Secure and dependable restricted earth fault protection for electric power generators and transformers

Detection of, and protection against faults within a restricted earth fault (REF) zone of a transformer or a generator is disclosed herein. Security of the REF protection element uses comparison of a negative-sequence reference quantity. The REF condition is only detected when there is sufficient ground involvement and a fault in the reverse detection has not been detected. Dependability of the REF protection element in low-impedance grounded systems is improved by ensuring that the element operates when a zero-sequence reference quantity and a neutral operate quantity are orthogonal to each other. The REF protection element further determines an open CT condition and blocks detection of an REF fault upon determination of the open CT condition. A tripping subsystem may issue a trip command based upon detection of the REF condition.

RELATED APPLICATIONS

TECHNICAL FIELD

This disclosure relates to the secure and dependable detection of internal faults on electric power delivery system equipment. More particularly, this disclosure relates to the secure protection element performance for external faults and dependable detection of internal faults when applied to low-impedance grounded systems.

In the following description, numerous specific details are provided for a thorough understanding of the various embodiments disclosed herein. However, those skilled in the art will recognize that the systems and methods disclosed herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In addition, in some cases, well-known structures, materials, or operations may not be shown or described in detail in order to avoid obscuring aspects of the disclosure. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more alternative embodiments.

DETAILED DESCRIPTION

Electric power delivery systems are used to transmit power from sources to loads, and include various kinds of equipment to facilitate transmission. Generators play the important role of generating the electric power that is transmitted, distributed, and consumed using the electric power delivery system. Generators may be embodied in many different forms and may be in electrical connection with the electric power delivery system in different ways. Transformers are used to transfer electric power from a system at a first voltage to another system at a second voltage. For example, transformers may be used to transform power at generation voltage levels to power at transmission voltage levels; and other transformers may transform power at transmission voltage levels to lower distribution voltage levels. In AC electric power delivery, transformers may be multi-phase, and are critical pieces of equipment for the reliable delivery of power. In order to maintain the health of electric power transformers, IEDs are often used to detect conditions of the electric power equipment such as transformers and generators, and take protective actions such as opening circuit breakers to remove the electric power transformer from service. Electric faults between windings, or between windings and ground must be securely and quickly detected so that power may be removed before the transformer is damaged. It should be noted that although many embodiments herein are described as the monitoring and protection of electric power transformers, certain embodiments may also apply to other electric power system equipment such as electric power generators.

To properly isolate a fault, and maintain reliable delivery of electric power, IEDs must differentiate between faults external to the transformer, and internal faults. Restricted earth fault (REF) protection uses ground current in the transformer neutral and zero-sequence current at the terminals. REF protection is adequate for many conditions because it does not respond to load current. However, it lacks security under certain conditions such as CT saturation for an external fault. Furthermore, typical REF protection may not detect certain faults for resistive grounded transformers, or where external fault detection is used to block REF in an effort to increase security.

What is needed is restricted earth fault protection that is secure, dependable, and retains speed. Disclosed herein are systems and methods for securely detecting an internal fault on a transformer.

Reference throughout this specification to “one embodiment” or “an embodiment” indicates that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. In particular, an “embodiment” may be a system, an article of manufacture (such as a computer readable storage medium), a method, and/or a product of a process.

The phrases “connected to,” “networked,” and “in communication with” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, and electromagnetic interaction. Two components may be connected to each other, even though they are not in direct physical contact with each other and even though there may be intermediary devices between the two components. A computer may include a processor such as a microprocessor, microcontroller, logic circuitry, or the like. The processor may include a special purpose processing device such as an ASIC, PAL, PLA, PLD, Field Programmable Gate Array, or other customized or programmable device. The computer may also include a computer readable storage device such as: non-volatile memory, static RAM, dynamic RAM, ROM, CD-ROM, disk, tape, magnetic, optical, flash memory, or other computer readable storage medium.

The described features, operations, or characteristics may be combined in any suitable manner in one or more embodiments. It will also be readily understood that the order of the steps or actions of the methods described in connection with the embodiments disclosed herein may be changed, as would be apparent to those skilled in the art. Thus, any order in the drawings or detailed description is for illustrative purposes only and is not meant to imply a required order, unless specified to require an order. In the following description, numerous details are provided to give a thorough understanding of various embodiments. One skilled in the relevant art will recognize, however, that the embodiments disclosed herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of this disclosure.

FIG. 1illustrates a block diagram of a transformer110of an electric power delivery system that includes REF protection. The transformer includes windings112connected in a delta-wye configuration. Circuit breakers114and116may be used to disconnect the transformer from the source side and/or the system140side of the transformer110. As illustrated, the REF protection in the transformer system is restricted to a zone between the three-phase current transformer118and the neutral-current transformer124that are connected to the wye winding of the transformer110. In particular, the three-phase current transformer118and the neutral-current transformer124are wired to cancel current during external faults outside of the REF protection zone, and drive secondary current to an REF element130when the fault is inside of the REF protection zone. Although illustrated as single lines and single transformers, the electric power delivery system may be three-phase; and the three-phase current transformer118may consist of three sets of primary and secondary winding (i.e. three single-phase current transformers). The neutral-current transformer124may be connected between the neutral point of winding112and ground128.

The REF element130may be embodied as a module in an IED such as protective relay102. The protective relay102may receive the current signals from the three-phase current transformer118and the neutral-current transformer124, and perform various functions such as REF protection using such currents.

A traditional REF element would use terminal current signals3I0134obtained using the current transformer118and neutral current signals IN136. Specifically, the terminal current signals would be zero-sequence current3I0signals summed in a manner such that faults external to the restricted zone would be canceled (and as such, the REF relay would not operate for such external faults), but would pick up for faults internal to the restricted zone.

If a fault is present in the wye windings112, the sum of the zero-sequence three-phase current3I0134and the neutral current IN136is not zero. For example, if an internal ground fault occurs at circuit breaker116, then the system140may contribute some zero-sequence current measured by the three-phase current transformer118. The zero-sequence current measured by the three-phase current transformer118, however may not be the same amount of current measured by the neutral-current transformer124(i.e., neutral current136IN). As such, the sum of the three-phase current3I0134and the neutral current136is not zero, thereby indicating that a fault condition may be present within the restricted zone.

The current signals3I0134and IN136from the current transformers may be obtained by the protective relay102and used by the REF element130. Upon detection of an anomalous condition, the protective relay102may issue an alarm and/or a trip command104to open the circuit breaker116, and to electrically remove the transformer110from the system140. For example, upon detection of a fault condition, the protective relay102may send a trip command104to the circuit breaker116to trip (i.e., switch to open) and disconnect the transformer110from the system140in order to protect the transformer110and/or the system140from damage that may otherwise occur due to the fault. Additionally, or alternatively, the protective relay102may send an alarm signal to indicate that a fault exists.

Although not shown inFIG. 1, the protective relay102may include a microprocessor, a non-volatile memory, and/or a user interface. The microprocessor may include any type of processing circuitry, such as one or more processors, general-purpose microprocessors, special-purpose microprocessors, application-specific integrated circuits (ASICs), or some combination thereof. For example, the microprocessor may include one or more reduced instruction set (RISC) processors. The processor may process instructions stored in the memory to determine operations and faults, as will be discussed in detail herein. Moreover, the processor may process the instructions to command components to operate equipment such as the circuit breakers114,116based on determined faults, and so forth.

The memory may be configured to store instructions, data, and/or information, such as an algorithm used for determining internal or external ground faults based on stored data (e.g., predetermined current thresholds) and/or received data (e.g., three-phase current134and neutral current136). The memory may be a tangible, non-transitory, computer-readable medium that stores sensor data and/or instructions executable by the processor. Thus, in some embodiments, the memory may include random access memory (RAM), read-only memory (ROM), rewritable non-volatile memory, flash memory, hard drives, optical discs, and the like.

Furthermore, in some embodiments, the protective relay102may be communicatively coupled to and/or include a user interface that provides information to and/or receives information from a user. In some embodiments, the user may control or override the protective relay102, such as to manually command a maintenance operation or a mitigating operation to prevent potential damage that may occur in the transformer110due to a fault. The user interface may include any suitable combination of input and output devices, such as an electronic display, a touchscreen, stylus, keypad, button, and/or the like, to enable communicating system fault and/or system information to a user. Moreover, in some embodiments, the protective relay102may be communicatively coupled to and/or include a communication interface that may enable communication with any suitable communication network, such as wiring terminals, a cellular network, WiFi network a personal area network (PAN), local area network (LAN), wide-area network (WAN), or the like. For example, the communication interface may enable the controller102to communicate with a user interface implemented on a user's mobile device, which may also be communicatively coupled to the communication network.

Although briefly mentioned above, the REF monitoring and protection described herein may be applied to a generator as well as to a transformer. In instances where a generator is monitored and protected, the transformer110ofFIG. 1is simply replaced with a generator, where the CT118is in electrical communication with the terminals of the generator, and the neutral grounding CT124is in electrical communication with a neutral ground connection of the generator.

FIG. 2illustrates a block diagram of an implementation of an REF element130to determine internal and external faults. Inputs to the REF element130may include the zero-sequence current3I0134as a reference quantity and the neutral current IN136as an operate quantity. The REF element130may operate in accordance with user settings252stored at commissioning or setting of the REF element130. Generally, a torque may be calculated from the reference quantity134and the operate quantity136. The torque may be compared with a threshold, to determine whether the detected fault is internal or external. The REF element130asserts an internal fault signal232or an external fault signal234depending on the comparison of the torque and threshold. As mentioned above, traditional REF relay implementations may suffer from a lack of security or dependability. In various implementations, to correct for a lack of security, the REF relay implementation may sacrifice dependability. The systems and methods described herein improve both security and dependability of REF protection without sacrificing speed. Briefly, the systems and methods described herein use negative-sequence current from the terminals as well as zero-sequence current from the terminals to detect a phase fault hence securing the REF element130for external faults without adding delay timers to verify internal faults. In certain embodiments, the REF element is designed such that for a low-resistance grounded system, dependability is improved when the neutral fault current is resistive and the terminal zero-sequence current is inductive or capacitive. In certain embodiments, the REF element may be disabled upon detection of an open CT condition, adding further security.

FIG. 3illustrates a simplified logic diagram for the calculation of reference and operate quantities that may be used for REF protection in accordance with several embodiments herein. In particular, a zero-sequence reference quantity IRREF312may be determined by normalizing a zero-sequence current3I0signal302obtained from the terminals. Block320may normalize the zero-sequence current3I0302using the CT ratio CTR of the terminal current transformer118, the CT ratio CTRN of the neutral current transformer124and the nominal neutral input current INOM-N. Similarly, the negative-sequence reference current quantity IQREF314may be calculated by normalizing the negative sequence current3I2304obtained from the terminal current transformer118. Other normalizing factors may be selected and used.

The operate quantity IOREF316may calculated by normalizing the neutral-ground current IN306, obtained using current transformer124. The normalization330may use the nominal neutral input current INOM-N.

With the reference quantities IRREF312and IQREF314and the operate quantity IOREF316, the methods and systems herein may determine whether a fault condition exists, and whether the fault condition is internal to the restricted earth fault zone or external to the restricted earth fault zone.

FIG. 4illustrates a logic diagram for detecting a phase fault using the negative-sequence reference quantity IQREF314, the operate quantity IOREF316, and the zero-sequence reference quantity IRREF312. In particular, the negative-sequence reference quantity IQREF314is compared with a pickup setting402in comparator406. The pickup setting402may be in per-unit, and may be selected in accordance with REF fault detection guidance. The pickup setting402may be a residual current sensitivity pickup setting. In various embodiments, pickup setting402may be selected to be greater than the maximum neutral operate current IOREF316and zero-sequence reference current IRREF312at steady state. Accordingly, when the negative-sequence reference quantity IQREF314exceeds the pickup setting, comparator406asserts to AND gate410.

A maximum of the operate quantity IOREF316and the zero-sequence reference quantity IRREF312is compared408against the negative-sequence reference quantity IQREF314multiplied by a scaling factor k2422. In various embodiments, the scaling factor k2422may be less than one. In one particular embodiment, the scaling factor k2422is 0.1. If the maximum value404is greater than the scaled factor of the negative-sequence reference quantity IQREF314, then comparator408asserts. The assertion of comparator408is inverted to AND gate410. Accordingly, AND gate410asserts a security signal412upon assertion of comparator406and a lack of assertion of comparator408. In other words, the logic determines a security signal412when the negative-sequence reference quantity IQREF314exceeds the pickup setting AND the scaled negative-sequence reference quantity IQREF314is greater than the maximum of the operate quantity IOREF316and the zero-sequence reference quantity IRREF312.

As may become apparent below, an internal fault cannot be determined upon assertion of the security signal412. Accordingly, presence of excess negative-sequence current reference quantity inhibits the assertion of an internal fault. The security signal412indicates negligible ground involvement in the fault.

In essence,FIG. 4illustrates an embodiment of adding security to REF detection under conditions of insufficient ground involvement. For example, when the zero-sequence reference quantity312and the operate quantity316are less than around one tenth of the negative-sequence quantity, then an REF element may lose security, and the detection thereof is blocked by assertion of the security signal412. In one embodiment, REF detection is blocked when the negative-sequence reference signal IQREF314exceeds the pickup setting402, and both of the zero-sequence reference quantity IRREF312and the operate quantity IOREF316are less than the scaled422(which may be 0.1) negative-sequence reference quantity IQREF314.

FIG. 5illustrates a logic diagram that continues the indication of an internal fault512and determination of an internal fault232. That is, the logic may be used to determine a fault within the restricted earth fault zone. In particular, the logic asserts the internal fault pickup signal512upon assertion of the REF enable signal532, and absence of a security signal412, absence of a reverse fault detection signal518, and in various embodiments, absence of an open CT detection signal506. In essence, instead of simply using a forward-fault detection signal to determine an internal fault, the embodiments herein determine an internal fault upon enablement of the REF element and absence of reverse-fault and phase-fault detection. The reverse fault detection signal518goes through a security timer720(as illustrated and described in conjunction withFIG. 7) and if the condition remains true for 30 ms declares an external, reverse ground fault signal234.

In the illustrated embodiment, an AND gate508receives an inverted reverse fault pickup signal518, an inverted supervisory signal from timer504, an REF enable signal532, and may receive an inverted open CT detection signal506. It should be noted that in various embodiments, as described below, the open CT detection signal may fall within the REF enable signal532. In certain embodiments, OR gate502may assert to a timer upon assertion of any of the security signal412and the reverse fault detection signal518. Timer504may include a pickup setting and a dropout setting. In various embodiments, the pickup may be set to zero such that the timer504asserts to AND gate508immediately upon assertion of OR gate502. In various embodiments, the dropout setting may be around 1 second such that the timer504remains asserted to AND gate508for 1 second after deassertion of the OR gate502. Because assertion from the timer504is inverted to AND gate508, then assertion of either of the security signal412or the reverse fault detection signal518will inhibit assertion of the internal fault pickup signal512while either of those signals are present and until expiration of the dropout timer504. The internal fault pickup signal512goes through a security timer520and if the condition remains true for 30 ms, declares an internal, forward ground fault signal232.

Accordingly, an internal fault512is detected upon assertion of the REF enable signal532and in absence of the reverse fault detection signal518and the security signal412. In other words, assertion of the reverse fault detection signal518or the security signal412may be said to block or inhibit detection of an internal fault512by the REF element. Input signals to the logic inFIG. 5may originate from various logical routines or external inputs. In various embodiments, the reverse fault signal518, open CT signal506, and/or the REF enable signal532may be determined using the logic described inFIGS. 6 and 7.

FIG. 6illustrates a logic diagram useful for determining the REF enable signal532, and may also be used to provide security for an open CT condition, and open CT signal506. The logic compares the operate quantity IOREF316against the pickup setting402in comparator604; and compares the zero-sequence reference quantity IRREF312against a scaled pickup setting402in comparator606. Generally, the REF enable signal532is asserted by AND gate612when both the operate quantity IOREF316exceeds the pickup setting402and the zero-sequence reference quantity IRREF312exceeds the scaled pickup setting. The pickup setting may be the same as the pickup setting402ofFIG. 4, or may be an alternative setting.

As can be seen, the open CT signal506is asserted based on the comparisons. In particular, when the operate quantity IOREF316is not greater than the pickup setting402and the zero-sequence reference quantity IRREF312does exceed the scaled pickup setting402, then AND gate608asserts to a pickup/dropout timer610. The timer asserts after a pickup time of assertion of comparators604and606, which may be around 10 seconds, and remains asserted for the dropout time. The dropout time may be around 30 seconds. The timer asserts the open CT signal506. While the open CT signal506is asserted, the REF enable signal is not asserted. That is, when the open CT condition is detected, restricted earth fault detection is not enabled.

The algorithm inFIG. 6even without the open CT detection portion is inherently secure for an external line-to-ground (LG) fault, where it is expected that a reverse fault would be detected (e.g., by torque comparison, described below) in the absence of CT saturation. Once CT saturation occurs, the saturated CT provides a secondary current with a phase lead lower than 80° with respect to the primary current.

As generally illustrated, the REF enable signal532is asserted when sufficient operate and reference current exists. The REF enable signal532is asserted when IOREF316exceeds the pickup setting402, and IRREF312exceeds a factor (in this case 0.8) of the pickup setting402. Taken together withFIG. 5, it is evident that an internal or forward ground fault may be determined when there is sufficient operate and reference current (i.e. IOREF316exceeds the pickup setting402, and IRREF312exceeds a factor of the pickup setting402), and an external or reverse fault pickup518has not asserted, and the security signal412has not asserted.

FIG. 7illustrates a logic diagram useful for determining a reverse fault signal518which may indicate a reverse fault, or fault outside of the restricted earth fault zone. In one embodiment, a restricted earth fault torque signal TorqueREF702is compared (using, e.g. comparator712) against a threshold706. When the torque signal702is less than a negative of the threshold706, then an external/reverse fault pickup signal518is asserted by comparator712. When the torque signal702is not less than the negative of the threshold706, an external/reverse fault pickup signal518is not asserted. As mentioned above, in various embodiments the external/reverse fault pickup signal518may be secured by a pickup timer720. Timer720may have a pickup time of around 30 ms. Accordingly, upon assertion of the external/reverse fault pickup signal518for the pickup time720, the external/reverse ground fault signal234is asserted.

The torque signal702may be calculated using the operate quantity IOREF316and the zero-sequence reference quantity IRREF312. In some embodiments, the torque signal702may be the real part of the product of the operate quantity IOREF316and the zero-sequence reference quantity IRREF312as illustrated in Equation 1:
TorqueREF=Re(IRREF·IOREF)  Eq. 1
The torque threshold706may be selected or calculated such that when the angle between the operating current IOREFand the reference current IRREFis within 80° from the ideal 180°, which corresponds to the minimum CT dimensions, a reverse fault pickup518is declared.

It should be noted previous REF detection methods checked that the torque signal702is greater than the threshold706to detect an internal, forward fault. This implied that the forward fault would be detected if due to system non-homogeneity or CT errors, the angle between IRREF312and IOREF316is within 80°. By using the external, reverse fault indication signal518from comparator712via the AND gate508to declare an internal fault, the angle between IRREF312and IOREF316need only be within 100°. In low-impedance grounded systems, i.e. when there is a low-impedance resistor that connects transformer winding112to ground128, the angle between the IRREF312and IOREF316can be close to 90° for an internal ground fault since the contribution from system140may be inductive or capacitive. The increase in angle from 80° to 100° provides greater dependability in systems where the transformer winding112or a generator stator winding is low-impedance grounded.

The embodiments herein are an improvement to existing restricted earth fault detection by calculating a security signal. The security signal may be calculated using a negative-sequence reference current quantity IQREF314as described herein, and seen inFIG. 4. Embodiments herein are also an improvement to existing restricted earth fault protection by detecting an open CT, and inhibiting the restricted earth fault protection upon detection of the open CT. Accordingly, the present improvements generally detect a fault within the restricted earth fault protection zone of a transformer by calculating a security signal using a negative-sequence reference current quantity IQREF314, and an open CT condition. A fault within the restricted earth fault protection zone is detected only in absence of the security signal, absence of the open CT condition, and absence of a reverse fault detection signal. The fault internal to the restricted earth fault protection zone of the transformer may be determined by comparing an operate quantity IOREF316and a zero-sequence reference quantity IRREF312.

FIG. 8illustrates a simplified block diagram of an IED for securely and rapidly detecting a fault within the restricted earth fault zone of a transformer, and effecting a protective action upon detection. IED800may be configured to perform a variety of tasks using a configurable combination of hardware, software, firmware, and/or any combination thereof. The illustrated embodiment includes hardware and software, and may be implemented in an embedded system, field programmable gate array implementations, and specifically designed integrated circuit. In some embodiments, functions described in connection with various software modules may be implemented in various types of hardware. Moreover, certain components or functions described herein may be associated with other devices or performed by other devices. The specifically illustrated configuration is merely representative of one embodiment consistent with the present disclosure.

IED800includes a network communications interface816configured to communicate with other IEDs and/or system devices. In certain embodiments, the network communications interface816may facilitate direct communication with another IED or communicate with another IED over a communications network. The network communications interface816may facilitate communications with multiple IEDs. The communications interface816may be used to monitor and determine if the communication channel is healthy and/or to determine an order of circuit breakers to trip. Note that any suitable communication network and/or communication channel may be used to communicate voltage data, quality of the communicated information, the biasing factors, or any other suitable data that may be communicated between the generators. Further, any suitable communication protocol to communicate the data may be used, such as Ethernet, Synchrophasor, DB9, peer-to-peer, or a proprietary protocol, among others.

IED800may further include a monitored equipment interface808to receive status information from, and issue control instructions to, a piece of monitored equipment. In some embodiments, the monitored equipment may be a transformer, a generator, a circuit breaker, or the like, and IED800may be configured to control the operation of the transformer, generator, and/or circuit breaker.

A local communication interface806may also be provided for local communication. The local communication interface806may be embodied in a variety of ways, including as a serial port, a parallel port, a Universal Serial Bus (USB) port, an IEEE 1394 Port, and the like.

In certain embodiments, IED800may include a sensor component810(e.g., sensor circuitry) to obtain electrical signals related to the transformer. The sensor component810may be configured to obtain branch current signals, zero-sequence voltage signals, neutral voltage signals, neutral current signals, or other such signals useful for determining a fault condition of the transformer. In the illustrated embodiment, sensor component810is configured to gather data directly from instrument transformers and may use, for example, A/D converters818that may sample and/or digitize filtered waveforms to form corresponding digitized current and voltage signals provided to data bus842. Inputs814a-cand814N may be electrically connected to current transformers in electrical communication with portions of a transformer arrangement, such as to the terminals of the transformer (via814a,814b,814c), a neutral-to-ground of the transformer (via814N) and the like. Conditioning circuitry812a-cand802N may reduce the voltage or current to a level appropriate for monitoring the terminator. A/D converters818may include a single A/D converter or separate A/D converters for each incoming signal. A current signal may include separate current signals from each phase of a three-phase electric power system. A/D converters818may be connected to processor824by way of data bus842, through which representations of electrical signals may be transmitted to processor824. In various embodiments, the representations of electrical parameters may represent parameters, such as currents, voltages, frequencies, phases, and other parameters associated with an electric power distribution system. Conditioning circuitry802a-cand802N may represent a variety of types of elements, such as voltage transformers, current transformers, status inputs, a breaker controller, etc. Sensor component810may be configured to receive digitized analog signals from merging units, which need little if any additional filtering, sampling, or processing before use by the processor824.

Processor824may be configured to process communications received via communications interface816, monitored equipment interface808, local communications interface806, and/or sensor component810. Processor824may operate using any number of processing rates and architectures. Processor824may be configured to perform various algorithms and calculations described herein. Processor824may be embodied as a general-purpose integrated circuit, an application specific integrated circuit, a field-programmable gate array, and/or any other suitable programmable logic device. In some embodiments, the processor824may be generally referred to as processing circuitry.

A transformer monitoring subsystem836may be configured to monitor the transformer using measured values (currents, voltages, etc.) and/or values received over communications. In particular, the transformer monitoring subsystem836may determine restricted earth fault condition in accordance with the several embodiments described herein. The transformer monitoring subsystem836may include instructions stored on non-transitory computer-readable storage media that, when executed using a processor, cause the IED to determine a restricted earth fault condition in accordance with the embodiments herein, and effect a protective action such as tripping a circuit breaker upon detection of the restricted earth fault condition.

A tripping subsystem832may be configured to issue a trip command based upon determination of the restricted earth fault condition. In various embodiments, the tripping subsystem832may be in communication with a breaker, recloser, merging unit, or other device that may be configured to interrupt an electrical connection between the transformer and an electric power delivery system.

In various embodiments, the tripping subsystem832may issue trip commands via an electrical or electromechanical interrupter, such as output circuitry833. In some embodiments, IED800may be configured to issue trip commands upon detection of the restricted earth fault condition or other protection elements. In various embodiments the IED800may be configured to communicate the determined restricted earth fault condition to other systems, and/or communicate to other systems that a trip command has been issued.

The above description provides numerous specific details for a thorough understanding of the embodiments described herein. However, those of skill in the art will recognize that one or more of the specific details may be omitted, or other methods, components, or materials may be used. In some cases, operations are not shown or described in detail. While specific embodiments and applications of the disclosure have been illustrated and described, it is to be understood that the disclosure is not limited to the precise configuration and components disclosed herein. Various modifications, changes, and variations apparent to those of skill in the art may be made in the arrangement, operation, and details of the methods and systems of the disclosure without departing from the spirit and scope of the disclosure.