Use and Maintenance of High Pressure Vacuum Contactor in Coal Washing Plant

The contacts of the vacuum contactor complete the circuit's division and integration within the sealed vacuum chamber. When the contact cuts off the current, there is only an arc formed by the metal vapor ions, and no gas collision is released. Due to the rapid diffusion and recombination of metal vapor ions, the arc can be rapidly extinguished and the original vacuum degree can be restored, and it can withstand multiple points and closing without reducing the breaking capacity. Its main features are: 1 compact structure, small size, light weight, fast action, low power required to divide and close; 2 long electrical and mechanical life, less maintenance workload; 3 large breaking capacity, allowing more frequent breaks , Suitable for frequent starting occasions; 4 does not produce high-pressure gas and toxic gases, no fire and explosion danger, no pollution to the environment; 垣 cut off the small inductor current is prone to cut off over-voltage and arc re-ignition over-voltage, usually from the enhanced operation Management and taking protective measures to suppress the over-voltage at the time of closing and closing. Due to the many features of the vacuum contactor, high pressure vacuum contactors are used in the high pressure startup cabinets of the coal washing plant, and the use effect is very good.

In years of use, we have summarized several issues that should be noted in use and maintenance.

1 point, over-voltage at the time of closing and its protection vacuum contactor have good breaking performance. Since the motor is an inductive load, a very high overvoltage is generated at both ends of the inductor due to sudden changes in the loop current at the time of the division and closing. For the over-voltage protection at the time of sub-switching and closing, the following measures can be taken: 1 Decrease the cut-off value and fundamentally reduce the over-voltage of the cut-off; 2 Install the RC absorber; 3 Set the RL protector; 4 Use the zinc oxide arrester MOA. East Washing Center mainly uses zinc oxide arrester MOA. This kind of protection is good for high voltage motor starting effect, simpler, suitable for installation in handcart cabinet. Used in the coal washing plant, there has been over-voltage breakdown, the protection of the equipment did not cause a major accident. The MOA is actually a non-linear varistor, which is extremely resistive at operating voltages. The leakage current is microamperes (lA) without affecting the operation of the power grid. When the overvoltage occurs, the resistance value drops sharply and shows a voltage regulation characteristic. Generally, the overvoltage can be limited to 2 times the phase voltage, and there is a certain capacitance between the valve plates, and the residual pressure has a suppression effect. For the zinc oxide surge arrester, a voltage breakdown test is required every year for 44 and a 2500V megger grounding rocker is used every quarter to check whether the insulation resistance meets the requirements.

2 Strictly control the closing and closing speed of the vacuum contactor When the closing speed of the vacuum contactor is too low, the wear of the large contact will increase due to the increase in the pre-breakdown time; in addition, the arc extinction chamber of the vacuum contactor generally uses brazing. The process, and gas treatment at a high temperature, so its mechanical strength is not high, vibration resistance is poor. If the closing speed of the vacuum contactor is too high, large vibrations will be caused, which will cause greater impact on the bellows and reduce the life of the bellows. Therefore, the opening speed of the vacuum contactor must be strictly controlled. In addition, it is required that the opening buffer and the closing buffer of the vacuum contactor have better characteristics, and the impact force at the time of opening or closing should be reduced as much as possible to ensure the service life of the vacuum interrupter.

Coal washing plant is mainly used for 6kV high-voltage motor start. Through multiple adjustments, we usually choose the closing speed of the vacuum contactor to be around 0.10.2m/s. This closing speed allows the optimum closing speed of the vacuum contactor. Setting the vacuum contactor opening speed to 0.30. 5m/s or so can shorten the arcing time when the vacuum contactor is opened. The maximum arcing time will not exceed 1.5 half-frequency power waves. When the current first zero-crossing value, the arc extinguishing chamber has sufficient insulation strength, which can ensure that the stroke of the contact within the power frequency half-wave reaches the full stroke. 3 strict control of the contact stroke to ensure that the vacuum contact stroke, can not be arbitrarily added or reduced the contactor of the vacuum contactor stroke, can not be mistaken for a large open distance is beneficial to the arc. Because the stroke of the vacuum contactor contact is relatively short, when the coal washing plant is used, the contactor of the vacuum contactor with a rated voltage of 6 kV is adjusted to 3.55 mm, and the contact stroke is only 12 mm. If the contact stroke is excessively increased, The contactor will cause excessive stress on the bellows after closing, causing damage to the bellows and damaging the vacuum inside the contactor's sealed housing; too short a stroke of the contact may cause poor contact of the vacuum contactor.

4 Strictly control the load current In the coal washing plant, high pressure vacuum contactors are selected according to their overload capacity. The rated current of the high-voltage vacuum contactor is more than 10 times the rated current of the motor, which ensures the overload capacity of the vacuum contactor and prevents the thermal insulation formed by the vacuum between the contacts of the vacuum contactor and the housing. Therefore, the heat on the contact and the conductive rod is mainly conducted along the conductive rod. Ensure that the operating temperature of the vacuum contactor does not exceed the allowable value to ensure the normal use of the vacuum contactor.

5 Strict acceptance inspection The vacuum contactor has undergone strict acceptance before leaving the factory. However, after the on-site installation, the relevant parameters must be tested and reviewed to prevent changes in the equipment during transportation and after the adjustment of the equipment. It is the problem after the actuator and the vacuum contactor are connected. The main retest parameters are: closing, opening the same period, open distance, compression stroke, closing and opening speed, closing and opening time, DC contact resistance, fracture insulation level and transmission acceptance test.

6 The overhaul and overhaul period of the vacuum contactor should be flexibly controlled according to the relevant regulations and combined with the actual operating conditions. The operation inspection in the coal washing plant is that the number of times of normal operation (combined and divided load currents) has reached 2,000 times and the rated short-circuit current has been opened and disconnected after 10 inspections. According to the coal preparation plant's production, we basically check it once every quarter. The main contents of our usual inspection include: vacuum degree of arc extinguishing chamber, good contact of auxiliary contacts, insulation resistance of lightning arresters, correct switching of armature starting and maintaining state, looseness of mechanism fasteners, and whether open distance and departure are Meet the requirements.

7 In the use of the vacuum interrupter in the coal washing plant, the degree of vacuum of the contactor is periodically tested according to the inspection requirements. Because the vacuum interrupter is a key component of the vacuum contactor. It is supported by glass or ceramic and sealed, there are dynamic and static contacts and shield inside, there is negative pressure in the room, the vacuum degree is 1.33X (10-51)Pa, which can guarantee the arc extinguishing performance when it breaks. Insulation level. When the degree of vacuum is reduced, its breaking performance is significantly reduced. Therefore, the vacuum interrupter must not be impacted by any external force. It is strictly forbidden to tap, hand clapping, and no force can be applied during handling and maintenance. Do not place anything on the vacuum contactor to prevent the vacuum interrupter from breaking when dropped. When repairing, the bolts of the arc extinguishing chamber should be tightened to ensure even force.

8 Frequent failures in the use of coal washing plants In the vacuum contactor fault of the coal washing plant, the highest failure rate is that the contactor cannot maintain a continuous blow (commonly known as a blow gun). During processing, it was found that the main causes were: 1) Keeping the coil burned or its circuit breaking; 2) Conversion of the auxiliary contacts was unreasonable; 3) Conversion of the auxiliary contacts was unreasonable; 4) The voltage was too low. Common among these is the unreasonable conversion of auxiliary contacts. When handling, the auxiliary switch is usually moved slightly back and the mechanical lock position is adjusted.

Again, the higher failure rate in the coal washing plant is: the contactor rejects after power on. Analysis of the reasons may have the following points: 1 electric circuit or coil closing circuit disconnection; 2 coils open circuit; 3 poor contact of auxiliary contacts; 4 bridge rectifier diode damage; freewheeling diode damage and 6 foreign objects stuck to the armature. Among them, the common reason is that the bridge rectifier diode is damaged and the auxiliary normally-closed conversion contact point is in poor contact.

Second, the more prone to failure is: the coil is burned or damaged. The main reasons are: 1 The voltage does not match; 2 coils are subject to long-term moisture or corrosive gas; 3 The normally closed contacts of the auxiliary contacts do not open after the contactor is closed. The common reason is that the normally closed contact of the auxiliary contact does not open after the contactor closes. In the process, it is generally to replace the coil and adjust the position of the auxiliary switch (move forward) or repair the contact.

In addition, the failures that are more likely to occur at the coal washing plant are: the contactor moves too slowly and adversely. The reasons are as follows: (1) Loose iron fastening bolts are loose; (2) The gate springs are not suitable for counterforce; (3) The friction between the rotary arm and the adjusting nut is too large. This type of failure is mainly due to the loosening of iron core fastening bolts.

In short, high-voltage vacuum contactor maintenance is small, the failure rate is not high. As long as the vacuum contactor is inspected in accordance with the specified time, failure will generally not occur, which can reduce the labor intensity of maintenance personnel.

Now working at Shendong Coal Company's washing and processing center, he is mainly engaged in electrical repair and management of coal preparation plant.

(Continued from page 63) The machine throughput has been increased by 501/h compared to the past, which is equivalent to 37.5t/h of clean coal (recovery rate is 75%). The factory processing fee is 45 yuan / t clean coal, then the cost savings can be: (yuan) In summary, through the use of flocculants, flocculants, can bring the daily direct economic benefits are: Practice has proved that condensation The rational use of agents and flocculants not only enabled the plant to achieve the goal of closed water circulation and clean coal washing, but also ensured the quality of clean coal products, saved production costs, and achieved good economic and social benefits.

He studied coal chemical engineering and is currently director of coal quality workshop of Shaqu Coal Preparation Plant.

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