What it is and when you need it
Substation secondary engineering, often called P&C design, covers everything that protects, controls and meters the power system: which relays each bay gets and with which functions, how currents and voltages reach them, how they trip their breaker, how equipment is operated from the panel or from the control center, and where the power that feeds all of it comes from. The result is schemes, wiring drawings and the protection and control panel design that is later built, installed and tested.
A mistake here is invisible in the yard, but it shows up on the day of the fault: a trip that never arrives, a reversed polarity, an interlock that allows a dangerous switching operation. That is why it pays to have the circuits designed by people who also know how they are tested and commissioned.
We do it for medium, high and extra-high voltage (EHV) substations and for industrial facilities:
- New substations, starting from the primary engineering.
- Expansions, when a new bay must be integrated into the existing bus differential, breaker failure or control system.
- Retrofits from electromechanical panels to numerical relays.
- Generation interconnections, with the protection the utility or grid operator requires.
This design is part of our engineering design and studies service.
What is included
- Protection, control and metering schemes per bay: protection functions with their ANSI device numbers (IEEE C37.2), main and backup protection, tripping, reclosing, breaker failure and metering.
- Three-line diagrams of the current and voltage circuits, with ratios, accuracy classes, polarities and grounding points.
- Wiring and terminal block diagrams: trip and close circuits, trip coil supervision, anti-pumping, alarms and indication, with designations per IEC 81346-1 and drawings per IEC 61082-1.
- Panel design: front layout, internal arrangement, bill of materials and specification for the panel builder.
- AC and DC auxiliary systems: load schedule, battery and charger sizing, distribution panels and selectivity.
- Signal lists for each bay to the local control, the SCADA and the control center.
- Interlocking logic between breakers, disconnects and grounding switches.
How we work
Secondary engineering is desk work: it is done on drawings, manuals and lists, not on the equipment. That is why our team does it remotely, from Bogotá (UTC−5), for projects anywhere in the world, with no travel costs.
- Design basis. We start from the approved single-line diagram, the requirements of the utility or transmission owner, the local code you indicate and the selected relay brand.
- Schemes and three-line diagrams. We define functions, instrument transformers and tripping per bay, and review them with you before drawing the detail.
- Wiring, terminal blocks and panels. We develop the drawings the panel builder and the installer will use.
- Auxiliaries and signals. We close the load balance, the batteries and the signal lists.
- Review and approval. We address comments until the issued-for-construction version.
If the existing information is not enough, for example an old panel without drawings, it has to be surveyed on site: with a visit from our team (in Colombia, or elsewhere on request) or by your own staff following a checklist of what to record.
What we need from you
- Single-line diagram and primary engineering drawings.
- Existing drawings and terminal block schedules, for an expansion or a retrofit.
- Relay make and model, or the specification your utility requires.
- Signal requirements from the utility, the transmission owner or the control center.
- Rated system frequency (50 Hz or 60 Hz) and auxiliary DC voltage.
- Photos of the panels and of the equipment nameplates.
Standards and criteria
- Fault clearing time. Many utilities and grid codes set a maximum clearing time for the main protection. We select the scheme and the breakers with that limit in mind, adapted to the local code and the utility requirements that you give us.
- Interconnection documentation. Transmission owners usually ask for elementary AC and DC diagrams, interlocks, the protection and control system and the protection schemes with their setting criteria. We prepare the package in the format they request.
- IEEE C37.2 for device function numbers; IEC 60617 or IEEE 315 for symbols; IEC 61082-1 and IEC 81346-1 for drawing presentation and equipment and terminal designations.
- IEEE 946 for DC auxiliary system design, with battery sizing per IEEE 485 (lead-acid) or IEEE 1115 (nickel-cadmium).
What you receive
- Protection, control and metering schemes per bay.
- Three-line, wiring and terminal block diagrams.
- Panel drawings and the specification for their manufacture.
- AC and DC auxiliary system calculation reports.
- Signal lists and interlocking matrix.
- Cable schedules and bills of materials.
- A complete engineering package for your review, with revision control.
Why Tiza Group
- We design what we know how to test: our team carries out protection testing, factory and site acceptance tests and commissioning, and designs circuits so they can be verified.
- From drawing to relay: the schemes are coordinated with the protection coordination study and with remote relay configuration for the main relay brands.
- Complete engineering: integrated with primary engineering and communications engineering.
- Remote by default, worldwide, with site visits only when they add value. Tell us about your project.