Ground fault detection method and device

Abstract

The invention provides a ground fault detection method and device. The device comprises an isolation DC-DC converter, a contactor KM1, diodes D1, D2 and D3, bulbs LP1 and LP2, indicating lamps LED1 and LED2, resistors R1 and R2, a voltage detection unit V and a controller. According to the invention, the power supply of the load can be switched from the DC bus to the isolated power supply without changing the power supply circuit of the transformer substation; meanwhile, load grounding fault detection and identification are automatically completed, manual operation is reduced, and detection efficiency is improved; high-efficiency isolation maintenance without power failure is realized, continuous power supply of important equipment is ensured, and safe and stable operation of a transformer substation is guaranteed.

Description

Technical Field

[0001] The invention relates to power supply and distribution technology, and in particular to a ground fault detection method and device. Background Art

[0002] At present, the treatment of DC ground loss fault in substation usually adopts the manual operation of the pulling method, that is, a branch is selected through the DC insulation monitoring device, and then the load is disconnected to check whether the ground loss signal of the insulation monitoring device disappears. This method has low maintenance efficiency and may also cause power outages in non-fault subsystems, affecting the safe operation of the substation.

[0003] In view of this, the present invention proposes a ground fault detection method and device to achieve fault detection and isolation maintenance of substation equipment without power outage. Summary of the invention

[0004] The purpose of the present invention is to propose a ground fault detection method and device, which can switch the power supply of the load from the DC bus to the isolated power supply without changing the power supply line of the substation; at the same time, automatically complete the detection and identification of the load ground fault, reduce manual operation, and improve the detection efficiency; realize efficient isolation and maintenance without power outage, ensure the continuous power supply of important equipment, and ensure the safe and stable operation of the substation.

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

[0006] A ground fault detection device includes an isolated DC-DC converter, a contactor KM1, diodes D1, D2, D3, bulbs LP1, LP2, indicator lights LED1, LED2, resistors R1, R2, a voltage detection unit V and a controller;

[0007] The positive pole of the input end of the isolated DC-DC converter is connected to the cathode of the diode D1, and the positive input cable of the device is led out from the anode of the diode D1; the negative pole of the input end of the isolated DC-DC converter leads out the negative input cable of the device; the positive input cable and the negative input cable are used to connect the DC bus side access point;

[0008] The positive pole of the output end of the isolated DC-DC converter is connected to the diode D3 and the contactor KM1 in sequence, and then the positive output cable of the device is led out, wherein the anode of the diode D3 is connected to the positive pole of the output end of the isolated DC-DC converter; the negative pole of the output end of the isolated DC-DC converter is connected to the contactor KM1, and then the negative output cable of the device is led out; the positive output cable and the negative output cable are used to connect the load side access point;

[0009] The positive and negative output terminals of the isolated DC-DC converter are grounded through resistors R1 and R2, respectively, and R1 = R2;

[0010] The two ends of the bulb LP1 are connected to the cathode of the diode D1 and the negative input cable respectively.

[0011] The anode of the diode D2 is connected to the positive output cable, and the cathode of the diode D2 is connected to one end of the bulb LP2, and the other end of the bulb LP2 is connected to the negative output cable;

[0012] The voltage detection unit V is used to detect the input voltage Us, the output voltage Ud and the output positive terminal to ground voltage Um of the device;

[0013] The controller is electrically connected to the voltage detection unit V, the isolated DC-DC converter, the indicator light LED1, the indicator light LED2, and the contactor KM1 respectively, and is used to control the isolated DC-DC converter, the indicator light LED1, the indicator light LED2, and the contactor KM1 according to the voltage detected by the voltage detection unit V.

[0014] Preferably, one end of the resistor R1 is connected to the cathode of the diode D3, and the other end of the resistor R1 is grounded; one end of R2 is connected to the negative electrode of the output end of the isolated DC-DC converter, and the other end of the resistor R2 is grounded.

[0015] Preferably, the input voltage Us is the voltage between the positive and negative poles of the input end of the isolated DC-DC converter, the output voltage Ud is the voltage between the cathode of the diode D3 and the negative pole of the output end of the isolated DC-DC converter, and the output positive pole to ground voltage Um is the cathode to ground voltage of the diode D3.

[0016] Preferably, the indicator light LED2 is a dual-color indicator light.

[0017] Preferably, the load is connected to the DC bus through the circuit breaker CB1, so as to control whether the DC bus supplies power to the load through the circuit breaker CB1; the DC bus side access point and the load side access point are respectively located on both sides of the circuit breaker CB1.

[0018] Preferably, the controller controls the isolated DC-DC converter, the indicator light LED1, the indicator light LED2 and the contactor KM1 according to the voltage detected by the voltage detection unit V, specifically:

[0019] After the device is correctly connected to the DC bus side access point and the load side access point, the controller adjusts the output of the isolated DC-DC converter according to the input voltage Us and the output voltage Ud, so that the output voltage Ud continuously approaches the input voltage Us;

[0020] When Ud = Us, the controller controls the indicator LED1 to flash green and sends a closing signal for the contactor KM1. After the contactor KM1 is engaged, it controls the indicator LED1 to remain green and on steadily.

[0021] After completing the load power supply switching, the controller compares the positive terminal voltage Um of the output terminal with respect to the ground with the output voltage Ud:

[0022] If Um > Ud / 2, control the indicator LED2 to flash red, which is used to indicate that a negative ground fault has occurred on the load side;

[0023] If Um < Ud / 2, control the indicator LED2 to remain red and on steadily, which is used to indicate that a positive ground fault has occurred on the load side;

[0024] If Um = Ud / 2, control the indicator LED2 to remain green and on steadily, which is used to indicate that no ground fault has occurred on the load side.

[0025] A method for detecting a ground fault, which is implemented by using the above-mentioned ground fault detection device, and includes the following steps:

[0026] S1. When isolation and maintenance are required, connect the positive input cable and the negative input cable to the access point on the DC bus side, and connect the positive output cable and the negative output cable to the access point on the load side; hang the device at both ends of the circuit breaker CB1. At this time, the contactor KM1 remains in the open state;

[0027] S2. If the polarities connected to the device are correct, LP1 and LP2 light up; otherwise, they do not light up. If LP1 and LP2 do not light up, change the cable connection method until both LP1 and LP2 light up;

[0028] S3. After the indicator LED1 remains green and on steadily, manually intervene to disconnect the circuit breaker CB1 to complete the load power supply switching;

[0029] S4. Judge the ground fault on the load side according to the lighting condition of the indicator LED2. When the indicator LED2 remains green and on steadily, the load has no fault. Manually intervene to close the circuit breaker CB1, remove the cables from the access point on the DC bus side and the access point on the load side, and the load is powered by the DC bus again to complete the ground fault detection of the load.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention does not need to change the power supply line of the substation, and can senselessly switch the power supply of the load from the DC bus to the isolated power supply; at the same time, it automatically completes the detection and identification of the load ground fault, reduces manual operation, and improves the detection efficiency; realizes efficient isolation and maintenance under the condition of no power outage, ensures the continuous power supply of important equipment, and guarantees the safe and stable operation of the substation. Description of the Drawings

[0032] Figure 1 It is the principle diagram of the device of the present invention. DETAILED DESCRIPTION

[0033] The following is combined with Figure 1 , the technical solution of the present invention is specifically described.

[0034] The present invention provides a ground fault detection device, comprising an isolated DC-DC converter, a contactor KM1, diodes D1, D2, D3, bulbs LP1, LP2, indicator lights LED1, LED2, resistors R1, R2, a voltage detection unit V and a controller;

[0035] The positive pole of the input end of the isolated DC-DC converter is connected to the cathode of the diode D1, and the positive input cable of the device is led out from the anode of the diode D1; the negative pole of the input end of the isolated DC-DC converter leads out the negative input cable of the device; the positive input cable and the negative input cable are used to connect the DC bus side access point;

[0036] The positive pole of the output end of the isolated DC-DC converter is connected to the diode D3 and the contactor KM1 in sequence, and then the positive output cable of the device is led out, wherein the anode of the diode D3 is connected to the positive pole of the output end of the isolated DC-DC converter; the negative pole of the output end of the isolated DC-DC converter is connected to the contactor KM1, and then the negative output cable of the device is led out; the positive output cable and the negative output cable are used to connect the load side access point;

[0037] The positive and negative output terminals of the isolated DC-DC converter are grounded via resistors R1 and R2 respectively; and R1 = R2;

[0038] The two ends of the bulb LP1 are connected to the cathode of the diode D1 and the negative input cable respectively.

[0039] The anode of the diode D2 is connected to the positive output cable, and the cathode of the diode D2 is connected to one end of the bulb LP2, and the other end of the bulb LP2 is connected to the negative output cable;

[0040] The voltage detection unit V is used to detect the input voltage Us, the output voltage Ud and the output positive terminal to ground voltage Um of the device;

[0041] The controller is electrically connected to the voltage detection unit V, the isolated DC-DC converter, the indicator light LED1, the indicator light LED2, and the contactor KM1 respectively, and is used to control the isolated DC-DC converter, the indicator light LED1, the indicator light LED2, and the contactor KM1 according to the voltage detected by the voltage detection unit V.

[0042] In this embodiment, one end of the resistor R1 is connected to the cathode of the diode D3, and the other end of the resistor R1 is grounded; one end of the R2 is connected to the negative terminal of the output of the isolated DC-DC converter, and the other end of the resistor R2 is grounded.

[0043] In this embodiment, the input voltage Us is the voltage between the positive and negative terminals of the input of the isolated DC-DC converter, the output voltage Ud is the voltage between the cathode of the diode D3 and the negative terminal of the output of the isolated DC-DC converter, and the voltage Um of the positive terminal of the output with respect to ground is the voltage of the cathode of the diode D3 with respect to ground.

[0044] In this embodiment, the indicator LED2 is a two-color indicator.

[0045] In this embodiment, the load is connected to the DC bus through the circuit breaker CB1 to control whether the DC bus supplies power to the load through the circuit breaker CB1; the access points on the DC bus side and the load side are respectively located on both sides of the circuit breaker CB1.

[0046] In this embodiment, the controller controls the isolated DC-DC converter, the indicator LED1, the indicator LED2, and the contactor KM1 according to the voltage detected by the voltage detection unit V. Specifically:

[0047] After the device is correctly connected to the access points on the DC bus side and the load side, the voltage detection unit sends the detection results of the input voltage Us (DC bus voltage) and the output voltage Ud to the controller. The controller adjusts the output of the isolated DC-DC converter according to the input voltage Us and the output voltage Ud, so that the output voltage Ud continuously approaches the input voltage Us;

[0048] When Ud = Us, the output voltage of the isolated DC-DC converter is synchronized with the DC bus voltage, reaching the access condition. At this time, the controller controls the indicator LED1 to flash green and sends a closing signal for the contactor KM1. After the contactor KM1 is energized, it controls the indicator LED1 to stay green.

[0049] After completing the load power supply switching, the voltage detection unit detects the voltage Um of the positive terminal of the output with respect to ground (DC bus positive terminal voltage with respect to ground) and sends it to the controller for comparison with Ud:

[0050] If Um > Ud / 2, control the indicator LED2 to flash red to indicate a negative ground fault on the load side;

[0051] If Um < Ud / 2, control the indicator LED2 to stay red to indicate a positive ground fault on the load side;

[0052] If Um = Ud / 2, control the indicator LED2 to stay green to indicate that there is no ground fault on the load side.

[0053] A method for detecting a ground fault, the method being implemented by using the above-mentioned ground fault detection device, comprises the following steps:

[0054] S1. When a DC ground failure occurs and needs to be isolated for maintenance, connect the positive input cable and the negative input cable to the DC bus side access point (access point 1), and connect the positive output cable and the negative output cable to the load side access point (access point 2); connect the device to both ends of the circuit breaker CB1, and at this time, the contactor KM1 remains in the disconnected state;

[0055] In normal operation, the circuit breaker CB1 is closed and the DC bus directly supplies power to the load;

[0056] S2. If the polarity of the device is correct, LP1 and LP2 will light up, otherwise they will not light up. If LP1 and LP2 are not lit, change the cable connection method until both LP1 and LP2 light up.

[0057] S3, when the indicator LED1 turns green for a long time, the circuit breaker CB1 is disconnected manually to complete the load power supply switching; at this time, the load is only powered by the isolated power supply, and the next step of ground fault detection is carried out;

[0058] The above process can realize the inductive switching of the load from the DC bus power supply to the isolated power supply, ensuring the continuous power supply operation of the load;

[0059] S4. The load side ground fault is judged according to the lighting condition of the indicator LED2. When the indicator LED2 is green and on for a long time, the load has no fault. The circuit breaker CB1 is closed manually. The diode D3 prevents the DC bus current from reversely flowing into the isolated DC-DC converter. The cable is removed from the DC bus side access point and the load side access point (access point 1 and access point 2). The load is powered by the DC bus again, and the load ground fault detection is completed.

[0060] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

Claims

1. A ground fault detection device, characterized in that: It includes an isolated DC-DC converter, a contactor KM1, diodes D1, D2, D3, bulbs LP1, LP2, indicator lights LED1, LED2, resistors R1, R2, a voltage detection unit V and a controller; The positive pole of the input end of the isolated DC-DC converter is connected to the cathode of the diode D1, and the positive input cable of the device is led out from the anode of the diode D1; the negative pole of the input end of the isolated DC-DC converter leads out the negative input cable of the device; the positive input cable and the negative input cable are used to connect the DC bus side access point; The positive pole of the output end of the isolated DC-DC converter is connected to the diode D3 and the contactor KM1 in sequence, and then the positive output cable of the device is led out, wherein the anode of the diode D3 is connected to the positive pole of the output end of the isolated DC-DC converter; the negative pole of the output end of the isolated DC-DC converter is connected to the contactor KM1, and then the negative output cable of the device is led out; the positive output cable and the negative output cable are used to connect the load side access point; The positive and negative output terminals of the isolated DC-DC converter are grounded through resistors R1 and R2, respectively, and R1 = R2; The two ends of the bulb LP1 are connected to the cathode of the diode D1 and the negative input cable respectively. The anode of the diode D2 is connected to the positive output cable, and the cathode of the diode D2 is connected to one end of the bulb LP2, and the other end of the bulb LP2 is connected to the negative output cable; The voltage detection unit V is used to detect the input voltage Us, the output voltage Ud and the output positive electrode to ground voltage Um of the device; The controller is electrically connected to the voltage detection unit V, the isolated DC-DC converter, the indicator light LED1, the indicator light LED2, and the contactor KM1 respectively, and is used to control the isolated DC-DC converter, the indicator light LED1, the indicator light LED2, and the contactor KM1 according to the voltage detected by the voltage detection unit V.

2. A ground fault detection device according to claim 1, characterized in that: One end of the resistor R1 is connected to the cathode of the diode D3, and the other end of the resistor R1 is grounded; one end of R2 is connected to the negative electrode of the output end of the isolated DC-DC converter, and the other end of the resistor R2 is grounded.

3. A ground fault detection device according to claim 1, characterized in that: The input voltage Us is the voltage between the positive and negative poles of the input end of the isolated DC-DC converter, the output voltage Ud is the voltage between the cathode of the diode D3 and the negative pole of the output end of the isolated DC-DC converter, and the output end positive pole to ground voltage Um is the cathode to ground voltage of the diode D3.

4. A ground fault detection device according to claim 1, characterized in that: The indicator light LED2 is a dual-color indicator light.

5. A ground fault detection device according to claim 1, characterized in that: The load is connected to the DC bus through the circuit breaker CB1, so as to control whether the DC bus supplies power to the load through the circuit breaker CB1; the DC bus side access point and the load side access point are respectively located on both sides of the circuit breaker CB1.

6. A ground fault detection device according to claim 5, characterized in that: The controller controls the isolated DC-DC converter, the indicator light LED1, the indicator light LED2 and the contactor KM1 according to the voltage detected by the voltage detection unit V, specifically: After the device is correctly connected to the DC bus side access point and the load side access point, the controller adjusts the output of the isolated DC-DC converter according to the input voltage Us and the output voltage Ud, so that the output voltage Ud continuously approaches the input voltage Us; When Ud = Us, the controller controls the green light of the indicator LED1 to flash and issues a closing signal for the contactor KM1. After the contactor KM1 is closed, it controls the green light of the indicator LED1 to stay on; After completing the load power supply switchover, the controller compares the positive terminal voltage Um of the output with the output voltage Ud to the ground: If Um > Ud / 2, control the red light of the indicator LED2 to flash, indicating that a negative ground fault has occurred on the load side; If Um < Ud / 2, control the red light of the indicator LED2 to stay on, indicating that a positive ground fault has occurred on the load side; If Um = Ud / 2, control the green light of the indicator LED2 to stay on, indicating that no ground fault has occurred on the load side.

7. A method for detecting a ground fault, which is implemented by using the ground fault detection device described in claim 6, and includes the following steps: S1. When isolation and maintenance are required, connect the positive input cable and the negative input cable to the DC bus side access point, and connect the positive output cable and the negative output cable to the load side access point; hang the device at both ends of the circuit breaker CB1, and at this time, the contactor KM1 remains in the open state; S2. If the polarity of the device connection is correct, LP1 and LP2 light up, otherwise they do not light up; if LP1 and LP2 do not light up, change the cable connection method until both LP1 and LP2 light up; S3. After the green light of the indicator LED1 stays on, manually intervene to disconnect the circuit breaker CB1 to complete the load power supply switchover; S4. Judge the ground fault on the load side according to the lighting condition of the indicator LED2. When the green light of the indicator LED2 stays on, the load is fault-free. Manually intervene to close the circuit breaker CB1, remove the cable from the DC bus side access point and the load side access point, and the load is powered by the DC bus again to complete the ground fault detection of the load.

Images