Leakage protection principle and application

Abstract: installation of leakage protection in low voltage distribution systems are electrical shock and most cost-effective measures or cause a fire due to leakage of electrical current to prevent damage. Based on the characteristics of leakage protection, combined with the practical application of common problems and solutions, the paper leakage protection of the important role of the working principle, the use of simple and precautions described and analyzed.

GFCI is an electrical safety device, widely used in low voltage distribution systems. With the continuous development of China's economic level, electrical safety issues has been growing attention. When the project is completed, an important seat leakage protection against electric shock and ground fault protection appliances, has been the focus of inspection. However, leakage protection in applications, often there are some mistakes and errors, improper use may damage the economy and personal safety.

1 kind of leakage protection .

1.1 leakage protection plug   leakage protection plug is zero sequence TA, leakage release and the composition of the main switch and load the insulating housing, leakage protection and manually with a pass off road features, it does not have overload and short circuit protection, these products are mainly used in electrical plugs wet environments, such as bathrooms installed in the plug of water heater or solar water heaters, electric heaters being used.

1.2 leakage protection socket   leakage protection socket is made or leakage circuit breaker and GFCI receptacle combination, so that outlet circuit connected devices with leakage protection. It is mainly used as power leakage protection requires a smaller load of mobile equipment, and household appliances.

1.3 leakage protection relays   leakage relays from zero sequence TA and relays, it has to detect and determine the function of a signal from the relay contacts, control circuit breakers, contactors cut circuit or the control signal element audible signal.

1.4 leakage protection circuit breaker   leakage circuit breaker is to install leakage protection circuit breaker on the basis of components constitute, in the protection with leakage, overload and short circuit protection .   leakage circuit breaker according to secondary leakage circuit breaker technology can be divided with two protection with 3 protection pole and three-pole earth leakage circuit breaker protection with a 4-pole four-pole earth leakage circuit breaker. According to the structure is divided into two kinds of electromagnetic and electronic. Due to leakage protection circuit breaker with leakage protection and also contains all the protection circuit breakers, it is most commonly used in low-voltage distribution system leakage protection.

2 leakage protection works       leakage protection from zero-sequence current transformer, leakage trip, tripping mechanism, the main switch. composed of five parts test buttons. TN-S to the ground by way of examples, the leakage protector installed in the line, the primary winding is connected to the grid lines, and the secondary coil of the leakage protection trip connection. When electrical equipment during normal operation, the line was balanced in the current state of the transformer in the current vector sum is zero. Because there is no residual current primary coil, it will not sense the secondary coil, leakage protection switching device is in a closed state operation. Leakage occurs when electrical equipment or electrical shock when someone is at the point of failure to produce shunt, secondary leakage current into the earth, return transformer neutral point, resulting in transformer current into and out of the imbalance, there will be the fault current at zero sequence current produced in flux toroidal transformer, when the current value of the current value of the hit action leakage protection defined, it will lead to the secondary side enough to force the trip coil induced voltage excitation, forcing the main switch tripped, cutting off power supply circuit.

. 3 leakage protection range of applications

3.1 Anti-personal direct contact should be installed operating current of 30mA leakage protection   leakage protection while operating current according to different levels, operating current is smaller, more sensitivity high. There are more commonly used operating current 300mA, 30mA, 100mA, such as the level of leakage protection. According to the International Electrotechnical Commission standard determined by the body when AC 50Hz current does not exceed 30mA, the body does not occur in ventricular fibrillation and death, it is the degree of moisture and the body, not directly related to the level of contact voltage. Therefore, the International Electrotechnical personal standards in all anti-shock provisions are specified using no more than 30mA of operating current leakage protection. Accordingly in humid environments such as bathrooms and other places of electric shock hazards can be fitted with a large operating current of 30mA leakage protection to anti-personal electric shock. 10mA leakage protection and leakage protection 30mA when the anti-shock effect the same person, you can make and death from ventricular fibrillation. Due to leakage protection 10mA complex production process, expensive, and electrical equipment such as during some special environmental work, the normal leakage current is large, easily lead to malfunction. The consequences of frequent power outages often malfunction of electrical leakage protection protector shorted or removed, so that the ground fault protection circuit period, resulting in dangerous consequences. Therefore, personal accident prevention action shock call Tibet installed leakage current of 30mA protection.

3.2 electrical fire protection   distribution line when a short circuit fault often burst, and in the majority of short-circuit ground fault is unidirectional, that phase line and the earth, electrical equipment enclosure, short metal structures between the pipes. Both ground-fault accident caused by personal electric shock, but also phase short circuit, one-way likely to cause a short circuit electrical fire. "Low-voltage power distribution design specification" provides distribution lines should have ground fault protection appliances. When arcing ground fault on fire, because the arc current, circuit breakers, fuses are often not cut off the power before the fire, and leakage protection movement is able to immediately cut off the power. Therefore, in addition to the hand-held, install leakage protection 30mA instantaneous action on the mobile device terminal line, it should also install leakage protection circuit breaker function with a little delay in the movies always trunk, it is primarily used to prevent ground electrical fires and line failure caused the accident on the ground potential rise.

3.3 must install leakage protection devices and place

a. Handheld and mobile electrical equipment should be installed with high sensitivity 30mA leakage protection. Daily life and production, often using some hand-held and portable electrical equipment, such as plant maintenance welder frequently used. Risk of electric shock and mobile hand-held electrical equipment max. This is because these devices are often mobile, easily damaged insulation shell touch the ground fault occurs. The operator in the event of an electric shock, unable to shake off. Whether or not fitted with 30mA leakage protection, when stationary equipment electrical shock can be people standing instability fall, but it will not happen due to ventricular fibrillation and shock death. Therefore, handheld and mobile equipment must be equipped with 30mA instantaneous action leakage protection.

b. Installed in the wet, corrosion and other harsh environment places electrical equipment.

c. Construction site construction machinery electrical equipment, temporary power and repair the power supply.

d. Public and civil outlet circuit.

3.4 Alarm leakage protection application & nbsp; For some a load, the power in the event of leakage cut off its power supply, it will cause an accident or major economic loss. For this type of load, shall be fitted with an alarm leakage protection, only an alarm signal leakage, do not act on the power off. & nbsp; need to install alarm leakage protection devices and places have:

a. Channel lighting in public places.

b. Elevators and fire class equipment.

c. For power theft and alarm.

d. Other special equipment and premises are not allowed blackouts.

3.5 do not need to install leakage protection device

a. Use safety voltage supply electrical equipment.

b. Under normal environmental conditions with a double or reinforced insulation of electrical equipment.

c. Use an isolation transformer powered electrical equipment.

d. Taking local equipotential ungrounded electrical equipment connected to the security measures in place to use.

e. In the absence of indirect contact electric shock electrical equipment in hazardous locations.

. 4 Accident Analysis & nbsp; In the following cases, even if the air-leakage protection, electric shock may still occur:

a. People simultaneously hit the line and neutral line.

b. People standing height, while touching the line and the wall, this time may be less than the current flowing through the body leakage current, but still may give rise to spasm, causing falls and other secondary damage.

c. In the TN system, if the PE line short circuit, then the insulation of electrical equipment is damaged, such as the use of leakage protection is not to prevent direct electrical shock, the leakage protection may not operate, PE line charged, resulting in personal injury.

d. In TN systems, installation of protection and are not fitted with leakage protection devices, such as a shared PE line, when not fitted with leakage protection of electrical equipment insulation damage while live shell, install leakage protection device housing also little, it may cause personal injury.

5 Conclusion .

proper selection and installation of leakage protection is to prevent personal electric shock and electrical fires effective way, in the design and construction of electrical construction as long as a reasonable choice and installed correctly, to protect personal safety and to prevent damage to the equipment, as well as the prevention of fire will have a significant effect. However, due to the limitations of leakage protection itself, we can not put this as a protective measure to protect foolproof.