Challenging Ground Grid Design

A customer needed a gas-insulated switchgear (GIS) substation built on a small urban site as part of a power infrastructure upgrade and expansion. Beta provided the engineering, procurement, and construction support for the 115kV indoor GIS, switchyard and control building.

The customer was planning later expansions for the substation, so the project included provisions for a GIS build-out. We designed all aspects of the project to meet the future requirements, including the electrical, civil and building design. The completed substation was designed for additional two outgoing 115kV feeders for a future expansion to meet load growth requirements.

Because of the small footprint, the project required extensive coordination of equipment deliveries and construction activities. The small footprint also posed challenges for ground grid design to achieve the touch and step potentials to meet the substation operational safety standards. A ground grid design typically requires an adequate area to bring the step and touch potentials within the standard limits. Also, the site was located on granite bedrock, making the soil highly resistive. All this, combined with the high source fault current, made the ground grid design challenging. Beta’s engineering team developed a solution implementing several ground wells to fulfill the ground grid design objective and meet the IEEE standards, specifications and client expectations.

The project also had to be designed and installed around environmentally sensitive areas, so we created specific permit designs up front to obtain the permits on time. Our engineering and GIS experience helped us overcome this project’s unique challenges and meet our customer’s goals.

Detailed Scope of Work

• Redundant switchgear protection for reliability

• Capable of accommodating an additional two bays for future expansion

• Design and construction support of the control building

• Environmental permitting from local authorities

• Four-bays breaker and half-bus configuration

• Compact design on urban site

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