Resistor Cabinet

FAQ Guide

In the power grid system, the resistor cabinet is one of the most important equipment. The resistor cabinet evolved from the resistor, but its role is more than that of the resistor. The biggest role is to protect the circuit. It is responsible for ensuring that the equipment can operate safely and effectively when grounded.

The resistor cabinet is a key equipment in the power system, which is used to reduce the grounding resistance, improve the grounding protection level and prevent electrical accidents. When selecting the resistor cabinet, it is necessary to consider factors such as resistance requirements, system voltage, environmental conditions, equipment capacity, etc. to ensure the safe and stable operation of the equipment and perform regular maintenance to extend its service life.

If the resistor cabinet is not used and maintained correctly, it may cause equipment damage, casualties, and grid stability problems. Therefore, knowing how to use the resistor cabinet correctly is crucial for the operation and maintenance of the grid. This article will answer common questions about the use of resistor cabinets and help readers understand the relevant information about resistor cabinets more clearly.

1. What are the working principles and advantages of the resistor cabinet?

The resistance cabinet is a device specially used to reduce the grounding resistance. Its basic principle is to add a resistor between the grounding electrode and the grounding grid to reduce the grounding resistance value, thereby improving the effect of grounding protection. Grounding resistance can be controlled and monitored with an accurate resistor cabinet, which includes resistors, switches, and protection devices.

The advantages of using a resistor cabinet are as follows:

• Protect resistors: In the resistor cabinet, resistors can be well protected from mechanical shock, dust, moisture, and other harsh environments, thereby extending the service life of the resistors.
• Control current: The resistor cabinet can control the voltage and current of the external power supply, thereby controlling the current of the load circuit, thereby achieving protection and control of the equipment.
• Adjusting voltage: The resistor cabinet can adjust the voltage of the load circuit by adjusting the resistance value of the resistor, thereby meeting the voltage requirements of different loads.
• Limit overcurrent: In the process of protecting equipment, the resistor cabinet can also limit overcurrent to prevent damage to the equipment caused by excessive current.

With the rapid development of the power industry, resistor cabinets have not only been well developed but also have a wide range of applications. They can be used in power plant power systems, substation power supply systems, and industrial and mining enterprise power distribution systems.

2. What are the types of resistor cabinets?

Resistor cabinets can be divided into three types: transformer neutral point grounding resistor cabinet, generator neutral point grounding resistor cabinet, and low voltage grounding resistor cabinet.

1). Low voltage grounding resistor cabinet

Basic components: resistor, disconnector, intelligent monitor, zero-sequence current transformer, leakage protection relay, breakdown fuse. Used in 0.22kV-0.66kV low-voltage systems, when the power system is powered off due to ground fault, the low-voltage grounding resistor cabinet plays a role, which can avoid the need for immediate tripping when single-phase grounding occurs. At the same time, fuses are used as protective electrical appliances, thereby reducing the chance of burning out electrical equipment during operation.

2). Transformer neutral point grounding resistance cabinet

The basic configuration includes a transformer, resistor, current transformer, resistor cabinet, resistor cabinet intelligent monitoring device, and disconnector. In the 6kV-35kV power supply system, the grounding capacitance current is large. When the current is greater than the specified value, arc grounding overvoltage may occur. After installing the transformer grounding neutral point grounding resistor cabinet, a resistive current can be injected into the fault point, and its resistance component current is 1.05-1.1 times the capacitance component current. The fault current can be limited to a moderate level, the sensitivity of the relay protection can be improved, and at the same time, only local slight damage may occur to the fault point, and the transient overvoltage can be limited to 2.6 times the normal relative neutral point voltage, preventing arc overvoltage from damaging the main equipment, and having a significant effect on ferromagnetic resonance overvoltage.

3). Generator neutral point grounding resistor cabinet

It is a complete set of grounding equipment, generally equipped with resistors, current transformers, intelligent monitoring devices for resistor cabinets, vacuum contactors, resistor cabinets, and other main accessories. Single-phase grounding is a common fault during the operation of the generator. Installing a generator grounding resistor cabinet can limit the fault current to an appropriate value, improve the sensitivity of the relay protection to trip, and at the same time, only local slight burns may occur at the fault point, limit the transient overvoltage to 2.6 times the normal voltage to the neutral point voltage, limit the reignition of the arc, prevent the arc gap overvoltage from damaging the main equipment, and effectively prevent ferromagnetic resonance overvoltage, thereby ensuring the safe operation of the generator.

3. How to select the resistor cabinet?

When selecting a resistor cabinet, you must first consider the following factors:

• Grounding resistance requirements: Determine the required grounding resistance value based on the actual situation of the power system and select the appropriate grounding resistance cabinet model.
• System voltage level: The rated voltage of the grounding resistor cabinet should match the voltage level of the power system to ensure the safe operation of the equipment.
• Environmental conditions: Consider the environmental conditions of the equipment, such as temperature, humidity, corrosion, etc., and select appropriate materials and protective measures. Pay attention to heat dissipation to avoid accidents caused by overheating.
• Equipment capacity: According to the capacity and load of the power system, select the appropriate grounding resistance cabinet capacity to meet the needs of the system.
• Safety and reliability: The design should meet the requirements of safety and reliability, be able to prevent accidents such as electrical fires and electric shocks, and ensure the safe operation of the power system.
• Easy operation and maintenance: It is convenient for on-site operators and equipment maintenance managers to carry out inspection, replacement, and other work.

3. How to select the resistor cabinet?

When selecting a resistor cabinet, you must first consider the following factors:

• Grounding resistance requirements: Determine the required grounding resistance value based on the actual situation of the power system and select the appropriate grounding resistance cabinet model.
• System voltage level: The rated voltage of the grounding resistor cabinet should match the voltage level of the power system to ensure the safe operation of the equipment.
• Environmental conditions: Consider the environmental conditions of the equipment, such as temperature, humidity, corrosion, etc., and select appropriate materials and protective measures. Pay attention to heat dissipation to avoid accidents caused by overheating.
• Equipment capacity: According to the capacity and load of the power system, select the appropriate grounding resistance cabinet capacity to meet the needs of the system.
• Safety and reliability: The design should meet the requirements of safety and reliability, be able to prevent accidents such as electrical fires and electric shocks, and ensure the safe operation of the power system.
• Easy operation and maintenance: It is convenient for on-site operators and equipment maintenance managers to carry out inspection, replacement, and other work.

4. How to correctly install and debug the resistor cabinet?

To use the grounding resistor cabinet correctly, first, ensure that it is installed correctly and complies with relevant standards and regulations. The following are the key points to pay attention to during installation and commissioning.

• The grounding resistor cabinet should be installed in a dry, well-ventilated, dust-free place to prevent acid, alkali, and corrosive gases, and avoid direct sunlight and high-temperature environment.
• At the same time, the grounding system of the resistor cabinet should comply with local regulations and standards, and the various parts of the equipment should be correctly connected according to the wiring diagram to avoid wrong wiring or dotted wiring. The wiring should be firm and reliable to ensure its effectiveness and safety.
• Necessary safety protection measures should also be taken for the equipment, such as installing protective covers, identification plates, etc., to ensure the safe operation of the equipment.
• After the resistor cabinet is installed, it needs to be debugged to ensure the normal operation of the equipment. The following points should be noted during the debugging process:
  • Check the equipment wiring: ensure that the equipment wiring is correct and firm, without short circuits, open circuits, etc.
  •  Check equipment status: Check whether the equipment’s switches, protective devices, etc. are in normal working condition.
  • Test grounding resistance: Use professional testing instruments to test grounding resistance to ensure that the grounding resistance value meets the requirements. When measuring large grounding resistance, you cannot measure it according to the general wiring method. You can refer to the provisions of the ammeter and voltmeter measurement methods to select the buried point.
  • Debug the protection device: debug the protection device of the grounding resistance cabinet to ensure that it can work normally and protect the equipment from electrical accidents in time.

Before operating the grounding resistor cabinet, you should first check whether its appearance and fasteners are intact, and make sure that all switches and circuit breakers are in the off state. Then, you should operate in the prescribed order, first turn on the power switch, and then gradually turn on the circuit breaker and load switch. During operation, the working status and temperature of the grounding resistor cabinet should be checked regularly to ensure its normal operation.

If the grounding resistor cabinet fails or has an abnormal situation, it should be handled in time. For example, if the grounding current is too large or too small, the resistance value of the resistor should be adjusted; if the circuit breaker trips or an abnormal situation occurs, it should be checked and repaired immediately. When handling a fault, safe operating procedures should be followed and the stability and reliability of the grounding resistor cabinet should be ensured.

5. How to maintain the resistor cabinet?

In order to ensure the long-term stable operation of the grounding resistor cabinet, regular operation and maintenance work is required. Specifically, the following contents are included:

• Check the equipment status regularly: Check the equipment regularly, including its appearance, wiring, switches, etc., to ensure that it is in normal working condition.
• Test the grounding resistance regularly: Use professional testing instruments to test the grounding resistance regularly to ensure that the grounding resistance value meets the requirements.
• Clean equipment: Clean the equipment regularly to remove dust, debris, etc., and keep the equipment clean and tidy.
• Maintain protective devices: Maintain protective devices regularly to ensure they can work properly and protect equipment from electrical accidents in a timely manner.

6. Conclusion

The grounding resistor cabinet is an important piece of equipment in the power system. Its use involves many aspects such as selection, installation, commissioning, operation, and maintenance. When using the grounding resistor cabinet, you need to pay attention to the above items to ensure the normal operation and safety and stability of the equipment. At the same time, the operation and maintenance of the equipment also need to be carried out regularly to ensure the long-term stable operation of the equipment and extend its service life.