Search

Premium Membership ♕

Save 50% on all EEP Academy courses with Enterprise Membership Plan and study specialized LV/MV/HV technical articles & guides.

Home / Technical Articles / The most common Gas-Insulated Switchgear (GIS) faults and a case of 220kV CB cubicle

GIS operation & tricky situations

Over decades since its inception, GIS switchgear demand is still prevalent in these present times due to its compact built, reliability, and maintenance advantages compared to conventional Air-insulated switchgear. Even the strong negative effect on the environment when its gas is released into the atmosphere did not influence the GIS popularity.

The most common Gas-Insulated Switchgear (GIS) faults and how to perform investigation
The most common Gas-Insulated Switchgear (GIS) faults and how to perform investigation

SF6 gas is used in this technology owing to its very high dielectric strength characteristics compared to conventional switchgear. When used at a certain pressure, it is, by far, one of the best options as an insulating and or arc-quenching medium.

Gas Insulated Substation (GIS) is one type of power substation system similar to the conventional substations but with the advantages of compact design, thereby significantly reducing the amount of space occupied.

Typical installation of this system is of the indoor type, thus reducing exposure of components to outside weather and corrosive atmosphere. Construction is modular with various standard designs of phase segregated type, or three-phase encapsulated type with minimal dimensions emphasizing its compactness and very reliable assembly.

This system utilizes Sulfur Hexafluoride (SF6) gas due to its outstanding dielectric properties for all parts insulation.

This article has been written by the author working in operation and maintenance of SF6 Gas Insulated Switchgear for a long time. It gives practical knowledge of the most common GIS faults and how to perform investigation and maintenance.

A case study of 220kV CB cubicle and an internal mechanical defect that could cause a potential switching disaster has been described in the last chapter.

Table of Contents:

  1. GIS Main Components
    1. Circuit Breaker
    2. Hydraulic Operating Mechanism
    3. Switch Disconnect / Earthing Switch
    4. Current Transformer / Voltage Transformer
    5. Busbar
    6. SF6 Gas Monitoring Manifolds
  2. The Most Typical GIS Faults
    1. SF6 Gas Leak
    2. Mechanical Component Defects
    3. Gas Humidity Content
    4. Insulation Breakdown
  3. A Case of Internal Mechanical Defect to Cause Potential Switching Disaster
    1. Incident Timeline
    2. Investigation Findings
    3. Impacts
    4. Actions Taken
  4. Conclusion

1. GIS Main Components

1.1 Circuit Breaker

GIS breaker is typically designed with a single pressure puffer type driven by a hydraulic operating mechanism at the front end. The grounded metal cylinder housing accommodates, in this case, a single pole interrupter fixed on an insulating mount and support insulator for each phase.

It is composed of moving and fixed sections, as shown in the figure. The moving section includes the nozzle, moving contact, moving arcing contact, the puffer cylinder connected to the hydraulic operating mechanism through an insulating rod, and its insulating support.
The fixed section comprises a fixed contact, fixed arcing contact, and mounting support.

During the initial stage of operation, the puffer cylinder moves and compresses the SF6 gas inside the cylinder. The compressed gas then flows in the direction of the arc contacts to effectively extinguish the arcing generated. The gas pressure further increased due to the heat produced during arcing whilst the arcing current was large.

The access cover on top allows GIS engineers to inspect and replace nozzles and arcing contacts.

Figure 1 – SF6 Gas Insulated Switchgear Circuit Breaker Chamber

SF6 Gas Insulated Switchgear Circuit Breaker Chamber
Figure 1 – SF6 Gas Insulated Switchgear Circuit Breaker Chamber

Figure 2a – Cross-section drawing of a SF6 Gas Insulated Switchgear Circuit Breaker

Cross-section drawing of a SF6 Gas Insulated Switchgear Circuit Breaker
Figure 2a – Cross-section drawing of a SF6 Gas Insulated Switchgear Circuit Breaker

Figure 2b – Cross-section drawing of a SF6 Gas Insulated Switchgear Circuit Breaker

Cross-section drawing of a SF6 Gas Insulated Switchgear Circuit Breaker
Figure 2b – Cross-section drawing of a SF6 Gas Insulated Switchgear Circuit Breaker

Go back to the Contents Table ↑


1.2 Hydraulic Operating Mechanism

The three-pole typical operating box is generally located at the front of the circuit breaker. It houses the hydraulic operating mechanism and monitoring unit for individual single-pole operation of a circuit breaker.

The operating mechanism is composed of an oil pump, oil tank, main valve unit, pressure switches, and gauges, all arranged as one block unit and connected directly to the main cylinder making it a compact and more reliable hydraulic operating mechanism.

It’s essential to maintain the operating pressure of the hydraulic operating mechanism to operate the switchgear properly. Operating pressure for the GIS switchgear ranges typically from 30 to 40 MPa. A lower value will give an alarm command to the system.

Figure 3 – SF6 Gas Insulated Switchgear Hydraulic Mechanism (click to zoom)

SF6 Gas Insulated Switchgear Hydraulic Mechanism
Figure 3 – SF6 Gas Insulated Switchgear Hydraulic Mechanism

Go back to the Contents Table ↑


1.3 Switch Disconnect / Earthing Switch

In this example, the line disconnector is housed along with the earthing switches emphasizing its compact build and simplicity. Both of these devices usually are motor or manually driven. The disconnector typically has a switching capability of bus transfer current. The bus disconnector is connected internally to each bus enclosure.

The earthing switch is normally provided with a motor-charged spring operation mechanism. Earthing switches which are normally installed at both sides of the circuit breaker, are linked together by an operating rod and can be operated by a common operating mechanism.

Earthing mechanism is equipped with a removable bolted link from the earth point to allow primary injection and other essential tests.

Figure 4 – SF6 Gas Insulated Switchgear Switch Mechanism

SF6 Gas Insulated Switchgear Switch Mechanism
Figure 4 – SF6 Gas Insulated Switchgear Switch Mechanism

Figure 5 – SF6 Gas Insulated Switchgear Switch Mechanism

SF6 Gas Insulated Switchgear Switch Mechanism
Figure 5 – SF6 Gas Insulated Switchgear Switch Mechanism

Figure 6 – Maintenance Earthing Switch Mechanism

SF6 Gas Insulated Switchgear Switch Mechanism
Figure 6 – Maintenance Earthing Switch Mechanism

Figure 7 – Cross-section of a SF6 Gas Insulated Switchgear Switch Mechanism

Cross section of a SF6 Gas Insulated Switchgear Switch Mechanism
Figure 7 – Cross section of a SF6 Gas Insulated Switchgear Switch Mechanism

Go back to the Contents Table ↑


1.4 Current Transformer/Voltage Transformer

The voltage transformer is the common induction type. The current transformer typically is a foil-insulated bushing type with a ring and a core mounted in CT housing. Insulation in the high voltage side is equipped with SF6 gas, and its winding discs use plastic foils for effective insulation.

Premium Membership Required

This technical article/guide requires a Premium Membership. You can choose an annually based Plus, Pro, or Enterprise membership plan. Subscribe and enjoy studying specialized technical articles, online video courses, electrical engineering guides, and papers. With EEP’s premium membership, you get additional essence that enhances your knowledge and experience in low- medium- and high-voltage engineering fields.

Check out each plan’s benefits and choose the membership plan that works best for you or your organization.

50% Discount 💥 – Save 50% on all video courses with Enterprise Membership plan.

Log In »Purchase »

Premium Membership

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you to shape up your technical skills in your everyday life as an electrical engineer.
More Information
author-pic

Lark C. Cosedo

A graduate of Bachelor of Science in Electrical Engineering from the University of San Carlos, Cebu, Philippines. Currently working as Electrical Senior Engineer at Oman Water and Wastewater Services Company (OWWSC), Sultanate of Oman. Currently holding a license as a Professional Electrical Engineer (PEE), an Asean Engineer (AER) and an Asean Chartered Professional Engineer (ACPE). I have more than 20 years of experience in the various fields of Electrical Engineering majority from the Middle East Regions comprising of Greenfield Aluminum Plants, Gov’t. Wastewater Services and Electronic Manufacturing Industry. Field of expertise are mostly from the Operation and Maintenance of Power Systems, Commissioning and start-ups, Operation and Maintenance Projects and Procurements. Possesses various Electrical Authorizations, currently as Senior Authorized Electrical Person (SAEP), H3 accreditation ranging from LV systems up to 220kV HV systems and with Accreditation for Safe Operation and Maintenance of HV systems from Faraday Institute, Cyprus.

Leave a Comment

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

35  +    =  thirty six

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Hand-Crafted Courses
MV Switchgear Components