WO2008018940A2 - Systems and methods for detecting high-impedance faults in a multi-grounded power distribution system - Google Patents
Systems and methods for detecting high-impedance faults in a multi-grounded power distribution system Download PDFInfo
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- WO2008018940A2 WO2008018940A2 PCT/US2007/011602 US2007011602W WO2008018940A2 WO 2008018940 A2 WO2008018940 A2 WO 2008018940A2 US 2007011602 W US2007011602 W US 2007011602W WO 2008018940 A2 WO2008018940 A2 WO 2008018940A2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- the present invention relates generally to detecting high- impedance faults in multi-grounded electric power distribution systems.
- High-impedance faults are difficult to detect on multi- grounded electrical power distribution systems.
- One reason for this difficulty is that many of the loads on the system are single-phase in nature. The system can therefore be quite unbalanced when a major single-phase lateral is out of service.
- the conventional ground fault protection has to be set above the maximum foreseeable unbalance to avoid false tripping. Conventional ground fault protection is thus not effective for HIF protection.
- the second reason that HIFs are difficult to detect is that the HIF current level is typically small. For example, the HIF current level may range anywhere from about zero amperes to less than 100 amperes depending upon the ground surfaces that a power conductor contacts.
- HIF protection is not to protect the power system and apparatus from damage resulting from an HIF. Rather, the objective of implementing secure HIF protection is to remove an unsafe public condition, which may also avoid or minimize any attendant legal issues relating to the condition.
- a detection device indicates the occurrence of an HIF 1 a utility has to make a decision based upon the circumstances. For example, it may be more dangerous to trip the electrical power to a traffic light at a busy traffic intersection or to a hospital. For such reasons, utilities cannot tolerate false alarms from HIF detection devices.
- a general object of the present invention is to therefore provide improved systems and methods for detecting an HIF in a multi-grounded distribution system.
- Another object of the present invention is to provide improved systems and methods for detecting an HIF that is secure from false detections.
- a further object of the present invention is to provide improved systems and methods for detecting an HIF that may be easily incorporated into existing distribution relays and related equipment.
- the present invention is directed to systems and methods for detecting a high-impedance fault in a multi-grounded electrical distribution system.
- the system includes a current acquisition circuit, which acquires a digital representation of at least one phase current, and a processor, which examines the digital current quantity and, based on statistics, determines whether or not a fault is present.
- the processor develops a long- term histogram that represents the normal level of odd harmonic current in the monitored phase. Based on this long-term histogram, the processor calculates a threshold, against which the monitored odd-harmonic current is measured. If this threshold is exceeded some number of times, a high-impedance fault is present on the monitored phase.
- a method for detecting high-impedance faults is also disclosed.
- a current is digitally acquired, and the odd harmonic content of the current is measured.
- the odd harmonic content is conditioned, and a first histogram is calculated over a sufficiently long period of time to be representative of the normal level of odd harmonic current within the monitored phase.
- a threshold is calculated.
- the measured odd harmonic current is compared against this threshold, and if the threshold is exceeded more than a calculated number of times within a window of time, a high-impedance fault is present on the monitored phase.
- a second histogram may be built over a predetermined time period, and used to update the first histogram or, based on a statistical comparison with the first histogram, can be used to indicate the presence of abnormal odd harmonic current activity, potentially indicating the presence of a high-impedance fault on the monitored phase.
- FIG. 1A is a diagram of a typical electrical distribution system illustrating placement of high-impedance fault (HIF) detection devices in various locations between a substation and end users in accordance with the present invention.
- HIF high-impedance fault
- FIG. 1B is a line diagram of a portion of the electrical distribution system of FIG. 1 in which a distribution feeder includes HIF detection in a substation relay and in a recloser in accordance with the present invention.
- FIG. 2 illustrates a block diagram of an HIF detection process for one of the phases of the electrical power distribution system, such as the A- phase, in accordance with the present invention.
- FIG. 3 is a diagram which illustrates further details of an exemplary implementation of the Sum of Difference Current (SDI) block shown in FIG. 2 in accordance with the present invention.
- SDI Sum of Difference Current
- FIG. 4 is a waveform illustrating the calculation of difference current and the Sum of Difference Current on a time-domain current waveform in accordance with the present invention.
- FIG. 5 is a schematic diagram illustrating further details of an exemplary implementation of the infinite-impulse-response (HR) Limiting
- FIG. 6 is a schematic diagram illustrating further details of an exemplary implementation of freeze conditions for the HR Limiting Averager implementation shown in FIG. 5 in accordance with the present invention.
- FIG. 7 is a schematic diagram illustrating further details of an exemplary implementation of the Trending and Memory block shown in FIG. 2 in accordance with the present invention.
- FIG. 8 is a schematic diagram illustrating further details of an exemplary implementation for the Adaptive Tuning Logic block shown in FIG. 2 in accordance with the present invention.
- FIG. 9 is a schematic diagram illustrating further details of an exemplary implementation of enable conditions for the Adaptive Tuning Logic block shown in FIGS. 2 and 8 in accordance with the present invention.
- FIG. 10 is a schematic diagram illustrating further details of an exemplary implementation for the Decision Logic Counters block shown in FIG. 2 in accordance with the present invention.
- FIG. 11 is a diagram of the counting regions for the variable rd in
- FIG. 7 for the Trending and Memory block and the variable dt shown in FIG. 10 for the Decision Logic Counters in accordance with the present invention.
- FIG. 12 is a diagram illustrating how the number of counts is generated as a function of the ratio, rd, in accordance with the present invention.
- FIG. 13 is a schematic diagram illustrating the details of generating a clear condition for the Decision Logic block shown in FIG. 10 in accordance with the present invention.
- FIG. 14 is a flowchart illustrating the methods employed in detecting an HIF in a multi-grounded distribution system in accordance with the present invention.
- FIG. 15A illustrates a block diagram of an alternate embodiment of the HIF detector shown in FIG. 2 for one of the phases of the electrical power distribution system, such as for the A-phase, in accordance with the present invention.
- FIG. 15B illustrates a block diagram for an enhancement portion of the alternate embodiment of the HIF detector shown in FIG. 15A in accordance with the present invention.
- FIG. 15C illustrates a block diagram for a one-cycle special filter of the alternate embodiment of the HIF detector shown in FIG. 15A and for the enhancement portion shown in FIG. 15B, in accordance with the present invention.
- FIG. 15D illustrates a block diagram for further details of the decision logic in the alternate embodiment of the HIF detector shown in FIG. 15A and for the enhancement portion shown in FIG. 15B, in accordance with the present invention.
- FIG. 16 illustrates a block diagram of an alternate preferred embodiment of a HIF detector for one of the phases of an electrical power distribution system, in accordance with the disclosed invention.
- FIG. 17 illustrates a histogram of odd-harmonic current data captured and used in accordance with the disclosed invention.
- FIG. 18 illustrates a block diagram for further details of the
- FIG. 19 illustrates a block diagram for further details of the Decision block in the alternate preferred embodiment of the HIF detector shown in FIG.
- FIG. 1A illustrates an exemplary electrical power distribution system, generally designated 100.
- Electrical power distribution system 100 provides electrical power, such as from a substation 114 to an end user location 110 and to a load center 120.
- Figure 1A also depicts possible locations of detection devices for detection of high-impedance faults in an electric power distribution system from a substation 114 to end-users, such as at 110.
- many of the devices in FIG. 1A constitute a high-impedance fault detection system and coordinate with each other using the fault current magnitudes, the number of arcing counts and/or communication signals.
- Such devices may include, for example, a fault indicator with HIF detection 101; a pole-top recloser with HIF detection and coordination 102; a fault Indicator with HIF detection 103; a video camera 104 with communication means; an electronic fuse with HIF detection 106; a loss of voltage detection 108 with communication means; an end user location 110 which may automatically call upon loss of service; a video camera 112 with communication means; a substation 114 with wireless, power-line carrier, fiber and other communications; a sectionalizer 116 with HIF detection; an electronic fuse 118 with HIF detection; a loss of voltage detection device 126 with communication means; a signal injection device 128; a signal receiving and alarming device 130 and 132; an altimeter or laser range finder 134 with a down- conductor detection device; and/or a fault indicator 136 with loss of voltage alarm [0039]
- the loss of voltage at an end user location 110 is one of the most reliable detection methods of high-impedance fault caused by downed conductors
- a loss of voltage condition is detected, either by an end user location 110 or by a detection device 108 or 126, such as a loss of voltage detection, the condition is communicated back to an operator of the system, either by a customer call or a communication signal through a fiber, radio, wireless, power line carrier or other communication channels. The operator then sends out someone to locate the fault.
- All the detection algorithms designed for a substation detection device can be fitted or simplified to fit in a device such as pole-top recloser controls 102 with HIF detection and coordination, sectionalizers 116, electronic smart fuses 106 and 118 and fault indicators 101 and 103.
- a device such as pole-top recloser controls 102 with HIF detection and coordination, sectionalizers 116, electronic smart fuses 106 and 118 and fault indicators 101 and 103.
- FIG. 1A also includes other types of devices to compliment the entire high-impedance fault detection system.
- a video camera 104 that has image pattern recognition program or a visual monitoring system, such as one disclosed in U.S. Patent No. 5,805,813, can be used to detect a downed conductor and communicate the information to system operators through wireless or other communication systems.
- An altimeter 134 or a laser range finder can also be used to detect a dramatic position change of conductors and alarm system operators.
- a signal injecting and receiving system 128, 130 and 132 can be also installed in a distribution system to detect a broken conductor and provide alarms. It is much like the loss of voltage system described earlier.
- FIG 1B is a subset of FIG. 1A in terms of high-impedance fault protections and distribution feeder configurations.
- FIG 1B shows the concept of coordination between the substation feeder relay 150 and the recloser control 156 for a high-impedance fault 160 that occurs downstream to the recloser control 156.
- a main feeder 152 provides electrical power from a substation 114 to a plurality of single-phase or three-phase lateral lines 164, 166 and 168. Each of lateral lines 164, 166 and 168 is protected by a fuse 154, 158 and 162, respectively.
- the HIF detection techniques of the present invention can be implemented into existing intelligent electronic devices (IEDs), such as relays.
- IEDs such as relays.
- the IED may include, for example, feeder relay 150 and recloser 156 shown in FIG. 1B.
- the HIF techniques of the present invention are within the processing capabilities of existing IEDs such that existing IEDs may be retrofitted with the present invention.
- these HIF detection techniques include the following four elements or characteristics.
- the tuning is active whenever there is no HIF detected on the system.
- FIG. 2 shows a block diagram 200 of the HIF methods for the A- phase current. Similar processing should also be implemented for the B- and C- phase currents in a three-phase distribution system.
- An input quantity such as A- phase current 202 is input to a sum of difference current (SDI) 300, which calculates a quantity on which the HIF detection is based. This quantity is called SDI 212 for sum of difference current.
- SDI sum of difference current
- An UR (infinite-impulse-response) limiting averager 600 provides a stable SDI reference 214.
- the trending and memory 800 compares SDI with this SDI reference 214 from HR Limiting Averager.
- the trending and memory block then memorizes the time and a ratio if SDI is a set- threshold above the average. These results from the trending and memory 800 are then used by the decision logic 1100 to derive a final decision of HIF occurrence on the monitored phase of the distribution system.
- the adaptive tuning 900 monitors the feeder background noise during normal system operations and establishes a comparison threshold 210 for the trending and memory 800. This comparison threshold 210 is also used by HR limiting averager 600 to limit the input magnitude to the HR limiting averager when it is too large.
- the Blocking Conditions block 1700 detects system conditions other than high-impedance faults and then blocks the functions such as adaptive tuning 900 and the decision logic 1100.
- the quantity to be used in HIF detection is important to the detection success. Since the HIF fault current magnitude, either the root mean square (RMS) value or the magnitude of the fundamental system frequency component, is much below the maximum possible load unbalance at the substation, other quantities need to be searched or evaluated for HIF detection.
- Each distribution feeder, such as feeder 152 in FIG. 1B 1 has a certain amount of harmonic energy during normal operations. This energy is normally dominated by the odd-harmonic energy. All harmonic and off-harmonic contents contain the information of arcing high-impedance faults. Because normal system operations produce little even and off-harmonic energy, the even or off-harmonic energy generally provide better fault indications. Off-harmonics may include non- integer multiples of a fundamental frequency.
- FIG. 3 the details of the SDI block 300 in FIG. 2 are shown in greater detail.
- the power system frequency is tracked and the three- phase currents from a power distribution feeder, such as feeder 152, are sampled at an integer number of samples per cycle.
- a variable name without a subscript is a collective term for a variable, such as SDI, for example.
- SDI k is a specific SDI value at the time instance k.
- FIG. 5 uses a sampling rate of 32 samples per cycle.
- the subscript k refers to the present sampling time
- k-1 refers to the previous sampling time.
- K-32 refers to the time of 32 samples ago, which separates in time exactly one cycle from present sampling time k for a 32- sample-per-cycle sampling rate.
- the SDI calculation uses two memory blocks.
- the first memory 304 in FIG. 3 is one-cycle long.
- Memory 304 saves one-cycle worth of current samples 302 and provides a one-cycle old sample in the difference calculation 306.
- the other memory 312 may be from two to several cycles long to save several cycles worth of the absolute values of difference currents from the difference calculation 306 and to provide all samples for the summation calculation by summer 314.
- Dl on line 308 is calculated at the sampling rate of the currents.
- SDI on line 316 may be calculated once every two cycles.
- FIG. 4 shows the difference current and the SDI calculation on a time-domain current waveform 406.
- the frequency magnitude response of the one-cycle difference calculations by the SDI calculator in FIG. 3 has a magnitude response which is zero at every harmonic frequency point including the DC and the fundamental frequency. Therefore, all harmonic contents including the DC and the fundamental frequency of the current are blocked after the difference calculation of the SDI current in FIG. 3.
- the frequency components near the half harmonics are amplified by the difference calculation, that is, the gain of the frequency response is greater than one.
- the frequency contents of the difference current on line 316 of the SDI therefore contain only off harmonics.
- SDI represents a measure of the average total off-harmonic content of a current over a two-cycle window. This makes SDI a desirable quantity for use in HIF detection.
- the MR limiting averager is shown in greater detail in FIG. 5.
- the MR limiting averager provides a reliable reference average, SDI-REFR on an output line 606.
- a reliable reference average is important to successful HIF detection.
- An infinite-impulse-response (HR) type of averaging with a fixed time constant is used because long-time memory effects can be achieved efficiently with fewer calculations and memory units.
- a relatively long time constant is preferably chosen to provide a stable reference during faults. For example, a one-second time constant may be used.
- the input to the averager 600 is preferably limited.
- FIG. 5 shows the details of the MR input limiting averager 600.
- the averager output, SDI_REF k follows the general first order HR equation
- SDI_REF k (1 - ⁇ ) • x in + ⁇ • SDI_REF k _, ,
- ⁇ relates to the time constant and Xi n -, can take two possible values according to the output of comparator 608.
- the input to the positive polarity of the comparator 608 is SDI k from line 602, and the input to the negative polarity of the comparator 608 is sd+SDI_REF k -i.
- Constant s can be any integer larger than one.
- the variable d will be introduced below with respect to the adaptive tuning and it can be treated as a constant here.
- the comparator output will be a logic 1 if SDI
- the freeze input on line 604 to the HR limiting averager 600 is a logic 1 and the HR limiting average calculation is suspended.
- these non-HIF conditions may include large difference currents and some difference voltages.
- the HR freeze/M clear input on line 604 of the HR limiting averager 600 in FIG. 5 may be generated as shown in FIG. 6.
- An N-cycle memory 712 stores current samples IK from the monitored phase of the electrical distribution system. Absolute values of these current samples I k on line 714 are compared to a threshold at comparator 716.
- an N-cycle memory 722 stores N voltage samples V k from the monitored phase of the electrical distribution system. Absolute values of voltage samples V k on line 724 are compared to a threshold at comparator 726. Those voltage samples which exceed the threshold are time delayed in a timer 728, which provides the dV_DISTURB output on line 704. The outputs dl_DISTURB and dV_DISTURB are then input to an OR gate 706. The outputs of OR gate 706 are stored in a table 708. Those values of current or voltage which exceeded the thresholds may then initiate a freeze of the HR limiting averager 600 on input line 604 in FIG. 5. Otherwise, this input to the averager will clear the memory in the averager.
- the trending and memory 800 of FIG. 2 is shown in greater detail in FIG. 7. Once the detection quantity SDI and its average SDI_REF are established by the sum of difference current 300 and by the IIR limiting averager 600, respectively, the HIF signatures or information can be extracted from these quantities.
- the purpose of the trending and memory 800 is to record unusual changes of SDI that is related to HIF on the system and to memorize these changes for the decision logic 1100.
- the trending and memory logic 800 thus provides information regarding how much and how often SDI exceeds SDI-REF plus a margin d.
- the portion of the logic below the comparator 805 in FIG. 7 runs at the rate of every SDI update, or 30Hz when SDI is calculated every two cycles as in the prior example.
- the rest portion of the logic runs whenever comparator 805 outputs a logic 1.
- the absolute value of the difference between SDI 802 and SDI_REF 803, or dSDI 804, goes to the positive input of the comparator 805.
- the negative input of the comparator is connected to a variable d.
- the variable d will be introduced in the Adaptive Tuning subsection, paragraphs 0058-0062 below, and can be treated as a constant here.
- comparator 805 When dSDI is greater than d, the output of comparator 805 will be a logic 1. Otherwise the comparator output is a logic 0. A logic 1 from comparator 805 closes the switch 807, which takes a record of the time at which the switch 807 closes. The recorded time is saved in a memory block 816 which has enough units to save the maximum possible number of t k within one second. When the comparator is operating at a rate of 30 Hz, the maximum number of t k is also 30 and the memory should have 30 units.
- a logic 1 output from the comparator 805 also enables on line 810 a ratio calculation at block 812 of dSDI to d.
- the calculated ratio values, rd k are saved in another memory 818 that has the same number of units as memory 816.
- the outputs on lines 820, 822 and 824 of the trending and memory logic 800 are sets of t, the old time value W and rd, respectively, within previous one second time.
- the number of t and rd records within the previous one second is n, which is another output on line 820.
- the freeze input is a logic 1
- the memories 817 and 818 are cleared and their updates are also suspended.
- These non-HIF conditions may include large difference current changes and smaller difference voltage changes.
- variable d is used in both HR limiting averager 600 and in trending and memory 800.
- FIG. 8 provides further details of the adaptive tuning logic 900 of FIG. 2.
- the comparator 910, timer 914 and the corresponding upper- row d update calculation run periodically, such as once every five minutes.
- the rest of the logic, such as comparator 912 and timer 916, runs more frequently or continuously, such as every one-second.
- n is the number of times that SDI was above its average plus the margin d within previous one second of time, as explained above with respect to the trending and memory logic 800.
- the value n is added up for five minutes in an accumulator 908 and its output is n5 on line 906, which in this example is the number of times that SDI was above its average plus the margin d within previous five minutes of time.
- a first comparator 912 of the adaptive tuning logic 900 compares the value of n to a threshold P 2 . If n is greater than p 2 , the output of comparator 912 is a logic 1, otherwise, the output of comparator 912 is a logic 0. If the output of comparator 912 is a logic 1 for a consecutive period of Dpu 2 seconds, as is determined by the timer 916, the timer 916 outputs a logic 1, which enables the bottom row of block 918 to initiate an update calculation of the margin d. At the same time, the logic 1 output of timer 916 goes to an input of AND gate 917 to force its output to a logic 0.
- d k d k +h 2 -SDI_REF k .
- a second comparator 910 of the adaptive tuning logic 900 compares the value of n5 to a threshold pi. If n5 is less than pi, the output of comparator 910 is a logic 1, otherwise, the output of comparator 910 is a logic 0. If the output of comparator 910 is logic 1 for a consecutive period of Dpui minutes as is determined by the timer 914, the timer 914 outputs a logic 1, which enables the upper row d update calculation in the upper row of block 918.
- d k d k - h, .SDI_REF k .
- hi may be a value in the range of 0 to 25 percent and the margin d may be decreased by about two percent of the average.
- both outputs of timers 914 and 916 are logic 0, the AND gate 917 outputs a logic 1 , which enables the middle row of block 918 to update the calculation for the margin d.
- the new value for margin d may be kept the same as the prior value.
- the AT Enable input 924 of FIG. 8 determines when the update for d takes place. Ideally, the tuning process should be continuous as long as there is no HIF or other faults on the system. The tuning should be also enforced within certain period of time after a breaker closure is detected and currents are detected.
- FIG. 9 shows the enable conditions for the adaptive tuning logic
- OR1 gate 1026 and timer 1032 Part of the enable logic, OR1 gate 1026 and timer 1032, is also used to freeze MR limiting averager 600, as shown in FIG. 5.
- FIG. 10 shows further details of the decision logic 1100, also previously shown in FIG. 2.
- FIGS. 2 and 7 provides rich information regarding to "how much” and “how often” that SDI overcomes its reference plus a learnt margin d.
- the information of "how much” is represented by a set of ratios, ⁇ rd ⁇ .
- the information of "how often” is represented by the value of n, the number of times that SDI went above the threshold within previous one second.
- the first block 1102 of the decision logic 1100 in FIG. 10 calculates a set of time differences, ⁇ dt ⁇ , using the set of time, ⁇ t ⁇ and t o i d from the trending and memory 800.
- the time difference can provide the time characteristic of randomness signature of the high-impedance faults.
- This information can be used in more sophisticated artificial intelligence methods of classification and pattern recognition, such as neural networks, expert systems or decision trees. For this invention, however, we choose to use a pair of counters 1116 and 1118, as shown in FIG. 10.
- the decision logic 1100 may run at a rate of once per second. In this example, it utilizes two counters; counter 1116 for providing an HIF fault output 1120 and counter 1118 for providing an HIF alarm output 1122. For each pair of (rd.dt) in previous one-second segment, the decision of count or no-count for fault or alarm, and the number of counts are determined in the counting scheme. For example, for each one-second segment, if the number of counts for HIF fault is greater than q-i, as is determined by comparator 1112, the comparator 1112 outputs a logic 1. Counter 1116 accumulates the number of logic 1s from comparator 1112.
- counter 1112 If three occurrences are accumulated within five one-second segments, counter 1112 outputs a logic 1 to indicate a high-impedance fault detection.
- the HIF alarm decision is derived in a similar way through comparator 1114 and counter 1118.
- Comparator 1114 may use a different detection threshold from that used by comparator 1112 as indicated at comparator inputs 1108 and 1110 in FIG. 10.
- FIG. 11 shows an entire dt-rd plane 1200, which is divided into three regions: a fault count region 1202, an alarm count region 1204 and a no count region 1206.
- the dt axis 1208 has units of 2-cycles. For example, a value of 30 represents 30 2-cycIe periods, or one second for 60Hz power systems. If ⁇ rd.dt ⁇ pair falls in the no count region 1206, no number of counts are generated for alarm and fault in the decision logic 1100. If ⁇ rd.dt ⁇ pair falls in the alarm count region 1204, only counts are generated for HIF alarm. If ⁇ rd.dt ⁇ pair falls in the fault count region 1202, counts are generated for both HIF fault and alarm.
- FIG. 12 shows a graphical representation of how the number of counts is generated as a function of the ratio, rd, for each ⁇ rd.dt ⁇ pair that is determined to be countable in the plane 1200 of FIG. 11. For example, if the rd value in a ⁇ rd.dt ⁇ pair is 4, and the pair falls in the fault count region 1202, then two counts are generated for this pair of ⁇ rd.dt ⁇ . Further, if the ⁇ rd.dt ⁇ pair is the only occurrence in a one-second segment, then the total of two counts is used in the operations of comparators 1112 and 1114 of the decision logic 1100.
- FIG. 13 shows the enable logic 1400 for the adaptive tuning logic 900 in FIG. 8 for a three-phase distribution system.
- the logic 1400 is similar to the enable logic 1000 in FIG. 9.
- OR gate 1414, timer 1420, comparator 1405, AND gate 1407 and timer 1422 in FIG. 13 are similar to corresponding elements 1028, 1034, 1029, 1030 and 1036 in FIG. 9, respectively.
- the times from the A, B and C-phases are input on lines 1408, 1410 and 1412 to block 1418 to provide for three-phase monitoring in the enable logic 1400 of FIG. 13.
- the enable logic 1000 of FIG. 9 is suited for single phase monitoring.
- the enable logic 1400 in FIG. 13 determines three-phase event conditions.
- the input ⁇ tfo on line 1408 represents the set of time incidences that the A-phase SDI difference is above the tuned threshold within the previous second
- the input ⁇ t ⁇ on line 1410 represents the set of time incidences that the B-phase SDI difference is above the tuned threshold within the previous second
- the input ⁇ t ⁇ c on line 1412 represents the set of time incidences that the C- phase SDI difference is above the tuned threshold within the previous second.
- Function block 1418 determines if there are common values from the ⁇ A , ⁇ QB and ⁇ t ⁇ c inputs.
- timer 1424 changes state, such as to a logic 1.
- the output 1430 of timer 1424 then changes state for a predetermined time, such as for Ddo ⁇ seconds, to block the decision logic.
- FIG. 14 illustrates an embodiment of a method of detecting high- impedance faults in a multi-grounded distribution system.
- the power system quantities l ⁇ , .... l ⁇ -3 2 , •• ⁇ are sampled.
- Block 1506 receives these power system quantities from block 1502 and calculates the absolute values of one-cycle difference filter, DI k H I k - 1 M z I-
- Block 1508 receives the absolute values of one-cycle difference filter from block 1506 and calculates the sum of absolute differences, such as in accordance with the equation
- SDI k ⁇ DI k . n .
- Block 1510 receives the margin, d ⁇ _ from block 1518, and the sum of absolute difference from block 1508 and establishes a reference, SDI_REF ⁇ , with an HR limiting averager. This reference is also supplied to the adaptive tuning and set threshold margin block 1518.
- the ratio, rd ⁇ dSDI K / d ⁇ , is determined at block 1514 and this ratio is supplied to the adaptive tuning and set threshold margin block 1518 and to the decision logic at block 1516.
- Adaptive tuning 1518 also receives the ratio rdk from block 1514.
- Blocking conditions at block 1522 are provided to the decision logic at block 1516 and to the adaptive tuning and set threshold margin block 1518.
- the decision logic at block 1516 then sets counters, defines fault count/no-count regions and alarm count/no-count regions.
- Block 1524 receives information from decision logic block 1524 and determines if an HIF condition exists. If so, block 1526 is informed to take a safety measure. If not, the method returns to block 1502 to continue monitoring for an HIF.
- FIG. 15A illustrates an alternative preferred embodiment 1600 of a system or method for determining an HIF condition, as compared to the preferred embodiment 200 shown in FIG. 2.
- the blocks of the lower level correspond to the blocks of FIG. 2, namely: 1) the Sum of Difference Current (SDI) 1621 corresponds to the Sum of Difference Current (SDI) 300, 2) HR Limiting Averager 1622 corresponds to HR Limiting Averager 600, 3) Trending and Memory 1624 corresponds to Trending and Memory 800, 4) Adaptive Tuning 1626 corresponds to Adaptive Tuning 900, 5) Blocking Conditions 1630 corresponds to Blocking Conditions 1700 and 6) Decision Logic 1628 corresponds to Decision Logic 1100.
- an enhancement portion 1601 see FIG.
- FIG. 15B shows the enhancement portion 1601 separately from the more detailed embodiment shown in FIG. 15A.
- the enhancement portion 1601 provides a separate HIF output HIF_A on line 1611, which may be combined by a gate 1632 with the output on line 1629 from the preferred embodiment 200 shown in FIG. 2.
- the first element in the enhancement portion 1601 is a one-cycle special filter 1602, which is shown in greater detail in FIG. 16C.
- the output IAs of special filter 1602 is formed by summing the outputs of two parallel filters 1612 and 1614.
- the first filter is a one-cycle cosine filter 1612 plus a phase adjustment and the second filter is a half-cycle differentiator 1614.
- power system quantities are filtered by each filter 1612 and 1614 separately and then summed by a summer to provide output IAs.
- Those skilled in the art can also combine two filters together and from a one-cycle FIR filter.
- Output IAs of special filter 1602 thus contains frequency contents of a signal around all odd harmonics in the pass band:
- the accumulator 1604 accumulates the absolute values of output IAs.
- the output ISMA of accumulator 1604 may be defined by the following equation
- N s may range from one cycle of samples to ten cycles of samples.
- the finite impulse response (FIR) smoothing block 1606 calculates an average of the output ISMA from accumulator 1604 to smooth out the random changes of the signal content. For instance, the FIR smoothing block could average the incoming ISMA signals using the following equation:
- the infinite impulse response (HR) limiting averager 1608 may be similar in function to the previously described MR limiting averager 600 shown in FIG. 5.
- the HR limiting averager 1608 provides a long-term reference for the signal contents from the one-cycle special filter 1602. In order to make this reference stable in case of sporadic large excursions of input, the output of NR limiting averager may be limited in accordance with the following equation
- ISMAREF is the output of the HR limiting averager 1608 and ISMA is the input to the HR limiting averager 1608.
- the subscript k represents a value of a variable at the specific time instant k.
- the subscript k-1 represents a value of a variable at time instant k-1, which is one processing instance older than time instant k.
- the FIR smoothing function 1606 smoothes the signal content to a smoothed signal quantity on its output line 1616. This smoothed signal quantity on line 1616 and the ISMAREF signal on output line 1617 of the HR limiting averager are both routed to the decision logic 1610.
- FIG. 15D illustrates an exemplary embodiment of the decision logic 1610.
- the decision logic 1610 compares the smoothed signal quantity from FIR smoothing 1606 and the ISMAREF signal from HR limiting averager 1608 with corresponding adaptive thresholds 1618 and 1620. If the smoothed signal quantity is above the corresponding adaptive threshold 1618 plus the signal ISMAREF for a corresponding certain time period, as set by timer 1619, and if the output of an AND gate 1623 is a logic zero, then the decision logic 1610 outputs a logic one to signify the detection of an arcing high-impedance fault HIF on the monitored distribution feeder.
- the thresholds 1618 and 1620 used in the decision logic are adaptive in nature and are derived in a similar manner to the previously described adaptive tuning 900 in FIG. 8. If the smoothed signal quantity on line 1616 is above the corresponding adaptive threshold 1620 plus the signal ISMAREF for a corresponding certain time period, as set by timer 1625, and if this condition is true for all A, B and C three phases, then the output of AND gate 1623 is a logic one.
- a logic one output from AND gate 1623 represents system three-phase conditions other than a high-impedance fault, such as a distribution capacitor bank assertion. The logic one output of AND gate 1623 clears timer 1619 and thereby disables any high-impedance fault detection.
- FIG. 16 illustrates an additional alternative preferred embodiment.
- This embodiment builds on the embodiment of FIGs. 15A, 15B, and 15C.
- the Detection Signal Generation block 2001 incorporates the One- Cycle Special Filter 1602 and Accumulator (Absolute Values) 1604, which are discussed above.
- the FIR Smoothing block 2003 is identical to the FIR Smoothing block 1606 of FIGs. 15A and 15B; and the HR Limiting Averager 2005 is identical to the MR Limiting Averager 1608 of FIGs. 15A and 15B.
- the basic operating principle of the embodiment disclosed by FIG. 16 differs substantially from the operation of the earlier discussed embodiments.
- the basic operation of this embodiment is the maintenance of a long-term histogram comprised of events indicating the level of odd harmonic current in the monitored phase.
- a sample histogram is illustrated in FIG. 17.
- a histogram shows the number of times within a predetermined time period that the measured odd harmonic current falls within a particular range.
- the Statistics block 2009 builds both the long-term histogram and the short-term histogram. In addition, Statistics block 2009 also compares the short-term histogram and the long-term histogram, and based on this comparison either generates an alarm or uses the short-term histogram to update the long- term histogram. The operation of Statistics block 2007 is further detailed in FIG. 18.
- the dlSMA signal is used to update the HISLIMA signal, which establishes a reference level of odd harmonic current within the monitored phase.
- the HISLIMA Calculation block 2023 updates the HISLIMA signal, representing a maximum level of harmonic currents within the monitored phase current, using the following equation:
- HISLIMA k max(l 0 • dISMA k , HISLIMA k _ ⁇ )
- HISLIMA is limited to a range of (0.01 - 1.0) x INOM, wherein INOM is a system dependent constant. HISLIMA is initialized at 0.01 x INOM.
- Unit Generator block 2025 calculates which counter within the short-term histogram (as illustrated in FIG. 17) will be incremented.
- the counter to be incremented is determined with the following equation:
- C n represents the number of the counter to be incremented, within the short-term histogram (see FIG. 17).
- the short-term histogram is updated in the Short-term Histogram Counter block 2027.
- the statistical mean and standard deviation of the short term histogram is calculated in the Short-term Histogram Statistics Calculation block 2029, and compared with the statistical mean and standard deviation of the long term histogram in block 2039.
- the mean and standard deviation for the short-term histogram are calculated using the following equations:
- Long-term Histogram Statistics Calculation block 2033 calculates the mean and standard deviation of the long-term histogram, using the same equations as used for the short-term histogram. The statistical quantities of the short-term histogram are then compared with the statistical quantities of the long- term histogram. If both of the inequalities in the following pair of equations are satisfied, a statistically significant difference is present in the monitored phase, and the HA output is asserted.
- HA signal can give early notification of an impending fault, but is not actually used to alert of a fault. That function is performed by the Decision Logic block 2011 , described below.
- the contents of the short-term histogram are used to update the long-term histogram, thereby ensuring that moderate changes in odd harmonic current within the monitored phase will not lead to a false HIF detection.
- Update block 2035 updates the long- term histogram is updated in accordance with the following equation:
- the subscript L refers to a counter value of the long-term histogram
- the subscript S refers to a counter within the short-term histogram
- the subscript n refers to a specific counter
- the subscript k refers to the present processing interval
- k-1 refers to the previous processing interval
- ⁇ relates to a histogram updating time constant in the equation as defined earlier.
- the HA output is asserted and for a predetermined time period therafeter, update of the long-term histogram is disabled by Delay block 2037.
- maxi. corresponds to the highest number of the counter that contains a nonzero count value.
- a counter is incremented within the NFA Count / Comparison block 2063.
- the NFA Count / Comparison block 2063 accumulates an event count for a predetermined period. The event count is compared against a threshold generated using the following equations: - -* )
- the Decision Logic block 2011 accomplishes this through the use of an additional 3-phase threshold, defined by the following equation:
- This equation is very similar to the equation used to calculate dlSMFPU, except that the constant STD3PU is used instead of the constant STDFPU. Generally, the constant STD3PU will be somewhat smaller than the constant STDFPU. Comparator 2065 will register when dlSMA exceeds dlSM3PU, and if dlSMA exceeds dlSM3PU for a predetermined time period pickup timer 2067 will assert its output.
- timer 2067 is ANDED with similar signals from other phases by AND gate 2069, and if all three phases detect higher than normal levels of odd harmonics - as determined by comparison with dlSM3PU - timer 2071 will disable NFA Count / Comparison block 2063 from registering a HIF for a predetermined time.
- the embodiment discussed in FIG. 16 relies on the establishment of a steady reference from the MR Limiting Averager block 2005.
- the HR Limiting Averager block 2005 could average the first one second worth of samples and output that as ISMAREF, and use the equations detailed above to modify ISMAREF after "steady state" operation was achieved.
- the long-term histogram must be established before reliable HIF detection can be achieved using the embodiment of FIG. 16. One way to accomplish this would be to monitor a particular phase for a period of time to establish the histogram before running the disclosed HIF algorithm. For instance, the long-term histogram could be built up for one day prior to enabling the fault detection algorithm to execute.
Abstract
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CA2659791A CA2659791C (en) | 2006-08-04 | 2007-05-15 | Systems and methods for detecting high-impedance faults in a multi-grounded power distribution system |
BRPI0714604-3A BRPI0714604A2 (en) | 2006-08-04 | 2007-05-15 | system and method for detecting a high impedance fault in a multi-grounded power distribution system, circuit, and methods for generating a digital output signal consisting substantially of odd harmonics in a digital input signal, for detecting the occurrence of an event within at least one digital signal and to disable a high impedance fault detector in a multi-grounded three-phase power distribution system |
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US11/499,620 US7720619B2 (en) | 2006-08-04 | 2006-08-04 | Systems and methods for detecting high-impedance faults in a multi-grounded power distribution system |
US11/499,620 | 2006-08-04 | ||
US11/803,386 | 2007-05-14 | ||
US11/803,386 US7945400B2 (en) | 2006-08-04 | 2007-05-14 | Systems and methods for detecting high-impedance faults in a multi-grounded power distribution system |
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CN103279650A (en) * | 2013-05-10 | 2013-09-04 | 国家电网公司 | Sampling value synchronization interpolation algorithm with data delay jitter or loss compatible |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5521946A (en) * | 1994-01-07 | 1996-05-28 | The 3Do Company | Multi-phase filter/DAC |
US5561605A (en) * | 1993-08-20 | 1996-10-01 | Eaton Corporation | Arc detection using current variation |
US6934654B2 (en) * | 2003-03-21 | 2005-08-23 | Schweitzer Engineering Laboratories, Inc. | System and method for exact compensation of fundamental phasors |
-
2007
- 2007-05-15 WO PCT/US2007/011602 patent/WO2008018940A2/en active Application Filing
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5561605A (en) * | 1993-08-20 | 1996-10-01 | Eaton Corporation | Arc detection using current variation |
US5521946A (en) * | 1994-01-07 | 1996-05-28 | The 3Do Company | Multi-phase filter/DAC |
US6934654B2 (en) * | 2003-03-21 | 2005-08-23 | Schweitzer Engineering Laboratories, Inc. | System and method for exact compensation of fundamental phasors |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN103279650A (en) * | 2013-05-10 | 2013-09-04 | 国家电网公司 | Sampling value synchronization interpolation algorithm with data delay jitter or loss compatible |
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