JP2007006673A - Digital protective relay system for main circuit of generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a digital protective relay system that reduces the detection points of quantity of state and operation amount of the main circuit of a generator, without impairing the protection functions. <P>SOLUTION: The digital protective relay system of the main circuit of the generator is provided with a main transformer 2, connected to a system via a circuit breaker 1, in light of the fact that the operation of the phases of a voltage and a current is possible by digital operation and that chronological monitoring is possible, a generator 3 connected to the low-voltage side of a main transformer, a station service transformer 4 connected to the output end of the generator, and an exciting power supply transformer 6, that supplies exciting power of the generator connected to the output end of the generator. In this protective relay system, current transformers are installed, respectively, to measure the system side current A of the main transformer, the neutral point side current B of the generator, the secondary side current D of the station service transformer, and the secondary side current C of the excitation power supply transformer. The phase differences between the current detection values obtained from each current transformer and voltage detection values E of the output end voltages of the generator are computed. Based on these phase differences, short-circuiting failures of the main circuit of the generator are detected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital protection relay system for a generator main circuit, and in particular, can make use of the characteristics of digital computation to reduce the detection points and the computation amount of the state quantity of the generator main circuit without impairing the protection function. The present invention relates to a digital protection relay system.

  FIG. 4 shows a schematic configuration of a generator main circuit facility of a conventional power plant and a generator main circuit protection system. The generator main circuit includes a generator 3 connected to a power transmission system via a main transformer circuit breaker 1 and a main transformer 2, and a generator between the generator 3 and the main transformer 2, as shown in the figure. An in-house transformer 4 and an excitation power transformer 6 connected to the output terminal are included. The electric power generated by the generator 3 is transmitted to the system outside the power plant via the main transformer 2 and the main transformer circuit breaker 1, and at the same time is necessary for power generation via the in-house transformer 4. Excitation power is supplied from the excitation power transformer 6 to the field winding 5 that excites the generator 3 by supplying power to the load in the power plant.

  In the generator main circuit configured as described above, a generator main circuit protection relay system is installed for the purpose of appropriately detecting and disconnecting an accident point when an electrical accident such as a short circuit occurs. In the example of FIG. 4, an analog protection relay is applied, and a process using a mechanical or electrical circuit using a quantity of electricity (state quantity) obtained from a current and voltage detection point installed in the generator main circuit. To detect electrical accidents.

  As shown in Table 1, the protection items required for such a generator main circuit are basically short circuits (including overload and overcurrent), ground faults, overexcitation for electromagnetic equipment, and synchronous machines. It can be broadly divided into field loss, reverse phase current, and reverse power and frequency detection for turbine protection, which is a driving source of the generator. When protecting with an analog protective relay, a protective relay system is constructed by combining the protection items in Table 1 with single-element protective relays having independent and dedicated operating principles and operating mechanisms. In addition, for each analog protection relay, an instrument transformer for detecting current and voltage state quantities is basically required.

  In addition, in order to prevent damage to the main engine and the spread of accidents when one protective relay malfunctions, in principle, two protective relays with different operating principles for one protection item. Reliability is ensured by the main protection / rear protection provided in combination.

87G: Generator ratio differential relay 87GMT: Generator-main transformer ratio differential relay 44G: Distance relay 64G1, 64G2: Generator ground fault relay 59 / 95G: Generator-transformer overexcitation relay 59G: Overvoltage relay 40G : Field loss relay 87ET: Excitation power transformer ratio differential relay 46G: Generator reverse phase current relay 67G: Generator reverse power relay 95G: Frequency relay 51ET: Excitation power transformer overcurrent relay 64F: Generator field ground Inductor relay 51NMT: Neutral point overcurrent relay of main transformer 87HT: In-station transformer ratio differential relay 51HT: In-station transformer overcurrent relay 64HT: In-station transformer ground fault relay On the other hand, voltage and current of generator main circuit The state quantity is converted into a digital quantity, loaded into a microprocessor (CPU), and processed according to software prepared in advance. Digital protective relays that detect more accidents are used.

  However, the conventional digital protective relay device of the generator main circuit follows the configuration of the analog protective relay as it is. In other words, the method of detecting an accident is a software mechanism of each analog protection relay, and the detection points of the state quantities of voltage and current are the same as those of the analog protection relay.

  In addition, the protection function is also provided for each protection item, taking over the protection concept of the analog protection relay as it is. However, since the conventional digital protection relay device for the generator main circuit is configured to perform the respective arithmetic processing of main protection / rear-end protection related to the protection item with one CPU, it does not necessarily lead to improvement in reliability. There is a case.

  That is, when the main protection operation is inoperative, there is a high possibility that the back-up protection operation is also inoperative. Therefore, it is highly possible that the backup operation of the main protection / rear protection cannot be expected. Moreover, since all calculations are performed by one CPU, since a plurality of calculations are performed, the amount of calculation processing is large, and the number of detection points for the state quantities of voltage and current is large. Therefore, there was a problem that the cost was high.

  As conventional digital protective relay devices, those described in Patent Documents 1 and 2 are known.

JP-A-7-59253

  An object of the present invention is to realize a digital protection relay system capable of reducing the detection points and the calculation amount of the state quantity of the generator main circuit without impairing the protection function.

  In order to solve the above problems, the present invention replaces the conventional digital protection calculation in view of the fact that the calculation of the phase of voltage and current can be performed by digital calculation and that time series monitoring is possible. The digital protection relay system that can reduce the detection points and the amount of calculation of the state quantity of the generator main circuit without impairing the protection function has been realized.

  Specifically, the present invention comprises a main transformer connected to the system via a circuit breaker, a generator connected to the low-voltage side of the main transformer, and an in-house connected to the output end of the generator In a digital protection relay system for a main circuit of a generator comprising a transformer and an excitation power transformer connected to an output end of the generator and supplying excitation power of the generator, the system side of the main transformer Current transformer, neutral point side current of the generator, secondary side current of the in-house transformer, and secondary current of the excitation power transformer are installed, respectively, Calculating a phase difference between the current detection value obtained from the generator and the voltage detection value of the output terminal voltage of the generator, and detecting a short circuit accident in the generator main circuit based on the phase difference. .

  For example, if a short-circuit accident occurs in the generator main circuit, the current direction of the generator main circuit changes, so that the current value of the healthy phase in the three-phase circuit is different from the current value of the short-circuit phase. The current value of the main circuit or the balance of each phase is different from the normal state. Therefore, the present invention makes use of the fact that the phase of voltage and current can be calculated by digital calculation and that the time series monitoring is possible, and the generator is based on the phase of the output terminal voltage of the generator. The basic principle is to detect a short-circuit accident by comparing the phase of the detected current value of each part of the main circuit and monitoring the change of the phase difference in time series. In other words, since the balance of each phase and the direction of current flow change between a healthy state and a short-circuit accident, the phase is monitored, compared with the previous state (when healthy), and fluctuations exceeding the set value If there is, detect it as an accident.

  In addition, when a short-circuit accident occurs in the main transformer, current flows toward the point of the accident, so that the current on the system side of the main transformer flows from the system side toward the generator on the contrary. Therefore, comparing the phase of the system current of the main transformer with reference to the output terminal voltage of the generator, it can be seen that the phase is reversed from the normal phase comparison result before the accident occurred. Can be detected.

  Further, for example, when a short circuit accident (external short circuit accident) occurs on the system side of the main transformer, the phase of the current and voltage of the generator main circuit changes suddenly and approaches a delay power factor of 90 °. Further, the system current of the main transformer is subjected to a short-circuit current that is suppressed by the initial reactance (Xd ″), the transient reactance (Xd ′), and the synchronous reactance (Xd) in time series according to the generator short-circuit current equation. In other words, when an accident occurs, a current that exceeds the rated current flows, but after a while, a current that is about the rated current flows, and after that, a current that is less than the rated current flows. The external short circuit accident can be detected by comparing the phase of the neutral point side current of the generator with the detected current value and monitoring in time series.

  In addition, with regard to reverse power that flows into the generator from the grid side, as described later, the current detection values of the main transformer grid side current and the neutral point current of the generator are taken in and detected. It is possible to calculate the phase difference between the value and the voltage detection value of the output terminal voltage of the generator, calculate the power value and the power direction of the generator main circuit based on the phase difference, and detect the reverse power.

  Further, the present invention provides a current of a system side current of the main transformer, a neutral point side current of the generator, a secondary side current of the in-house transformer, and a secondary side current of the excitation power transformer. Takes the detected value and the detected voltage value of the output of the generator, current phase comparison calculation, voltage / frequency calculation, zero phase voltage calculation, frequency calculation, power calculation, impedance calculation, reverse phase current calculation, Digital arithmetic unit that detects the main circuit accident including short circuit accident, ground fault, generator overexcitation, generator load imbalance, reverse power, low frequency by 8 operations of zero phase current calculation Can be provided.

  According to the present invention, it is possible to reduce the amount of digital protection relay operation, the number of instrument transformers, current transformers, and the like, and achieve a necessary protection function with a simplified system. As a result, a more rational generator main circuit digital protection relay system can be configured. Further, the reliability of the digital protection relay system can be improved by simplifying the system configuration. Furthermore, the digital protection relay system of the present invention can be multiplexed according to the reliability required by the power generation system, even for accidental failures peculiar to digital, since the digital protection relay system of the present invention is a simple system. Therefore, it is possible to improve the reliability by duplicating the digital protection relay system of the present invention according to the required reliability without adopting the concept of main protection / rear-end protection of the conventional analog protection relay. Can do.

  By the way, the current transformer installed on the system side (high voltage side) of the main transformer is generally separated from the building where the digital protection relay system is installed. Therefore, the cable for transmitting the detected current value becomes long and it is necessary to take measures against noise. Therefore, the present invention provides a signal converter that digitizes a current detection value detected by a current transformer installed on the system side of the main transformer and converts it into an optical signal, and transmits it to a digital protection relay system using an optical cable. Let According to this, not only the amount of conventional metal cable laying can be reduced, but also the noise countermeasure cost can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, the digital protection relay system which reduced the detection point and calculation amount of the state quantity of the generator main circuit, without impairing a protection function is realizable.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a configuration of a digital protection relay system for a generator main circuit according to an embodiment in which the present invention is applied to a power plant. As shown in the figure, the generator main circuit includes a generator 3 connected to the system via the main transformer circuit breaker 1 and the main transformer 2, and a generator output between the generator 3 and the main transformer 2. An in-house transformer 4 and an excitation power transformer 6 connected to the ends are included. The electric power generated by the generator 3 is transmitted to the system outside the power plant via the main transformer 2 and the main transformer circuit breaker 1, and at the same time via the on-site transformer 4 and the circuit breaker 16. Power is supplied to a load in the power plant necessary for power generation, and excitation power is supplied from the excitation power transformer 6 to the field winding 5 that excites the generator 3. Further, the neutral point circuit of the generator 3 is grounded with high resistance by a secondary resistor 15.

  The digital protection relay system of this embodiment includes a digital protection relay device 10, a current transformer CT11 installed on the high voltage side of the main transformer, a current transformer CT12 installed on the neutral point side of the generator 3, Current transformer CT13 installed on the secondary side of the in-house transformer 4, current transformer CT14 installed on the secondary side of the excitation power transformer 6, and instrument transformer installed on the output end side of the generator 3 PT17.

  FIG. 2 shows an embodiment of the digital protective relay device 10. The digital protection relay device 10 takes in the detected value of the voltage or current detected by PT17, CT11, 12, 13, 14 installed in the generator main circuit via the input converter 20, and an analog / digital conversion unit 21 is A / D converted and input to the arithmetic processing unit 22. The arithmetic processing unit 22 determines whether or not there is an accident in the generator main circuit by performing protective arithmetic processing in accordance with preset digital protective relay software. When the arithmetic processing unit 22 detects an accident, the detection result is output to the settling / display unit 24 via the transmission unit / I / O unit 23 and an operation command is output to an output relay that drives a circuit breaker and the like. It is designed to protect the generator main circuit.

  Table 2 shows a comparison of protection items and protection elements of the digital relay device 10 of this embodiment. As shown in Table 2, the protection items are basically short circuit (including overload and overcurrent), ground fault, overexcitation, field loss, reverse phase current, and reverse power and frequency reduction of turbine protection. .

Corresponding to the protection elements (1) to (8) in Table 2, the arithmetic processing unit 22 has a protective arithmetic function as shown in FIG. That is, the current phase comparison unit 101 takes the detected voltage value E of PT17 and the detected current values A to D of each CT11, CT12, CT13, and CT14, performs a protection operation, and outputs a protection output (1). It has become. The voltage / frequency (V / F) detection unit 102 takes in the detected voltage value E of the PT 17 and performs a protection calculation, and outputs a protection output (2). The Vo detection unit 103 takes in the voltage detection value E of PT17, detects the zero-phase voltage, and outputs a protection output (3). The F detection unit 104 takes in the voltage detection value E of the PT 17 to detect a frequency drop and outputs a protection output (4). The power detection unit 105 takes in the detection current of the voltage detection value E and the CT12 value of PT17, detects reverse power, and outputs a protection output (5). The impedance detection unit 106 takes in the detection current of the voltage detection value E and CT12 value of PT17, detects the loss of the field, and outputs the protection output (6). The I ₂ detection unit 107 takes in a detection current of CT12 value, detects a reverse phase current, and outputs a protection output (7). The Io detection unit 108 takes in a CT12 value detection current, detects a zero-phase current, and outputs a protection output (7).

  The details and operation of the accident detection function of each part of the digital protective relay device 10 configured as described above will be described for each accident.

(Short-circuit detection)
When a short circuit accident occurs in the generator main circuit, the current direction of the generator main circuit changes, and the current value of the healthy phase in the three-phase circuit differs from the current value of the short circuit phase so that the generator main circuit The current value or the balance of each phase is different from the normal state. The phase of the detected current value of each part detected by CT11, CT12, CT13, CT14 is compared on the basis of the phase of the detected voltage of PT17 which is the output terminal voltage of the generator, and the change of the phase difference is further time-sequentially. To detect a short-circuit accident.

  For example, if a short-circuit accident occurs in the generator main circuit, the current direction of the generator main circuit changes, so that the current value of the healthy phase in the three-phase circuit is different from the current value of the short-circuit phase. The current value of the main circuit or the balance of each phase is different from the normal state. Therefore, in this embodiment, the phase of the output terminal voltage of the generator is used as a reference, the phase of the detected current value of each part of the generator main circuit is compared, and the change in the phase difference is further monitored in time series. A short-circuit accident is detected. In other words, since the balance of each phase and the direction of current flow change between a healthy state and a short-circuit accident, the phase is monitored, compared with the previous state (when healthy), and fluctuations exceeding the set value If there is, detect it as an accident.

  In addition, when a short-circuit accident occurs in the main transformer, current flows toward the point of the accident, so that the current on the system side of the main transformer flows from the system side toward the generator on the contrary. Therefore, comparing the phase of the system current of the main transformer with reference to the output terminal voltage of the generator, it can be seen that the phase is reversed from the normal phase comparison result before the accident occurred. Can be detected.

  Further, for example, when a short circuit accident (external short circuit accident) occurs on the system side of the main transformer, the phase of the current and voltage of the generator main circuit changes suddenly and approaches a delay power factor of 90 °. Further, the system current of the main transformer is subjected to a short-circuit current that is suppressed by the initial reactance (Xd ″), the transient reactance (Xd ′), and the synchronous reactance (Xd) in time series according to the generator short-circuit current equation. In other words, when an accident occurs, a current that exceeds the rated current flows, but after a while, a current that is about the rated current flows, and after that, a current that is less than the rated current flows. The external short circuit accident can be detected by comparing the phase of the neutral point side current of the generator with the detected current value and monitoring in time series.

  Furthermore, since the short circuit current is suppressed by the reactance of the generator and changes in time series as shown in FIG. 5, the change in the current location of the main circuit of the generator is monitored, and the change as shown in FIG. Can be detected as a short-circuit accident.

  Table 3 summarizes the detection methods for these short-circuit accidents.

(Ground fault)
First, detection of a ground fault in the primary side of the generator 3, the excitation power transformer 6, the primary side of the main transformer 2, and the primary side of the in-house transformer 4 will be described. In the present embodiment, transformer grounding (high resistance grounding) with a secondary resistor 15 is applied in order to prevent damage to these devices when a ground fault occurs in these parts. This grounding method suppresses the ground fault current that flows between the main circuit and the ground in the event of a ground fault by the secondary resistor 15 connected to the secondary side of the ground transformer, and measures are taken to prevent serious damage to the equipment. ing.

  When a ground fault occurs, the voltage balance of the generator main circuit is lost, resulting in a three-phase imbalance, and a zero-phase voltage Vo is generated in the generator main circuit. Conventionally, the zero-phase voltage Vo at the time of the ground fault has been detected as a voltage generated at both ends of the secondary resistor 15. In this embodiment, the zero phase voltage Vo is calculated and detected as a vector sum of the phase voltages of the generator main circuit voltage. That is, based on the voltage detection value E detected by PT17, the zero detection voltage Vo is obtained by the Vo detection unit 103, and a ground fault is detected when the set value is exceeded.

  Next, a ground fault on the system side of the main transformer 2 will be described. The system side of the main transformer 2 is generally an ultra-high voltage system such as 2 kV to 500 kV, so that direct grounding is applied for the purpose of instantaneously detecting a ground fault in accordance with the grounding system of the transmission system. Yes. Therefore, when a ground fault occurs on the system side of the main transformer 2, a large ground fault current flows to the ground fault point. This ground fault current flows from both the generator side and the system side, and basically the same event as the phase short circuit on the system side of the main transformer 2, and thus can be detected by the above-described short-circuit accident detection method. Further, it is possible to more directly detect the zero phase component included in the detected current value A of CT11 having a large contribution to the ground fault current from the vector sum of the phase currents from the impedance distribution. The detection of the ground fault is performed by the current phase comparison unit 101 in FIG.

(Overexcitation detection)
Since overexcitation occurs due to voltage increase or frequency decrease, the V / F detection unit 102 calculates the voltage to frequency ratio based on the voltage and frequency of the voltage detection value E detected by the PT 17. Detect. That is, when the value of V / F exceeds a set value determined by the overexcitation withstand capability of the main transformer, the in-house transformer, the excitation power transformer, and the generator, it is detected as an overexcitation state.

(Field loss detection)
When the field of the synchronous generator is lost, the impedance trajectory of the generator main circuit changes abruptly. Therefore, based on the current detection value B detected by CT12 and the voltage detection value E detected by PT17, power generation The impedance trajectory of the main circuit is obtained and the loss of field is detected based on this. That is, when field loss occurs, the impedance of the generator circuit decreases and approaches the generator reactance. When this impedance value falls within the set value range, it is detected as a field loss.

(Reverse phase current detection)
When the load of the generator 3 is in a three-phase unbalanced state, the current of the generator main circuit includes a reverse phase component, and the end of the rotor coil of the generator 3 is locally heated. In order to prevent this, the I ₂ detection unit 107 takes in the detection current B of CT12 and decomposes it into a positive phase current, a negative phase current, and a zero phase current to obtain a negative phase current. When it exceeds, a protection output (7) is output.

(Reverse power detection)
The reverse power is a state in which power flows into the generator 3 from the system in the reverse manner, and the power detection unit 105 takes in the detection current B of CT12 and the detection voltage E of PT17, and based on these, the generator Detection is performed by calculating the power value and power direction of the main circuit and monitoring whether power is flowing into the generator 3.

(Low frequency detection)
The low frequency is protection of the turbine blades due to a decrease in the operating frequency of the generator 3. The F detection unit 104 detects the low frequency by taking in the detection voltage E of the PT 17 and calculating the frequency.

  As described above, according to the present embodiment, the detected voltage value E of PT17 and the detected current value A of each CT11, CT12, CT13, and CT14 for all the protection items required in the generator main circuit. Based on ~ D, it can be detected.

  Of course, the higher the reliability, the more desirable, but the reliability required depends on the scale of the power generation equipment itself, the operation on the system side, etc., and it is also important to consider the cost performance. The above embodiment is based on a single system, but has fewer components than the conventional configuration, but has the same reliability, and can be easily multiplexed externally according to the required reliability of the power generation equipment. Is possible. Therefore, the reliability can be improved by multiplexing according to the required reliability of the power generation equipment, and a system configuration having a high degree of freedom with respect to the required reliability can be obtained.

(Embodiment 2)
FIG. 3 shows the configuration of a digital protection relay system for a generator main circuit according to another embodiment in which the present invention is applied to a power plant. The present embodiment differs from the embodiment of FIG. 1 in that a signal converter 25 that digitizes the current detection value A of CT11 and converts it into an optical signal is provided in the vicinity of CT11, and the current detection value converted into an optical signal. A is transmitted to the digital protection relay device 10 by the optical cable 26. Since others are the same as those in FIG. 1, the same reference numerals are given and description thereof is omitted.

It is a figure which shows the structure of the digital protection relay system of the generator main circuit of one Embodiment formed by applying this invention to a power plant. It is a detailed block diagram of the digital protection relay of FIG. 1 embodiment. It is a figure which shows the structure of the digital protection relay system of the generator main circuit of other embodiment formed by applying this invention to a power plant. It is a block diagram of the analog protection relay system of the conventional generator main circuit. It is a diagram explaining the method of monitoring the electric current of a generator main circuit and detecting a short circuit accident.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Circuit breaker for main transformer 2 Main transformer 3 Generator 4 In-station transformer 5 Field winding 6 Excitation power transformer 10 Digital protection relay device 15 Secondary resistor 101 Current phase comparison part 102 V / F detection part 103 Vo detection unit 104 F detection unit 105 Power detection unit 106 Impedance detection unit 107 I ₂ detection unit 108 Io detection unit CT11 Current transformer CT12 Current transformer CT13 Current transformer CT14 Current transformer PT17 Instrument transformer

Claims (3)

A main transformer connected to the system via a circuit breaker, a generator connected to the low voltage side of the main transformer, an in-house transformer connected to the output end of the generator, and the output of the generator In the digital protective relay system of the generator main circuit comprising an excitation power transformer connected to the end and supplying the excitation power of the generator,
A current transformer for measuring the system side current of the main transformer, the neutral point side current of the generator, the secondary side current of the in-house transformer, and the secondary side current of the excitation power transformer, respectively. Install and calculate the phase difference between the current detection value obtained from each current transformer and the voltage detection value of the output terminal voltage of the generator, and based on the phase difference, short circuit accidents of the generator main circuit A digital protection relay system for a generator main circuit, characterized in that a digital arithmetic unit for detection is provided. A main transformer connected to the system via a circuit breaker, a generator connected to the low voltage side of the main transformer, an in-house transformer connected to the output end of the generator, and the output of the generator In the digital protective relay system of the generator main circuit comprising an excitation power transformer connected to the end and supplying the excitation power of the generator,
A system-side current of the main transformer, a neutral-point-side current of the generator, a secondary-side current of the in-house transformer, a current detection value of a secondary-side current of the excitation power transformer, and a generator Takes the voltage detection value obtained from the voltage detection point installed on the output side, current phase comparison calculation, voltage / frequency calculation, zero phase voltage calculation, frequency calculation, power calculation, impedance calculation, reverse phase Detects accidents in the main circuit of the generator, including short-circuit accidents, ground faults, generator overexcitation, generator load imbalance, reverse power, and low frequency, through eight calculations: current calculation and zero-phase current calculation A digital protection relay system for a generator main circuit, characterized in that a digital arithmetic unit is provided. In the digital protection relay system of the generator main circuit according to claim 1 or 2,
A signal converter for digitizing the current detection value detected by the current transformer and converting it to an optical signal is provided in the vicinity of the current transformer for detecting the system side current of the main transformer, and converted into an optical signal. A digital protection relay system for a main circuit of a generator, wherein the detected current value is transmitted to the digital arithmetic unit by an optical cable.

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