Low voltage circuit breaker, leakage circuit breaker selection
In the selection of circuit breaker, low-voltage circuit breakers and residual current circuit breaker accounted for a large share of.
One, the selection of low voltage circuit breaker
Low voltage circuit breaker selection should be based on the specific conditions of use, choose to use category, selection of the rated voltage, rated current, rated current tripping device and a shunt, undervoltage tripping device of voltage and current parameters, reference samples of products provide protection characteristic curve selected protection characteristics, and need to short-circuit characteristics and sensitivity coefficient calibration. When compared with the addition of a circuit breaker or other protection between electrical with request, should choose choose type circuit breaker. As an example, using DZ20 circuit breaker for reference.
1 rated voltage and rated voltage low-voltage circuit breakers rated voltage rated current of Ue and Ie. Should be not less than the line, the normal rated working voltage and current or current calculation. Circuit breakers rated working voltage and the switching capability and use categories, with a circuit breaker products can have several rated working voltage and the corresponding switching capability and use categories.
2 long time delay trip setting current Ir1 selected circuit breaker tripping device for long time delay setting current Ir1; should be greater than or equal to the calculation of the load current circuit, according to the calculation of the load current of 1-1.1 times determined; at the same time should not be greater than the line allowed long term current 0.8-1 times.
3 instantaneous or short time delay trip setting current Ir2 selected circuit breaker instantaneous or short time delay trip setting current Ir2 > line peak current. Distribution circuit breaker to be less than the peak current of 1.35 times to determine the principles, motor protection circuit when the action time is greater than 0.002s to be less than 1.35 times the starting current to determine the principles, if the action time is less than 0.02s, it should be no less than the starting current to increase 1.7-2 times. These coefficients are considering setting error and the starting current of the motor may change and other factors added.
4 short circuit breaking capacity and short-time withstand capability check low-voltage circuit breakers rated short circuit breaking capacity and rated short-circuit making capacity shall not be less than the installation position of the prospective short-circuit current. When time is larger than 0.0.2s, can not consider the short-circuit current of the aperiodic component, namely the periodic component of short circuit current effective value as the maximum short circuit current; when the time is less than 0.02s, consideration should be given to the non periodic component, namely the short circuit current first period as the maximum short circuit current. If the check results show breaker on-off capacity is not enough, should take the following measures.
1) in the circuit breaker side other additional protection appliances ( such as a fuse ) as a back-up protection.
2) the current limiting circuit breaker, according to manufacturer's characteristic let-through current or limiting factor ( i.e. the actual breaking current peak value and the expected peak short-circuit current ratio) corresponding to the selected product.
3) when the election of large capacity circuit breaker. Short circuit protection circuit breaker must be in a closed position bearing the unrestricted short circuit current transient value, but also can be within the specified time delay range load short-circuit current. The short-time load short-circuit current value should not exceed the rated capacity of the circuit breaker, otherwise should also take measures or change the circuit breaker specification. Circuit breaker product samples are generally given products rated peak withstand current and rated current ( Is current). When the AC current, short-time withstand current should be not restricted periodic component of short circuit current effective value.
Two, leakage circuit breaker selection
Leakage circuit breaker with two functions, one is the circuit breaker function, two with leakage protection function. Circuit breaker function and the general low-voltage circuit breaker, leakage protection zero sequence transformer detection by residual current, i.e. by detecting protected circuit in phase and neutral line current instantaneous value, judgement of leakage current to ground changes. Therefore, circuit breakers, such as the common DZ47LE leakage circuit breaker function part selection and the general low-voltage circuit breaker with same. Leakage protection function section ( hereinafter referred to as the protector of leakage of electricity ) selection should consider two basic conditions, a leakage protector of leakage current action must escape network normal leakage current, two is the leakage protector of leakage current action must be less than the minimum igniting current caused by fire or body safety current, according to the selection of leakage protection for the main objective to determine the. General selection according to the following principles.
( 1) selection of earth leakage protective device rated operating current according to the national standard GB13955-92" leakage protector installation and operation of" regulation, selection of earth leakage protective device rated operating current according to the electrical lines in the normal leakage current is determined, and should fully take into account the protected circuit and device may occur as a normal leakage current value, when necessary through the actual measurement is achieved by protecting circuit and equipment leakage current value.
( 2) selection of earth leakage protective device rated current according to the national standard" leakage protector installation and operation of" regulation, earth leakage protective device rated operation current for leakage shall be not less than the normal electrical wiring and equipment leakage current of the maximum value of 2 times.
( 3) the electrical wiring and equipment installation of leakage current value and classification of the leakage protection properties of the complexes
1) for single electric equipment, leakage protection action current should not be less than the normal operation and measurement of leakage current of 4 times. In order to prevent leakage cause accident getting an electric shock and fire.
2) the distribution line leakage protection action current should not be less than the normal operation and measurement of leakage current of 2.5 times, also should meet the maximum leakage currents with a normal operation of electric equipment leakage current of 4 times. In order to prevent leakage caused by fire.
3) for the whole network protection, current action shall be not less than 2 times the actual leakage current. The entire network with comprehensive leakage protection, prevent leakage caused by fire.
( 4) in general, different rated residual operating current leakage protection device can be selected according to the following principles. As commonly used models: DZ47LE-32
1) rated residual operating current of 30mA and below the earth leakage protective device, used for direct contact and TT system protection; and do not directly contact, IT neutral non grounding system and complete exposure conditions (such as construction sites, swimming pools, and other entertainment ) protection.
2) rated residual operating current of 50mA and above the earth leakage protective device, used for non direct contact and TT system and prevent fire protection.
3) configured to selectively protection shall ensure that in addition to the direct contact and TT system can be protected, but also on the lower level with 30mA selective leakage protection system protection. Only isolated incidents circuit, other circuit should still keep power supply.
The above data of electrical switch factory provide for reference, www.jiandq.com