The Tan Delta Tester is an essential tool for testing the insulation quality of transformer bushings. This article will outline the procedure for conducting Tan Delta(C&DF) tests on 220/132kV transformer bushings.
1. Safety Preparations
1.1 Pre-test Safety Requirements
- Obtain work permit and clearances
- Ensure transformer and bushings are completely isolated
- Install proper grounding
- Establish safety barriers and warning signs
- Verify all personnel have appropriate PPE
- Clean bushings thoroughly before testing
1.2 Required Equipment
- Power Factor (Tan Delta) test set (12kV minimum Like ISA TDX5000 etc)
- Tap adapter for bushing tap connection
- Test leads and cables
- Grounding cables
- Temperature and humidity meters
- Bushing data sheets
- Test record forms
2. Test Conditions
2.1 Environmental Requirements
- Ambient temperature: 10°C to 40°C
- Relative humidity: < 85%
- No rain or condensation
- Bushing surface must be clean and dry
- Record oil temperature for correction factors
3. Test Configurations
3.1 220kV Bushings Test Modes
1. UST Mode (C1 Test)
- Connect test voltage to bushing tap
- Ground bushing conductor and tank
- Measure C1 capacitance and Tan δ
2. GST Mode (C2 Test)
- Connect test voltage to bushing conductor
- Ground bushing tap and tank
- Measure C2 capacitance and Tan δ
3.2 132kV Bushings Test Modes
1. UST Mode (C1 Test)
- Connect test voltage to bushing tap
- Ground bushing conductor and tank
- Measure C1 capacitance and Tan δ
2. GST Mode (C2 Test)
- Connect test voltage to bushing conductor
- Ground bushing tap and tank
- Measure C2 capacitance and Tan δ
4. Test Procedure
4.1 General Steps
1. Record nameplate data of each bushing
2. Note factory test values for comparison
3. Clean bushings and tap connections
4. Verify tap cover gasket condition
4.2 Testing Sequence
1. Test each bushing individually
2. For each bushing:
- Perform C1 test (UST mode)
- Perform C2 test (GST mode)
- Record test voltage, current, and power factor
- Measure capacitance values
- Take three readings for consistency
4.3 Test Voltage Levels
- C1 test: 10kV
- C2 test: 10kV
- Maintain stable voltage throughout test
5. Acceptance Criteria
5.1 New Bushings (at 20°C)
- Power Factor (Tan δ):
- C1 ≤ 0.4%
- C2 ≤ 0.7%
- Capacitance deviation from nameplate:
- C1: ±5%
- C2: ±10%
5.2 Service-aged Bushings (at 20°C)
- Power Factor (Tan δ):
- C1 ≤ 0.7%
- C2 ≤ 1.0%
- Investigate if:
- Change from previous test > 0.3%
- Capacitance change > 3%
6. Data Recording
6.1 Required Measurements
- Test voltage and current
- Power factor (Tan δ)
- Capacitance values (C1 and C2)
- Temperature during test
- Humidity during test
- Time and date of test
6.2 Documentation
- Bushing serial numbers
- Test equipment details
- Test configuration diagrams
- Operator and witness signatures
7. Temperature Correction
1. Record actual test temperature
2. Use manufacturer's correction curves
3. Apply correction formula:
PF(20°C) = PF(T) × K
where K is temperature correction factor
Compared with old results and FAT reports.After the test is complete, the bushings are reconnected to the power source and the ground. The readings obtained from the Tan Delta Tester should be compared to the standard values provided by the manufacturer to determine the insulation quality of the bushings. If the values are within the acceptable range, the bushings are deemed to be in good condition. However, if the values are outside the acceptable range, further investigation is required to diagnose the problem.