IEC TS 62271-304:2010 pdf – High-voltage switchgear and controlgear – Part 304: Design classes for indoor enclosed switchgear and controlgear forrated voltages above 1 kV up to and including 52 kV to be used in severeclimatic conditions
IEC TS 62271-304:2010 pdf – High-voltage switchgear and controlgear – Part 304: Design classes for indoor enclosed switchgear and controlgear forrated voltages above 1 kV up to and including 52 kV to be used in severeclimatic conditions.
8.2 Control requirements
The temperature needs to be controlled within limits of less than ±3 K. During the tests, it shall be varied cyclically between 30 C to 50 C. The temperature gradient shall be at least 0.5 K/mm, The distribution of temperature in the whole volume of the chamber should be within the same tolerances.
The humidity also needs to be controlled within close limits over a range from below 80 % to over 95 % of rePative humidity.
6.3 Energizing facilities
A three-phase high-voltage source shall be provided so that the equipment to be tested can be energised during the test The source used for this purpose shall be able to maintain the rated voltage with a tolerance of 0 to —5 % during the climatic cycles The voltage shall be recorded continuously during the whole duration of the tests for the purpose of checking possible disruptive discharges.
A source is required for applying diagnostic test voltages up to at least the dry power- frequency withstand voltage of the equipment to be tested, This source shall have a protective device operating in less than 0,1 s in the event of a disruptive discharge.
The sources shall comply with IEC 60060-1.
7 Selection and arrangement of the equipment for test
7.1 SelectIon of the equipment
Ageing test is to be made on a functional unit completely assembled and fitted with all its components as for service, measuring transformers included. The functional unit and its components shall be new and clean.
7.2 Arrang.ment of Ih. equipment
The equipment to be tested shall be installed in the climatic test room, as given in 6,1, in its normal service position. The test arrangement of the functional unit shall not be more favourable than the normal service arrangement, especially in respect of the external connections.
A.1 Remarks on the climatic cycle
The climatic cycle described in this technical specification is the same described in the first edition of IEC 60932, This climatic cycle has proved satisfactory for more than 15 years.
The aim of this climatic cycle is to produce condensation on the insulation parta of the switchgear in order to prove the dielectric behaviour under this condition
Condensation always occurs Immediately when the temperature of the object Is lower than the dew point of the ambient air. The object described in 7.1 consists of several components with their own thermal time constants. If the time constants of all components are long In comparison with the half of the climatic cycle, the temperature of all components alternates slightly around the mean temperature or the climatic cycles. Therefore the temperature of the object is nearly half of the cycle below the dew point of the ambient air and condensation occurs for this time at least.
A.2 Origin of the apparition of a conductive layer, produced by the cyclic
presence of condensation on insulating parts of high voltage switchgear
This explanation has been given by competent chemists working in collaboration HV test laboratories, alter proceeding to several analysis of deposits from insulating services having been naturally exposed to condensation for years (In the network) or artificially for weeks (method A of the first edition of IEC 60932).
Atmospheric air is essentially (78%) composed of nitrogen (N2). In presence of high voltage (surface) discharges, and catalysed by UV radiation due to corona effect, some N2 combines with H20 from condensation, to produce small quantities of HNO2 and HNO2.These acids dissolved In H20 react with metals like Al, Ag. Cu. or Fe and produce conductive nitrous salts, which are deposited and concentrated in some places during drying. The presence of those Irregular conductive paths give way to tracking of the insulating surfaces. Nitrous salts have been detected by spectrographic analysis of deposits on insulating surfaces after the application of the method A.
When using method B of the first edition of IEC 60932, spectrographic analysis mainly showed the presence of deposits of NaCI, small amounts of metal chloride salts and traces of nitride salts. Chemical concentration was higher, but exposure time was much less.
Inter-laboratory comparison focused on usual epoxy insulating parts showed a good relationship between the final results of application of method A and method B of first edition of IEC 60932.