System, method and device to preserve protection communication active during a bypass operation

Provided is an intelligent electronic device for protection, monitoring, controlling, metering or automation of electrical power system. The system, method and device of the present invention preserves current differential protection active during a breaker bypass or similar operation. A current differential protection system is coordinated by one relay (transfer), which simultaneously establishes and handles multiple two-terminal 87L protection zones with several relays. This “enhanced multiple-terminal system” requires no change to protection settings on any local or remote relays during a bypass process.

CROSS-REFERENCE TO RELATED APPLICATIONS

BACKGROUND OF THE INVENTION

The present invention generally relates to electric power systems including intelligent electronic devices (IEDs) for protecting, monitoring, controlling, metering and/or automating electric power systems and associated power lines. More specifically, the present invention relates to a system, method and device for preserving current differential protection communication active during the process involved in a breaker bypass or similar operation.

Electric utility systems or power systems are designed to generate, transmit and distribute electrical energy to loads. In order to accomplish this, power systems generally include a variety of power system elements such as electrical generators, electrical motors, power transformers, power transmission lines, buses and capacitors, to name a few. As a result, power systems must also include IEDs and procedures to protect the power system elements from abnormal conditions such as electrical short circuits, overloads, frequency excursions, voltage fluctuations, and the like.

Generally, IEDs are also used for protecting, monitoring, controlling, metering and/or automating electric power systems and associated power lines. For example, certain IEDs and procedures may act to isolate some power system element(s) from the remainder of the power system upon detection of an abnormal condition or a fault in, or related to, the power system element(s). IEDs may include protective devices such as protective relays or otherwise, remote terminal units (RTUs), power line communication devices (PLCs), bay controllers, supervisory control and data acquisition (SCADA) systems, general computer systems, meters, and any other comparable devices used for protecting, monitoring, controlling, metering and/or automating electric power systems and their associated power lines.

In one example, a particular type of IED generally known as a current differential protective relay protects an associated power line by analyzing the current at different terminals of the line. The general implementation of a current differential protective relay is illustrated inFIG. 1A. A current differential protective relay R1measures the current I1situated at one bus102via current transformer CT1on an associated power line108. Another protective relay R2measures the current I2situated at another bus104via current transformer CT2on the same power line108. The current vector quantity I2(magnitude and angle) measured by protective relay R2is transmitted to the current differential protective relay R1via communication link130.

During operation, the current differential protective relay R1then calculates a vector sum of the currents [Σ(I1, I2)]. Under no-fault conditions, the resulting vector sum equals about zero amperes. In contrast, the occurrence of a fault or other abnormal condition is detected when the resulting vector sum does not equal about zero amperes. Upon detection of a fault or abnormal condition, the current differential protective relay R1sends a trip signal or command to an associated circuit breaker110to isolate the condition.

In order to fully isolate the fault condition, it is to be noted that the other protective relay R2is also a current differential protective relay. In this arrangement, the other current differential protective relay R2may be adapted to concurrently receive the current measurement I1from current differential protective relay R1via communication link130and calculate a vector sum therefrom.

When protecting, monitoring, controlling, metering and/or automating electric power systems and associated power lines, it is often beneficial to reroute data streams such as communication signals therein in order to calculate maintenance on protective devices or on power system elements associated thereto. For example, a power system element may require maintenance wherein the power system element and its associated protective device must be isolated from its associated power line. In order to maintain power distribution through the power line, power may be rerouted around the element that requires maintenance. In order to maintain protection, control, monitoring etc. of the power line, data streams such as communication signals must also be rerouted.

U.S. Pat. No. 6,639,330 for a “Transfer Relay for Computer Base Equipment” describes a power switching transfer relay to automatically switch an electrical load, such as that drawn by a computer or other sensitive electrical or electronic equipment, from a primary power source to a secondary, or backup, power source upon interruption or loss of the primary source. The transfer relay includes a power relay and two control relays that are arranged to switch the electrical power input from the primary source to the backup source upon failure of the primary power source in the space of less than one cycle, and to actuate an alarm upon loss of the primary power source, loss of the backup power source, or the occurrence of a relay fault.

U.S. Pat. No. 5,347,417 for a “Power Supply Protection System Applied to Optical Subscriber Network” describes a system for protecting a remote power supply for supplying power to an optical subscriber network, via a pair of power supply lines, from a remote power supply apparatus, with the power supply branch apparatuses inserted into the power supply lines in correspondence with each power receiving circuit respectively mounted in subscriber transmission nodes. Each of the power supply branch apparatuses comprises relay contacts inserted into its own power supply branch lines connected between the power supply lines and its own power receiving circuit, and a relay energized by an overcurrent detector or first and second communication units to change over the relay contacts. The relay contacts are opened and closed subscriber by subscriber sequentially to detect a faulty portion, and thereafter, the power is fed again selectively to the subscribers which have not experienced the fault.

U.S. Pat. No. 5,132,867, for a “Method and Apparatus for Transfer Bus Protection of Plural Feeder Lines” describes a microprocessor based tie relay for controlling a tie circuit breaker between a main bus and a transfer bus to which any one of a number of feeder lines may be connected through a disconnect switch when the feeder circuit breaker associated with that feeder line is out of service. Settings for the protection characteristics of each of the feeder relays controlling the feeder circuit breakers are stored in non-volatile memory together with a default protection characteristic suitable for protecting any of the feeder lines. The appropriate protection characteristic for the feeder line connected to the transfer bus is selected for use by the tie relay in controlling the tie circuit breaker. This selection may be made manually by an operator, or preferably automatically by the microprocessor of the tie relay which monitors the states of the feeder circuit breakers and of the disconnect switches and selects the settings associated with the feeder line whose feeder circuit breaker is open and disconnect switch is closed. If the microprocessor does not recognize only one feeder line connected to the transfer bus, the default protection characteristic is selected and an alarm is generated.

U.S. Pat. No. 5,041,737 for a “Programmable Bus-Tie Relay having a Plurality of Selectable Setting Groups” describes a bus-tie relay apparatus which includes a multi-position mechanical switch and a logic circuit responsive to the position of the mechanical switch for producing digital signals on five digital line, wherein a valid digital signal comprises the presence of high conditions on two, and two only, of said digital lines. A sensor senses the condition of the digital lines and retrieves the values of a relay element setting group from memory associated with that digital signal. A plurality of such relay element setting groups are stored in the apparatus, each one of which comprises values corresponding to the characteristics of an in-place relay associated with a particular one power line in a group thereof.

FIG. 1Bgenerally provides an illustration of a traditional system for applying IEDs, such as protective devices, in order to maintain protection, monitoring, controlling, metering and/or automating of an associated power line. It should be clear that whileFIG. 1Band other figures (including those illustrating the embodiments of the present invention) show two power lines emanating from a single substation, the methods and systems described herein may be generally extended to more or less than two lines, delivered to one or more substations. In the described systems, local protective relays R1, Rn-1are associated with respective circuit breakers110,111for primary protection. For primary protection, local protective relays R1, Rn-1are current differential protective relays similar to those described with respect toFIG. 1A.

In the arrangement ofFIG. 1B, local protective relays R1, Rn-1receive current measurements I2, Infrom remote protective relays R2, Rnvia communication link130b,130ain order to preserve current differential protection on power lines108,109as discussed with respect toFIG. 1A. Upon detection of a fault or abnormal condition on power lines108,109, the local protective relay R1, Rn-1associated with that particular power line108,109signals a corresponding circuit breaker110,111to isolate the condition. In order to fully isolate the fault condition, it is to be noted that remote protective relays R2, Rnare also current differential protective relays.

Circuit breakers (e.g.,110and111) are high maintenance devices that experience some wear each time they interrupt a fault condition. Accordingly, a substation is typically constructed such that each primary circuit breaker110,111may be taken out of service for maintenance purposes or replacement while leaving its associated power line108,109associated therewith energized. In these instances, prior art arrangements have isolated the primary circuit breaker110,111along with its associated local protective relay R1, Rn-1in order to provide for secondary protection on the energized power line108,109. The local protective relay R1, Rn-1associated with the primary circuit breaker110,111is commonly referred to as the primary relay.

A method for isolating a primary circuit breaker such as110or111while providing secondary protection in such instances is commonly referred to as a breaker bypass operation. As shown inFIG. 1B, one traditional arrangement for providing secondary protection in such instances includes having a transfer bus106associated with a main or primary bus102. In this arrangement, to isolate or take primary circuit breakers110,111out of service, all other lines are typically connected to the main bus102by proper configuration of switches S2, S5, and other switches as illustrated.

For example, all other power lines are connected to the main bus102by closing switch S2, and opening switch S5. During a breaker bypass operation, switch S5, is closed, whereas switches S1, S2, are opened such that power lines108,109are now connected to transfer bus106. Accordingly, current differential protection of either power line108,109is now maintained through protective relay Rxand circuit breaker114. The circuit breaker114which provides secondary protection is commonly referred to as a transfer breaker, tie breaker, or coupler breaker, whereas its associated relay Rxis commonly referred to as a transfer breaker, tie breaker, or coupler relay. Communication (e.g., communication of current vector quantities as discussed above) between remote relays R2, Rnand transfer relay Rxmay be optionally routed through communications switch200.

Nevertheless, the arrangement ofFIG. 1Bposes a number of challenges for current differential protection of power lines. For example, current differential protection generally cannot be maintained during the entire bypass process due to the resulting parallel lines that feed a protected power line through both the main and transfer buses during the switching process of a breaker bypass operation. The hypothetical condition of keeping line current differential protection active on the local and remote relays during the switching process, would inaccurately cause these relays to detect a fault or abnormal condition on the power line. This is because the switching process of a bypass operation on the aforementioned bus arrangement, creates a parallel feed path onto the bus, changing the local measured quantity, which causes the vector sums of the currents to be unequal to zero on each relay.

In order to overcome this shortcoming, during a breaker bypass or similar operation, current differential protection is often disconnected and replaced by backup protection such as step-distance. This, however, compromises the quality of the power line protection as step-distance protection is generally known to be slower and less reliable than current differential protection. Most faults associated with a breaker bypass operation generally occur due to human error. For example, operators may inadvertently cause a bus-to-ground fault while they intend to create a parallel current path that will allow for isolation of the circuit breaker. Therefore, during manual modifications to the bus configurations during a bypass operation, the risk of causing a fault is the highest.

Accordingly, it is an object of the invention to provide a system and method for maintaining current differential protection of a power line even during a breaker bypass operation.

This and other desired benefits of the preferred embodiments, including combinations of features thereof, of the invention will become apparent from the following description. It will be understood, however, that a process or arrangement could still appropriate the claimed invention without accomplishing each and every one of these desired benefits, including those gleaned from the following description. The appended claims, not these desired benefits, define the subject matter of the invention. Any and all benefits are derived from the multiple embodiments of the invention, not necessarily the invention in general.

SUMMARY OF THE INVENTION

In accordance with the invention, an intelligent electronic device for protection, monitoring, controlling, metering or automation of power lines in an electrical power system is provided. The system, method, and devices of the present invention are adapted to provide protection of a power system. In other embodiments, a system, method, and device are provided which preserve line current differential protection during a breaker bypass or a similar operation.

In one embodiment, a system is provided for maintaining current differential protection of a power line using a plurality of IEDs. The system generally includes a local IED associated with a location of the power line. The local IED is adapted to measure and transmit the current vector quantity associated with the location of the local IED. A remote IED associated with a location of the power line is further provided, wherein the remote IED is adapted to measure and transmit the current vector quantity associated with the location of the remote IED.

A transfer IED in communication with the local and remote IEDs is adapted to receive the currents vector quantities transmitted by the local and remote IEDs.

The transfer IED is further associated with a second location on the same bus arrangement as the local IED interconnected with the protected power line. This second location may be on a power line which is parallel to the power line of the local and remote relays. The transfer IED calculates the sum of the currents associated with its own location in the bus and the currents received from the local and remote IEDs. When the sum of the currents is not equal to about zero amperes, the transfer IED transmits a signal to cause tripping of a circuit breaker associated therewith, thereby isolating the protected power line.

In accordance with yet another embodiment of the invention, the transfer IED is further adapted to transmit the current measured by the transfer IED and the current measured by the remote IED to the local IED. In turn, the local IED is adapted to receive the current quantity sent by the transfer IED, which is the vector sum of the currents measured by the transfer and the remote IED. The local IED will utilize the received current quantity and its own current measurement to evaluate a whether to assert a tripping signal to the associated local circuit breaker, in case these quantities do not add up to zero amperes.

In accordance with yet another embodiment of the invention, the transfer current differential IED is further adapted to transmit the current measured by the transfer IED and the current measured by the local IED to the remote IED. In turn, the remote IED is adapted to receive the current quantity sent by the transfer IED, which is the vector sum of the currents measured by the transfer and the local IED. The remote IED will utilize the received current quantity and its own current measurement to evaluate whether to assert a tripping signal to the associated remote circuit breaker, in case these quantities do not add up to zero amperes.

In accordance with yet another embodiment of the present invention, each of the transfer, local and remote IEDs are current differential IEDs which preserve line current differential protection during a breaker bypass or a similar operation.

In yet another embodiment of the present invention, a method for maintaining current differential protection of a power line in a power system is provided including the steps of measuring the current associated with a location of the power line; measuring the current associated with another location of the power line; measuring the current associated with a location of second power line interconnected with first power line; calculating the sum of the currents associated the locations of the first and second power lines; and transmitting a signal to a circuit breaker associated with the second power line when the sum of the currents is not equal to about zero amperes.

In yet another embodiment of the present invention a method for maintaining current differential protection of a power line in a power system is provided including the steps of measuring the current associated with a location of the power line; measuring the current associated with another location of the power line; measuring the current associated with a location of second power line interconnected with first power line; calculating the sum of the current associated with the first location of the first power line and current associated with the location of the second transmission associated the locations of the first and second power lines; and transmitting a signal to a circuit breaker associated with the second location of the second power line when the sum of the currents is not equal to about the current associated with the second location of the second power line.

It should be understood that the present invention includes a number of different aspects or features which may have utility alone and/or in combination with other aspects or features. Accordingly, this summary is not exhaustive identification of each such aspect or feature that is now or may hereafter be claimed, but represents an overview of certain aspects of the present invention to assist in understanding the more detailed description that follows. The scope of the invention is not limited to the specific embodiments described below, but is set forth in the claims now or hereafter filed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to a method and apparatus for customization of an IED. Generally, IEDs are used for protecting, monitoring, controlling, metering and/or automating electric power systems and associated power lines. IEDs may include protective devices such as protective relays, or otherwise, RTUs, PLCs, bay controllers, SCADA systems, general computer systems, meters, and any other comparable devices used for protecting, monitoring, controlling, metering and/or automating electric power systems and their associated power lines.

Although the embodiments described herein are preferably associated with protective devices, such as protective relays including transfer relays, local relays and remote relays, it is contemplated that the embodiments may also be associated with any suitable power system control or protective devices such as those mentioned or described above or below.

FIG. 2Aillustrates an embodiment of the invention for providing protection during a circuit breaker110bypass or similar operation using a transfer relay Rcto simultaneously establish and coordinate a three-terminal protection with a local relay Raand a remote relay Rb, which communicate with the transfer relay Rcon a two-terminal protection mode.

During primary protection of power line108, local current differential protective relay Rameasures the current I1situated at one bus102via current transformer CT1on an associated power line108. Another remote protective relay Rbmeasures the current I2situated at another bus104via current transformer CT2on an associated power line108. Current I2measured by remote relay Rbis transmitted to local relay Ravia communication link130.

The communication link130may be a wired link such as a fiber optic, regular metallic, Ethernet copper wired or a wireless link such as digital radio, RF or microwave communication. Current I2may be further communicated on the communication link130as time-aligned vector (magnitude and phase angle) quantities. A secured communication may further be achieved by using known encryption technologies such as data encryption standard (DES), triple DES (3DES), advanced encryption standard (AES), Rivest Cipher (RC4). The current I2may be further communicated on the communication link130as time-aligned vector quantities.

For purposes of this embodiment, communication among protective devices may be generally achieved by a bidirectional communications means. For example, data streams or communication signals maybe transferred as described in U.S. Pat. No. 5,793,750 for “System for Communicating Output Function Status Indications Between Two or More Power System Protective Relays” and U.S. Pat. No. 6,947,269 for “Relay-to-Relay Direct Communication System in an Electric Power System.”

During protection of a two-terminal line, the local relay Racombines the current I1that it measures with current I2measured and communicated by the remote relay Rb. The local relay Racalculates a vector sum of the currents (Σ(I1, I2)). Under normal conditions, the resulting vector sum equals about zero amperes. In contrast, the occurrence of a fault or other abnormal condition is detected when the resulting vector sum does not equal about zero amperes. Upon detection of a fault or abnormal condition, local relay Rasends a trip signal to an associated circuit breaker110to isolate the condition.

The bus arrangement containing circuit breaker110is designed such that it may take circuit breaker110out of service for maintenance purposes or replacement while leaving its associated power line108therewith energized and protected by a transfer relay Rc. For example, during a bypass or similar operation, circuit breaker110may be isolated. However, unlike traditional bypass arrangements (e.g., as described with respect toFIG. 1B), communication to and from local relay Rais not terminated, but rather rerouted to transfer relay Rc. More specifically, protection is established by communication between the transfer relay Rcand each of the local relay Raand the remote relay Rb.

In an embodiment, in order to initiate a bypass or similar operation, an operator may signal to communication switch200to reroute communications. For example, the operator may initiate such via control inputs202. More specifically, an operator may signal to communication switch200to cease communication between the local relay Raand the remote relay Rband, instead, commence communication between the transfer relay Rcwith each of the local relay Raand the remote relay Rb. An example of a communications switch that may be used for this application is that described in U.S. Patent Application No. 60/718,365 for a Method and Apparatus for Routing Data Streams Among Intelligent Electronic Devices or the SEL 2126 Fiber Optic Transfer Switch manufactured by Schweitzer Engineering Laboratories, Inc., both of which are incorporated herein in their entirety and for all purposes.

In this new configuration, transfer relay Rcis configured to receive currents quantities I1, I2respectively measured by local and remote relays Ra, Rb. The transfer relay Rcis further adapted to measure transfer current Ix. With these values, transfer relay Rccalculates a vector sum of the transfer current Ixand the currents I1, I2respectively transmitted by local and remote relays Ra, Rb[Σ(I1, I2, Ix)]. Under normal conditions, the resulting vector sum equals approximately zero amperes. It shall be noted that this is the case because under normal conditions, I I2I generally equals to I Σ(I1, Ix) I. In contrast, the occurrence of a fault or other abnormal condition is detected when the resulting vector sum does not equal zero amperes. Upon detection of a fault or abnormal condition, the transfer relay Rcsends a trip signal to an associated circuit breaker114to isolate the condition.

FIG. 2Billustrates an embodiment of the invention for preserving current differential protection active during a circuit breaker bypass or similar operation using a transfer relay Rxto establish a multiple feed line terminal. The embodiment ofFIG. 2Bdiffers from the embodiment ofFIG. 2Ain that all of transfer relay Rx, local relay R1, and remote relay R2are current differential relays.

Like the arrangement ofFIG. 2B, the bus arrangement containing circuit breaker110is designed such that it may take circuit breaker110out of service for maintenance purposes or replacement while leaving its associated power line108therewith energized and protected by a transfer current differential relay Rx. For example, during a bypass or similar operation, circuit breaker110may be isolated. However, unlike traditional bypass arrangements, communication to and from local current differential relay R1is not isolated, but rather rerouted to transfer current differential relay Rxin accordance with an aspect of the present invention. More specifically, current differential protection is maintained by establishing communication between the transfer current differential relay Rxand each of the local current differential relay R1and the remote current differential relay R2.

In one embodiment, in order to initiate a bypass or similar operation, an operator may close switch S5. The operator further signals to communication switch200to reroute communications via control inputs202. More specifically, an operator may signal to communication switch200to cease communication between the local current differential relay R1and the remote current differential relay R2and, instead, commence communication between the transfer current differential relay Rxwith each of the local current differential relay R1and the remote current differential relay R2.

In one embodiment, the control inputs202may be optionally controlled by a multiplexer (or MUX)204. It is to be noted that the communications switch200and the MUX204are included to reduce the number of communications channels involved and for automation purposes. In another embodiment (not shown), the communication between the transfer current differential relay Rxwith each of the local current differential relay R1and the remote current differential relay R2may be initiated by directly linking each of the local current differential relay R1and the remote current differential relay R2to transfer current differential relay Rxwithout a communications switch or a MUX.

Referring back toFIG. 2B, in the depicted configuration, communication between the transfer current differential relay Rxwith each of the local current differential relay R1and the remote current differential relay R2establishes a bypass or similar operation. Transfer current differential relay Rxis configured to receive currents I1, I2respectively measured by local and remote current differential relays R1, R2. The transfer current differential relay Rxis further adapted to measure transfer current Ix. Transfer current differential relay Rxcalculates a vector sum of the transfer current and the currents received from local current differential relay R1and remote current differential relay R1[Σ(I1, I2, Ix)]. Under normal conditions, the resulting vector sum equals about zero amperes. It shall be noted that this is the case because under normal conditions, I I2I generally equals to I Σ(I1, Ix) I. In contrast, the occurrence of a fault or other abnormal condition is detected when the resulting vector sum does not equal about zero amperes.

Simultaneously, transfer current differential relay Rxfurther calculates a vector sum of the currents Σ(I2, Ix) and Σ(I1, Ix) and communicates these vector sums back to local current differential relay R1and remote current differential relay R2, respectively through corresponding communications links130b,140band130a,140a. Local current differential relay R1calculates a vector sum of the current measured I1and the vector sum Σ(I2, Ix) received from transfer current differential relay Rx(Σ(I1, I2, Ix). Under normal conditions, the resulting vector sum equals about zero amperes. In contrast, the occurrence of a fault or other abnormal condition is detected when the resulting vector sum does not equal about zero amperes.

Remote current differential relay R2calculates a vector sum of the current measured I2and the vector sum Σ(I1, Ix) received from transfer current differential relay Rx(Σ(I2, I1, Ix). Under normal conditions, the resulting vector sum equals about zero amperes. In contrast, the occurrence of a fault or other abnormal condition is detected when the resulting vector sum does not equal about zero amperes. Upon detection of a fault or abnormal condition, the associated relay R1, R2, or Rxsends a trip signal to an associated circuit breaker110, or114to isolate the condition. In this way, the tripping of circuit breaker110and114fully isolates a fault associated power line108and the parallel power line106. It is to be noted that additional relays Rn-1, Rn, breakers, and communications links (not shown) may further be added and provided protection in accordance with the teachings above.

The main advantage of the invention, which is built into the transfer current differential relay (e.g., Rx), is the high system reliability achieved by preserving current differential protection during the entire process of a bypass operation. In addition, when setting up a multiple-terminal line system, the transfer current differential relay (e.g., Rx) in accordance with the teachings of the present invention will not require any connected IEDs to adjust its settings to communicate using any special mode other than the standard two-terminal current differential mode. This is important because the actual implementation requires less communications channels and less commissioning time, because no IED settings are required to be controlled remotely on the local or remote relays (e.g., R1, R2).

In yet another embodiment, communication links140aand140bmay be combined into a single communication link. In such an embodiment, a multiplexer (MUX) may replace the communications switch200in order to simplify communication traffic from the plurality of communication links140a,140binto a single channel communication link. Examples of MUXs known in the art that may be used herein include the Focus MUX manufactured by Pulsar Technologies, Inc., the Jungle MUX manufactured by General Electric Company, and the IMUX manufactured by RFL Electronics Inc.

FIG. 3Aillustrates an embodiment of the invention for consummating circuit breaker bypass operation after preserving current differential protection active during a circuit breaker bypass or similar operation using a transfer current differential relay Rxto establish a multiple feed line terminal as illustrated inFIG. 2B.

After rerouting the communications among the current differential relays Rx, R1, R2in accordance with the bypass operation as illustrated inFIG. 2B, the local circuit breaker110may be safely isolated by opening switch S1and S2. Because of the rerouting of communications as discussed with respect toFIG. 2B, current differential protection is maintained for power line108and power line109. Also, during normal conditions, the current values Ix, I2respectively measured by transfer current differential relay Rxand remote current differential relay R2are approximately equal upon a successful bypass or similar operation.

In order to restore local breaker110or place local feed line152back to service, the process reverses by closing local breaker110and the switches S1, S2associated therewith.

In order to ensure proper restoration of the local breaker, transfer current differential relay Rxcalculates a vector sum of the transfer current and the currents received from local current differential relay R1and remote current differential relay R1[Σ(I1, I2, Ix)]. Under normal conditions, the resulting vector sum equals about zero amperes. In contrast, if the local breaker is improperly restored or if there is an abnormal condition thereof, the resulting vector sum does not equal about zero

Simultaneously, transfer current differential relay Rxfurther calculates a vector sum of the currents Σ(I2, Ix) and Σ(I1, Ix) and communicates these vector sums back to local current differential relay R1and remote current differential relay R2, respectively through corresponding communications links130b,140band130a,140a. Local current differential relay R1calculates a vector sum of the current measured I1and the vector sum Σ(I2, Ix) received from transfer current differential relay Rx(Σ(I1, I2, Ix). Under normal conditions, the resulting vector sum equals about zero amperes. In contrast, if the local breaker is improperly restored or if there is an abnormal condition thereof, the resulting vector sum does not equal about zero Remote current differential relay R2calculates a vector sum of the current measured I2and the vector sum Σ(I1, Ix) received from transfer current differential relay Rx(Σ(I2, I1, Ix). Under normal conditions, the resulting vector sum equals about zero amperes. In contrast, if the local breaker is improperly restored or if there is an abnormal condition thereof, the resulting vector sum does not equal about zero

If a fault or abnormal condition is not detected, a restoration operation is initiated to open transfer switch S5while closing switches S1and S2associated with the previously bypassed circuit breaker110. In contrast, if a fault or abnormal condition is detected, the associated current differential relay R1, R2, or Rxwill communicate a trip signal to open its associated circuit breakers110,111, or114.

The transfer current differential relay Rxmay further be adapted to coordinate with communication switch200to disconnect communication links between130aand140a, and between130band140b. Moreover, transfer current differential relay Rxmay further be adapted to re-establish links between communication link130aand130b. As such, the transfer bus106is freed up to service another local feed line such as local feed line154in the system through the communication switch200using the system and method of the present invention or any other bypass means.

As illustrated inFIG. 3B, in accordance with yet another aspect of the present invention, the transfer current differential relay Rxmay further be adapted to communicate with local current differential relay Rn-1and remote current differential relay Rnin order to provide current differential protection during a bypass or similar operation using similar principles as discussed in greater detail with respect toFIG. 2B and 3A. In yet another embodiment ofFIG. 3B, communication links140a,140b,140cand140dmay be combined into a single communication link. In such an embodiment, a multiplexer (MUX) may replace the communications switch200in order to simplify communication traffic from the plurality of communication links140a,140b,140c,140dinto a single channel communication link.

As illustrated inFIG. 3C, in accordance with yet another aspect of the present invention, the transfer current differential relay Rxmay further be adapted to include both transfer relay capability with that of a communication switch200in a single device300. The single device300may further optionally include a MUX204therein.

As illustrated inFIG. 3D, transfer current differential relay Rxmay be adapted to preserve current differential protection active during a bypass or similar operation for a plurality of relays R1, R2, R3, R4, Rnassociated with a power line. The equations of this figure represent the vector sum of measured current at which each current differential relay operates under a normal condition wherein no fault or other abnormal condition exists on the power line. For example, current differential relay R4detects a normal condition when IR4=Σ(Ix, I1, I2, I3, . . . In), whereas a fault condition or an abnormal condition is detected when IR4≠Σ(Ix, I1, I2, I3, . . . In). Upon detection of a fault, current differential relay R4may be adapted to send a trip signal to an associated circuit breaker to isolate the condition.

In the embodiments of the present invention as illustrated inFIGS. 2A-3D, the transfer current differential relay Rxis the only affected relay which requires modification of settings contained therein; therefore, this present invention system and method is flexible and may be readily implemented throughout the power system.

In accordance with an aspect of the present invention,FIG. 3Eillustrates a block diagram of an IED300for preserving current differential protection active for a plurality of current differential relays R1to Rnduring a bypass or similar operation. This IED300may be utilized for transfer current differential relay Rxfunctionality in the embodiments of the invention as described above.

In one embodiment, IED300measures the transfer current Ixincluding any or all three phases of the current IxA, IxB, IxC. Simultaneously, IED300is adapted to receive input data352from a plurality of serial inputs carrying digitized vector current quantities I1to In(and any or all three phases thereof) measured and communicated by respective current differential relays R1to Rn(not shown in this figure). This input data may be transmitted over a plurality of communications links (e.g., if connected directly to the relays or a communications switch) or a single communication link (e.g., if connected to a MUX).

The measured analog transfer current vector quantities IxA, IxB, IxCmay be filtered using low pass filters312,314316; optionally multiplexed through MUX322; and digitized through an analog to digital (A/D) converter324. The resulting digitized current values may further be respectively filtered through digital band pass filters326,328,330to further reduce noise.

A micro-controller336is provided to calculate a vector sum of the transfer current quantities IxA, IxB, IxCand the measured currents I1, I2, I3. . . Inreceived from current differential relays [Σ(I1, I2, I3. . . Ix)]. Under normal conditions, the resulting vector sum equals about zero; therefore, an optional no trip signal is communicated at communication port346which may be connected to an associated circuit breaker. In contrast, if a fault or abnormal condition is detected, the resulting vector sum does not equal about zero; therefore, a trip signal is communicated at communication port344which may be connected to an associated circuit breaker.

Simultaneously, transfer current differential relay Rxfurther calculates a vector sum of the currents for each current differential relay, wherein IR1=Σ(Ix, I2, I3, . . . In); IR2=Σ(Ix, I1, I3, . . . In) and IR3=Σ(Ix, I1, I2, . . . In). The transfer current differential relay Rxis adapted to transmit these values to corresponding current differential relays via communication ports338,340,342. Each current differential relay determines whether a normal or an abnormal condition exists on the power line. For example, a normal condition is detected when IR3=Σ(Ix, I1, I2, . . . In), whereas a fault condition or an abnormal condition is detected when IR3≠Σ(Ix, I1, I2, . . . In). As discussed above, upon detection of a fault, current differential relay R3may be adapted to send a trip signal to an associated circuit breaker to isolate the condition.

In an alternate embodiment of IED300, the input data352may interface with a field programmable gate array (FPGA)350or an equivalent programmable logic device. The FPGA may be adapted to provide a data interface which includes DBPF326,328,330and micro-controller336. As the system becomes more complex, one or more FPGAs with multiple microcontrollers may be included to perform other specific protection, monitoring, controlling, metering and/or automating functions.

As illustrated inFIG. 3F, in yet another embodiment of IED300, the communication ports338,340,342,344, and346ofFIG. 3Emay be replaced with a single communications link358. An example of a suitable communication link is a network communication link358such as an Ethernet wide area network (not shown). The communication link358may be adapted such that multiple data frames may be sent and received through the same link358. The IEC 61850 standard communication protocol is an example of a suitable protocol for fast communications between IEDS. In the embodiment ofFIG. 3F, the communication link358may further be adapted to communicate the digitized current vector quantities I1, I2, I3. . . Inmeasured and transmitted by their respective relays.

In accordance with an aspect of the present invention,FIG. 4Aillustrates a method wherein a transfer current differential relay Rxcommunicates with each of the plurality of current differential relays R1, R2. . . Rnin order to preserve current differential protection of an associated power line. In step450, a transfer current differential relay Rxreceives current vector quantities I1, I2. . . Infrom associated relays through a suitable communication link(s). Preferably, the current vector quantities transmitted to the transfer current differential relay Rxare time-aligned in order to maintain power system synchronization. Concurrently, the transfer current differential relay Rxmeasures its local current vector quantity Ixthrough its current transformer. It is to be noted that the transfer current differential relay Rxmay be adapted to measure any or all three phases of the current Ix.

In step452, the transfer current differential relay Rxis adapted to calculate the vector sum of calculate a vector sum of the transfer current value Ixand the measured currents I1, I2, . . . Inreceived from current differential relays [Σ(I1, I2, . . . Ix)]. Simultaneously, transfer current differential relay Rxfurther calculates a vector sum of the currents for each current differential relay, wherein IR1=Σ(Ix, I2, . . . In); IR2=Σ(Ix, I1. . . In) and IRn=Σ(Ix, I1, I2, . . . In-1). The transfer current differential relay Rxis adapted to transmit these values to corresponding relays via a suitable communication port Com1, Com2. . . Com n, respectively.

In step454, the transfer current differential relay Rxdetermines whether the vector sum of transfer current value Ixand the measured currents I1, I2, . . . Inreceived from relays [Σ(I1, I2. . . Ix)] equals about zero amperes. Under normal conditions, the resulting vector sum equals about zero amperes. Therefore, in such cases, the method is reestablished in order to monitor fault conditions on the associated line. In contrast, if a fault or abnormal condition is detected, the resulting vector sum does not equal about zero; therefore, a trip command is communicated as shown at456which may be communicated to an associated circuit breaker.

In accordance with yet another aspect of the present invention,FIG. 4Billustrates a method wherein a current differential relay R1associated with the transfer current differential relay RxofFIG. 4Acommunicates with such in order to preserve current differential protection of an associated power line. In step460, current differential relay R1measures its local current vector quantity I1through its current transformer. Concurrently, this current vector quantity I1is transmitted to transfer current differential relay Rx.

In step462, current differential relay R1receives the vector sum of currents IR1transmitted from transfer current differential relay Rx(IR1=Σ(Ix, I2, . . . In)), the calculation of which is explained in detail above with respect toFIG. 4A.

In step464, the transfer current differential relay Rxdetermines whether the vector sum of the measured current value I1and vector sum of currents IR1equals about zero amperes. Under normal conditions, the resulting vector sum equals about zero amperes. Therefore, in such cases, the method is reestablished in order to monitor fault conditions on the associated line. In contrast, if a fault or abnormal condition is detected, the resulting vector sum does not equal about zero; therefore, a trip command is communicated as shown at466which may be communicated to an associated circuit breaker.

While this invention has been described with reference to certain illustrative aspects, it will be understood that this description shall not be construed in a limiting sense. Rather, various changes and modifications can be made to the illustrative embodiments without departing from the true spirit, central characteristics and scope of the invention, including those combinations of features that are individually disclosed or claimed herein. Furthermore, it will be appreciated that any such changes and modifications will be recognized by those skilled in the art as an equivalent to one or more elements of the following claims, and shall be covered by such claims to the fullest extent permitted by law.