator manufacturer. Generators .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Ground Fault Protection Ground fault protection schemes for generators are determined by the type of grounding system that is used for the generator.17-SAMSS-510 specifies that standby/emergency generators be solidly-grounded wyeconnected. SAES-P-114 does not specify a type of ground fault protection scheme for these solidly-grounded standby/emergency generators. The SAES-P-114 specified method for grounding large unit-transformer-connected generators is high resistance grounding (Figure 33). provides more sensitive ground fault differential protection than the phase fault differential device 87G. Large size direct-connected generators use the same ground fault device (51N) as the medium size generators plus two additional sets of ground fault relays. however. also provides the ground fault protection. ANSI Device 87GN. One set (ANSI Device 50GS) provides start-up ground overcurrent protection and the other set. Power Distribution Department. an MCCB or LVPCB as illustrated in Figure 32. Solidly-Grounded The SAES-P-114 specified method of grounding for both medium and large direct-connected generators is low resistance grounding. High Resistance-Grounded Generators - Saudi Aramco DeskTop Standards 59 . See Figure 31. SAES-P-114 does specify that ground fault protection schemes for standby/emergency generators must be reviewed by the Manager. however.
High Resistance Grounding Saudi Aramco DeskTop Standards 60 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Figure 33.
). therefore. this Module will not provide procedures for selecting relays for unit-transformer-connected generators. ammeters. are also part of the modular packages. These operating factors include measuring and displaying a full range of mechanical.. voltmeters. For these reasons. The generator manufacturer will supply the g enerator with their own standard package of instrumentation and alarms.e. during startup. Because of this low ground fault current magnitude. ANSI Device 59S as illustrated in Figure 33 is only intended for ground fault protection during the time that the generator is disconnected from the system. The function of the generator instrumentation and alarms with a multitude of sensors and displays is to give the operator reliable. and thermal data.. the protection is in service only during the time that the circuit breaker is open. ANSI Device 87 (not shown) is also not usually sensitive enough to detect low-level ground faults. etc. i. Alarms. fuel supply lubrication. the resistor (R) limits the available fault current to very low magnitudes (3 . Saudi Aramco DeskTop Standards 61 . direct. Small Generators Small standby/emergency generators are usually modularpackaged units that include basic sets of electrical instruments (frequency meters. ordinary overcurrent relays may not be sensitive enough to detect the fault. very sensitive overvoltage relays (ANSI Device 59GN) are used to detect generator ground faults. event recorders. and continuous information about a variety of critical generator operating factors. Note: This section on high resistance grounding is for informational purposes only. such as temperature.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Referring to Figure 33. Instrumentation and Alarms There are no standards that specify the minimum recommended types of instrumentation and alarms for generators. cooling apparatus. electrical.25 amperes). additional instrumentation and alarm packages are limited only by the imagination of the user. The relay operating circuit is connected by means of an auxiliary switch (52/b) on the circuit breaker and. etc.
measuring. etc. vibration. recording. the electrical system alarms and instrumentation are relatively minor in nature compared to the massive requirements for monitoring.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Large Generators For large generators. the manufacturer will typically recommend a minimum package of instrumentation and alarms. etc.. temperature. As with small generators. information about the generator mechanical system such as fuel. Saudi Aramco DeskTop Standards 62 .
36. and 37) show information given in NEMA MG-1.25 2.5 50 62.8 PF 1 2 3 5 7. 35.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications WORK AID 1: RESOURCES USED TO DETERMINE IF GENERATOR TECHNICAL CONSTRUCTION SPECIFICATIONS ARE CORRECT Work Aid 1A: NEMA MG-1 The following figures (Figures 34. kVA 1.8 125 156 187 219 kW @ 0.5 75 93.75 6. Table 22-1) Saudi Aramco DeskTop Standards 63 .3 37.7 25 31.5 10 15 20 25 30 40 50 60 75 100 125 150 175 kVA 250 312 375 438 500 625 750 875 1000 1125 1250 1563 1875 2188 2500 2812 3125 3750 kW @ 0.8 PF 3500 4000 4500 5000 6000 7000 8000 10000 12500 15000 20000 25000 30000 35000 40000 50000 60000 Figure 34. Kilovolt-Ampere and Kilowatt Ratings for Synchronous Generators (Reference: NEMA MG-1.5 18.5 3.25 9.4 12. Part 22 that is used to determine correct technical specifications for synchronous generators.8 PF 200 250 300 350 400 500 600 700 800 900 1000 1250 1500 1750 2000 2250 2500 3000 kVA 4375 5000 5625 6250 7500 8750 10000 125000 15625 18750 25000 31250 37500 43750 50000 62500 75000 kW @ 0.
Table 22-3) Saudi Aramco DeskTop Standards 64 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Three-Phase Voltage 208Y / 120 240 480 600 2400 4160Y / 2400 4800 6900 13800 Figure 35. Voltage Ratings for Synchronous Generators (Reference: NEMA MG-1.
Speed Ratings for Synchronous Generators (Reference: NEMA MG-1. Table 22-2) Saudi Aramco DeskTop Standards 65 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Speed. rpm No. Poles 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 36 40 44 48 52 60 hertz 3600 1800 1200 900 720 600 514 450 400 360 327 300 277 257 240 225 200 180 164 150 138 50 hertz 3000 1500 1000 750 600 500 429 375 333 300 273 250 231 214 200 188 167 150 136 Figure 36.
Temperature Rise for Synchronous Generators (Reference: NEMA MG-1-22. collector rings. pole tips. and miscellaneous parts (such as brushholders. it is recommended that the temperature rises of the generators given in the above table be reduced as indicated by the following information. Note: Temperature rises in the above table are based upon generators rated on a continuous duty basis. etc. Values by Which the Temperature Rises in the Above Table Should be Reduced (°C) 10 20 Ambient Temperature (°C) Above 40 up to and including 50 Above 50 up to and including 60 Figure 37.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Item Machine Part Method of Temperature Determination Temperature Rise (°C) per Class of Insulation System A B F H 1 Armature winding (a) All kVA ratings (b) 1563 kVA and less (c) Over 1563 kVA (1) 7000 volts and less (2) Over 7000 volts Embedded detector Embedded detector 65 60 85 80 110 105 135 125 Resistance Embedded detector 60 70 80 90 105 115 125 140 2 Field winding Resistance 60 80 105 125 3 The temperature attained by cores. However. for the ranges of ambient temperature given. it is recognized that synchronous generators may be required to operate in an ambient temperature higher than 40°C.40) Saudi Aramco DeskTop Standards 66 . amortisseur windings. For successful operation of the generator in ambient temperatures higher than 40°C. Note: Temperature rises in the above table are based on a reference ambient temperature of 40°C.) shall not injure the insulation of the machine in any respect. brushes.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Work Aid 1B: 17-SAMSS-510 For the content of Work Aid 1B. Work Aid 1A). The stator amperes must be equal to the value determined by using the rated kVA. Step 3: Stator Amps . rated stator volts. Work Aid 1C: Applicable Evaluation Procedures Step 1: kVA . In accordance with NEMA MG-1-22.Evaluate the generator technical specification given for kVA and determine if it is correct. Evaluate this specification in accordance with NEMA MG-1. Table 22-3 (refer Figure 35.13. Step 2: Stator Volts .Evaluate the generator technical specification given for stator amps and determine if it is correct. voltage ratings for synchronous generators must be in accordance with NEMA MG-1. Table 22-1 (refer Figure 34. The technical specification for the kVA must be equal to the value required by the proposed or given operating conditions for which the generator will be applied.Evaluate the generator technical specification given for stator volts and determine if it is correct. Work Aid 1A). and the following equation: IT = where: I T = stator amps VT = rated stator volts Saudi Aramco DeskTop Standards 67 . refer to Handout 1. Evaluate this specification in accordance with NEMA MG-1. and the kVA specification must be equal to one of the approved ratings shown in NEMA MG-1.
synchronous generators shall be rated on a continuous duty basis. the excitation voltages for field windings shall be 62. Table 22-2 (refer Figure 36. Work Aid 1A). Saudi Aramco DeskTop Standards 68 .5. Evaluate this specification in accordance with NEMA MG-1.15. 125. In accordance with NEMA MG-1-22.12. Evaluate this specification in accordance with NEMA MG-1. Evaluate this specification in accordance with NEMA MG-1. speed ratings shall be as shown in NEMA MG-1.Evaluate the generator technical specification given for power factor and determine if it is correct. In accordance with NEMA MG-1-22.Evaluate the generator technical specification given for exciter volts and determine if it is correct.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications kVA3Φ = rated kVA Step 4: Power Factor . These excitation voltages do not apply to generators of the brushless type with direct-connected exciters.Evaluate the generator technical specification given for synchronous speed and determine if it is correct. 375. Step 5: Synchronous Speed .10. Step 6: Exciter Volts . Step 7: Frequency .Evaluate the generator technical specification given for the type of cooling system and determine if it is correct.14. frequencies shall be 50 and 60 hertz. and the rating shall be expressed in kilovolt-amperes available at the terminals at 0. Evaluate this specification in accordance with NEMA MG-1.Evaluate the generator technical specification given for frequency and determine if it is correct. and 500 volts direct current. Step 8: Cooling System Type . In accordance with NEMA MG-122. In accordance with NEMA MG-1-22.8-power-factor lagging (overexcited). 250.
Select closed-cooling type for service conditions where serious interference with the ventilation of the generator does exist. For generators rated 500 kVA and below. The rotor type should be either salient-pole or round.Evaluate the generator technical specification given for the type of rotor and determine if it is correct. 3600 rpm generators and four-pole.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications The cooling system type should be either open-cooling type or closed-cooling type depending on service operating conditions.Evaluate the generator technical specification given for the type of stator winding and determine if it is correct. (b) Step 9: Stator Winding Type . Saudi Aramco DeskTop Standards 69 . (b) Step 10: Rotor Type . In accordance with industry recommended practice: (a) Select open-cooling type for service conditions where no serious interference with the ventilation of the generator exists. In accordance with industry recommended practice: (a) Round-type rotors should be used for two-pole. In accordance with typical industry practice: (a) For generators rated greater than 500 kVA. The stator winding type should be either mush wound or form wound depending on generator rating. the stator winding type should always be form wound. the stator winding type may be either form wound or mush wound depending on individual design and application. design. 1800 rpm generators. and/or application.
40. or shoe-sleeve type. the observable temperature rise under rated load conditions of each of the various parts of the synchronous generator above the temperature of the cooling air shall not exceed the values given by the table provided in NEMA MG-122. Evaluate these specifications in accordance with NEMA MG-1 and 17-SAMSS-510. Generators rated 500 kVA or greater and designed as one-bearing machines. Saudi Aramco DeskTop Standards 70 . cylindrical-sleeve type. Work Aid 1A). Generators rated 500 kVA or greater and designed as two-bearing machines should use cylindrical-sleeve type bearings. should use shoe-sleeve type bearings. and the temperature rises given in the table are based on a maximum temperature of 40°C for this external air. The temperature of the cooling air is the temperature of the external air as it enters the ventilating openings of the machine. (Note: One-bearing machines are designed to have the drive end of their rotor supported by the prime mover.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications (b) Salient-pole rotors should be used for generators with eight or more poles and speeds less than 1800 rpm.) (b) (c) Step 12: Insulation Class and Temperature Rise . Step 11: Bearing Type .40 (refer to Figure 37.Evaluate the generator technical specification given for the insulation class and temperature rise and determine if they are correct.Evaluate the generator technical specification given for the type of bearing and determine if it is correct. The bearing type should be either anti-friction. In accordance with industry recommended practice: (a) Generators rated less than 500 kVA may use either anti-friction or cylindrical-sleeve type bearings depending on design and application. In accordance with NEMA MG-1-22.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Refer to 17-SAMSS-510 (Work Aid 1B.101-1985 (1) Neutral grounding for large and medium size directconnected synchronous generators is in accordance with Table 1. WORK AID 2: RESOURCES USED TO SELECT GENERATOR MINIMUM PROTECTION REQUIREMENTS Work Aid 2A: ANSI/IEEE Standard C37. Low Resistance Grounding Scheme Saudi Aramco DeskTop Standards 71 . Method III (Figure 38). Figure 38. Handout 1) to determine any additional Saudi Aramco requirements for insulation class and temperature rise rating.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications (2) The minimum required generator protection scheme for large and medium size direct-connected synchronous generators shall be Scheme 10 (Figure 39). Both IEEE Schemes 10 and 16 shut down the generator under fault conditions. Figure 39. IEEE Ground Fault Protection Scheme 10 Figure 40. IEEE Ground Fault Protection Scheme 16 Saudi Aramco DeskTop Standards 72 .
102-1987 (1) The generator neutral or grounding transformer neutral will generally be grounded through a low ohmic value resistor as illustrated in Figure 41.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Work Aid 2B: ANSI/IEEE Standard C37. Direct-Connected Generators Saudi Aramco DeskTop Standards 73 . Figure 41.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications (2) Supplementary sensitive ground fault protection shall be provided as illustrated in Figure 42. IEEE Supplementary Sensitive Ground Fault Protection Scheme Saudi Aramco DeskTop Standards 74 . Figure 42.
f. serial number. d. refer to Handout 2. Work Aid 2E: Applicable Selection Procedures Step 1: Collect the following minimum nameplate data (as applicable) from the generator specifications: a. Manufacturer’s name. l. refer to Handout 1. h. e. c. or other suitable identification Kilovolt-ampere output Power factor Time rating Temperature rise for rated continuous load Rated speed in rpm Voltage Rated current in amperes-per-terminal Number of phases Frequency Maximum ambient temperature Insulation system designation - Saudi Aramco DeskTop Standards 75 . Chapter 5 For the content of Work Aid 2C. Work Aid 2D: 17-SAMSS-510 For the content of Work Aid 2D. i. g. k. j. b.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Work Aid 2C: SAES-P-114 (25 APR 94).
5.5.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Step 2: Small Standby/Emergency Generators: Note: This step applies to diesel-driven standby/emergency generators rated 480 V. b. 1000 kVA or less as per SAES-P-114. See Section 5. Select an ampacity rating for the molded case circuit breaker at 125% of the emergency generator’s full-load amperes (FLA). proceed to Step 2F. Section 5.25 FLA Saudi Aramco DeskTop Standards 76 .1 of Work Aid 2C. This Module assumes that protection of small standby/emergency generators is built-in protection provided by the manufacturer. a. Emergency Generator One-Line Diagram c. MCCB ampacity rating = 1. Figure 43. Sketch a simple one-line diagram of the system as illustrated in Figure 43. Note: If using a low voltage power circuit breaker (LVPCB) for main breaker protection.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications d. Standard Ampere Ratings 200 A 225 A 250 A 300 A 350 A 400 A 450 A 500 A Standard Ampere Ratings 600 A 700 A 800 A 1000 A 1200 A 1600 A 2000 A Figure 44. Standard MCCB Ampacity Ratings (NEC Article 240-6) Saudi Aramco DeskTop Standards 77 . Select the ampacity rating of the next standard size MCCB from the following list (Figure 44).
000 -35.000 40.000 25.000 -30.000 35.000 35.000 20. Line No.000 100.000 30. MCCB Interrupting Ratings Saudi Aramco DeskTop Standards 78 .000 -35. Select a line number MCCB from the following list (Figure 45) based on the size of the MCCB ampacity rating from Step 2d and the available short circuit current (SCA). Frame Size (amps) (AF) Rated Continuous Current (amps) (AT) 125-200 70-225 70-225 70-225 70-225 200-400 200-400 200-400 300-600 300-800 300-800 600-800 600-1000 700-1200 800-1600 800-2000 Interrupting Current Rating (AIC) (amps) 480 Volts Sym Asym 18.000 100.000 30.000 100.000 -35.000 100.000 30.000 30.000 25. Note: The ratings in Figure 45 are typical from one MCCB vendor.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications e. other vendors may have different ratings.000 40.000 100.000 40.000 35.000 35.000 --- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 225 225 225 225 225 400 400 400 600 800 800 800 1000 1200 1600 2000 Figure 45.000 100.000 22.
150. sensor size. 800 100. 200. When a solid-state trip (SST) device is provided. it shall have long-time and short-time phase units only. 300. 150. LVPCB Frame and Sensor Ratings Saudi Aramco DeskTop Standards 79 . 1200. 400. Frame Size (amperes) 800 1600 200 Available Sensor Ratings (amperes) 50. 2000 Figure 46. 100. 400. 300. 600. 400. 600. 200. the LVPCB shall have a continuous current rating not less than the generator maximum rated load current. 200. 800. 150. 1600. Select the LVPCB frame. 300. 800.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications f. 600. Where a low voltage power circuit breaker (LVPCB) is used as main circuit breaker protection. and interrupting ratings from Figures 46 and 47 based on the generator’s fullload amperes (FLA) and available short circuit current (SCA). 1600 100. except that a ground unit shall also be provided when zone-selective interlocking is installed on the feeder circuits supplied by the generator. 1200.
000 65.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Frame Size (amps) Interrupting Ratings.000 50.000 Figure 47. LVPCB Interrupting Ratings g.000 50.000 65. RMS Symmetrical Amperes With Instantaneous Trip 480 Volts Short Time Ratings 30 cycles (With Short-Delay) 480 Volts 30. Saudi Aramco DeskTop Standards 80 . Select a solidly-grounded neutral (wye-connected) grounding system.000 800 1600 2000 30.
101-1985. Table I. Sections 5. See Figure 38 of Work Aid 2A.101-1985. Table I. b. Direct-Connected Synchronous Generators This step applies to medium.5 MVA as per SAES-P-114.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Step 3.4. Schemes 10 and 16. and 5. 5.6. Select required generator protection per SAES-P114 (Work Aid 2C). d. Note: Medium. c. Select generator ground fault protection per ANSI/IEEE Standard C37. Generator Connection E. Select generator minimum protection per Drawing No.094 of SAES-P-114 (Figure 48 of this Work Aid). Saudi Aramco DeskTop Standards 81 . direct-connected synchronous generators with a voltage rating of 600 to 13. See Figures 39 and 40 of Work Aid 2A and Figure 42 of Work Aid 2B. Section 5.800 volts and kVA ratings greater than 1000 kVA but not exceeding 12.8. Grounding Method III.7. a. Select a low resistance grounding scheme per ANSI/IEEE Standard C37. SAESP114.
Medium.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Title: 21504-48.EPS from CorelDRAW! Creator: CorelDRAW! CreationDate: Mon Jun 19 11:33:45 1995 Figure 48. Direct-Connected Generator Protection Scheme Saudi Aramco DeskTop Standards 82 .
a.5 MVA. and 5. b.092 of SAES-P-114 (Figure 49 of this Work Aid). Select required generator protection per SAES-P114 (Work Aid 2C). 5. Select generator minimum protection per Drawing No. Sections 5.7. Table I.101-1985. Section 5. Saudi Aramco DeskTop Standards 83 .101-1985. c.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Step 4. Schemes 10 and 16. See Figures 39 and 40 of Work Aid 2A and Figure 42 of Work Aid 2B. Select a low resistance grounding scheme per ANSI/IEEE Standard C37. Large Direct-Connected Synchronous Generators Note: This step applies to large. SAESP114. Select generator ground fault protection per ANSI/IEEE Standard C37. as per SAESP-114. Table I.2. See Figure 38 of Work Aid 2A. direct-connected synchronous generators with a voltage rating of 13. Grounding Method III. Generator Connection E. d.6.8.800 volts or above and a kVA rating greater than 12.
Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications Title: 21504-49. Large. Direct-Connected Generator Protection Scheme Saudi Aramco DeskTop Standards 84 .EPS from CorelDRAW! Creator: CorelDRAW! CreationDate: Mon Jun 19 11:34:38 1995 Figure 49.
The source of field current for a generator. The automatic control element of a prime mover that regulates it to a constant rotational speed. Magnetic lines of force. commutator directly-connected generator excitation excitation system exciter fault field flux generator governor grounding system Saudi Aramco DeskTop Standards 85 .Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications GLOSSARY brushless exciter A main field exciter consisting of a rotating armature within a stationary field. The machine which supplies DC current to the generator field winding. A system comprising all interconnected grounding facilities in a specific area. A generator whose output terminals are connected to the power distribution system without the interposition of a power transformer. A mechanical rectifier used on DC exciters to rectify the AC voltage on the rotating armature to DC current for the field winding of the generator. thus eliminating the need for collector rings and brushes. The magnetic field of a generator. synonymous with rotor. including its means of control. The process of establishing and maintaining the magnetic field of a generator. usually causing an electrical device to fail to perform as required. The AC voltage produced on the armature is rectified to a DC voltage by rotating rectification components assembled onto the shaft of the exciter. An insulation failure or breakdown in the continuity of a conductor. A machine that converts rotational mechanical energy into electrical energy.
A rating given to the insulation system of a generator that identifies the maximum temperatures at which the insulation is designed to operate. The value obtained when the sum of the products of output phase voltages and resistive components of output line currents of a generator are divided by one-thousand. thus limiting fault current within the range of 100 and 1200 amperes. The value obtained when the sum of the products of phase voltages and line current outputs of a generator are divided by onemillion. inner-cooled machine insulation class kilowatt (kW) low resistancegrounded system low system voltage medium voltage system megavolt-ampere (MVA) megavolt-ampere reactive (MVAR) megawatt (MW) Saudi Aramco DeskTop Standards 86 . and with total ground fault current generally less than 10 amperes.000 V. A generator in which the stator coil coolant flows internally through the coils. A system with line-to-line voltage in the range of 1001 and 15. The value obtained when the sum of the product of output phase voltages and resistive components of output line currents of a generator are divided by one-million. with resistive ground fault current greater than or equal to the system charging current. The value obtained when the sum of the products of output phase voltages and the reactive components of output line currents of a generator are divided by one-million. parallel rings and lead bushings with heat transfer consequently occurring by means of direct contact between the conductors and the cooling medium. A system with line-to-line voltage of 1000 V and less.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications high-resistance grounded system A system with the intentional insertion of resistance between a generator or transformer neutral and ground. A system with the intentional insertion of resistance between a generator or transformer neutral and ground.
In common usage. The value of lagging power factor at which the stator-windinglimited capability curve meets the rotor-winding-limited capability curve. the decimal fraction by which volt-amperes must be multiplied to obtain watts. A system with the intentional insertion of reactance between a generator neutral and ground with total ground fault current between 25 percent and 100 percent of three-phase fault current. overcurrent relay overexcited generator overvoltage relay power factor prime mover rated MW rated power factor reactance grounded system regulator resistance temperature detectors (RTD) Saudi Aramco DeskTop Standards 87 . The excitation system controlling mechanism which senses a change in the voltage or current at each phase of the generator terminals and that corrects for this change by adjusting the field current or tripping the generator off-line.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications motoring The condition of a generator when it is driven by the power from other generation sources of the distribution system. Such a relay is referred to as ANSI Device 51. Instrumentation elements that are made of a material for which the electrical resistivity is a known function of temperature. A relay that functions when the current in an AC circuit exceeds a predetermined value. The maximum continuous MW output of a generator which can be delivered at rated power factor without exceeding the temperature limits of winding components. this term usually implies the special case of motoring when the fuel or steam supply of the prime mover has been interrupted and the generator remains connected to the system. Such a relay is referred to as ANSI Device 59. that are located throughout the machine. and that indicate various strategic winding and iron temperatures. The real power to apparent power ratio. The engine or machine that drives the generator. A generator whose stator voltage is higher than that of the distribution system and is supplying reactive power (VARs) to the system. A relay that functions on a given value of overvoltage.
A temperature sensing device used in a manner similar to an RTD but composed of two dissimilar metals which produce a measurable voltage that varies with temperature. A generator where the output terminals are connected to the distribution system through an interposing transformer.Engineering Encyclopedia Generators Evaluating Generator Mechanical and Electrical Specifications short circuit solidly-grounded system stator synchronism An abnormal electrical connection that is of extremely low resistance and that usually results in excessive current flow. temperature rise rating thermocouple (TC) ungrounded system unit-connected generator unit-transformer voltage regulator winding Saudi Aramco DeskTop Standards 88 . all of the same phase or polarity. A transformer designed and constructed especially to interpose and transform voltages between a generator and its distribution system. A system with an intentional and direct connection to ground. The condition of an AC generator when its output voltages are the same frequency and zero-degree phase angle difference as are the voltages of the generator bus. The temperature rise rating given on a generator nameplate describing the limit of expected rise in temperature over ambient. A grouping of inter-connected coils. The stationary element of the generator magnetic circuit and its associated electrical windings and leads. generally exhibiting very high ground fault current magnitudes. A system with no intentional connection to ground but with coupling through the stray capacitance of the phase conductors. The automatic control component of the excitation system through which the output voltage of the generator is established and maintained.
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