What a Substation Engineering Design Includes

What a substation engineering design is

The engineering design is the set of calculations, drawings, specifications and lists that define a substation before it is built. It tells the buyer which equipment to order, the manufacturer how to build the panels, the installer where everything goes, and the utility that the installation is safe and does not harm its system.

Electrical codes in most countries require a design for every substation, and the utility asks for it before it grants the connection. The topics of a detailed design usually include risk analysis, lightning risk, insulation coordination, short-circuit and ground fault levels, grounding, mechanical calculation of structures, single-line diagrams, construction drawings, specifications and safety clearances. The designer states in the design report which topics do not apply and why. Which standards govern depends on the country and the utility; IEC 61936-1 and IEEE 80 are common references.

This guide is for anyone about to hire a design: what it must include, what information you need to provide, what you should receive and how it is approved.

The four parts of the design

The four depend on each other. The short-circuit current sets the rating of the breakers and the grid design; the protection scheme defines how many cores the current transformers need; the communications network depends on which signals travel by GOOSE. That is why it is best for one team to do them, or for someone to coordinate the interfaces.

Basic engineering and detailed engineering

Projects talk about two stages:

• Basic engineering. It fixes the big decisions: the busbar configuration (from single bus to breaker-and-a-half), the single-line diagram, the general layout, the voltage levels and the main equipment. It is used to estimate costs, request the utility’s connection concept or tender the project.
• Detailed engineering. It develops everything needed to buy, manufacture and build: calculation reports, construction drawings, point-to-point wiring, panel drawings, specifications and bills of material.

Some local codes also use the term “basic design” for a reduced version reserved for very small installations. A substation needs the detailed design.

What information you need to provide

The quality of the design depends on the input information. Have ready:

• The feasibility response or connection concept, with the connection point and the short-circuit level given by the utility.
• The utility’s technical standard or the transmission owner’s requirements.
• The site survey and the soil study, and the soil resistivity if it has already been measured.
• In expansions: updated drawings, single-line diagram, terminal block lists, nameplate data and photographs of the equipment that stays.
• The preferred or required relay brand, and the control center requirements.
• The expected load or generation and its growth.

What does not exist is surveyed in the field. The rest of the design can be done from the designer’s office.

Which deliverables to ask for

• Calculation reports covering the items required by the applicable code, those that do not apply and why.
• Single-line diagram with ratios and classes of instrument transformers and protection functions.
• Physical layout drawings, ground grid and lightning protection.
• Schematics, three-line diagrams, wiring and terminal blocks consistent with the single-line diagram.
• Technical specifications of each device and panel, ready to quote.
• Studies: short circuit and protection coordination, at the very least.
• Lists of cables, materials and signals.
• Revision control: each drawing with its version and the list of changes.

How the design is approved

On a distribution system, the utility reviews the design against its technical standard and the local regulation. Many regulators require utilities to publish their technical rules and set review times for the study or design, and give the user a fixed period to answer any comments. The detail is in drawing and design requirements for the utility.

On a transmission system, the grid code usually sets the order: connection agreement, the user’s design and submission to the transmission owner of designs, calculation reports, specifications and drawings. These typically include the list of standards, single-line and elementary diagrams, interlocks, protection schemes with their setting criteria, and telecommunications schemes. The transmission owner reviews and approves them within a set time, counted from when the documentation is complete. Equipment is purchased only after approval.

After that come construction, the inspection and certification required by the local code, in which the inspection body checks that what was built matches the design, and commissioning.

Warning signs when comparing offers

• “Complete design” without a list of deliverables. A serious offer says which drawings, reports and specifications it delivers.
• No short-circuit study. Without it you cannot verify the equipment ratings or calculate the grid.
• Ground grid without measured resistivity. With an assumed value, the real step and touch voltages cannot be verified.
• Primary and secondary without coordination. If different teams do them, ask who answers for the interfaces.
• No one handles the utility’s comments. Returns are normal; define who resolves them and whether they are included.
• Drawings without revision control. The installers end up working on an old version.
• A designer who has never commissioned. Wiring and scheme errors show up in the tests.

We design your substation

Our team does primary engineering, secondary engineering, communications engineering and studies for medium, high and extra-high voltage substations and for industry. The work is done remotely from our office in Bogotá, for clients worldwide, adapted to your local code and your utility’s requirements. See the engineering design and studies service and send us the scope through contact; we will propose a plan.

Related guides

• Drawing and design requirements for the utility
• Grounding grid
• Short-circuit study
• Substation protection schemes
• Substation communications architecture
• Energization with the utility

References

• IEC 61936-1:2021, Power installations exceeding 1 kV AC and 1.5 kV DC – Part 1: AC.
• IEEE Std 80, IEEE Guide for Safety in AC Substation Grounding.
• The electrical code and the utility or transmission owner requirements that apply to the project.

Frequently asked questions