121 / 2018-08-24 22:36:30

The impact of power system transient faults on partial discharge behavior and insulation aging of polyimide nanocomposite films

Polyimide,nanocomposite,transient faults,partial discharge,lifetime,aging

When the transient faults occur in power system, the applied AC sinusoidal voltage waveform becomes asymmetrical due to the occurrence of change in current in power system resulting its average value becomes greater or less than zero and not equidistance from zero anymore. This asymmetrical response (transient naturally) in result of the fault is termed as DC-offset and the high voltage equipment can be damaged by it, especially equipment’s insulation failure. In order to exactly figure out the impact of DC-offset on partial discharge characteristics parameters and aging of insulation material (lifetime), an experimental setup has been organized to measure partial discharge and insulation aging under DC-offset comprising AC high voltage stress. The organized experimental setup is consisted of the following:
1. A Copper made sphere to plane electrode arrangement has been made.
2. An arbitrary waveform generator (Agilent 33500B) and high voltage power amplifier (Trek Model 50/12). The amplifier’s output voltage range is from 0 kV to  50 kV with DC to 1.4 kHz adjustable frequency.
3. A temperature control module comprised test chamber with 220 ℃ maximum tolerable temperature.
4. To capture the impulse current initiated by surface discharge, which flows through ground wire, a current transducer was used. The transducer bandwidth and sensitivity is nearly 500 kHz to 120 MHz and 1 mA-4.2 mV.
5. To determine high frequency sinusoidal voltage, a voltage probe has used.
6. A high-speed digital oscilloscope with 5 GS/s maximum sampling frequency and capability of sampling bandwidth in GHz.
The frequency of 1 KHz has been chosen for partial discharge (PD) and insulation aging measurements of both the pure and the titania nanocomposite films. 1%, 2% and 5% titania nanocomposite films were fabricated using In-Situ polymerization technique. Before testing each sample, anhydrous alcohol was used to clean each film and after cleaning, each film was dried for 2 hours under 60℃. In order to ensure the reliability of experimental data, each test has been conducted at least five times. Based on obtained partial discharge data for both the pure and PI nanocomposite films during the test until a moment before the occurrence of sample breakdown, detailed discussion and reasoning has been given regarding maximum and mean partial discharge amplitudes and the total partial discharge numbers for the sake of explaining the DC-offset impact on partial discharge characteristic parameters and insulation aging. Besides, phase resolved partial discharge (PRPD) patterns have been obtained for the sake of knowing various relatives partial discharge densities.
Considering the detailed analysis of experimental results for both the pure polyimide and polyimide nanocomposite films, it has been extracted that the fault initiated DC-offset do have impact on partial discharge characteristics parameters and insulation aging which initiates the insulation degradation and bring it to its failure.