Greetings! You have made the first step into one of the most interesting topics: Partial Discharge (PD)! Among a broad range of insulation tests, PD measurements are used to detect localized defects and anomalies within electrical insulation systems. Introduced to the power industry several decades ago, the measurements were mainly performed in the factories and during the R&D processes. In the last two decades, significant technology advances were made allowing PD measurements to be performed consistently both in the factory and in the field, at different stages in the service life of many medium-voltage (MV) and high-voltage (HV) apparatus.
The goal of this PD Bulletin is to increase awareness toward PD measurements and provide a platform of unbiased technical references on the topic of partial discharge. The content of the PD bulletin will be constantly updated and will cover many aspects of PD measurements for a wide range of MV and HV assets.
We encourage you to give us your feedback on our new PD Bulletin and make suggestions on the content you would like to see. The PD bulletin team whole heartily welcomes you!
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A Study of the Pulse Propagation Behavior in a Large Turbo Generator
Want to know how signal is propagated inside a rotating machine? The experiment described in this paper was performed by drilling at several locations in a Turbo generator and inject artificial PD pulses at these locations.
The measurement is then taken with both a frequency selective PD measurement system and a wideband digital oscilloscope. Such signal propagation behavior would greatly affect the measurement sensitivity and should be considered before we conduct a PD measurement on machines.
Other Articles of Interest:
- Assessment of the Condition of Dry-Type Transformers by Means of Partial Discharge Diagnosis Using a Mobile Voltage Source
- Experiences with the Acoustic Localization of Partial Discharge in Liquid-Immersed Power and Distribution Transformer with Help of UHF Measurement Technology
- On-site Testing of High-voltage Cable Systems
- Partial Discharge Measurements on Rotating Machines – Experience and Innovation
- A Guide for Partial Discharge Measurements on medium voltage (MV) and high voltage (HV) appartus - Part 1
- A Guide for Partial Discharge Measurements on medium voltage (MV) and high voltage (HV) appartus - Part 2
What is the divider ratio or calibration factor?
The divider ratio (for MPD600 users) or the calibration factor (for MPD800 users) is a multiplying factor that is applied to the calculated apparent charge value. It is used during the calibration process. When a calibration pulse is injected across a test object, part of the energy will circulate through the stray capacitance of the system and therefore, will not reach the sensor. The divider/calibration factor corresponds to the ratio between the measured charge at the sensor and the charge of the injected calibration pulse.
What is the measured center frequency (fcenter) and measured frequency bandwidth (Δf)?
When using the frequency domain integration, a bandpass filter is applied to every recorded PD pulse. The parameters fcenter & Δf define the cut-off frequencies of that filter (fcenter ± Δf/2). The filtered signal is afterward integrated to obtain the apparent charge.
Will partial discharge measurements detect every type of defects in my test object?
No. Partial discharge measurements will only detect anomalies that generate partial discharges. Depending on the asset, some defects creating PD could also go undetected for different reasons (e.g. PD attenuation, user errors and high level of interference).