subject: On The Small Circuit Breaker Protection And Role Performance - China Multifunctional Drilling Rig [print this page] Breaker in the electrical system in the building the use of great use are not the same, so a more comprehensive understanding of its performance and correct use of great significance.
MCB (Miniature CircuitBreaker), also known as miniature circuit breakers (Micro CircuitBreaker), is a place suitable for family use or similar over-current protection circuit breaker (hereinafter referred to as MCB), previously known as the line protection switch (circuit breaker) . Its main purpose is to protect the line at the end of the wire (or cable) and electrical equipment, different from the trunk and main branch used industrial power distribution circuit breaker and motor protection circuit breaker. It is used extensively for residential, hotels, office buildings, shopping malls and other places, are building electrical areas, should meet the IEC364 "building electrical requirements" provisions.
1 MCB's rated current choice and the choice of current overload protection
MCB's rated current In, the calculation of the protected circuit current IB, the protected line (conductor) is allowed to continue current IZ, the relations are as follows:
IB In IZ (1) I2 1.45IZ (2) Which I2 load circuit breaker for the line passing through a certain delay time must be current within the movement.
MCB put into operation, should meet the equivalent of our country by IEC898 GB10963 "for household and similar over-current protection circuit breaker," the standard states:
Agreed not to release current I1 = 1.13In, not tripping time t 1h (the time when In 63A) and non-tripping time t 2h (when In> 63A pm).
Agreed tripping current I2 = 1.45In, tripping time t <1h (the time when In 63A) and the trip time t 2h (when In> 63A pm).
Agreed tripping current I3 = 2.55In, tripping time 1s 32A).
MCB overload characteristics (the agreement is not tripping current, and agreed upon tripping current, etc.) to determine, based on the following factors:
As noted above, MCB circuit used in the end, according to the supply (with) electric Statutes, namely: power supply network voltage deviation, three-phase power supply voltage tolerance is7%, single phase for electric voltage tolerance is +7% and -10%. General considerations for the -7%. To maintain an adequate electricity power, when the voltage deviation of -7%, which is the supply voltage is only 93% of the rated voltage, the current will increase to 1.0752In, plus the power current limit of normal fluctuation allowed +5% (0. 05) both add to 1.1252In, rounded 1.13In. At this point do not allow the natural movement MCB (circuit breaker with the provisions of the 1.05In industrial action does not allow the same meaning). The overload is equivalent to 1.131.3In = 1.45In (1.3In overload circuit breakers for industrial use to the current action, this circuit breaker used to protect transformers and cables).
GB10963 "for household and similar over-current protection circuit breaker" and IEC898 standards of the same name, are set 2.55In and its action time, taking into account the current end of the load in small motors (such as refrigerators, air conditioners, washing machines and kitchen equipment in the micro-motor) must survive its starting current, because these micro-motor can not be starting the same time, so be it 2.55In.
2 MCB's short-circuit protection and selection
On the short-circuit protection, IEC898 and GB10963 were divided into A, B, C, D are four types. British Standard BS3871 is divided into 1,2,3,4-based. But VDE0641/6.78 (German standard) and CEE (European Community electrical products original acronym CENELEC Standards Committee) standards are not classified.
Four types of short-circuit protection are:
A Type: particularly suitable for measuring circuit in the transformer protection circuit with specialty wire protection and limited semiconductor protection (its long delay overload protection with B, C, D class of the same). Short circuit protection is 2In ~ 3In, no action is 2In (not movement time should be greater than 0.1s)? Than 3In must be action (movement time t <0.1s). A type of users, but very few. MCB short-circuit protection type A class is generally not mentioned, but the provisions of B, C, D categories (type).
B type: for residential and outlet circuit. Short circuit protection is 3In ~ 5In, that 3In no action (not movement time should be greater than 0.1s)? Than 5In must be action (movement time t <0.1s).
C-type: first used to connect high-current electrical equipment such as lights and motors. Short circuit protection is 5In ~ 10In, that 5In not move (no action time should be greater than 0.1s)? Than 10In must be movement (movement time <0.1s).
D-type: Suitable for pulse current generated electrical equipment, solenoid valves and capacitors. Short circuit protection is 10In ~ 50In, that 10In no action (no action time greater than 0.1s), must be greater than 50In movement (movement time <0.1s).
A-type> 2In, <3In; B type> 3In, <5In; C-type> 5In, <10In; D-type> 10In, <50In. Thus be interpreted as action also qualified, not action also qualified.
Now appears, choose B, C are two types of large (on the street for protection, whether incandescent, fluorescent, halogen, high-pressure mercury lamp, high pressure sodium lamp, metal halide lights, they start current is 4 times the rated current to 7 times, so must choose C).
D-type is also used as a small motor short circuit protection. For example C45AD and PX200CAD other models. Their instantaneous current setting value is 10 times 14 times In (factory adjusted in 14In). This D-type products without long delay overload protection. Over-current protection by the electric
