ELECTRICAL TEST VT CT INSTRUMENT TRANSFORMERS

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  

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