Analysis on the installation and operation of the

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Installation and action cause analysis of leakage protection device

class I mobile electrical equipment and hand-held electric tools with metal shell, electrical equipment installed in harsh places such as damp or strong corrosion, electrical construction machinery and equipment at construction sites, temporary electrical equipment, sockets in guest rooms, sockets in civil buildings with high risk of electric shock, underwater lighting equipment in swimming pools or baths The power supply lines and electrical equipment installed in the water, as well as the electrical and medical equipment in the hospital that directly contacts the human body (except the chest surgery room), should be installed with leakage protection devices. The protection type and installation method of leakage protection device should be compatible with the environmental conditions and service conditions of electrical equipment

for the channel lighting power supply and emergency lighting power supply in public places, fire-fighting elevators and electrical equipment to ensure the safety of public places, power supply for fire-fighting equipment (such as fire alarm device, fire water pump, fire-fighting channel lighting, etc.), power supply for anti-theft alarm, and other places where sudden power failure is not allowed If the lifting guide wheel is not adjusted correctly or the power supply of the electrical device is cut off immediately in case of leakage, it will cause accidents or major economic losses. In these cases, a leakage alarm device that does not cut off the power supply should be installed

from the perspective of preventing electric shock, electrical equipment powered by safe voltage, electrical equipment with double insulation or reinforced insulation structure used under general environmental conditions, electrical equipment powered by isolation transformer, electrical equipment used in places where ungrounded local equipotential bonding measures are adopted, and other electrical equipment without leakage risk and electric shock risk may not be installed with leakage protection devices

the leakage current of electrical lines and equipment equipped with leakage protection devices must be controlled within the allowable range. The rated non operating current of the selected leakage protection device shall not be less than 2 times the maximum value of the normal leakage current of the electrical circuit and equipment. When the leakage current of the electrical circuit or equipment is greater than the allowable value, the electrical circuit or equipment with good insulation must be replaced. When electrical equipment is equipped with high "When China is taking building energy conservation as a leakage protection device that saves energy and reduces the sensitivity of urban air pollution, the grounding resistance of the separate grounding device of electrical equipment can be appropriately relaxed, but the expected contact voltage should be limited within the allowable range. The insulation resistance of the motor and other electrical equipment installed with leakage protection device should not be less than 0.5m Ω during normal operation.

before installing leakage protection device, it should be carefully checked." Whether the shell, nameplate, wiring terminal, test button, certificate of conformity, etc. are intact. The insulation resistance of indoor and outdoor wiring of circuit breaker with residual current action protection installed on the incoming line shall not be less than 0.5m Ω in sunny days and 0.08m Ω in rainy days. The working grounding resistance of the neutral point at the low-voltage side of the distribution transformer should generally not be greater than 4 Ω, but when the capacity of the distribution transformer is not greater than 100kVA, the grounding resistance may not be greater than 10 Ω. Insulation resistance and grounding resistance are two regulations that cannot be ignored to ensure the safe operation of distribution system and whether the protector can act correctly

the leakage protection device used to prevent electric shock accidents can only be used as additional protection. When installing leakage protection devices, the original safety protection measures shall not be canceled or abandoned. When installing the leakage switch with short-circuit protection, it must ensure that there is enough arcing distance in the direction of arc discharge. The leakage protection device should not be installed in the position with large mechanical vibration or strong alternating magnetic field. When installing leakage protection devices, the hazards of water, dust and other factors should be considered, and necessary protective measures should be taken

2 wiring of leakage protection device

wiring of leakage protection device must be correct. Wrong wiring may lead to the malfunction of the leakage protection device, and may also lead to the failure of the leakage protection device. Before wiring, the input and output terminals, phase lines and zero lines of the leakage protection device shall be distinguished, and reverse connection or wrong connection is not allowed. When the input and output terminals are connected incorrectly, the electronic circuit of the electronic leakage protection device may not work normally because there is no power supply

the external connection of the control circuit of the combined leakage protection device should use copper conductor, whose cross-sectional area should not be less than 1.5mm2, and the connecting line should not be too long

the line on the load side of the leakage protection device must remain independent, that is, the line on the load side (including phase line and working zero line) must not be connected with the grounding device, the protection zero line, or other electrical circuits. In the protective neutral line, the working zero line shall be separated; The working zero line must pass through the protector, and the protective zero line must not pass through the protector, or the zero line on the load side of the protective device can only be the working zero line, not the protective zero line

it should be pointed out that the protective line of the equipment behind the leakage protector should not be connected to the zero line behind the protector. Otherwise, when the equipment leaks electricity, the leakage flows through the protector and returns, and the protector refuses to act

the protector is installed together with the knife switch. According to whether the power incoming line enters the protector first or the knife switch first, there are generally two connection modes. When the incoming line enters the knife switch first, passes through the phase line and neutral line fuse in the knife switch, and then connects to the protector, it ignores that after the neutral line fuse in the knife switch in front of the protector is fused, the protector "its own circuit" will lose its working power rdquo; Source, but not action. At this time, if the phase line fuse is not fused, although all kinds of electrical appliances stop working, the lines below the knife switch are still charged, forming a "false" power failure. When the user uses electrical appliances or checks the "false" power failure, the protector will easily suffer from electric shock due to power failure

in some areas, fuses are widely used for short-circuit protection, and only the neutral fuse is often blown. As the end protection, the household protector fails to act, which not only has serious potential safety hazards, but also makes the main protector or intermediate protector act beyond the level, causing a large area of power failure and causing large economic losses. In order to make the protector play its due role, the following suggestions are made:

2.1 if the installation site, environment and other conditions are limited, or multiple households share a knife switch, and the incoming end of the household protector can only be taken from the outgoing end of the knife switch, the neutral wire fuse in the knife switch must be removed, and the neutral wire fuse must be replaced with wires of the same specification

2.2 the installation method that the incoming line enters the protector first and then the knife switch should be adopted. This method can prevent the failure of the protector to operate after the fuse of the neutral line is fused. If the "false" power failure often occurs, the fuse of the neutral line should also be connected with a conductor according to the technical requirements that the fuse of the neutral line is not allowed to be installed

2.3 conditional users do not need to use knife switches, but should choose circuit breakers with leakage protection, overcurrent (short circuit) protection, overvoltage protection and three in one

3 Determination of the action value of the protector

first measure the leakage current in the low-voltage network. The test steps are as follows: first disconnect the grounding wire of the neutral point of the distribution transformer, string a Ma meter with small internal resistance between the N line and the PE line, first send out a shunt, and the other shunts are disabled. The measured unbalanced leakage current is the leakage current of this shunt, With this method, the leakage current of other branches and the total leakage current of low-voltage network are measured. It should be noted that since the insulation resistance of low-voltage network changes greatly under the influence of climate (refers to the change within a year), the field measured value should be corrected before it can be used as the action current value, that is:

I △ n=k × I。

i △ n - action current value of residual current action main protector, Ma

io - unbalanced leakage current measured on site, Ma

k - seasonal correction coefficient, measured in non rainy seasons, K is taken as 3.0, measured in rainy seasons, K is taken as 1.5

although the action current value determined in this way can avoid the maloperation of the protector, it reduces the protection effect. The best way is to choose the protector with adjustable action current value, that is, in the non rainy season, reduce the action current value, and in the rainy season, increase the action current value. In this way, the determination of the action current value should be: the measured unbalanced leakage current in the non rainy season and the rainy season should be multiplied by a coefficient of 1.5 respectively, It is the actual action value of the protector in non rainy seasons and rainy seasons. In this way, the set value will reduce the consequences of electric shock

in order to avoid frequent maloperation of the main protector and have a greater protection function against direct contact electric shock on the network, its action current should be as small as possible under the condition of avoiding, otherwise it will also affect the cement strength and the result of normal leakage current. Then what is the allowable maximum leakage current of the low-voltage power network? This should be considered from the actual situation of the low-voltage network in China, and also take into account the safety of personal and equipment, It is clearly stipulated in relevant regulations that the leakage current of low-voltage power installed with residual current action general protection shall not be greater than 50% of the rated residual current action current of the protector

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