What is a three-level distribution of two levels of protection one, one box, one brake, one leak

Update date:2017-10-28 Source:MAXGE


Three Phase Metal Box

Level 3 distribution: equipped with total distribution box, distribution box, switch box, three standard electric boxes. The switch box shall be in line with one machine, one box, one brake and one leak. All kinds of electrical appliances in the three kinds of electric boxes shall be qualified products;

Three Phase Metal Box

Two levels of protection: select the total distribution box and the leakage protector in the switch box that meet the capacity requirement and quality.

This is conducive to the maintenance of the on-site electricalsystem and the construction safety, which is also an embodiment of the standardization management and civilized construction in the field. Therefore, it is very important to make reasonable setting for "three level distribution, two level protection". First you have to understand what a three-phase four-wire power supply circuit is: three-phase four-wire system means three wires (U, V, W) in three-phase ac power supply, a zero line (N). The voltage between each two lines is 380V, known as line voltage, and the voltage of any line and zero line is 220V, which is called phase voltage. Therefore, the bulb of 220V, regardless of the power, should be connected to the phase voltage, that is, one connecting the zero line, the other one to connect a fire line.

Three Phase Metal Box

In low voltage power supply system, most using three phase four wire system power supply, because this way can provide two kinds of different voltage - line voltage (380 v) and phase voltage (220 v), can adapt to the needs of different users. In three phase four wire system, if is completely symmetrical three-phase load (the nature of the impedance and the same size, the impedance triangles are congruent triangles), the zero line dispensable, three-phase asynchronous motor, for example, three phase winding is completely symmetrical, connected into a star, even in the absence of the zero line, also can get three-phase symmetrical three-phase winding voltage, electric function work as usual. But for the residential buildings, schools, institutions and shopping malls, the zero line plays an important role. Although these places in the design, installation, power supply circuit is the balance of two phase load close to as far as possible, but this kind of balance is relative and imbalance is absolute, and are changing every moment. In this case, if the zero line is interrupted, the neutral voltage of the three-phase load will be shifted. 

The direct result of the neutral point potential displacement is the three-phase voltage imbalance, some phase voltage may be considerably more than rated voltage (in extreme cases will be close to 380 v), light burning appliances, or cause major accidents such as fire; And some phase voltage is much lower than the appliance of rated voltage (in extreme cases can close to 0 v), light electrical appliances will not work, or will be burned electrical appliances (because the voltage is too low, air conditioners, refrigerators and washing machines and other equipment of the motor can't start, after a long time will be destroyed). Since the three-phase load is random, the voltage imbalance is also random.

 when the neutral point potential displacement occurred this problem, many students even some electricians can't understand, and the theoretical calculation involves deep electrician foundation knowledge, such as the electromotive force and the impedance of the plural representation and the complex arithmetic, etc.), especially when the load is not pure resistance, calculation is quite tedious, students can also be difficult to understand, in most cases there's no need to calculate.

 

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www.maxge.com All Rights Reserved.

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