765kV Transformer Tan Delta Test Case

I.Test Informtion

①Before the test ,we shuould disconnected all leads from the transformer.And then,we connected test cables by a crane ,because the transformer is very high.

Figure 2  765kV transformer

②Firstly,we used UST model to test the transformer.The UST configuration is used for measurements between two terminals of a test specimen that are not grounded or that can be removed from ground. In the UST configuration, current flowing in the insulation between the voltage lead and the measuring lead of the instrument is measured and current flowing to ground is not measured.In Figure 3 example below you measure the capacitance and dissipation factor between high-voltage winding (HV) and low-voltage winding (LV), C = CHL.

Figure 3  UST Modle

Figure 4 On-site Display

Wait until our test is finished,you could print test data.As shown in Figure 5:

Figure 5 UST Test Result

③Second,we used GST model.The GST configuration permits testing of a grounded insulation specimen through the specimen's ground. All current flowing to ground is measured. The wiring method is as follows:

Figure 6 GST Model

Figure7 GST Test Result

④ Finally,used GSTg to test.The GSTg configuration allows unwanted currents, to bypass the measuring circuit and enables smaller sections of insulation to be tested individually. Only the ground currents are measured, using a GST-Guard configuration. Current flowing to terminals with the guard connection is not measured.The wiring method is as follows:

Figure 8 GSTg Model

GSTG function, the capacitance and dielectric loss of C1 and C2 can be measured at the same time in one wiring.It is very easy and save time.

Figure 9 GSTg Test Result

III.Test Summary