The control building is the substation building that houses the protection and control panels of each bay, the substation automation system (SAS) with its HMI, the communications to the control center, time synchronization, metering, fault recording and the AC and DC station service. It receives from the switchyard the currents, voltages and statuses of the equipment, and sends back the trip and switching commands. The local code and the utility set requirements for its location, ventilation, fire detection and indication of the real state of the equipment.
What the control building is
The control building (also control house or relay house) is the building of the substation that houses the secondary equipment: the equipment that measures, protects, controls, communicates and records. The switchyard holds the power equipment; the control building holds the intelligence that decides when to open a breaker and tells the operator what is happening.
Control cables run between the switchyard and the building: currents and voltages from the instrument transformers, breaker and disconnect switch statuses, equipment alarms and, in the opposite direction, the trip and close commands. In digital substations, part of that copper is replaced by optical fiber carrying IEC 61850 messages.
What is inside
| System | Equipment | What for |
|---|---|---|
| Protection | Relays per bay, bus protection and breaker failure protection | Detect faults and trip the right breaker |
| Control | Bay controller, local/remote selectors, interlocks | Operate the equipment and block dangerous switching |
| Automation (SAS) | Servers, local HMI, gateway or RTU | See and operate the substation, and send data to the control center |
| Communications | Station network switches, routers, firewalls, teleprotection, multiplexers | Link the devices to each other and to the remote end of the lines |
| Time | GNSS clock and its distribution | Give events and oscillography the same time |
| Metering and recording | Revenue meters, fault recorder, power quality | Billing, fault analysis and grid supervision |
| Station service | AC panels, chargers, batteries, DC panels | Power everything above and the switchyard mechanisms |
Protection and control panels
Each bay has its control and protection panel with its relays, the bay controller, terminal blocks, test switches and auxiliary trip relays. At high and extra-high voltage it is common to duplicate the main protection, with separate DC supplies and trip coils, so that a single equipment failure does not leave the bay unprotected.
Relays are the devices that change most over the life of the substation: new settings after grid changes, control logic, SCADA integration. Our team configures them remotely; see remote relay configuration.
Automation and SCADA
The substation automation system gathers the information from all relays and controllers, shows it on the local SCADA and HMI and sends it to the control center through the RTU or gateway. The control levels define whether a command can be given from the control center, from the HMI, from the panel or from the equipment in the switchyard.
Communications and time
The substation communications network links relays, controllers and servers, normally with redundancy; see substation network redundancy. Teleprotection equipment and multiplexers carry the protection signals to the remote end of each line. The GNSS clock distributes time to every device; without a common time, reconstructing a fault from the events becomes very difficult. The options are compared in PTP, NTP or IRIG-B.
Station service
The AC station service feeds chargers, operating mechanism motors, heating, lighting and air conditioning. The DC system feeds relays, controllers and trip coils from the chargers and batteries, normally in a separate, ventilated room. If you need to estimate the bank capacity, you can use our free battery sizing tool.
Centralized or distributed
- Does the substation have few bays and a compact switchyard?
- YesCentralized control building: all panels in one building, with control wiring coming in from the switchyard
- No, it is large or extra-high voltageIs the goal to shorten copper wiring and separate the bays?
- YesSwitchyard kiosks per bay or per diameter, linked by fiber to the main building with SCADA, communications and general services
- NoCentralized building with cable trenches and longer control wiring
In a digital substation with a process bus, the merging units and breaker interfaces sit in the switchyard, and the control building receives only fiber.
Typical requirements
The local code and the utility set the requirements for control rooms and kiosks. They usually cover:
- A location where the most intense fire in the substation does not affect the operation of the control building equipment.
- Construction materials with high fire resistance, and openings and ducts sealed so that fire does not spread.
- Rooms free of combustibles, not used as workshop or storage, ventilated and dry.
- Indication in the control room of the position of the switching devices, showing the real state of the switching in progress.
- Fire detection in control rooms and kiosks with control, protection or communications panels, with the alarm sent to the control system together with those of the battery charger and the secure power supplies.
- Automatic fire detection and suppression in remotely controlled or unattended substations, unless competent staff is permanently present.
IEEE 979, the IEEE guide for substation fire protection, is a common reference for these topics.
Control building tests at commissioning
In substation commissioning, the control building concentrates much of the work. In general, the following are verified:
- Control wiring against the drawings, insulation and continuity of the current, voltage and trip circuits.
- Protection by secondary injection, with trips to the real breaker; see protective relay commissioning.
- Interlocks, logic and control from each level.
- Each signal in the substation signal list from the equipment to the HMI and the control center, with point-to-point testing.
- Station service: transfers, chargers, battery autonomy and alarms.
We can help with your control building
Our team configures protection, controllers and communications for medium, high and extra-high voltage substations and industrial plants: remotely, worldwide, when the equipment is already installed, and on site for integration, testing and commissioning, in Colombia, or elsewhere on request. We load and modify logic, interlocks and signals remotely with remote relay and controller configuration, without waiting for a site visit. Contact us.
Related guides
- SCADA, SAS, DCS and HMI: differences in the power sector
- Point-to-point signal testing: SAS and SCADA
- Substation protection schemes
- Substation automation
- Centralized protection and control
- Gateway and redundant links to the control center
References
- IEC 61850 (series), in particular IEC 61850-4 (system and project management) and IEC 61850-7-4 (logical nodes).
- IEC 62381: FAT, SAT and SIT of automation systems.
- IEC 61936-1: power installations exceeding 1 kV AC.
- IEEE 979, IEEE Guide for Substation Fire Protection.
- IEEE C37.2: electrical power system device function numbers.
Frequently asked questions
What is the difference between a control building and switchyard kiosks?
In a centralized control building all the panels are in a single building and the control wiring comes in from the whole switchyard. In the distributed approach, each bay or group of bays has a kiosk next to its equipment with its relays and controllers, and the main building keeps SCADA, communications and the general station service. The distributed approach shortens the copper wiring in large substations.
What happens in the control building if DC power is lost?
The relays and the trip coils are fed from the battery DC system. Without it the substation is left without protection and without control, even if the power equipment stays energized. That is why the charger, the batteries and the DC voltage supervision are critical, and their alarms must reach the control center.
Does an unattended substation still need a control building?
Yes. Unattended substations are operated from a remote control center, but the relays, controllers, communications and station service are still in the building or in kiosks. Fire detection and suppression there are usually required to be automatic, unless there is permanent staff.