Abstract:
A protective wall system enclosing a danger zone around an alternator includes a front wall disposed at a front end of the wall system; a back wall disposed at a back end of the wall system; and a first side wall and a second side wall connecting the front wall and the back wall, wherein the front and the back wall extend parallel to a longitudinal axis of the alternator, and wherein the front wall, the back wall and the first and second side walls are gas-tight. The wall system further includes a gas-tight bottom; a first casing enclosing a rotor and a stator of the alternator, wherein a service area surrounds the first casing; and at least one air guiding device configured to guide at least one of gas and heat from a bottom part of the alternator to an upper part of the alternator.

Description:
Priority is claimed to European Patent Application No. EP 08172077.3, filed Dec. 18, 2008, the entire disclosure of which is incorporated by reference herein. 
     The present invention concerns an acoustic delimitation of an alternator. 
     BACKGROUND 
     The environment around an alternator is exposed to a constant risk of explosion if gaseous hydrogen, which is an extremely flammable substance, is used for cooling. There are many possible sources of hydrogen leakage around an alternator, allowing hydrogen to leak out into the atmosphere, such as leaky spots at the wave guide seals, interfaces and air-tight transitions, as well as drill holes made by man or instrumentation plug-ins, etc. The circumference of the alternator is classified in zone  2  according to the definition of the norm EN 60079-10. 
     The design of new alternators therefore must be improved as to protection against the risk of explosion. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is therefore to increase the safety around an alternator for workers. 
     The present invention solves the above problem by providing a protective wall system enclosing a danger zone around an alternator. Said wall system comprises a front wall at a front end, a back wall at a back end and two side walls connecting the front wall with the back wall. The side walls extend essentially parallel to a longitudinal axis of the alternator. The alternator, which preferably is cooled by hydrogen (H 2 ), has a rotor and a stator and is enclosed by a first casing. A service area surrounds the first casing. In order for the danger zone to be gas-tight, all walls, i.e. the front wall, back wall and side walls are gas-tight. Furthermore, said wall system has a gas-tight bottom. The distance from the first casing to the side walls is at least 1.50 meters. Preferably, the distance between the first casing and each wall is at least 1.50 meters. This distance from the alternator is kept such that the inspections in the danger zone can be comfortably realized and that preferably the evacuation in case of an emergency can be carried out under maximum safety conditions. 
     Said wall system is provided with means for guiding gas and/or heat from a bottom part of the alternator toward the upper part thereof, such as a ventilation system. The wall system allows the personnel working close to the alternator to be protected from being affected for instance by a possible explosion. In the case of a hydrogen leak, the acoustic wall allows a hydrogen-free zone. By the inclusion of a ventilation system, hydrogen leaking from the bottom part of the alternator is efficiently guided toward the upper part of the alternator. In addition to a protection from gas and/or heat and/or fire, the wall preferably also serves to protect the personnel in the machine hall from the noise caused by the alternator and from its field of current. 
     In a first preferred embodiment of the present invention, the wall system further comprises a roof, preferably at a distance of at least 1.50 meters from the first casing. Thereby, the walled-in zone can be completely closed, allowing the best acoustic delimitation and hazard protection. If a roof is provided, the enclosed space must be ventilated. 
     According to a further preferred embodiment, said first casing is flanked by a first cooling compartment at its front end and a second cooling compartment at its back end. Each cooling compartment can be flanked by an axial bearing flange, each bearing flange preferably being provided with a wave guide seal. The back end axial bearing flange can be connected to a turbine arrangement. The front end axial bearing flange preferably is connected to an exciter, said exciter preferably being enclosed in a second casing. A ventilation device can be attached to the first casing, said first casing preferably comprising at least one ventilation channel. 
     It can be of additional advantage if at least one air inlet is provided at the bottom of the wall system under the ground level beneath the first casing, enabling air to enter into the danger zone from below. Furthermore, it is of advantage if at least one air guiding device is provided beneath the alternator casing, said air guiding device preferably being able to receive air from a cooling compartment and to guide the air into the alternator casing through at least one air duct. The wall system for instance can comprise air guiding plates permeable to air at the bottom periphery of the wall system below the first casing. The ventilation system is further improved if at least one fan is provided in an area enclosed by the wall system. 
     A next preferred embodiment is characterized in that a barrier wall arranged perpendicular to the longitudinal axis of the alternator and parallel to the front wall and the back wall is located between the front wall and the back wall. Said barrier wall preferably is located in the area of the exciter. The barrier wall preferably is or has an automatic sliding door. Said additional barrier wall divides the area enclosed by the wall system into two main chambers, of which the chamber between the front wall and the barrier wall can be an annular space, providing an additional safety room for personnel. According to another preferred embodiment, the wall system further encloses a control panel for the operation and/or service of the alternator and/or other electrical devices enclosed by the wall system. Said control panel or other instrumentation for control and/or maintenance of the alternator or other machines or devices can be housed e.g. in said annular space. 
     The wall system advantageously comprises fire-resistant and/or acoustic panels. Acoustic panels preferably are easily removable in case of high maintenance operations. Preferably, the wall panels and pillars on which they are fixed can resist a hydrogen explosion. 
     It is of further advantage if the wall system, preferably the front wall thereof, can be penetrated through at least one, preferably only one door of access. The door preferably opens in the direction of exit and preferably permits a fast evacuation of the hazardous area in the case of an emergency within. This provides for personnel an easy access to and exit from the danger zone or, if provided, into or out of an additional safety room. 
     The form of the protective wall system can be optimized according to the size of the zones to be protected. Preferably, the enclosed area is divided into different danger zones, which can be assigned to different danger zone categories according to norm EN 60079-10. 
     Further embodiments of the present invention are outlined in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings preferred embodiments of the invention are shown in which: 
         FIG. 1  is a perspective view of a protective wall system for an alternator delimitation; 
         FIG. 2  is a perspective view of a protective wall system for an alternator delimitation according to a second embodiment without a barrier wall; 
         FIG. 3  is a cut along the barrier wall of the protective wall system according to a third embodiment, corresponding to the embodiment of  FIG. 1  with a roof; 
         FIG. 4  is a cut through the first side wall of the protective wall system of  FIG. 3 ; 
         FIG. 5  is a schematic top view of the protective wall system of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same,  FIG. 1  shows a protective wall system  1 , provided on a base  31  and enclosing an alternator housed by first casing  8 , i.e. an alternator casing, and two cooling compartments  16 ,  17 . A service floor  7  is enclosed as well. The wall system  1 , which encloses an essentially rectangular floor plan, comprises a first side wall  5  and a second side wall  6 , which are connected to each other by a front wall  3  and a back wall  4 , and also comprises a bottom. The side walls  5 ,  6  are arranged essentially parallel to the longitudinal axis  2  of the alternator  35  (see  FIG. 3 ), and the front wall  3  and the back wall  4  are arranged essentially perpendicular to the longitudinal axis  2  of the alternator  35 . In the embodiment shown in  FIG. 1 , a barrier wall  10  is provided between the front wall  3  and the back wall  4 , the barrier wall  10  being arranged essentially parallel to the front wall  3  and the back wall  4 . In the embodiment of  FIG. 1 , the barrier wall  10  is arranged in the area of an exciter, housed by a second casing  19 . The barrier wall  10  defines an additional chamber, i.e. area  11  within the area enclosed by the wall system  1 . The area between the front wall  3  and the barrier wall  10  is an annular space  11 , which is partitioned from the danger zone around the alternator  18 , i.e. the service area, by the barrier wall  10 . Personnel can enter the space  11  through a personnel service door  9 , e.g. in order to operate or service a control panel  12 , shown in  FIG. 5 . The alternator casing  8  rests on supporting structures  49  on the service floor  7 , while the cooling compartments  16 ,  17  also rest on supporting structures  50  on the service floor  7 . The alternator casing  8  shown has a cylindrical shape, with its longitudinal axis  2  provided essentially parallel to a ground level plane  51  defined by the service floor  7  (see  FIG. 4 ). The cooling compartments  16 ,  17  are each flanked by an axial bearing  25 ,  26 , the front end axial bearing  25  being located between the first cooling compartment  16  and the front wall  3 , and the back end axial bearing  26  being located between the second cooling compartment  17  and the back wall  4 . However, between the front end axial bearing  25  and the front wall  3 , the exciter  18  for an electric generator is arranged, said exciter  18  having the purpose to generate a rotating magnetic field and being housed in a second casing  19 . Gaseous hydrogen, H 2 , is used for cooling the alternator  35  during its operation. The hydrogen is introduced into the cooling compartments  16 ,  17  from below. 
     At the back end of the wall system  1 , the alternator  35  is connectable to a turbine, e.g. a gas turbine (not shown). 
     In the embodiment shown in  FIG. 2 , no barrier wall  10  is provided between the front wall  3  and the back wall  4 . The barrier wall  10  is either not existent in this embodiment, or it is retracted, as for instance if the barrier wall is a sliding door, which can be opened and closed as needed. 
     The cut through the wall system  1  of  FIG. 3  provides a view along the longitudinal axis  2  of the alternator  35 . The alternator  35  is housed in a first casing  8 , which is supported and/or fastened to the service floor  7  by supporting strictures  49 . Below the service area, in an area let into the ground, an air guiding device  23  is located within an air tank  37 . The area arranged below the service floor  7 , the service floor being located essentially at the ground level  51 , is provided with air guiding plates  22  having air inlets. These plates  22  allow air to be introduced into the danger area (Zone  2 ) surrounding the alternator casing  8  from below. The air guiding device  23  built on leg stands  58  guides air through ducts  52  into the inside of the alternator  35 , as can be seen in  FIG. 4 . 
     A tubular formed ventilation device  13  is connected to the top of the first casing  8 , and extends essentially parallel to the longitudinal axis  2  of the alternator  35 . 
     The wall system according to  FIG. 3  corresponds to the wall system  1  of  FIG. 1 , however, additionally provided with a roof  30 . Said roof  30  has a planar area extending essentially parallel to the plane defined by the service floor  7 , as well as two inclined areas  34  flanking said planar area of the roof  30 . The distance c 1  between the top of the cooling compartments  16 ,  17  and the roof  30  is at least 1.50 meters. 
     In  FIGS. 3-5 , the area enclosed by the wall system  1  and marked by slanted lines is defined as “Zone  2 ”, which is defined as the danger zone according to norm EN 60079-10. The wall system  1  according to the present invention encloses said danger zone around the alternator  35 , i.e. it&#39;s casing  8  and other apparatus provided for the operation and/or cooling of said alternator  35 . All electrical apparatus&#39; provided in the danger zone are designed to function and assure a normal level of protection in “Zone  2 ”. A safety distance of at least 1.50 meters is necessary between the alternator and all other electrical equipment not designed for a “Zone  2 ”. Accordingly, the distance a 1 , a 2  between the periphery of the alternator casing  8  and the base of the supporting structures  50  of the cooling compartments  16 ,  17  is at least 1.50 meters, as is the distance b 1 , b 2  between the first or second side, respectively, of the cooling compartment  16 ,  17  and periphery of the ventilated area  41 . The distance c I between the cooling compartment  16 ,  17  and the roof  30  is also at least 1.50 meters, as is the distance d 1  between the bottom of the air guiding device  23  and the bottom periphery of the air  37 , i.e. the bottom periphery of “Zone  2 ” or the ventilated area  41 . 
     On top of the alternator casing  8  is mounted a ventilation device  13 , which has connections to ventilation channels  39 ,  40 . In  FIG. 5 , four ventilation channels  39 ,  40 ,  46 ,  47  are shown, of which two ventilation channels  39 ,  46  are provided adjacent to the first cooling compartment  16 , while two further ventilation channels  40 ,  47  are provided adjacent to the second cooling compartment  17 . The ventilation channels  39 ,  40 ,  46 ,  47  are arranged such that they extend into the alternator casing  8  and preferably are completely enclosed by the alternator casing  8 . 
     In the far right end of  FIG. 4 , at the front end of the wall system  1 , on ground level  51 , the exciter  18  for generating a rotating magnetic field in order to provide a current for the alternator  35  is provided partially within the safety room, i.e. space  11  defined between the front end wall  3  and the barrier wall  10 . The roof  30  covers the area enclosed by the barrier wall  10  and the back end wall  4 , as well as the two side walls  5 ,  6 . The roof  30  is designed to be domed and thus provides more space for air to circulate within the ventilated area  41 . The front end bearing flange  25  is connected to the exciter  18  and is already located within the danger zone. Adjacent to the front end bearing flange  25 , the front end cooling compartment  16  is attached, followed along the longitudinal axis  2  by the alternator casing  8  housing the alternator stator  36  and rotor  42 . A back end cooling compartment  17  is mounted at the back end of the alternator casing  8 , followed along the longitudinal axis  2  by a back end bearing flange  26 . Said back end bearing flange  26  is connected over an interface  48  to a turbine, located outside of and therefore no longer enclosed by the wall system  1 . 
     Beneath the alternator casing  8 , at least two air guiding devices  23  are located, of which one is located essentially below the first cooling compartment  16  and another one is located below the second cooling compartment  17 . Each air guiding device  23  is provided with at least one duct  52 , leading from the air guiding device  23  into the alternator casing  8  from below. 
     Air entering the air tank  37  through the air guiding plates  22  from below is distributed and/or circulated annularly around the alternator casing  8  throughout the danger zone. 
     Circulating air enters a cooling compartment  16 ,  17 , preferably both cooling compartments  16 ,  17 , through at least one air inlet  53 ,  55  located at the top of the cooling compartment  16 ,  17 . The air is then cooled in the cooling compartment  16 ,  17  and exits the cooling compartment  16 ,  17  through at least one air outlet  54 ,  56  into air guiding device  23 . Here it can be stored and/or conditioned before being guided through at least one air duct  52  directly into the alternator casing  8 , and/or into the alternator  35  itself for cooling. Additionally, at least one fan (not shown) can be provided within the ventilated area to promote circulation. The ventilated area  41  around the alternator casing is formed as an annular space  11 , allowing the air to circulate around the casing&#39;s cylindrical circumferential surface. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Protective wall system 
           2  Longitudinal axis of  35   
           3  Front wall 
           4  Back wall 
           5  First side wall 
           6  Second side wall 
           7  Service floor 
           8  first casing/alternator casing 
           9  Personnel access door 
           10  Barrier wall 
           11  Safety room 
           12  Control panel 
           13  Ventilation device 
           14  Air inlet 
           15  Air outlet 
           16  Front end cooling compartment 
           17  Back end cooling compartment 
           18  exciter 
           19  Second casing/exciter casing 
           20  Front end wave guide seal 
           21  Back end wave guide seal 
           22  Air guiding plate 
           23  Air guiding device 
           24  Valve box 
           25  Front end bearing flange 
           26  Back end bearing flange 
           27  Detector of exciter 
           28  Leakage detector 
           29  Balancer of rotor 
           30  Roof 
           31  Base of  1   
           32  Base of  16 ,  17   
           33  Periphery of  41   
           34  inclined area of  30   
           35  alternator 
           36  Stator of  35   
           37  air tank 
           38  magnetic axis 
           39  First ventilation channel 
           40  Second ventilation channel 
           41  Ventilated area 
           42  Rotor of  35   
           43  Slot of  36   
           44  First set of coils 
           45  Second set of coils 
           46  Third ventilation channel 
           47  Fourth ventilation channel 
           48  Interface to turbine 
           49  Supporting structures of  8   
           50  Supporting structures of  16 / 17   
           51  Ground level 
           52  Duct from  23  to  35   
           53  Air inlet into  16   
           54  Air outlet from  16   
           55  Air inlet into  17   
           56  Air outlet from  17   
           58  Leg stand of  23   
         a 1  distance between  8  and base of  50  facing  5   
         a 2  distance between  8  and base of  50  facing  6   
         b 1  distance between first side of  16 / 17  and periphery of  41   
         b 2  distance between second side of  16 / 17  and periphery of  41   
         c 1  distance between top of  16 / 17  and  30   
         d 1  distance between lower periphery of  23  and lower periphery of  37   
         R direction of rotation of  36