What should be paid attention to when using the leakage relay
The matters needing attention when using the leakage relay are the following:
(1) Leakage relay is suitable for low-voltage power distribution system where the neutral point of the power supply is directly grounded or grounded through resistance and reactance. For systems where the neutral point of the power supply is not grounded, it is not appropriate to use a leakage relay. Because the latter cannot constitute a leakage electrical circuit, even if a ground fault occurs and the rated operating current of the leakage relay is greater than or equal to this, the protector cannot operate in time to cut off the power circuit; or rely on the human body to connect the fault point to form a leakage electrical circuit , Promote the leakage relay action, cut off the power circuit. However, it is still not safe for the human body. Obviously, it must have the conditions of the grounding device. When the electrical equipment leaks and the leakage current reaches the operating current, it can immediately trip in 0.1 seconds and cut off the main circuit of the power supply.
(2) The working neutral line N of the earth leakage relay protection line should pass the zero-sequence current transformer. Otherwise, after switching on, an unbalanced current will cause the leakage relay to malfunction.
(3) The zero protection line (PE) is not allowed to pass the zero sequence current transformer. When the protective circuit (PE) passes through the zero-sequence current transformer, the leakage current passes through the PE protection line and then passes through the zero-sequence current transformer, which causes the current to cancel, and the leakage current value cannot be detected on the transformer. When a fault occurs, the leakage relay does not work, and it can not provide protection.
(4) The working neutral line of the control circuit cannot be repeatedly grounded. On the one hand, during repeated grounding, under normal operating conditions, a part of the operating current returns to the neutral point of the power supply through repeated grounding, and an unbalanced current will appear in the current transformer. When the unbalanced current reaches a certain value, the leakage relay will malfunction. On the other hand, when the leakage occurs due to a fault, the leakage current on the protection line may also pass through the individual line of the current transformer and return to the neutral point of the power supply, which cancels The leakage current of the transformer causes the protector to refuse to operate.
(5) The working neutral line N and the protective line (PE) behind the leakage relay cannot be combined into one. If the two are combined into one, when a leakage fault occurs or the human body is shocked, the leakage current flows back through the current transformer, and the result is similar to situation (3), causing the leakage relay to refuse to operate.
(6) The wires between the protected electrical equipment and the leakage relay cannot touch each other. If there is line-to-line collision or zero-to-line crossover, the zero-sequence balance current value will be immediately destroyed, causing the leakage relay to malfunction. In addition, the protected electrical equipment can only be installed in parallel behind the leakage relay, and the wiring must be correct It is also forbidden to connect electrical equipment to the connection point of the experimental button.