Chinese Standards for Relay Protection
Relay protection plays a crucial role in ensuring the reliable operation of electrical power transmission and distribution systems. It is responsible for promptly detecting and isolating faults, thereby preventing damage to equipment and ensuring the safe and stable operation of the entire power system. In China, the development and implementation of relay protection systems are governed by a set of Chinese standards and regulations that are designed to ensure the effectiveness and reliability of protection schemes.
Chinese standards for relay protection are developed and published by the China Electrical Power Research Institute (CEPRI) and the State Grid Corporation of China (SGCC). These standards are aligned with the International Electrotechnical Commission (IEC) standards to ensure compatibility and interoperability with global practices. The key relay protection standards in China include the DL/T 526-2012 “Relay Protection and Automatic Equipment Common Specifications”, which provides a comprehensive overview of the general requirements, principles, and practices related to relay protection.
DL/T 526-2012 outlines the fundamental principles of relay protection and offers guidelines for selecting and setting up protection schemes in power systems. It defines the different types of protection functions, such as overcurrent, distance, differential, and pilot protection, and provides specific criteria for their application and coordination. The standard also addresses issues like communication interfaces, testing and commissioning procedures, and maintenance requirements, ensuring that relay protection systems are designed, installed, operated, and maintained in a standardized and reliable manner.
To illustrate the practical application of relay protection standards in China, let’s consider a numerical example. Assume we have a 220 kV transmission line that requires protection against faults such as short circuits or line-to-line faults. We will focus on the application of distance protection, which is widely used for transmission line protection.
In this example, the relay setting calculation will be based on the following parameters:
- Line impedance: 50 + j100 Ω
- Length of the transmission line: 50 km
- Nominal voltage: 220 kV
- Fault resistance: 0 Ω
The relay settings for distance protection can be calculated using the following formula:
Let’s assume we want to set the relay to operate for a fault at a distance of 40 km from the relay location. Using the formula, the relay setting would be:
The relay will be set to operate when the voltage at its location drops below 176 kV, indicating that a fault has occurred within the protected zone.
In practice, relay protection schemes in China often employ multiple relays in a coordinated manner to ensure reliable and selective fault detection and isolation. These schemes may involve combinations of overcurrent, distance, and differential protection relays, along with communication channels for sharing data and coordinating actions between relays.
In conclusion, Chinese standards for relay protection play a vital role in ensuring the reliability and safety of electrical power transmission and distribution systems. These standards provide guidelines for the application, selection, and coordination of protection schemes, ensuring the effective detection and isolation of faults. By adhering to these standards, power system operators in China can minimize the impact of faults and enhance the overall stability and reliability of the grid.