A substation can be controlled from the switchyard, the bay, the station and the control center, but only one level holds the authority at a time. The local/remote switches (device 43) of each level decide which: in local, the lower level is in control and rejects the commands from above. In IEC 61850 that authority is represented by LocKey, Loc and LocSta in the CSWI node.
Why there are control levels
A breaker or a disconnector can receive commands from several places: the pushbutton in its switchyard cabinet, the bay controller display, the HMI in the control room and the SCADA of the control center, sometimes hundreds of kilometers away. If all of them could operate at once, two operators could give opposite commands to the same device without knowing it. The control hierarchy prevents that with one rule: only one point holds the authority at any moment.
The hierarchy is the same in a transmission, distribution or industrial substation.
The four levels
| Level | Where it is | Who uses it |
|---|---|---|
| Switchyard | Control cabinet of the breaker or the disconnector | Maintenance, emergencies, switching with the device in sight |
| Bay | Bay controller and its display, or the bay control panel | Local operation of one bay, testing |
| Station | Local HMI or SCADA in the control room | Substation operator |
| Control center | Remote SCADA of the utility or the plant | Normal operation of remotely controlled substations |
In the switchyard, the switch and pushbuttons are in the breaker control cabinet or in that of the motor-operated disconnector. At bay level, the bay controller concentrates control, interlocking and position indication. At station level, the SCADA and HMI system shows the whole substation to the operator, and toward the control center a gateway translates the commands, usually with IEC 60870-5-104 or DNP3 (IEEE 1815).
Each level has its switch. With the switchyard switch in local, the device only obeys its cabinet and rejects everything from above. With the switchyard switch in remote and the bay switch in local, the bay is in control. And so on upward: a command from the control center only gets through if every intermediate switch is in remote.
- 01Control centerSends the command to the gateway over IEC 60870-5-104, DNP3 or another protocol
- 02Station levelPasses only if the station switch is in remote
- 03Bay levelPasses only if the bay switch is in remote
- 04Interlocking and synchronismThe controller checks the conditions of the device
- 05Switchyard levelThe cabinet accepts the command only with its switch in remote
The local/remote switch (43)
IEEE C37.2 assigns number 43 to the manual transfer or selector device, which changes control circuits or operating modes. The local/remote switch is its most common case. It can be a physical key switch (in the cabinet and on the bay panel), a pushbutton with indication on the controller, or an object in the HMI for the station level.
Some frequent design rules:
- The switch position is reported to the upper level as a signal, so that the remote operator knows why the command will be rejected.
- The switchyard switch is usually physical, because it protects the person working on the equipment against a remote command.
- Opening the crank access of a motor-operated mechanism cuts the control supply, which in practice works as a forced local.
- Protection trips do not go through the switch: a trip opens the breaker in any position of the control switch.
How it is represented in IEC 61850
IEC 61850-7-4 includes in the CSWI node (switch controller) the data that model control authority:
- LocKey: the position of the local/remote key.
- Loc: the resulting local control behavior.
- LocSta: control authority at station level, which distinguishes the local HMI from the control center.
With these data the controller knows whether to accept a command according to its origin. An IEC 61850 command carries the identity of its sender (orCat, the originator category), so the controller can reject a station-level or remote command when the authority is below. The actual implementation and the names of the HMI objects vary between manufacturers.
Why switchyard control bypasses interlocks in some designs
In conventional schemes, logic interlocking lives in the bay controller. If the cabinet pushbutton acts directly on the motor or the coil, without going through the controller, an operation from the switchyard is protected only by the mechanical interlock and whatever wiring the cabinet has. Some designs do this on purpose, to be able to operate with the controller out of service; others wire a permissive from the controller to the cabinet. The decision must be explicit in the engineering, and the operating procedure must state which checks are made before operating from the switchyard.
What goes wrong in practice
- Switch left in local after maintenance: the control center cannot operate and finds out during a contingency.
- Station switch in local when the substation should be under remote control.
- Switch position not reported or wrongly mapped in the gateway, so the control center sees “remote” and the command is rejected.
- Two levels with authority at the same time because of a logic error, which allows simultaneous commands.
- Switchyard control that does not respect interlocks without the operator knowing.
How it is verified
During commissioning, each level is tested to accept commands when it holds the authority and reject them when it does not, with the switch of each level in each position. The test confirms that the switch position reaches the HMI and the control center correctly, that protection trips act in any position, and that switchyard control respects the interlocks the design requires. The full test up to the control center is part of the system end-to-end tests.
Are you integrating a substation into a control center, or checking why remote commands are rejected? At Tiza Group we configure the control hierarchy in controllers, HMIs and gateways remotely through our remote relay configuration service, and we test it up to the control center in Colombia, or elsewhere on request. Contact us with your project details.
Related guides
- Select before operate (SBO): how the command works
- Breaker closing permissives: what blocks the close
- Interlock bypass: release, risks and control
- Automatic switching sequences in substations
References
- IEEE C37.2, Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations (device 43).
- IEC 61850-7-4, Compatible logical node classes and data object classes (CSWI: LocKey, Loc, LocSta).
- IEC 61850-7-2, Abstract communication service interface (control model, originator category).
- IEC 62271-102:2018, Alternating current disconnectors and earthing switches (manual operation and cutting the control supply).
Frequently asked questions
Why can the control center not operate when the local SCADA can?
Because control authority is at station level. With the station switch in local, the substation only accepts commands from its local HMI or SCADA and rejects those from the control center. That switch has to be set to remote, in coordination with the system operator.
Does control from the switchyard cabinet respect the interlocks?
It depends on the design. In many schemes the cabinet control goes through a minimum hardwired interlock and the mechanical one, but not through the full controller logic. That is why switchyard control is kept for maintenance and emergencies, with a procedure and the device position confirmed on site.
What ANSI number does the local/remote switch have?
IEEE C37.2 assigns number 43 to manual transfer or selector devices, which change control circuits or operating modes. The local/remote switch is its most common application in substations.