The SIPROTEC 6MD85 and 6MD86 are Siemens' modular bay controllers on the SIPROTEC 5 platform, for medium-voltage switchgear and high and extra-high voltage yards. They control and interlock breakers and disconnectors, check synchronism, measure, record faults, can act as a PMU and carry protection functions from the SIPROTEC library. They are configured with DIGSI 5 and integrated over IEC 61850. The 6MD61, 6MD63 and 6MD66 are the SIPROTEC 4 generation.
What it is and where it is used
The Siemens SIPROTEC 6MD85 and 6MD86 are the bay control units (BCUs) of the SIPROTEC 5 platform. Siemens presents them as modular controllers for medium-voltage switchgear and for high and extra-high voltage yards, with integrated operation and protection functions. In older substations the 6MD61, 6MD63 and 6MD66 are found, from the SIPROTEC 4 generation.
A bay controller is the device that handles the breakers and disconnectors of a bay: it receives their positions, executes the open and close commands from the operator or SCADA, applies the interlocking and checks synchronism before closing. In many transmission substations the controller is separate from the protective relays; in others, a single IED does both. For the general concept, see the guide on bay controller.
Variants: 6MD85, 6MD86 and 6MD6x
| Model | Application | Main difference |
|---|---|---|
| SIPROTEC 6MD85 | Medium to high voltage bays | Five standard variants; 4 current and 4 voltage inputs, 11 to 75 binary inputs and 9 to 41 binary outputs |
| SIPROTEC 6MD86 | Medium to extra-high voltage bays | Seven standard variants; 4 or 8 measurement inputs; controlled switching and per-phase control |
| SIPROTEC 4 6MD61 / 6MD63 / 6MD66 | Existing bays | Previous generation, configured with DIGSI 4 |
Both SIPROTEC 5 models are expanded with input and output modules of the same platform, so a standard variant grows according to the needs of the bay.
Main functions
According to Siemens’ public information, the 6MD8 devices provide:
| Function | ANSI | What it adds to the bay |
|---|---|---|
| Switching device control with select-before-operate | — | Safe opening and closing from the HMI, SCADA or control center |
| Bay and substation interlocking | — | Prevents improper operations; DIGSI 5 templates for typical cases (GOOSE interlocking) |
| Synchronism check | 25 | Allows the breaker to close only with compatible voltages (guide) |
| Automatic voltage control | 90 | Transformer tap changer regulation |
| Phasor measurement unit (PMU) | — | Synchrophasors according to IEEE C37.118 |
| Fault recording | — | Oscillography to analyze bay events |
Siemens also mentions control of arc-suppression (Petersen) coils, test functions and, in the 6MD86, controlled switching (point-on-wave) and per-phase breaker control. Additional protection functions come from the SIPROTEC 5 library and depend on what is ordered.
Communications and IEC 61850
- Up to four plug-in communication modules, for different and redundant protocols.
- IEC 61850-8-1 (MMS and GOOSE) and IEC 61850-9-2 client for process bus sampled values; see digital substation IEC 61850.
- Long-distance serial protection communication.
- Cybersecurity: role-based access control, signed firmware, authenticated network access and secure event logging.
Configuration is done with DIGSI 5, with application templates for standard bays, interlocking and extended control, and a graphical logic editor. Network redundancy and additional protocols (for example PRP and HSR or IEC 60870-5-104) depend on the installed module; see Siemens DIGSI software.
More data from the 6MD86 technical profile
The 6MD86 profile that Siemens publishes (2020 edition) adds data that is useful for specifying:
- Hardware. Housing width from 1/3 to 2/1 of 19 inches. When the number of inputs and outputs requires it, the device is expanded with a second row; the profile cites more than 240 binary inputs with the IO230 module as an example. The boards come with a conformal coating as standard for harsh environments.
- Protocols per module. Besides IEC 61850-8-1 and 9-2 client, the plug-in modules can carry IEC 60870-5-103, IEC 60870-5-104, Modbus TCP, DNP3 serial and TCP, and PROFINET IO, including PROFINET IO S2 redundancy. The fixed RJ45 Ethernet port is used for DIGSI 5 and for IEC 61850 (reports and GOOSE).
- Network. Virtual network partitioning with VLANs per IEEE 802.1Q, and reliable transmission through the PRP and HSR redundancy protocols.
- Cybersecurity. Role-based access control, security event logging, signed firmware and network access authenticated with IEEE 802.1X; Siemens states that it meets the requirements of NERC CIP and of the BDEW white paper.
- Basic power quality. Voltage unbalance, voltage variations (swell, sag, interruption), total harmonic and demand distortion (THD and TDD) and harmonics.
- Fault recording. Memory for a maximum recording time of 80 s at 8 kHz or 320 s at 2 kHz.
- Browser access. Web pages of the device with information, diagnostics, phasor diagrams and the single-line diagram, without installing DIGSI.
- Applications. Besides control, the profile proposes it as selective protection of overhead lines and cables fed from one or several ends when protection communication is used, with protection-class current transformers, and in substations with a breaker-and-a-half layout. Overcurrent can be configured as an emergency function.
The number of standard variants depends on the Siemens document: the 2020 profile lists six variants for the 6MD86, while the current product page lists seven. When specifying, use the manufacturer’s current ordering list, not a figure from an old document.
Points of attention in engineering and commissioning
- Which signals are assigned to each module. The communication modules are a limited resource (up to four): if the project needs IEC 61850, a protocol to the control center, redundancy and PROFINET, the assignment is defined when the device is ordered.
- Control with interlocks between bays. If the logic depends on GOOSE from other bays, the behavior on a lost message or invalid quality is decided in the design and tested. The modes described in test blocks and bay isolation are tested as well.
- Synchronism. The check 25 requires that the voltages on both sides reach the device and that the phase references are well defined; in bays with a transformer, the vector group phase shift must be compensated.
- DIGSI 5 and firmware version. Compatibility between the two is verified before opening an existing project, using the manufacturer’s documentation for that version.
- Document the data model. The SCL file exported from the device is the one used by SCADA or the gateway; see IEC 61850 SCL files.
Frequently asked technical questions
- 6MD85 or 6MD86 manual: Siemens publishes them by SIPROTEC 5 version; DIGSI 5 must be compatible with the device firmware.
- The close command does not execute: it is usually an interlock that is not met, a synchronism condition or a disconnector position read incorrectly (inconsistent double-point contacts).
- Interlocks between bays by GOOSE: if a message does not arrive or arrives with invalid quality, the interlock blocks; see GOOSE does not arrive or arrives late.
- Replacing a 6MD63 or 6MD66 with a 6MD85: it is not a configuration copy; the platform, the tool (DIGSI 4 to DIGSI 5), the inputs and outputs and the IEC 61850 model all change.
If your device is no longer manufactured
The 6MD61, 6MD63 and 6MD66 belong to SIPROTEC 4, the generation before SIPROTEC 5. Moving to a 6MD85 or 6MD86 means redoing the interlocking logic, the input and output mapping and the SCADA integration. We design the replacement, configure the new device and test it before energizing; see engineering design and studies.
How we can help
Our team configures SIPROTEC bay controllers: control logic and interlocking, synchronism check, IEC 61850 integration with SCADA and the gateway, and functional tests of the bay. We load and modify logic, interlocks and signals remotely, worldwide, through remote configuration of SIPROTEC relays and controllers, without waiting for a site visit. See control, protection and communications configuration and, for the communications part, IEC 61850 engineering. To request a quotation, write to us through contact.
Related guides
- Bay controller (BCU)
- Siemens DIGSI software
- Synchronism check 25
- IEC 61850 SCL files
- SEL-451 controller
- ABB REC670, REC650 and REC615 bay controller
- Ingeteam INGEPAC EF CD and ZIV IRF bay controller
- Siemens 7UT82, 7UT85, 7UT86 and 7UT87 relay (SIPROTEC 5)
- Command levels in substations and the local/remote selector
- Select-before-operate (SBO): how control commands work
References
- Siemens, SIPROTEC 6MD85 and SIPROTEC 6MD86 product pages.
- IEC 61850 (series), communication networks and systems for power utility automation.
- IEEE C37.118.1, synchrophasors.
- IEEE C37.2, standard for electrical power system device function numbers.
Frequently asked questions
What is the Siemens 6MD85?
It is the modular bay controller of Siemens' SIPROTEC 5 platform. It controls and monitors the switching devices of a bay, with interlocking, synchronism check, measurement and fault recording, and it can include protection functions. Siemens offers it in standard variants with 4 current inputs, 4 voltage inputs and between 11 and 75 binary inputs.
What is the difference between the 6MD85 and the 6MD86?
Both are SIPROTEC 5 bay controllers. According to Siemens, the 6MD86 has more standard variants, supports 4 or 8 current and voltage measurement inputs and adds functions such as controlled switching (point-on-wave) and per-phase breaker control. Which one is used depends on the bay configuration and on what the engineering requires.
Where can I find the 6MD85 manual?
Siemens publishes the SIPROTEC 5 manuals by firmware version, together with the DIGSI 5 application templates. The manual for one version may not match the installed device, so check the firmware version first.