Transformer Tan Delta Tester

A: A transformer dielectric loss tester is a precision instrument specifically designed to measure the dielectric loss factor (tanδ) and capacitance (Cx) of a transformer’s insulation system. It applies a high-voltage AC signal to the transformer’s insulation, measures the phase difference between the current and voltage, and calculates the tanδ value to determine whether the insulation is damp, aged, or has localized defects.

A: tanδ is an indicator of energy loss in insulating materials under the influence of an AC electric field. A lower tanδ value indicates better insulation performance. Measuring tanδ allows for the sensitive detection of overall defects in insulation, such as general moisture ingress or aging, and is one of the core methods for assessing the insulation condition of high-voltage electrical equipment.

A: There are primarily two core wiring methods, selected based on whether the test specimen is grounded:
Forward Connection: Used when the low-voltage end of the transformer winding is insulated from ground, providing higher measurement accuracy.
Reverse Connection: Used when the low-voltage end of the transformer winding is directly grounded; this is also the most common wiring method in the field.

A: Mainstream portable, fully automatic models all feature a built-in adjustable high-voltage power supply ranging from 0 to 10 kV. Routine transformer dielectric loss tests do not require any external high-voltage equipment; the entire test can be completed with a single unit. Only for special tests on ultra-high-voltage or extra-large-capacity transformers can an external high-voltage source be used for expanded functionality; routine field testing requires no external equipment at all.

A: In addition to the transformer itself, it can simultaneously test high-voltage bushings, current transformers (CTs), voltage transformers (PTs/CVTs), high-voltage circuit breakers, insulators, high-voltage power cables, and capacitive insulation equipment. This single instrument serves multiple purposes, covering all routine insulation test items in substations.

A: - The transformer under test must be completely de-energized, voltage-tested, and fully discharged; the test circuit must be safely isolated from live equipment;
- Wipe the surfaces of the transformer bushings and terminals to remove oil, dust, and condensation, ensuring they remain dry and clean to prevent surface leakage from affecting test data;
- Ensure the instrument’s dedicated grounding lead is securely grounded, with grounding resistance meeting on-site safety requirements;
- Arrange test leads according to specifications, keeping high-voltage and measurement leads away from live busbars and high-current equipment to avoid crossing or tangling and minimize interference.

A: Absolutely not. The instrument outputs high voltage throughout the entire process—including voltage ramp-up, testing, and voltage ramp-down. It is strictly prohibited to touch the test specimen, high-voltage leads, test clamps, or terminals. A safety warning zone must be established, and unauthorized personnel must not enter the test area.

A: No. After the test concludes, the instrument will automatically reduce the voltage and fully discharge the test specimen and high-voltage circuit. You must wait until the high-voltage indicator light has completely turned off, the screen displays a message indicating discharge is complete, and the instrument has reset before disconnecting the leads. It is strictly prohibited to disconnect the leads immediately after the test to prevent electric shock from residual charge.

A: It is not recommended. Excessively high air humidity, condensation on the test specimen’s surface, or moisture absorption can cause significant surface leakage current, resulting in severely inflated and distorted tanδ data that fails to accurately reflect the transformer’s internal insulation condition. Testing should be conducted in a clear, dry environment with humidity below 80%.

A: tanδ is the ratio of active loss to reactive loss in the insulating medium. A lower value indicates better insulation performance and lower heat loss. If the tanδ value exceeds the standard or shows a significant increase compared to historical data, it suggests that the transformer’s insulation may be affected by moisture, degraded insulating oil, aged insulating paper, or internal localized defects. This indicates a decline in insulation performance and a risk of operational failure.

A: For routine preventive testing of transformers, the standard test voltage is 5 kV or 10 kV, with 10 kV being the preferred rated test voltage. Specific settings must follow the “Regulations for Preventive Testing of Power Equipment” and the transformer’s factory technical specifications; testing must not exceed the rated voltage arbitrarily.

A: The most common cause is excessive power-frequency electromagnetic interference at the site, followed by improper wiring, a dirty or damp test specimen surface, unreliable grounding, and damaged or leaky test leads. Solution: Enable the instrument’s anti-interference mode, ensure proper wiring and reliable grounding, clean and dry the test specimen surface, and move away from strong interference sources to stabilize data and ensure repeatability.

A: Standard accuracy for mainstream compliant models: measurement error for the dielectric loss tangent (tanδ) is ≤±0.1%, and measurement error for capacitance (Cx) is ≤±0.5%. These specifications fully comply with national power testing standards and IEC international standards, and meet the accuracy requirements for substation handover, pre-commissioning, and factory testing.

A: First, check whether the power supply is connected properly, the voltage matches the requirements, and the power cord is intact. For models with built-in batteries, check if the battery is sufficiently charged and if charging is proceeding normally. After ruling out power supply issues, check if the instrument’s fuse has blown. Non-professionals must not disassemble the instrument for repair.

A: The instrument is equipped with comprehensive protection mechanisms. In the event of overvoltage, overcurrent, short circuits, poor grounding, test specimen insulation breakdown, or excessive interference, it will immediately shut down automatically and discharge by reducing voltage. This is a safety protection action and will not damage the instrument. After shutdown, first disconnect the power and discharge the instrument, then troubleshoot for wiring errors, test specimen faults, or grounding issues. Once the abnormalities are resolved, retest.

A: Negative values or abnormally high readings are caused by interference or wiring errors: First, check whether the wiring is correct, the grounding is reliable, and the test leads are short-circuited or leaking current; enable the frequency-modulation anti-interference mode, rewire according to specifications, move away from interference sources, clean the test specimen’s surface, and retest to restore normal operation.

A: First, check for short circuits in the wiring, whether the test specimen has suffered a breakdown, and whether the grounding wire is securely connected. If the instrument door is not properly closed, there is a wiring error, or the protection circuit is triggered, the high-voltage output will be forcibly locked out. Once wiring and test specimen issues are resolved, the voltage will increase normally.

A: Yes. As a precision metrological testing instrument, the calibration interval is one year under normal usage conditions. It must be sent to an accredited metrology institution for calibration to obtain a calibration certificate, ensuring the accuracy and reliability of test data and meeting power testing compliance requirements.

A: The instrument should be stored in a dry, well-ventilated environment free of corrosive gases and strong magnetic fields. Avoid direct sunlight, severe vibration, and impact. During transportation, use the original shock-resistant carrying case and ensure adequate moisture and shock protection to prevent damage to the internal high-voltage modules and precision sampling units.