Transmission and distribution equipment

CIGRE Study Committee (SC) A3 is responsible for the collection of information, technical evaluation of power system studies, and technical analyses of both AC and DC substation equipment from distribution through transmission voltages which are not explicitly dealt with by other SCs:

• Devices for switching, interrupting, or limiting currents including circuit breakers, load switches, reclosers, ring-main units disconnectors, earthing switches and fault current limiters wherever installed.
• Surge arresters, capacitors, busbar and equipment insulators, instrument transformers, bushings, and all other equipment within the substation not specifically covered under another equipment study committee’s scopes.

This scope is well suited to address the technical needs of utilities that require technical and sustainable solutions for emerging problems and challenges in changing network conditions. The examples of A3 activities includes the following:

• Innovative design and technologies (e.g. DC circuit-breakers)
• Requirements for equipment in changing network conditions
• Incorporation of intelligence into HV equipment (e.g. Controlled switching)
• Monitoring and diagnostics of transmission & distribution equipment
• New and improving testing techniques
• Reliability assessment and lifetime management of ageing equipment
• Difference of designs and requirements in T&D equipment

2019 was a very busy and interesting year for A3 SC in which we have been reshaping the committee and expending our reach to put us in position to better serve the industry needs in the future. 

First, we worked on strengthening our activities within Distribution. We have been working to include more distribution experts within A3 SC, and this will continue in 2020. Also, members of SC A3 strategic committee participated in CIRED conference in Madrid where we made good contacts which can help both organizations in the future.

Second, we established the relationship with IEC TC 38 Instrument Transformers committee that should enable A3 to better cover the rapid developments in voltage and current sensing, data processing and analytics. This is very important considering that more and more smarts and sensors are being embedded inside T&D equipment.

Third, SC A3 is working towards expending its geographic presence to the countries where we have a few active members in the Working Groups. The strategic Working Group meeting was held in Cairo in March 2019 in connection with a participation of a conference on “Future on Electricity Grids”. In addition to participating in the conference and connecting to a lot of local experts, SC A3 strategic members gave a tutorial on a Switching Equipment

Also, the regular SC meeting took place on Thursday 12th of September in combination with the 5th CMDM conference in Bucharest (Romania). The progress of AGs and WGs were reported. The members discussed the future technical work.

Lastly, we formed the Utility Advisory board (UAB) to be the ‘Voice’ of utilities at Cigre. The UAB will consist of Cigre members employed by utilities. The task would be to discuss the needs of utilities, correlate those needs and formulate a strategic plan from a utility point of view to advise Cigre of the requirements of utilities with respect to the tasks of A3. In 2020 the plan is to have the first UAB meeting and start growing the team.

In 2019 we have also looked in a rearview mirror and compared the workload now to the workload a decade ago. In the chart below, one can see that there has been an increase in number of active Working Groups – in 2009 we had 9 active Working Groups and in 2019 we had 13. We have 2 Working Groups dealing with Distribution and 2 Working Groups covering DC equipment, and in 2009 we had none. Also, an important note is that now we have more Joint Working Groups (JWG), because the subjects are more complex and require the expertise from different Study committees. This will continue in the new decade and we can expect to see more and more JWG in the future.

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In 2019 all the activities related to SC A3 are listed in the table below:

The progresses of active WG’s managed by SC A3 are summarized below:

WG A3.30 finished the work. The TB will be published in early 2020. The TB will present a review on recommendable practices for detecting and mitigating potential overstress in substation equipment. The WG has focused on identification of the different kinds of stresses affecting HV equipment, standardized stress limits, stress evaluation procedures, and utilities’ practices on how to work around the overstress in short-term planning or in system operation. Stressing factors related to electrical, environmental, and operational causes were considered. These results were compiled in a risk matrix, including cross-referencing the stressing factors with the relevant equipment standards.

WG A3.31 will provide guidelines on non-conventional instrument transformers, especially focusing on testing, calibration and communication. After the tutorial delivered during the CIGRE symposium in 2013, the WG lost momentum and key experts. The current plan for this WG is to publish the Electra paper instead of Technical Brochure.

WG A3.35 finished their work. The TB was published under the number 757 in 2019. The TB “Guidelines and Best Practices for the Commissioning and Operation of Controlled Switching Projects” give an excellent l update on the knowledge of controlled switching technology and to provide guidelines for the commissioning and operation of controlled switching projects, including some lessons or pitfalls to avoid. The Working Group was disbanded.

WG A3.36 is investigating simulation tools focusing on temperature rise tests by following up on the activity of WG A3.24. The WG discussed the electromagnetic phenomena, such as joule losses, skin effect and proximity effect, and thermal phenomena, including conduction, convection and radiation, which are considered in today’s multi-physics simulations. In 2016 two benchmark devices were designed and manufactured to reproduce those physical phenomena in a typical MV and HV arrangement. In 2018 Temperature rise tests have been performed on both devices. In 2019 the results of the multi physic simulations that are done on the benchmark devices were compared against the test results. The differences of the different simulations as well as the differences to the test results were discussed and analysed. The publication of the results of this very interesting Working Group to what extent can simulations replace real tests is expected in 2020.

WG A3.38 is investigating the state of the art of shunt capacitor switching in distribution and transmission systems including filter banks. A particular intention is to compare the switching performance verified in type tests and the actual performance in service. A survey was carried to collect experience of users with different switching devices in different applications, and the trends in the use of capacitors in changing networks. The TB publication is also planned in 2020.

WG A3.39 is collecting field experience with Metal Oxide Surge Arresters (MOSA), focusing on the reliability issues on system and equipment since they have a function to protect other equipment in the substation. The WG clarifies consistency of design and testing requirements for MOSA’s based on field experience. A reliability survey can help to understand how actual field stresses can be covered by the requirements on MOSA’s, including the consequences of short-circuit. The WG will also cover reliability of MOSA in HVDC applications. The WG held a Workshop to exchange the field experience on MOSA in Beijing, China, with many experts in China. A detailed reliability survey on MOSA and other equipment was drawn up and distributed to various utilities. The TB is expected to be delivered in 2021.

WG A3.40 was established in 2018 and is investigating the technical requirements and testing consideration that will help to develop efficient and reliable MVDC switches and circuit breakers.

WG A3.41 was also established in 2018. The WG collects information focusing on the interrupting and switching performance with SF6 free switching equipment and investigate these capabilities during the expected lifetime under typical switching conditions. In addition, a technical feasibility of EHV circuit breakers will be briefly addressed by considering cost and economic aspects.

WG A3.42 was the third Working Group established in 2018. The content of the WG is to study the frequency and detailed phenomena of the major incidents of conventional instrument transformers, and provide the possible causes analysis, countermeasures, adequate diagnostic techniques and recommendation for improvement. The WG may also suggest additional type testing and routine testing requirements of instrument transformers to reduce the possibility of incidents.

JWG A3.43/ CIRED started theirs work in end of 2018. This WG focuses on what to do with the data collected from diagnostic activity and monitoring systems to assess the switchgear condition and estimate its end of life. The WG will collect and analyse the volunteered information provided by utilities and manufacturers about the way how the end-of-life of T&D switchgear is estimated. The final target is having a toolbox to enhance the use of monitoring and diagnostic data in a shared and more comprehensive way to reach a more quantitative description of the current state of the switchgear condition.

In 2019 three new A3 Working Groups were established and one JWG in which A3 will support C4 SC. We were positively surprised by a large number of nominations for these Working Groups.

JWG A3/A2/A1/B1.44 will investigate the consequence for the electrical equipment of situations in the transmission and distributions systems in which the operating voltage can temporarily exceed the highest voltage for the equipment (Um).

WG A3.45 will investigate methods for identification of frequency response characteristic of voltage measurement systems. Due to the change in energy production the influence on the power quality of the energy is given. Continuous voltage signals beginning from DC as an offset up to several 10 kHz can appear. For transient voltage signals, the resulting frequency may be in the range from 0.5 MHz up to 10 MHz. The relevant instrument voltage transformers based on the conventional technology as well as on the non-conventional low power technologies (both analogue and digital) will be analysed and categorized. Discussions about physical dependencies and influences on the accuracy will be made.

WG A3.46 is the first Working Group which deals with topic Generator Circuit-Breaker. Therefore, the topic of the WG is quite broad and covers the history, the current state of the art and possible future applications. Additional experiences on requirements and their background of generator circuit breakers as well as their testing possibilities shall be given.

In addition to the work of the Working Groups, SC A3 has continued their work on 4th T&D Equipment reliability survey. The preliminary data was published and presented at CMDM 2019 conference. Further data from utilities have been requested and will be included in the paper that will be presented at CIGRE 2020.

At the end, here is an outlook of the future SC A3 events. The highlight in 2020 will be the Paris session in August, where the main work of the SC will focus on. After 2020 SC A3 is planning the following future events.

• CIGRE SC A3 colloquium or Joint events with other SCs, 2021; New Delhi India
• CIGRE SC A3 & D1 colloquium, 2021 or 2023 Moscow Russia (planned not finally fixed)
• CIGRE SC A3 & B3 colloquium, 2023, United States (planned not finally fixed)

Contact

• Contact of the Chair and/or the Secretary of the Study Committee

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