Abstract: insulation coordination is an important issue related to the safety of electrical equipment products, and has always been paid attention to from all aspects. Insulation coordination was first used in high voltage electrical products. In China, the accident caused by insulation system accounts for 50% to 60% of the electric products in China. It is only two years since the concept of insulation coordination is formally quoted in low voltage switchgear and control equipment. Therefore, it is a more important problem to deal with and solve the insulation coordination problem in the product correctly, and enough attention should be paid to it.
Key words: insulation and insulation materials of low voltage switchgear
0 Introduction
The low voltage switchgear is responsible for the control, protection, measurement, conversion and distribution of electric energy in the low voltage power supply system. As the low-voltage switchgear goes deep into the production site, public place, residential and other places, it can be said that all places where electrical equipment is used should be equipped with low-voltage equipment. About 80% of the power energy in China is supplied through low-voltage switchgear. The development of low-voltage switchgear is derived from material industry, low-voltage electrical appliances, processing technology and equipment, infrastructure construction and human beings The living standard of the people, so the level of low voltage switchgear reflects the economic strength, science and technology and living standard of a country from one side.
1. Basic principle of insulation coordination
Insulation coordination means that the electrical insulation characteristics of the equipment are selected according to the service conditions and surrounding environment of the equipment. Only when the design of the equipment is based on the strength of the function it bears in its expected life, can the insulation coordination be realized. The problem of insulation coordination not only comes from the outside of the equipment but also from the equipment itself. It is a problem involving various factors, which should be considered comprehensively. The main points are divided into three parts: one is the use conditions of the equipment; the other is the use environment of the equipment; the third is the selection of insulation materials.
1.1 the use conditions of equipment the use conditions of equipment mainly refer to the voltage, electric field and frequency used by the equipment.
1.1.1 relationship between insulation coordination and voltage. In considering the relationship between insulation coordination and voltage, the voltage that may occur in the system, voltage generated by equipment, required continuous voltage operation level, and the danger of personal safety and accident shall be considered.
① Classification of voltage and overvoltage, waveform.
A. continuous power frequency voltage, with constant R, m, s voltage;
B. temporary overvoltage, power frequency overvoltage for a long time;
C transient overvoltage, over-voltage for a few milliseconds or less, is usually high damping oscillation or non oscillation.
——Over voltage in the front of slow wave: a transient overvoltage, usually in one direction, reaching the peak value between 20 μ stp5000 μ s, and the wave tail duration T2 ≤ 20ms.
——Fast wave front overvoltage: a transient overvoltage, usually in one direction, reaching peak value of 0.1 μ s T120 μ s, wave tail duration T2 ≤ 300 μ s.
——Steep wave front overvoltage: a transient overvoltage, usually in one direction, reaching peak value at a time of TF ≤ 0.1 μ s, total duration of 3MS, and with superimposed oscillation, with an oscillation frequency of 30kHz of 100MHz.
D. combined (temporary, slow forward, fast, steep) overvoltage.
According to the above overvoltage type, the standard voltage waveform can be described.
② The relationship between long-term AC or DC voltage and insulation coordination should consider rated voltage, rated insulation voltage and actual working voltage. In the normal and long-term operation of the system, the rated insulation voltage and actual working voltage should be considered. In addition to meeting the requirements of the standard, we should pay attention to the actual situation of China's power grid. In the current situation that the quality of power grid is not high in China, when designing products, the actual possible working voltage is more important for insulation coordination.
③ The relationship between transient overvoltage and insulation coordination is related to the condition of controlled over-voltage in the electrical system. There are many kinds of overvoltage in the system and equipment. The influence of overvoltage should be considered comprehensively. In low voltage power system, overvoltage may be affected by various variable factors. Therefore, the overvoltage in the system is evaluated by statistical method, reflecting the concept of probability, and it can be determined whether protection is needed by probability statistics Control.
1.1.2 the over-voltage category of equipment shall be divided into IV class directly from the overvoltage category of low-voltage power grid power supply equipment according to the long-term continuous voltage operation level required by the equipment use conditions. The equipment of overvoltage category IV is the equipment used at the power supply end of the distribution device, such as ammeter and current protection equipment of the previous stage. The equipment of overvoltage class III is the task of installation in the distribution device, and the safety and applicability of the equipment must meet the special requirements, such as the switchgear in the distribution device. The equipment of overvoltage class II is the energy consuming equipment powered by distribution device, such as the load for home use and similar purposes. The equipment of overvoltage class I is connected to the equipment which limits the transient overvoltage to a very low level, such as electronic circuit with over-voltage protection. For equipment not directly supplied by low voltage grid, the maximum voltage and serious combination of various situations that may occur in system equipment must be taken into account.
返回顶部