Grounding and zeroing in power engineering

Update date:2018-04-03 Source:MAXGE

Grounding and zeroing in power engineering

  Grounding is to make a good metal connection between the uncharged metal part and the grounding body under normal conditions to protect personal safety. The grounding resistance requirement is: Re<4 ohms. When the electrical equipment is charged due to insulation damage, the short-circuit current at the ground will flow along both the grounding body and the human body. The current value flowing through each path is proportional to the size of its resistance, and the resistance of the grounding body is smaller, flowing through The current of the human body is smaller. Usually, the resistance of the human body is hundreds of times larger than the resistance of the grounded body, so the current flowing through the human body is only a few hundredth of the current flowing through the grounded body. When the grounding resistance is small, the current flows through the body. The body's current is almost equal to zero, so the body can avoid the risk of electric shock.

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   The electrical equipment adopts zero connection, that is, the shell is connected to the neutral line. When the insulation of a certain phase is damaged, the current forms a single-phase short circuit (that is, a short-circuited shell) that forms the relative neutral line through the shell of the device. The short-circuit current immediately affects the phase. The melt blows or the action of other protective elements to cut off the power, thereby eliminating the risk of electric shock.

Common grounding zero

  In the low-voltage system, they are all technical measures to prevent electric shock caused by electric leakage; the requirements for grounding measures are basically the same as those for requiring zero-crossing measures; grounding and zero-connection require a certain grounding device, and the grounding body of each grounding device. The construction and connection of the ground wire are basically the same.

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The difference between ground zero

  Different protection principles. Grounding is to limit the voltage to ground after equipment leakage, so that it does not exceed the safety range. In high-voltage systems, grounding, in addition to limiting voltage to ground, in some cases, also contributes to the action of the grid protection device. Zero-to-zero connection is to make the equipment leakage through the zero-crossing line to form a single-phase short circuit, prompt the protection device on the line to operate, and cut off the power of the faulty equipment.

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  The scope of application is different. Grounding is applicable to high and low voltage power grids that are generally not grounded, and also applicable to low voltage power grids that have taken other safety measures. Zeroing is only applicable to power grids that are directly grounded at the neutral point. The line structure is different. If grounding measures are taken, there may be no working neutral line in the power grid and only a protective grounding line is provided; if a zero-crossing measure is taken, a working zero line must be set up to use the working zero line for zero protection. The protection of the zero line should not be connected to the switch or fuse. When a fuse or other breaking device is installed on the work zero line, it must also be installed with a ground wire or a neutral line.

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