Fundamentals of Electrician: Basic knowledge of air switch

Air switch is a very important electrical appliance in low-voltage distribution network and electric drive system, which integrates control and various protection functions. In addition to contacting and breaking the circuit, it can also protect the circuit or electrical equipment from short circuit, serious overload and undervoltage, and can also be used to switch the circuit infrequently.

& gt& gt& gt& gt principle

There are three tripping modes: thermal tripping, electromagnetic tripping and compound tripping. When the line is generally overloaded, the overload current can not make the electromagnetic trip work, but it can make the thermal element generate a certain amount of heat, make the bimetal bend upward when heated, push the lever to disengage the hook from the lock, disconnect the main contact and cut off the power supply. When the line is short-circuited or the current is seriously overloaded, the short-circuit current exceeds the instantaneous tripping setting current value, and the electromagnetic release generates enough suction force to attract the armature to impact the lever, so that the hook rotates upward around the rotating shaft seat and disengages from the lock catch, and the lock catch disconnects three pairs of main contacts and cuts off the power supply under the action of the reaction spring.

The tripping mechanism of the switch is a set of connecting rod devices. When the main contact is closed by the operating mechanism, it is locked in the closed position by the locking hook. If there is a fault in the circuit, the related trip will release the lock hook in the trip mechanism, so the main contact will be quickly disconnected under the action of the trip spring. According to the different protection functions, the release can be divided into overcurrent release and pressure loss release.

& gt& gt& gt& gt function

Under normal circumstances, the armature of the overcurrent release is released; In case of serious overload or short circuit fault, the coil connected in series with the main circuit will generate strong electromagnetic attraction, which will attract the armature downwards and push the unlocking hook to disconnect the main contact. The working principle of undervoltage release is just the opposite. When the voltage is normal, electromagnetic attraction attracts the armature and the main contact is closed. Once the voltage drops seriously or the power is cut off, the armature is released and the main contact is disconnected. When the power supply voltage returns to normal, it must be switched on again to work, thus realizing voltage loss protection.

The origin of the name & gt& gt& gt& gt

Because there are many insulation methods, such as oil switch, vacuum switch and other inert gas (sulfur hexafluoride gas) switches. Air switch is a switch that uses air to extinguish arc, so it is called air switch. Air is used to extinguish the arc generated during the switching process. So it's called an air switch.

& gt& gt& gt& gt auxiliary accessories

1. The auxiliary contact is mechanically connected with the opening and closing mechanism of the main circuit of the circuit breaker. It is mainly used to display the opening and closing state of the circuit breaker, which is connected to the control loop of the circuit breaker, and controls or interlocks its related appliances through the opening and closing of the circuit breaker.

For example, output signals to signal lamps, relays, etc.

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The rated current of the shell frame of molded case circuit breaker is 100A, which is a single-break changeover contact. The structure of 225A and above is a bridge contact, and the agreed heating current is 3a. The rated current of shell frame is above 400A, and two normally open and two normally closed can be installed, and the agreed heating current is 6 A.. The number of times of operation performance is the same as the total number of times of circuit breaker operation performance.

2. The alarm contact is used for the circuit breaker accident alarm contact, which only acts when the circuit breaker trips. It is mainly used for free tripping when the load of circuit breaker is overloaded, short-circuited or undervoltage. The alarm contact is switched from the original normally open position to the closed position, and the indicator lamp, bell and buzzer in the auxiliary circuit are turned on to display or remind the fault tripping state of the circuit breaker.

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Because the probability of circuit breaker tripping freely due to load failure is not too high, the service life of alarm contact is110 of the service life of circuit breaker. Generally, the working current of alarm contact will not exceed1a. 3. The parallel trip is a trip excited by a voltage source, and its voltage can be independent of the main circuit voltage. The shunt release is an accessory for remotely operated brakes. When the power supply voltage is equal to 70% of the rated control power supply voltage and any voltage between 1 10%, the circuit breaker can be reliably disconnected. Parallel tripping is a short-time working system, and the coil energizing time should not exceed 1S generally, otherwise it will burn the wire.

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In order to prevent the coil from burning, a microswitch is connected in series with the parallel trip coil. When the shunt release is attracted by the armature, the microswitch switches from the normally closed state to the normally open state. Because the control circuit of the power supply of the shunt release is cut off, even if the button is manually pressed, the shunt release will not be energized, thus avoiding the occurrence of coil burning. When the circuit breaker is closed again, the microswitch is in the normally closed position again.

4. Under-voltage release The under-voltage release is a release that delays or does not delay the opening of the circuit breaker when the terminal voltage of the circuit breaker drops to a certain specified range. When the power supply voltage drops (even slowly) to 70% to 35% of the rated working voltage, the undervoltage release should work. When the power supply voltage is equal to 35% of the rated working voltage of the release, the undervoltage release should be able to prevent the circuit breaker from closing; When the power supply voltage is equal to or greater than the rated working voltage of 85% undervoltage release, the circuit breaker should be reliably closed in thermal state. Therefore, when there is a certain voltage drop in the power supply voltage in the protected circuit, the circuit breaker can automatically turn off to cut off the power supply, thus protecting the load electrical appliances or electrical equipment under the circuit breaker from undervoltage damage. When in use, the coil of the undervoltage release is connected to the power supply side of the circuit breaker, and the circuit breaker can only be closed after the undervoltage release is energized, otherwise the circuit breaker cannot be closed.

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& gt& gt& gt& gt operation accessories

1. The electric operating mechanism is an accessory for the remote automatic opening and closing of the circuit breaker. There are two kinds of electric operating mechanisms: motor operating mechanism and electromagnet operating mechanism. The motor operating mechanism is a circuit breaker with rated current of 400A or above in the shell frame of plastic case circuit breaker, and the electromagnet operating mechanism is suitable for circuit breakers with rated current of 225A or below in the shell frame of plastic case circuit breaker. Both electromagnets and motors have the same suction and rotation direction, and can only be opened and closed by the position of the cam inside the electric operating mechanism. When the circuit breaker is operated by an electric operating mechanism, it should be able to ensure that the circuit breaker can be reliably closed at any voltage between 85%- 1 10% of the rated control voltage.

2. The rotary operating handle is suitable for molded case circuit breakers. The mechanism for rotating the operating handle is installed on the cover of the circuit breaker. The rotating shaft of the handle is installed in its mechanism matching hole, and the other end of the rotating shaft passes through the door hole of the chest of drawers. The handle of the rotary handle is installed on the exposed spindle head above the door of the complete set of equipment, and the round or square seat of the handle is fixed on the door with screws. This installation can make the operator rotate clockwise or counterclockwise outside the door through the handle of the handle to ensure the closing or opening of the circuit breaker. At the same time, rotating the handle can ensure that the cupboard door cannot be opened when the circuit breaker is closed; Only when the rotary handle is in the opening or re-locking position can the door of the switchboard be opened. In case of emergency, when the door panel needs to be opened when the circuit breaker is "closed", you can press the red release button on the edge of the rotary handle seat. 3. The extension handle is an external extension handle, which is directly installed on the handle of the circuit breaker. It is generally used for manual opening and closing operation of large-capacity circuit breakers of 600A and above.

4. The handle locking device is to install a card on the handle frame, punch holes in the handle and lock it with a padlock. It is mainly used to prevent people from closing circuit breakers by mistake, so as to protect the safety of maintenance personnel or the reliable use of electrical equipment.