Capacitance current compensation method for arc suppression coil and arc suppression coil control cabinet

Abstract

The application belongs to the field of nuclear power plant auxiliary power system neutral point grounding mode design, and particularly relates to a capacitor current compensation method of arc suppression coil and an arc suppression coil control cabinet. L The method comprises the following steps: step S1, collecting and judging the on-off state of the feeder switch on each line of the auxiliary power distribution network, so as to judge whether the line is in a closed state; step S2, judging whether a single-phase grounding fault occurs on the line; and step S3, the arc suppression coil control unit automatically puts in the corresponding coil turns by calculation and control, so as to provide an over-compensation current I L of not more than 10% for the auxiliary power distribution network to offset the capacitor current in the line where the single-phase grounding fault occurs. The application can quickly compensate the capacitor current when the grounding fault occurs in any state of the nuclear power plant, and truly realizes zero response.

Description

Technical Field

[0001] This invention belongs to the field of neutral point grounding design in nuclear power plant auxiliary power systems, specifically relating to a method for compensating the capacitive current of an arc suppression coil and an arc suppression coil control cabinet. Background Technology

[0002] According to the "Code for Design of Overvoltage Protection and Insulation Coordination of AC Electrical Installations" (GB / T50064-2014), for 10kV systems where a single-phase ground fault exceeds 10A and operation under ground fault conditions is required, a neutral point resonant grounding method should be adopted. Taking a nuclear power plant as an example, when the unit is operating at full power, the station service capacitor current reaches 23.34A, and when the auxiliary transformer is under load, the maximum capacitor current reaches 36.41A. Considering all factors, it was decided to configure arc suppression coils at the neutral point of the low-voltage side of the high-voltage station service transformer and the auxiliary transformer of each unit.

[0003] The conventional method for calculating the capacitor current in a system utilizes the change in electrical quantity caused by impedance variation: when the system is unbalanced, a zero-sequence current will flow through the zero-sequence loop (see...). Figure 1 By adjusting the angle of the arc suppression coil (changing X...) L This causes a change in zero-sequence impedance, which in turn changes the current flowing through the arc suppression coil and the voltage across the arc suppression coil. At this time, the system capacitance can be calculated by establishing the following state equations based on the monitored changes in electrical quantities, and thus the capacitor current can be obtained, as shown in formulas (1) and (2).

[0004] Formula (1)

[0005] Formula (2)

[0006] U0 refers to the system unbalanced voltage, with the unit being V;

[0007] X L This refers to the reactance of the arc suppression coil, measured in Ω.

[0008] X C This refers to the capacitive reactance of the capacitor being measured, measured in Ω.

[0009] I0 refers to the zero-sequence current, measured in amperes (A).

[0010] I C This refers to the single-phase grounding capacitive current, measured in amperes (A).

[0011] U e This refers to the rated line voltage of the plant's power system, measured in volts (V).

[0012] The capacity of the arc suppression coil is determined mainly based on the magnitude of the capacitive current during a single-phase ground fault in the system, with a certain margin.

[0013] Formula (3)

[0014] Q L This refers to the compensation capacity, measured in kVA.

[0015] K refers to the compensation coefficient, which can be set to 1.1.

[0016] However, because the three-phase system of a nuclear power plant is too balanced in its actual normal operation, effective electrical quantities cannot be measured on-site. Summary of the Invention

[0017] The purpose of this invention is to provide a method for canceling capacitive current in the circuits of a nuclear power plant's auxiliary power system when real-time measurement is not possible.

[0018] To achieve the above objectives, the technical solution adopted in this invention is a capacitor current compensation method for an arc suppression coil, used to provide over-compensation current I to the plant power distribution network when a single-phase ground fault occurs in a nuclear power plant. L It includes the following steps:

[0019] Step S1: Collect and determine the open / closed status of feeder switches on each line in the plant power distribution network, thereby determining whether the line is in a closed state.

[0020] Step S2: Determine whether a single-phase ground fault has occurred on the line;

[0021] In step S3, the arc suppression coil control unit will calculate and control the arc suppression coil to automatically engage the corresponding number of coil turns, providing the plant's power distribution network with a single-phase ground fault current I not exceeding that before compensation. C 10% of the overcompensated current I L It is used to offset the capacitive current in the line where the single-phase ground fault occurs.

[0022] Furthermore, in step S1, an auxiliary contact is set at the loop switch of the line where the feeder switch is located. The on / off signal of the auxiliary contact is used to determine whether the loop switch is on or off, thereby determining whether the line is in a closed state.

[0023] Furthermore, in step S2, the line selection device of the plant power arc suppression coil determines whether the single-phase ground fault has occurred in the line and provides a corresponding ground fault signal.

[0024] further,

[0025] Prior to step S1, the capacitive current I in each of the lines in the closed state is obtained in advance. CnThe magnitude; determining the overcompensation current I provided by the arc suppression coil after a single-phase ground fault occurs on each of the aforementioned lines. L Size;

[0026] The capacitive current I of each of the aforementioned lines Cn The size is obtained either through pre-calculation or through actual measurement during the commissioning phase of the nuclear power plant;

[0027] The overcompensation current I was calculated in advance. L Specifically, it is based on the sum of the capacitive currents I of all the lines where the feeder switches are in the closed state under the current operating condition. Cn∑ and the capacitor current I of the fault circuit Cn Determine the single-phase ground fault current I before compensation C This allows for the determination of the overcompensation current I required by the arc suppression coil in the fault circuit. L The magnitude of the compensated single-phase ground fault current I C2 The magnitude is not greater than the single-phase ground fault current I before compensation. C 10%; the fault circuit refers to the line where the single-phase ground fault occurs;

[0028]

[0029]

[0030] in the formula

[0031] I C This refers to the single-phase ground fault current before compensation;

[0032] I C2 This refers to the compensated single-phase ground fault current, I. C2 = I L - I C ;

[0033] I Cn∑ This refers to the sum of the capacitive currents of the lines when all the feeder switches are in the closed state during the current operating condition;

[0034] I Cn This refers to the capacitive current of the faulty circuit;

[0035] I L This refers to the overcompensated current.

[0036] To achieve the above objectives, the present invention also discloses an arc suppression coil control cabinet for a capacitor current compensation method for an arc suppression coil as described above, wherein the auxiliary contact is connected to the arc suppression coil control cabinet to transmit the on / off signal; the arc suppression coil control cabinet is equipped with a microcomputer system, which is used to determine whether the circuit is in a closed state based on the on / off signal.

[0037] Furthermore, the microcomputer system is also used to receive the ground fault signal generated in step S2.

[0038] Furthermore, the microcomputer system is also used to determine which line is in a closed state and which has experienced a single-phase ground fault based on the on / off signal and the ground fault signal, and to determine the overcompensation current I calculated in advance. L The arc suppression coil control cabinet is controlled to input the corresponding number of arc suppression coil turns.

[0039] Furthermore, the auxiliary contacts are connected to the arc suppression coil control cabinet via hardwire or bus to transmit the on / off signal.

[0040] The beneficial effects of this invention are as follows:

[0041] 1. This invention changes the method of "online measurement of single-phase ground fault capacitive current" to "online calculation of single-phase ground fault capacitive current", and calculates the capacitive current of the nuclear power plant's auxiliary power system (medium-voltage auxiliary power system) by judging the closing status of the circuit switch.

[0042] 2. The microcomputer system of the arc suppression coil control cabinet can quickly compensate for the capacitive current when a ground fault occurs in any state of the nuclear power plant through on / off signals, ground fault signals, and calculated and preset capacitive currents of each line, thus truly achieving zero response. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the zero-sequence loop (i.e., the zero-sequence equivalent circuit) described in the background section;

[0044] Figure 2 This is a schematic diagram of the connection between the auxiliary contact and the arc suppression coil control cabinet as described in a specific embodiment of the present invention (schematic diagram of an emergency busbar section of a nuclear power plant). Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0046] This invention provides a method for compensating the capacitive current of an arc suppression coil, used to provide an overcompensation current I to the plant's power distribution network when a single-phase ground fault occurs in a nuclear power plant. L It includes the following steps:

[0047] Step S1: Collect and determine the open / closed status of feeder switches on each line in the plant power distribution network to determine whether the line is in a closed state.

[0048] Step S2: Determine whether a single-phase ground fault has occurred on the line;

[0049] In step S3, the arc suppression coil control unit will calculate and control the arc suppression coil to automatically engage the corresponding number of coil turns, providing the plant's power distribution network with a single-phase ground fault current I not exceeding that before compensation. C 10% of the overcompensation current I L It is used to offset the capacitive current in a line where a single-phase ground fault occurs.

[0050] In step S1, an auxiliary contact is set at the circuit switch of the line where the feeder switch is located. The on / off signal of the auxiliary contact is used to determine whether the circuit switch is on or off, thereby determining whether the line is in a closed state.

[0051] In step S2, the line selection device of the plant power arc suppression coil determines whether a single-phase ground fault has occurred on the line and gives the corresponding ground fault signal.

[0052] Before step S1, the capacitive current I in each line in the closed state is also obtained in advance. Cn The magnitude of the overcompensation current I provided by the arc suppression coil after a single-phase ground fault occurs on each line; L Size;

[0053] Since online measurement of capacitive current is not possible with arc suppression coils during normal operation of a nuclear power plant, the capacitive current I of each line is... Cn The size is obtained either through pre-calculation or through actual measurement during the commissioning phase of the nuclear power plant;

[0054] The compensation current I has been calculated in advance. L Specifically, it is based on the sum of the capacitive currents I of all lines where all feeder switches are closed under the current operating conditions. Cn∑ and the capacitor current I of the fault circuit Cn Determine the single-phase ground fault current I before compensation C This allows for the determination of the overcompensation current I required by the arc suppression coil in the fault circuit. L The magnitude of the compensated single-phase ground fault current I C2 (i.e., overcompensated current I) L Compared with the single-phase ground fault current I before compensation C The result of the subtraction (see the left side of Formula 5) is not greater than the single-phase ground fault current I before compensation. C 10%; a fault circuit refers to a line where a single-phase ground fault occurs;

[0055] Formula (4)

[0056] Formula (5)

[0057] In formula 4 and in formula 5

[0058] I C This refers to the single-phase ground fault current before compensation.

[0059] I C2 It refers to the compensated single-phase ground fault current, I C2= I L - I C ;

[0060] I Cn∑ It refers to the sum of the capacitive current of the lines where all feeder switches are closed under the current operating conditions;

[0061] I Cn This refers to the capacitive current of the faulty circuit;

[0062] I L This refers to overcompensation current.

[0063] The present invention also discloses an arc suppression coil control cabinet for a capacitor current compensation method for an arc suppression coil as described above, wherein auxiliary contacts are connected to the arc suppression coil control cabinet to transmit on / off signals; the arc suppression coil control cabinet is equipped with a microcomputer system, which is used to determine whether the circuit is in a closed state based on the on / off signals.

[0064] The microcomputer system is also used to receive the ground fault signal generated in step S2, that is, to determine whether a single-phase ground fault has occurred in the line and send the ground fault signal of the line with the single-phase ground fault to the microcomputer system of the arc suppression coil control cabinet.

[0065] The microcomputer system is also used to determine which line is in a closed state and has experienced a single-phase ground fault based on the on / off signal and the ground fault signal, and to determine the overcompensation current I calculated in advance. L The arc suppression coil control cabinet is activated to engage the corresponding number of arc suppression coil turns, providing a pre-set overcompensation current I to the plant power distribution network. L .

[0066] The auxiliary contacts are connected to the arc suppression coil control cabinet via hardwire or bus to transmit on / off signals.

[0067] The calculation method to pre-determine the magnitude of the capacitive current in each line under closed-loop conditions is based on the calculation formula for capacitive current in Chapter 3 of the Electrical Primary Section of the "Electrical Design Manual for Power Engineering".

[0068] Formula (6)

[0069] Formula (7)

[0070] Among them: I C ---Single-phase grounding capacitance current (A);

[0071] U e ---Rated line voltage of the plant power system (kV);

[0072] ω --- angular frequency;

[0073] f e ---Rated frequency (Hz);

[0074] C---Capacitance per phase to ground in the plant power system (μF).

[0075] The capacitors in medium and high voltage power supply systems are mainly cable capacitors.

[0076] The capacitance value of each phase of the cable to ground in the calculation is determined based on the cable data provided by the cable manufacturer and the length data in the cable laying software of the construction drawings.

[0077] Multiplying the obtained cable capacitance value by 1.25 gives the approximate capacitance value for the following components (including the capacitance of the plant transformer windings, motors, and power distribution equipment).

[0078] The capacitance current of the plant's power distribution network can also be measured through on-site testing.

[0079] Taking the emergency busbar of a nuclear power plant as an example (see...) Figure 2 The auxiliary contacts at each feeder switch are led out to the arc suppression coil control cabinet of the high-voltage plant transformer and auxiliary transformer.

[0080] The microcomputer system of the arc suppression coil control cabinet determines whether the line is in operation (i.e., in a closed state) through on / off signals (i.e., load connection signals), and then calculates the pre-calculated capacitive current of each line. When a single-phase ground fault occurs in the plant power system, the microcomputer system of the arc suppression coil control cabinet will automatically transfer an overcompensation current of no more than 10% of the corresponding capacitive current to the faulty line through calculation, thereby achieving the effect of offsetting the capacitive current.

[0081] The device described in this invention is not limited to the embodiments described in the specific implementation. Other implementation methods derived by those skilled in the art based on the technical solution of this invention also fall within the scope of technical innovation of this invention.

Claims

1. A method for compensating the capacitive current of an arc suppression coil, used to provide an overcompensation current I to the plant's power distribution network when a single-phase ground fault occurs in a nuclear power plant. L It includes the following steps: Step S1: Collect and determine the open / closed status of feeder switches on each line in the plant power distribution network, thereby determining whether the line is in a closed state. Step S2: Determine whether a single-phase ground fault has occurred on the line; In step S3, the arc suppression coil control unit will calculate and control the arc suppression coil to automatically engage the corresponding number of coil turns, providing the plant's power distribution network with a single-phase ground fault current I not exceeding that before compensation. C 10% of the overcompensated current I L This is used to offset the capacitive current in the line where the single-phase ground fault occurs; Prior to step S1, the capacitive current I in each of the lines in the closed state is obtained in advance. Cn Size; Determine the overcompensation current I that the arc suppression coil needs to provide after a single-phase ground fault occurs on each of the aforementioned lines. L Size; The capacitive current I of each of the aforementioned lines Cn The size is obtained either through pre-calculation or through actual measurement during the commissioning phase of the nuclear power plant; The overcompensation current I was calculated in advance. L Specifically, it is based on the sum of the capacitive currents I of all the lines where the feeder switches are in the closed state under the current operating condition. Cn∑ and the capacitor current I of the fault circuit Cn Determine the single-phase ground fault current I before compensation C This allows for the determination of the overcompensation current I required by the arc suppression coil in the fault circuit. L The magnitude of the compensated single-phase ground fault current I C2 The magnitude is not greater than the single-phase ground fault current I before compensation. C 10%; the fault circuit refers to the line where the single-phase ground fault occurs; Official (4) Official (5) In formula 4 and in formula 5 I C This refers to the single-phase ground fault current before compensation; I C2 This refers to the compensated single-phase ground fault current, I. C2 =I L - I C ; I Cn∑ This refers to the sum of the capacitive currents of the lines when all the feeder switches are in the closed state during the current operating condition; I Cn This refers to the capacitive current of the faulty circuit; I L This refers to the overcompensated current.

2. The method for compensating the capacitive current of an arc suppression coil as described in claim 1, characterized in that: in In step S1, an auxiliary contact is set at the circuit switch of the line where the feeder switch is located. The on / off signal of the auxiliary contact is used to determine whether the circuit switch is on or off, thereby determining whether the line is in a closed state.

3. The method for compensating the capacitive current of an arc suppression coil as described in claim 2, characterized in that: in In step S2, the line selection device of the plant power arc suppression coil determines whether the single-phase ground fault has occurred on the line and gives the corresponding ground fault signal.

4. An arc suppression coil control cabinet for use in the capacitor current compensation method of an arc suppression coil as described in claim 3, characterized in that: The auxiliary contact is connected to the arc suppression coil control cabinet to transmit the on / off signal; the arc suppression coil control cabinet is equipped with a microcomputer system, which is used to determine whether the circuit is in a closed state based on the on / off signal.

5. The arc suppression coil control cabinet as described in claim 4, characterized in that: The microcomputer system is also used to receive the ground fault signal generated in step S2.

6. The arc suppression coil control cabinet as described in claim 5, characterized in that: The microcomputer system is also used to determine which line is in a closed state and which has experienced a single-phase ground fault based on the on / off signal and the ground fault signal, and to determine the overcompensation current I calculated in advance. L The arc suppression coil control cabinet is controlled to input the corresponding number of arc suppression coil turns.

7. The arc suppression coil control cabinet as described in claim 6, characterized in that: The auxiliary contacts are connected to the arc suppression coil control cabinet via hardwire or bus to transmit the on / off signal.

Images