BS/EN 60137-2017 pdf download.Insulated bushings for alternating voltages above 1000 V.
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).
• ambient air and immersion media temperature if deviating from normal values (see 5.3 and Table 4) (relevant to bushings according to 3.16 to 3.22);
• type of immersion medium (relevant only to partly or completely immersed bushings according to 3.19 to 3.22);
• minimum level of immersion medium (relevant only to partly or completely immersed bushings according to 3.19 to 3.22);
• maximum operating pressure of immersion media (relevant only to partly or completely immersed bushings according to 3.19 to 3.22):
• type of insulating gas (relevant only to gas-filled, gas-insulated and gas-impregnated bushings according to 3.5 to 3.7 when the gas of the equipment Is In communication with that of the bushing);
• rated filling pressure of gas for insulation (see 3.30) (relevant only to gas-filled, gas- insulated and gas-impregnated bushings according to 3.5 to 3.7 when the gas of the equipment is in communication with that of the bushing);
• maximum internal operating gas pressure (see 3.31) (relevant only to gas-filled, gas- insulated and gas-impregnated bushings according to 3.5 to 3.7 when the gas of the equipment is in communication with that of the bushing);
• maximum external operating gas pressure (see 3.32) (relevant only to partly or completely gas-immersed bushings according to 3.19 to 3.21):
• angle of mounting if exceeding the standard values (see 4.6):
• minimum nominal specific creepage distance (see 4.7) (relevant only to the outdoor part of bushings according to 3.17, 3.18 and 3.20):
• unusual climatic conditions (extreme high and low temperatures, tropical humidity, severe contamination, high wind);
• seismic conditions, if qualification is required (see 5.4).
6.1.6 Design
The purchaser should provide requirements about the following, where applicable:
• for bushings supplied without a conductor: diameter, type (cable, solid or hollow stem), material and position of the conductor with which the bushing will be fitted in operation:
• particular dimensional requirements, if any:
• test tap or voltage tap if required (see 3.38 and 3.39):
• the length of earthed sleeve located next to the flange or other fixing device, if any:
• general information concerning the position of the bushing In relation to the earthed parts of the apparatus for which the bushing is foreseen (see 7.1):BS/EN 60137-2017 pdf download.