Low-voltage switchgear insulated with the problem - low voltage, complete sets of equipment, switching equipment - net electrical industry

Sub-section 17D Technical Committee drafted entitled "to IEC439 complement one on the insulation coordination of the requirements" of technical documents, the issue formally with the introduction of insulation to low-voltage switchgear and control equipment. On the current situation in our country, the high, low-voltage electrical products, equipment, insulation coordination is still a major problem, and because of low voltage switchgear and control equipment with a formal reference to the concept of insulation, only the last two years to do. Therefore, the correct address and solve the problem with insulation products, is a more important issue.

Key words: low-voltage switchgear insulated with insulation material 1. Low-voltage switchgear insulated with issues raised Insulation coordination problem is an electrical equipment products related to the important issue of security has always been the attention from all sides. The first application of insulation coordination in high-voltage electrical products. In 1987, the International Electrotechnical Commission (IEC) Technical Committee on the drafting of sub-section 17D called "supplementary one on IEC439 requirements on insulation coordination," technical paper, insulation coordination problem formally introduced to the low-voltage switchgear and control equipment. On the current situation in our country, the high, low-voltage electrical products, equipment, insulation coordination is still a major problem, there are statistics, China's electronic products, due to insulation system caused 50% of incidents -60%, and because of low voltage switchgear and control equipment insulated with a formal reference to the concept, but the things the past two years. Therefore, the correct address and solve the problem with insulation products, is a more important issue.

2. The basic principles of insulation coordination Insulation coordination means that under the conditions of use of equipment and environment to select the device electrical insulating properties, and only in the equipment design is based on their expectations of life in the role of exposure intensity, insulation coordination can be achieved. Insulation problems with equipment not only from outside but also from the device itself, is a matter of various factors, the question needs to be taken into account, the points are divided into three parts: First, use of equipment; Second, the use of equipment environment The third is the selection of insulation materials.

(A) use of equipment Equipment refers to equipment used primarily use the voltage, electric field and frequency.

1. Insulation coordination and voltage. In considering the insulation coordination of relations with the voltage, the system should consider the possible voltage, the voltage produced by the device to require continuous voltage operation levels, and personal safety, accident risk.

1 classification of voltage and over-voltage waveform. A) continuous frequency voltage, with constant r, m, s voltage B) a temporary over-voltage, long duration power frequency overvoltage C) transient over-voltage, the duration of a few milliseconds or less over-voltage, usually high oscillation or oscillation damping.

? Slow wave-front overvoltage: A transient voltage is usually a one-way, peak time was 20 s <Tp <5000 s between the wave tail duration T2 20ms.

? Fast wave-front overvoltage: A transient voltage is usually a one-way, peak time is 0.1 s <T1 <20 s, wave tail duration T2 300 s.

? Steep wave-front overvoltage: A transient voltage is usually a one-way, peak time for Tf 0.1 s, the total duration of <3ms, and with a superimposed oscillation, the oscillation frequency to 30kHz <f <100MHz between.

D) joint (for the time being, before the slow wave, fast wave-front, steep wave front) over-voltage.

Voltage according to the above types, can be described by a standard voltage waveform. 2 long-term AC or DC voltage and insulation coordination of relations, to consider the rated voltage, rated insulation voltage, the actual operating voltage. In the system normal, long-running process, the main consideration Rated insulation voltage and the actual operating voltage, which in addition to the standard requirements, but also pay attention to consider the actual situation of China's power grid. The quality of our network is not yet in the present case of a high design products for insulation coordination, the actual operating voltage may be more important.

3 transient over voltage and insulation coordination of relations, which was charged with the electrical system overvoltage conditions. In the systems and equipment, there are many forms of over-voltage, over-voltage to fully consider all effects of the low voltage power systems, over-voltage may be subject to a variety of variable factors, so the system in the over-voltage is assessed by statistical methods, reflects a concept of probability, probability and statistics methods can be adopted to determine the need for protection and control.

2. Equipment Overvoltage category According to the use of equipment condition, level of long-term sustained voltage operation, low voltage power supply directly from the device over-voltage category is divided into . Overvoltage category grade equipment is used in power distribution equipment end equipment such as meters and pre-current protection devices. Overvoltage category grade equipment is installed in the power distribution device in the task, and the use of equipment must meet safety and applicability of the special requirements, such as power distribution equipment in the switching equipment. Overvoltage category -class equipment is powered by the energy-consuming equipment distribution equipment, such as household and similar loads. Overvoltage category level device is connected to limit the transient over-voltage very low level of equipment such as electronic circuits with overvoltage protection. For non-low-voltage power supply directly from the device, the system must take into account the maximum possible voltage equipment and various situations of serious composition.

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