Techniques for ultra-high voltage and very fast transients

Ultra-high voltages (UHV) are used in a range of sectors, from medical imaging to the electrical network. However, many applications lacked the pre-normative research required to support the standardisation required for safe and effective work.

This project supported standardisation of ultra-high voltage (UHV) measurement techniques and provided guidance for High Voltage (HV) metrology in three different industrial sectors.

Firstly, it addressed the need for standardisation in HV measurements for medical X-ray equipment, both for medical staff safety and more accurate x-ray dosing for patients. New standards were also required for operators of the high voltage direct current (HVDC) electricity grid, for the detection and prevention of insulation failures caused by partial discharge (PD) events – an electrical fault that can damage equipment.

The project also addressed the need for improved methods and standards for detecting ‘Very Fast Transients’ (VFT) – nano-second electrical surges caused by removing power loads – which can cause grid failures. The lack of traceable measurement techniques, which are critical for detecting failures in the grid, especially in substations such as Gas Insulated Switchgear (GIS), was also addressed.

This project conducted in-situ calibration of voltage and current in x-ray machines. An SI-traceable reference system was developed to measure x-ray pulses (up to 150 kV) to calibrate x-ray generators and instrumentation used in clinical diagnostic radiology units. A technical procedure was proposed to amend IEC 61676, simplifying the characterization of x-ray HV units used in radiology dosimetry.

Traceable measurements of practical peak voltage and exposure time ensured a better control of the dose delivered, ensuring good diagnostic performance while minimising radiation dose.

For HVDC grids, four calibration systems for low-level PD calibrators were designed, integrating a ‘Charge Sensitive Preamplifier’ to overcome signal to noise issues in lower pulses. These were validated via an inter-comparison exercise and, as a result, new SI traceable measurement services were established in Europe for PD calibrators down to 0.1 pC.

To evaluate automatic diagnosis insulation tools using ultra-high frequency sensors, a new GIS testing set-up was designed, simulating an actual substation, and is capable of traceably measuring VFT over-voltages. It can also be used in conjunction with probes representing different PD defects to evaluate automatic diagnosis tools. A new recorder, PXIe-5164, for measuring very fast transient currents was also developed and commercialised.

Project results inputted into international standard IEC 61676 specifying measurements for dosimetry equipment and into, IEC 61083-1, IEC 60270, and IEC 61869-1 relating to measurements for instrumentation in the electrical network.

As well as new instrumentation and improved methodology, new measurement services now exist in Europe, helping to protect patient safety and to implement more stable energy grids.