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Current Transformer Testing


Testing Procedures

  • Insulation Resistance test.
  • CT Resistance, Excitation curve, Ratio & Polarity test.
  • Current Transformer Loop test.
  • Primary Injection Test.
Download: CT Test Format

Equipment Required

  1. Insulation Resistance tester: Megger mit1020. 
  2. CT Analyzer
  3. Multimeter.
  4. Primary Injection Kit: ODEN AT
Picture
Insulation Tester
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CT Analyzer
Picture
Multimeter

Insulation Resistance Test

  • Use Megger mit1020 to measure insulation resistance.
  • Insulation Resistance Tests to be done:
    • Primary winding - Ground      (Apply 5000V for 1 minute)
    • Primary winding - Secondary winding      (Apply 2500V for 1 minute)
    • Secondary winding - Secondary winding      (Apply 2500V for 1 minute)
    • Secondary - Ground      (Apply 1000V for 1 minute)

CT Characteristics Test 

  • Use CT Analyzer to test CT Characteristics.
  • ​Connection on CT Analyzer will be same as the shown figure.
  • Repeat the test for the other phases and the other secondary cores.
  • Refer to CT Analyzer User Manual to find how to use CT Analyzer & how to enter CT Data.
Picture
Connection Circuit

CT Loop Resistance Test

  • Measure CT resistance from CT terminal blocks (CT Side).
  • Measure Loop resistance from CT terminal blocks (Load Side).
  • Measure the Total Loop resistance (CT resistance + Load resistance + wiring resistance). 

CT Primary Injection Test

  • Core Identification Test:
    • In this test we confirm the CT secondary connection.
    • Inject low current (for example: 50A).
    • Use small jumper to short the CT secondary from CT box, the measurement will be gone at panel.
    • Repeat this test for all phases and cores.
  • Short & Isolate Facility Test:
    • In this test we confirm the CT short & isolate facility for correct connection.
    • Inject low current (for example: 50A).
    • Short CT links then Isolate the external wiring to confirm CT circuit will not be opened.
  • Single Earth Point Test:
    • For all CT Loops, each loop must have only one earth point, otherwise secondary current will be divided.
    • Open all earth point in the loop, check with buzzer that there is no earth link is closed, then close only one point.
    • For all protection & measurement CTs, Close the earth point in the nearest point to the CT.
    • For High Impedance Differential Protection, Close the earth point in the nearest point to the Relay.
  • Primary Injection Test:
    • After confirming all previous steps, CT is ready now to the primary injection test.
    • Use the ODEN AT kit to inject high current (for example: 500A).
    • Measure the secondary current in all loop up to the end of this loop.
Picture
ODEN AT
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CT Terminal Block
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  • Home
    • Site Map
    • About Substations
  • Formats
    • Auxiliary Relays
    • Equipments Formats
    • Protection Formats >
      • Energization Tests
    • Functional Test Format
  • Manuals
  • Software
  • Support
    • Testing & Commissioning
    • Test Procedures
    • Relays Calculations
    • Relays Configuration
    • Tutorials
    • References
    • Label Design
  • Blog
  • About Me