PRE-COMMISSIONING TEST CAPACITIVE VOLTAGE TRANSFORMER

PRE-COMMISSIONING TEST PROCEDURE FOR CAPACITIVE VOLTAGE TRANSFORMER

CAPACITIVE VOLTAGE TRANSFORMER Purpose

This procedure is prepared to carry out various pre-commissioning tests to be conducted in systematic manner for CVT to ensure the healthiness and performance of the equipment

Scope

This procedure covers the Pre commissioning test for CVT as for the following

Continuity test
Secondary Winding resistance test
Insulation Resistance Test
Polarity test
Ratio test
Tan delta test

Pre-Testing Checks

Check out the working condition of ELCB(30 mA)
Check the insulation of power cable for equipment
Ensure proper earthing and rubber mats available at the work location.
Calibrated Testing equipment should be used and calibration reports available with engineers for the same
Check out the insulates hand tools available with the technician
Ensure the Healthiness of the test leads (Check for any insulation Damages)
Ensure appropriate PPE’s available at sites

Resources – Tools and Equipment Required

For Continuity Test
1. Multimeter with leads

For Insulation Resistance measurement Test (IR Test):
1. Test Leads
2. 500 V, 5000 V Insulation Tester
3. Insulated Hand Tools

Winding resistance test
1. Multimeter with leads

Polarity test
1. 9V battery
2. Galvano meter
3. Connecting leads

Ratio test
1. Single phase Variac 28 A / auto transformer
2. Step-up transformer 230/5000 V
3. Multimeter
4. Connecting leads
5. Single phase AC supply

Tan delta test
1. Tan delta kit
2. Connecting leads

Operational Sequence of work(Test Procedure)

Obtain the work permit from the client
Ensure zero energy in the CVT
Ensure the external wires are removed from CVT
Ensure the all connections are in tight before testing

Insulation Resistance(IR) Test

Connect the 5000 VIR kit earth lead with earth and connect Positive lead with CVT primary side
Connect 5000 V IR kit the positive lead to primary and earth lead to secondary each core
Connect 5000 V IR kit the positive lead to core and earth lead to earth
Connect the positive lead to any core and earth lead to another core if applicable
Select the required voltage range in IR kit and apply the voltage to the CVT
Note the IR values from IR kit
Discharge the voltage from the CVT with respect to earth.

DO’S

DON’TS

Remove the CVT primary earth
Check all the CVT primary and secondary wires are isolated
Check the calibration due of the test equipment
Ensure zero resistance when line and earth are shorted and switched on to know the zero value for the proper working of kit.
Keep some distance while doing the test.
After Insulation resistance test completion, note down the values and discharge the CVT terminals and remove the test cables
Ambient temperature must be noted.

Don’t touch any cables and the kit when it is in running condition.
Don’t remove the cables without discharging.
Don’t test with damaged cables and improper clips
Don’t work in wet (rainy) conditions
Don’t lose your concentration while testing.

Polarity test

Connect the galvanometer to secondary terminal –a1/a2/a3 (positive)
Connect the galvanometer to earth –( negative )
Apply pulse voltage of 9 V battery to primary + positive and earth negative
Check the deflection in the galvanometer
It must be in clock-wise direction
Above mentioned test to repeated remaining cores

DO’S	DONT’S
Check the connections as per the diagram. Check the CVT secondary cable continuity from CVT secondary to CVT terminal block. Check whether the battery is charged or not Verify the galvanometer in good condition	Don’t use low batteries for testing Don’t apply the charge continuously (apply single pulse)

Ratio test

Connect the single phase variac 28 A and step-up transformer230/5000 V
Connect the step-up transformer across the primary terminals(P1) and earth
Connect the variac in A.C supply extension board with ELCB rated with 30 mA
Inject the voltage across the primary terminal and earth
Note down the corresponding secondary voltage at various cores between phase and earth
Switch off the supply to the primary injection kit

DO’S	DONT’S
Apply the voltage in the primary terminals only Secondary side should be kept open	Don’t apply voltage across the secondary terminals

Winding resistance test

Connect the multimeter leads to the CVT secondary winding Terminals
Note down the winding resistance value
Repeat the above procedure for remaining cores

DO’S	DON’Ts
Measure with calibrated multimeters Note the ambient temperature Remove the secondary terminals to isolate the CT Clean the secondary terminals and measure the resistance.	Measure the CT winding resistance for individual cores Primary winding resistance should not be measured (Only the secondary) Loose connections should be avoided in the CVT secondary terminals. Don’t measure the terminals with dust in CVT secondary terminals.

Continuity test

Connect the multimeter leads to the CVT secondary winding Terminals
Observe the beep sound in multimeter
Repeat the above procedure for remaining cores

Tan delta test

Top and middle stacks:

Apply 10 KV between flanges of Top/Bottom stacks
Carry out measurements in UST mode at 10 KV

Bottom stack connected to EMU PT

Connect HV of the test kit at the top flange of bottom stack HF point to be grounded Earth connection of the neutral of the PT to be opened/isolated from ground
Top of CVT to be guarded LV lead of the kit to be connected at the top of the CVT guarding
Carry out measurements in GST mode at 10 KV
Repeat the test with neutral of PT connected to ground
In case Tan delta value negative/erratic only capacitance value are to be monitored

Control Measures

OCP for IR and Ratio test for CVT is available with testing engineers
Ensure PTW system in place for the particular bay
Ensure all supply to the equipment is dead
Unauthorized persons should not be allowed to enter Testing area
Barricade the testing area with warning tape
Proper supervision, conduct job specific toolbox meeting and barricading the entire area
Calibrated equipment shall be used
Insulated hand tools shall be used
Avoid joints for power cable and supply has to be taken via ELCB
Avoid Lone working
Use appropriate insulated hand gloves