Patent ID: 12259413

DETAILED DESCRIPTION

FIG.1shows a fault protection system10according to some embodiments. The fault protection system10is configured to detect a fault in an electric power system12, e.g., a power generation, distribution, and/or transmission system. In particular, the fault protection system10is configured to detect a fault internal to a fault protection zone14of the electric power system12.

The fault protection system10as shown includes a differential measurer16, e.g., in the form of differential measurement circuitry. The differential measurer16is configured to obtain a differential measurement signal18. The differential measurement signal18in some embodiments indicates, as a function of time, the difference between currents or voltages measured at two or more terminals or boundaries20of the fault protection zone14. For example, in some embodiments involving two terminals20, the differential measurement signal18may indicate, as a function of time, the difference between a current measured at one terminal20and a current measured at the other terminal20. The difference in these and other cases may effectively amount to what is left after summing the currents or voltages going into or out of the fault protection zone14, e.g., such that the differential measurement signal18represents how that difference changes over time. In some embodiments where the differential measurement signal18indicates this difference in terms of currents, the differential measurement signal18may be a phasor or instantaneous summation of current flows into the fault protection zone14, e.g., a summation of measurements from the terminals of a transmission or distribution line. In this case, phasor or instantaneous summation of current flows normally is a small or zero value but will increase in proportion to fault current when a short circuit occurs.

In some embodiments, the differential measurer16itself measures at least some of the currents or voltages at the two or more terminals or boundaries20in order to obtain the differential measurement signal18. In other embodiments, the differential measurer16receives measurements of the currents or voltages at the two or more terminals or boundaries20from other equipment, and then derives the differential measurement signal18from the received measurements. In still other embodiments, the differential measurer16receives the differential measurement signal18itself from other equipment (not shown).

No matter how the differential measurer16obtains the differential measurement signal18, the fault protection system10further includes a cross-correlator20, e.g., in the form of cross-correlation circuitry. The cross-correlator20cross-correlates the differential measurement signal18with a reference signal22, e.g., over a correlation window that spans a maximum possible duration of a fault to be detected. In some embodiments, the reference signal22is the differential measurement signal that is expected upon occurrence of a fault internal to the fault protection zone14. In these and other embodiments, then, the reference signal22may characterize a change that is expected to occur over time in the difference between currents or voltages measured at the two or more terminals or boundaries20upon occurrence of a fault internal to the fault protection zone14. Such change may be or include a step change, a ramp change, a sinusoidal change, and/or an exponential change, as a few examples.FIG.1for instance shows the reference signal22as characterizing a step change, Regardless of the particular nature of the reference signal22, the stronger the time-domain correlation between the differential measurement signal18and the reference signal22, the greater the likelihood that a fault has occurred. In some sense, then, the cross-correlation performed by the cross-correlator20amounts to fault waveform function versus reference function cross-correlation.

In any event, the cross-correlator20generates a fault detection signal24as the output of, or as a function of, the cross-correlation between the differential measurement signal18and the reference signal22.FIG.1for instance shows the fault detection signal24as being a triangular pulse over time.

The fault protection system10further includes a fault detector26, e.g., in the form of fault detection circuitry. The fault detector26performs fault detection, for detecting a fault internal to the fault protection zone14, as a function of the fault detection signal24. For example, in some embodiments, the fault detector26detects a fault internal to the fault protection zone14if a magnitude of the fault detection signal24exceeds a detection threshold, e.g., TH as shown inFIG.1. In one such embodiment, the magnitude must exceed the detection threshold for at least a threshold amount of time.

Alternatively or additionally, as another example, the fault detector26may compare the fault detection signal24with an expected fault detection signal that is expected upon occurrence of a fault internal to the fault protection zone14, e.g., where the expected fault detection signal may be a triangular pulse. In this case, the fault detector26performs fault detection as a function of that comparison, e.g., so as to detect a fault if the comparison indicates the fault detection signal24is similar to the expected fault detection signal at least to a certain extent.

For instance, the comparison in some embodiments involves taking samples of the expected fault detection signal, multiplying each sample by a respective sample of the fault detection signal24in a window, and then summing the resulting products. The window may then be moved sample by sample, as new process sample sets come in over time, and the comparison repeated. The sequence of summation values will jump in value if the shape of the incoming sample changes match the shape of the expected fault detection signal. Imperfect matches show up as lesser jumps. No changes or other types of changes show up as an unchanging sequence of summation values, or as variations not showing the expected jump in value.

In any event, based on the fault detection performed by the fault detector26, the fault protection system10in some embodiments controls a fault isolation device (not shown) that disconnects the electric power system12from a fault, e.g., by deenergizing and/or isolating the faulted segment of the power system. The fault isolation device may for instance be a circuit breaker. In some embodiments as shown, for example, fault detection performed by the fault detector26produces a fault detection decision or metric28that indicates whether or not the fault detector26detects a fault. In this case, the fault protection system10may control the fault isolation device using or as a function of the fault detection decision or metric28.

Alternatively or additionally, the fault protection system10may be used in conjunction with other fault detection measurements and/or logical and sequence processing to yield a decision of whether or not to operate a fault isolation device for isolating the faulted segment. In some embodiments, for example, existing legacy protection functions, such as overcurrent relaying, may operate in parallel with cross-correlation embodiments herein, with the fault isolation device being triggered if any of the mechanisms detect a fault.

Alternatively or additionally, the fault protection system10may send a fault notification signal to indicate occurrence of a detected fault. The fault notification signal may for instance alert electric power system personnel of the detected fault, so that actions may be taken to address the fault.

Consider now additional details about the nature of the differential measurement signal18. The currents or voltages that form the basis for the differential measurement signal18may be any type of currents or voltages. The currents or voltages may for example be instantaneous waveform measurements, or may be measurements extracted from these instantaneous values. For example, the currents or voltages may be power-frequency phasor measurements of magnitude and angle extracted by Fourier transform or other mathematical transform from the instantaneous waveform values.

Furthermore, in addition to the selection of the type of waveform measurements to be used, there are selections for which power system quantities are to be used for application of embodiments herein. For example, the currents or voltages may be phase-specific currents or voltages, i.e., so as to be specific to a certain alternating current (AC) phase. In this case, the differential measurement signal18is a phase-specific differential measurement signal that indicates, as a function of time, the difference between currents or voltages measured for a specific phase at the two or more terminals or boundaries20of the fault protection zone14.FIG.2Aillustrates one example of these embodiments.

As shown inFIG.2A, phase-specific measurements M1-1, M1-2, and M1-3represent currents or voltages measured respectively for 1st, 2nd, and 3rdphases at a first terminal or boundary20-1of the fault protection zone14. Likewise, phase-specific measurements M2-1, M2-2, and M2-3represent currents or voltages measured respectively for the 1st, 2nd, and 3rdphases at a second terminal or boundary20-2of the fault protection zone14. In this example, the differential measurer16obtains the phase-specific measurements M1-3and M2-3which represent currents or voltages measured for the 3rdphase at the first and second terminals or boundaries20-1,20-2. The differential measurer16computes the difference between these currents or voltages for the 3rdphase, as represented by the phase-specific measurements M1-3and M2-3, in order to obtain the differential measurement signal18in the form of a phase-specific differential measurement signal. The differential measurement signal18inFIG.2Athereby indicates, as a function of time, the difference between currents or voltages measured for the 3rdphase at the terminals or boundaries20-1,20-2of the fault protection zone14.

As another example, the currents or voltages may be residual currents or residual voltages. A residual current measured at a certain terminal or boundary20may be understood as the instantaneous sum of multiple phase-specific currents measured at that certain terminal or boundary20, e.g., in terms of the sum of synchronized measurement or synchrophasor values for multiple phases. Similarly, a residual voltage measured at a certain terminal or boundary20may be understood as the instantaneous sum of multiple phase-specific voltages measured at that certain terminal or boundary20, e.g., in terms of the sum of synchronized measurement or synchrophasor values for multiple phases. Generally, then, the differential measurement signal18in some embodiments may indicate, as a function of time, the difference between residual currents or residual voltages measured at the two or more terminals or boundaries20of the fault protection zone14. A differential measurement signal that indicates the difference between residual currents measured at the two or more terminals or boundaries20may be referred to herein as a differential residual current measurement signal, whereas a differential measurement signal that indicates the difference between residual voltages measured at the two or more terminals or boundaries20may be referred to herein as a differential residual voltage measurement signal.FIG.2Billustrates one example of these embodiments.

As shown inFIG.2B, the differential measurer16obtains the instantaneous sum of the phase-specific measurements M1-1, M1-2, and M1-3(which represent currents or voltages measured respectively for the 1st, 2nd, and 3rdphases at the first terminal or boundary20-1of the fault protection zone14). The result of this instantaneous sum is a residual current or voltage R1for the first terminal or boundary20-1. The differential measurer16also obtains the instantaneous sum of the phase-specific measurements M2-1, M2-2, and M2-3(which represent currents or voltages measured respectively for the 1st, 2nd, and 3rdphases at the second terminal or boundary20-2of the fault protection zone14). The result of this other instantaneous sum is a residual current or voltage R2for the second terminal or boundary20-2. The differential measurer16then computes the difference between the residual current or voltage R1for the first terminal or boundary20-1and the residual current or voltage R2for the second terminal or boundary20-2, in order to obtain the differential measurement signal18in the form of a differential residual measurement signal. The differential measurement signal18inFIG.2Bthereby indicates, as a function of time, the difference between residual currents or voltages measured at the terminals or boundaries20-1,20-2of the fault protection zone14.

Note, though, that the currents or voltages that form the basis for the differential measurement signal18are not raw current or voltage instantaneous sample values. Instead, in some embodiments, the currents or voltages that form the basis for the differential measurement signal18are synchrophasor current or voltage measurements, e.g., as extracted by phasor measurement units (PMUs) at the terminals or boundaries20and/or as computed by discrete Fourier transform (DFT) processing. In one or more embodiments, then, the differential measurement signal18indicates, as a function of time, the difference between synchrophasor currents or voltages (e.g., DFT-computed magnitude and angle measurements of currents or voltages) measured at the two or more terminals or boundaries20of the fault protection zone14. In these embodiments, the fault protection system10may effectively detect buried evidence of a fault that would not otherwise be readily detectable by observing the DFT-computed magnitude and angle measurements alone. The fault protection system10in particular uncovers a subtle change in the outputs of the differential DFT phasor calculated values by comparing it with the shape of the change produced by a fault, e.g., looking for a congruent or similarly-shaped change.

Note further that, althoughFIG.1shows fault detection as being performed based on a single differential measurement signal18, the differential measurement signal18shown may be just one of multiple differential measurement signals based on which fault detection is performed.

In some embodiments, for example, fault detection may be performed based on multiple differential measurement signals, one relating to currents and another relating to voltages. That is, one differential measurement signal may be a differential current measurement signal that indicates, as a function of time, the difference between currents measured at the two or more terminals or boundaries20. And another differential measurement signal may be a differential voltage measurement signal that indicates, as a function of time, the difference between voltages measured at the two or more terminals or boundaries20. In this case, the fault detector26may cross-correlate the differential current measurement signal with a reference current signal and cross-correlate the differential voltage measurement signal with a reference voltage signal, resulting in multiple fault detection signals, one for current and one for voltage. The fault detector26may correspondingly perform fault detection as a function of these fault detection signals. For example, the fault detector26may detect a fault if at least one of the fault detection signals indicates occurrence of a fault.FIG.3Aillustrates one example of these embodiments.

As shown inFIG.3A, the differential measurer16obtains the instantaneous sum of phase-specific current measurements C1-1, C1-2, and C1-3measured at the first terminal or boundary20-1, resulting in a residual current R1C for the first terminal or boundary20-1. The differential measurer16also obtains the instantaneous sum of phase-specific current measurements C2-1, C2-2, and C2-3measured at the second terminal or boundary20-2, resulting in a residual current R2C for the second terminal or boundary20-2. The differential measurer16then computes the difference between the residual current R1C for the first terminal or boundary20-1and the residual current R2C for the second terminal or boundary20-2, in order to obtain one differential measurement signal18in the form of a differential residual current measurement signal18C. This differential residual current measurement signal18C thereby indicates, as a function of time, the difference between residual currents measured at the terminals or boundaries20-1,20-2of the fault protection zone14.

The differential measurer16inFIG.3Afurther obtains the instantaneous sum of phase-specific voltage measurements V1-1, V1-2, and V1-3measured at the first terminal or boundary20-1, resulting in a residual voltage R1V for the first terminal or boundary20-1. The differential measurer16also obtains the instantaneous sum of phase-specific voltage measurements V2-1, V2-2, and V2-3measured at the second terminal or boundary20-2, resulting in a residual voltage R2V for the second terminal or boundary20-2. The differential measurer16then computes the difference between the residual voltage R1V for the first terminal or boundary20-1and the residual voltage R2V for the second terminal or boundary20-2, in order to obtain another differential measurement signal18in the form of a differential residual voltage measurement signal18V. This differential residual voltage measurement signal18V thereby indicates, as a function of time, the difference between residual voltages measured at the terminals or boundaries20-1,20-2of the fault protection zone14.

In this example, the fault protection system10includes one cross-correlator200that cross-correlates the differential residual current measurement signal18C with a reference current signal220, resulting in a fault detection signal24C for current. And the fault protection system10further includes another cross-correlator20V that cross-correlates the differential residual voltage measurement signal18B with a reference voltage signal22V, resulting in another fault detection signal24V, this time for voltage. The fault detector26correspondingly performs fault detection as a function of these fault detection signals24C,24V, e.g., by detecting a fault if at least one of the fault detection signals24C,24V indicates occurrence of a fault.

In other embodiments, fault detection may be performed based on multiple differential measurement signals, one for each of multiple phases, where each differential measurement signal is as described above inFIG.2Awith respect to differential measurement signal18but is specific to a respective one of the multiple phases. In this case, then, the differential measurer16may obtain, for each of multiple phases, a phase-specific differential measurement signal that indicates, as a function of time and for that phase, the difference between currents or voltages measured at the two or more terminals or boundaries20of the fault protection zone14. The cross-correlator20may then generate, for each of the multiple phases, a phase-specific fault detection signal by cross-correlating the phase-specific differential measurement signal for that phase with a reference signal (which may be the same or different for different phases). This results in multiple phase-specific fault detection signals, one for each phase. The fault detector26may correspondingly perform fault detection as a function of the phase-specific fault detection signals. For example, the fault detector26may detect a fault if at least one of the phase-specific fault detection signals indicates occurrence of a fault.FIG.3Billustrates one example of these embodiments.

As shown inFIG.38, the differential measurer16obtains phase-specific measurements M1-1and M2-1which represent currents or voltages measured for the 1stphase at the first and second terminals or boundaries20-1,20-2. The differential measurer16computes the difference between these currents or voltages for the 1stphase, as represented by the phase-specific measurements M1-3and M2-3, in order to obtain a phase-specific differential measurement signal18-1. Similarly, the differential measurer16obtains phase-specific measurements M1-2and M2-2which represent currents or voltages measured for the 2ndphase at the first and second terminals or boundaries20-1,20-2. The differential measurer16computes the difference between these currents or voltages for the 2ndphase, as represented by the phase-specific measurements M1-2and M2-2, in order to obtain another phase-specific differential measurement signal18-2. Furthermore, the differential measurer16also obtains phase-specific measurements M1-3and M2-3which represent currents or voltages measured for the 3rdphase at the first and second terminals or boundaries20-1,20-2. The differential measurer16computes the difference between these currents or voltages for the 3rdphase, as represented by the phase-specific measurements M1-3and M2-3, in order to obtain still another phase-specific differential measurement signal18-3.

The fault protection system10as shown includes one cross-correlator20-1that cross-correlates the phase-specific differential measurement signal18-1for the 1stphase with a reference signal22-1, resulting in a phase-specific fault detection signal24-1for the 1stphase. The fault protection system10also includes another cross-correlator20-2that cross-correlates the phase-specific differential measurement signal18-2for the 2ndphase with a reference signal22-2, resulting in a phase-specific fault detection signal24-2for the 2ndphase. And the fault protection system10further includes still another cross-correlator20-3that cross-correlates the phase-specific differential measurement signal18-3for the 3rdphase with a reference signal22-3, resulting in a phase-specific fault detection signal24-3for the 3rdphase.

The fault detector26may correspondingly perform fault detection as a function of these phase-specific fault detection signals24-1,24-2, and24-3. For example, the fault detector26may detect a fault if at least one of the phase-specific fault detection signals24-1,24-2, and24-3indicates occurrence of a fault.

In still other embodiments, such as those based on the combination ofFIGS.2A and2B, the combination ofFIGS.2A and3A, or the combination ofFIGS.3A and3B, fault detection may be performed based on multiple differential measurement signals, one differential measurement signal relating to residual currents or residual voltages and at least one other differential measurement signal being a phase-specific differential measurement signal. That is, one differential measurement signal indicates, as a function of time, the difference between residual currents or residual voltages measured at the two or more terminals or boundaries20of the fault protection zone14. And at least one other differential measurement signal indicates as a function of time, the difference between currents or voltages measured for a specific phase at the two or more terminals or boundaries20of the fault protection zone14. In this case, the cross-correlator20may generate one fault detection signal from the differential measurement signal relating to residual currents or voltages and at least one, phase-specific fault detection signal from the phase-specific differential measurement signal(s). The fault detector26may then perform fault detection based on all fault detection signals. For example, the fault detector26may detect a fault if the fault detection signal generated from the differential measurement signal relating to residual currents or voltages and at least one of the phase-specific fault detection signals each indicate occurrence of a fault internal to the fault protection zone14, e.g., at the same time.

Generally, then, embodiments herein may exploit any combination of the different types of differential measurement signals disclosed herein. For example, embodiments herein may exploit (i) one or more differential current measurement signals, e.g., for one or more phases; (ii) one or more differential voltage measurement signals, e.g., for one or more phases; (iii) a differential residual current measurement signal; (iv) a differential residual voltage measurement signal; or (v) any combination of (i), (ii), (iii), and/or (iv).

In some embodiments, the fault protection system10is implemented by one or more processing circuits (e.g., one or more microprocessors or digital signal processors, DSPs) of a microprocessor relay, or other logic and computing platform such as a real-time automation controller. In other embodiments, the fault protection system10may be implemented by a networked application server computer connected to a super or lower-level phasor data concentrator (PDC).

In view of the above, some embodiments herein generally apply cross-correlation mathematical computations to electrical measurements (e.g., from three phases) and the residual or phase-summation values from the electric power system12to detect a change of value that is obscured by the noise of routine random measurement variations. This general type of measurement correlates noise-obscured changes or signals with a reference change or signal function. Examples of reference functions include a unit step function, a specific sinusoidal or exponential function, or other mathematical function that describes what the newly appearing signal should look like in the absence of noise or random variation that is obscuring it.

FIG.4shows the mathematical results of cross-correlation calculations that can give an impulse indication over time that a particular anticipated waveform is buried in the analyzed noisy signal.

Some embodiments use the cross-correlation calculation between a step function representing a unit step increase of envelope magnitude, and the magnitude value of residual or phase synchrophasor differential currents. This contrasts with discrete Fourier transform (DFT) filtering methods in conventional relays that are, in effect, utilizing the cross-correlation of raw waveform samples with reference power frequency sine and cosine waves over a time window of samples—for example over one or over three power cycles. Low-current, high-impedance ground faults that cannot be detected by a simple threshold comparison are expected to yield a triangle-wave impulse spanning the alignment of the incoming change signal with the reference function.

Some embodiments herein may be performed on real-time streams of voltage or current measurements from protected electric power apparatus or system sections, e.g., fault protection zone14. Synchrophasors comprise a particular implementation of the DFT with time-synchronized sampled data. The resulting magnitude (or phase) envelope can be subjected to further correlation as described above, e.g., by cross-correlator20.

Consider now a concrete example of some embodiments herein. This example will use the cross-correlation or covariance calculation between a step function and the magnitude value of residual or phase synchrophasor currents to detect a low-current, high-impedance ground fault that cannot be detected by a simple threshold comparison.

IRN(t) represents the differential residential current measurement signal18as the differential of the sums of the three-phase current synchrophasors from two or more line terminals of the fault protection zone14at a time t. If a low-current ground fault occurs, it will yield a ragged step change in the average value of the magnitudes of the differential residual current IRN(t) for successive checking times t=0, 1, 2, etc. The low-current ground fault signal is obscured by noisy variations of phasor values of IRN(t), so that a simple comparison with a detection threshold cannot be used to recognize the change and make a tripping decision.

The sequence of IRN(t) phasor magnitudes is cross-correlated with the reference signal22in the form of a simple unit step function by multiplication and summation over the window of examination, for example 3 to 10 power cycles. As the fault inception slides into alignment with the reference signal22, the covariance function will peak, and then will decline again as the fault window slides out of alignment over time. The peak is subjected to a threshold check for whether the differential IRN(t) change could be a fault. The indication is necessarily a triangular pulse following the moment of the fault change, as opposed to the sustained indication that one could observe with higher fault current. The crossing of the detection threshold is used to issue a trip and latch the event occurrence indicator.

The degree of filtering and sensitivity from the cross-correlation calculation is a function of the width of the time window used for the cross-correlation calculation. Some embodiments filter out the magnitude value variations and expose the step change, while not making the window so long that creeping variations of value outside the fault moment confuse the result. A window of 3 to 10 power cycles or phasor values may be used in some embodiments.

Some embodiments also use an additional security check comprising the simultaneous cross-correlation of the individual phase differential currents (the differential of terminal current values for each phase) with the reference step function, looking for one phase in particular showing a triangular peak aligned with that from the response of the IRN(t) to the step. That would identify the faulted phase and help confirm that this is a fault.

Consider a simple example to illustrate some embodiments. For an example window of 8 power cycles and one P-Class synchrophasor magnitude per power cycle (60 phasor frames per second), the reference unit step function R(t) with a window of 8 cycles has the series of eight values −1, −1, −1, −1, 1, 1, 1, 1 going from the furthest time back to the present time. In other words R(t−7)=−1 and R(t)=1.

If the just received and most recent value of the differential residual current magnitude is IRN(t), the last eight magnitude values are available in the rolling file of data that updates as each new value arrives in real time. Call the newest and seven next older values IRN(t), IRN(t−1), IRN(t−2), . . . , IRN(t−7).

Cross-multiply each of the eight values of the reference step function over time with its respective IRN(t) value, and sum the eight products to obtain the value of the fault detection signal magnitude S at time t:
S(t)=K*Σt=−7t=0(R(t)*IRN(t))

where K is a scaling constant that is taken as 1 here.
S(t)=−IRN(t−7)−IRN(t−6)−IRN(t−5)−IRN(t−4)+IRN(t−3)+IRN(t−2)+IRN(t−1)+IRN(t)

S(t) is then stored in the time sequence of values for S, where S exemplifies the fault detection signal24inFIG.1.

Each time a new incoming sample arrives, the window moves forward by one sample and the calculation of S(t) is repeated.

If the IRN(t) current magnitude is changing only gradually over time, the values of S(t) will be approximately zero.

If a step change occurs in the value of IRN(t), even if small, the near-zero value of S(t) will begin to increase until the step change of the reference (between t−4 and t−3) is aligned with the step change of IRN(t). The value of S(t) will then decline as the step of IRN(t) moves out of the window. The resulting triangle-wave sequence is subjected to a peak magnitude check, or else compared to a reference threshold triangle for a more careful check, to determine if the step magnitude corresponds to a possible low-level ground fault.

In some embodiments, the fault protection system10further includes a change detector that implements supervision for phase currents or line voltages so that major change events like line energization or sudden large load increases do not trigger a fault trip response.

Different time windows from 3 to 10 or 20 cycles can be used, depending on the desired result. The tradeoff is degree of noise filtering and detection sensitivity versus slow trip decisions. Overly long windows may be less helpful because of instability of arcing ground fault current.

Alternatively or additionally to a step change, the reference signal22in other embodiments may be a unit ramp (e.g., of 3 cycles) with constant step-like values before and after the ramp. In some embodiments, there is an odd number of samples in the window, and for the example of a 7 cycle window some embodiments may use the R(t) sequence −1, −1, −1, 0, 1, 1, 1. This may better fit the fault appearance function considering the time response of the DFT in the PMU-relay to a step-change fault. Other embodiments use a longer ramp for the reference signal22, such as the nine-sample sequence −2, −2, −2, −1, 0, 1, 2, 2, 2, 2. Generally, the reference signal22may use greater number resolution and may closely replicate the step response of the PMU-relay DFT calculation, e.g., which can be observed in a laboratory test. In a real-time programmable automation controller platform, there is no penalty of note for using real number multiplications instead of just changing signs as one multiplies by −1.

Ultimate performance in some embodiments depends on the resolution capabilities of the PMU relay. For example, some embodiments that use a step change refence signal detect occurrence of a 25,000 ohm fault upon detecting a magnitude change of 5 or 10 counts in the binary value.

Some embodiments may be implemented, as an example, using Transmission Line Falling Conductor (TFCP) 87LN protection on a section of a 69 kV transmission system. A real-time programmable automation controller, fed by PIM relays, may record synchrophasor streams. Correlation is performed in real time on real-time programmable automation controller incoming data streams.

In view of the above modifications and variations,FIG.5shows a method performed by a fault protection system10according to some embodiments. As shown, the method comprises obtaining a differential measurement signal18(Block100). In some embodiments, the differential measurement signal18indicates, as a function of time, the difference between currents or voltages measured at two or more terminals or boundaries20of a fault protection zone14of an electric power system12. In one or more such embodiments, the differential measurement signal18indicates, as a function of time, the difference between residual currents or residual voltages measured at the two or more terminals or boundaries20of the fault protection zone14. In one or more other embodiments, the differential measurement signal18is a phase-specific differential measurement signal that indicates, as a function of time, the difference between currents or voltages measured for a specific phase at the two or more terminals or boundaries20of the fault protection zone14.

In any event, the method further comprises generating a fault detection signal24by cross-correlating the differential measurement signal18with a reference signal22(Block110). In some embodiments, the reference signal22is the differential measurement signal that is expected upon occurrence of a fault internal to the fault protection zone14. Alternatively or additionally, the reference signal22may characterize a change (e.g., a step change) that is expected to occur over time in the difference between currents or voltages measured at the two or more terminals or boundaries20upon occurrence of a fault internal to the fault protection zone14.

Regardless, the method further comprises performing fault detection, for detecting a fault internal to the fault protection zone14, as a function of the fault detection signal24(Block120). In some embodiments, for example, performing fault detection comprises detecting a fault internal to the fault protection zone14if a magnitude of the fault detection signal24exceeds a detection threshold.

FIG.6shows the fault protection system10as implemented according to some embodiments. As shown, the fault protection system10includes processing circuitry210. The processing circuitry210may implement the differential measurer16, the cross-correlator20, and/or the fault detector26inFIG.1, or may otherwise be configured to perform the method inFIG.5. The processing circuitry210in some embodiments, for example, executes instructions stored in memory230such that the fault protection system10operates as described above.

In some embodiments, the fault protection system10further includes measurement circuitry230. The measurement circuitry230may for instance measure at least some of the currents or voltages at the two or more terminals or boundaries20. In this case, the measurement circuitry230may provide the measurements to the processing circuitry210, in order for the processing circuitry210to obtain the differential measurement signal18from those measurements. Or, the measurement circuitry230may itself form the differential measurement signal18and the processing circuitry210may obtain the differential measurement signal18from the measurement circuitry230.

In other embodiments, the fault protection system10alternatively or additionally includes communication circuitry220. The communication circuitry220may for instance receive measurements of at least some of the currents or voltages at the two or more terminals or boundaries20. In this case, the communication circuitry220may provide the measurements to the processing circuitry210, in order for the processing circuitry210to obtain the differential measurement signal18from those measurements. Or, the communication circuitry220may receive the differential measurement signal18itself and the processing circuitry210may obtain the differential measurement signal18from the communication circuitry220.

Generally, then, the fault protection system10described above may perform the methods herein and any other processing by implementing any functional means, modules, units, or circuitry. In one embodiment, for example, the fault protection system10comprises respective circuits or circuitry configured to perform the steps shown inFIG.3. The circuits or circuitry in this regard may comprise circuits dedicated to performing certain functional processing and/or one or more microprocessors in conjunction with memory. For instance, the circuitry may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory may include program instructions for executing instructions for carrying out one or more of the techniques described herein, in several embodiments. In embodiments that employ memory, the memory stores program code that, when executed by the one or more processors, carries out the techniques described herein.

Those skilled in the art will also appreciate that embodiments herein further include corresponding computer programs.

A computer program comprises instructions which, when executed on at least one processor of the fault protection system10, cause the fault protection system10to carry out any of the respective processing described above. A computer program in this regard may comprise one or more code modules corresponding to the means or units described above.

Embodiments further include a carrier containing such a computer program. This carrier may comprise one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

In this regard, embodiments herein also include a computer program product stored on a non-transitory computer readable (storage or recording) medium and comprising instructions that, when executed by a processor of the fault protection system10, cause the fault protection system10to perform as described above.

Embodiments further include a computer program product comprising program code portions for performing the steps of any of the embodiments herein when the computer program product is executed by a computing device. This computer program product may be stored on a computer readable recording medium.

Notably, modifications and other embodiments of the disclosed invention(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention(s) is/are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure, Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.