What Is the Principle of Frequency Conversion Anti-Interference of Dielectric Loss Tester?

The most troublesome part of conducting dielectric loss testing in a substation is not the operation, but the interference - the 50Hz power frequency electromagnetic field generated by surrounding equipment penetrates into the measurement circuit, completely submerging the measurement signal that was originally only a few milliamps or even microamperes, and the data is meaningless. Traditional dielectric loss meters rely on shielding and electromagnetic balance to resist interference, but they often fall short in strong interference scenarios. Frequency conversion anti-interference technology fundamentally solves this problem.

The core logic of frequency conversion anti-interference

The plan for HZ-2000H is to measure at two frequencies, 45Hz and 55Hz, instead of 50Hz, and then calculate the equivalent dielectric loss value at 50Hz.

The principle is very straightforward: when the measurement system operates at 45Hz or 55Hz, the Fourier transform digital filtering algorithm is used to extract only the signal components at 45Hz (or 55Hz) frequency, and all other frequencies (including 50Hz interference) are filtered out. The manual provides a rigorous mathematical derivation, and the conclusion is that even if the interference amplitude reaches 200 times the measured signal, this frequency selective measurement can still accurately extract the signal of the target frequency, completely unaffected by interference.

Anti-interference index

HZ-2000H is clearly marked as frequency conversion anti-interference, which can still achieve the specified accuracy (tg δ ± (1%+0.00040)) under 200% interference. This means that even if the surrounding interference current is twice the measured current, the instrument can still measure correctly. This indicator has been verified in strong interference environments such as 500kV substations and GIS indoor environments.

Why choose 45Hz and 55Hz

These two frequencies are symmetrically distributed on both sides of 50Hz, with a difference of 5Hz each. They are far enough to ensure that the measurement filter can effectively isolate 50Hz interference; It is close enough that the difference between the dielectric loss values at 45Hz and 55Hz and the 50Hz value is very small (most actual insulation materials have slow changes in dielectric loss with frequency near the power frequency), and the error of extrapolating the 50Hz value from two points can be ignored.

Is frequency conversion always necessary

Under mild interference conditions, single frequency 50Hz measurement can be directly selected for faster speed, and the results correspond directly to the power frequency without the need for calculation. Only in strong interference environments (such as substation sites, GIS rooms, and high-voltage lines) must the frequency conversion mode be selected (50 ± 5Hz). HZ-2000H supports any single frequency within the range of 40-70Hz, as well as automatic dual frequency conversion, flexibly responding to various on-site conditions.