ELECTRICAL TEST VT CT INSTRUMENT TRANSFORMERS
VISUAL AND MECHANICAL INSPECTION
- Inspect for physical damage and compliance with design drawings.
- Check mechanical clearances and proper operation of all disconnecting and grounding devices associated with voltage transformers.
- Verify proper operation of grounding devices for withdrawable voltage transformer and shorting devices for current transformers.
- Verify that the insulation of the CT’s meets the voltage rating of the equipment.
- When CT’s are applied with cable terminations the grouped cable screen must extend beyond the CT.
ELECTRICAL TESTS
Current transformers shall have secondary saturation tests done and the test results recorded.
Confirm transformer polarity electrically.
Burden tests will be made at the secondary leads of the CT to assure accurate translation of primary current.
Verify connection at the secondary CT leads by driving a low current through the leads and checking for this current at applicable devices.
Confirm transformer winding ratio(s).Measure insulation resistance of transformer winding with five hundred volt megger.
Measure transformer primary insulation with applicable over-potential tests see manufacturer’s instructions or refer to this article high potential test.
Verify connection of secondary VT leads by applying a low voltage to the leads and checking for this voltage at applicable devices.
Check for VT secondary load with secondary voltage and current measurements. Make sure load is less than VA of the VT.
CURRENT TRANSFORMER TEST DATA
| PLANT | |
| SUBSTATION | |
| CIRCUIT | |
| B.I. NO. |
MAGNETIZATION CURVE
|
VOLTS |
CT 1
milliA |
CT-2
milliA |
CT 3
milliA |
CT 4
milliA |
CT 5
milliA |
CT 6
milliA |
CT 7
milliA |
CT 8
milliA |
CT 9
milliA |
CT 10
milliA |
CT 11
milliA |
CT 12
milliA |
RATIO TEST (CURRENT)
| CT 1 | CT 2 | CT 3 | CT 4 | CT 5 | CT 6 | CT 7 | CT 8 | CT 9 | CT 10 | CT 11 | CT 12 | |
| Primary Amps | ||||||||||||
| Secondary
Amps |
||||||||||||
| Ratio |
|
| CT Burden | ||||||||||||
| Voltage Across CT | ||||||||||||
| Insulation Resistance |
POLARITY IDENTIFICATION MARKS
Voltage Transformer Test Data
| Manufacturer | |
| Serial No. | |
| Voltage Rating | |
| Rating (VA) | |
| Connection | |
| Polarity | Additive Subtractive |
Insulation Resistance Test
| Temperature ( deg. C) | |
| Megger voltage: 500/100/2500/5000 |
WINDING RESISTANCE TEST SINGLE PHASE VT
| H1 to H2 | ohms | X1 to X2 | ohms | ||
| H3 to H4 | ohms | X3 to X4 | ohms |