Review of field acceptance hipot & PD testing of medium voltage underground cables
There are some well-defined guides and standards regarding factory testing of medium voltage shielded cables in laboratories provided by IEEE, IEC, ANSI/ICEA, and CSA. These guides cover AC withstand and PD testing of XLPE and EPR cables and accessories, such as 50/60Hz AC Hipot and PD tests which are routinely conducted on every reel of cable produced at the factory. All terminations, splices, and separable connectors are tested with more or less the same test method using different test levels and timing.
Design of Triangle Loop Antenna for Partial Discharge Impulse Signal Detection
The objective of this study was to evaluate the performance of a triangle loop antenna to assess its use as a potential sensor in partial discharge (PD) impulse signals detection. PD impulse signals were measured over a frequency up to 100 MHz at 3 kV through Needle-Plate Electrode experiment. The experiment was conducted to create an artificial PD acting as a breakdown that causes insulation failure. Subsequently, the characteristic of PD impulse signals was captured by triangle loop antenna with variation of diameters and number of turns. The number of turns is up to three turns and diameters of triangle loop antenna intervals are 6 cm, 8 cm and 10 cm. Then, the Fast Fourier Transforms (FFT) analysis was carried out to measure the frequency bandwidth. The results revealed that an experimental frequency is 32.01 MHz. Then, it can be observed that the amplitude value of peak-to-peak voltage (Vpp) for three turns 10 cm diameter of triangle loop antenna higher than the amplitude value for one turn and two turns of triangle loop antennas.
Partial Discharge Measurements over the Frequency Range 0.1 Hz to 50 Hz
The need for partial discharge (corona) measurements at very low frequencies is explained, and the results of tests on epoxy resin and polyethylene samples are given for the frequency range 0.1 Hz to 50 Hz. As no suitable commercial generator was available, a new type of low-frequency low-noise generator has been developed. The discharge detection system includes a pulse discrimination system for eliminating unwanted pulses from outside the test component. This was particularly useful when measuring discharges in a short length of cross-linked polyethylene cable and in a stator bar sample, in the presence of discharges over the ends. Traditional display methods are not suitable at low-frequency and the paper describes possible alternative recording techniques. One of these is a multi-channel pulse height analyzer, which facilitates the comparison of results over the complete frequency range. Discharge characteristics have also been recorded on a storage oscilloscope. The results obtained show that the inception voltage is virtually constant over the frequency range 0.1 Hz to 50 Hz, and also indicate how the partial discharge characteristics are affected by frequency, void size, temperature and humidity.