The selection and setting of the rated current of the breaker overflow tripping device

Update date:2017-10-23 Source:maxge

We generally choose circuit breakers to meet the breaking capacity according to the circuit expected short circuit current, but the calculation of the circuit expected short circuit current is a very tedious work. This paper will briefly introduce how to select and use low voltage circuit breakers in low voltage system.

Keywords:

 low-voltage distribution system

Circuit breaker short circuit

Underpressure trip

The introduction

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Circuit breaker is widely used in low-voltage power distribution system. In the design of low voltage distribution system, attention should be paid to the selectivity of circuit breaker, selection and setting of the rated current of the circuit breaker, and ensure the function of the current tripping device. When the temperature of the environment is greater than or less than the calibration temperature value, the rated current value of the low voltage circuit breaker should be adjusted according to the temperature and load capacity correction factor provided by the manufacturer.

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Several current parameters of the circuit breaker

The rated current In the circuit breaker is the current that the tripping device can pass In the long run, which is the rated current of the tripper.

The rated current Inm of the circuit breaker shell frame, with the same basic geometry size and the same structure similar to the structure or the maximum release rated current in the plastic shell. It determines the maximum rated current value of the solver that can be installed. For example, dw15-1600 rated circuit breaker of 800A, 1600A is the rated current Inm of the circuit breaker, and the rated current In the circuit breaker is 800A.

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The overcurrent tripping device can be divided into overload tripping device and short circuit (electromagnetic) tripping device, with long delay action current (Ir1), short delay action current (Ir2) and instantaneous action current (Ir3). The Ir1 In the dw15-1600 In zhengtai is (0.7 ~ 1) In, the Ir3 is (1 ~ 3) In, and there is no short time delay trip. Changshu CW2-1600A.

The Ir1 is (0.4 ~ 1) In, Ir2 is (0.4 ~ 15) In+ OFF, and the short time delay time is 0.1s -- 0.4 s, which is 4, and the Ir3 is 1.6KA ~ 35 KA + OFF.

The rated limit of the circuit breaker (Icu) : according to the conditions specified in the test procedure, it does not include the breaking capacity of the circuit breaker to carry its rated current capacity; In this case, the circuit breaker sets the test voltage and other specified conditions to break the current value without considering the circuit breaker to carry its rated current.

The test procedure of the Icu is o-t - CO.

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Its specific test is that the current adjustment of the line to the expectations of short circuit current value (such as 380 v, 50 ka), and the test button does not close, the participants circuit breaker in the closing position, press the test button, circuit breaker through 50 ka short circuit current, circuit breaker OPEN circuit (OPEN O) immediately and extinguishing arc, circuit breaker should be in good condition, and to switch again. T for intermittent time, generally for 3 min, at this time line in the hot standby state state) (test button is pressed, the breaker again through (CLOSE C) and then open circuit (O) (electricity to flow through to test examination circuit breaker in peak electric and thermal stability and dynamic and static contact bounce of wear). This program is CO. The circuit breaker can be completely divided, extinguish the arc, and do not exceed the specified damage, and it is determined that its ultimate breaking capacity test is successful.

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Rated short circuit breaking capacity running Ics, is refers to the circuit breaker in the specified test voltage and under the condition of the other provisions of a smaller than the rated short circuit breaking current limit of breaking current value, in the in a specified test procedure O - t - CO - t - CO movements, rated current of the circuit breaker should continue to carry it. It has more time than the Icu test program. Ics is a percentage of the Icu. For universal and molded case circuit breakers.

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The value of the Ics is slightly different, and the plastic shell allows the minimum to be 25% of Icu, which allows Ics to be least 50% of Icu, and Ics=Icu circuit breakers are very rare. The Ics of DW45 intelligent universal circuit breaker in China is 62.5% ~ 65% Icu.

Current setting of the circuit breaker

The rated current of the undervoltage circuit breaker is not less than the calculation current of the line, namely In greater than or equal to Ijs(Ijs for the calculation current of the protected distribution line).

The long delay action current of the circuit breaker (Ir1) is mainly used to protect the load. In general, the Ir1 takes the line calculation current of 1.1 times, namely Ir1 is greater than or equal to 1.1 x Ijs(Ijs to calculate current for the protected distribution lines)

The current (Ir2) should avoid the peak current Ipk of the line, usually according to the following type:

Ir2 acuity 1.2 x (Ipk +Ijs') Magnetic relay

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Among them:

Ipk is the starting current of the largest motor in the line Ijs (Ijs) calculates current for circuits other than the one with the maximum starting current

The setting time of short delay action of circuit breaker is usually divided: 0.1s, 0.2s, 0.3s and 0.4s. In order to ensure the selectivity of protection device action, the class difference between the upper and lower level circuit breakers is usually 0.1 ~ 0.2

S, the action time should also meet the thermal effect requirement of the protected line.

The instantaneous action current of the circuit breaker should satisfy Ir3 greater than or equal to 1.3 x (Ipk +)

In order to meet the selectivity between the circuit breakers of the protected circuit, the Ir3 is also required to exceed 1.1 times the short-circuit current of the circuit breaker protected by the lower circuit breaker.

The selectivity of the circuit breaker over current protection action

In circuit breaker protection of distribution systems, when the electrical failure occurs, is apart from the point of failure of circuit breaker action recently fault amputated, and other circuit breaker no action at all levels, so as to limit fault caused power outages in the smallest range, make other trouble-free remained normal power supply, power supply circuit of the selectivity of this is required by a circuit breaker. The selectivity of circuit breaker is very important in the design of low voltage distribution system. It can bring convenience to users and guarantee the continuity of power supply circuit.

The circuit breakers used in low voltage distribution systems can be divided into two categories: selectivity and non-selectivity. Selective low voltage circuit breaker, its instantaneous characteristics and short time delay characteristics are applicable to short circuit action, while long delay characteristics are applicable to overload protection.

In the low-voltage distribution system, to ensure that the selective action between upper and lower two levels of circuit breaker, general circuit breaker using selective circuit breaker at the next higher level, the level of circuit breaker adopts nonselective circuit breaker or selective circuit breaker, main is to use the short time delay trip time delay or delay action time is different.


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