What are the causes of DC system ground faults?

The hazards of DC system grounding, DC system is generally used for substation control bus, closing bus, UPS uninterruptible power supply, and is also used as other power supply and logic control loop. The DC system is an insulation system with an insulation resistance of tens of megaohms, and in its normal operation, the positive and negative electrodes of the DC system have equal insulation resistance to the ground, and the voltage to the ground is also relatively balanced. When a point of grounding occurs, the voltage of the positive and negative electrodes to the ground changes, the voltage of the grounding electrode decreases, the voltage of the non-grounding electrode increases, and the reliability of the control loop and power supply will be greatly reduced, but it will generally not cause the secondary failure of the electrical control system.

However, when the DC system has two or more points of grounding, it is very easy to cause the logic control loop to malfunction, DC fuse, so that the protection and automatic devices, the control loop lose power supply, in the complex protection circuit with two points of grounding, but also some relays may be short-circuited, can not be tripped, resulting in skipping tripping, resulting in the expansion of the accident. The regulations strictly stipulate that the DC system is grounded at multiple points with the same pole, and all the work of the DC system should be stopped, which is also based on the uncertainty of the nature of its fault, and the hazards of the positive grounding of the DC system, when the DC positive grounding occurs, it may cause the malfunction of protection and automatic devices.

Because the tripping coil and relay coil of the general circuit breaker are connected to the negative power supply, if another DC ground occurs on these circuits, it may cause malfunction. The DC negative electrode is grounded, which may also cause the protection and automatic device to refuse to operate. Because the circuit breaker's jumping and closing coils and protective relays will be short-circuited by the grounding point when these circuits are a little more grounded, the coils will not be able to operate.

At the same time, the short-circuit current of the DC loop will cause the fuse of the power supply to be blown off, and the relay contact may be burned out, and the fuse will lose the protection and operation of the power supply. <>

When the positive electrode is grounded in the DC system, there is a possibility of protection malfunction. Because the trip coils of the electromagnetic operating mechanism are usually connected to the negative power supply, if these circuits are grounded or insulated poorly, it will cause protection malfunction. When the negative pole of the DC system is grounded, if there is a point of grounding in the circuit, it may short-circuit the tripping or closing circuit, causing the protection or circuit breaker to refuse, or burning the relay, or causing the fuse to blow, etc.

When the positive pole of the DC system is grounded, there will be a possibility of protection malfunction;

When the negative pole of the DC system is grounded, there will be a possibility of protection rejection;

A little grounding in the DC system will not cause direct harm to the DC system, but the fault must be eliminated in time, otherwise another point of grounding in the DC system may cause serious harm to the entire power system.

DC grounding includes one point of ground and two points of ground:

One point of grounding may cause the protection and automatic device to fail or refuse to act, while two point of grounding may not only cause the relay protection, signal, automatic device to fail or refuse to act, but it can also cause the DC fuse to blow, making the protection and automatic installation fail. When the control circuit is powered off, in the complex protection circuit, the two points of the same pole are grounded, and some relays may be short-circuited, resulting in inability to act and tripping, resulting in a skipping trip, resulting in the expansion of the accident.

In a DC system, the positive and negative electrodes of DC are insulated from the earth. When one pole is grounded, no harm is caused because there is no ground current path. However, it is not allowed to run one pole to ground for a long time, because when the same pole is grounded and the other ground is grounded, it may cause malfunction of the signal device, relay protection or control circuit.

One ground point after another can cause a DC short circuit.

If the DC positive is grounded, it may cause the relay to malfunction. Since the general trip coils (such as the outgoing intermediate relay coil and the trip closing coil, etc.) are connected to the negative power supply, if these circuits are grounded or poorly insulated, the relay protection will malfunction. The grounding of the DC negative electrode is the same as the grounding of the positive electrode.

If the circuit is grounded a little more, it may cause the relay protection to refuse, and the accident will increase by leaps and bounds.

Grounding both poles at the same time can short-circuit a tripping or closing circuit, potentially blowing not only the fuse but also the relay contacts.

One point grounding of the DC system does not affect the normal operation of the DC system, but it will increase the voltage of the non-grounding electrode to the ground, and the long-term operation is easy to develop into a two-point grounding, which will cause the misoperation or rejection of circuit breakers and protection devices, resulting in serious consequences and must be dealt with in time.

1) Judge the polarity of DC grounding. When the DC system is well insulated, the voltage of the positive electrode to the ground and the negative electrode to the ground are basically equal. If the voltage of the positive pole to ground is the voltage between the positive and negative poles when it is normal, and the voltage of the negative pole to the ground is zero, it means that the negative pole is completely grounded; If the voltage of the negative pole to ground is measured as the voltage between the positive and negative poles when it is normal, and the voltage between the positive pole and the ground voltage is zero, it means that the positive electrode is completely grounded.

In the case of an incomplete ground fault, the degraded pole has a lower (non-zero) voltage to ground, while the other pole has a higher voltage to ground. According to the operation mode, operation situation, climate impact, construction scope, etc., the judgment is made, and the causes that may cause grounding are analyzed.

2) If there is someone working in the secondary circuit in the station, it should be stopped immediately, and the secondary wiring should be checked to see if there is a grounding point.

3) The secondary circuit is unmanned and the DC system can be divided into relatively independent systems to narrow the search range. Note: Do not lose DC power to protection or control during the search grounding process.

4) For unimportant DC loads, such as accident lighting, test power supply, etc., the instantaneous power failure method can be used to find out whether the branch feeder has a grounding point, that is, a feeder switch is pulled instantaneously, and then quickly closed, if the grounding signal disappears instantaneously, and the positive and negative voltage to the ground returns to normal, the grounding fault point is within this range.

5) For the more important DC load, the transfer load method can be used to find the grounding point. For example, the more important shunt on the bus where the fault is located is transferred to another DC bus in turn, and whether the "DC grounding" signal is transferred with it, whether the voltage of the positive and negative poles to the ground is restored to normal, and which shunt the grounding point is located in.

6) If the grounding occurs in a rainy day and is a non-metallic grounding, it should be focused on checking whether the terminal box, local operation box, and terminal row of the mechanism box are watery and wet. If there is rain, you can dry it and observe whether the grounding phenomenon disappears.

1) When the DC system is found to be grounded, it should be reported to the dispatcher on duty and the grounding point should be quickly found. Before looking for a grounding point, the insulation monitoring device should be used to determine which pole is grounded and to what extent.

2) In order to quickly find out the DC grounding point, we should first consider whether the secondary circuit such as the DC circuit, the protective screen, and the terminal box are working, whether the equipment is under construction, and whether there is rain. Or according to the actual situation of the climate and on-site work (including the operation of the reverse gate), the circuit is divided and closed test. Typically, the DC system is split first, separating the loops from the parallel loops, and then cutting off the feeds one by one.

3) When looking for one, one person looks at the watch, and one person pulls the gate (the cut-off time is 1-2s). The sequence is: accident lighting, closing power supply, signal power supply, control power supply, charger and battery each with a section of bus, and then pull the DC segmented isolation switch; Use a charger or silicon rectifier to bring the full load, and pull the battery main isolation switch (at this time, the reclosing of the electromagnetic mechanism switch should be withdrawn or the closing power supply should be pulled).

4) If it is found that a certain circuit is grounded, the circuit should be divided into several sections to reduce the scope of the fault until the fault point is found and eliminated. If the grounding occurs in the control or protection circuit, the protection personnel should be notified to assist, and the grounding should be found carefully, and before disconnecting the power supply, it is required to take measures to prevent the protection from malfunctioning, such as exiting the outlet pressure plate, etc., at this time, it must be carried out after obtaining the consent of the dispatcher.

5) When installing the microcomputer insulation monitoring device, the grounding alarm light is on, and the sound alarm is at the same time, and the display screen can display the ratio of the grounding polarity, the grounding branch number and the voltage value to the ground, which should be handled in accordance with the provisions of Article (4). If several circuits have a ground fault at the same time, the display will take turns to display the information of these branches, which should be handled separately. If there is no road number display after the alarm, the ground fault does not occur within the monitoring range of the sensor or the bus is grounded.

6) When finding the grounding of the DC system, attention should be paid to taking measures to prevent protection malfunction, and deactivate the relevant protection devices if necessary. If the safety distance from the primary equipment is not enough to eliminate the fault point, you should contact the dispatcher and deactivate the relevant equipment.

At the same time, it is forbidden to work on the secondary circuit, and the search should be careful not to cause a short circuit and cause another point to ground, and should be carried out with a high internal resistance voltmeter.

7) When the voltage of the DC system is abnormal, if the power supply of transistor protection device, integrated circuit protection and microcomputer protection is automatically cut off, the power supply will be restored after the abnormality is eliminated. The corresponding protection device pressure plate should be withdrawn to prevent the protection from malfunctioning.

How to deal with the grounding fault in the high-voltage DC system: 1. The voltage transformer fuse is fused 1) When the voltage transformer is fused by the high-voltage fuse, the fuse phase voltage is reduced but not zero due to the load of the voltage secondary circuit, and the other two-phase voltage should be kept as normal phase voltage or slightly lower. At the same time, because the phase failure appears on the high-voltage side of the transformer, the low-voltage side of the transformer will have a V-sequence voltage, which is higher than the fixed value of the grounding signal, and a grounding signal will be issued.

The voltage transformer was withdrawn, and the fuse was replaced and put into operation. 2. When the low-voltage fuse of the voltage transformer is fused, the reflection on the secondary side is basically similar to that of the high-voltage fuse, but because the fuse fuse occurs on the low-voltage side, it will only affect the voltage of a certain winding, and there will be no zero sequence voltage. In this case, the ** signal alarm "voltage transformer disconnection", the fuse phase voltage is zero, and the other two phase voltages are normal, which can be confirmed as the low voltage fuse blowing.

Summary. Hello, happy to answer your questions<>

Your question is: how to deal with the grounding fault of the HVDC system, and the answer I provide for you after inquiry is: Hello, the grounding fault of the HVDC system is handled as follows

Situation 1: If after inspection, the fault is in the control and signal loop of a certain line, because the control outdoor terminal box, mechanism box, secondary cable, etc. involved in the line should be reported to the dispatcher and the relevant superiors, and professionals are required to cooperate with the search. Scenario 2:

The DC disc uses the pull method to find all the feed shunts of the DC grounding, and when the grounding signal does not disappear after selection, the fault may be in the DC bus or the battery pack. Hope it helps<>

How to deal with the grounding fault in the HVDC system.

Hello, happy to answer your questions<>

Your question is: how to deal with the grounding fault of the HVDC system, and the answer I provide for you after inquiry is: Hello, the grounding fault of the HVDC system is handled as follows

Situation 1: If after inspection, the fault is in the control and signal loop of a certain line, because the control outdoor terminal box, mechanism box, secondary cable, etc. involved in the line should be reported to the dispatcher and the relevant superiors, and professionals are required to cooperate with the search. Scenario 2:

The DC disc uses the pull method to find all the feed shunts of the DC grounding, and when the grounding signal does not disappear after selection, the fault may be in the DC bus or the battery pack. Hope it helps<>

Hello dear, the following is an extended information about your question, which can provide you with reference <><

If the fault is found in the control and signal loop of a certain line, the control outdoor terminal box, mechanism box, secondary cable, etc. involving the line should be reported to the dispatcher and the relevant superiors, and professionals are required to cooperate with the search. The differential pressure method uses a balanced resistor in the system, and there is no voltage shift due to the balance of the system in normal times. When there is a grounding fault, the voltage is offset, for example, the positive bus of the negative grounding fault passes R1 to the ground, and the ground to Rx forms a leakage current, and the normal branch without grounding cannot leak current.

There is a leakage current flowing through the grounding branch A branch C and the grounding point. Ground faults are found by clamping the leakage current. The signal analyzer is R1 and R2 resistors are intermittent switching, generally that is, 1-10 seconds switching once).

The clamp meter used in the differential pressure method must be a DC clamp meter based on the Hall principle. Comparison of DC clamp meter and AC clamp meter: The advantage is the principle of magnetic balance and strong resistance to external radiation.

The disadvantage is that it is 5-10 times more expensive than AC clamp meters. Another disadvantage is that it is limited by the range and can be blocked. Hope it helps, thank you for kissing <>

Hello dear! A little grounding of the DC system is very dangerous for electrical safety, and the main hazards are as follows:1

Arcs or flames can occur due to system grounding interruptions, and the pressure of the arc or flame is very high and can cause damage to the surrounding environment. 2.A little grounding causes a circuit to malfunction, generating excessive current and burning out components on the device.

3.Due to the unstable grounding state of the DC system, the power supply ** voltage is unstable, which will not only affect the normal operation of the equipment, but also lead to damage to the equipment. 4.

A little grounding can also lead to electromagnetic interference, and even introduce high-voltage electricity into manufacturing equipment, thus affecting the normal operation of the equipment. 5.A little grounding can also cause the overcurrent protector to not work properly, which can lead to safety hazards.

6.A little grounding also affects the measurement and control of the equipment on the system, which in turn affects the normal operation of the system. Therefore, in order to ensure the safety of the DC system, it is necessary to properly ground and ensure the stability of the grounding state.

To this end, the following measures are taken:1Use the correct grounding method, the correct grounding method can safely and effectively avoid the harm of grounding at one point; 2.

Regularly check the condition of the system grounding point to ensure that the grounding is good; 3.Choose high-quality grounding equipment to prevent sudden changes in grounding status; 4.Strengthen the maintenance of related equipment to ensure system security; 5.

Strengthen the learning of electrical safety knowledge to ensure the safety of operators.