Abstract
Signal injection method (SIM) is widely applied to the insulation parameters’ measurement in distribution network for its convenience and safety. It can be divided into two kinds of patterns: injecting a specific frequency signal or several frequencies’ groups, and scanning frequency in a scheduled frequency scope. In order to avoid the disadvantages in related researches, improved signal injection method (ISIM), in which the frequency characteristic of the transformer magnetizing impedance is taken into consideration, is proposed. In addition, optimization for signal injection position has been accomplished, and the corresponding three calculation methods of line-to-ground capacitance has been derived. Calculations are carried out through the vector information (vector calculation method), the amplitude information (amplitude calculation method), the phase information (phase calculation method) of voltage and current in signal injecting port, respectively. The line-to-ground capacitance is represented by lumped parameter capacitances in high-voltage simulation test. Eight different sinusoidal signals are injected into zero-sequence circuit, and then line-to-ground capacitance is calculated with the above-mentioned vector calculation method based on the voltage and the current data of the injecting port. The results obtained by the vector calculation method show that ISIM has a wider application frequency range compared with signal injection method with rated parameters (RSIM) and SIM. The RSIM is calculated with the rated transformer parameters of magnetizing impedance, and the SIM based on the ideal transformer model, and the relative errors of calculation results of ISIM are smaller than that for other methods in general. The six groups of two-frequency set are chosen in a specific scope which is recommended by vector calculation results. Based on ISIM, the line-to-ground capacitance calculations through the amplitude calculation method and phase calculation method are compared, and then its application frequency range, which can work as a guidance for line-to-ground capacitance measurement, is concluded.
Highlights
In distribution network, the number of grounding fault reaches 70% in all types of system faults, and over 70% of them are transient faults [1]
When the current signal is injected be affected the magnetizing because the injecting transformer is be normally in through theby open-delta of the 10impedance kV potential transformer (PT) in bus, the measurement accuracy may affectedsmall by the size, and prone to be saturated
The improved signal injection method (ISIM) is operated through vector information, amplitude information and phase information of the injecting port
Summary
The number of grounding fault reaches 70% in all types of system faults, and over 70% of them are transient faults [1]. The injection pattern of current signal is: the open-delta secondary side of potential transformer (PT) in bus [10,21] and the secondary winding of arc suppression coil [9,22]. For the traditional injection patterns [9,10,21,22], the power is injected to the secondary side of the transformer such as PT or arc suppression coil with a high turn ratio. When the current signal is injected be affected the magnetizing because the injecting transformer is be normally in through theby open-delta of the 10impedance kV PT in bus, the measurement accuracy may affectedsmall by the size, and prone to be saturated.
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