Product Introduction
Transformer Dielectric Loss Factor Tester (also known as variable frequency anti-interference tan delta tester) is a core special test instrument for power industry to evaluate insulation condition of high-voltage electrical equipment. It is mainly used to measure dielectric loss factor (tanδ) and capacitance Cx of capacitive test objects including power transformers, bushings, CT, PT, capacitors and high-voltage cables. Matching special model with constant temperature oil cup can test dielectric loss of transformer insulating oil under high temperature. Adopting digital variable frequency Schering bridge measurement structure, the instrument is equipped with dual different frequency anti-interference technology (45/55Hz, 47.5/52.5Hz), which effectively eliminates 50Hz power frequency electromagnetic interference in substation site to ensure stable and accurate test data. Built-in SF6 gas-filled high-precision standard capacitor, integrated functions of automatic zero boost, instant breakdown short-circuit protection, automatic temperature compensation, data storage and printing. One operator can finish full-automatic measurement. Widely used in transformer factory test, new equipment handover test, substation preventive test and insulation evaluation after overhaul.
Test Principle
When AC high voltage is applied to insulating medium, capacitive reactive current and resistive loss current will be generated. Dielectric loss factor tanδ equals resistive current divided by reactive current. Moisture, aging, oil contamination, air gap and sealing damage inside insulation will cause obvious increase of tanδ value, which is a sensitive index to predict potential insulation defects inside transformer. The instrument outputs different-frequency test voltage via variable frequency high voltage source, collects amplitude and phase of voltage and current of test sample synchronously, and calculates tanδ and capacitance at high speed. Interference filtering algorithm based on data difference of two test frequencies eliminates on-site power frequency noise. Built-in standard capacitor serves as measurement benchmark to realize high-precision bridge balance calculation. Two main types: Equipment tan delta tester (reverse connection for winding and bushing test); Insulating oil tan delta tester (with 90℃ constant temperature oil cup for liquid insulation oil quality inspection).
Core Functions
- Four standard wiring modes: reverse connection, positive connection, CVT self-excitation, external high voltage mode, fully meet test demands of transformer and supporting equipment
- Dual frequency anti-interference: optional 45/55Hz & 47.5/52.5Hz, stable reading under strong electromagnetic field
- 0.5kV~10kV continuously adjustable high voltage, automatic zero boost and auto step-down after test completion
- Built-in temperature compensation algorithm to automatically correct tanδ deviation caused by temperature change
- Multi safety protection: grounding interlock, overvoltage, overcurrent, instant high voltage cut-off upon breakdown with audio-visual alarm
- Large local data storage, test report export via USB flash disk, built-in thermal printer
- Industrial touch screen with Chinese & English bilingual menu, one-click full-automatic measurement
General Technical Specifications
| Item | Technical Index |
| High Voltage Output | 0.5kV～10kV continuous adjustable |
| Output Frequency | 45/55Hz, 47.5/52.5Hz, fixed 50Hz optional |
| Tanδ Measuring Range | 0.001%～100%, resolution 0.0001% |
| Tanδ Accuracy | ±(Reading×0.5% + 0.00005) |
| Capacitance Range | 3pF～1μF (internal HV); max 30μF (external HV) |
| Capacitance Accuracy | ±(Reading×0.5% + 0.5pF) |
| Standard Capacitor | Built-in 50pF SF6 gas-filled standard capacitor |
| Storage Capacity | Store ≥1000 groups of test data |
| Operating Condition | Temp: -10℃~50℃, Humidity ≤80%RH (no condensation) |
| Protection Grade | IP20 integrated portable aluminum alloy chassis |
Applicable Test Objects
- Oil-immersed power transformer: measure tanδ of HV/LV winding with bushing to ground and independent tanδ of bushing tap to judge winding moisture, insulation aging and bushing sealing failure
- Transformer auxiliary equipment: CT, PT, CVT, high voltage bushing, busbar insulator
- Energy storage & power distribution equipment: HV shunt capacitor, dry reactor, medium & high voltage power cable
- Insulating oil test (special oil tan delta model): test tanδ and volume resistivity of new oil & running transformer oil at 90℃ to identify oil oxidation, impurity and moisture pollution
Product Advantages
- Strong anti-interference performance: dual different frequency digital filter ensures stable reading under complex electromagnetic environment of substation and power plant, no shielding room required
- Integrated portable design: boost unit, standard capacitor and operation terminal integrated inside mainframe, no extra auxiliary equipment for field maintenance
- High safety reliability: grounding interlock protection, high voltage cut off within millisecond once breakdown to avoid electric shock hazard
- Easy operation: full automatic test flow without manual bridge balance adjustment, easy to operate for new staff
- Traceable data: fully record test voltage, frequency, temperature, tanδ and capacitance, support standardized report export to meet power acceptance standard
- Multi-function integrated: one instrument completes all capacitive insulation tests for transformer, bushing, CT, PT and cable, reduce procurement cost
Executive Standards
DL/T 962-2005 <General Technical Specifications for Dielectric Loss Tester>
DL/T 474.3-2018 <Guide for Electrical Test of Power Equipment — Measurement of Dielectric Loss>
GB/T 1409 <Recommended Methods for the Determination of Permittivity and Dielectric Loss Factor of Electrical Insulating Materials at Power, Audio and Radio Frequencies>
IEC 60243-1 <Electrical strength of insulating materials>
Typical Application Scenarios
Transformer manufacturers: type test & factory insulation inspection
Power grid corporation: annual preventive test & post-overhaul inspection
Power plants: regular insulation evaluation of main transformers for thermal, PV and wind power station
Third-party power testing institute & power maintenance company: handover test and fault diagnosis
Standard Field Test Procedure
- Safety preparation: cut off power supply, fully discharge for over 10min, short three-phase windings, single-point reliable grounding for instrument, clean dirt on bushing surface
- Wiring: adopt reverse connection mode, short-circuit and ground all non-test windings, connect HV shield cable to tested winding
- Parameter setting: select dual frequency mode, set test voltage 10kV, input ambient temperature for compensation
- Start full-automatic test; instrument completes boost, data acquisition and step-down automatically
- Record data and repeat test for HV & LV winding; fully discharge again and remove wiring after all tests finished
- Compare test data with factory & historical records, evaluate insulation condition combining insulation resistance and oil analysis results
Safety Operation Specification
Max test voltage reaches 10kV, set warning fence around operation area with full-time supervisor
Use special discharge rod for full discharge after each wiring change and test completion
Connect instrument ground terminal to earth independently; series shared ground is forbidden
Bushing tan delta test is forbidden under rainy and high humidity (RH＞80%) condition, surface leakage will cause false high reading
High voltage module and standard capacitor are precision high-voltage components, disassembly without manufacturer authorization is prohibited
The specific operation of transformer dielectric loss factor testers (also called as Transformer Tan Delta Tester) of different models and manufacturers may vary. When using, you should read the instruction manual of the tester in detail and test in strict accordance with relevant standards and operating procedures. If you need, you can consult the sales staff of Shanghai DEMIKS Electric Technology Power co.,ltd. For more power test equipment, please visit the website: www.demikspower.com
