AS NZS 60137:2020 pdf free.Insulated bushings for alternating voltages above 1000 V (IEC 60137:2017
(ED.7.0) MOD).
5.5 Very fast transients (VFT)
In the case of unusual transient stresses to capacitance graded bushings connected to gas- insulated switchgears, special investigations may be agreed upon between purchaser and supplier to cover the behaviour of the bushings.
Tests are only meaningful as long as all parties understand the limitations of how closely the test arrangements simulates the service conditions.
It is not the steep front of the very fast voltage step generated at a VFT test that is dangerous to the bushing. It is the resonant ringing voltage occurring over the bushing that may feed internal resonance circuits inside the bushing to high overvoltages. A VFT test will therefore only test the bushing for the ringing frequencies determined by the setup.
5.6 Transformer insulating liquid
Transformer bushings according to this standard are normally intended for use in transformers filled with mineral oil complying with the requirements of IEC 60296 and 60422.
Where other insulating liquids are used details shall be given by the transformer manufacturer.
6 Ordering information and markings
6.1 Enumeration of characteristics
6.1.1 General
When ordering, the purchaser shall furnish as much of the following information as necessary,
as well as any additional information needed to determine clearly the required characteristics. The minimum distance to earthed parts of the end of the bushing which is intended to be immersed in insulation liquid shall be provided by the supplier. In case distances are below the values for the standard arrangements indicated in suppliers documentation, the purchaser may also provide the necessary geometry to evaluate the particular set-up.
6.1.2 Application
Application, including type of apparatus for which the bushing is intended, and the corresponding IEC apparatus standard shall be given.
Attention shall be drawn to any features (including tests) of the completed apparatus which may affect the design of the bushing (see 7.3).
6.1.3 Classification of bushings Classification according to 3.2 to 3.22.AS NZS 60137 pdf download.