How to set relay protection

Relay protection is an important technical means to ensure the safe operation of electrical equipment in power system. It can quickly and accurately cut off the fault part when the power system fails or runs abnormally, prevent the accident from expanding and ensure the stability and safety of the power system. Therefore, setting relay protection devices scientifically and reasonably is of great significance for improving power supply reliability and reducing equipment damage.

First, the basic principles of relay protection

The setting of relay protection should follow the four basic principles of "selectivity, quickness, sensitivity and reliability":

1. Selectivity: It means that when a fault occurs, only the fault part is removed, so as not to affect the normal operation of the non-fault part as much as possible. This requires that the action range and time of relay should be reasonably coordinated.

2. Quick action: that is, the protection device should remove the fault as soon as possible to reduce the damage of the fault current to the equipment.

3. Sensitivity: The protection device should have sufficient response ability to all kinds of faults within the protected range, and it should be able to operate reliably even in the minimum operation mode.

4. Reliability: It means that the protection device does not refuse to move when it needs to move, and does not misoperate when it does not need to move.

Second, the main content of relay protection settings

1. Determine the scope of protection

Before setting up relay protection, it is necessary to make clear the equipment range protected by each protection device, such as generator, transformer, transmission line, motor, etc., and select the corresponding protection type and setting value accordingly.
　　. Choose the appropriate protection type

Common relay protection types include: overcurrent protection, differential protection, distance protection, directional protection, under-voltage protection, zero sequence current protection, etc. Different protection methods should be selected under different equipment and different operation modes.

3. Setting value calculation and coordination

Setting value refers to the threshold of starting action of protection device. When setting, short circuit calculation and load calculation should be carried out according to the maximum and minimum operation modes of the system, and parameters such as operating current, voltage and time should be set reasonably. At the same time, the time and setting value should be coordinated between the upper and lower protection to ensure selectivity.

4. Consider the change of operation mode
　　The operation mode of power system will change with the change of load, and the protection setting should adapt to different operating conditions to ensure correct operation in all modes.

5. Auxiliary protection and backup protection settings

On the basis of main protection, appropriate backup protection (such as near backup and far backup) should be set up to improve the reliability of the system.

Three, the common problems and countermeasures in relay protection settings

In the actual setting process, problems such as inaccurate setting value, misoperation, refusing action and improper protection coordination may be encountered. Therefore, the training and technical management of relay protection personnel should be strengthened, and the calibration and setting value of protection devices should be checked regularly. At the same time, the short-circuit current calculation and protection coordination analysis should be carried out by computer simulation software to improve the scientificity and accuracy of setting.

Fourth, summary

Relay protection setting is a highly technical and professional work, which directly affects the safe operation of power system. Only on the basis of deeply understanding the system structure, accurately grasping the equipment parameters and operating characteristics, combined with scientific setting methods and strict management measures, can the relay protection operate efficiently and reliably, and provide a solid guarantee for the stable operation of the power system.