The function of air-break disconnectors in high voltage power systems is to provide electrical and visible isolation of one part of the system. The isolation generally takes two forms:
- Isolation related to normal day-to-day operation of the power system. For example, shunt reactors required only during light load periods are switched out using circuit breakers and then isolated by disconnectors during peak load periods.
- Isolation related to repair or maintenance on transmission lines or station equipment such as transformers, circuit breakers and so on.
High voltage air-break disconnectors and earthing switch come in a variety of types and mounting arrangements.The four most commonly used types are:- Vertical break type
- Centre side break type
- Double side break type
- Pantograph type
The high voltage disconnector and earthing switch routine tests are for the purpose of revealing faults in material or construction. They do not impair the properties and reliability of a test object. The routine tests shall be made wherever reasonably practicable at the manufacturer’s works on each apparatus manufactured, to ensure that the product is in accordance with the equipment on which the type tests have been passed. By agreement, any routine test may be made on site.
The following items are the routine testing items of high voltage disconnector switch according to IEC 62271-1,IEC 62271-102 Standards:
1-Dielectric test on the main circuit:
A dry, short-duration power-frequency with 50 or 60 Hz voltage test shall be applied.The test voltage shall be that specified in column 2 of the following tables , according to the relevant IEC standards.In these values, the altitude factor should be considered.
When the insulation of disconnector and earth switch is provided only by solid-core insulators and air at ambient pressure, the power-frequency voltage withstand test may be omitted if the dimensions between the conductive parts – between phases, across open switching devices and between conductive parts and the frame – are checked by dimensional measurements.
When dielectric test applied on earthing switches, the test voltage shall be applied with the earthing switch in the open position in these condition:
– between adjacent insulated terminals with the bases earthed.
– between all the insulated terminals connected together and the bases earthed.
2-Dielectric test on auxiliary and control circuits in operating mechanism:
- Inspection of auxiliary and control circuits, and verification of conformity to the circuit diagrams and wiring diagrams:
The nature of the materials, the quality of assembly, the finish and, if necessary, the protective coatings against corrosion shall be checked. A visual inspection is also necessary to check the satisfactory installation of the thermal insulation.The conductors and cables and heaters(resistance check)shall be checked for proper routing. - Functional tests:
A functional test of all low-voltage circuits(such relays,contactor,interlocking magnet) shall be made to verify the proper functioning of auxiliary and control circuits in conjunction with the other parts of the disconnector switch . interlocking cassette must be checked. - Verification of protection against electrical shock:
Protection against direct contact with the main circuit and safe accessibility to the auxiliary and control equipment parts liable to be touched during normal operation shall be checked by visual inspection. - Dielectric tests:
Only power frequency tests shall be performed.The test voltage shall be 1 kV or 2 kv with a duration of 1 s with 50 or 60 HZ frequency.
3-Measurement of the resistance of the main circuit:
For the routine test, the d.c. voltage drop or resistance of each pole of the main circuit shall be measured under conditions as nearly as possible similar, with regard to ambient air temperature and points of measurement, to those under which the corresponding type test was made.The measured resistance shall not exceed 1,2 × Ru, where Ru is equal to the resistance measured before the temperature-rise test.
4-Design and visual checks:
The disconnector and earthing switches shall be checked to verify its compliance with the purchase specification.
5-Mechanical operating tests:
Operating tests are made to ensure that the disconnectors or earthing switches show the specified operating behaviour within the specified voltage and supply pressure limits of their operating mechanisms.During these tests, which are performed without voltage on, or current flowing through the main circuit, it shall be verified that the disconnectors or earthing switches open and close correctly when their operating mechanisms are energized.
This item also must be chek:
- angle of operating mechanism out put shaft.
- measuring torque of operating mechanism output.
- operating mechanism motor current.
- operating times.
– 10 close-open operating cycles at the minimum(85%)supply voltage.
– 10 close-open operating cycles at the maximum (110%)supply voltage.
–50 close-open operating cycles at the nominal (100%)supply voltage.
During these operating cycles the operating characteristics such as operating time and maximum energy consumption shall be recorded or evaluated. With disconnectors having manual mechanisms only, the maximum forces shall be recorded. Satisfactory operation of the auxiliary contacts and position indicating devices (if any) shall be verified.
After these tests, no parts of the disconnector or earthing switch shall be damaged.For disconnectors and earthing switches with a rated voltage of 52 kV and above, the mechanical operating routine tests may be performed on sub-assemblies.
The main circuit resistance shall be measured before and after the mechanical endurance test.the resistance shall not vary by more than 20 % from the value measured before the test.
References:
- International Standard :IEC 62271-1 High-voltage switchgear and controlgear
Part 1: Common specifications . - International Standard :IEC 62271-102 High-voltage switchgear and controlgear –
Part 102: Alternating current disconnectors and earthing switches. - Current interruption using high voltage air-break disconnectors Article by Peelo, D.F. hindhoven: Technische Universiteit Eindhoven
- High Volt Company catalogue.
- vanguard instruments company(doble) catalogue.
- Alpha Elektrotechnik AG Company disconnector switch catalogue.
