Selection elements of
circuit breaker
1. The rated current of the circuit breaker refers to the current that the trip unit in the circuit breaker can pass for a long time, also known as the rated current of the
circuit breaker trip unit. There are multiple rated currents in the same series, and there are multiple rated currents in the same rated current. The size and breaking capacity of the
circuit breaker are not the same, so when selecting, the model must be filled in completely, that is, the rated current of the circuit breaker within the rated current of the specific shell frame. The rated current classification is selected according to the priority coefficient: on the one hand, it meets and meets the needs of the maximum rated current of the circuit and electrical components; on the other hand, it is for standardization to obtain the best use of wires and processing benefits.
The current setting value of the trip unit means that the trip unit is adjusted to the operating current value. It refers to the multiple of the rated current In, which is the operating current value. Nowadays, for some electronic trips, the overload long delay rated current is adjustable, and the adjusted current is actually the rated current, which can be passed for a long time. Maximum current. The rated working current is the actual working current of the contacts under a certain working voltage when the
circuit breaker is equipped with auxiliary contacts. The current is 3A or 6A, which is used for control and protection circuits.
2. Rated insulation voltage
The rated insulation voltage is the voltage value of the designed
circuit breaker, and the clearance and creepage distance should be determined with reference to this value. Some circuit breakers do not specify the rated insulation voltage, and the maximum value of the rated working voltage should be regarded as the rated insulation voltage. In any case, the maximum rated working voltage does not exceed the rated insulation voltage. The rated insulation voltage of the
circuit breaker and the power frequency test voltage . Rated working voltage refers to the voltage value related to the making and breaking capacity and the use category. The rated working voltage of molded case circuit breakers is mostly 50Hz, 380V, but there are also 50Hz, 600V, and the rated working voltage of 380V, 50Hz circuit breakers are absolutely not allowed. To a power supply voltage of 660V or 1140V.
The rated control power supply voltage is the voltage when the
circuit breaker is equipped with a shunt release and motor-drive mechanism accessories. There are two voltages: AC and DC. When selecting, be sure to indicate AC or DC.
3. Rated ultimate short-circuit breaking capacity
The rated ultimate short-circuit breaking capacity refers to the breaking capacity under specified conditions. After operating according to the prescribed test procedure, the
circuit breaker will continue to carry its rated current regardless of the fact. Rated operating short-circuit breaking capacity refers to the breaking capacity under specified conditions. After following the prescribed test procedures, it must be considered that the circuit breaker continues to carry its rated current.
4. Attachment function
As a derivation and supplement of the circuit breaker function, accessories add control means and expand protection functions to the
circuit breaker. They are an inseparable part of the circuit breaker, mainly including auxiliary contacts, alarm contacts, shunt release, and undervoltage Accessories such as trip unit, electric operating mechanism, external rotating operating handle, etc.
(1) Auxiliary contacts are mainly used to display the opening and closing status of the
circuit breaker but cannot display whether the fault has tripped or not. It is connected to the control circuit of the circuit breaker. The rated current of the circuit breaker shell frame is 100 as a single break point changeover contact, and 225 Bridge contact structure and above, the agreed heating current is 3A; the frame rated current 400 and above can be installed with two normally open and two normally closed, and the agreed heating current is 6A.
(2) The alarm contact is mainly used to trip freely when the load of the
circuit breaker is overloaded, short-circuited or under-voltage. The working current of the alarm contact is: AC380V, 0.3A, DC220V, 0.15A, generally not more than 1A, and the heating current can be in the range of 1 to 2.5A.
(3) The shunt release is an accessory for remote control and opening. Its voltage can be independent of the main circuit voltage. The shunt release is a short-time operating system, and the coil energization time generally cannot exceed 1s, otherwise the coil Will burn. In order to prevent the coil from burning out, the
circuit breaker connects a micro switch in series with the shunt release coil. When the shunt release is energized, the armature pulls in, and the micro switch is converted from normally closed to normally open, due to the power supply of the shunt release. The control circuit is cut off, even if the button is pressed artificially, the shunt coil is always no longer energized. To avoid coil burnout, when the circuit breaker is buckled and closed again, the micro switch is in the normally closed position again. The shunt release has a variety of control voltages and different power frequency, which can be used for different occasions and different power sources.
(4) The undervoltage release is used for long-term voltage protection of the circuit and power supply equipment. When in use, the undervoltage release coil is connected to the power supply side of the
circuit breaker. The circuit breaker can be closed after the undervoltage release is energized, otherwise the circuit breaker is closed. No gates. The user should confirm whether the working voltage of the line and the undervoltage release are consistent. The working range of undervoltage is (70%～35%)Un. The undervoltage release also has a variety of rated working voltages and different power frequency, which can be used for different occasions and different power sources.
(5) The electric operating mechanism is used for automatic control of
circuit breakers and for remote closing and opening. There are two types of electric operating mechanism and electromagnetic operating mechanism: the electric operating mechanism is driven by a motor and is generally suitable for
circuit breakers with frame-level rated currents of 400A and above, and electromagnet operating mechanism is suitable for circuit-breakers with frame-level rated currents of 225A and below.
