The circuit breaker structure

The circuit breaker structure

The circuit breaker structure is mainly composed of the following four parts.

1. Sensor components

The sensing element is also called the sensing element (such as overcurrent tripping device, undervoltage tripping device, shunt tripping device, etc.), which can sense the abnormal situation in the circuit and the command of the operator, or the signal of other relay protection system, and make the executing element act through the transmission element. There are many types of sensing elements that operate on different principles.

(1) Hot bimetal trip

The hot bimetal release is a release with anti-time protection characteristics. It mainly senses the size of overload current and uses the current to overheat the bimetal sheet to bend the bimetal sheet. The greater the current through the hot bimetal sheet, the faster its bending deformation, the shorter the action time of the release.

(2) electromagnetic tripping device

Electromagnetic tripping device is composed of current coil, iron core, armature and reaction spring. When the overcurrent passes through the current coil, the electromagnetic force generated on the armature is enough to overcome the spring force of the counterforce spring and attract to the iron core, resulting in instantaneous action. Changing the size of the spring force can change the action current value, which is mainly used for the protection of large short circuit current. If the damping device (oil damper or clock delay mechanism) is used, the delayed action can also be obtained.

Shunt trip is also an electromagnetic trip, which is composed of voltage coil, iron core, armature and a reaction spring, powered by a control power supply. It can be in accordance with the operator's command or relay protection signal to make the scoring tripper action, thus making the circuit breaker open. One or two shunt trippers can be installed on a circuit breaker to meet the control requirements.

Undervoltage trip is also an electromagnetic trip that can sense changes in the supply voltage. When the power supply voltage is normal (rated voltage), the armature is in the state of drawing. When the power supply voltage drops to a certain value (usually 35% to 75% of the rated voltage), the armature of the undervoltage tripping device is insufficient, and the armature is released under the action of the reactive spring to break the circuit breaker.

(3) electronic tripping device

The electronic tripping device consists of a sensor, an electronic circuit and a tripping actuator. Electronic tripping device can easily obtain long delay, short delay, instantaneous protection characteristics and grounding protection, etc., has obvious advantages, while developing rapidly.

The sensor of the electronic release is a current transformer, which is installed in the main circuit of the circuit breaker and reflects the change of the main current through an appropriate current ratio. Transformer has two forms, one is the iron core speed saturation transformer, its secondary output can be used as the working power supply of electronic circuit, its low current area linearity is good, can also be used to collect the change of current signal. The other is hollow transformer without iron core, which has good linearity and is mainly used for signal acquisition. In order to improve the reliability and accuracy of tripping device, two kinds of transformer can be used to compose the sampling circuit simultaneously. Modern intelligent circuit breaker adopts this way. The tripping actuator of an electronic tripping device can be composed of a shunt tripping device, an undervoltage tripping device or a magnetic converter.

Working principle of shunt trip: the electronic circuit finally triggers the signal sent to the shunt trip, so that the shunt trip is drawn, so that the circuit breaker is broken. Undervoltage trip also uses the final trigger signal of the electronic circuit is sent to the undervoltage trip, the undervoltage trip will be short connected, so that the undervoltage trip action to break the circuit breaker. The advantages of these two ways are simple structure and strong universality; Disadvantage is that the electronic circuit to provide larger power, and slower speed of action, in the old products more used. In the new intelligent circuit breaker, the magnetic flux converter is used as the tripping actuator, which consumes small power, fast action speed, small volume and weight, and works reliably.

The so-called flux converter is a kind of electromagnetic system similar to the working principle of polarization relay. When the circuit breaker is in the normally closed position, the core of the flux converter is attracted by permanent magnetic steel. When the current occurs, the signal processed by the sensor to the microprocessor makes the coil current flow, providing a reverse magnetic flux, offset the permanent magnetic steel suction, the iron core under the action of the reaction spring to pop up, and promote the mechanism of the trip to break the circuit breaker. Because the current causing the reverse flux is very small, the power required for tripping is small.

2. Trip actuator

Tripping actuator includes main contact and arc extinguishing chamber, and auxiliary contact is also an actuator. The contact performs the task of connecting and breaking the circuit, and the arc extinguishing chamber works with the contact to help extinguish the arc generated when the contact is breaking. There are many types of contact systems, such as single break point contact, double break point contact (bridge contact, rotary contact), single chip contact, parallel contact, and pair contact and plug-in contact, which are analyzed on a case-by-case basis. Arc - extinguishing chamber has grid type and narrow slot type. Ac circuit breakers are mostly grid type and DC circuit breakers are mostly narrow slot type.

3. Transfer element

The parts that undertake the transmission and transformation of force, including transmission mechanism, free tripping mechanism, spindle, traction bar, etc. The transmission mechanism converts manpower or electricity into closing force to make the circuit breaker close. The main shaft will be three - phase or three - phase N contact a closed or broken.

The free tripping mechanism is a special property of low-voltage circuit breaker, which changes the connection between transmission mechanism and contact system into flexible connection. When the free tripping mechanism is buckled again, the transmission mechanism, especially the manual transmission mechanism, can directly drive the contact system to close; When the free tripping mechanism is tripping, the connection between the transmission mechanism and the contact system is released, and the transmission mechanism cannot drive the contact system to close.

4. Other attachments

Constitute a complete circuit breaker, but also can have many accessories, such as auxiliary contact, secondary terminal, OK indicator, separator, etc., for the user to choose.