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List of the table of contents of this article:

• 1, What is neutral point direct grounding? Why ground directly
• 2, What is a large grounding current system?
• 3, belongs to the neutral point operation mode of the large grounding current system. Why the system
• 4, What is a small current grounding system? What is a high-current grounding system?
• 5 、 High-current grounding systemHow long can it be used

What is neutral point direct grounding? Why direct grounding

1. The direct grounding method of the neutral point is to directly connect the neutral point to the earth. If a single-phase grounding occurs during the operation of the system, a single-phase short circuit will be formed, and the grounding current is large, causing the circuit breaker to trip and remove the fault. This kind of high-current grounding system is not equipped with an insulation monitoring device.

2. After the neutral point is directly grounded, the neutral point potential of the power system is fixed at zero potential. Even if a single-phase grounding failure occurs, because the earth's charge capacity is infinite, the earth's potential (that is, the center point potential) is still zero, so the phase voltage is not fault-to-ground. It won't change.

3. Neutral point direct grounding system, also known as large grounding current system. When a phase is grounded in this system, another contact point other than the neutral point appears, which constitutes a short-circuit loop. The ground fault phase current is very large. In order to prevent damage to the equipment, the power supply must be cut off quickly, resulting in low power supply reliability and power outages.

4. So as to greatly reduce the cost. The neutral point grounding method involves the safety, reliability and economy of the power grid; at the same time, it directly affects the selection of the insulation level of the system equipment, the overvoltage level and the relay protection method, communication interference, etc. Generally speaking, the neutral point grounding method of the power grid is also the voltage neutral point grounding method of the transformer at all levels in the substation.

What is a large grounding current system?

High-current grounding system is a safety measure widely used in electrical equipment. In the power system, equipment and cables may fail, resulting in current leakage, which may cause danger to personnel and equipment. The high-current grounding system can guide these currents to the ground, thus protecting the safety of personnel and equipment.

High-current grounding and small-current grounding are both grounded by neutral points in the power system, which are distinguished according to the main operating characteristics. The small grounding current system is also known as the ineffective grounding system. Including neutral point non-grounding, extinguishing arc coil grounding, and high-impedance grounding system.

When a single-phase grounding fault occurs in a neutral point direct grounding system (including a system grounded by a small impedance), the grounding short-circuit current is very large, so this system is called a high-current grounding system.It adopts a system that is not grounded at the neutral point or grounded by an arc coil.

The system voltage level is 110KV and above, and the neutral point direct grounding system is called high-current grounding system. The system voltage level is 35KV and below, and the neutral point is not grounded or compensated with an arc extinguishing coil is called a small current grounding system.

Large grounding current system is also known as effective grounding system. Including neutral point direct grounding and low-impedance grounding systems. Usually, this kind of system has X0/X1≤3 and R0/X1≤1.

Why is the neutral point operation mode of the large grounding current system? There are two categories of neutral point operation mode of the unified

power system: one is the direct grounding of the neutral point or the grounding through low resistance, which is called the large grounding current system. Second, the neutral point is not grounded or grounded by the arc extinguishing coil, which is called a small grounding current system.

One category is directly grounded by the neutral point or grounded by low-impedance, called high-current grounding system; the other category is ungrounded at neutral points, grounded by arc-removing coils or high-impedance grounding, which is called a small grounding current system.

There are two types of point operation mode in the power system. There are two types of point grounding mode in the power system: one is the neutral point direct grounding or low impedance grounding, which is called the large grounding current system; the other is the neutral point is not grounded, which is grounded through arc coil or high impedance grounding, which is called the small grounding current system.

For the first grounding of equipment, there are mainly direct grounding, through resistance grounding and grounding through arc extinguishing coil. In a system above 220kV, the neutral point of the main transformer is directly grounded, which is called a high-current grounding system.

In a broad sense, the operation mode of the power system refers to the method and form of electrical equipment operation. For example, the power grid can be divided into different operation modes of open-loop and closed-loop, circuit breakers can be divided into remote control and near-control, and relay protection can cast signals and trips.

What is a small current grounding system? What is a high-current grounding system?

1. High-current grounding and small-current grounding are grounded by neutral points in the power system, which are distinguished according to the main operating characteristics. The small grounding current system is also known as the ineffective grounding system. Including neutral point non-grounding, extinguishing arc coil grounding, and high-impedance grounding system.

2. Large grounding current system -- a three-phase system that is directly grounded at the grounding point of the grounding power system. When a single-phase grounding fault occurs, the grounding short-circuit current is very large, so it is called a large grounding current system. Generally, 110kV and above systems or 380/220V three-phase four-wire systems.

3. In the system where the neutral point is directly grounded, when a single-phase grounding fault occurs, the grounding short-circuit current is large. This system is called a high-current grounding system. Generally, the system of 110kv and above adopts a high-current grounding system.

4. The system voltage level is 110KV and above, and the neutral point direct grounding system is called high-current grounding system. The system voltage level is 35KV and below, and the neutral point is not grounded or compensated with an arc extinguishing coil is called a small current grounding system.

5. For the grounding of the primary equipment, there are mainly direct grounding, resistance grounding, and extinguishing arc coil grounding. In a system above 220kV, the neutral point of the main transformer is directly grounded, which is called a high-current grounding system. In the 110 and 66kv systems, the neutral point arc coil of the main transformer is more grounded, which is called the small current grounding system.

What is a high-current grounding system?

High-current grounding system is a safety measure widely used in electrical equipment. In the power system, equipment and cables may fail, resulting in current leakage, which may cause danger to personnel and equipment. The high-current grounding system can guide these currents to the ground, thus protecting the safety of personnel and equipment.

High-current grounding and small-current grounding are both grounded by neutral points in the power system, which are distinguished according to the main operating characteristics. The small grounding current system is also known as the ineffective grounding system. Including neutral point non-grounding, extinguishing arc coil grounding, and high-impedance grounding system.

Neutral point direct grounding system (including small resistance)Anti-grounding system) When a single-phase grounding fault occurs, the grounding short-circuit current is large, so this system is called a high-current grounding system. It adopts a system that is not grounded at the neutral point or grounded by an arc coil.

The system voltage level is 110KV and above, and the neutral point direct grounding system is called high-current grounding system. The system voltage level is 35KV and below, and the neutral point is not grounded or compensated with an arc extinguishing coil is called a small current grounding system.

Generally speaking, China's "large grounding current system" refers to a voltage level of 110kV and above. Because the neutral point of the transformer in its operation is grounded, when a single-phase grounding fault occurs, the grounding current is relatively large, so it is called so.

High-current connectionHow long can the ground system be used?

KV is mostly a small-current grounding system, that is, a neutral point non-grounding system, so the short-circuit current is not large when single-phase grounding occurs. In order to meet the normal power supply of the electrical load, it can allow fault operation for 1 to 2 hours. The KV line is single-phase grounded and can run for 1-2 hours, which is related to the grounding method of the 10kv system.

In order to prevent the expansion of the fault, causing interphase short circuit or single-phase arc light grounding, causing the system to resonate and cause overvoltage, resulting in system paralysis, it is stipulated that the operation time with fault after grounding shall not exceed 2 hours. It is recommended to measure the zero-sequence current and pull the path within these two hours.

It seems that only when the insulation resistance drops to the point where we can't stand it or involve the safety of personnel and equipment is the limit of allowing grounding operation.Before this red line, it has been allowed to run.

The neutral point ungrounded system is mainly used in power supply systems above 110KV. Neutral point direct grounding and extinguishing arc coil grounding are mainly used in power supply systems of 35KV and below. If the ungrounded system occurs single-phase grounding, the system can operate normally within two hours. The fault point must be found to deal with, otherwise the fault will be expanded.