In field operation and maintenance, a practical problem is often encountered: the same dielectric loss tester produces stable measurement results in the laboratory, but repeatedly exceeds limits at a substation site due to electromagnetic interference. If selection only considers nominal accuracy and ignores the anti-interference implementation method and protection logic, later operation and maintenance costs will rise significantly. The following provides a comparative explanation of common solutions from the perspective of field use.
Field interference mainly comes from adjacent energized equipment, busbar electric field coupling, and potential differences in the grounding grid. Some instruments use direct power-frequency measurement, relying on shielding and multiple averaging, and have limited anti-interference capability; another type uses variable-frequency measurement, shifting the test frequency away from 50 Hz to avoid power-frequency interference at the source. The KD-9600 Variable-Frequency Anti-Interference Dielectric Loss Tester belongs to the latter category. It has a built-in variable-frequency power supply and can measure at frequencies such as 45 Hz and 55 Hz, then convert the result to obtain the power-frequency equivalent dielectric loss value, making it suitable for strong interference environments such as substations.
Conventional power-frequency dielectric loss testers have a simple structure and lower cost, and can meet usage requirements in laboratories or distribution rooms with relatively little interference; however, in 220 kV and above substations, it is often necessary to switch power sources or add shielding measures, increasing the time required for a single measurement. The advantage of the variable-frequency solution is that measurement can be completed without additional shielding, and the operating procedure is close to laboratory habits. Compared with automatic balanced bridge solutions, the variable-frequency method responds faster on test objects with larger capacitance and has relatively relaxed requirements for power supply capacity.
The instrument has high-voltage short-circuit, breakdown, and overcurrent protection. When grounding detection is not passed, the voltage boost circuit is locked to avoid live connection. Misoperation prevention design and electric shock protection can immediately cut off the high-voltage output in the event of accidental contact. For voltage rise during measurement of large-capacity test objects (capacitive voltage rise effect), the instrument automatically tracks the output voltage and makes adjustments, reducing data deviation caused by voltage drift. For field operation and maintenance personnel, these logics are directly related to the safety boundary of each voltage application.
It is suitable for measuring tgδ and capacitance of high-voltage electrical equipment in workshops, laboratories, and scientific research institutions. Common objects include transformer bushings, current transformers, voltage transformers, coupling capacitors, and power cables, etc. When measuring large-capacity test objects, it is recommended to pay attention to the capacitive voltage rise compensation status and record data in combination with ambient humidity.
