WO2004040732A1 - Protection contre les defauts d'isolement a la terre pour machines synchrones - Google Patents

Protection contre les defauts d'isolement a la terre pour machines synchrones Download PDF

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Publication number
WO2004040732A1
WO2004040732A1 PCT/EP2003/050709 EP0350709W WO2004040732A1 WO 2004040732 A1 WO2004040732 A1 WO 2004040732A1 EP 0350709 W EP0350709 W EP 0350709W WO 2004040732 A1 WO2004040732 A1 WO 2004040732A1
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Prior art keywords
phase
voltage
neutral point
winding
order harmonic
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PCT/EP2003/050709
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English (en)
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Sture Lindahl
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Alstom Technology Ltd
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Priority to AU2003286190A priority Critical patent/AU2003286190A1/en
Publication of WO2004040732A1 publication Critical patent/WO2004040732A1/fr

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/06—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric generators; for synchronous capacitors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/50—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the appearance of abnormal wave forms, e.g. ac in dc installations
    • H02H3/52—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the appearance of abnormal wave forms, e.g. ac in dc installations responsive to the appearance of harmonics
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
    • H02H3/081—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current and depending on the direction

Definitions

  • the present invention relates to electric machines such as synchronous electric generators, in particular constructed for generating high voltages, and it further relates to protection circuits for such electric machines.
  • Small generators may, according to Tidestr ⁇ m, S. H:son (editor): "Ingenj ⁇ rshandboken/Allman Elektroteknik", 3rd ed., Nordisk Rotogravyr, Swiss, 1959, have a solidly earthed neutral node.
  • the short circuit protection system can also detect earth faults.
  • a sensitive differential protection can, also according to the book by Tidestr ⁇ m, also detect earth faults if the rated current of the generator is less than 500 A.
  • C w is the zero sequence capacitance of the generator winding [F/phase],
  • C b is the zero sequence capacitance of the buswork [F/phase],
  • C a is the zero sequence capacitance of the auxiliary transformers [F/phase], and
  • C is the zero sequence capacitance of the step-up transformer [F/phase].
  • High earth fault currents may damage the iron core of the generator if the fault clearance time is too long.
  • the risk for damage is small if the earth fault current is lower than 15 A when there is an earth fault on one generator phase terminal.
  • C.W. Walker "Relay Protection in Hydro-Electric Power Stations of the Snowy Mountains Authority", The Institution of Engineers, Australia, Electrical Engineering Transactions, Vol. EET-5, No. 2, pp. 311 - 316, September, 1969, the safe limit is 5 A.
  • Earth fault protections for generators and transformers connected to a unit will be described.
  • Earth fault protection systems for generators connected to a common busbar will also be described.
  • the task of the earth fault protection is to detect earth faults on the winding of the generator, on the associated buswork, on the primary winding of the auxiliary transformer and on the primary winding of the step-up transformer.
  • a single phase-to-earth fault will cause an increase of the voltage on the other phases and on the neutral point.
  • the voltage rise depends on the fault location and on the fault resistance.
  • the healthy phases will assume full phase-to-phase voltage if an earth fault without fault resistance occurs at the terminal of one winding of the generator.
  • the neutral point will assume full phase-to-neutral voltage.
  • the voltage rise will decrease when the fault resistance increases.
  • the voltage rise will be negligible if the earth fault occurs on the phase winding close to the neutral point.
  • a neutral point overvoltage relay To detect an earth fault in the windings of a generating unit a neutral point overvoltage relay, a neutral point overcurrent relay, a zero sequence overvoltage relay or a residual differential protection circuit may be used. These protection schemes are simple and have served well during many years. However, at the very best, these simple schemes protect only 95% of the stator windings. They leave at least 5 % close to the neutral end without earth fault protection. Under unfavourable conditions the blind zone may extend up to 20 % from the neutral. There are several methods to detect an earth fault close to the neutral point.
  • Fig. 1 illustrates some fundamental properties of some types of earth fault protection methods. The intention of the figure is to illustrate general methods and to define some classes of earth fault protections.
  • the windings 1 A , 1 B , lc of a generator have their line ends connected to output terminals 3 A , 3B, 3 C and their neutral ends connected to a common node 5 or N, called the neutral or neutral point or node, that through some resistive component, here represented by an earth resistor R is connected to ground.
  • Circuits using line end earth fault protection can detect earth faults on almost the entire generator winding but have a blind zone close to the neutral point.
  • the size of the blind zone may be 5 - 20 %.
  • the main task of circuits using neutral end earth fault protection is to detect earth faults close to the neutral point.
  • Such protection circuits may cover 20 - 40 % of the winding.
  • these protection circuits can detect earth faults close to the line terminals.
  • a circuit for combined earth fault protection that comprises line end earth fault protection and a neutral end earth fault protection can be used.
  • circuits for total earth fault protection based on a method that makes it possible to detect earth faults anywhere along the entire generator winding.
  • Neutral point overvoltage protection methods, neutral point overcurrent protection methods, zero sequence overvoltage protection methods and residual differential protection methods are all various kinds of line end earth fault protection methods. Methods using neutral point overvoltage protection are applied for earth fault protection of unit-connected generators.
  • FIG. 2 such a circuit of overvoltage protection is shown.
  • a single-phase auxiliary voltage transformer 7 that is connected to the generator neutral node 5, N in parallel to the earth resistor R provides signals to the overvoltage protection controller 9.
  • Such a protection device detects earth faults on the generator windings, on the buswork and on the primary winding of the auxiliary transformer. It can also detect earth faults on the primary winding (medium voltage) of the step-up transformer in electric power generating units without generator breaker and while the generator breaker is closed.
  • the blind spot near the neutral point may be as small as 5 %.
  • FIG. 3 a circuit diagram of a circuit for overcurrent protection is shown.
  • a single-phase current transformer 11 has a primary winding that has a low resistance and is connected in the line connecting the neutral point N to earth. The primary current is thus equal to the current that flows from the neutral node 5 of the generator to earth.
  • the second winding of the transformer 11 is connected to a protection circuit or controller 9' detecting a neutral point overcurrent state.
  • the blind zone near the neutral point may be 20 - 30 %.
  • a method using zero sequence overvoltage protection can also detect faults in the generator system.
  • Fig. 4 a circuit for such zero sequence overvoltage protection is illustrated.
  • Three single-phase voltage transformers 13 A , 13 B , 13 C energize the zero sequence overvoltage protection.
  • the primary winding 13'A, 13' B , 13' C of each voltage transformer has one end connected to a phase conductor such as the phase winding terminals 3 A , 3 B , 3 C and the other end connected to ground.
  • the secondary winding 13" A , 13" B , 13" C of each voltage transformer are connected in series with each other to form a broken delta or closed loop in which an overvoltage controller 9" is connected, a point of the loop at a terminal of the controller also connected to ground.
  • Each voltage transformer 13 A , 13 B , 13 C provides over its secondary winding a voltage that has an implitude error and a phase error in relation to the voltage over the primary winding. This means that the secondary zero sequence voltage may not represent the primary zero sequence voltage exactly. To avoid unwanted operation, the zero sequence overvoltage setting must be higher that the neutral point overvoltage setting.
  • Lohage and co-workers have documented practice for the earth fault protection in hydro power plants owned by the Swedish company Vattenfall, see B. Andersson, H. Broman, P. -A. Eriksson, S. Fredriksson & L. Lohage: "Generatorskydd i Vatten- kraftstationer", Rapport, Vattenfall, November, 1982.
  • large hydropower units comprising generator breakers have one circuit for neutral point overvoltage protection and one circuit for zero sequence overvoltage protection.
  • the circuit for neutral point overvoltage protection must cover at least 95 % of the stator windings of the generator.
  • a combined circuit for earth fault protection that can detect earth faults anywhere along the generator winding replaces the circuit for neutral point overvoltage protection.
  • the delay before this sensitive protection gives an alarm is usually 1.2 second.
  • a circuit for zero sequence overvoltage protection covers about 80 % of the generator winding. Normally, the delay before alarm is 0.4 second.
  • the busbar has one or more transformer bays. Usually, the busbar has no feeder bays. In such plants it is common practice that the generators have unearthed neutral points. Often, there is a requirement to limit the overvoltage on the busbar in the case where only one generator is in service. This case determines the maximum size of the resistor connected to the neutral point of the generator. When all generators having such resistors are in service, the total earth fault current may become too high.
  • Some busbars may have a bay for an earthing transformer with a neutral point resistor. In such cases, the system has a high-impedance earthed neutral.
  • Some power utilities use a combined earthing transformer and station auxiliary transformer.
  • Some plants may have only a step-up transformer with an Y- or Z-connected winding connected to the busbar. This neutral point can be used to connect a neutral point resistor. It is not necessary to install neutral point resistors at each generator if an earthing transformer is provided having a neutral point resistor if the step-up transformer has a neutral point resistor.
  • Neutral point overvoltage protection circuits, neutral point overcurrent protection circuits and zero sequence overvoltage protection circuits cannot select the faulty generator if several generators are connected to one common busbar.
  • Fig. 5 shows the stator windings of a generator having a circuit for residual differential protection that can select the faulty generator in the case where several generators are connected to a common busbar. Only one three-phase current transformer is required if the neutral point of the generator is unearthed. Unavoidable amplitude errors and phase errors of the current transformer limit the sensitivity of the earth fault protection.
  • the fault current from the generator may be very high and may contain a substantial DC component.
  • the fault currents may cause a false secondary zero sequence current. A risk exists that this false current will cause unwanted operation of the earth fault protection circuit.
  • the short circuit protection circuit may block the earth fault protection circuit for external short-circuits.
  • the closing of the generator breaker may cause transient residual currents. These currents may limit the sensitivity of the residual differential protection circuit.
  • FIG. 5 shows such a protection circuit including a controller 9'" that is connected to the three-phase current transformer 15: 15 A , 15 B , 15 C and one neutral point current transformer 17 similar to the transformer 11 of the circuit illustrated in Fig. 3.
  • the primary windings of the three-phase transformer 15 are thus portions of the phase windings 1 A , 1 B , lc that have a low resistance.
  • the secondary windings are connected in parallel to each other and to the controller 9"'.
  • overvoltage (or overcurrent) generator earth fault protection provide straightforward, secure and dependable earth-fault protection.
  • they suffer from two disadvantages, see C. H. Griffin & J. W. Pope: "Generator Ground Fault Protection Using Over- current, Overvoltage, and Undervoltage Relays", IEEE Trans, on Power Apparatus and Systems, Vol. PAS-101, No. 12, pp. 4490 - 4501, December, 1982.
  • the induced EMF in many synchronous generators contains harmonics. It is possible to use the third harmonic to detect earth faults close to the neutral point and in the neutral point equipment. The induced third harmonic voltages cause a third harmonic current that flows through the neutral point resistor R.
  • each relay When combined to form a protection system, each relay covers the blind zone of the other.
  • a combined protection system will detect earth faults anywhere on the stator winding.
  • FIG. 6 shows a synchronous machine directly connected to a power network, such as is the case for said installed machines, and having a circuit for earth fault protection.
  • a set of current transformers 21 , 21 B , 2 lc are connected to sense the current in the phase windings at a relative distance x from the neutral point 5 of the synchronous generator, the current transformers thus dividing the phase windings 1A, 1B, lc into two portions.
  • the phase winding termmals 3A, 3B, 3C are through circuit breakers connected 25A, 25B, 25C to the rails 27A, 27B, 27c of the three-phase busbar to which other power generating units can be connected in the similar way.
  • the overcurrent relay or control circuit has nominal sensitivity for the third harmonic (150 or 180 Hz) of the nominal frequency (50 or 60 Hz) in the power system.
  • the overcurrent relay has a very low sensitivity for the fundamental frequency.
  • the relative distance x from the neutral point 5 of the synchronous machine is defined by
  • N 0 is the number of turns per phase from the neutral point to the location of the current transformer
  • N tol is the total number of turns per phase from the neutral point to the phase terminal of the synchronous machine.
  • the current transformers 21 A , 21 B , 21 c are connected in parallel, in a Holmgren-connection, to excite the overcurrent relay 23 with the residual current.
  • the protection circuit illustrated in Fig. 6 is based on the fact that the induced voltage of many generators and especially a Powerformer contains a sufficient amount of harmonics of order n , where n is defined by:
  • the third harmonic is of practical importance but this circuit is not restricted to the use of third harmonic. In some applications it may be advantageous to use one or several harmonics of higher order possibly in combination with the third harmonic.
  • the third-harmonic restricted earth fault protection is used in some existing power plants, where the adjacent power network is effectively earthed. Analysis has shown that the third-harmonic restricted earth fault protection should work well in such effectively earthed power networks and measurements have also been performed confirming the analysis. It has not been proven that it will work properly in non-effectively earthed power networks.
  • the capacitive earth fault current is in the range from 48 to 49 amperes
  • the Petersen coil, the arc suppression coil has a rated current of 56 amperes and the neutral point resistor in the power network has a rated current of 30 amperes.
  • the Petersen coil or arc suppression coil has a setting range from 169 to 304 amperes and a rated apparent power of 11 430 kVA whereas the neutral point resistor has a rated current of 200 amperes.
  • the exact value of the capacitive earth fault current is not known but it can be assumed to be in the range of 200 to 300 amperes.
  • the magnitude decreases from 2.4 kV to 0.4 kV at the earth fault.
  • Fig. 8 the magnitude of the third harmonic at the neutral of the Powerformer generator as measured at a sudden earth fault from 100% of rated voltage in the workshop test is shown. The magnitude increases creases from 2.0 kV to 4.8 kV at the earth fault.
  • Fig. 9 the magnitude of the third harmonic of the difference of one third of the residual voltage at the phase termmals and the neutral point voltage of the considered Powerformer generator is shown. The magnitude remains fairly stable at 4.4 kV.
  • Fig. 10 the magnitude of the positive sequence voltage of the Powerformer generator is shown as measured at a sudden earth fault from 100% of rated voltage in the workshop test on 2000-06- 15 (Case 4).
  • the initial value of the magnitude of the positive sequence voltage is 110 kV. The magnitude then decreases due to the removal of the excitation.
  • the magnitude of the induced third harmonic as estimated from Fig. 9 decreases when the induced positive sequence voltage (fundamental frequency) decreases, see Fig. 10.
  • the decrease of the third harmonic is faster than proportional. Initially the relative third harmonic is equal to 0.04 but it decreases to 0.02 at the end of the recording.
  • I a [A] is the armature current
  • / practice [A] is the rated armature current
  • I f [A] is the calculated field current
  • I fn [A] is the calculated field current at rated output power.
  • the field current has been calculated using a linear model of the synchronous machine and a direct axis synchronous reactance of 114 percent.
  • Engelhardt has published, see K.H. Engelhardt: "A Composite Ground Fault Detection Scheme for High Resistance Grounded Generator Stators", Paper 74-SP-140, Transactions of the Engineering and Operating Division, Canadian Electrical Association, Vol. 13, pt. 3, pp. 1 - 11, September 1974, results of measurement of the third harmonic voltage on three generators in Canada.
  • the measured third harmonic voltages range from 2 to 11 percent.
  • the maximum value of the induced third harmonic voltage ranges from 2 to 8 percent of the fundamental frequency voltage.
  • the induced harmonic voltage seems to vary with the excitation of the synchronous machine. No simple explanation of the variation of the ratio of the third harmonic at the neutral and the third harmonic at the phase terminal can be found.
  • the problem solved by the invention is how to protect an electric synchronous generator from earth faults occurring in the phase windings, in particular how to protect an electric synchronous generator having a neutral point that is not connected to earth or is connected to earth through a high or very high impedance.
  • three elements can be combined to form a phase-segregated 100% earth fault protection scheme and circuit; namely (1) a directional element, (2) a fault detector element and (3) a range control element.
  • a synchronous electric generator has in the common way phase windings in which voltages are induced.
  • the phase windings are connected at one end to each other at a neutral point. They have at an opposite end phase terminals on which the generated voltages are supplied.
  • First extracting means such as current transformers and fourier filters are provided for extracting the third or higher order harmonic currents in the phase windings at locations at the neutral point.
  • first calculating means for calculating, from the extracted third or higher order harmonic currents, a directional criterion for each phase winding.
  • Such a directional criterion indicates the relative magnitude of the third or higher order harmonic current for the considered phase winding reduced by the third or higher order harmonic currents of the other phase windings.
  • First comparing means compare the directional criteria to a normal value valid for correctly operating phase windings.
  • a signal is provided, in the case where at least one of the directional criteria deviates too much from the normal value, to a control device for issuing an alarm signal and/or for disconnecting or disabling the phase windings.
  • the criterion that most deviates from the normal value can indicate the phase, in which the fault has occurred.
  • a fault detection criterion can also be calculated that distinguishes between the cases where the extracted third or higher order harmonic currents totally have or have not a sufficient magnitude, the control device being prevented from taking any action if said currents totally have not the sufficient magnitude.
  • a range control detection criterion can be calculated that distinguishes between the cases where the sum of the third or higher order harmonic voltages on the generator terminals have or have not a sufficient magnitude, the control device being prevented from taking any action if said sum has not the sufficient magnitude.
  • the voltages can be obtained from second extracting means extracting the voltages at the phase winding termmals, the second extracting means e.g. comprising voltage transformers and fourier filters.
  • Fig. 1 is a schematic circuit diagram of three-phase windings for which the range of different types of earth fault protection is illustrated,
  • Fig. 2 is a circuit diagram of three-phase windings having neutral point overvoltage protection
  • FIG. 3 is a circuit diagram of three-phase windings having neutral point overcurrent protection
  • Fig. 4 is a circuit diagram of three-phase windings having zero sequence overvoltage protection
  • Fig. 5 is a circuit diagram of three-phase windings having residual differential protection
  • - Fig. 6 is a circuit diagram of three-phase windings having third-harmonic restricted earth fault protection
  • Fig. 7 is a diagram of the magnitude of the third hannonic as a function of time at the phase terminal of a Powerformer generator
  • Fig. 8 is a diagram of the magnitude of the third harmonic as a function of time at the neutral point of a Powerformer generator
  • - Fig. 9 is a diagram of the magnitude of the third harmonic of the difference of the (residual voltage)/3 at the phase terminals and the neutral point voltage as a function of time of a Powerformer generator
  • Fig. 10 is a diagram of the magnitude of the positive sequence voltage as a function of time of a Powerformer generator
  • Fig. 11 is a diagram of reactive power plotted as a function of active power for a Powerformer generator showing operating states where harmonic voltages have been measured
  • Fig. 12 is a diagram illustrating harmonic voltages derived from measurements at the operating states of Fig. 11,
  • Fig. 13 is a diagram of measured and predicted third order harmonic voltages at the operating states of Fig. 11,
  • Fig. 14 is a diagram of measured maximum and minimum third harmonic voltages
  • - Fig. 15 is a diagram of generated third harmonic voltages as measured by Marttila
  • - Fig. 16 is a diagram of measured generated third order harmonic, third order harmonic at the neutral and third order harmonic at the phase terminal as a function of active output power
  • - Fig. 17 is a diagram of measured ratio of the third order harmonic at the neutral point and the third harmonic at the phase terminal as a function of active output power
  • - Fig. 18 is a schematic of a synchronous electric machine or generator having a circuit for phase selective, 100% earth fault protection.
  • the directions of the third harmonic currents flowing in the three phase windings close to the neutral point can be used.
  • a protection circuit using the directions of the third harmonic currents is illustrated in ' Fig. 18.
  • the three phase windings 1A, 1B, lc of the generator have their line ends connected to output terminals 3 A , 3 B , 3 C and their neutral ends connected to a common node 5 or N, the neutral point or node.
  • the neutral point of the synchronous machine can be high-impedance earthed or high-reactance earthed but this is not necessary.
  • Current transformers 31A, 31B, 31c are connected at the neutral ends of the windings and thus their primary windings have a low resistance and are actually portions of the phase windings , 1B, lc
  • the secondary windings are connected to one-cycle Fourier-filters 33 A , 33B, 33C extracting values of the third order harmonic complex currents I a _, h_, I _ from the total complex phase currents I a , , I c detected by the current transformers and including load currents, other harmonics and transient currents.
  • phase A For a faulty phase winding, say phase A, it appears that the third order harmonic current -I A3 flowing from the neutral point N into the faulty phase winding is equal to the sum of the third order harmonic currents IB3, IC3 flowing from the healthy phase windings, such as 1 B , lc towards the neutral point, the same relation also holding for the detected third order harmonic complex currents I_3, e, Ic -
  • a directional criterion D a , D b , D c is calculated in a block 35 as defined by the following equations
  • the directional criteria have several important properties. When all phase windings 1 A , 1 B , lc are healthy, the values of the directional criteria D a , D b , D c are all equal to 1/3. For a faulty phase winding the directional criterion becomes equal to 1 and is equal to 1/2 for the two healthy phases windings. This is a direct consequence of Kirchhoff s current law applied to the neutral point N. Assume that an earth fault has occurred in phase winding 1 A close to the neutral point and that the third harmonic current in phase winding 1 B and the third harmonic current in phase winding lc both are equal to I 3 . Then
  • the induced third order harmonic voltage in phase winding 1B is equal to the induced third harmonic voltage in phase winding lc.
  • the third harmonic impedance of phase winding 1 B is equal to the third harmonic impedance of phase winding l ⁇ .
  • the third harmonic voltage on the generator terminals 3 A , 3 B , 3 C is equal to zero.
  • phase winding 1B is equal to the third harmonic voltage Vc3 on the terminal 3c of phase winding lc. It is also assumed that the third harmonic impedance of phase winding 1 B is equal to the third harmonic impedance of phase winding lc- It is further assumed that the induced third harmonic voltage in phase winding 1 B is equal to the induced third order harmonic voltage in phase winding lc. The third order harmonic voltage on said phase terminals will then cause a third order harmonic current AI 3 to flow in phase winding 1 B and in phase winding l c .
  • the directional criteria D a , Db, D c now become:
  • the directional criteria D a , Db, D c are evaluated in a block 37 and it is first determined whether they are all sufficiently equal to 1/3. Then it may e.g. be tested whether the directional criteria deviates only by some small quantity ⁇ from the target or normal value 1/3, i.e. whether
  • the circuit breakers 25 A , 25 B , 25c can be activated and an alarm signal triggered as indicated in the decision block 39. It can also then be tested whether only one of the directional criteria is sufficiently large, i.e. has a value larger than some suitable threshold value, e.g. equal to 3/4. In the case where this is true it can also be signalled to the decision block or control device 39 that the phase winding associated with the directional criterion having the large value probably is the phase winding in which an earth fault has occurred.
  • the circuit breakers 25 A , 25 B , 25 C are connected between the output termmals or line termmals 3A, 3B, 3c of the phase winding and the rails 27A, 27B, 27 C of a three-phase busbar to which other power generating units can be connected in the similar way.
  • the directional criteria D a , Db, D c may assume erratic values during normal operation when the (complex) third order harmonic currents are small and not have the same phase (are not aligned). Therefore it is necessary to combine the results obtained by analyzing the directional criteria with a signal from a fault detector. For this purpose the following quantity can also be calculated in the block 35:
  • This quantity is compared to a threshold value T ED in a block 41 to provide a fault detection criterion FD according to
  • the fault detection criterion is thus operative or active if the total amount of third harmonic currents exceeds a threshold.
  • the threshold value T FD is set so that the result of the comparison in the block 37 of the direction criteria can be considered reliable in the case where the fault detection criterion FD has a high value, i.e. is equal to 1. Then, if the result of the comparison in block 37 indicates a fault, the respective measures should be taken.
  • the fault detection criterion FD can have a low value, i.e. be equal to 0, if the third harmonic voltage source at or close to the neutral point N is short-circuited.
  • the combination of the directional criteria and the fault detection criterion constitutes a non-unit protection, which may start and perhaps operate also at external faults, i.e. faults not located within the considered synchronous generator.
  • Time grading is normal practice for earth fault protections in non-effectively earthed power networks. The reason is that the earth fault current depends mainly on the shunt elements in the network and not on the series elements. This means that the distance to the fault has a minor influence on the fault current and polarizing voltages. It is, however, an advantage to define a range control element that limits the forward reach of the directional criteria.
  • the third order harmonic content of the residual voltage measured at the terminals of the generator may be a suitable quantity for range control.
  • Several experimental investigations show that the third order harmonic content of one third of the residual voltage measured at a terminal of a synchronous machine is close to one half of the induced third order harmonic voltage in one phase winding. The use of this quantity is that it may be used as an earth fault detector when the generator is disconnected from the power network.
  • a range control criterion RC can then be defined according to: f, 1 ( ,_- TM TR ⁇ U ⁇ E) i * f -22_ + r b ⁇ ? 3 . + V c _l 3 _ > T ⁇
  • V 3A , V iS , V C are the third order harmonic voltages on the generator terminals 3 A , 3 B , 3 C and T RC is a suitably chosen threshold value.
  • the voltages are extracted by voltage transformers 43 A , 43 B , 43 C having their primary windings connected to the respective phase windings at the generator terminals and having their secondary windings connected to Fourier filters 45 A , 45 B , 45c.
  • the third harmonic voltages extracted in the filters are provided to a block 47 in which the quantity (V a 3 + Vb3 + V C 3) ⁇ is calculated. This quantity is in a block 49 compared to the threshold T RC and the range control criterion RC is obtained.
  • This criterion is directly supplied to the control block 39 to stop the issuing of signals to the circuit breakers in the case where the criterion RC has a low value, i.e. is equal to 0.

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  • Control Of Eletrric Generators (AREA)

Abstract

L'invention concerne un circuit de détection des défauts de mise à la terre ou de protection contre ces défauts, conçu pour un générateur électrique synchrone et mettant en application des courants harmoniques de troisième ordre (Ia3, Ib3, Ic3) extraits (35A, 35B, 35C) dans les enroulements de phase (1A, 1B, 1C) dans des emplacements au niveau du point mort (N, 5). Des critères directionnels (Da, Db,Dc) sont calculés (35) pour chaque enroulement de phase à partir de ces courants harmoniques de troisième ordre, ces critères indiquant l'intensité relative du courant harmonique de troisième ordre réduite par l'autre de ces courants d'harmonique de troisième ordre. Ces critères directionnels sont comparés (37) à une valeur normale et signalés, quand au moins l'un de ces critères dévie trop de la valeur normale, à indice positif de contrôle (39) servant à déconnecter ou à invalider les enroulements de phase. Deux autres critères, un critère de détection de défaut (FC) et un critère de contrôle de portée (RC) sont également calculés (41; 49) et peuvent empêcher le dispositif de contrôle d'émettre un signal. Ce circuit de détection peut détecter les défauts d'isolement à la terre apparaissant à proximité du point neutre et peut être utilisé sur toutes les machines synchrones possédant un point neutre isolé ou mis à la terre par l'intermédiaire d'une impédance importante et qui sont reliés directement soit à un réseau électrique non effectivement mis à la terre, soit un réseau électrique effectivement mis à la terre, par exemple, des générateurs haute tension du type PowerformerTM.
PCT/EP2003/050709 2002-10-29 2003-10-13 Protection contre les defauts d'isolement a la terre pour machines synchrones WO2004040732A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003286190A AU2003286190A1 (en) 2002-10-29 2003-10-13 Earth fault protection for synchronous machines

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0203174A SE0203174D0 (sv) 2002-10-29 2002-10-29 Earth fault protection for synchronous machines
SE0203174-8 2002-10-29

Publications (1)

Publication Number Publication Date
WO2004040732A1 true WO2004040732A1 (fr) 2004-05-13

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SE (1) SE0203174D0 (fr)
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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102006004800A1 (de) * 2006-01-23 2007-08-02 Siemens Ag Schutzeinrichtung mit einem Leistungsschalter, insbesondere einem Niederspannungs-Leistungsschalter
AT504920B1 (de) * 2007-04-04 2008-09-15 Univ Graz Tech Erdschlussortung durch fremdstrom
EP2501009A1 (fr) * 2011-03-10 2012-09-19 Hitachi, Ltd. Machine rotative électrique
US9960659B2 (en) 2011-11-16 2018-05-01 Vestas Wind Systems A/S Protection of a permanent magnet generator
EP3499252A4 (fr) * 2017-10-18 2019-06-26 China Electric Power Research Institute Company Limited Procédé et dispositif de détection des défauts monophasés à la terre basés sur l'induction d'un champ électrique et moyen de stockage
CN112180290A (zh) * 2020-09-29 2021-01-05 西安热工研究院有限公司 一种发电机定子接地故障定位方法
CN113203950A (zh) * 2021-04-30 2021-08-03 华中科技大学 海洋核动力平台发电机定子接地故障程度诊断方法和系统
CN117538632A (zh) * 2023-08-08 2024-02-09 沈阳工业大学 换流变压器接地故障诊断装置及方法

Families Citing this family (1)

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Publication number Priority date Publication date Assignee Title
CN114256827B (zh) * 2021-12-17 2022-09-16 华中科技大学 一种海洋核动力平台网源直连系统接地故障消弧方法

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US4297738A (en) * 1979-10-29 1981-10-27 Electric Power Research Institute, Inc. Apparatus for and method of detecting high impedance faults on distribution circuits with delta connected loads
DE3402126A1 (de) * 1983-11-30 1985-06-05 BBC Aktiengesellschaft Brown, Boveri & Cie., Baden, Aargau Einrichtung zum schutz mehrphasiger elektrischer maschinen

Patent Citations (2)

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Publication number Priority date Publication date Assignee Title
US4297738A (en) * 1979-10-29 1981-10-27 Electric Power Research Institute, Inc. Apparatus for and method of detecting high impedance faults on distribution circuits with delta connected loads
DE3402126A1 (de) * 1983-11-30 1985-06-05 BBC Aktiengesellschaft Brown, Boveri & Cie., Baden, Aargau Einrichtung zum schutz mehrphasiger elektrischer maschinen

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102006004800A1 (de) * 2006-01-23 2007-08-02 Siemens Ag Schutzeinrichtung mit einem Leistungsschalter, insbesondere einem Niederspannungs-Leistungsschalter
US8149550B2 (en) 2006-01-23 2012-04-03 Siemens Aktiengesellschaft Protective device having a circuit breaker, in particular a low-voltage circuit breaker
AT504920B1 (de) * 2007-04-04 2008-09-15 Univ Graz Tech Erdschlussortung durch fremdstrom
DE102008016711A1 (de) 2007-04-04 2008-10-09 Technische Universität Graz Erdschlussortung durch Fremdstrom
EP2501009A1 (fr) * 2011-03-10 2012-09-19 Hitachi, Ltd. Machine rotative électrique
JP2012189403A (ja) * 2011-03-10 2012-10-04 Hitachi Mitsubishi Hydro Corp 回転電機
US9960659B2 (en) 2011-11-16 2018-05-01 Vestas Wind Systems A/S Protection of a permanent magnet generator
EP3499252A4 (fr) * 2017-10-18 2019-06-26 China Electric Power Research Institute Company Limited Procédé et dispositif de détection des défauts monophasés à la terre basés sur l'induction d'un champ électrique et moyen de stockage
CN112180290A (zh) * 2020-09-29 2021-01-05 西安热工研究院有限公司 一种发电机定子接地故障定位方法
CN112180290B (zh) * 2020-09-29 2024-03-08 西安热工研究院有限公司 一种发电机定子接地故障定位方法
CN113203950A (zh) * 2021-04-30 2021-08-03 华中科技大学 海洋核动力平台发电机定子接地故障程度诊断方法和系统
CN113203950B (zh) * 2021-04-30 2022-02-15 华中科技大学 海洋核动力平台发电机定子接地故障程度诊断方法和系统
CN117538632A (zh) * 2023-08-08 2024-02-09 沈阳工业大学 换流变压器接地故障诊断装置及方法

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