How to choose the extra current of leakage protector

It is very important to select the additional leakage current of the leakage protector correctly and reasonably: on the one hand, the leakage protector can act selectively when the electric shock or leakage current exceeds the allowable value; on the other hand, the leakage protector should not act under the action of normal leakage current to prevent unnecessary economic losses caused by power supply interruption.

The additional leakage action current of leakage protector shall meet the following three conditions:

(1) In order to ensure personal safety, the additional leakage action current should not be greater than the human safety current value, which is internationally recognized as the human safety current value not higher than 30 ma;

(2) In order to ensure the reliable operation of power grid, the extra leakage action current should avoid the normal leakage current of low voltage power grid;

(3) In order to ensure the selectivity of multi-level maintenance, the additional leakage action current of the next level should be less than that of the previous level, and the additional leakage action current of each level should be 2-215 times of the differential protector.

The first stage leakage protector is installed at the outlet of the low voltage side of the distribution transformer.

The line of this level of maintenance is long and the leakage current is large, and the maximum additional leakage action current shall not exceed 100mA without perfect multi-level maintenance; for the power grid with perfect multi-level maintenance, the leakage current is 75ma in non rainy season and 200mA in rainy season, and for the power grid with large leakage current, it is 100mA in non rainy season and 300mA in rainy season.

The second stage leakage protector is installed at the outlet of branch line, which has short maintenance line, low power consumption and low leakage current. The additional leakage action current of leakage protector should be between that of upper and lower level protector, generally 30-75 ma.

The third level leakage protector is used to maintain single or multiple electrical equipment, which is the maintenance equipment to directly prevent personal electric shock. The power consumption and leakage current of the line and equipment to be maintained are small, generally less than 10mA. The leakage protector with additional action current of 30mA and action time less than 0.1s should be selected.