IEC 60076-3-2013 pdf free

IEC 60076-3-2013 pdf free.Power transt formers – Part 3: Insulation levels, dielectric tests and external clearances in air.
The insulation requirements for power transformers and the corresponding insulation tests are given with reference to specific windings and their terminals.
For liquid-immersed or gas-filled transformers, the requirements apply to the internal insulation only. Any additional requirements or tests regarding external insulation which are deemed necessary shall be subject to agreement between manufacturer and purchaser. If the purchaser does not specify any particular requirements for external clearances then the provisions of Clause 16 shall apply. If the purchaser intends to make the connections to the transformer in a way which may reduce the clearances provided by the transformer alone, this should be indicated in the enquiry.
Bushings shall be subject to separate type and routine tests according to IEC 60137 (including appropriate bushing test levels for the particular transformer test level), which verify their phase-to-earth insulation, external as well as internal.
When a transformer is specified for operation at an altitude higher than 1 000 m, clearances shall be designed accordingly. It may then be necessary to select bushings designed for higher insulation levels than otherwise required for operation at lower altitudes, see Clause 16 of this standard and IEC 60137.
The manufacturer may shield the bushing terminals if necessary during the dielectric tests but any shielding of the earthed parts closest to the terminals shall form part of the transformer structure in-service except for shielding required only during partial discharge measurement.
Bushings and tap-changers are specified, designed and tested in accordance with the relevant IEC standards. The dielectric tests on the complete transformer constitute a check on the correct application and installation of these components. In the case of tap-changers which according to IEC 60214-1 are not subjected to dielectric routine tests at the tap-changer manufacturer’s works then the tests performed according to this standard also serve as the only dielectric tests routinely performed on this component.
The temperature of the insulation system shall not be less than 10 °C during the tests, but temperatures higher than those given in IEC 60076-1 may be used.
The transformer shall be completely assembled as in service in respect of all elements that might influence the dielectric strength of the transformer. It is normally assumed that the insulating liquid or gas is not circulated during the tests and coolers do not need to be assembled. Any equipment designed to collect or detect free gas produced by faults in the insulation shall be installed and monitored during the tests. If free gas is detected during any test, the nature and cause of the gas shall be investigated and any further actions shall be agreed between purchaser and manufacturer
NOTE 1 External overvoltage protection devices such as surge arresters do not need to be assembled and bushing spark gaps can be removed or their spacing Increased to avoid operation during the tests.
NOTE 2 It is common practice for larger transformers for oil samples to be taken for dissolved gas analysis before and alter dielectric tests.
Liquid immersed transformers shall be tested with the same type (mineral, ester, silicone. etc.) and specification (with respect to the properties that might affect the test performance) of liquid that it will contain in service.
NOTE 3 Some purchasers can require that the insulating liquid be circulated on OD cooled transformers during an IVPD test to detect the possibility of static electrification, but this is a very specific requirement and is not covered by this standard.
Transformers for cable box connection or direct connection to metal-enclosed SF6 installations should be designed so that temporary connections can be made for dielectric tests, using temporary bushings, if necessary. By agreement between manufacturer and purchaser, the service liquid to SF6 bushings may be replaced by appropriate liquid to air bushings for test, in this case the design of the end of the bushing inside the transformer including the positions of the live parts and the clearances of the substitute bushings inside the transformer shall be the same (within the normal variation of dimensions of the bushing associated with manufacturing tolerances) as those of the in-service bushings.IEC 60076-3 pdf free download.