Advantages and disadvantages of fixed-time overcurrent protection and inverse-time overcurrent protection.

1, definite time overcurrent protection

Advantages:? Timing overcurrent protection is simple and reliable, and it depends entirely on choosing the action time to obtain selectivity. The selective cooperation between superiors and subordinates is relatively easy, and the time limit is set by the time relay according to the calculated parameters. It can ensure the selectivity of the action, the sensitivity of the action can meet the requirements, and the setting and debugging are more accurate and convenient.

Disadvantages: In the line with multilevel protection, the overcurrent protection near the power supply has a long time limit and poor quick action, and its sensitivity coefficient is low in the heavy load line.

2. Inverse time overcurrent protection

Advantages: the external wiring is simple, the number of relays is greatly reduced, and only one GL current relay is needed, which can use AC operating power supply and realize current quick break protection; When the line is short-circuited near the power supply, the protection action time limit is short.

Disadvantages: the time limit coordination is complicated, although the action time limit of each line is shorter when it is short-circuited near the power supply end than when it is short-circuited at the end; Difficult debugging; In terms of sensitivity, accuracy and rapidity, it is far less than the relay protection device composed of electromagnetic relay.

Extended data:

Protection principle

Time-limited overcurrent protection can be divided into fixed-time overcurrent protection and inverse-time overcurrent protection according to its action time characteristics. Fixed time limit, that is, the action time of the protection device is fixed, which has nothing to do with the size of short-circuit current; Inverse time, that is, the action time of the protection device is inversely proportional to the short-circuit current reflected in the relay. The greater the short-circuit current, the shorter the action time, and the inverse time-limit characteristic is also called inverse time-limit characteristic.

App application

In engineering practice, current quick-break protection and time-limited current quick-break protection are widely used as main protection, while time-limited overcurrent protection is used as backup protection. When the protection device is close to the power grid terminal, the action time limit of its overcurrent protection is not long. In this case, it can be used as both main protection and backup protection.

Baidu Encyclopedia-Fixed Time Limit Overcurrent Protection

Baidu Encyclopedia-Inverse Time Overcurrent Protection