A non-full-phase protection method and device for machine-end circuit breaker

Abstract

The present invention relates to the field of relay protection technology, and is a method and device for non-full-phase protection of a machine-end circuit breaker. When the generator set is in a grid-connected operating state, there is voltage on both sides of the machine-end circuit breaker, one or two phases of voltage on both sides of the machine-end circuit breaker meet the adaptive difference judgment condition, and there is no differential current to start the lockout, then the non-full-phase protection is activated by the first delay; when the machine-end circuit breaker trips and there is voltage on both sides of the machine-end circuit breaker, if the main transformer high-voltage side circuit breaker trips, and the self-generated zero-sequence voltage on the low-voltage side of the main transformer is greater than the first preset threshold or the main transformer side voltage is unbalanced, then the non-full-phase protection is activated by the second delay; if the main transformer high-voltage side circuit breaker does not trip, and the self-generated zero-sequence voltage on the machine-end side is greater than the second preset threshold or the machine-end side voltage is unbalanced, then the non-full-phase protection is activated by the third delay. The adaptive difference judgment method is used to realize the non-full-phase protection of the machine-end circuit breaker, thereby improving the reliability of the non-full-phase protection. The overall performance of the unit protection device is effectively improved.

Description

Technical Field

[0001] The present invention relates to a non-full-phase protection method and device for a machine-end circuit breaker, belonging to the technical field of relay protection. Background Art

[0002] Currently, the widely used circuit breaker non-full-phase protection is generally composed of three-phase inconsistent position triggering and zero-sequence and negative-sequence current judgment criteria. This criterion for circuit breaker non-full-phase protection has been widely used in conventional phase-splitting circuit breaker protection. Generator-side circuit breakers are generally three-phase interlocking and do not provide three-phase inconsistent contacts. The phase-splitting circuit breaker non-full-phase protection scheme cannot be directly applied to the non-full-phase operation of the generator-side circuit breaker. When the generator-side circuit breaker non-full-phase protection only uses the current judgment criterion, the current setting must be set low to ensure sensitivity. Long-term operation may cause protection misoperation and reduce protection reliability. If the current setting is increased, the sensitivity is reduced, and the value of configuring this protection is lost. There have been multiple field incidents where the pull rod of a single phase of the generator-side circuit breaker has broken, resulting in non-full-phase. This has caused the unit to be subjected to negative-sequence current for a long time, posing a threat to the safety of the generator. In the existing current judgment protection scheme, when the circuit breaker is operating under light load conditions and the current is not full-phase, it is very small and difficult to exceed the negative sequence current setting value, and it is impossible to effectively judge that the machine-side circuit breaker is not full-phase.

[0003] In addition, some non-full-phase protection uses the voltage on both sides of the unit circuit breaker, and through the voltage signal excess principle such as fundamental amplitude comparison or voltage phase comparison, it is necessary to adjust multiple fixed values ​​based on experience in actual use. The protection sensitivity is seriously dependent on the setting of different empirical fixed values. When the fixed value setting is more sensitive, there is a risk of false operation. The protection usually requires that the voltage of each phase on both sides is greater than 80% to 90% of the rated voltage, and there are many restrictions on the use of protection. Summary of the Invention

[0004] The object of the present invention is to provide a method and device for non-full-phase protection of a machine-end circuit breaker, so as to solve the problem of inaccurate action judgment of the non-full-phase protection of the machine-end circuit breaker.

[0005] To achieve the above object, the solution of the present invention includes:

[0006] The present invention provides a non-full-phase protection method for a machine-end circuit breaker. When a generator set is in a grid-connected operating state, there is voltage on both sides of the machine-end circuit breaker, one-phase or two-phase voltages on both sides of the machine-end circuit breaker meet an adaptive difference judgment condition, and there is no differential current to start the lockout, then the non-full-phase protection is actuated through a first delay; the adaptive difference judgment condition is: the number of difference points per cycle of the same-phase voltage on both sides of the machine-end circuit breaker is greater than a set number of points, and within the first delay range, the ratio of the total time satisfying the condition |U2α-U3α|>Uset to the first delay is greater than a fourth preset threshold; wherein U2α and U3α are the effective amplitudes of the corresponding same-path voltages on both sides of the machine-end circuit breaker, Uset is a fixed parameter, the high-voltage side of the main transformer is used to connect to the power grid, and the low-voltage side of the main transformer is connected to the generator set through the machine-end circuit breaker.

[0007] Beneficial effect: When the generator set is connected to the grid, if the voltage of one phase or two phases on both sides of the machine-side circuit breaker meets the preset conditions of the adaptive difference and the error flow starts the lockout, the non-full-phase protection of the machine-side circuit breaker will be delayed.

[0008] Furthermore, the high-voltage side of the main transformer is connected to the power grid through the main transformer high-voltage side circuit breaker. When the machine-side circuit breaker trips and there is voltage on both sides of the machine-side circuit breaker, the machine-side circuit breaker non-full-phase protection is performed if any of the following conditions are met:

[0009] Case 1: If the circuit breaker on the high-voltage side of the main transformer trips, and the zero-sequence voltage generated on the main transformer side of the generator-side circuit breaker is greater than the first preset threshold or the voltage on the main transformer side is unbalanced, the non-full-phase protection will be activated after the second delay;

[0010] Case 2: If the circuit breaker on the high-voltage side of the main transformer does not trip, and the self-generated zero-sequence voltage on the machine-side voltage of the machine-side circuit breaker is greater than the second preset threshold or the machine-side voltage is unbalanced, the non-full-phase protection will be activated after the third delay.

[0011] Beneficial Effects: When the generator-end circuit breaker trips and there is voltage on both sides of the generator-end circuit breaker, it is determined whether the main transformer high-voltage side circuit breaker has tripped. If the main transformer high-voltage side circuit breaker trips and the self-generated zero-sequence voltage of the main transformer low-voltage side of the generator-end circuit breaker is greater than a first preset threshold or the main transformer side voltage is unbalanced, the non-full-phase protection is activated after the second delay. If there is voltage on both sides of the generator-end circuit breaker, the main transformer high-voltage side circuit breaker has not tripped, and the self-generated zero-sequence voltage of the generator-end side of the generator-end circuit breaker is greater than a second preset threshold or the generator-end voltage is unbalanced, the non-full-phase protection is activated after the third delay. This completes the judgment of protection action when the generator-end circuit breaker trips.

[0012] Furthermore, the first delay time t1 is set according to the delay of avoiding the protection action of abnormal voltage at the machine end.

[0013] Beneficial effect: The first delay time t1 is determined by delaying the protection action to avoid abnormal voltage at the machine end.

[0014] Furthermore, the second delay time t2 is adjusted according to the time it takes for the generator-end voltage to decay below the set voltage or the smaller value of the maximum delay time of the generator-end zero-sequence overvoltage stator grounding protection.

[0015] Beneficial effect: The second delay time t2 is set by obtaining the smaller value of the time when the machine-end voltage decays below the set voltage or the maximum delay time of the machine-end zero-sequence overvoltage stator grounding protection.

[0016] Furthermore, the third delay time t3 is set according to the larger value of the time when the terminal phase voltage decays below the set voltage during shutdown or the maximum delay of the unit zero-sequence overvoltage stator grounding protection.

[0017] Beneficial effect: The third delay time t3 is set by obtaining the time when the phase voltage at the machine end decays below the set voltage or the larger value of the maximum delay of the unit zero-sequence overvoltage stator grounding protection.

[0018] Furthermore, the voltages on both sides of the machine-end circuit breaker must be greater than the secondary rated value by a set multiple, and the set multiple is greater than 0 and less than 1.

[0019] Beneficial effect: It avoids unreliable protection caused by secondary disconnection of the machine-side circuit breaker.

[0020] Furthermore, if the following condition is met: |U2α(i)-U3α(i)|>Uset(i), it is determined that the same-phase voltage points on both sides of the machine-end circuit breaker are abnormal, where α is the same-phase voltage of the machine-end circuit breaker's phase A voltage, phase B voltage, phase C voltage, zero-sequence voltage, or self-generated zero-sequence voltage, and U2α(i) and U3α(i) are the sampling points of the machine-end circuit breaker corresponding to the same voltage at the same moment.

[0021] Beneficial effect: The acquisition of abnormal points is completed, ensuring the implementation of adaptive difference judgment.

[0022] Furthermore, when the generator set is in a grid-connected state, the machine-end circuit breaker is in a closed state.

[0023] The present invention also provides a non-full-phase protection device for a machine-end circuit breaker, comprising a processor and a memory, wherein the processor is configured to execute computer program instructions stored in the memory to implement any of the above-mentioned non-full-phase protection methods for the circuit breaker.

[0024] Beneficial effect: This device can realize the above-mentioned non-full-phase protection method of the machine-end circuit breaker, improve the safety of the non-full-phase protection action, and effectively improve the overall performance of the unit protection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a wiring diagram of the secondary analog input of the unit protection device of the present invention;

[0026] Figure 2 This is a schematic diagram of the voltage transformer wiring on both sides of the machine-side circuit breaker (GCB) of the present invention;

[0027] Figure 3 This is a flow chart of the present invention for determining if the machine-side grid is not fully connected;

[0028] Figure 4 This is a flow chart of the non-full-phase discrimination of the machine-end tripping of the present invention;

[0029] Figure 5 It is a logic diagram of the non-full-phase protection of the machine end of the present invention. DETAILED DESCRIPTION

[0030] The overall concept of the present invention is to use the principle of dynamic integrated differential protection of unit protection current and voltage to perform non-full-phase protection, making full use of the unit protection differential protection current ( Figure 1 The two sets of differential protection of CT1 and CT3, CT3 and CT4) and the three-phase voltage on both sides of the machine-end circuit breaker ( Figure 1 、 Figure 2 The system calculates the differential current of the group differential protection and the adaptive difference between the corresponding phase voltages on both sides of the circuit breaker (point A PT2 and point B PT3). When the main transformer differential current or the unit differential current is activated and the differential current reaches the preset threshold, the differential current is used to determine whether the partial-phase protection is blocked, and the partial-phase protection is reliably inoperative. If neither differential current is activated, and the adaptive difference between the voltages on both sides is determined to meet the conditions, the protection will operate after a delay. The system can also adaptively determine the circuit breaker partial-phase protection method based on different operating conditions such as grid-connected operation and unit tripping, and coordinate with other protections to ensure the effective integration of sensitivity and selectivity of the partial-phase protection.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0032] Method Example:

[0033] An embodiment of a method for non-full-phase protection of a machine-side circuit breaker according to the present invention comprises the following steps:

[0034] 1. When the generator-end circuit breaker is operating in non-full-phase mode, there is no short-circuit fault point at points A and B on either side of the circuit breaker, and there is no differential current on either side, so the differential protection will not activate. Differential protection will not activate due to non-full-phase operation of the generator-end circuit breaker; that is, when the differential current activates, the non-full-phase protection does not need to operate. Furthermore, theoretical analysis shows that when the unit is operating normally and connected to the grid, or when other equipment on either side of the generator-end circuit breaker experiences a short-circuit fault, points A and B on either side of the circuit breaker are equivalent to the same point. The theoretical values ​​of the in-phase voltages of PT2 and PT3 on both sides of the generator-end circuit breaker are consistent, with the only difference being the two sets of voltage transformers. To prevent large voltage errors caused by inconsistent transient characteristics of the voltage transformers on both sides of the circuit breaker during a fault, differential protection differential current is used to activate and lock the generator-end circuit breaker's non-full-phase protection during a short-circuit fault. This ensures reliable protection and prevents false or ineffective operation of the non-full-phase protection.

[0035] 2. When the machine-side circuit breaker is not in full-phase operation, there will be a difference in the corresponding voltages on both sides of the circuit breaker port, and the difference in the disconnected phase voltages is not a steady-state difference. The actual grid-connected operation of the unit is in a comprehensive dynamic balance condition of load changes, excitation regulation, active and reactive power fluctuations, etc. Each control adjustment factor will simultaneously affect the actual amplitude and angle of the disconnected phase voltages on both sides of the circuit breaker, causing deviations. The voltage difference between the disconnected phases on both sides is a fluctuating and unstable feature. When the machine-side circuit breaker is not in full-phase, the difference in voltages on both sides cannot be calculated using simple steady-state criteria such as amplitude and angle differences. By adopting the adaptive difference criterion, a comprehensive judgment is made: theoretically, the difference between two voltages of the same phase exceeds the deviation characteristics of normal operation, indicating that there is a fault in the connection of the two circuits of the same phase and voltage. The protection device adopts a dynamic adaptive algorithm to determine the difference between the two groups of voltages through the adaptive difference judgment method, without the need to set other fixed values ​​externally. Such as Figure 3 As shown in the figure, when one or two phase voltages meet the adaptive difference judgment conditions and there is no differential current to start the lockout, the protection will be activated after a delay of t1. The protection delay is set according to the protection action delay to avoid abnormal voltage at the machine end (overvoltage, low voltage, etc.).

[0036] Among them, the adaptive difference judgment condition is:

[0037] 1) Collect the voltages corresponding to PT2 and PT3 on both sides of the circuit breaker. Synchronous sampling points U2α(i) and U3α(i) are compared using the equation: |U2α(i)-U3α(i)|>Uset(i), where α represents the corresponding voltage on the same phase, such as UA, UB, UC, or 3U0 (zero-sequence voltage or self-generated zero-sequence voltage); i represents the sampling point at the same moment, and U2α(i) and U3α(i) represent the simultaneous sampling points of PT2 and PT3 on the same phase. The number of points N per cycle difference between the same-phase voltages on both sides is recorded. When N is greater than the set number of points N0, which is the third preset threshold, the voltage data difference determination is initiated. This number of points is related to the sampling frequency and is set by the protection design manufacturer.

[0038] 2) When N>N0, within the protection delay range, the corresponding voltage effective value amplitude is used for judgment: |U2α-U3α|>Uset, where Uset is the fourth preset threshold; the total time T that meets the conditions is recorded, and T is compared with the delay time set for the protection. When the duty cycle is greater than the coefficient β, the protection is activated after the delay time. If the duty cycle is not met, it is considered to be an instantaneous fluctuation.

[0039] 3) The relevant parameter settings such as Uset(i), N0, Uset, β, etc. can be dynamic parameters or fixed parameters, which are set by the protection design manufacturer and do not require external settings.

[0040] 4) During normal operation, set the three-phase voltage effective value threshold U>30%Ue (Ue is the secondary rated value) to avoid unreliable protection when the PT secondary line is broken.

[0041] 3. To avoid abnormal voltage on both sides of the machine-side circuit breaker due to electrical testing and other reasons before the unit is connected to the grid and put into operation, the closing of the machine-side circuit breaker can be used as the judgment condition for protection grid connection. The judgment logic is as follows: Figure 5 shown.

[0042] 4. When the machine-side circuit breaker and the main transformer high-voltage side circuit breaker trip at the same time, the machine-side circuit breaker is not in full-phase operation, and the voltages on both sides of the phase that the circuit breaker is not disconnected are the same. At this time, the machine-side voltage decays slower than the main transformer low-voltage side voltage. The judgment process is as follows: Figure 4 As shown, the self-generated zero-sequence overvoltage of the voltage transformer on the low-voltage side of the main transformer is used, and a higher set value (which can be set to 15V) or a three-phase voltage unbalance criterion is set. After delayed action, the protection delay t2 is set according to the time when the machine-end voltage decays below 20V or the maximum delay time of the machine-end zero-sequence overvoltage stator grounding protection, whichever is smaller.

[0043] 5. When the main transformer does not trip and the generator-side circuit breaker trips, the generator-side circuit breaker is not operating in full-phase mode. The voltage on the low-voltage side of the main transformer is normal, and the voltages on both sides of the phases not tripped by the circuit breaker are consistent. The generator-side voltage transformer generates a zero-sequence overvoltage (settable to 20V) or three-phase voltage imbalance, and the protection is delayed. The protection delay t3 is set to the larger of the time it takes for the generator-side phase voltage to decay below 20V when the generator is shut down, or the maximum delay for the zero-sequence overvoltage stator ground fault protection.

[0044] 6. For non-full-phase protection of the machine-side circuit breaker, the external access circuits such as the tripping and closing status of the machine-side circuit breaker, the tripping and closing status of the circuit breaker on the high-voltage side of the main transformer, and the voltage and current on each side can be used to comprehensively determine whether the main transformer trips when the machine-side circuit breaker trips during non-full-phase operation, and automatically switch the protection judgment scheme.

[0045] This method comprehensively analyzes the characteristics of electrical quantity changes when the generator's machine-side circuit breaker is operating in a non-full-phase condition, eliminates the drawbacks of steady-state solutions such as voltage amplitude difference and angle difference, cancels the constraints that the three-phase voltage must be greater than 80% to 90% of the rated voltage, expands the application scope of non-full-phase protection, and explains in principle the effective technical methods for ensuring the reliability of non-full-phase protection. The present invention uses the external circuit originally connected to the unit protection device to identify the working conditions through dynamic information such as voltage, current, and the input and output of each circuit breaker, thereby realizing adaptive protection of non-full-phase when the machine-side circuit breaker is connected to the grid and non-full-phase when the machine-side circuit breaker trips. The present invention adds an intelligent design of the non-full-phase protection function module to the unit protection device without adding new access resources and affecting the performance of the original protection device, thereby increasing the intelligent function of the unit protection device and effectively improving the intelligent operation and maintenance management capabilities of the on-site machine-side circuit breaker equipment. The present invention proposes a method for setting fixed values ​​and coordinating protections for non-full-phase protection, thereby avoiding other problems caused by setting fixed values ​​due to differences in experience among different personnel, improving the standardization and ease of use of the non-full-phase protection design, having promotion value, and being a feasible method for ensuring the safe and stable operation of equipment.

[0046] Device Example:

[0047] The present invention provides a non-full-phase protection device for a machine-side circuit breaker, comprising a memory, a processor, and an internal bus. The processor and memory communicate and exchange data with each other via the internal bus. The processor may be a processing device such as a microprocessor (MCU) or a programmable logic device (FPGA); and the memory may be any type of memory that stores information using electrical energy, such as RAM or ROM. The processor is configured to execute program instructions stored in the memory to implement the non-full-phase protection method for a machine-side circuit breaker described in the method embodiments of the present invention. This method has been described in detail in the method embodiments and will not be repeated here.

Claims

1. A non-full-phase protection method for a machine-side circuit breaker, characterized in that: When the generator set is in grid-connected operation, there is voltage on both sides of the generator-end circuit breaker, one or two phase voltages on both sides of the generator-end circuit breaker meet the adaptive difference judgment conditions, and there is no differential current start lock of the main transformer differential and the generator differential, then the non-full-phase protection will be activated after the first delay; The adaptive difference judgment condition is: the number of points of difference per cycle of the same-phase voltage on both sides of the machine-end circuit breaker is greater than the set number of points, and within the first delay range, the ratio of the total time satisfying the condition |U2α-U3α|>Uset to the first delay is greater than the coefficient, and the first delay is the delay time set by the protection; Among them, U2α and U3α are the effective amplitudes of the corresponding same-line voltages on both sides of the machine-end circuit breaker, Uset is the fourth preset threshold and a fixed parameter; if |U2α(i)-U3α(i)|>Uset(i), it is determined that the same-phase voltage points on both sides of the machine-end circuit breaker are abnormal, α is the same-phase voltage of the machine-end circuit breaker's phase A voltage, phase B voltage, phase C voltage, zero-sequence voltage or self-produced zero-sequence voltage, U2α(i) and U3α(i) are the simultaneous sampling points of the machine-end circuit breaker's corresponding same-line voltages; the high-voltage side of the main transformer is used to connect to the power grid, and the low-voltage side of the main transformer is connected to the generator set through the machine-end circuit breaker.

2. The non-full-phase protection method for the machine-side circuit breaker according to claim 1, characterized in that: The high-voltage side of the main transformer is connected to the grid through the high-voltage side circuit breaker of the main transformer. When the generator-side circuit breaker trips and there is voltage on both sides of the generator-side circuit breaker, the generator-side circuit breaker is not fully protected if any of the following conditions are met: Case 1: If the circuit breaker on the high-voltage side of the main transformer trips, and the zero-sequence voltage generated on the main transformer side of the generator-side circuit breaker is greater than the first preset threshold or the voltage on the main transformer side is unbalanced, the non-full-phase protection will be activated after the second delay; Case 2: If the circuit breaker on the high-voltage side of the main transformer does not trip, and the self-generated zero-sequence voltage on the machine-side voltage of the machine-side circuit breaker is greater than the second preset threshold or the machine-side voltage is unbalanced, the non-full-phase protection will be activated after the third delay.

3. The non-full-phase protection method for machine-side circuit breaker according to claim 1, characterized in that: The first delay time t1 is set according to the delay of avoiding the protection action of abnormal voltage at the machine end.

4. The non-full-phase protection method for a machine-end circuit breaker according to claim 2, characterized in that: The second delay time t2 is set according to the smaller value between the time when the machine-end voltage decays below the set voltage and the maximum delay time of the machine-end zero-sequence overvoltage stator grounding protection.

5. The non-full-phase protection method for a machine-end circuit breaker according to claim 2, characterized in that: The third delay time t3 is set according to the larger value between the time when the terminal phase voltage decays below the set voltage during shutdown and the maximum delay of the unit's zero-sequence overvoltage stator grounding protection.

6. The non-full-phase protection method for machine-side circuit breaker according to claim 1, characterized in that: The voltages on both sides of the machine-side circuit breaker must be greater than the secondary rated value by a set multiple, and the set multiple must be greater than 0 and less than 1.

7. The non-full-phase protection method for a machine-end circuit breaker according to claim 1, characterized in that: When the generator set is in a grid-connected state, the machine-end circuit breaker is in a closed state.

8. A non-full-phase protection device for a machine-end circuit breaker, characterized in that: The method comprises a processor and a memory, wherein the processor is used to execute computer program instructions stored in the memory to implement the non-full-phase protection method for a machine-end circuit breaker according to any one of claims 1 to 7.

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