Grounding methods and safety requirements for power transformers

Grounding methods and safety requirements for power transformers

1、 Grounding method

The grounding methods of power transformers mainly include transformer body grounding, transformer core grounding, and transformer neutral point grounding. Among them, the grounding method of the neutral point of the transformer can be further divided into star grounding, direct grounding, and indirect grounding.

1. Star grounding: also known as electrical neutral point connection grounding, can effectively limit the voltage rise in case of local insulation damage to equipment and provide effective overvoltage protection.

2. Direct grounding: Construction and maintenance are relatively simple, but the grounding current is large and prone to grounding faults.

3. Indirect grounding: Connected to the ground through a reactor or inductor, the magnitude of the grounding current can be controlled, with minimal impact on the overall electrical characteristics of the power system.

2、 Safety requirements

To ensure the safe operation of power transformers, the following requirements must be met:

1. The grounding device should comply with relevant electrical and engineering installation specifications and standards. The spacing between grounding bodies should be greater than 5m, 1.5m from buildings, and 3m from lightning rods. At the same time, the distance between the grounding main line and the lead wire should be greater than 100mm, and the grounding main line and the grounding electrode should be connected with pipe clamps.

During the installation of transformers, the tightness of components should be ensured, especially the cleanliness and flatness of flange connections, to prevent oil leakage, air intake, water ingress, and other phenomena.

The treatment of insulating oil is crucial, and it should be ensured that it is not contaminated by impurities such as moisture, gas, and hard objects to maintain good insulation performance.

For large computer rooms or important equipment, a mesh grounding method can be used to improve anti-interference ability and ensure consistency of potential reference points. However, it should be noted that the construction of the mesh system is complex and costly.

5. The fire resistance level of oil immersed transformer rooms and high-voltage distribution equipment rooms should not be lower than level two, and they should be independently constructed or separated by firewalls. At the same time, fire alarm devices and fire extinguishing facilities suitable for the capacity of oil immersed transformers and building scale should be installed.

When selecting the grounding method, it is necessary to comprehensively consider factors such as the usage of the transformer, system safety, and stability. For example, in situations where it is necessary to prevent ground faults and balance three-phase loads, it may be considered to connect an arc suppression coil at the neutral point.

Overall, the grounding method of power transformers is closely related to safety requirements. The correct grounding method and strict safety measures are key to ensuring the stable operation of transformers and safeguarding personal safety.