1. Selection of bay control unit
In order to enable the bay control unit to complete the relay protection task correctly, we should comprehensively consider the selection from several aspects such as device reliability, response time, maintenance and debugging, and additional functions when designing and selecting.
1.1 The choice of the reliability of the bay control unit
The signal input of the bay control unit is the same as that of the traditional relay protection. The voltage and current signals are introduced from the voltage transformer and current transformer, which are converted into the standard signal that meets the requirements of the protection device by the transmitter, and the low order is removed by the filter. With high-order harmonics and other interference signals, the analog quantity is converted into a digital signal by an A/D converter. The CPU performs calculations on the input digital signal and compares it with the set value to make a judgment, and then decides whether to alarm or trip.
In order to meet the reliability requirements of the device, the measurement and protection input signals of the device are processed and output by unrelated processing units in the device, so that the device can not only ensure the measurement accuracy, but also have sufficient margin in the case of the most serious failure. When the current is 20 times the normal value, the general engineering reliability requirements can be met without A/D overflow and saturation.
1.2 Selection of response time of bay control unit
The software workflow of the protection device is roughly as shown in the figure below: It can be seen from the figure that the response time of the protection device is closely related to the software used by the device and the electrical quantity calculation method, and users generally do not know it.
When designing and selecting models, we can only judge the pros and cons of the protection device from the three indicators of its calculation accuracy, response time and calculation amount. The calculation accuracy, calculation amount and response time of the device are contradictory to each other. The calculation accuracy is poor and the calculation amount is small, the response time is fast, and vice versa, the response time is slow. Generally speaking, the end user of the power grid determines that the calculation amount of the device should be more than 3 times, its calculation accuracy is higher than 0.2%, and its longest response time should be less than 30ms to meet the response time requirements of general engineering.
1.3 Selection of other functions of the bay control unit
There are a large number of integrated chips in the integrated protection device, and maintenance of the protection device requires high professional technical knowledge. When selecting models, we should try our best to choose protection devices with modular and universal hardware. By replacing the modules, the hardware failures of the protection devices can be eliminated and work efficiency can be improved. In addition, the protection device should have its own EPROM module, and the setting value of the protection device can be stored in the EPROM in digital form. The field staff can call the setting value at any time to debug the equipment without rewriting the data.
In order to cooperate with the entire project automation monitoring system, the protection device should have a communication function, can easily form a network through the data bus, and can transmit its information to the higher-level automation monitoring system after the protection device operates.