Biofouling on outdoor insulation

Lars Jonsson, ABB Sweden

A large number of publications on biofilm formation on HV outdoor insulation, both ceramic and polymeric insulators commonly report a reduction in hydrophobicity, which reduces the wet flashover voltage. It is suspected that polymeric materials are more prone to biological growth compared to ceramic materials and that certain polymeric materials are more affected than others.

This paper will present comparative study results conducted in a laboratory environment between different types of materials used for HV bushings.

Off and On-line Acceptance Testing and Diagnostic testing of Distribution Cables

Karl Haubner, Doble Australia

The industry requires simple and cost-effective commissioning and diagnostic tools that accurately assess the cable insulation condition.  More searching Acceptance Testing and ongoing Condition Monitoring is an important strategy to improve the reliability of Medium Voltage distribution cable networks.

This paper will present the most commonly performed offline diagnostic tests of Insulation Resistance, TDR, tan δ measurements, Partial Discharge measurements (using both VLF and DAC voltages) the Monitored Withstand Test and the outer sheath tests and their ability and sensitivity to determine different defects. 

Using several case-studies the benefit of each of these techniques and how the combination of the above tests can identify weaknesses to build up a comprehensive picture of the insulation condition of the cable to improve the reliability of the network will be presented.

Lessons Learned when Introducing & Applying Continuous Condition Monitoring Systems

Brian Sparling, Dynamic Ratings, USA

The market offers plenty of sensors, IEDs (Intelligent Electronic Devices), on-line continuous monitoring systems with analysis algorithms, and software systems for condition evaluation of HV substation equipment.  However, for those substation owners who have had exposure and experience with these systems and feel they have a need for it, the path can be a large task with no guidance on where and/or how to begin to move forward from their current position.  There are no written manuals from IEC and/or IEEE Standards on this topic although the IEEE and Cigré, have published guides that do provide guidance on how best to approach this project.

This paper will explore and detail the methods used by other substation asset owners who have moved forward from Time Based Maintenance to Condition Based Maintenance, with the expected impact of increasing reliability of the system and reducing the risk of unexpected failure of monitored equipment inside the substation.

Practical Fault Simulation on an Earthing Transformer using SFRA, A unique analysis approach towards simplifying SFRA results to assist with deformation diagnosis in Earthing Transformers

Hayden Sherwood, Excess Power Equipment, Australia

Earthing Transformers are an integral part of power and distribution systems around the world, although, little consideration is given to their ongoing monitoring and maintenance. The failure of an earthing transformer can cause a multitude of issues including compromised stability and safety of the electrical network. The necessity to maintain both safety and stability of electrical networks highlights valuable real-world applications for a SFRA earthing transformer testing toolkit.

This paper will present Simulation and Other results providing evidence that (for the given test subject) defect detection is possible using SFRA benchmarked comparisons.

Experience with Partial Discharge Testing on High Voltage assets

Seokhoon Hong, OMICRON electronics, Hong Kong

Partial Discharge measurement is one of the well-known techniques for insulation condition assessment on high voltage (HV) assets.  In this paper, the challenges faced by on-site PD measurement on HV assets including power transformer bushings, gas insulated switchgears, voltage transformers and HV cables are discussed. The conventional and UHF PD measurement technique with different types of PD sensors are presented.

Natural/Synthetic esters usage from an OLTC perspective

Dr Thomas Smolka, Reinhausen Australia

Requests for transformers filled with esters are on the increase, due to their advantages that mineral has a better moisture tolerance, higher fire point and being more environmental friendly.

Apart from these advantages, alternative insulating liquids present different chemical, mechanical and electrical properties which require special care with the selection of components and materials to guarantee the reliable operation of the transformer during the lifetime.

This paper will present the technical considerations of the utilization of natural and synthetic esters in combination with on load tap changers, including materials, new insulation levels and construction requirements and discuss the additional needs to retrofil transformers originally filled with mineral oil, now using some type of ester in general.

Restoring a Tumut 2 generator step up transformer to service after a h.v. bushing failure

Stuart Ednie, Snowy Hydro Limited, Australia

Tumut 2 is a hydro-electric power station, set some 244 underground near Cabramurra in New South Wales. Management of power transformers in under-ground vaults always requires care and attention as the consequences of an oil fire are elevated. Tumut 2 is no exception to this where the transformer vaults are connected to the machine hall and access tunnel via a sizeable corridor.

The Tumut 2 generator step up (GSU) transformers are single phase, 3 winding, 50/25/25 MVA 330/ /12.5/12.5 kV, and OFW. The transformers were commissioned to service in 1962. The 4 generators at Tumut 2 are connected to the 330 kV grid via 2 of, banks of these transformers A common spare exists that can be connected to the generators via 330 kV and 12.5 kV link transfer and without physical movement. On September 6, 2016 Tumut 2 transformer 91391 failed while on soak test (energised by generator alone).

The purpose of this paper is to present the procedure and proving method developed for the Tumut 2 scenario. In this way, if other industry participants have to restore a transformer to service where similar technical concerns exist, then the Tumut 2 experiences can be considered.

Test Results from In-service Transformers: Unparalleled Truth or Misconceived Information

Ami Singh, Scottish & Southern Energy, UK

With an ageing transformer fleet in the electricity industry, the asset engineers are often faced with familiar expectations of increased equipment reliability and early intervention into a developing fault. The transformer asset engineer is equipped with tools varying from offline electrical test results and periodic oil sampling, to online measurements from bushings and gas in oil analysers. Whilst these tools provide useful information, the asset engineer’s challenge is to make informed decisions based on these indicators. Decisions can be difficult when conflicting results from different tests or techniques are obtained, or when limited industry guidance is available for certain situations. Facing situations that do not result in a conventional “black” (no-go or fail) or “white” (go or pass) outcomes, but rather “grey” (not clear) result is at the realm of a transformer asset engineer. 

This paper presents results from in-service transformers where the asset owner has observed varying results from multiple techniques.

Field-testing of cast resin transformers in wind farms, industrial and marine applications under constricted space conditions

Dr Alexander Kraetge, OMICRON electronics, Germany

Our modern life strongly depends on the reliability and availability of electrical power system at any time. The electricity network has been facing challenges with the integration of renewable energy resources and the increased use of e-mobility. Power equipment used to connect renewables can face very specific and increased stress when sources of fluctuating nature are involved.

Large scale wind and solar farm often utilize transformers of different types within one farm. Smaller transformers connecting the single units to a bus feeder and several feeders than lead to the substation with one or more substation transformers which connect the farm to the power grid. While these substation transformers typically do not show increased failure rates, several countries report failure rates higher than usual for the smaller transformers. This occurs to both liquid-filled and dry-type transformers especially for wind farms.

This paper will present several test results and discuss methods of performing the induced voltage test on-site with portable equipment and the application of digital PD measurement equipment for sensitive PD detection in noisy environments.

Unusual DGA results in wind turbine transformers

Preet Singh (Grad. Student),  Trevor Blackburn (Assoc. Prof.)

UNSW School of Electrical Engineering & Telecom, Australia

The increasing use and grid connection of wind turbine farms (both on and off-shore) has led to some emerging problems involving the interconnecting cables between turbines and also the turbine unit transformers that are used to step voltage up from the low voltage output from the turbine inverters to the 33kV or 22kV of the grid system that they feed into.

The cable problems encountered have been primarily on off-shore wind farms and have been determined to be the result of switching transient voltages from the hard-switching IGBTs used in modern voltage source inverter systems used to generate the 50/60Hz voltage for grid connection.

This paper reports on some surveys of Australian wind turbine transformer DGA results and a comparison with the DGA test results for some standard oil-filled distribution transformers.  In addition to presenting the preliminary results of the DGA analysis, this presentation will also look at the possible source of electrical discharge activity and characteristics in wind turbine farms and whether preventative steps are possible.