Discipline · detailed engineering
High-voltage substation electrical engineering for AIS and GIS stations up to 765 kV, applied also to renewable pooling stations, BESS connections and HVDC station AC yards: single-line diagrams, layouts, calculations, equipment selection and schedules prepared from the project specification and approved equipment data.
Section 01
Electrical detailed engineering is the stage at which a tender or basic design becomes a set of drawings and calculations that suppliers and site teams can build from. CoreGrid prepares AIS and GIS substation electrical design for AC voltages up to 765 kV, whether the work is a greenfield switchyard, a pooling substation for a renewable plant, a BESS connection or an extension to an existing station, as each package defines.
The design basis is assembled from the project’s own documents: the single-line diagram and utility criteria; substation voltage, bus scheme and the number and type of bays; fault levels; insulation levels and statutory safety clearances; site and equipment constraints; relay scheme interfaces; any available general arrangement and technical specification; manufacturers’ guaranteed technical particulars (GTP) and drawings; soil information where earthing or foundations depend on it; and the master deliverable list (MDL).
Where an input is missing we say so, record the assumption we propose and ask the client to confirm it. Nothing is silently assumed. Because the electrical design drives civil and structural work, loads, levels and positions are passed to those disciplines as controlled interface data rather than informally.
| Input | Why it matters |
|---|---|
| Single-line diagram and utility criteria | Defines the bus scheme, bays and ratings |
| Fault levels and insulation levels | Drive conductor, earthing and clearance design |
| Technical specification and MDL | Set deliverables, formats and codes |
| Vendor GTP and drawings | Fix dimensions, weights and terminal loads |
| Soil resistivity data | Needed for earth grid and foundations |
| Site layout and constraints | Limit arrangement, routes and access |
Section 02
Primary drawings fix how the switchyard is arranged and connected. The single-line diagram (SLD) shows the bus scheme, bays, transformers, line entries and ratings. The electrical key diagram (EKD) is a project-specific diagram whose content and format follow the client’s specification. The switchyard general arrangement places the equipment on the site with plan and sectional views, so that bus levels, clearances and connections can be checked.
From these we develop the plot plan, equipment mounting and termination interfaces, bus connection arrangements (strain, flexible or rigid as specified), line and bus terminations, transformer and reactor interfaces, ground connection points and the interfaces between equipment and supporting structures. Line, bus and equipment clearances are checked against the project criteria using approved vendor dimensions, and the drawings carry an electrical legend so each symbol and tag is defined.
Section 03
Conductors and busbars are selected for continuous current, operating temperature and fault withstand, with the standards and margins recorded. For flexible buses the sag-tension calculation fixes how the conductor hangs and what tension it passes to gantries and equipment terminals under the specified temperature and wind conditions.
We keep two things separate that are often confused. The system short-circuit level is an input, supplied by the client or from a system study. The mechanical effect of that current on conductors, spacers, insulators, terminals, equipment and supports is a calculation we prepare, and its results become loads for structure and foundation design. Spacer and insulator spacing checks and conductor clearances under the specified loading complete the group.
Section 04
Earthing design starts from measured soil resistivity and the fault current and duration the grid must carry. We develop the grid topology, size conductors and electrodes, and calculate grid resistance, ground potential rise (GPR) and the step and touch voltages against the allowable limits set by the project criteria. The earth grid layout and equipment bonding details turn the result into drawings that can be installed.
For non-uniform or multi-layer soil we model the grid in SES-CDEGS. Direct stroke lightning protection (DSLP) is handled alongside: shielding calculations by the project’s chosen method, a layout of masts and shield wires with heights and coverage, and the surge arrester and insulation coordination inputs. We do not promise a target resistance or a safety outcome before the calculation has been completed against the project’s criteria. Where soil data are poor or incomplete, we say so and record the assumption.
Section 05
Equipment ratings are selected or checked against the single-line diagram, fault level, insulation level and duty of each bay. We prepare selection and rating checks for current transformers, CVTs and voltage transformers (ratios, classes, burdens and cores), surge arresters, circuit breakers, disconnectors and earth switches, and the interfaces of power transformers and shunt reactors, including neutral grounding resistor (NGR) sizing where in scope.
Scrutiny of manufacturers’ GTP and drawings is part of the same work, so that deviations from the specification are raised before drawings are issued and before equipment is manufactured.
Section 06
Protection and control work falls into three levels that are often confused. We are clear in each proposal which one is included.
Interface coordination covers control room layouts and interfaces, interlocking philosophy, relay and SCADA input/output interfaces and signal lists, prepared where the contract includes them. Protection and control schematics follow the client’s scheme and the panel supplier’s design when they are in scope. Relay logic programming, SCADA integration and commissioning are carried out by the panel and SCADA suppliers; we review their documents and support commissioning where contracted.
Section 07
Auxiliary systems keep a substation controllable and safe. We prepare the AC auxiliary (LTAC) single-line diagram and load list, the DC system single-line diagram and load schedule, and the sizing of the station battery and battery charger from duty cycles, DC loads and autonomy periods specified by the client. Distribution boards (ACDB and DCDB) and panel interfaces are defined so that panel suppliers can work from agreed data.
Cable work includes sizing and voltage drop, routing and the trench and tray interface with civil design, the cable schedule and block diagrams. DG set and UPS interfaces are designed when the project includes them and provides the inputs.
Section 08
Illumination design covers indoor and outdoor yard lighting: the calculation of illuminance against the project criteria, usually in DIALux evo, fixture positions and mounting heights, normal and emergency lighting circuits, and coordination with structures, equipment and cable routes. Emergency lighting is provided to the extent the project specifies. Photometric data come from the fixture manufacturer, and results are stated against the data used.
Section 09
Power-system studies are offered by scope rather than excluded. Short-circuit, load flow, reactive power, harmonic and insulation coordination studies are prepared or reviewed as each project commissions them, using the client’s system data; earthing studies are prepared directly. Each proposal states the basis of every study.
Section 10
| Infrastructure | Electrical focus |
|---|---|
| AIS/GIS substations | Bus schemes, yard and hall layouts, SCF, earthing, DSLP, equipment ratings, auxiliary systems |
| Solar, wind and hybrid plants | Collection networks, plant SLDs, inverter and transformer interfaces, plant earthing, evacuation scheme |
| Pooling substations | Collector bay scheme, pooling transformers, metering, utility protection and SCADA interfaces |
| Battery energy storage | Sizing basis, PCS and transformer interfaces, auxiliaries, protection, EMS/SCADA interface |
| Transmission lines | Conductor selection, losses and corona, clearances, line entries into substations |
| HVDC stations | AC switchyard and filter yard layouts, converter transformer yard interfaces, station earthing |
Section 11
What a typical electrical package can include. The contract and MDL decide what a given project contains.
| Drawings | Calculations | Documents |
|---|---|---|
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Section 12
Confirm the single-line diagram, design criteria and deliverable list.
Develop the general arrangement from approved equipment arrangement and clearances.
Check vendor data for dimensions, weights, ratings and terminal loads.
Prepare calculations with traceable inputs and stated limits.
Issue drawings with revisions, transmittals and register entries.
Check loads, levels and positions against civil and structural design.
Independent check of calculations and drawings before submission.
Submit for approval and respond to comments through the CRS.
Revise, close comments and issue in the status the project defines.
Each stage ends with a hand-over that can be checked against the MDL. “Issued for approval” differs from “approved” and from “issued for construction”, and we use those terms as the project defines them.
Submitted for the client’s or consultant’s review. It is a proposal for acceptance, not an approved document.
The formal response of the approving party, which may carry comments. Only the client, owner’s engineer or consultant can give it.
Released for use at site, in the status and under the convention the project defines. Revision labels differ between projects.
Section 13
A calculation and drawing set for the earth grid and its connections, prepared from soil data and fault duty.
Sizing and arrangement of the station DC supply from the load schedule and duty cycle the client specifies.
Conductor and bus design with the mechanical effects of short-circuit current, giving loads for civil design.
The general arrangement and sections for the yard, coordinated with civil, cable and earthing drawings.
Potential deliverables, not guaranteed scope. Each item above is something CoreGrid can prepare where a project calls for it. A given contract includes only what its specification and MDL list. Examples are described in general terms and contain no project data.
Send us the tender extract, single-line diagram, master deliverable list or the specific calculation you need. We will confirm scope, inputs and a realistic submission sequence before any work starts.