High voltage disconnector
High voltage disconnector is an important switch device in the electrical system of power plant and substation, which needs to be used together with high voltage circuit breaker. It is used for connecting, cutting off or changing lines of high voltage equipment under the condition of voltage and load. Its main functions are: to ensure the safety of high-voltage electrical appliances and devices in maintenance work, to isolate the voltage, can not be used and cut off, input load current and short-circuit current, can only be used for some switching operations that do not produce strong arc, that is to say, it does not have arc extinguishing function; according to the installation location, it can be divided into indoor type and outdoor type, according to the number of insulation pillars, single Column type, double column type and three column type, with optional equipment for each voltage level.
High voltage disconnector can ensure the safety of high-voltage electrical appliances and devices in the maintenance work, and plays the role of Isolating voltage. It can not be used to cut off, input load current and break short-circuit current. It can only be used for some switching operations that do not produce strong arc, that is to say, it does not have arc extinguishing function. According to different installation locations, it can be divided into indoor type and outdoor type, and it can be divided into indoor type and outdoor type according to the number of insulation pillars Column type, double column type and three column type, with optional equipment for each voltage level. It can also reliably isolate the power-off part of the high-voltage distribution device from the live part, so as to ensure the safety of the maintenance work. All contacts of the high-voltage disconnector are exposed in the air with obvious breaking points. The disconnector has no arc extinguishing device, so it can not be used to cut off the load current or short-circuit current. Otherwise, under the action of high-voltage, the breaking point will produce a strong arc, which is difficult to extinguish itself, and even may cause flashover (short circuit between phases or phases), burn the equipment and endanger personal safety It is a serious accident of “pulling disconnector with load”.
High voltage disconnector can also be used to switch some circuits to change the operation mode of the system. For example, in a double bus circuit, a high voltage disconnector can be used to switch the operating circuit from one bus to another.
1. Altitude: no more than 1000m;（The excess needs to be explained in advance）
2. Ambient air temperature: – 30 + 40;
3. Relative humidity of surrounding environment: the daily average is no more than 95%;
4. The monthly average value is not more than 90%. The earthquake intensity does not exceed 8;
5. Safe place: no fire, inflammable, explosive, serious pollution, chemical corrosion and violent vibration.
The disconnector has no arc extinguishing device and can not be operated with load.
For 10-110kV disconnector, under normal conditions, its allowable operating range is as follows:
1. Open and close voltage transformer and arrester.
2. Charging current of opening and closing bus.
3. The no-load current and the no-load current of the transformer do not exceed 5A.
High voltage disconnectors are divided into indoor type and outdoor type. The outdoor type includes single pole switch and three pole disconnector, which is often used as the first circuit breaker isolating switch to separate the power supply line from the user; the indoor type is often connected in series with the high-voltage circuit breaker to ensure the reliability of power failure. In addition, in the high-voltage complete set of power distribution equipment, the disconnector is commonly used as voltage transformer, lightning arrester, transformer used in power distribution station and high-voltage control appliance of metering cabinet.
Outdoor disconnectors should be installed horizontally in the open air, so that the supporting porcelain bottle with porcelain skirt can really play a rain proof role; for indoor disconnectors, when installed vertically, the static contact is above, and the ground with bushing can be installed at a certain angle. In general, the static contact is connected to the power supply, and the moving contact is connected to the load. However, when the disconnector installed in the receiving cabinet adopts the cable incoming line, the power supply is at the moving contact side. This connection method is commonly known as “switching into fire”. Both sides of disconnector shall be firmly connected with busbar and cable ground. In case of contact between copper and aluminum conductor, copper aluminum transition joint shall be used to prevent electrochemical corrosion.
The dynamic and static contacts of the disconnector should be aligned, otherwise side strike will occur when closing, which will cause uneven pressure on the contact surface of the dynamic and static contacts after closing, resulting in poor contact.
The operating mechanism and transmission machinery of the disconnector shall be well adjusted so that the opening and closing operation can be carried out normally without resistance. It also meets the requirements of three-phase synchronization, that is, the three-phase moving contacts act at the same time when opening and closing, and the deviation in different periods should be less than 3mm. In addition, when the contact is in the closing position, the moving contact should have enough penetration depth to ensure that the contact area meets the requirements, but it is not allowed to close too far. It is required that there is a gap of 3-5mm between the moving contact and the base of the static contact, otherwise the supporting porcelain bottle of the static contact will be broken when the closing is too strong. When the contact is pulled apart, the distance between the movable contact and the fixed contact shall be less than 65 mm, or the effective distance between the open contact and the fixed contact shall be less than 65.
Disconnectors are equipped with manual operating mechanism, generally using cs6-1 type. During operation, the positioning pin shall be pulled out first, and the opening and closing action shall be decisive and quick. At the end of operation, it is necessary to use the positioning pin to pin it after the operation, and visually inspect whether the position of the moving contact meets the requirements.
When the single pole disconnector is operated with insulating rod, the phases on both sides should be closed first and then the middle phase should be closed; when opening, the sequence is opposite.
It must be emphasized that both closing and opening operations should be carried out without load or when the load is within the allowable operating range of the disconnector. Therefore, before operating the disconnector, it is necessary to check that the circuit breaker in series with it is in the off position. If the load of the disconnector is a transformer within the specified capacity range, all low-voltage loads of the transformer must be shut down first, and then the disconnector can be opened after no-load; during power transmission, check that the main switch at the low-voltage side of the transformer is in the off position before closing the disconnector.
In case of misoperation of disconnector with load, it is necessary to calmly avoid misoperation in the opposite direction. That is: when the load is found to be switched on by mistake, it shall not be opened immediately; when it is found that the switch is opened with load, it shall not be closed again (if the switch is opened a little, it can be closed immediately if sparks are found).
Patrol inspection shall be conducted for the disconnector in operation. It should be done once a shift in a attended substation and at least once a week in an unattended substation.
The content of daily inspection is mainly to observe the relevant ammeter, whose operating current should be within the normal range; secondly, according to the structure of the disconnector, check that the conductive part is in good contact without overheating and discoloration, the insulation part is in good condition, and there is no flashover and discharge trace; thirdly, there is no abnormality in the driving part (no distortion, deformation, pin shaft falling off, etc.).
The connection point of disconnector connecting plate is overheated and discolored, indicating poor contact and high contact resistance. During maintenance, the connection point should be opened, the contact surface should be filed flat and polished with sandpaper (but the zinc plating on the switch connecting plate should not be removed), and then the screw should be tightened and spring gasket should be used to prevent loosening. The side strike of the moving contact can be eliminated by rotating the screw of the fixed contact or moving the position of the supporting insulator slightly; when the three-phase is different, it can be overcome by adjusting the screws at both ends of the rod insulator to change its effective length.
The contact pressure between the contacts can be realized by adjusting the clamping spring, and the clamping degree can be checked with a feeler gauge.
Generally, Vaseline can be coated between contacts to reduce friction resistance, prolong service life and prevent contact oxidation.
When the disconnector is in the off position, the pull-out angle or distance between contacts does not meet the requirements, it should be adjusted through the rod insulator.
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