Method of detecting a fault in an exciter rectifier of a synchronous generator

Abstract

In a method for detecting a fault in an excitation rectifier of a synchronous generator (1), a field current (3) is measured on a stationary DC side of an excitation source (2) or a voltage is measured on a DC side of a stationary rectifier (7). Furthermore, a frequency analysis is used to determine the amplitude of the fundamental and of all non-zero integer multiples of the fundamental frequency from the measurement signal. A per-unit current fault factor Xi or a per-unit voltage fault factor Xu is calculated, a reference fault-free per-unit current factor Xi_ref or a reference fault-free per-unit voltage factor Xu_ref is measured, and a reference per-unit fault factor Xi_err or Xu_err is determined, and a per-unit fault detection threshold Xi_threshold or Xu_threshold is determined. A fault signal is issued when the determined per-unit fault factor Xi or Xu exceeds and / or the DC component of the measured field current (3) exceeds an allowed operating range and / or the rms value of the counter-electromotive force of the synchronous generator (1) falls below a value corresponding to a minimum allowed operating field current (3).

Description

Technical Field

[0001] This invention relates to detecting faults in the excitation rectifier of a synchronous generator and determining the type of fault. The proposed invention is intended for use with generators having external excitation. Background Technology

[0002] Common methods for diagnosing faults in rectifiers are, in most cases, based on continuous assessment of voltage drops across individual power electronic devices. During rectifier operation, a mismatch between a given power electronic device and its periodically alternating conducting phase (when the voltage in the forward (conducting) direction on the power electronic device should be small) and non-conducting phase (when the reverse or blocking voltage on the power electronic device should be large) indicates a fault in that device. However, this method uses rather complex analog circuitry and may not be suitable for rotating rectifiers mounted on the rotor of a brushless synchronous machine.

[0003] Another way to detect faults in a rectifier is to continuously measure the current on its AC side and determine the average or root mean square (rms) value from the measured phase current values. A fault signal is issued if the RMS values ​​or average values ​​are disproportionate between phases, or if the values ​​vary significantly from normal operation. However, in most cases, this method requires the installation of additional current sensors that are not typically part of the rectifier, and similar to the methods described above, it cannot be used for rotating rectifiers. For example, in the literature: N.M. Freire, J.O. Estima, and A.J. Marques Cardoso, “Open Circuit Fault Diagnosis in PMSG Drives for Wind Turbine Applications”... Open-Circuit Fault Diagnosis in PMSG Drives for Wind Turbine Applications The principle is described in IEEE Transactions on Industrial Electronics, Vol. 60, No. 9, pp. 3957-3967, September 2013, doi: 10.1109 / TIE.2012.2207655. The pulse count of the rectifier is used in some known rectifier fault diagnosis methods. The pulse count is defined as the ratio of the frequency of the first harmonic AC component of the rectified voltage of the rectifier to the first harmonic voltage on the AC side of the rectifier.

[0004] Unless a fault in the power electronics of the rotating rectifier of a brushless synchronous generator is reliably detected, the rotating exciter will be overloaded by current and thus heated to a great extent when the RMS value of the terminal voltage of the main synchronous generator remains constant. This causes the rotating exciter insulation to age faster and can result in significant economic losses for the power plant where the machine is installed.

[0005] For example, documents ES2738649A1 and ES2738649B2 disclose a technical solution for assessing excitation system faults based on measuring the magnetic leakage field of a brushless synchronous generator. However, this method requires the installation of dedicated sensors to measure the magnetic leakage field, which is not always feasible and is very expensive.

[0006] The invention described below enables reliable detection of faults in the power electronics of rotating and stationary rectifiers without the need for additional specialized sensors and other measuring instruments. Summary of the Invention

[0007] This invention relates to a method for detecting faults in a rectifier operating in a fault-free state in continuous current mode on its DC side. Generally, these are rectifiers that are part of the excitation source of a synchronous generator. For rectifiers being diagnosed, a fault is defined as a short circuit or open circuit occurring at the location of the faulty power electronic device. The detection method is based on evaluating the higher harmonic content in the spectrum of the measured signal. When diagnosing faults in rotating rectifiers, the primary measurement is the field (excitation) current entering the device with rotating magnetic coupling, while for stationary rectifiers, it is advantageous to use complementary measurements of the rectified output voltage to detect the fault.

[0008] Frequency analysis of the measured signals (always current and complementary voltage) generates the amplitude of the fundamental wave and all its non-zero integer multiples, up to the value corresponding to the product of the fundamental wave and the number of pulses p of the rectifier being diagnosed. The frequency of the fundamental wave is equal to the AC supply voltage of the rectifier being diagnosed. The obtained amplitude values ​​up to the order (p-1) of the frequency spectrum of the measured quantity are normalized using the p-th harmonic magnitude and summed to obtain the fault factor per unit (in the case of current signals, the fault factor per unit current is identified as Xi, and in the case of voltage signals, the fault factor per unit voltage is identified as Xu). In the next step, the distance between the current value of the fault factor per unit Xi or Xu and the fault-free state is analyzed. When a predetermined threshold is exceeded, a fault signal for the power electronics of the rectifier being diagnosed is issued.

[0009] To reliably detect threshold fault conditions, for rotating rectifiers, the terminal voltage of the powered synchronous generator is also sensed. For the rectifier being diagnosed, a threshold fault condition refers to a permanent short circuit or permanent disconnection at the DC terminal of at least one DC pole of the rectifier from the load, which occurs when all power electronic components belonging to the cathode or anode group of the rectifier are permanently open-circuited under fault conditions.

[0010] To identify faulty power electronic devices in a rotating rectifier, the angular displacement (position) of the rotor of the powered synchronous generator is sensed and multiplied by the number of pole pairs of the rotating magnetically coupled devices that form the rotating exciter together with the rectifier under diagnosis. To identify faulty power electronic devices in a stationary rectifier, the position of the space vector of the AC supply voltage in the stationary coordinate system is calculated, typically using the Clark transform. The space vector calculation can be performed throughout the operation of the rectifier or only as needed after fault detection. Based on the electrical angle of the rectifier under diagnosis to be determined in this way, and taking into account the control angle, the conduction angle of the device whose measurement signal exhibits an abnormal shape can be determined. For rotating rectifiers, only anomalies in the waveform of the field current of the device with rotating magnetic coupling, which, together with the rotating rectifier under diagnosis, forms the rotating exciter, are examined. For stationary rectifiers, it is advantageous to also analyze anomalies in the waveform of the rectified voltage.

[0011] The excitation source includes a rectifier that can be diagnosed based on a determined fault factor Xi or Xu per unit, and typically has (but is not limited to) one of the following topologies: a) The excitation source includes a stationary controlled thyristor rectifier, which is powered from an AC source (usually an AC grid or another rotating AC source located on the same axis as the synchronous generator), and its DC terminal is electrically connected to the excitation (field) winding of the synchronous machine.

[0012] b) The excitation source includes a rotating rectifier whose DC terminal is electrically connected to the excitation (field) winding of the synchronous machine, and whose AC terminal is connected to a device with rotating magnetic coupling (typically connected to a rotating exciter of the reverse synchronous type located on the same axis as the synchronous generator), which is powered either from an AC source (typically the AC grid or another rotating AC source located on the same axis as the synchronous generator) via a controlled rectifier, or via a controlled DC source including a DC / DC converter.

[0013] The described method can be used to detect faults in one or more power electronic components of a rectifier under diagnosis. For rotating rectifiers, the fault type is determined based on the RMS value of the terminal voltage of the synchronous generator and by observing the fault factor Xi per unit current, which has pre-calculated or experimentally determined values ​​for each fault type, stored in a control computer. On the other hand, for stationary rectifiers, in addition to comparing the fault factor Xi or Xu per unit current with pre-calculated or experimentally determined values, it is also necessary to determine the average current value on the DC side of the rectifier in order to determine the fault type.

[0014] The described invention overcomes the problems of existing schemes for protecting rectifiers operating in continuous current mode by reliably detecting faults and determining their type. The proposed scheme requires only common hardware (HW) equipment for the control computer (typically an excitation controller), requires no additional instrumentation, and is very simple and robust in its commissioning. Tuning involves setting only one parameter, the fault detection threshold Xi_threshold per unit current. If a complementary fault factor Xu per unit voltage is used, the voltage threshold Xu_threshold must also be set. Attached Figure Description

[0015] Exemplary embodiments of the proposed invention are described with reference to the accompanying drawings, the purpose of which is to diagnose faults in the power electronic devices of a rectifier operating in continuous current mode, in which: Figure 1 It is a connection configuration of a synchronous generator having an excitation source including a static controlled thyristor rectifier; Figure 2 It is a connection configuration of a synchronous generator with an excitation source including a device having a rotating magnetic coupling connected to its output; the excitation system with rotating magnetic coupling is powered either from an AC source via a thyristor rectifier or via a DC / DC converter.

[0016] Figure 3 This is a block diagram describing an algorithm for detecting faults in power electronic devices of stationary and rotating rectifiers operating in continuous current mode. Detailed Implementation

[0017] Exemplary embodiments describe applications in which the rectifier typically operates in continuous current mode, i.e., the necessary conditions for diagnosing faults in its power electronics are met based on the methods specified in this invention. These are excitation circuit topologies of a synchronous generator (SG) 1, whose excitation source 2 is composed of either a static rectifier 7 or a rotating rectifier 4.

[0018] Figure 1 A variation of the excitation source 2 for the synchronous generator 1 used for external excitation is shown, which implements a wound rotor via a static controlled thyristor rectifier 7. The static controlled thyristor rectifier 7 is powered from an AC source (typically an AC grid or other rotating AC source located on the same axis as the synchronous generator 1).

[0019] The proposed excitation rectifier fault diagnosis is also applicable to Figure 2The circuit diagram for the excitation source 2 of the brushless synchronous generator is shown. The brushless synchronous generator 6 includes a component consisting of a rotating magnetically coupled device 5 (typically a reverse-synchronous type rotating exciter located on the same axis as the synchronous generator 1), a rotating rectifier 4, and the synchronous generator 1. The rotating magnetically coupled device 5 is powered either from an AC source (typically an AC grid or other rotating AC source located on the same axis as the synchronous generator 1) via a stationary controlled thyristor rectifier 7 (this is the power supply method shown in the first power supply diagram 10), or via a DC / DC converter 8 whose DC input terminal is connected to the AC source (typically connected to the AC grid or other rotating AC source located on the same axis as the synchronous generator 1) via a diode rectifier 9 (this is the second power supply option shown in the second power supply diagram 11).

[0020] The fault detection principles for rotating rectifier 4 and stationary rectifier 7 are based on the frequency (Fourier) analysis of the measured field current 3 and voltage 13 signals, respectively. Fundamental amplitude calculation block 17 outputs the amplitude of all non-zero integer multiples of the fundamental frequency from the harmonic analysis of the measured signals, up to the harmonics equal to the product of the fundamental frequency and the number of pulses p of rectifier 4 or 7. The fundamental frequency is equal to the frequency of the AC power supply voltage of rectifier 4 or 7. Fault diagnosis of the power electronics of rectifier 4 or 7 is performed using a fault factor Xi per unit current and / or a fault factor Xu per unit voltage, see fault factor calculation block 18. If the continuously evaluated fault factor Xi per unit current exceeds the defined fault detection threshold Xi_threshold per unit current or the fault factor Xu per unit voltage exceeds the defined fault detection threshold Xu_threshold per unit voltage (see block 19), for a duration longer than one cycle of the fundamental frequency, signal 26 indicates a fault in rotating rectifier 4, or signal 27 indicates a fault in stationary rectifier 7. Since the source of the fault could be either the rotating rectifier 4 or the stationary rectifier 7, the final signal 30 of the excitation source 2 fault is composed of the signal 26 of the rotating rectifier 4 fault, the signal 27 of the stationary rectifier 7 fault, and the signal 30 transmitted via the rotating rectifier 4 fault signal 26. Figure 3 The proposed logic processing of the excitation process is determined by the logical summation of the excitation process completion signal 29 shown.

[0021] During normal operation of synchronous generator 1 (i.e., after the excitation process of synchronous generator 1 has been completed, as indicated by signal 29), detection is also performed when the DC component of the measured field current 3 exceeds the permissible operating range. Figure 1 and Figure 2 Faults in the topology.

[0022] Furthermore, a fault is detected when the excitation process of synchronous generator 1 is completed (see indication of signal 29), and when the RMS value of the back electromotive force of generator 1 is lower than the RMS value of the back electromotive force of synchronous generator 1 specifically for the minimum permissible operating field current 3, wherein the value of field current 3 is within the operating range defined for said synchronous generator 1. To determine the back electromotive force of the described synchronous generator 1, the measured terminal voltage 14 is used.

[0023] The excitation process refers to the state in which the synchronous generator 1 reaches its operating speed and the required field current 3 rises from 0 to the required value derived from the grid voltage.

[0024] The tuning of the proposed method involves setting a fault detection threshold Xi_threshold per unit current or a fault detection threshold Xu_threshold per unit voltage (see Block 19). Tuning is performed as follows: Under fault-free machine conditions, the fault factor Xi or Xu is measured per unit to determine a reference fault-free per unit factor Xi_ref or Xu_ref. Furthermore, under intentional fault conditions, the fault factor Xi or Xu is measured per unit, where one of the power electronic devices in rectifier 4 or 7 is not conducting. This determines a reference fault factor Xi_err per unit current or a reference fault factor Xu_err per unit voltage. In Block 19, the fault detection threshold Xi_threshold or Xu_threshold is determined by the arithmetic mean of the values ​​of the reference fault-free per unit current factor Xi_ref and the reference fault factor Xi_err, or the values ​​of the reference fault-free per unit voltage factor Xu_ref and the reference fault factor Xu_err.

[0025] The proposed method is capable of assessing the type of fault caused by a short circuit or open circuit in one or more power electronic devices of rectifier 4 or 7. The type of fault is determined by comparing the magnitude of the DC component of the field current 3 (block 24), the RMS value of the terminal voltage 14 of the synchronous generator 1 (block 25), and the fault factor Xi or Xu per unit (block 18) with values ​​pre-calculated or experimentally determined for each type of excitation rectifier fault and stored in the control computer 12 (typically in the excitation controller). Figure 3 The block diagram clearly illustrates the algorithm used to detect faults in the power electronic components of rectifier 4 or 7 and faults in excitation source 2. The basic diagnostic signals, as described above, are the field current 3 and the measured voltage 13 on the DC side of the static rectifier 7.

[0026] To identify the faulty power electronic device, for the rotating rectifier 4, the rotor displacement angle 15 of the powered synchronous generator 1 is sensed. The rotor displacement angle 15 is multiplied by the number of pole pairs pp of device 5 (reference block 22), which has rotating magnetic coupling that forms a rotating exciter together with the diagnosed rotating rectifier 4. To identify the faulty power electronic device of the stationary rectifier 7, the position of the space vector of the measured terminal voltage 16 of the AC source in the stationary coordinate system is calculated, typically using the Clark transformation (reference block 23). Based on the electrical angle of the diagnosed stationary rectifier 7 determined in this way, taking into account the control angle, the conduction angle of the device in which the measured signal exhibits an abnormal shape (reference block 20) ​​can be determined (reference block 21). For the rotating rectifier 4, anomalies in the waveform of the field current 3 of device 5 with rotating magnetic coupling are examined (reference block 20), which, together with the diagnosed rotating rectifier 4, forms a rotating exciter. For the stationary rectifier 7, it is advantageous to also analyze anomalies in the waveform of the measured voltage 13 on the DC side of the stationary rectifier 7 (reference block 20).

[0027] List of reference numerals

[0028] 1. Synchronous generator

[0029] 2. Excitation source

[0030] 3. The field (excitation) current measured on the stationary DC side of excitation source 2, i.e. The field current on the stator of the device 5 with rotating magnetic coupling, or the current on the DC side of the static rectifier 7; 4 Rotary rectifier 5. Devices with rotating magnetic coupling (typically a reverse-synchronous type rotating exciter located on the same shaft as synchronous generator 1). 6 Brushless Synchronous Generator 7. Static Rectifier 8 DC / DC converters 9. Diode excitation rectifier 10 A first power supply block for supplying power from an AC source (typically an AC grid located on the same shaft as the synchronous generator 1 or other rotating AC source) to a device 5 with rotating magnetic coupling via a static rectifier 7. 11 A second power supply block for supplying power to the device 5 with rotating magnetic coupling via the DC / DC converter 8, the DC input terminal of which is connected to an AC source (typically an AC grid or other rotating AC source located on the same shaft as the synchronous generator 1) via a diode rectifier 9. 12. Control computer, typically an excitation controller in which algorithms for diagnosing faults in the rotating rectifier 4 and / or the stationary rectifier 7 are implemented. 13. Measured voltage on the DC side of static rectifier 7 14. Terminal voltage of synchronous generator 1 15. Rotor displacement angle of synchronous generator 1 determined from mechanical sensors 16. Measurement terminal voltage of the AC source supplying power to the static rectifier 7 17. A block for calculating the fundamental amplitude (FFT) and the amplitude of all non-zero integer multiples of the fundamental frequency (up to the harmonics whose frequency is equal to the product of the fundamental frequency and the number of pulses of rectifier 4 or 7), where the fundamental frequency is equal to the frequency of the AC power supply voltage of rectifier 4 or 7. 18. A block for calculating the fault factor X, which is calculated by quotient, where the denominator is the amplitude of the highest determined frequency component of the measured field current 3 or the measured voltage 13, and the numerator is the sum of the values ​​of the other lower determined frequency components of the field current 3 or the measured voltage 13. 19. The fault detection threshold Xthreshold is determined as the arithmetic mean of the reference fault-free factor Xref determined under fault-free conditions of the rectifier being diagnosed and the factor Xerr determined under the condition that one power electronic device in rectifier 4 or 7 is not conducting. 20. Detect abnormal blocks in the waveform of the measured field current 3 or measured voltage 13. 21. Identify the active cycle block of the faulty power electronic device in rectifier 4 or 7 under fault-free conditions. This cycle is based on the electrical angle value of the rectifier being diagnosed, at which time the waveform of the measured magnetic field current 3 or voltage 13 will exhibit abnormal distortion. 22 The number of pole pairs pp of the rotating magnetically coupled device 5 is used as the product of the number of pole pairs pp and data regarding the current rotor displacement angle 15 of the synchronous generator 1 to continuously determine the electrical angle of the rotating rectifier 4. 23. A space vector transformation (typically using Clark transformation) is used to continuously determine the electrical angle of the stationary rectifier 7 by using the angle of the space vector representing the measured AC power supply voltage 16 in the stationary coordinate system. 24. Calculate the average value from the waveform of the measured quantity. 25. Calculate the RMS value from the waveform of the measured quantity. 26 Rotary Rectifier 4 Fault Signal 27 Static Rectifier 7 Fault Signal 28 Static rectifier 7 control angle 29 Excitation program completion signal, synchronous generator 1 operating mode. 30 Excitation source 2 fault signal

Claims

1. A method for detecting faults in the excitation rectifier of a synchronous generator (1), characterized in that, The field current (3) is measured on the stationary DC side of the excitation source (2), and further, the frequency of the measured field current (3) is determined based on the frequency analysis. The amplitude of the fundamental wave, the frequency of the fundamental wave is equal to the frequency of the AC power supply voltage of the rotating rectifier (3) containing power electronic devices or the stationary rectifier (7) containing power electronic devices, and The amplitude of all non-zero integer multiples of the fundamental frequency of the harmonics whose frequency is equal to the product of the fundamental frequency and the number of pulses of the rectifier (4) or (7). Furthermore, the quotient is used to calculate the fault factor Xi per unit current, where the denominator is the amplitude of the highest determined frequency component of the measured field current (3), and the numerator is the sum of the values ​​of the other lower determined frequency components of the field current (3). Under fault-free conditions, calculate the reference fault-free current factor Xi_ref, then de-energize at least one power electronic device of rectifiers (4) and (7), and determine the reference fault factor Xi_err. The arithmetic mean of the reference fault-free current factor Xi_ref and the reference fault factor Xi_err was used to determine the fault detection threshold Xi_threshold per unit current. Furthermore, during the operation of rectifiers (4) and (7), the fault factor Xi per unit current is continuously calculated, wherein a fault signal for excitation source (2) is issued under the following conditions after the excitation procedure of synchronous generator (1) indicated by signal (29) is completed. - The time that the fault factor Xi per unit current is higher than the fault detection threshold Xi_threshold per unit current is longer than one cycle of the fundamental frequency, and / or - The measured DC component of the field current (3) exceeds the permissible operating range, and / or - The RMS value of the back electromotive force of the generator (1) is less than the RMS value of the back electromotive force of the generator (1) determined for the minimum permissible operating field current (3) under the field current (3), the value of which is within the permissible operating range defined for the synchronous generator (1), wherein the back electromotive force of the synchronous generator (1) is determined from the measured terminal voltage (14).

2. The method according to claim 1, characterized in that, In addition, when the magnitude of the DC component of the field current (3) and the rms value of the back electromotive force of the synchronous generator (1) are within the allowable operating range, the fault type of the excitation source (2) caused by a short circuit or open circuit of one or more power electronic devices of the rectifiers (4) and (7) is determined by comparing the continuously determined fault factor Xi per unit current with the value stored in the control computer (12) for each fault type of the rectifiers (4) and (7) in advance or experimentally determined.

3. The method according to claim 1 or 2, characterized in that, Additionally, the rectified voltage (13) is measured on the DC side of the static rectifier (7), and frequency analysis is used to determine the amplitude of the fundamental wave from the measured rectified voltage (13), as well as the amplitude of all non-zero integer multiples of the fundamental wave frequency up to the harmonics whose frequency is equal to the product of the fundamental wave and the number of pulses of the static rectifier (7), the fundamental wave frequency being equal to the frequency of the AC power supply voltage of the static rectifier (7). Furthermore, the quotient is used to calculate the fault factor Xu per unit voltage, where the denominator is the amplitude of the highest determined frequency component of the measured rectified voltage (13), and the numerator is the sum of the values ​​of the other lower determined frequency components of the rectified voltage (13). Under fault-free conditions, the reference fault-free voltage factor Xu_ref is measured per unit voltage, then the electrical connection of at least one power electronic device of the static rectifier (7) is disconnected, and the fault factor Xu_err per unit voltage is determined. The arithmetic mean of the reference fault-free voltage factor Xu_ref and the reference fault factor Xu_err per unit voltage was used to determine the fault detection threshold Xu_threshold per unit voltage. Furthermore, during the operation of the static rectifier (7), the fault factor Xu per unit voltage is continuously determined, wherein if the time for which the fault factor Xu per unit voltage is higher than the fault detection threshold Xu_threshold per unit voltage is longer than one cycle of the fundamental frequency after the excitation of the synchronous generator (1) indicated by the signal (29) is completed, a fault signal for the static rectifier (7) is issued.

4. The method according to any one of claims 1 to 3, characterized in that, At least one harmonic frequency is omitted in the sum of the numerators of the calculation of the fault factor Xi per unit current and / or the fault factor Xu per unit voltage (18).

5. The method according to any one of claims 1 to 4, characterized in that, The measured terminal voltage (16) on the AC side of the static rectifier (7) is used to calculate the space vector of the voltage using Clark transformation. The position of the space voltage vector is then compensated by subtracting the control angle of the static rectifier (7). The position of the space vector of the terminal voltage (16) on the AC side of the static rectifier (7) is determined by using the value of the position of the space vector of the terminal voltage (16) on the AC side of the static rectifier (7) derived at the moment when the waveform shape of the rectified voltage (13) measured compared to the fault-free condition is abnormal.

6. The method according to any one of claims 1 to 4, characterized in that, The phase and / or specific power electronics at the fault location of the rotating rectifier (4) are determined by multiplying the rotor displacement angle (15) of the synchronous generator (1) by the number of pole pairs pp (22) of the rotating magnetically coupled device (5) derived at the moment when the waveform shape of the field current (3) measured relative to the fault-free condition is abnormal.

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