Work of an EMPIR energy project has drawn interest from the electricity industry

<p><em>Supply Reliability of Future HVDC and HVAC Grids using Qualified PD Analyzers</em></p>

Supply Reliability of Future HVDC and HVAC Grids using Qualified PD Analyzers

Energy networks are transitioning from alternating current (AC) to high voltage (HV) direct current (DC), which is more efficient over long distances. However, established measurement methods, instrumentation, and standards for AC are not always applicable to DC grids.

Partial discharges (PD) cause a short circuit in a part of the electrical insulation (dielectrics) through "sparks" that can cause insulation degradation until it is completely broken. . This can cause a series of repeating, transient, high frequency pulses of current that can damage insulation and degrade power quality.

The rate and amplitude of PD pulses are smaller under high voltage DC (HVDC) than similar AC voltages (HVAC), making them harder to detect. Thus, instrumentation for detecting PD events need to be sensitive and require accurate, low-level calibration to ensure the stability of DC networks.

Completed EMPIR project Techniques for ultra-high voltage and very fast transients (15NRM02, UHV) addressed this problem, establishing measurement services in Europe for PD calibrators down to and below the level required by networks. The project also contributed to a revision of the International Electrotechnical Commission (IEC) standard IEC 60270 High-voltage test techniques - Partial discharge measurements.

During the project a synthetic PD calibrator was developed that integrated real data of ‘noise’ from grid installations such as wind plants and electrical substations and DC plants. However, at the end of this project in 2019 this instrument still required metrological validation.

The new PD calibration technique has now been further developed in the current EMPIR project Metrology for future energy transmission (19ENG02, FutureEnergy).

During this project the new synthetic PD generator has been used in three different validation exercises.

A PD comparison was carried out in 2021 among four HV laboratories that use PD measuring systems in accordance with the IEC 60270 standard. These results show that the PD analyser could produce results in accordance with the requirements of the IEC 60270 standard.
A second series of qualification tests were carried out in 2022 with three commercial continuous PD monitoring systems used for HVAC grids with the data supplied to an artificial intelligence platform for PD recognition developed by REE (the Spanish Transmission Service Operator). The synthetic PD generator injected PD signals into different locations of the testing set up to emulate insulation defects in different grid subsystems. Results obtained show that the percentage of successful recognitions achieved by the AI platform depends on the PD clustering capability of the commercial PD monitoring system used, varying from 60 % to 95 % in the best of cases.
In 2022 the robustness of the synthetic PD calibrator was evaluated in a Round Robin Test involving two metrological institutes and three universities. Tests showed that some analysers were able to measure within the specified tolerance (±10 % for offline measurements and ± 30 % for online measurements and continuous monitoring) under noise conditions (up to 50 % for offline measurements and up to 200 % for online measurements).

The PDP calibrator will allow the qualification of commercialized partial discharge analysers, currently without minimum requirements established by any international standard. Qualified PD analysers will allow diagnoses to be more reliable than they currently are and prevent diagnostic errors that could lead to severe network failures (blackouts, explosion, fires).

Alf-Peter Elg who coordinated the project said about the calibrator:

“The Round Robin has been successfully completed. A synthetic PD generator capable of reproducing calibration PD trains in the range of 2 pC to 15000 pC and PD pulse trains representing insulation defects in HVDC and HVAC grids has been developed. This generator allows performance and functionality tests for qualification of PD analysers used for offline or online measurements and continuous PD monitoring in HVAC and HVDC grids”.

Project collaborator and equipment manufacturer, HAEFELY, is interested in adopting the new PD calibrator, as has the high voltage equipment manufacturer HIGHVOLT, presently constructing a new HVDC highway through Germany.

The standardisation organisation IEC group “Power electronics for electrical transmission and distribution systems”, (IEC TC22F ) are also very interested in the exploration of the technique for a new standard in this area in the future.

Supporting higher transmission voltages using DC will reduce losses during electricity transmission, currently equivalent to 150 million tons of CO2 per year.

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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