安科瑞 华楠

Abstract: the necessity of applying residual current relay in intelligent building is analyzed, the main functions, working principle, classification situation of ASJ residual current relay are introduced, and the principles and precautions in selecting residual current protection circuit breaker are indicated.

Keywords: ASJ residual current relay; intelligent building; application.

1. Background

The residual current relay is to detect the residual current and compare the residual current value with the reference value. When the residual current value exceeds the reference value, An electrical appliance that sends out a mechanical opening and closing signal. The residual current relay is usually composed of a combined residual current protection device with low voltage circuit breaker or low voltage contactor. It is mainly suitable for TT and TN system distribution lines with rated voltage of 50 Hz, and below. It can also provide indirect contact protection for personal electric shock, so it can be widely used in intelligent building 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

3.2 Technical Parameters

3.3 Typical Application Schematic

4.Examples of application of residual current relay in intelligent building

4.1Intelligent residential buildings and hotel rooms

The electric iron, hair dryer and electric kettle in residential and hotel have high frequency of use, which are prone to wire breakage and water splashing to socket, which seriously endanger personal safety and need to monitor leakage current and protect it. The residual current relay is installed in the intelligent residential building and hotel room, which can cut off the power supply and protect the personal safety in the case of leakage or electric shock.

4.2 Swimming Pool in Intelligent Building

Modern sports fields and hotels are mostly intelligent buildings with swimming pool. In order to ensure the swimming pool is clean, the general swimming pool is equipped with circulating water pump system. Swimming pool is a crowded place. In order to ensure the safety of personnel, the circulating water pump system of swimming pool should be equipped with residual current relay. Ensure timely tripping, cutting off power supply and protecting personal safety when leakage fault occurs in circulating water pump system.

4.3 Intelligent construction site

Intelligent construction sites are commonly used to bulk cement and concrete mixers, tower cranes and other construction machinery, hand drills, cutting machines and other mobile power tools, need to supply them temporary power. The general construction site environment is wet, the personnel is numerous, the structure is complex, the electric equipment is mostly mobile, and the distribution line is long and complex, easy to be damaged by the external force, it is easy to cause the leakage and endanger the safety of personnel. Therefore, the residual current relay with rated residual current about 30mA should be set up in the construction site.

5.Summary

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.

Bibliography

1、Solutions for enterprise micro-grid system