Aim/Purpose of the IR Test:

  1. To ensure that, each winding of the Current Transformer, has sufficient Insulation Resistance with respect to Earth (CT Body) and between the two Secondary Cores.

Principle:

Insulation Resistance is the Ratio of the Applied Voltage (DC) to the total Leakage Current. Leakage current should be as small as possible , therby IR Value should be as high as possible (R=V/I).

Isolation required for the Test:

  1. Breaker in Off condition, both Isolators in Open Condition.
  2. Remove the secondary wires in CT MK Box which is placed on ground.

Test Procedure:

  1. Record the Ambient Temperature, Weather conditions and note down the CT Details , Test Kit Details and details of the Testing engineer.
  2. Primary to Earth : Connect the Test kit Red Lead to the Primary stud of the CT and Black Lead to the Earth. If CT is on the Ground, the Black lead of the Test kit, be connected to the Body of the CT. Start the Megger, with 5 KV Test Voltage and note down the Value.
  3. Primary to Secondary: Connect the Red Lead of the Meggar to the CT Primary Stud and connect the Black Lead to the CT Secondary. In case of a Connected CT, remove the Secondary connections from the CT MK, and connect the Blck Lead of the Meggar to the each Secondary Core. Run the Test with 5 KV Test Voltage
  4. Secondary to Earth: Red Lead of the Megger connected to each CT Core Secondary and Black Lead is kept commob to Earth. Run the Test with 1 KV Test Voltage.
  5. Secondary to Secondary (Core to Core): Test Leads are connected between Secondary Wires of two Cores. Test is carried out at 1 KV Vtg.

Recording the Test Results:

Note down the following Data:

  1. Place: Write the Name of Substation or Place
  2. Feeder/Transformer/spare: Write the Name of Feeder or the Tfr

  3. Phase: R/Y/B

  4. CT Make, Serial Number & DOM: Say ABB/546544/01.05.2012

  5. Test Kit Make & Sr. No: Megger 12121315

  6. Date of Caliberation of the Test Kit: 
  7. Atmospheric Condition: Sunny/rainy/ Cloudy    Ambient Temperature: 

  8. Taken by: Name of the Engineer

  9. Test Voltage: 1KV/5KV
  10. Test Time: 30 sec

Please find below Table for IR Value Test of a 22 KV 3 Core CT:

SR No.Test PointTest VtgDate of Test 10.12.17Prev. dt. 09.12.17StandardRemark
1P-E5KV1000M (Min)
2P-1S5KV1000M (Min)
3P-2S5KV1000M (Min)
4P-3S5KV1000M (Min)
51S-E1KV50M (Min)
62S-E1KV50M (Min)
73S-E1KV50M(Min)
81S-2S1KV50M(Min)
91S-3S1KV50M(Min)
102S-3S1KV50M(Min)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Please find below Table for IR Value Test of a 220  KV 5 Core CT:

SR No.Test PointTest VtgDate of Test 10.12.17Prev. dt. 09.12.17StandardRemark
1P-E5KV1000M (Min)
2P-1S5KV1000M (Min)
3P-2S5KV1000M (Min)
4P-3S5KV1000M (Min)
5P-4S5KV1000M (Min)
6P-5S5KV1000M (Min)
51S-E1KV50M (Min)
62S-E1KV50M (Min)
73S-E1KV50M(Min)
84S-E1KV50M (Min)
95S-E1KV50M (Min)
101S-2S1KV50M(Min)
111S-3S1KV50M(Min)
121S-4S1KV50M(Min)
131S-5S1KV50M(Min)
142S-3S1KV50M(Min)
152S-4S1KV50M(Min)
162S-5S1KV50M(Min)
173S-4S1KV50M(Min)
183S-5S1KV50M(Min)
194S-5S1KV50M(Min)

 

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