Abstract
Transient voltages in the power grid are the key for the fault analysis of a power grid, optimized insulation design, and the standardization of the high-voltage testing method. The traditional measuring equipment, based on electrical engineering, normally has a limited bandwidth and response speed, which are also featured by a huge size and heavy weight. In this paper, an integrated optical electric-field sensor based on the Pockels effect was developed and applied to measure the transient voltages on the high-voltage conductors in a non-contact measuring mode. The measuring system has a response speed faster than 6 ns and a wide bandwidth ranging from 5 Hz to 100 MHz. Moreover, the sensors have the dimensions of 18 mm by 18 mm by 48 mm and a light weight of dozens of grams. The measuring systems were employed to monitor the lightning transient voltages on a 220 kV overhead transmission line. The switching transient voltages were also measured by the measuring system during the commissioning of the 500 kV middle Tibet power grid. In 2017, 307 lightning transient voltages caused by induction stroke were recorded. The characteristics of these voltage waveforms are different from the standard lightning impulse voltage proposed by IEC standards. Three types of typical switching transient voltage in 500 kV AC power grid were measured, and the peak values of these overvoltages can reach 1.73 times rated voltage.
Highlights
The wide existence of the transient voltage in the power grid threatens the insulation system of high-voltage plants, which often causes the grid faults [1]
In 2017, a total of 832 pieces of data were recorded by the two measuring systems. 650 pieces of data were recorded by the system in Z-substation and 184 pieces of data had been recorded by the system in the Y-substation. 307 pieces of data can be synchronized with a ground flash recorded by the lightning location system of China (LLS)
Once a lightning stroke was recorded by two measuring systems, the double-end traveling wave location method (DTLM) is activated to determine the position along the Yan-Zhuang line and nearest to the lightning stroke point
Summary
The wide existence of the transient voltage in the power grid threatens the insulation system of high-voltage plants, which often causes the grid faults [1]. The fastest transient voltages (i.e., very fast front overvoltage, VFFO) usually appear at a gas-insulated switchgear (GIS), which. Sci. 2019, 9, 1951 is caused by the operation of the GIS disconnectors [2,3,4]. For the fast-front transient voltages, the rising time is normally in the range of 0.1 μs to 20 μs [5]. In terms of a transient voltage caused by normal operation, the rising time is in the range of microseconds. It is noted that these transient voltages are usually superimposed on the power-frequency voltage, which requires a wide bandwidth and fast response speed for the voltage measuring system to be well measured
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