Generally speaking, leakage relays are electronic current-operated relays, mainly composed of the following components: zero-sequence current transformer, electronic circuit, test circuit and output relay. The working principle of the leakage relay is as follows: the zero-sequence transformer passes through the main line. When there is no leakage in the main line, the vector sum is equal to zero or very small.
However, if there is a leakage in the main line, the zero-sequence transformer can sense that the vector sum is unbalanced, and the current vector will also send a signal to the zero-sequence transformer and send the signal to the host for amplification. We can check whether the leakage current exceeds the set value. If the current exceeds the set value, we can send the test result to the executive agency for maintenance, etc. Another method is that if there is a leakage in the main line, the indicator light will light up, and the output relay will have a certain action and send a signal.
In the CPU of the leakage relay, advanced chips are used, and the detection of leakage signals is completed by the zero-sequence current transformer, which can convert the detected leakage current of the protected line into a millivolt-level AC voltage signal, and then pass it through signal rectification, amplification and filtering to obtain a DC voltage, cooperate with the corresponding control circuit to drive the execution circuit, and realize the control purpose of cutting off the power supply of the protected line. The implementation process is: signal detection-filtering-two-stage amplification-control circuit-drive execution circuit-cut off the power supply of the protected line.
The current transformer of this device uses high-performance permalloy as the magnetic material of the iron core to ensure that the output of the current transformer has good linearity within a certain range.
The factor that mainly affects the reliability of theleakage relay system is the odd multiple harmonic current of the line frequency. Therefore, this circuit uses a set of active low-pass filters. The filter mainly filters out odd harmonic AC components, and then performs AC-DC conversion processing to ensure the correct operation of the leakage relay.
This is the core component of this device, mainly including FLASHROM, RAM, TM2RX, A, D conversion, serial communication, etc. It is the central processing unit of the entire system, and its instruction fetching, judgment, and execution are all completed by it.
The digital display is used to display the leakage current of the line and the delay time for the system to trip, mainly composed of a digital driving circuit and an LED digital display, and the execution circuit is mainly composed of an optocoupler and a relay driving circuit.
The extended serial communication interface is adopted.
The human-machine interface circuit mainly completes the setting of the protection setting value and the system delay tripping time.
The power supply circuit of the leakage relay provides the working power supply for the single-chip system, including a group of isolation power supplies.