CT Purpose To accurately reduce the primary current to a value suitable for relays and meters. (5 or 1 amps). Provide isolation from the high voltage system.
Testing and Verification NETA -National Electrical Testing Association Recommendations: –Perform polarity test. –Perform ratio-verification test using voltage or current method –Perform an excitation test. –Measure circuit burden.
Ratio and Polarity Ratio must be verified so that relays and meters will operate and indicate correctly. Polarity must be correct if relays are to look in the correct direction, and for meters to indicate correctly.
Ratio and Polarity Errors Taps may have been connected to the wrong terminals or may have been labeled incorrectly. Wrong number of turns on CT secondary. Shorted turns. Wrong polarity markings.
Saturation Voltage Excitation characteristics and saturation voltage must be known to verify that the CT will perform as required by providing required output voltage during fault conditions.
Typical test circuit of variac volt and amp meters
Time Study Time to test 5-tap CT (ten ratios and one excitation curve) with older style equipment for: –Ratio –Polarity and phase-angle –Excitation and Saturation –Winding Resistance –Insulation resistance –Time=52 minutes With DCT-2000x5, time < 5 minutes
Adwel solution The DCT-2000 offers the most advanced features in automated multi-ratio CT testing. Product available in two models: –DCT-2000x2 –DCT-2000x5 – Test Plan Driven
Key Features of DCT-2000x2 Automated testing of one winding of a CT for: –Ratio –Polarity and phase-angle –Excitation and Saturation –Winding Resistance –Insulation resistance
Other Features Saturation voltage (knee point) is calculated. Winding resistance is measured Insulation resistance is measured Full 75 key keyboard Store 200 files. Store 140 test plans in x5.
Other Features Up to 2000 Vac output Up to 2 amps output Burden output: 20 amp @ 20 volts Circuit impedance measurement in burden mode. Transfer results to PC with USB Transfer results to memory stick
PC Based Software Results stored in database. –Sort on twelve fields. Generate full report form including data and color graphs of all curves. Files compatible with word processing and spread sheets.
Modes of Operation Auto mode: –Allows DCT to automatically complete a series of tests. Manual mode: –Allows operator to manually raise and lower the voltage to make diagnosis. Burden mode: –Current source for secondary injection
Comparison of models Both models have identical features regarding tests, output, range, accuracy, keyboard, printer, memory capacity, memory stick, software and database. Differences are listed below.
Test Automation X2: –Check boxes on test screen are used to select the tests to be performed in automatic sequence. X5: –A test plan conducts the required tests on up to ten ratios on a multi- ratio CT. Saves 140 plans.
Extent of Automation X2: –Completes all selected tests for one winding. X5 –Completes all selected tests for up to ten ratios.
Conclusion Contact your local representative or Adwel International for questions or further information.