Measurements and Analysis of Partial Discharges at HVDC Voltage with AC Components

Abstract

This paper presents the methodology for phase-resolved partial discharge measurements in HVDC systems with a DC voltage containing trace AC harmonics or a DC voltage ripple. The measurement result of partial discharges is an indicator of the current condition of the high-voltage power devices’ insulation system. The voltage waveforms in HVDC systems are not ideal DC, because different disturbances occurring naturally in these systems can affect the DC voltage. The AC harmonics related to the AC source voltage, and the voltage ripples provided by the power converter topology, can be found in the HVDC voltage. This paper proposes a novel approach to partial discharge measurement in DC networks. The synchronization to the particular AC harmonics appearing in DC voltage was applied to the PD measurements. The analyses were performed on the model sample containing a void inclusion, which was placed between electrodes fed by the DC voltages with the imposed chosen AC harmonics. Two scenarios were analyzed at a constant DC level: one with a variable AC magnitude and the second with a variable frequency of an AC source adjusted to the harmonics: 50, 150, 300, and 350 Hz. It was observed that the superimposed AC voltage component resulted in an intensification of PDs.

The Dynamic Change in the Reliability Function Level in a Selected Fire Alarm System during a Fire

“…According to the article's authors and available source literature studies, there are no standards and legal requirements in this regard [60][61][62][63]. Proceeding with the design process requires prior testing of the electroclimate, including vibrations and noise [64][65][66][67]. Such solutions (environmental measurements and assessment) also mean a lower probability of ESS false alarms [68][69][70][71].…”

New Synthetic Partial Discharge Calibrator for Qualification of Partial Discharge Analyzers for Insulation Diagnosis of HVDC and HVAC Grids

“…Furthermore, when the voltage remains constant in an HVDC grid, the rate of PD pulses due to a defect, such as a cavity in the insulation, is negligible since they appear mainly when the voltage changes [7]. Even for commissioning and maintenance tests of HVDC cable systems, power frequency voltages are applied instead of direct voltage [10][11][12][13] because PD measurements are easier in HVAC than in HVDC. PD monitoring of HVDC cable systems is currently challenging [5][6][7].…”

“…A digital recorder (9) with a 250 MHz bandwidth is placed below the open test cell (8) to acquire output voltages from the reference HFCT sensors ( 6) and (7). A computer keyboard (13) with a built-in screen ( 14) is available as a user interface to control and manage the qualification tests. The AWG generator can use an internal memory of 4 GB or an external memory of 240 GB.…”

“…Figure13. Frequency response of the reference HFCT: amplitude and phase shift of the transfer impedance Z t expressed in (mV/mA) and in degrees ( • ), and fitting of the transfer impedance using the mathematical expression(12).…”

Recent Trends in Power Systems Modeling and Analysis

“…Nevertheless, harmonics, displaying different amplitudes and frequencies, are also found in DC voltages and currents, which are intrinsic to the AC/DC conversion process. In [17], a test procedure is proposed to measure partial discharges (PDs) within a dielectric sample with a void. The sample is tested under DC voltage excitation, with a superimposed AC ripple.…”