Circuit breaker:

Also known as automatic switch, it is an electrical appliance that not only has the function of manual switch, but also can automatically protect against voltage loss, undervoltage, overload and short circuit. It can be used to distribute electric energy, start asynchronous motors infrequently, protect power lines and motors, and automatically cut off the circuit when they have serious overload, short circuit, undervoltage and other faults. Its function is equivalent to the combination of fuse switch and over and under heating relay. Moreover, after breaking the fault current, there is generally no need to change the parts, which has been widely used.

Classification:

According to the operation mode, it can be divided into electric operation, energy storage operation and manual operation.

According to the structure, it can be divided into universal type and plastic shell type.

According to the use category, it can be divided into selective type and non selective type.

According to the arc extinguishing medium, there are oil immersed type, vacuum type and air type.

According to the action speed, there are: fast type and ordinary type.

According to the number of poles, there are: single stage, second stage, third stage and fourth stage.

According to the installation mode, it can be divided into plug-in type, fixed type and drawer type.

Interpretation of circuit breaker model

At present, the model of circuit breaker in China is generally composed of text symbols and numbers according to the provisions of national technical standards. Its representative meaning is:

Product letter code, represented by the following letters:

S - low oil circuit breaker;

D - multi oil circuit breaker;

K - air circuit breaker;

L-sulfur hexafluoride circuit breaker;

Z - vacuum circuit breaker;

Q - gas producing circuit breaker;

C - magnetic blowing circuit breaker.

Device location code:

N - indoor;

W - outdoor.

Design sequence code:

Represented by the numbers 1, 2, 3.

Rated voltage, KV.

Other supplementary working characteristic marks:

G - improved type;

F - split phase operation.

Rated current, a.

Rated breaking current, Ka.

Special environment code.

Supplement:

GW-110(III)W-630

G ----- disconnector

W ----- outdoor use

110 --------- applicable to the system with rated voltage of 110kV

(III) ------ type III (design serial number)

630 --------- applicable to systems with rated current below 630A

GN22-10/2000

G ----------------- disconnector

N ----------------- indoor use

22 ----------- design serial number

2000 ----------- applicable to systems with rated current below 2000a

SW2-110II

S ----------- low oil circuit breaker

W ----------------- outdoor use

2 ----------------- design serial number

110 ----------- applicable to the system with rated voltage of 110kV

II ----------- type II switch in this series of switches

Low voltage circuit breaker:

Dwx15 and dwx15c series universal current limiting circuit breakers;

Dw17 (me) series universal circuit breaker;

Dz15 series plastic shell circuit breaker;

DZ20 series plastic shell circuit breaker;

Dz25 series plastic shell circuit breaker;

How to select circuit breaker correctly

(low voltage)

(1) The rated current of the circuit breaker is determined by the calculated current of the line;

(2) Check the breaking capacity of the low-voltage circuit breaker according to the maximum short-circuit current of the line

(3) Check the sensitivity of circuit breaker action according to the minimum short-circuit current of the line, that is, the minimum short-circuit current of the line shall not be less than 1.3 times of the short-circuit setting current of the circuit breaker;

(4) The short-circuit setting current of the circuit breaker shall avoid the normal working starting current of the line;

(5) The rated short-circuit making capacity (expected peak value of maximum current) of the circuit breaker shall be verified according to the short-circuit impulse current on the line (i.e. the maximum instantaneous value of short-circuit full current), that is, the latter shall be greater than the former.

For the selection of low-voltage circuit breaker, the use category shall be selected according to the specific use conditions, and the parameters such as rated working voltage, rated current, setting current of release, voltage and current of shunt and undervoltage release shall be selected. The protection characteristics shall be selected with reference to the protection characteristic curve provided by the product sample, and the short-circuit characteristics and sensitivity coefficient shall be verified. When there are coordination requirements with other circuit breakers or other protective appliances, selective circuit breakers shall be selected.

1. Rated working voltage and rated current rated working voltage ue of low voltage circuit breaker. And rated current ie. It shall not be lower than the normal rated working voltage and working current or calculated current of the line and equipment respectively. The rated working voltage of the circuit breaker is related to the on-off capacity and use category. The same circuit breaker product can have several rated working voltages and corresponding on-off capacity use categories.

2. Long time delay release setting current IR1 the setting current IR1 of the selected circuit breaker shall be greater than or equal to the calculated load current of the line, which can be determined by 1 ~ 1.1 times of the calculated load current; At the same time, it shall not be greater than 0.8-1 times of the long-term allowable current of the line conductor.

3. The setting current IR2 of the instantaneous or short delay release of the selected circuit breaker shall be greater than the line peak current. The distribution circuit breaker can be determined according to the principle of not less than 1.35 times of peak current. When the action time of motor protection circuit is greater than 0.02s, it can be determined according to the principle of not less than 1.35 times of starting current. If the action time is less than 0.02s, it shall be increased to not less than 1.7-2 times of starting current. These coefficients are added considering the setting error and the possible change of motor starting current.

4. Short circuit making and breaking capacity and short-time withstand capacity verification the rated short-circuit breaking capacity and rated short-circuit making capacity of low-voltage circuit breaker shall not be lower than the expected short-circuit current at its installation position. When the action time is greater than 0.02s, the aperiodic component of short-circuit current can be ignored, that is, the effective value of periodic component of short-circuit current can be taken as the maximum short-circuit current; When the action time is less than 0.02s, the aperiodic component shall be considered, that is, the full current in the first cycle of short-circuit current shall be taken as the maximum short-circuit current. If the verification results show that the on-off capacity of the circuit breaker is insufficient, the following measures shall be taken.

a) Add other protective appliances (such as fuses) at the power side of the circuit breaker as backup protection.

b) The current limiting circuit breaker can be selected according to the allowable current characteristics or current limiting coefficient (i.e. the ratio of the actual breaking current peak to the expected short-circuit current peak) provided by the manufacturer.

c) The circuit breaker with larger capacity can be selected. Various short-circuit protection circuit breakers must be able to carry unrestricted short-circuit current transient value in the closed position and short-circuit current within the specified time delay range. The short-circuit current value of this short-time load shall not exceed the rated short-time withstand capacity of the circuit breaker, otherwise measures shall be taken or the specification of the circuit breaker shall be changed. The rated peak withstand current and rated short-time withstand current (1s current) of the product are generally given in the product sample of circuit breaker. In case of AC current, the short-time withstand current shall be subject to the effective value of unrestricted short-circuit current periodic component.

5. The circuit breaker selected for sensitivity coefficient verification shall also be verified according to the short-circuit current. Sensitivity coefficient refers to the ratio of the minimum short-circuit current in the line (generally two-phase or single-phase short-circuit current at the motor terminal or the end of the distribution line) to the setting current of the instantaneous or delayed release of the circuit breaker. The sensitivity coefficient of two-phase short circuit shall not be less than 2. The sensitivity coefficient of single-phase short circuit can be 1.5 for DZ circuit breaker and 2 for other circuit breakers. If the sensitivity coefficient fails to meet the above requirements after verification, in addition to adjusting the setting current, the time-delay release can also be used as backup protection.

6. Parameter determination of shunt and undervoltage release the rated voltage of shunt and undervoltage release shall be equal to the rated voltage of the line, and the power category (AC and DC) shall be determined according to the control line. The rated control power supply voltage series specified in the national standard is DC (24), (48), 110, 125, 220 and 250V; AC (24), (36), (48), 110, 127, 220V, the data in brackets are not recommended.