At present, there are three types of holding of high and low voltage vacuum contactors on the market: electrical holding, mechanical holding and permanent magnet holding.
1. Electricity holding
The initial closing is full voltage, and when the closing is completed, the holding coil is connected in series in the suction coil. As long as the power is cut off during the switch, the energy storage reaction spring releases energy to make the contactor in the open position. Its advantages are as follows: the method circuit is simple and reliable, and the magnetic field of electrical energy conversion is fully utilized. It can be used to work in the case of 300 times/h to 600 times/h of operation cycles, in the case of this high-frequency cycle number of work, as long as you pay attention to the current carrying capacity of the contactor suction coil A/mm², whether according to the number of cycles, to determine the size of the current carrying capacity of the coil. Under normal circumstances, the temperature rise of the suction coil does not exceed 30K during high-frequency operation (when the average temperature of the working environment is 35 °C), so when the electric holding contactor is designed, the temperature rise of the entire magnetic system is the key part to consider, and the length of the magnetic circuit, the size of the magnetic flux area, whether the permeability of the material is appropriate, and whether the match with the coil is reasonable.
2. Mechanical retention
There are closing coils and opening coils, after the closing is completed and the power is off, the mechanical lock is kept in the closing position, the opening coil is energized when the opening is energized, the locking holding mechanism is tripped, and the energy storage reaction spring releases energy in the case of rapid opening. The advantages are as follows: the closing is maintained as a mechanical lock, the coil is not charged when working for a long time, and there is no problem of coil temperature rise. It should not be used when the number of operating cycles should not exceed 150 times/h. There are two disadvantages of mechanical latch contactors on the market today:
a. In the process of contactor, the long closed point of the contactor itself is used to disconnect the power supply. When there is still a distance between the suction and the suction, the long closing point should be disconnected, otherwise the opening distance of the long closing point is not enough, and the arc is not easy to extinguish. Therefore, it is necessary to leave a gap to allow mechanical locking time, which is about 3mm. In order to ensure the success of the locking, the traditional line can only use the method of sacrificing the terminal pressure to ensure the locking, which reduces the closing ability and dynamic and thermal stability of the contactor. To sum up, when the traditional line is closed, it can only be locked after the power is off, because when the power is off, there is a rebound effect under the action of the energy storage spring, the mechanical lock must seize this opportunity to forcibly lock, but it often fails, in order to lock successfully, the terminal pressure value can only be sacrificed at the time of rebound.
If the lock is made after the closing is all in place, the above defects can only be solved by locking and then powering off. That is to say, the long closing point of the contactor itself is changed to close in place, and the long closing point is opened after reliable locking. This requires the installation of a time relay for power-off delay action, and the coil must be improved accordingly to complete. The downside is that the cost will go up, so few people adopt it.
If the non-contact electronic circuit control is adopted, as long as the current time is greater than the closing 30~50mS, the defects caused by the traditional circuit can also be overcome, the disadvantage is that the electronic circuit has poor anti-overvoltage and overcurrent ability, and it is necessary to install an overvoltage absorption device to overcome.
b. The form of mechanical lock is divided into half-shaft lock and fork lock. The half-shaft type has a small force resolution point because its leverage ratio is large, and the fork lever ratio is difficult to make larger, and the force relief point is larger. Regardless of the form, the locking is the astosing and separation of two metal parts under load. Due to the frequent action of this anastomosis and separation, the strength and toughness of the metal parts are required, and the wear resistance is required, the material used in the manufacture of this metal parts is 45# or 40Cr steel, the use of high-frequency quenching, the hardening hardness is between HRC52~56, and the depth of the hardening layer is controlled between 1.5~1.8mm. High-frequency quenching can overcome the characteristics of ordinary quenching that hardness and strength cannot be taken into account. The lock parts through this heat treatment method have good surface hardness, good wear resistance, high fatigue strength and high toughness in the core. Theoretically, it is believed that the mechanical locking parts that have been treated with standardized heat treatment can be used for about 100,000 times, but most of the mechanical locking contactors on the market at present have not many locking devices that can reach 10,000 times.
To sum up, a qualified mechanical locking contactor should look at the treatment methods in three places: (1) whether the locking form is reasonable (2) whether the locking coil is before or after the power off (3) what is the material and heat treatment process of the locking parts. and the third affects the life of the lock, and the second affects the performance of the contactor.
3. Permanent magnet holding
The permanent magnet holding contactor has a closing coil and a opening coil, and a neodymium iron pin permanent magnet is placed in the magnetic circuit, and the full pressure is applied to the closing coil, so that the magnetic force generated by it is consistent with the force of the permanent magnet, under the action of the two resultant forces, the contactor is engaged, and the magnetic force generated by the permanent magnet keeps the contactor in the closed state. However, it should be noted that the permanent magnet holding force should be greater than the sum of the terminal pressure of the interrupter and the energy storage reaction spring reaction force in order to be reliable. When the switch is energized, the magnetic force generated on the coil should be opposite to the direction of the magnetic force of the permanent magnet, and the contactor is quickly opened under the action of the energy storage reaction spring to achieve the purpose of opening.
When the contactor is maintained by permanent magnet force, the coil is not electrified, and the temperature rise of the coil and the core does not need to be considered. At the same time, the contactor is held by a permanent magnet force, and there is no defect of the mechanical lock contactor, which is an ideal product to replace the mechanical holding contactor, and its operation cycle times are higher than that of the mechanical lock type, lower than the electrical holding, and in between.
The above three holding forms of contactors are only briefly analyzed and described here, and there is no comparison between the holding form and the performance of the whole contactor. The purpose of this article is just to help the majority of users when choosing a contactor to keep the form.
