If the tanδ value increases by more than 30% compared to historical data or exceeds the absolute limit (e.g., oil-paper insulation >0.8%), it is determined that the insulation is damp or aged, and immediate action is required to avoid explosion accidents. Commissioning tests: Before new equipment is put into operation, verify the consistency between factory data and on-site test data to rule out insulation damage during transportation and installation. Fault diagnosis: In a 500kV substation, the CVT dielectric loss exceeded the limit. After using a variable-frequency dielectric loss tester to eliminate interference, the data was confirmed to be accurate. Disassembly revealed water ingress inside the capacitor core, which timely prevented equipment breakdown. 5. Usage precautions Safety first: The dielectric loss tester outputs high voltage (up to 12kV). During testing, a safety area must be demarcated, dedicated personnel must supervise, and it is strictly forbidden to connect or disconnect wires while energized. Shielding measures: In strong interference environments, be sure to use the shielding wires provided with the instrument, and reliably ground the low-voltage end of the test object (such as the CT end screen) or ground it through the instrument. Surface cleanliness: Dirt and moisture on the surface of the test object can significantly increase surface leakage current, leading to inflated tanδ values. Before testing, the surface must be cleaned and dried, and if necessary, a shielding ring should be installed. Temperature conversion: The dielectric loss value is greatly affected by temperature. The ambient temperature and equipment temperature during testing must be recorded and converted to 20°C for comparison (conversion coefficients vary for different insulating materials). Summary If you need to purchase or rent a dielectric loss tester: Routine maintenance: Choose the variable-frequency anti-interference models from Wuhan UHV or Wuhan Moen, which offer the best cost performance and fully meet the requirements of State Grid/China Southern Power Grid. Scientific research/arbitration: If the budget is sufficient and there is an extreme requirement for accuracy, OMICRON can be considered. Key point: Do not only look at the price; anti-interference capability is the core factor determining whether the instrument can "measure accurately and reliably" on site. Do you need selection advice for a specific voltage level (such as 500kV), or do you want to know specific test wiring methods? The Dielectric Loss Tester (also known as "tan delta tester") is the "gold standard" instrument in power systems for evaluating the insulation condition of high-voltage electrical equipment. It measures the dielectric loss tangent (tanδ) and capacitance (C) of insulating materials to sensitively reflect overall moisture, aging, deterioration, or local defects in equipment. In the context of smart grid operation and maintenance in 2025-2026, the dielectric loss tester has evolved from a traditional single-function instrument to a high-precision, anti-interference, fully automated intelligent diagnostic terminal. 1. Core functions and testing principles Core indicators: tanδ (dielectric loss factor): Reflects the magnitude of energy loss in insulating materials under AC voltage. The larger the tanδ, the worse the insulation performance. It is the most sensitive indicator for judging overall moisture and aging of insulation (more sensitive than insulation resistance testing). Cx (capacitance): Monitoring changes in capacitance can detect large-area short circuits, open circuits, or geometric dimension changes inside the insulation. Applicable equipment: Capacitive equipment: Current transformers (CT), capacitive voltage transformers (CVT), coupling capacitors, bushings, surge arresters. Other high-voltage equipment: Transformer windings, generator stators, high-voltage cables, etc. Testing principle: Digital upgrade based on the Schering Bridge principle. A test voltage (usually 10kV, but can be customized) is applied, and the phase difference between the current signal and voltage signal flowing through the test object is collected. High-speed DSP/FPGA calculates tanδ and Cx. 2. New technology trends in 2025-2026 According to the latest industry standards (such as the DL/T 962-202X revision) and new products from mainstream manufacturers, the current technology shows the following breakthroughs: A. Ultimate anti-interference capability (core pain point solution) Background: The electromagnetic environment at substations is extremely complex, and power frequency interference often causes traditional instruments to have fluctuating data or even fail to test. New technologies: Variable frequency anti-interference technology: Automatically scans and locks onto non-power frequency frequencies (such as 45Hz/55Hz, 47.5Hz/52.5Hz, etc.) for testing, avoiding 50Hz interference from the source. Digital filtering + AI algorithms: New generation instruments (such as those from Wuhan UHV and OMICRON's latest models) have built-in adaptive digital filters that can still output stable and accurate data in environments where the interference current is 10 times greater than the test current. Heterodyne synchronous sampling: Uses high-precision phase-locked loop technology to ensure sampling synchronization and eliminate frequency drift errors. B. Intelligence of "self-excitation method" and "reverse connection method" CVT-specific self-excitation method: For capacitive voltage transformers (CVT), no external high-voltage source is needed. The high voltage is generated using the CVT's own electromagnetic unit for measurement, making wiring simple and safe, and it has become standard. Fully automatic reverse/forward connection switching: The instrument's internal relays automatically switch wiring modes to adapt to different grounding conditions of the test object (such as bushings with grounded bases using the reverse connection method), eliminating the need for manual rewiring. C. Multi-channel parallel testing and vector analysis Three-channel/six-channel synchronization: High-end models support simultaneous testing of three-phase equipment (such as three-phase CTs), completing A/B/C phase data acquisition in one go, improving efficiency by 3 times, and directly calculating three-phase unbalance. Vector diagram display: The screen displays voltage and current vector diagrams in real time, helping experts intuitively analyze phase relationships and determine interference sources. D. Digitalization and IoT integration Cloud diagnosis: Test data is automatically uploaded to the PMS system or cloud database, combined with historical data for trend analysis to predict insulation life. Electronic fence and GPS: Test records are automatically bound to geographic location and timestamps, preventing data falsification and meeting the digital team assessment requirements of State Grid/China Southern Power Grid.
