Switchyard Design Checklist

This post provides a structured checklist for reviewing the design and validating the design of electrical switchyards.

Scope

This checklist provides general guidance for planning and reviewing electrical switchyard designs.

Reference Standards 

• Relevant IEC standards (IEC 61936-1 & IEC 60529). 

• Relevant IEEE standards (IEEE 80 & IEEE 81).

• National electrical regulations & safety rules.

• Utility or grid operator requirements.

• Applicable engineering design guides.

Design Procedure

The overall switchyard design must be developed by considering the following aspects:

• The required switchyard voltage level must be identified based on the system requirements.
• The power input and output capacity must be determined according to the project load demand.
• The incoming and outgoing power transmission lines must be confirmed and incorporated into the electrical design.
• The switchyard location and orientation must be selected with respect to the overall power plant layout and transmission line paths.
• An appropriate switching scheme as per NEMA SG-4 & NEMA SG-6 must be selected considering system reliability, maintenance flexibility and cost.
• The system fault level information must be obtained from the utility (or) system studies.
• The design short circuit level for the switchyard equipment must be established accordingly.
• The Basic Insulation Level (BIL) must be determined based on the system voltage and insulation coordination requirements.
• The required electrical clearances must be established based on the voltage level and insulation requirements.
• The busbar type must be selected whether rigid busbar (or) flexible conductor busbar.
• Major switchyard equipment such as circuit breakers, isolators, current transformers (CTs), voltage transformers (PTs) and lightning arresters must be selected.
• The switchyard type must be determined such as Gas Insulated Switchgear (GIS), Air Insulated Switchyard (AIS), outdoor switchyard (or) indoor switchyard.
• The environmental and pollution levels at the project site must be evaluated.
• The insulator creepage distance requirements must be determined based on the pollution severity.
• The necessary safety and regulatory requirements must be identified and incorporated into the design.

Design Particulars

The detailed design of the switchyard must consider the following parameters:

• The required phase-to-ground and phase-to-phase clearances must be established according to the system voltage.
• The incoming and outgoing line termination arrangements must be confirmed with respect to the transmission line orientation.
• The grade level and the equipment foundation levels must be determined based on the electrical site conditions and flood levels.
• The switchyard layout configuration must be finalized based on considering the equipment arrangement and maintenance accessibility.
• The earthing grid design must be developed and step potential and touch potential levels must be evaluated for the electrical safety.
• A suitable lightning protection system must be designed for the switchyard.
• Adequate yard lighting arrangements must be established for a safe operation and maintenance.
• The necessary structural and foundation design parameters must be provided to the civil engineering team.
• The cable routing system such as cable trenches (or) cable trays must be finalized.
• The communication system requirements between the switchyard and control room must be defined.

Equipment Installation Checkpoints

During equipment installation planning the following points must be verified:

• For circuit breakers the foundation level and operating cubicle arrangement must be finalized.
• For isolators the operating height and foundation requirements must be confirmed.
• For power transformers the oil drainage system and fire protection arrangements must be get finalized. 
• Adequate maintenance (preventive) access and cable entry provisions must be provided for the transformers.
• For lightning arresters the adequate electrical clearances must be ensured.
• For bus post insulators the insulator height and mounting arrangements must be verified.
• For instrument transformers (CTs and PTs) adequate spacing from the adjacent equipment must be maintained.

Cable Trenches

The cable routing system must be designed with the following considerations:

• Main and branch cable trenches must be provided for the routing power and control cables.
• The cable trench dimensions must be standardized while allowing the provision for future expansion.
• Bay wise symmetry must be maintained in cable routing to ensure an organized installation and easier maintenance.

Access Nodes

Proper access arrangements must be provided for equipment installation and maintenance:

• Safe and adequate access to all the switchyard equipment must be ensured.
• Maintenance access routes must be designed to facilitate the inspection and servicing activities.
• Approach roads must be provided to allow transportation and installation of heavy equipment.

Control Room

The control room design must address the following requirements:

• The control room elevation and layout must be determined considering cable routing and accessibility.
• Adequate space must be provided for protection panels, control panels, communication systems and auxiliary equipment.
• Provision must be made for future expansion of control and protection systems.
• Adequate ventilation and environmental control systems must be provided where ever required.

Maintenance Facilities

Maintenance provisions must be included in all switchyard design:

• Dedicated maintenance areas and equipment handling provisions must be provided.
• Adequate storage facilities and maintenance power tools must be arranged for the equipment servicing.

Safety

The switchyard design must incorporate the necessary safety precautions/measures:

• Proper fencing and security arrangements must be installed around the switchyard.
• Suitable fire protection systems must be provided for the equipment and cable installations.
• Fire extinguishers and emergency response equipment must be installed at the appropriate locations.
• Insulating mats, safety signage and warning boards must be provided to ensure a personnel safety.

Statutory Clearances

The design must obtain all the necessary statutory approvals:

• Approval must be obtained from the relevant electrical authorities and inspectorates.
• Compliance with the power grid operator requirements and utility regulations must be ensured.
• Necessary environmental and electrical safety clearances must be obtained before the project execution.

Checklist