HKel Electrical Appliances (Shanghai) Co., Ltd. is a professional low-voltage electrical appliances OEM licensing production and sales as one of the enterprises. Hangkai Professional Molded Case Circuit Breaker Manufacturer, mainly produces HKM1 Molded Case Circuit Breaker, HKM3 Molded Case Circuit Breaker, providing product maintenance, type selection, knowledge and other services. Tel: 021-57161889
MoreThe selection of molded case circuit breaker can be divided into two aspects: parameter selection and type selection.
Parameter selection includes: voltage, current, frequency, mechanical load, dynamic and thermal stable current and duration, voltage withstanding capacity, operation performance, environmental conditions, etc.
Type selection should be determined by technical and economic comparison according to construction commissioning, operation and maintenance, investment and other conditions.
Firstly, the parameters on the circuit breaker nameplate are explained in detail (drawings):
In: Rated working current. The permissible current for long-term continuous operation should not exceed its rated current.
Ii: Short circuit instantaneous tripping current. If the current exceeds this, it will trip immediately.
Icu: rated limit short circuit breaking capacity. The circuit breaker can reliably break the maximum short circuit current, after breaking this current, the circuit breaker can not continue to carry its rated current. It just can't be used anymore.
Ics: rated short circuit breaking capacity. Circuit breakers can continue to carry the interrupting capacity of their rated current capacity. That is, the maximum short-circuit current can be reliably interrupted by the circuit breaker. After the short circuit current is cut off, the circuit breaker can still be used.
Category A: Category A circuit breaker is usually used as the incoming line of distribution cabinet or terminal circuit breaker, which requires quick break if there is short circuit fault.
Class B is mainly used as the main switch of low-voltage incoming line. It has short-circuit and short-delay protection. It cooperates with the lower circuit breaker to make current selectivity, so it needs Icw (rated short-term withstand current), because it needs to bear short-circuit current for a certain period of time.
Knowing the above parameters can determine the breaking capacity and different prices of two kinds of circuit breakers.
Four key elements to be noticed in the selection process are as follows:
1. Current Class of Circuit Breaker Shell
Circuit breaker shelf current level refers to the rated current of the maximum tripper installed in the circuit breaker shell of the same size. The rated current refers to the current that the tripper in the circuit breaker can pass through for a long time, also known as the rated current of the circuit breaker tripper. In the same series of circuit breakers, there are many kinds of shelf current grades, and in the same shelf rating current, there are many kinds of rated current. For example: DZ20 series has 100, 225, 400, 630, 800, 1250 shelf rating current, while 100 shelf rating current has 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A rating current; 225A shelf rating current has 100A, 125A, 160A, 180A, 200A, 225A rating current.
2. rated insulation voltage
The rated insulation voltage is the voltage value of the designed circuit breaker, and the electrical gap and creepage distance should be determined by reference to this value. Some circuit breakers do not specify rated insulation voltage. The maximum rated working voltage should be regarded as rated insulation voltage. In any case, the maximum rated working voltage should not exceed rated insulation voltage. The rated working voltage refers to the on-off capacity and the voltage value related to the use category. The rated working voltage of plastic case circuit breaker is mostly 50Hz and 380V, but there are also 50Hz and 600V plastic case circuit breakers with rated working voltage 380V and 50Hz. It is absolutely not allowed to use 660V or 1140V power supply voltage. The rated control power supply voltage is the voltage when plastic case circuit breaker is installed with excitation release and motor structure accessories. 。 There are two kinds of voltages: AC and DC. When selecting, AC or DC must be indicated.
3. rated limit short circuit breaking capacity
The rated limit short circuit breaking capacity refers to the breaking capacity under specified conditions. After operating according to the prescribed test procedure, the rated current of the circuit breaker is not considered to continue to be loaded. The rated short circuit breaking capacity refers to the breaking capacity under specified conditions. After following the prescribed test procedure, it is necessary to consider that the circuit breaker continues to carry its rated current. In order to meet the needs of different users, many circuit breaker manufacturers in China now divide the short-circuit breaking capacity of rated current of the same shelf level into different levels, such as CM1-100 of Changshu Switch Factory is divided into C basic type (25-35 kA), L standard type (35-50 kA), M higher breaking type (50-75 kA), H high breaking type (85-100 kA). Users should meet the ultimate short-circuit breaking capacity of circuit breakers when selecting, and the expected short-circuit current of the line can meet the requirements, so that the safety factor is not added artificially, so as to avoid waste. The rated operation short circuit breaking capacity can be 25%, 50%, 75% and 100% of the rated limit short circuit breaking capacity. Most of the circuit breakers are 50%-75%, and very few are 100%(Ics=Icu), such as Schneider's products in France.
4. Flying Arc Distance
When a circuit breaker breaks a large short-circuit current, its dynamic and static contacts are separated to produce arcs. Some arcs or ionized gases are ejected from the arc nozzle at the power supply end of the circuit breaker. The arc itself is a huge current, which can easily lead to the short-circuit and ground-to-ground fault between the exposed conductor and the exposed charged body (the metal shell of the complete set of equipment is grounded).
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