Calibration Proposal for UHF Partial Discharge Measurements at Power Transformers

Abstract

The continuous, non-intermitted service of electrical grids relies on the reliability of their assets, e.g., power transformers. Local insulation defects can result in serve failures such as breakdowns with severe subsequent costs. The prevention of such events is crucial. Hence, partial discharge (PD) activity at power transformers is evaluated directly in the factory before shipment. Additionally, PD activity can be monitored during service using the ultra-high frequency (UHF) method. In this contribution, a calibration procedure is proposed for the UHF method. The calibration process is required to ensure both, reproducibility and comparability of UHF measurements: Only a calibrated UHF measurement procedure can be introduced supplementary to IEC 60270 in acceptance tests of power transformers. The proposed calibration method considers two factors: The influence of the UHF-antenna's sensitivity and the PD recorder characteristics including accessories such as cable damping, pre-amplifier, etc. The former is addressed by a characterization of UHF sensors using the standard antenna factor (AF) in a gigahertz transverse electromagnetic (GTEM) cell. The PD recorder's influence is corrected by using a defined, invariable test signal as reference for all recording devices. A practical evaluation of the proposed calibration procedure is performed in a laboratory setup using different UHF recording devices and UHF sensors using artificial PD signals and real voltage-driven PD sources.

PD Signal Propagation in GIS: Ultra-High Frequency Detection-Based Modeling

“…A Gaussian pulse with rise-time of 300 ps is used at the input. Then, the sensitivity of the UHF sensor was obtained by calculating the antenna factor (AF) using [26]:…”

Modeling of the Winding Hot-Spot Temperature in Power Transformers: Case Study of the Low-Loaded Fleet

“…Since the expected values were known (they were measured directly for further model verification) the proposed method for model validation was based on the evaluation of the relative deviation of the predicted values from the expected values. That parameter was called relative mean prediction error (MPE) and was described by (5)…”

“…Power transformers are one of the most important electric power devices in the electrical power distribution system. To provide reliable and continuous power delivery, it is crucial to monitor and analyze various parameters, that allow to indicate any abnormalities in operation of each transformer unit, i.e., partial discharges [1][2][3][4][5], dissolved gas concentrations [6,7], vibrations [8], general insulation condition [6,9], temperature [10][11][12] and a number of others [6]. In order to support a continuous rating of transformers, various on-line monitoring systems (OMS) have been willingly implemented so far.…”

Radiation in the Optical and UHF Range Emitted by Partial Discharges

“…The UHF method recording signals from this range of EM waves is one of the most recently described and, in particular, implemented methods of PD detection and location. It has been found to remain on real objects, although it has been developed in laboratories [14]. The optical method consists of setting the optical fiber in the direction of the electrical discharge source and recording the optical spectrum in the range depending on the capabilities of the spectrophotometer matrix, from visible light and near ultraviolet (UV) light to wider ranges.…”