Abstract:
A system and method for operating a transferable feeder system on an electrical distribution system is provided. The system includes a controller that is disposed in communication with switches associated with feeders of a first substation and circuit breakers associated with a second substation. The first substation and second substation are electrically coupled in a manner to allow load transfer from the first substation to the second substation. The system is arranged to disconnect a first pair of circuits from the first substation before connecting the pair of circuits to the second substation while leaving a third circuit coupled to the first substation. During the entire process of transferring load from one substation to the second substation, customer load does not experience any interruption in electrical service.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to electrical power distribution networks and more particularly to a transferable feeder system that allows the transfer of loads from one substation to another substation without interrupting the flow of electrical power to the loads. 
         [0002]    Electrical power is typically produced at centralized power production facilities and transferred at high voltages to local substations. The local substations transform the electrical power to a medium or low voltage. The electrical power is subsequently distributed through feeders to local distribution networks. In general, electrical load may be transferred between distribution feeders that are connected to the same substation. 
         [0003]    It is more difficult, however, to switch loads between networks that receive power from different substations. Since power received by each substation may come from a different source, the electrical power at one substation may have different characteristics, such as voltage and phase angle for example, than an adjacent substation. While these differences may be small, they can be large enough to make the two networks incompatible for interconnection purposes. In general, to switch a load or a group of loads from one network to an adjacent network requires the physical disconnection of hardware from the original network and reconnection to the new network. This disconnection and reconnection requires momentary interruption of service while the change is made. 
         [0004]    Some circumstances, such as unusually high demand for example, may warrant the effort of switching loads from one network or substation to another. This is usually accomplished in areas where over-head wires are installed and connected load is radial. It should be appreciated that this type of switching is not readily applicable where underground networks are installed. 
         [0005]    One further issue is that such a change usually requires a momentary interruption in service. Electrical utilities have a number of metrics that are used to track performance and customer satisfaction. These metrics, which include the system average interruption frequency index (“SAIFI”), the customer average interruption duration index (“CAIDI”), and for some utilities, the momentary average interruption frequency index (“MAIFI”). SAIFI measures the average number of interruptions that a customer would experience during a time period, such as a year. CAIDI measures the duration of the interruption that a customer would experience, and is generally a few hours per year. MAIFI measures the number of power interruptions that have a duration of less than five minutes that a customer would experience during a given time period. 
         [0006]    Some or all of these metrics are also used by government regulators to aid in determining if the electrical utility is adhering to the regulations in maintaining a durable and reliable electrical service While circumstances may make it desirable to switch loads from one network to another, the process may have detrimental impacts on the utilities metrics. 
         [0007]    Thus, while existing electrical distribution systems are suitable for their intended purpose, there remains a need for improvements. In particular, there remains a need for improvement regarding the ability to change loads from one network or a substation to another without interrupting the flow of electrical power to the load. 
       SUMMARY OF THE INVENTION 
       [0008]    A method transferring electrical power to a load from a first substation to a second substation is provided. The method includes the step of opening a first pair of switches associated with the first substation, wherein the first pair of switches provides electrical power to a first and second circuit. A first pair of circuit breakers associated with the second substation are closed, wherein the first pair of circuit breakers provide electrical power to the first and second circuit. A second pair of switches associated with the first substation are opened, wherein the second pair of switches provide electrical power to a third and fourth circuit. Finally, a second pair of circuit breakers associated with the second substation are closed, wherein the second pair of circuit breakers provide electrical power to the third and fourth circuit. 
         [0009]    A method of operating a transferable feeder system is also provided. The method includes the step of determining an electrical phase angle difference between a first substation and a second substation. It is determined if the phase angle difference exceeds a threshold. A phase angle associated with the second substation is adjusted such that the phase angle difference is within the threshold. A first switch and a second switch associated with the first substation are opened, wherein the first switch and the second switch provide electrical current to a first and second circuit. A first circuit breaker and second circuit breaker associated with the second substation are closed, wherein the first circuit breaker and the second circuit breaker provide electrical current to the first circuit and the second circuit. A third switch and a fourth switch associated with the first substation are opened, wherein the third switch and forth switch provide electrical current to a third circuit and forth circuit. Finally, a third circuit breaker and forth circuit breaker associated with the second substation are closed, wherein the third circuit breaker and forth circuit breaker provide electrical current to the third and forth circuits. 
         [0010]    A transferable feeder system is also provided that includes a first substation having a first pair of feeders and a second pair of feeders, wherein each feeder in the first pair of feeders and the second pair of feeders has an associated switch. A second substation is provided having a third pair of feeders electrically coupled to the first pair of feeders, and a fourth pair of feeders electrically coupled to the second pair of feeders, wherein each feeder in the third pair of feeders and the fourth pair of feeders has an associated circuit breaker. At least one load is electrically coupled to the first pair of feeders, the second pair of feeders, the third pair of feeders and the fourth pair of feeders. A controller is associated with the first substation and the second substation, where the controller is disposed in communication with the switches associated with the first pair of feeders and the circuit breakers associated with the third pair of feeders. The controller includes a processor responsive to executable computer instructions for opening the switches associated with the first pair of feeders and closing the circuit breakers associated with the third pair of feeders in response to receiving a command signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Referring now to the drawings, which are meant to be exemplary and not limiting, and wherein like elements are numbered alike: 
           [0012]      FIG. 1  is a schematic illustration of a utility electrical transmission and distribution system; 
           [0013]      FIG. 2  is an schematic illustration of a portion of the electrical distribution system of  FIG. 1  with two interconnected distribution networks in accordance with one embodiment of the invention; 
           [0014]      FIG. 3  is a schematic illustration of an alternate embodiment of the interconnected distribution system of  FIG. 2 ; and, 
           [0015]      FIG. 4  is a flow chart illustration of an exemplary method of operating the interconnected distribution system of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  illustrates an exemplary embodiment of a utility electrical transmission and distribution system  20 . The utility system  20  includes one or more power plants  22 ,  24  connected in parallel to a main transmission system  26  by multiple step-up transformers  28 . The power plants  22 ,  24  may include, but are not limited to: coal, nuclear, natural gas, or incineration power plants. Additionally, the power plants  22 ,  24  may include one or more hydroelectric, solar, or wind turbine power plants. The step-up transformers  28  increase the voltage from that produced by the power plants  22 ,  24  to a high voltage, such as 138 kV for example, to allow long distance transmission of the electric power over main transmission system  26 . It should be appreciated that additional components such as transformers, switchgear, fuses and the like (not shown) may be incorporated into the transmission and distribution system  20  as needed to ensure the safe and efficient operation of the system. The transmission and distribution system  20  is typically interconnected with one or more other utility networks to allow the transfer of electrical power into or out of the transmission and distribution system  20 . 
         [0017]    The main transmission system  26  typically consists of high voltage transmission power lines, anywhere from 69 KV to 500 KV for example, and associated transmission and distribution equipment which carry the electrical power from the point of production at the power plant  22  to the end users located on local electrical distribution systems  30 ,  32 . The local distribution systems  30 ,  32  are connected to the main distribution system by area substations  34 ,  36  that are connected to the first distribution system  30  and second distribution system respectively. The area substations  34 ,  36  reduce the transmission voltage to distribution levels such as 13 KV, 27 KV or 33 KV for the end users. Area substations  34 ,  36  typically contain three or more transformers, switching, protection and control equipment as well as circuit breakers to interrupt faults such as short circuits or over-load currents that may occur. Substations  34 ,  36  may also include equipment such as fuses, surge protection, controls, meters, capacitors, load tap changers and voltage regulators. 
         [0018]    It should be appreciated that the substations  34 ,  36  may both be connected to a single power plant, such as first power plant  22  for example. Alternatively, they may be connected to the main transmission system  26  such that the substations  34 ,  36  receive electrical power from different power stations, such as substation  34  receives electrical power from first power plant  22  and substation  36  receives electrical power from second power plant  24  as illustrated in  FIG. 1  for example. 
         [0019]    The area substations  34 ,  36  connect to one or two local electrical distribution networks  38 ,  40  respectively. These local networks  38 ,  40  provide electrical power to an area, such as a residential area for example. The local networks  38 ,  40  also include additional equipment, such as transformers  48  that adapt the voltage from that output by the substations  34 ,  36  to that usable by the end customers. For example, the substation  34  may distribute electrical power at 13 kV. The transformer  48  lowers the voltage to 120V/208V, which is usable by a residence. The local networks  38 ,  40  may further have isolated end users such as an office building  42  or a manufacturing facility  44 . The area substation  34  typically has a plurality of feeder circuits that provide electrical power directly to isolated customers  42 ,  44 . As will be discussed in more detail below, the second area substation  36  includes a plurality of feeder circuits that provide an interconnection with the isolated customers  42 ,  44  and first substation  34 . 
         [0020]    Referring now to  FIG. 2 , an exemplary substation interconnection system will be described. The substation  34  receives electrical power from the main transmission network  26  via connection  50 . The connection  50  is part of a plurality of feeders within the substation  34 . A feeder is a device that allows the utility to receive the incoming electrical power and subdivide the electrical power into discrete branch circuits connected to the substation  34 . In the exemplary embodiment, several of the feeders  52  transfer power into circuits that connect to the local distribution network  38 . Usually, each feeder  52  includes a circuit breaker  54  that allows the connection and disconnection of the substation from the local network  38 . 
         [0021]    A second group of feeders  56 ,  58 ,  60 ,  62  are also coupled to connection  50 . The second group of feeders  56 ,  58 ,  60 ,  62  is coupled to the local network  38  via circuit breakers  64 ,  66 ,  68 ,  70 . In addition, the second group of feeders  56 ,  58 ,  60 ,  62  are further coupled to the isolated loads  42 ,  44  via medium voltage switches  72 ,  74 ,  76 ,  78 . A third group of feeders  80 ,  82  are also coupled to connection  50 . The third group of feeders  80 ,  82  is coupled to the isolated loads  42 ,  44  via circuit breakers  84 ,  86  and medium voltage switches  88 ,  90 . 
         [0022]    Substation  34  also includes a controller  92 . The controller  92  may be any suitable device capable of receiving multiple inputs and providing control functionality to multiple devices based on the inputs. Controller  92  includes a processor that is a suitable electronic device capable of accepting data and instructions, executing the instructions to process the data, and presenting the results. The processor may accept instructions through a user interface, or through other means such as but not limited to electronic data card, voice activation means, manually operable selection and control means, radiated wavelength and electronic or electrical transfer. Therefore, the processor can be a microprocessor, microcomputer, a minicomputer, an optical computer, a board computer, a complex instruction set computer, an ASIC (application specific integrated circuit), a reduced instruction set computer, an analog computer, a digital computer, a molecular computer, a quantum computer, a cellular computer, a superconducting computer, a supercomputer, a solid-state computer, a single-board computer, a buffered computer, a computer network, a desktop computer, a laptop computer, or a hybrid of any of the foregoing. 
         [0023]    The controller  92  is coupled to communicate with external devices via communications medium  93 , these devices include medium voltage switches  72 ,  74 ,  76 ,  78 ,  88 ,  90  and the circuit breakers  64 ,  54 ,  66 ,  68 ,  70 ,  84 ,  86 , and phase angle meter  100  for example. Controller  92  may also communicate with external devices, such as a controller  94  associated with substation  36  or a computer at a central control facility  96  via a communications medium  98 . It should be appreciated that the communications mediums  93 ,  98  may be any suitable communications means, including wired or wireless, capable of quickly and reliably transmitting information. The communications mediums  93 ,  98  may also be radio connection in the 900 MHz spectrum, a leased telecommunications line (e.g. X.25, T1), a fiber network, a PSTN POTS network, a DSL telecommunications line, a cable telecommunications line, a microwave connection, a cellular connection, or a wireless connection using the IEEE 802.1 standard. 
         [0024]    It should be appreciated that while the exemplary embodiment illustrates the controllers  92 ,  94  and central control  96  as discrete components, these devices may also be integrated into a single device that provides control functionality over both substations  34 ,  46 . Further, the functionality of the controllers  92 ,  94  that are described herein may be distributed among several controllers that provide the control functionality. In one embodiment, the controller  92 ,  94  functionality is distributed into controllers associated with the devices of the substations  34 ,  36 , such as the circuit breakers  64 ,  54 ,  66 ,  68 ,  70 ,  84 ,  86  and the medium voltage switches  72 ,  74 ,  76 ,  78 ,  88 ,  90  for example. 
         [0025]    The second substation  36  is arranged similarly to the first substation  34 . A connection  102  delivers electrical power from the main transmission system  26 . A first group of feeders  104  delivers the electrical power to the second local distribution network  40  via circuit breakers  106 . A second group of feeders  108 ,  110 ,  112 ,  114 ,  116 ,  118  are coupled to the feeders  56 ,  58 ,  60 ,  62 ,  80 ,  82  respectively Each feeder  108 ,  110 ,  112 ,  114 ,  116 ,  118  has an associated circuit breaker  120 ,  124 ,  126 ,  128 ,  130  that allows the individual feeders to be connected and disconnected from loads  42 ,  44  and their counter part feeders in substation  34 . As will be discussed in more detail below, during normal operation the circuit breakers  120 ,  124 ,  126 ,  128 ,  130  are in an open position, preventing the flow of electrical current to the loads  42 ,  44 . A phase angle meter  134  is installed to measure the phase angle characteristic of the electrical power at substation  36 . 
         [0026]    In addition to the feeders, circuit breakers and switches described above, substations  34 ,  36  may also include equipment such as fuses, surge protection, controls, meters, capacitors, and load tap changers for voltage regulation. 
         [0027]    In the exemplary embodiment, the loads  42 ,  44  are what are commonly referred to as “isolated loads”, meaning that the loads  42 ,  44  are directly connected to feeders  56 ,  58 ,  60 ,  62 ,  80 ,  82  and substation  34  and not interconnected with other branch circuits of substation  34 . These types of loads include facilities such as large commercial facilities, large multistory residential or office buildings (e.g. skyscrapers) and hospitals for example. Since these types of facilities have large power requirements, they may be arranged in a multibank configuration to receive electrical power via multiple connections that are coupled to circuits fed from different feeders. The facility will also typically have transformers  132  that change the electrical characteristics of the electrical power from a medium distribution voltage, such as 13 kV or 27 kV for example, to that usable by the facility, such as 265V/460V or 120V/208V for example. It should be appreciated that while two loads  42 ,  44  are illustrated in the exemplary embodiment, the invention is not so limited and any number of loads  42 ,  44  may be so connected. Further, the multibank configuration may have three or five connections as illustrated, or may have additional connections such as four or six connections for example. 
         [0028]    The methods and systems are not limited to the interconnection of discrete isolated loads. Referring to  FIG. 3 , another embodiment interconnection is illustrated. In this embodiment, the substations  34 ,  36  are configured as discussed above with the feeders  56 ,  58 ,  60 ,  62 ,  80 ,  82  of the first substation  34  coupled to the feeders  108 ,  110 ,  112 ,  114 ,  116 ,  118  of the second substation  36 . Similarly circuit breakers  64 ,  66 ,  68 ,  70 ,  84 ,  86 ,  120 ,  122 ,  124 ,  126 ,  128 ,  130  and the medium voltage switches  72 ,  74 ,  76 ,  78 ,  88 ,  90  allow the disconnection of the respective substations  34 ,  36 . A mini-grid or mini-network  138  is coupled to the substations  34 ,  36  via plurality of transformers  136  that connected and adapt each individual circuit from the feeders to the mini-grid  138 . The mini-grid  138  may be similar to local distribution network  38 , but smaller in size, whereas network  38  is fed from one substation  34 , the mini-grid  138  has access to two different sources of supply  34 ,  36 . 
         [0029]    Turning now to  FIG. 4 , the method of operating a substation feeder interconnection  140  will be described. The method  140  starts in block  142  and proceeds to query block  143  where it is determined if the phase angle is less than a desired threshold. A difference in the phase angles may cause a flow of circulating currents. The circulating currents increases in proportion to the phase angle, which results in a correspondingly larger current. For each set of interconnected loads, there will be a maximum current, and therefore a maximum phase angle differential, that can be tolerated by the connected loads and all other electrical equipment related to substation, such as feeders for example. In one study, for example, the loads were able to tolerate a phase angle differential of up to 8 degrees. This comparison is done for each electrical phase, meaning that an “A” phase in substation  34  is compared with the “A” phase of substation  36 . 
         [0030]    If query block  132  returns a positive, then the method  140  proceeds to block  145  where it is determined if operational methods may be used to reduce phase angle differential to within the desired threshold. If query block  145  returns a negative, meaning that the phase angle cannot be changed, the method  140  loops back to start block  142  and the process starts again. If the phase angle differential can be adjusted, the operator executes operational methods (not shown) in block  147  to alter the phase angle to within the desired threshold. 
         [0031]    Once the phase angle is within the desired threshold parameters, the method  140  proceeds to query block  144  where it is determined whether to switch loads, such as loads  42 ,  44  for example, from being supplied electrical power from the first substation  34  to an alternate supply from second substation  36 . It should be appreciated that this decision may be made in a number of ways. For example, an operator at a central facility may make the decision in light of the operating conditions of the local distribution networks  38 ,  40 . In another embodiment, the decision may be automated and the decision based on factors such as but not limited to power availability, load distribution on local network  38 , electrical power usage by the interconnected loads  42 ,  44 , the availability of electrical power from the main transmission system  26 , and the availability of electrical power from power plants  22 ,  44 . If query block  144  returns a negative, the method  140  loops back to start block  142  and starts again. 
         [0032]    If query block  144  returns a positive, a signal transmitted to switch the loads. The source of the transmission will depend on where the decision in query block  144  was made. For example, if an operator or a computer at a central facility  96  made the decision to switch the loads, the signal may be transmitted over communications medium  98  to controllers  92 ,  94 . 
         [0033]    The method  140  then proceeds to block  154 . In block  154 , a first pair of switches in the first substation  34  is opened. For example, in the exemplary embodiment, the medium voltage switches  72 ,  74  are opened. At this point, the flow of electrical power from the feeders  56 ,  58  to the load  42  is interrupted. However, because electrical current is still flowing through feeder  60 , load  42  does not experience a power loss. Similarly, since load  44  is still receiving the electrical current via feeders  62 ,  80 ,  82 , no power loss is experienced by load  44 . 
         [0034]    After the first pair of switches, medium voltage switches  72 ,  74  for example, are opened, a first pair of circuit breakers in second substation  36  are closed in block  156 . In the example where switches  72 ,  74  are opened, circuit breakers  108 ,  110  are closed restoring the flow of electrical current to the loads  42 ,  44 . In the exemplary embodiment, the opening of the switches and the closing of the circuit breakers are performed in a break-before-make relationship. This means that the current flow through the switches is completely halted (e.g. contacts open) before the circuit breakers begin to close. It should be appreciated that since the phase angles of the substations are within the desired threshold, the electrical power may be delivered to the loads from two different sources. 
         [0035]    After each pair of switches is opened in block  154  and closed in block  156 , the process proceeds to query block  155  where it is determined if there was any issue with the opening or closing of the switches. For example, due to a mechanical issue, one of the switches may have been incapable of opening or closing. If query block  155  returns a positive, the method  140  proceeds to block  157  where the transfer is aborted. The method  140  then performs a reverse transfer in block  159  for any switch pairs that were previously closed and opened. It should be appreciated that this reversal is also performed as a break-before-make relationship as described above. Once the switches have been returned to their normal state, the method  140  loops back to start block  142 . 
         [0036]    If there were no issues with the switching in query block  155 , then method  140  then proceeds to query block  158  where it is determined if all the feeders for loads  42 ,  44  have been transferred from the first substation  34  to the second substation  36 . If the query block  158  returns a negative, the method  140  proceeds to loop back via block  160  to transfer the next pair of switches and circuit breakers. This continues until all the feeders for loads  42 ,  44  have been transferred from the first substation  34  to the second substation  36 . In the example illustrated in  FIG. 2 , after the circuit breakers  108 ,  110  close, the medium voltage switches  76 ,  78  open. In the same break-before-make relationship, the circuit breakers  124 ,  126  close to restore the flow of electrical current. Finally, the medium voltage switches  88 ,  90  open followed by the closing of circuit breakers  128 ,  130 . This method of operation provides advantages in the transferring of loads  42 ,  44  from the first substation  34  to the second substation  36  without loss of service to the end customers. 
         [0037]    It should be appreciated that the first substation  34  may disconnect from the loads  42 ,  44  with the circuit breakers  64 ,  66 ,  68 ,  70 ,  84 ,  86  rather than the medium voltage switches  72 ,  74 ,  76 ,  78 ,  88 , and  90 . However, the use of the medium voltage switches  72 ,  74 ,  76 ,  78 ,  88 ,  90  provides an additional advantage in that some of the feeders, such as feeders  56 ,  58 ,  60 ,  62  may be shared with the local distribution network  38 . The use of the medium voltage switches allows feeder to provide power to the local distribution network when the feeder is disconnected from the isolated loads. 
         [0038]    Once all the feeders from the first substation  34  that are connected to the isolated loads  42 ,  44  are transferred to the second substation  36 , the query block  158  returns a positive and the method  140  loops back to the start block  142 . It should be appreciated that once the circumstances that warrant the transfer of the feeders is alleviated, the loads  42 ,  44  may be transferred back to the first substation  34  using the same process in reverse. Meaning that a pair of circuit breakers, such as circuit breakers  108 ,  110  for example, are opened and a pair of switches, such as medium voltage switches  72 ,  74  for example, are closed. The method of operation proceeds in this manner until all the feeders have been transferred back to the first substation  34 . 
         [0039]    It should be appreciated that the feeder interconnection system and method of operation disclosed herein provides a number of advantages in the switching of loads from one distribution network to another. The feeder interconnection system and method may minimize or eliminate the loss of service that may be experienced if loads were transferred to a new distribution network using alternative methods. The feeder interconnection system and method may also provide advantages in providing flexibility to an electrical utility to reconfigure the distribution of power to account for changing conditions. Finally, the system and method of operation allows the transferring of loads that are connected by an underground distribution network. 
         [0040]    An embodiment of the invention may be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. The present invention may also be embodied in the form of a computer program product having computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, USB (universal serial bus) drives, or any other computer readable storage medium, such as random access memory (RAM), read only memory (ROM), or erasable programmable read only memory (EPROM), for example, wherein, when the computer program code is loaded into and executed by a computer, the computer, as part of a programmable controller, becomes an apparatus for practicing the invention. Execution of the method includes interaction between the controller and the medium voltage switches installed on the feeders to verify the status of the switches, prior and after the commands are issued for their operation. The present invention may also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits. A technical effect of the executable instructions is to manage the transfer of loads from feeders associated with a first substation to an alternate supply of feeders associated with a second substation. 
         [0041]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.