Active small-resistance grounding system cable grounding fault prediction method

Abstract

The invention relates to an active small resistance grounding system cable grounding fault prediction method, which comprises the following steps of: 1, arranging a grounding fault transition resistor on a neutral point grounding resistor of a grounding transformer in parallel, and connecting a voltmeter and an ampere meter to the grounding fault transition resistor; 2, after the auxiliary power supply device is pressurized, detecting a zero-sequence voltage signal and a zero-sequence current signal of a fan cable line, and meanwhile, calculating that the resistance value of a grounding fault transition resistor is reduced when the grounding fault transition resistor has a grounding insulation fault by adopting an admittance method, and reflecting the single-phase grounding state of the cable through a resistance criterion; 3, performing prediction logic judgment as follows: when the system monitors that the resistance value of the grounding fault transition resistor is smaller than a prediction high constant value, sending out a prediction early warning signal after time delay; and when the system monitors that the resistance value of the grounding fault transition resistor is smaller than the predicted low constant value, a tripping signal is sent out after time delay. According to the invention, the identification level of protection on high-resistance faults can be greatly improved, and active prediction and early warning during normal operation of the cable are realized.

Description

Technical Field

[0001] The invention relates to a method for predicting cable grounding faults in an active low-resistance grounding system. Background Art

[0002] Cable grounding fault is a common fault in new energy plants and stations, and the potential harm is relatively large. As the capacity of new energy is increasing, the number of tripping caused by grounding faults due to cable joint failures is increasing. The wind, solar and storage new energy collection lines are generally 10~35kV voltage levels. The system uses a neutral point grounding method with a small resistance. Once a single-phase grounding fault occurs, it will immediately trip, which has a great impact on the operating efficiency of wind farms or photovoltaic stations. Summary of the invention

[0003] The technical problem to be solved by the present invention is: in view of the technical problems existing in the prior art, a method for predicting cable grounding faults in an active low-resistance grounding system is provided.

[0004] The objectives of the present invention are achieved through the following technical solutions.

[0005] The cable grounding fault prediction method of the active low-resistance grounding system includes the following steps: Step 1: The switch cabinet of the wind, solar and energy storage booster station is connected to the fan cable line, which includes a three-phase line and a neutral line. A grounding transformer neutral point grounding resistor is arranged in series on the center line, and auxiliary power supply devices are added at both ends of the neutral point grounding resistor of the grounding transformer. The auxiliary power supply device outputs a 20HZ low-frequency voltage; a grounding transformer is arranged on the three-phase line, and the grounding transformer is connected to the neutral point grounding resistor of the grounding transformer; A ground fault transition resistor is arranged in parallel with the neutral point grounding resistor of the grounding transformer, and a voltmeter and an ammeter are connected to the ground fault transition resistor; Step 2: After the auxiliary power supply device is pressurized, the zero-sequence voltage and zero-sequence current signals of the fan cable line are detected. At the same time, the ground fault transition resistance is calculated by the admittance method. When a ground insulation fault occurs, the resistance value of the ground fault transition resistance decreases, and the single-phase grounding state of the cable is reflected by the resistance criterion; Step 3: The prediction logic is as follows: (1) When the system detects the existence of zero-sequence current and zero-sequence voltage in the fan cable line, when the zero-sequence voltage is less than the voltage setting value, and the zero-sequence current is less than 0.5 of the current setting value, a loop alarm signal is issued after a delay; (2) The ground fault transition resistance has two ground resistance settings: 0.5 times R E The value is set to the predicted high value, 0.25 times R E The value setting predicts a low set value; When the system detects that the resistance value of the ground fault transition resistor is less than the predicted high set value, a prediction warning signal is issued after a delay; When the system detects that the resistance value of the ground fault transition resistor is less than the predicted low set value, a trip signal is issued after a delay.

[0006] The auxiliary power supply device comprises a bandpass filter, and the bandpass filter only passes 20 Hz low-frequency voltage signals.

[0007] The auxiliary power supply device and the ground fault transition resistor are both arranged in the switch cabinet of the wind, solar and energy storage new energy booster station.

[0008] In step 3, the delay for sending out the alarm signal or trip signal is 0.1s.

[0009] It also includes step 4: According to the project operation and maintenance management regulations, the auxiliary power supply device actively injects 20HZ low-frequency voltage into the wind turbine cable line on a monthly or quarterly basis to reduce interference with the power grid system.

[0010] The beneficial effects of the present invention are as follows: the present invention proposes an advanced active low-resistance grounding system cable grounding fault detection method, which actively predicts cable grounding insulation faults. The active injection cable grounding prediction method is applied to the low-resistance grounding system, which can greatly improve the protection's recognition level of high-resistance faults, solve the difficulty that the traditional low-resistance grounding protection cannot predict the grounding fault in advance, and realize active prediction and early warning during the normal operation of the cable. Compared with the shortcoming of the existing low-resistance system zero-sequence protection action that trips immediately, it can achieve active cable insulation monitoring and early fault isolation, protect the normal operation of new energy wind turbines and photovoltaic lines, and improve system reliability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is the principle diagram of the present invention; Figure 2 This is the logic diagram of the cable grounding prediction method for the active injection low-resistance grounding system. DETAILED DESCRIPTION

[0012] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0013] like Figure 1 As shown, a method for predicting cable grounding faults in an active low-resistance grounding system comprises the following steps: Step 1: The wind, solar and energy storage booster station switch cabinet is connected to the fan cable line, which includes a three-phase line and a neutral line. A grounding transformer neutral point grounding resistor Rn is arranged in series on the center line, and auxiliary power supply devices 1 are added at both ends of the neutral point grounding resistor Rn of the grounding transformer. The auxiliary power supply device 1 outputs a 20HZ low-frequency voltage; a grounding transformer JDB is arranged on the three-phase line, and the grounding transformer JDB is connected to the neutral point grounding resistor Rn of the grounding transformer; A ground fault transition resistor R is connected in parallel to the neutral point grounding resistor Rn of the grounding transformer. E , the ground fault transition resistance R E Connect a voltmeter and an ammeter.

[0014] Step 2: After the auxiliary power supply device 1 is pressurized, detect the zero-sequence voltage U of the fan cable line G0 and zero sequence current I G0 signal, and at the same time, the ground fault transition resistance R is calculated by the admittance method. E When a ground insulation fault occurs, the ground fault transition resistance R E The resistance value is reduced, and the single-phase grounding state of the cable is reflected through the resistance criterion; Step 3: The prediction logic is as follows: (1) When the system detects that there is a zero-sequence current I in the fan cable line G0 and zero sequence voltage U G0 , when the zero sequence voltage U G0 Less than the voltage setting value, and the zero-sequence current I G0 If the current is less than 0.5 of the set value, a circuit alarm signal will be issued after a delay; (2) Ground fault transition resistance R E There are two grounding resistance settings: 0.5 times R E The value is set to the predicted high value, 0.25 times R E The value setting predicts a low set value; When the system detects the ground fault transition resistance R E When the resistance value is less than the predicted high set value, a prediction warning signal is issued after a delay; When the system detects the ground fault transition resistance R E When the resistance value is less than the predicted lower set value, a trip signal is issued after a delay.

[0015] Furthermore, the auxiliary power supply device includes a bandpass filter 2, which only passes 20 Hz low-frequency voltage signals to prevent 50 Hz voltage from flowing back into the power supply.

[0016] Furthermore, the auxiliary power supply device and the ground fault transition resistor RE They are all installed in the switch cabinet of the wind, solar and energy storage new energy booster station.

[0017] Furthermore, in step 3, the delay for sending the alarm signal or the trip signal may be 0.1 s.

[0018] Furthermore, it also includes step 4: according to the engineering operation and maintenance management regulations, on a monthly or quarterly basis, the auxiliary power supply device 1 actively injects 20HZ low-frequency voltage into the wind turbine cable line to reduce interference to the power grid system.

[0019] Furthermore, the auxiliary power supply circuit considers fault alarm. When it is lower than the set value, it is considered that the grounding warning protection plus power supply circuit is faulty, the protection outlet is locked and an alarm signal is issued.

[0020] The principle of the present invention is: The present invention actively injects 20HZ low-frequency voltage at the neutral point of the grounding transformer at the wind, solar and energy storage booster station switch cabinet to monitor the zero-sequence current and voltage of the wind turbine cable line in real time. When a high-resistance grounding fault with insulation degradation occurs in a phase of the wind turbine cable line, the device immediately starts early warning prediction.

[0021] (1) Active injection cable grounding prediction This method adds a power supply device in the 35kV booster station switch cabinet. The low-frequency voltage output by the auxiliary power supply device is added to both ends of the neutral point grounding resistor Rn of the grounding transformer, and the low-frequency signal is injected into the zero-sequence loop of the cable to the ground through the grounding transformer. A bandpass filter is set to pass only the 20Hz low-frequency voltage signal to prevent the 50Hz voltage from flowing back into the power supply.

[0022] (2) Under normal circumstances, the injected low-frequency current is mainly capacitive current flowing through the ground capacitance. When the ground insulation is damaged, the injected current appears as resistive current.

[0023] (3) Prediction technology detects the injected low-frequency voltage and current, and detects the zero-sequence voltage U after filtering. G0 and zero sequence current I G0 Signal, the ground fault transition resistance R is calculated using the admittance method E When a grounding insulation fault occurs, the grounding transition resistance value will decrease, and the single-phase grounding state of the cable will be reflected through resistance judgment.

[0024] (4) The grounding resistance criterion reflects the size of the cable grounding resistance. There are two grounding resistance fixed values, 0.5 times R E The value is set to the high set value segment to act on the alarm, 0.25 times R E The value is set to the low setting stage to act on delayed tripping.

[0025] (5) Actively inject low-frequency signals on a monthly or quarterly basis according to the project operation and maintenance management regulations to reduce interference with the power grid system (6) Auxiliary power supply circuit considers fault alarm. When it is lower than the set value, it is considered that the grounding warning protection plus power supply circuit is faulty, the protection exit is locked and an alarm signal is issued.

[0026] The present invention is not affected by the grounding position of the low-resistance grounding system, nor by the operating conditions of the cable, and can work reliably under various operating conditions such as cable operation and deactivation. The present invention can actively monitor the slow aging of cable insulation, and the grounding resistance value and the resistance constant in the resistance criterion adopt a primary value. The active injection of the primary winding voltage is only 1 to 3% of the rated phase voltage, which will not damage the cable winding insulation, and the grounding transition resistance measurement accuracy is good. The manual active shutdown is realized to eliminate the fault. Ensure the safety of the wind, solar and storage new energy plant system.

[0027] The above description is only a preferred embodiment of the present invention and is not a limitation of the technical solution of the present invention. It should be pointed out that those skilled in the art can make further improvements and changes based on the technical solution of the present invention, and these improvements and changes should be covered within the protection scope of the present invention.

Claims

1. A cable grounding fault prediction method for an active low-resistance grounding system, characterized by: The steps include: Step 1: The switch cabinet of the wind, solar and energy storage new energy booster station is connected to a wind turbine cable line, the wind turbine cable line includes a three-phase line and a neutral line, a grounding transformer neutral point grounding resistor (Rn) is arranged in series on the center line, and auxiliary power supply devices (1) are added to both ends of the neutral point grounding resistor (Rn) of the grounding transformer, and the auxiliary power supply device (1) outputs a 20HZ low-frequency voltage; a grounding transformer (JDB) is arranged on the three-phase line, and the grounding transformer (JDB) is connected to the neutral point grounding resistor (Rn) of the grounding transformer; A ground fault transition resistor (R E ), the ground fault transition resistance (R E ) is connected with a voltmeter and an ammeter; Step 2: After the auxiliary power supply device (1) is pressurized, detect the zero-sequence voltage (U G0 ) and zero sequence current (I G0 ) signal, and at the same time, the ground fault transition resistance (R E ) When a ground insulation fault occurs, the ground fault transition resistance (R E ) decreases, and the single-phase grounding state of the cable is reflected through the resistance criterion; Step 3: The prediction logic is as follows: (1) When the system detects that there is zero-sequence current (I G0 ) and zero sequence voltage (U G0 ), when the zero sequence voltage (U G0 ) is less than the voltage setting value, and the zero-sequence current (I G0 ) is less than 0.5 current setting value, a circuit alarm signal is issued after a delay; (2) Ground fault transition resistance (R E )There are two grounding resistance settings: 0.5 times R E The value is set to the predicted high value, 0.25 times R E The value setting predicts a low set value; When the system detects the ground fault transition resistance (R E ) is less than the predicted high set value, a prediction warning signal is issued after a delay; When the system detects the ground fault transition resistance (R E ) is less than the predicted lower set value, a trip signal is issued after a delay.

2. The cable grounding fault prediction method for an active low-resistance grounding system according to claim 1 is characterized by: The auxiliary power supply device comprises a bandpass filter (2), and the bandpass filter (2) only passes 20 Hz low-frequency voltage signals.

3. The cable grounding fault prediction method for an active low-resistance grounding system according to claim 1 is characterized by: The auxiliary power supply device and the ground fault transition resistor (R E ) are all installed in the switch cabinet of the wind, solar and energy storage new energy booster station.

4. The cable grounding fault prediction method for an active low-resistance grounding system according to claim 1 is characterized in that: In step 3, the delay for sending out the alarm signal or trip signal is 0.1s.

5. The cable grounding fault prediction method for active low-resistance grounding system according to claim 1 is characterized by: The method further includes step 4: according to the engineering operation and maintenance management regulations, the auxiliary power supply device (1) actively injects 20 Hz low-frequency voltage into the wind turbine cable line on a monthly or quarterly basis to reduce interference with the power grid system.

Images