I ² t overcurrent protection technology of SSPC

Due to the inverse time characteristic of the overload capacity of the load, protective components in the distribution system must implement inverse time overcurrent protection for the load. As a traditional protective component used in power distribution systems, circuit breakers have a mechanical contact structure with high insertion resistance, manual reset required, short lifespan, large size requiring installation space, difficult to adjust protection points and protection time, and electromagnetic interference caused by arcing when contacts are disconnected, which is no longer suitable for the needs of the new generation of power distribution systems. SSPC adopts intelligent protection technology, which is divided into software I ² t overcurrent protection and hardware overcurrent protection. Overcurrent protection is based on inverse time characteristic protection, which can set protection points and protection times through the bus, and can be reset through the bus and signal lines.

The overcurrent protection function of SSPC is based on current acquisition and software algorithms. Current acquisition can not only collect the actual current size of each load, but also provide data sources for SSPC's overcurrent protection algorithm. Based on current collection data, the inverse time characteristic protection algorithm is implemented through software design, and the protection reference point and overcurrent protection curve are set online by connecting to the upper computer through the CAN bus. Circuit breakers are familiar to many engineering designers. In software, overcurrent protection algorithms are implemented by simulating the operation of circuit breakers. The following is a detailed description of the software algorithm. To simplify the algorithm, it is assumed that the ambient temperature is a constant value. Set as the conduction resistance of the circuit breaker, when current flows through the circuit breaker, a certain amount of heat accumulation will be generated on the circuit breaker.

For different users, the required inverse time characteristic is different, and the corresponding overcurrent protection curve needs to be adjusted according to the different load characteristics. Based on this algorithm, SSPC has implemented 8 overcurrent protection curves. The overload protection time corresponding to each curve is shown in Table 2. The protection maintenance delay time is a function of the current, and this characteristic curve is a collection of countless "points". The five test points specified in the parameters are included in the "overcurrent maintenance trip curve" and are part of this curve, not all requirements of the overcurrent protection curve. SSPC can select suitable curves according to different loads, which is beneficial for the normal operation of loads and distribution systems.