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Techimp's off‑line spot testing tests can detect any insulation problems in MV/HV assets at acceptance/commissioning stage (before it is put into service). Off‑line spot tests can also be performed to assess asset insulation condition during planned maintenance outages.
These tests are typically included in the routine test performed during an outage of the rotating machine. Thanks to an external voltage generator, it is possible to provide an external power supply so, spot PD tests can be performed after the proper sensor installation.Combining the results of other investigation techniques, a combined diagnosis can be release.
These tests consist in the application of a high voltage source by RTS - resonant testing system or directly connecting the HV Cable to the grid (without load).Techimp personnel will provide an accurate measurement in order to verify absence of dangerous Partial discharge phenomena discriminating between possible noises or disturbances.
Typical periodic check up of the MV cables involve outage of the cable, in such conditions the very low frequency test are the most fitting solution. In fact, comparing with the HV field, resonant test sets can be even more expensive than the cable system.VLF generators are easy to carry on and can be energized with normal LV power supply. Due to the mainly capacitive load a voltage generator working at 0.1 Hz can easily energize long cables with a relatively low power.The equipment under test is disconnected from the load and the noise is low enough to enable a time domain reflectometry analysis. Together with the Partial Discharge test it is possible to perform some macroscopic diagnostic techniques such as: polarization index and tangent delta of the cable under test.The combination of the diagnostic results of the 3 testing techniques covers very well the possible insulation ageing problems those can occur in the lifetime of the asset.
Partial discharge is one of the possible problems originating failures in transformers. Depending on the transformer size and voltage levels, PD test can be done in off-line condition by means of different typology of sensors. Since this type of test is considered as “not connected to the grid” an external power supply is required. Typically, Resonant Testing Systems are preferred.