Testing switchgear assemblies

Verification of dielectric properties, limited to power frequency voltage withstand test. This test is neither mandatory nor recommended, but may be required if a modification is carried out in the switchgear assembly at site. 

Wet test While an indoor type switchgear assembly requires only a dry power frequency voltage withstand test, the outdoor type switchgear assembly also needs a wet test under wet conditions to check the external insulation. For the test procedure refer to lEC 60060-1. 

The ambient temperature should be measured during the last quarter of the test by at least three thermometers or thermocouples placed equally around the switchgear assembly, at almost the centre level and at about I metre from the body of the enclosure. The ambient temperature to be considered must be the average of these readings and should be within 10-40°C. To ensure that the ambient temperature is unaffected by ntagnetic field, alcohol thermometers must be used and not mercury thermometers. 

During the test the main busbars are fed at the rated current, for which the switchgear assembly is designed. They are heated naturally and therefore no resistance of the main bus need be measured. The busbars are shorted at one end and the current is fed from the other through a variable-current injection set at a reduced voltage of 3-10 V, or enough to achieve the rated current. The arrangement saves on power requirement and consum-... 

Testing of metal-enclosed switchgear assemblies 14/427 Table 14.5 Temperature rise limits for buses, bus connections and other parts of a switchgear assembly... 

Figure 14.2 Temperature rise test on a switchgear assembly...

This test is applicable to all outdoor metal-enclosed switchgear and controlgear assemblies, as in lEC 60298, lEC 60694 and ANSI C-37/20C. The enclosure to be tested should be complete in all respects including its mounts, bushings (for HT switchgear assemblies, 1 kV and above) and wiring. One or more vertical units can be tested simultaneously as may be convenient, but not more than 3 m panel width can be tested at a time. For a multiple unit switchboard, however, at least two vertical units should be tested together to check the joints between the units. 

Testing of metal-enclosed switchgear assemblies 14/435 Insulation resistance method... 

Since a VT is associated with a switchgear, either with its assembly or with the switchyard, the above two tests are almost the same as those forthe switchgear assembly and as discussed in Chapter 14. The test requirements and procedure are also similar. 

Field tests Power frequency withstand test on the primary windings (for un-grounded VTs). The value of the test voltage and the test procedure, is almost the same as that for a switchgear assembly (Section 14.5). 

Testing a bus system is generally along similar lines to those for a switchgear assembly, discussed in Chapter 14. In this chapter we discuss additional tests that are specifically for a metal-enclosed bus system,... 

The procedure will be the same as that discussed for switchgear assemblies (Section 14.3.3). The test voltage may be applied for one minute as shown in Tables 32.1 (A) or (B) for series I and Table 32.2 for series II voltage systems. Any disruptive discharge or insulation breakdown during the application of high voltage will be considered to be dielectric failure. 

This will be carried out under similar parameters of room condition and the type of test voltage wave to those for a switchgear assembly (Section 14.3.5). The current in each phase should be within 2% of the specified test value (rated current). 

The test method and test results will generally be the same as for a switchgear assembly, discussed in Section 14.3.7. 

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