Basic principle of circuit breaker

Update date:2018-08-18 Source:MAXGE

When the power strip is short-circuited, the short-circuit current flows through the faulty power strip, flows through the cable conductor, and of course flows through the switchgear and causes an electrical fire. In an emergency, we certainly expect a switch electric appliance (circuit breaker) to perform a protective trip. After a short period of time, a main switch breaker performs trip protection.

When the normal running current flows through the circuit breaker, the heat detected by the protection and monitoring device in the circuit breaker is not large as time passes, and the limit value of the heat generation threshold is not exceeded. The circuit breaker will of course not perform the trip operation; When an abnormally large current flows through the device, the heat detected by the protection and monitoring device in the circuit breaker is large, and the circuit breaker performs a trip operation when the heat generation threshold is exceeded.

The threshold here refers to the protection setting of the circuit breaker.

We call the abnormal high current flowing through the circuit breaker an overcurrent. Overcurrent includes overload current and short circuit current.

That is to say, the larger the overcurrent, the shorter the time the circuit breaker operates, and the faster it performs line protection. This feature has a proper term called the inverse time protection feature of the circuit breaker.

circuit breaker

There are several places to explain:

First: the cold curve and the hot curve of the circuit breaker characteristic curve

The cold curve refers to the circuit breaker just sending power. The temperature inside the circuit breaker is consistent with the ambient temperature. The curve at this time is on the right side of the curve cluster. The hot curve refers to the stability of the circuit breaker after it has been powered. State, the curve at this time is in the middle or left side of the curve cluster.

The range of the hot curve and the cold curve in the abscissa is actually the range of short circuit protection of the circuit breaker. For example, the B characteristic is 4 to 7 times the rated current, and the C characteristic is 7 to 15 times the rated current.

Second: B characteristics and C characteristics of the circuit breaker characteristic curve

The B characteristic is used for lighting distribution control, and the C characteristic is used for power distribution control of general power distribution.

Third: about the overload protection curve and short circuit protection curve of the circuit breaker

When the line is overloaded, it may be because the voltage surge makes the current temporarily increase. When the voltage surges, the current will return to normal. Perhaps because the load is instantaneously heavier, the current is increased, but after the load is restored, the current is increased. Will also recover. As a result, the protection of the circuit breaker requires a certain time delay.

Let's look at the overload protection curve. For example, the abscissa of the B characteristic cold curve is 2 times the rated current, that is, the 2Ie position, and the ordinate value at this time is 6 seconds, indicating that the circuit breaker will perform the overload protection trip after 5 seconds. The 6 seconds here is the protection delay (note: the delay refers to the action time delay of the protection operating mechanism).

circuit breaker

When the line is short-circuited, this is an emergency and the circuit breaker must trip immediately.

Let us look at the B-characteristic cold curve with the abscissa of 4Ie, its action time is 0.02s, and the 5Ie position action time is 0.01s.

We see that there is a little inverse time characteristic between the 4Ie and 5Ie curves, but there is no inverse time characteristic after 5Ie.

We call the characteristic curve after 5Ie the definite time protection characteristic curve, and the time of all short circuit protection is 0.01s; the section of 4Ie to 5Ie is called short circuit short delay protection characteristic curve.

The purpose of the short-circuit short-delay protection feature is similar to the overload protection feature. It is expected that the short-circuit is a temporary temporary phenomenon. If the short-circuit disappears within 0.01 seconds, the circuit breaker will not be disconnected.

circuit breaker

Summarize the above knowledge:

1. The protection and monitoring device inside the circuit breaker can realize the line protection of over current;

2. The overload protection of the circuit breaker has anti-time limit protection characteristics;

3. The short circuit protection of the circuit breaker is divided into two sections, one of which has the anti-time limit short-circuit short-delay protection characteristic, and the other of which has the definite time protection characteristic.

In fact, the protection operation of the circuit breaker is carried out according to this principle. The corresponding curve is called the inverse time protection characteristic curve of the circuit breaker.


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www.maxge.com All Rights Reserved.

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