The maximum residual current total protection can

  • Detail

The total residual current protection can only be used as indirect contact protection

for more than 20 years, China's residual current protection technology has experienced four stages: spontaneous development, correct guidance launched by the government, formulation of national standards and industrial standards to regulate product quality, and healthy development. The widespread use of residual current protectors has played an important role in reducing electric shock casualties, reducing low-voltage line losses, and protecting electrical equipment in rural areas

however, with the development of the national economy and the rapid growth of rural power load, under the condition that rural power management workers do not know much about the relevant national standards, in rural reconstruction and construction projects, high-sensitivity fast residual current protectors still occupy the dominant position of the total protection, resulting in poor reliability of power supply in rural areas, After the occurrence of electric shock casualties, power supply enterprises should invest a lot of energy and financial resources to deal with the serious consequences of such accidents

1 types of electric shock in low-voltage distribution system

electric shock in 380/220v low-voltage distribution system is divided into direct contact electric shock and indirect contact electric shock

(1) direct contact electric shock. Direct contact electric shock refers to the contact between people, livestock and electrified bodies. Direct contact is divided into three types: phase line to ground contact, phase line to another phase line contact, and phase line to zero line contact. The residual current operated protector does not protect the electric shock hazard caused by the second line in the protected line

(2) indirect contact electric shock. Indirect contact electric shock refers to the contact between people and livestock and the exposed conductive parts of the equipment or field that becomes live under fault conditions because the high-speed railway has been put into operation. Indirect contact electric shock can be divided into contact voltage electric shock and step voltage electric shock: ① contact voltage electric shock: refers to the electric shock accident that occurs when the insulation of electric equipment is damp and aging, and the shell is charged, and when people touch the shell of electric equipment, they form a contact voltage with the ground; ② Step voltage electric shock: refers to the electric shock caused by the potential difference between the feet of human and livestock within the electric field circle formed by taking the falling place as the center and 5m as the radius when the broken phase falls to the ground caused by typhoon and lightning strike

2 national standards and residual current protection functions at all levels

2.1 national standards

national standards related to residual current protection include:

(1) technical standards for production and certification: GB General requirements for residual current operated protectors

(2) installation and operation standard: GB leakage protector installation and operation (now revised to GB, to be released soon)

2.2 GB main content and scope of application

(1) the main function of residual current protector is to provide indirect contact protection for people with fatal danger of electric shock. The residual current protector with rated residual action current not exceeding 30mA can also be used as direct contact supplementary protection when other protections fail, but it cannot be used as the only direct contact protection

(2) prevent electrical fire caused by grounding current

(3) protect electrical equipment

2.3 GB and protection responsibilities at all levels

(1) in order to reduce the power failure range of personal electric shock and grounding fault cutting off the power supply, residual current protection should implement hierarchical protection with coordinated action current and action time. Classified protection is generally divided into two levels, which can also be divided into three levels

(2) general protection and intermediate protection only undertake indirect contact electric shock protection

(3) the residual current protector installed at the current end shall adopt the residual current protector with low sensitivity and time delay

(4) for end protection of direct contact protection, high sensitivity rapid action residual current protector should be selected. The rated residual action current shall not exceed 30mA, and the action time shall be less than 0.1s

3 why the total protection can only be used as indirect contact protection

3.1 the total protection cannot be realized 6 Set up 16 offices in key cities such as Shenyang, Changchun, Beijing, Guangzhou, Wenzhou, Shenzhen, Xi'an, Chengdu, Zhengzhou, Changsha, Taiyuan, Wuhan, etc. all direct contact protection within the protection scope

(1) according to the research results published by iec-tc64 (article 497), there is no residual current protector in the world that can distinguish between human electric shock and residual current based on its advantages and disadvantages. In the second half of 2002, in order to expand the market and attract users, some illegal manufacturers in the residual current protection industry vigorously publicized that their products can distinguish between live animal electrocution and residual current, deceived agricultural power managers, and seriously violated the implementation rules of the compulsory product certification of low-voltage electrical appliances. At the same time, they also joined the false propaganda without scientific basis and without the detection and verification of authoritative institutions behind the back of the certification authority, which we need to be vigilant, In case of going astray

(2) according to the action principle of residual current protection, the residual current of the protected line changes with the change of climate and electrical load, and its size and phase are random variables; When a person gets an electric shock, the size of the electric shock current is different from the environment where the person gets an electric shock (such as water or dry mud), the natural condition of the person is different (such as body shape, age, gender, whether to wear shoes when getting an electric shock, and what shoes to wear). The resistance of the human body changes in the range of 500 ~ 4000 Ω, so the electric shock current is also random. For this reason, the total protection can not be realized when the direct contact electric shock occurs, and the electric shock current can be protected within the range of 20 ~ 440ma. For example, due to the misleading of false advertisements, the certification authority did not seek truth from facts and concealed the fact that the product had a dead zone for a long time. There were more than 100 manufacturers copying such products in the country, which deceived many places in the country in the agricultural transformation. The use of this product in these places not only caused electric shock casualties, but also seriously affected the reliability of power supply and caused immeasurable losses

(3) from the analysis of the relationship between the human body escape current and the rated residual action current, it is assumed that the protector can achieve no dead zone in principle, but when the human body is in direct contact with electric shock, the electric shock current is greater than the escape current (according to the literature published by iec-tc64w69, the minimum escape current for men is 9ma, and the average escape current is 15mA; the minimum escape current for women is 6mA, and the average escape current is 12mA.) When it is less than the rated residual action current, the protector will refuse to operate and still cannot protect the direct contact electric shock

3.2 the rated residual operating current and power supply reliability are a pair of contradictions that cannot be solved.

those high-sensitivity fast protectors used for general protection, such as phase and amplitude leakage relays and pulse leakage devices, can protect part of direct contact electric shock because of the sudden variable principle, high sensitivity, and because of the sudden variable principle, it must be made into a fast type (action time), Therefore, the reliability of power supply is poor and there are many misoperations. After years of investigation and research, due to the use of all kinds of electrical equipment that are basically more than 1 ton (such as household appliances with single-phase motors, the starting of medium frequency, high frequency and frequency conversion equipment), low-voltage electricity has been seriously polluted, and these pollution sources cannot be eliminated within 0.2S, so the total protection of action time still continues to malfunction, seriously affecting the reliability of power supply. For this reason, the total protection has to use the low sensitivity time-delay protector as the indirect contact protection

4 conclusion

(1) what kind of products should be selected for residual current total protection has been clearly defined in GB and BG. The national certification and Accreditation Administration also expressly stipulated in April, 2003 that the original CCEE certificate of phase and amplitude discrimination leakage relay and pulse leakage device cannot be converted into 3C certificate, that is, it can not be reproduced. This kind of protection has also completed the historical mandate of a special period and will be phased out. In the final analysis, the newly installed general protection will not use this product anymore; Low sensitivity time-delay protector shall be selected

(2) the national standard defines the responsibility of general protection, but it does not give up the responsibility requirements of end protection for direct contact electric shock protection and ensuring the reliability of power supply. The revised gb13955 clearly stipulates that "the hierarchical protection of residual current protection devices should be based on load end protection, which is an effective technical measure for low-voltage distribution systems to ensure power supply reliability and prevent direct contact electric shock. End protection must be installed for household and end-of-line electrical equipment". Therefore, the functional departments of power supply enterprises should do a good job in the installation, operation and management of end protection. At the same time, in order to prevent the direct contact electric shock accident caused outdoors from entanglement with the general protection responsibility, all grass-roots power supply stations must regulate the temporary use of electricity according to the provisions of dl/t to prevent the occurrence of electric shock accidents

Copyright © 2011 JIN SHI