Detailed introduction to the classification of isolation switches

The main functions of isolation switches are as follows:

(1) During equipment maintenance, isolation switches are used to isolate the electrified and non electrified parts, resulting in obvious disconnection points. The repaired equipment is isolated from the power system to ensure the safety of personnel and equipment.

(2) The isolation switch and Circuit Breaker are combined to perform switching operations to change the operating mode.

(3) Used to disconnect small current circuits and bypass currents.

(4) Perform the operation of closing the bypass (loop) current in a 500KV low current circuit using an isolation switch. But it must be calculated to meet the technical requirements of the isolation switch and relevant scheduling regulations before it can be carried out.

1.1 Structural Form
 

1.1.1 Classification of isolating switches

M0 level isolating switch: a mechanical switch with a lifespan of 1000 operating cycles, suitable for use in power transmission and distribution systems and meeting general requirements.

M1 level isolating switch: an isolating switch with an extended mechanical life of 3000-5000 operating cycles, mainly used in situations where isolating switches are operated in conjunction with circuit breakers of the same level.

M2 level isolating switch: With a mechanical lifespan of 10000 operating cycles, it is mainly used in situations where isolating switches and circuit breakers of the same level are operated in conjunction.

1.2.2 Main performance parameters of isolation switch

(1) Rated voltage (kV)

It refers to the maximum operating voltage of the isolation switch, which is the line voltage and also represents its insulation support strength. 

(2) Rated current (A)

It refers to the maximum operating carrying current of the isolation switch at 40 ℃.

(3) Rated short-circuit withstand current (thermal stability) kA/S

It refers to the ability of isolating switch contacts to resist the thermal welding caused by the short-circuit current for 3-4 seconds without damage.

(4) Rated peak withstand current (dynamic stability) kA

It refers to the ability of an isolation switch to withstand the repulsive force caused by short-circuit current without damage.

(5) Circuit contact resistance (μ Ω)

It refers to the conductivity performance of various electrical contact forms in the conductive circuit of the isolation switch, and is the technical capability for inspection, design, manufacturing process assembly.

1.3 Basic operation and maintenance requirements and measures

1.3.1 Basic requirements for isolating switches

According to the tasks and usage conditions of isolation switches in the power grid, their basic requirements are:

(1) After the isolation switch is separated, there should be a clear disconnection point for easy identification of whether the equipment is isolated from the power grid.

(2) There should be sufficient insulation distance between the breakpoints of the isolation switch to ensure that under overvoltage conditions, it will not cause breakdown and endanger the safety of the workers.

(3) In the event of a short circuit, the isolating switch should have sufficient thermal and dynamic stability, especially not automatically separate due to the action of electric force, otherwise it will cause serious accidents.

(4) Capable of breaking a certain capacitance current, inductance current, and circulating current.

(5) The synchronization of opening and closing should be good, with the best speed for opening and closing, in order to minimize operating overvoltage, arcing frequency, and line electrical interference as much as possible.

(6) The structure of the isolation switch should be simple, the action should be reliable, and it should have a certain mechanical strength; Metal components should be able to withstand oxidation without corrosion; Can reliably switch on and off in frozen environments.

(7) Isolation switches with grounding switches must be equipped with interlocking mechanisms to ensure the sequence of disconnecting the isolation switch first and then closing the grounding switch during power outages, and disconnecting the grounding switch first and then closing the isolation switch during power transmission.  

(8) There should be electrical interlocking between the isolation switch and the circuit breaker through auxiliary contacts to prevent accidental pulling and closing of the isolation switch under load.

(9)For Outdoor Isolating Switches used in cold climate regions, they should have the required ice breaking capability and be able to reliably open and close in frozen environments.

(10) For general outdoor non GIS or HGIS isolating switches, the external insulation creepage distance should meet the pollution level requirements of the installation site, and a certain margin should be left according to the design requirements.

 

The isolation switch should have three types of interlocking:

(1) The isolation switch and circuit breaker are locked together.

(2) Locking between isolation switch and grounding switch.

(3) Locking between busbar isolation switches.

There are three ways to chain

(1) Mechanical chain.

(2) Electrical interlocking.

(3) Electromagnetic lock (microcomputer anti misoperation locking).

 

1.3.3 Precautions for operating isolation switches

When operating the isolation switch, attention should be paid to:

(1) The circuit breaker and grounding switch of the corresponding circuit should be checked first to ensure that they have been opened and disconnected in place, and to confirm that the grounding wire of the power transmission range has been removed.

(2) The electric operating voltage of the isolation switch should be between 85% and 110% of the rated voltage.

(3) Manually close the isolation switch quickly and decisively, but do not apply excessive force at the end of the closing process. After closing, check whether the moving and stationary contacts are closed in place and whether the contact is good.

(4) Manual isolation switch should be started slowly and cautiously, and quickly when the moving contact just leaves the contact. After opening, check the disconnection of the moving and stationary contacts.

(5) If the isolation switch is stuck, the moving contact cannot be inserted into the stationary contact, or the closing is not in place during operation, the operation should be stopped until the defect is eliminated before continuing.

(6) During the operation of the isolation switch, special attention should be paid to quickly evacuate the site in case of abnormal conditions such as broken insulators to prevent personnel from being injured. After the closing operation of isolation switches such as GW6GW1, it is necessary to carefully check whether the upper and lower connecting arms of the operating mechanism have exceeded the dead center position.

(7) When operating the isolation switch remotely, a duty officer should be present on site to check its opening and closing positions, synchronization status, contact depth, and other items phase by phase to ensure that the isolation switch operates normally and its position is correct.

(8) Isolation switches should generally be operated in the main control room. When remote electrical operation fails, electric or manual operation can be carried out on-site, but permission must be obtained from the station master and technical director, and on-site supervision is required before proceeding.

(9) When the electrically operated isolation switch is operating normally, its operating power supply should be disconnected.

(10) When operating an isolation switch with a locking device, follow the usage regulations of the locking device and do not use the unlocking key or damage the locking device casually.

(11) Do not use isolation switches for the following operations:

1) Load operated opening and closing;

2) Power outage and transmission operation of distribution lines;

3) During lightning, pull and close the arc suppression coil;

4) When the system is grounded (neutral point ungrounded system) or there is an internal fault in the Voltage Transformer, pull and close the voltage transformer;

5) When the system is grounded, pull and close the arc suppression coil.

1.3.4 Direct operation with isolation switch

The following operations are allowed to be performed directly using isolation switches:

(1) When there is no grounding fault in the power grid, pull and close the voltage transformer.

(2) Pull and close the lightning arrester during the Yuan lightning activity.

(3) The capacitance current of 220KV and below busbars and equipment directly connected to the busbars shall be tested and allowed to circulate on 500KV no-load busbars and 3/2 connected busbars.

(4) When there is a grounding fault in the power grid, close the neutral point grounding switch of the transformer.

(5) The bypass isolation switch connected in parallel with the circuit breaker can pull the bypass current of the circuit breaker when it is closed.

(6) A no-load transformer, reactor, and capacitor with an excitation current not exceeding 2A and an no-load connection with an excitation current not exceeding 5A.

(7) For 3/2 circuit breaker wiring, when a certain series of circuit breakers is locked for opening and closing, an isolation switch can be used to disconnect the loop, but it should be noted that all other series of circuit breakers must be in the closed position.

(8) The double busbar single section connection method allows for the use of isolation switches to disconnect the circuit when one of the two bus tie circuit breakers or the section circuit breaker is locked for opening or closing. Before operation, it is necessary to confirm that the three circuit breakers are in the closed position and remove their operating fuses.

 

1.3.5 Inspection and maintenance of isolation switches

（1） Inspection content of isolation switch

 

(1) The supporting insulators of the isolation switch should be clean and intact, without any discharge or abnormal sounds.

(2) The contact and contact points should be in good condition, without screw breakage or looseness, severe heating and deformation.

(3) The lead wire should be loose, without severe swinging or burning or broken strands, and the equalizing ring should be firm and not skewed.  

(4) The mechanical parts such as the isolation switch body, connecting rod, and shaft should be deformed, and all components should be well connected and positioned correctly.

(5) The live part of the isolation switch should be free of debris.

(6) The operating mechanism box, terminal box, and auxiliary contact box should be closed and well sealed to prevent rain and moisture.

(7) There should be no abnormalities inside the operating mechanism box and terminal box, and the fuses, thermocouple relays, secondary wiring, terminal connections, heaters, etc. should be intact.

(8) The anti misoperation locking device of the isolation switch should be in good condition, and the electromagnetic lock and mechanical lock element should be damaged.

(9) Regularly use an infrared thermometer to measure the temperature of the contacts and connections of the isolation switch.

 

(10) The operating mechanism includes the operating connecting rod and components, whether there is any welding, deformation, rust, looseness, or detachment, and whether the connecting shaft pins and nuts are intact.

 

(11) Is the three-phase grounding switch in good contact when the isolation switch with grounding switch is grounded.

 

(12) After the isolation switch is closed, whether the two contacts are fully inserted into the blade, whether the contact between the contacts is good, and whether the temperature exceeds 70 ℃ under rated current.

(13) After passing through the short-circuit current of the isolation switch, the insulator of the isolation switch should be checked for damage and discharge marks, as well as for melting of the joints of the moving and stationary contacts.

 

（2） Operation and maintenance of isolation switches
 

(1) Regularly clear the bird's nest of the isolation switch.

 

(2) Regularly clean the mechanism box and terminal box.

 

(3) Regularly check the power switch (using a multimeter).

 

(4) Regularly inspect the heaters in the isolation switch mechanism box and terminal box and switch them on and off as required.

 

(5) Power off and rinse the 500KV isolation switch pillar with water.

 

During abnormal or overloaded operation of the equipment, abnormal weather, thunderstorms, and snowfall, special attention should be paid to checking the snow accumulation at the joints and contacts. During the switching operation, special inspections should be conducted on the isolation switch.

During normal operation, it is important to monitor the current of the isolation switch to ensure that it does not exceed the rated current; The temperature should not exceed 70 ℃. The joints and contacts of the isolation switch should not overheat during operation. Generally, color changing paint or temperature gauges (yellow, green, and red, representing 60 ℃, 70 ℃, and 80 ℃ respectively when melted) or infrared thermometers should be used for regular monitoring.

1.4 Common Defects and Classification

 

1.4.1 Common faults of isolation switches
 

In the operation and handling of isolation switches, abnormal situations such as overheating of contacts and contacts, malfunction of electric operation, three-phase different periods, and inadequate closing are prone to occur.