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- Product: CT and VT Test System
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Basic principle of accuracy testing is a comparison of unknown CT/VT with a high precision standard CT/VT. This comparison is performed with most precision microprocessor based comparator which 20 bit dual ADCs allows the precise detection of signal of standard CT/VT and CT/VT under test.
Possible Tests for CT/VT
Interturn Insulation Test (CT)
Only one CT will be tested with an open secondary winding and a primarily current up to 1 x IN or 1.2 x IN RMS (1 minute). The peak voltage on the secondary winding of the CT will be measured by a high-impedance peak-voltage meter. The primarily current increases until 1 x IN or 1.2 x IN continuously or stops, if the peak voltage of the CT reaches 4.5 kV on the open secondary winding. This high voltage of 4.5 kV usually appears only during a test with CTs, which have an extreme ratio, e. g. 1000 A : 1 A. Continuous decrease of the current to zero after the test.
Demagnisation (CT)
The demagnetisation will be performed generally for preparation of CTs for accuracy test. The current should be increased carefully e.g.up to 5 % while the CTs are secondary open.
Polarity Check (CT/VT)
This procedure checks the polarity between primary and secondary winding and guarantees the correct direction of energy fl ow. The polarity check takes place before the accuracy test.
Accuracy Test (CT/VT)
Carry out the accuracy test with free selectable test points e. g. 120 – 100 – 20 – 5 – 1 % IN (CT) or 80 – 100 – 120 % UN (VT) with the corresponding burden steps. A load point table can be prepared and entered according to own standards.
Process of CT/VT Testing
The test compares the ratio error of the CT or PT under test with the standard transformer of the test equipment.
The result of ratio error and phase displacement will be indicated.
The comparison takes place in a self-calibrating comparator
(measuring bridge).
The PC shows the following measurement results:
- Rated current (% IN) / rated voltage (% UN)
- Ratio error (%)
- Phase displace error (min)
- Frequency (Hz)
The PC stores the measurement results. The results are compared with the error values corresponding to the accuracy class. Finally a test protocol represents the results.
CTs or PTs, which errors are outside the allowable limits are marked as FAIL.
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Generation
|
16 kVA |
| Frequency | 50 Hz |
| Primary current | 1000 A |
| Primary voltage | 20 kV |
| Secondary current | 1 A / 5 A |
| Secondary voltage | 100 V / 100/sqrt 3V |
| Main functions |
CT testing up to 1200 A
VT testing up to 24 kV
Routine tests
- Interturn insulation test (CT)
- Demagnetization (CT)
- High voltage and insulation test (VT)
- Accuracy test incl. polarity test (CT/VT)
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| Components |
Electronic Voltage Regulating and Measuring Unit EVRMU16-04
Measuring bridge WM3000 I and U
Electronic compensated standard current burden ESCB200 and voltage burden ESVB200
Standard Current Module SCM1000-120-03
Test tables for CTs
HVT80, SVT, HV rail with grounding switch and grounding rail
Remote control
PC test system including test software CheckCon
|
| Scope of application | Testing of CT and VT |
Mode of Operation
- The operator has to insert the identifi cation-numbers of the VT or CT under test and to connect the primary and secondary terminals of the VT or CT.
- Then the operator can start the test, which will be done automatically the accuracy-test normally begins with the lowest (VT) or highest (CT) test point.
- To the next test point the voltage/current will be regulated up subsequently after the last test point the test voltage is regulated down to zero.
- To the next test point the voltage/current will be regulated up subsequently after the last test point the test voltage is regulated down to zero.
- If the VT or CT is completely tested the operator has to disconnect the tested VT or CT.
- After all tests the software application presents the test-results and all results will be stored in the data base.