Experimental test of dielectric response under impulse voltage excitation

Author： GOZ Electric Time：2024-08-16 09:20:11 Read：10

1. Experimental platform

    In this section, the Tektronix AFG3011C function/arbitrary waveform generator and Trek MODEL 30/20A high-voltage amplifier are used to build an impulse voltage excitation source, and the Tektronix MDO 3054 mixed domain oscilloscope is used to collect data on the voltage and current waveforms. The experimental platform structure is shown in the figure. The transient voltage excitation source can output a standard operating impulse voltage with an amplitude of 30 kV, a rising edge of 250μs, and a half-peak time of 2500 μs. By controlling the output signal of the arbitrary waveform generator, the wavefront, wave tail time, amplitude, and repetition frequency of the high-voltage pulse can be quickly adjusted. The impulse voltage applied to the central guide rod of the bushing is measured by a resistor divider with a voltage divider ratio of 2000:1, and the leakage current of the bushing end screen is measured by a 50Ω sampling resistor. The high and low voltage arm resistors and the current sampling resistor of the voltage divider are all non-inductive resistors. At the same time, the impedance and phase curves of the WK6500B high-precision impedance analyzer are obtained, and the impulse voltage and response current signals are further corrected in the frequency domain to eliminate the measurement error introduced by the resistance frequency response characteristics as much as possible.

2. Test results

    A standard operating impulse voltage with an amplitude of about 6kV is applied to the transformer bushing, and the waveforms and amplitude-frequency characteristics of the externally applied voltage and response current are measured as shown in the figure. As can be seen from the figure, the bushing end screen response current generates an amplitude of about 556.5mV and a voltage waveform with a rising edge of about 13.9μs on the 50Ω sampling resistor, which is converted into an end screen leakage current with an amplitude of about 11.13mA. The amplitudes of each frequency component of the externally applied impulse voltage signal gradually decrease with the increase of frequency, while the amplitude-frequency characteristics of the current waveform show a trend of increasing first and then decreasing.

    According to the oil-paper insulation dielectric response algorithm under impulse voltage excitation mentioned above, the applied voltage and response current signals are processed to obtain the frequency domain dielectric spectrum of the transformer bushing model under impulse voltage excitation, and compared with the frequency domain dielectric spectrum obtained by DIRANA product sweep frequency measurement, as shown in the figure. As can be seen from the figure, the transformer bushing dielectric response measurement method based on impulse voltage excitation proposed in this paper has high accuracy and can achieve rapid measurement of dielectric response.

Conclusion

    This paper proposes a fast measurement method for the dielectric response of transformer bushing under impulse voltage excitation. The rich frequency components contained in the impulse voltage signal are used as the excitation signal to obtain the bushing end screen response current and perform data processing and calculation, so as to measure the frequency domain dielectric response information of the bushing. Firstly, the dielectric response theory of oil-paper insulation and the calculation method of dielectric response under impulse voltage excitation are introduced; secondly, based on the frequency domain dielectric response of oil-paper insulation, the Debye model parameters are extended, and the dielectric response simulation model of transformer bushing under impulse voltage excitation is built in the Simulink platform. The standard operating impulse voltage is applied to the bushing and the response current signal is obtained to obtain the frequency domain dielectric spectrum of the bushing, thereby verifying the feasibility of impulse voltage as the dielectric response measurement excitation signal and the accuracy of the dielectric response algorithm; finally, an experimental platform is built to apply the standard operating impulse voltage to the bushing model to be tested, and the voltage and current signals are measured by the resistor divider and the sampling resistor, and the data is processed to obtain the dielectric response of the transformer bushing under impulse voltage excitation. The simulation and experimental results show that the measurement method based on impulse voltage excitation proposed in this paper can quickly and accurately obtain the dielectric response information of the transformer bushing.