Substation communications by voltage level: MV, HV, EHV

Short answer

Substation communications use the same building blocks at every level (IED, switch, clock, gateway and an external channel), but redundancy, protocol and time accuracy change. At medium voltage, Modbus or DNP3 and non-redundant links prevail; at high voltage, IEC 61850 with RSTP or PRP and IEC 104 to the control center; at extra-high voltage, PRP, duplicated teleprotection over separate routes, and PTP.

What is the same in every substation

Any substation, at 13.8 kV or at 500 kV, has the same communications building blocks:

IEDs for protection, control and metering in each bay.
A switch or concentrator that links them.
A clock that gives the time to all of them.
A gateway or RTU that translates the data for the control center.
An external channel: fiber, radio, cellular, power line carrier or a transport network, for remote SCADA and for teleprotection.

What changes with the voltage level is how much redundancy is required, which protocol is used inside and outside, how accurate the time must be and how many teleprotection channels there are. The substation communications network guide describes those blocks one by one; here we compare how they are combined at each level.

Medium voltage and distribution

In distribution substations, MV switchgear, reclosers and small industrial substations, simplicity prevails:

Protocols: Modbus RTU or TCP to the local SCADA, and DNP3 (IEEE 1815) or IEC 60870-5-104 to the distribution utility’s control center. IEC 61850 appears in new switchgear, sometimes only for GOOSE between panels.
Network: a simple star or an RSTP ring. A short network outage is usually acceptable because the trip is hardwired from the relay to the breaker.
External channel: fiber where available; otherwise radio or cellular, common for reclosers and rural substations.
Time: SNTP or IRIG-B; millisecond accuracy is enough to order events.
Teleprotection: uncommon; where it exists, it is usually a simple scheme over fiber or radio.

High voltage

At high voltage the substation is part of the transmission or sub-transmission system, and the requirements rise:

Protocols: IEC 61850 inside the substation, with MMS to the control system and GOOSE for interlocking and, in recent projects, for tripping. To the control center, normally IEC 60870-5-104 (or DNP3), with a signal list agreed with the grid operator.
Network: an RSTP ring or a dual star with PRP, depending on whether the design philosophy accepts the network reconfiguring for a few milliseconds.
Time: a GNSS clock with IRIG-B or SNTP for event time-stamping; PTP (IEEE 1588) if there are synchrophasors or a process bus is planned.
Teleprotection: at least one channel per line, over fiber (direct or multiplexed) or power line carrier, for the distance schemes and line current differential.

Extra-high voltage

At extra-high voltage the design rule is that no single failure of a communications device may leave a line unprotected:

Network: PRP with two physically separate LANs, with different power supplies and fiber routes, or HSR on the process bus where there is one.
Main 1 and main 2 protection with independent communication paths.
Duplicated teleprotection over separate routes: for example, one channel over the line’s own fiber and another over an alternate route or over power line carrier.
Time: two GNSS clocks with PTP and its power profile when there are sampled values or synchrophasors, plus IRIG-B for devices that require it.
Process bus in digital substations, with merging units and sampled values. A process bus also opens the option of gathering the functions of several bays into one or two devices, centralized protection and control, which shifts the redundancy requirement onto the network and the clock.

What varies, in one table

Aspect	Medium voltage	High voltage	Extra-high voltage
Internal protocol	Modbus, DNP3; IEC 61850 in new switchgear	IEC 61850 MMS and GOOSE	IEC 61850 MMS, GOOSE and, in a digital substation, SV
To the control center	DNP3 or IEC 104, sometimes over radio or cellular	IEC 104 over fiber or a transport network	IEC 104 with redundant links
Topology	Star or simple ring	Ring or dual star	PRP dual star, HSR rings on the process bus
Redundancy	None or RSTP	RSTP or PRP	PRP, with independent M1 and M2
Time	SNTP or IRIG-B (millisecond)	IRIG-B, SNTP and sometimes PTP	Power profile PTP, duplicated clocks
Teleprotection	Uncommon	One channel per line	Two channels over separate routes

The table describes common practice, not a requirement of any standard. Each utility sets its own philosophy, and a critical high-voltage substation may be designed to extra-high-voltage criteria.

What is added as the voltage level rises

01Medium voltageIED, switch, clock and gateway; one path
02High voltageIEC 61850, ring or dual star, IEC 104 and one teleprotection channel
03Extra-high voltagePRP, independent M1 and M2, teleprotection over two routes, and PTP
04Digital substationProcess bus with sampled values and merging units

Industrial and solar plants

An industrial plant or a solar farm with its own substation has the same building blocks, with two differences:

Two data destinations. The plant SCADA and the control center of the grid operator or transmission company. Each one asks for its own protocol and signal list, and between them sits a gateway with a firewall that separates the networks. The guide on integrating the substation into the plant SCADA explains it.
Monitoring requirements. Generating plants connected to the grid are usually required to be monitored in real time by the system operator, with the signals and measurements set by the local grid code and the utility’s requirements. Renewable plants may also have synchrophasor requirements: see SCADA and PMU monitoring for renewable plants.

In industry, process control usually speaks Modbus, PROFINET or EtherNet/IP, and the substation speaks IEC 61850. The joining point is a gateway or a PLC with both protocols; IEC 61850 in industrial plants covers that case.

Common specification mistakes

Copying the extra-high-voltage architecture at medium voltage, at a cost the project does not need.
The opposite: a high-voltage substation with GOOSE tripping over an RSTP ring without assessing the reconfiguration time.
No clock redundancy in a substation that depends on sampled values.
Main and backup teleprotection over the same fiber, which stops being redundant when the cable is cut.
A signal list agreed late with the control center, which forces the gateway to be redone.

Communications design with Tiza Group

The right architecture depends on the voltage level, the utility and the expected growth. Our team designs the network, redundancy, time synchronization and teleprotection channels of medium-, high- and extra-high-voltage substations, for utilities and industry, as part of our communications engineering service. The design is done remotely, without travel, for projects worldwide. If you already have the equipment, we configure your IEDs through remote relay configuration. Write to us with the voltage level and configuration of your substation.

References

IEC TR 61850-90-4:2020, Communication networks and systems for power utility automation – Network engineering guidelines.
IEC 61850-5, Communication requirements for functions and device models.
IEC 62439-2 and IEC 62439-3: MRP, PRP and HSR redundancy.
IEC/IEEE 61850-9-3:2016: PTP profile for power utility automation.
IEC 60870-5-104 and IEEE 1815 (DNP3).
IEC 60834-1: teleprotection equipment, command systems.

Frequently asked questions

Does a medium-voltage substation need IEC 61850?

It is not mandatory. Many distribution and industrial substations run on Modbus or DNP3 and a single link. IEC 61850 is justified when there are GOOSE interlocks between bays, several vendors to integrate, or a growth plan toward a digital substation.

Why is everything duplicated at extra-high voltage?

Because a fault not cleared in time at that level threatens system stability. The paths of main 1 and main 2 protection are therefore kept separate, from the substation network to the teleprotection channel, and no single failure of a communications device may leave the line unprotected.

What changes in a solar or industrial plant compared with a utility substation?

The building blocks are the same, but there are two destinations: the plant's own SCADA and the control center of the grid operator or transmission company, each with its own protocol and signal list. The boundary between them is handled with a gateway and a firewall.