This project is located in Maldives. The purpose of the residual current relay installed is to detect the residual current and compare the residual current value with the base value. When the residual current value exceeds the base value, it will send out a mechanical on-off signal (to make the mechanical switch tripped or the acousto-optic alarm device send out an alarm).Residual current relay usually with low voltage circuit breaker or low voltage contactor, etc combined residual current protection device, mainly applied to ac 50 hz, rated voltage 400 v and below the TT and TN system distribution circuit, used to ground fault protection electric circuit, prevent equipment damage caused by ground fault current and electrical fire accident, also can be used to provide indirect contact to person get an electric shock risk protection, and therefore is widely used in low voltage power supply and distribution system.
2.Main uses of residual current relay
2.1 Protection of Indirect Contact Electric Shock
The measure of indirect contact electric shock protection is to automatically cut off the power supply. GB 13955" the protection of indirect contact electric shock accident "stipulates :" the main measure of indirect contact electric shock accident protection is to adopt the protection mode of automatically cutting off the power supply to prevent the damage accident caused by the insulation damage of electrical equipment. When the circuit insulation damage caused by grounding fault. When the fault current value is less than the operating current value of the over-current protection device, the residual current protection device shall be installed ." According to the research, the safe value of contact voltage is 50V. For personal safety, when insulation failure occurs in any part of the electrical device, once the contact voltage exceeds 50V, it is necessary to automatically cut off the fault part of the power supply within the specified time. The over-current protection device is limited by the electrical circuit and equipment and its own action value, and can not automatically cut off the power supply. The residual current protection device is not affected by the load current and can be used in conjunction with the over-current protection device for indirect contact electric shock protection.
2.2 Ground fault protection
Grounding is the contact between a live conductor and the earth, a grounded metal shell or a component connected to the ground. Its failure may lead to personal electric shock casualties and equipment damage, and may cause electrical fire in serious cases. Ground fault protection used to be protected by over-current protection device. When the grounding fault current is greater than the fixed value of the over-current protection device, the fault circuit is cut off by the over-current protection device.
In TT system, the line with larger rated current and longer distribution line, grounding fault of live conductor, unsafe metallic grounding fault and arc grounding fault in TN system may occur that the grounding fault current is less than the setting current of over-current protection action, and the over-current protection device does not act. Residual current protection device, or circuit breaker with ground fault protection, can reliably carry out ground fault protection.
2.3 Electrical fire protection
Electrical fire is usually caused by electrical short circuit, which includes metal short circuit and arc short circuit. The former is a short circuit between live conductors (such as between phases, between phases and N lines). The fault current is calculated in kilo ampere. High temperature is easy to cause insulation oxidation and spontaneous combustion.
Although the fire hazard is great, it can be protected by circuit breakers and fuses with short circuit protection, and the power supply is cut off by instantaneous action of circuit breaker to avoid fire. The latter is a live conductor short circuit to the ground, mostly arc as the path, although the fault current is small, but on the one hand, the arc lasts for a long time, the local temperature is high, it is easy to ignite the surrounding combustible material and cause fire. Therefore, the fire hazard caused by arc short circuit is much greater than that of metal short circuit. The circuit breaker with residual current action protection function can cut off the support circuit without the operation of the over-current protection device to prevent the electrical fire caused by the arc short circuit.
3.ASJ Series of Residual Current Relay
3.1 Model & Function
Acrel ASJ series of residual current relays have been applied in many occasions, such as industry, civil, subway, intelligent building and so on, which has played a good protective effect and is worth promotional use.