Classic Case | Comprehensive Characteristic Test Report for Transformers

PART 1: Main Information of the On-Site Test

Test Date: 2025.11.13

On-site Tester: Gao Wenhao

Weather Conditions: Sunny

Test Location: A certain substation

Basic On-site Information: * Test Sample Type: Current Transformer

Voltage Level: 27.5KV

Test Item: Comprehensive characteristic test of transformer

Instrument Used: TCT-200F

Test Data: Yes

PART 2: Test Process

Step 1: Test Preparation

• The tested transformer is a 27.5KV current transformer.

• Its nameplate is shown in Figure 2.

  
  

  

 Figure 2

• Remove the wiring of the current transformer to disconnect it from the main circuit.

Step 2: Test Process

• First, ground the instrument reliably.

• Then, short-circuit the S1 K1 terminals and S2 K2 terminals of the instrument respectively and connect them to the secondary winding of the transformer to be tested.

• The secondary winding tested in this operation is 1S1-1S3.

• The remaining untested secondary windings are left open.

• Connect the P1 and P2 terminals of the instrument to the P1 and P2 copper busbars on the primary side of the transformer.

• The transformer casing should be grounded.

• The wiring is shown in the figure below.

• Through one-time wiring, items such as ratio, polarity, excitation characteristics, and winding DC resistance can be completed all at once.
  

Figure 3: Wiring Diagram

Figure 4: On-site Test Wiring

• Turn on the main unit and configure the settings.

• The parameters that can be set include the rated secondary current, class, and maximum test current.

• The instrument can then test out the ratio, polarity, DC resistance, and excitation characteristics.

  
  

Step 3: Result Judgment

• The theoretical ratio of the 1S1-1S3 winding is 320:1.

• The measured ratio value is 300:0.9364.

• The turns ratio is 319.91.

• The polarity is subtractive.

• These results meet the requirements.

• The volt-ampere characteristic test meets the requirements when compared with its factory values.

Figure 5: Test Results

PART 3: Test Summary (On-site Issues, Precautions, etc.)

• The volt-ampere characteristic test of a current transformer is only performed on the secondary winding that has requirements for relay protection.

• Before the test, the secondary winding leads of the current transformer and the CT grounding wire should all be removed.

• Reliable safety measures must be taken to prevent grounding.

• This ensures that each phase of the CT is reliably independent of the application equipment during the test.

• Otherwise, it may cause damage to the equipment.