Concepts for on-site HV testing of GIS after installation, extension, retrofit or repair

Introduction

Despite its importance as a commissioning or final verification step, on-site HV testing of GIS is an area in which users and other stakeholders may have limited experience. Typically, only utilities with a large fleet of GIS installations may have the necessary exposure to on-site HV testing to maintain the required know-how and experience in this specialised area. Therefore, a structured outline for the concepts of on-site HV testing of GIS is presented in this technical brochure.

Drivers for on-site HV testing of GIS – reliability assurance (commissioning, repair, extension, condition assessment)

Besides the important aspect of OEM quality assurance procedures, another key driver for on-site HV testing is the return of experience from users. Disruptive discharges after commissioning, extension or repair work can occur in installations worldwide. The latest CIGRE reliability surveys for GIS also show that dielectric failures are still a common failure mode.

In the collation of user experience in the formulation of this technical brochure it is evident that there is a variety of practices used by OEMs, third parties and users themselves. (Inter)national standards generally form the basis of common user specifications. However, the implementation of the test procedure to be used can depend on a multitude of factors that must be discussed and agreed with the influencing parties. The final choice of the on-site test procedure is mainly based on a combination of requirements in (inter)national standards, return of experience, and up-to-date quality assurance concepts to balance the best possible compromise when looking at costs, strategic relevance and redundancy of the substation, feasibility, and potential defect detection sensitivity. The design of the GIS and each specific installation contribute significantly to these factors.

Several user cases show significant enhancements onto the test procedures as recommended in IEC, IEEE, and other (inter)national standards. Based on feedback of user experience, it is more certain, than likely, that economics and market driven factors such as GIS penetration and service experience in some regions undoubtedly play a large role in influencing the user requirements. However, an established assessment of the tangible benefits of enhanced HV testing requirements appears to be a challenge, especially when transferring from specific circumstances towards typical application scenarios.

Operators of transmission and distribution systems may be set specific targets for availability and reliability by national regulatory authorities. Performance targets and financial penalties in cases where the reliability of the GIS may impact customers is understood to be a significant driver for some of the requirements in user 

specifications. The foremost advantages of GIS which greatly act as incentives for users in adopting the equipment, such as lower footprint and maintenance, can also be of concern in the event of repairs or extension being required which can have higher impact on availability and restoration times. Maintenance, repair, and extension works on GIS may require a high level of planning and longer outages over other technologies.