What Is MV Switchgear? Medium-Voltage Panel Types and Selection Criteria

Medium-voltage (MV) switchgear is a metal-enclosed assembly that safely combines the switching, protection and metering of electrical power in distribution networks, typically between 1 kV and 36 kV. In short, MV switchgear is the heart of every transformer substation and distribution point: it receives incoming MV power in a controlled way, interrupts it when necessary and distributes it safely to transformers and other feeders. On Turkish drawings and bills of quantities, an individual MV switchgear panel is called an "OG hücre" (MV cell).

An MV switchgear panel houses a circuit breaker or load-break switch, a disconnector and grounding switch, current and voltage transformers, protection relays, busbars and a cable connection compartment. These components are arranged in a compartmentalized enclosure designed to protect people and equipment from short circuits and internal arc faults.

The reference standard for all of these functions is IEC 62271-200 (adopted in Türkiye as TS EN 62271-200), together with the technical specifications of TEDAŞ (Turkish Electricity Distribution Company) for the Turkish distribution grid. Selecting the right MV switchgear is not about a single device: it determines system safety, service continuity and long-term operating cost.

MV switchgear combines three core functions in one enclosure: switching (opening and closing circuits), protection (interrupting the circuit under short circuit or overload) and metering and monitoring (reading current, voltage and energy values). How much of each function a panel performs defines its type and its role in the network.

Inside, the critical components are separated into compartments: the busbar compartment, the switching device compartment, the cable compartment and the low-voltage protection and control compartment. This compartmentalization contains a fault in one compartment before it spreads to the others, and during maintenance only the relevant compartment has to be de-energized while the rest of the system stays in service.

On the protection side, relays evaluate the signals coming from current transformers. For faults such as overcurrent, short circuit or ground fault, the relay sends a trip command to the circuit breaker and isolates the circuit within milliseconds. Correct relay coordination ensures that only the faulty feeder is disconnected while the rest of the network remains energized.

By network role, the most common MV switchgear panels are the load-break switch incoming/outgoing panel, which manages incoming and outgoing power with a load-break switch; the circuit-breaker incoming/outgoing panel, fitted with a relay-controlled breaker that trips automatically on faults; and the fused transformer protection panel, an economical solution that protects the transformer with a load-break switch and HRC fuse combination.

Metering panels complete the picture: current and voltage metering panels house the instrument transformers used for energy metering and billing, while voltage metering panels measure voltage only. Bus coupler panels connect two separate busbar sections, adding supply flexibility and redundancy.

The right type depends on transformer rating and protection requirements. A fused transformer protection panel is adequate and economical for smaller distribution transformers, whereas a circuit-breaker protection panel is preferred for larger ratings or for sites that need precise relay coordination. The selected protection panel is then combined with metering and incoming/outgoing panels into a complete switchgear line-up.

The difference lies in the insulating medium: in air-insulated switchgear (AIS), atmospheric air provides the insulation between conductors, while in gas-insulated switchgear (GIS) an insulating gas sealed inside a tight enclosure does the job. AIS is relatively easy to maintain and has a lower initial cost, but it takes up more floor space.

Gas-insulated switchgear is far more compact and almost entirely unaffected by ambient conditions such as humidity, dust, pollution and salt-laden air. That makes it the natural choice for compact substation buildings with tight space, coastal sites and industrial plants in heavy pollution classes. The trade-off is a higher initial investment.

With air insulation, one physical rule drives panel size: the higher the voltage, the larger the clearance (dielectric distance) required between conductors. In practice, a rough reference of about 1 kV per centimeter is used for air, which explains why 36 kV air-insulated panels are noticeably wider than 24 kV panels. Gas insulation shortens this distance and therefore delivers a much smaller footprint at the same voltage.

IEC 62271-200 defines the safety and performance level of MV switchgear through three main classifications: loss of service continuity (LSC), internal arc classification (IAC) and partition class (PM or PI). The LSC category indicates how much of the switchgear can remain energized when one compartment is opened for maintenance; LSC2 panels, for example, let the busbar stay live while work is carried out in the cable compartment, keeping outages to a minimum.

Internal arc classification (IAC) shows the level of protection for personnel and surroundings if an arc fault occurs inside the panel. A designation such as IAC A FLR states the accessibility type (A, restricted to authorized personnel) and which sides, Front, Lateral and Rear, were tested against internal arc, at a stated short-circuit current and duration. This is a directly life-safety-critical criterion.

Panels are also classified by the material of the partitions between compartments: metallic (PM) or insulating (PI). Matching these classes to project requirements ensures the switchgear stays safe not only in normal operation but also during faults and maintenance. Stating these classes explicitly in the specification prevents disputes during procurement and commissioning.

The key MV switchgear selection criteria are rated voltage, rated current, short-circuit withstand, functional type, insulation type (AIS or GIS), the IEC 62271-200 safety classes, site conditions, and protection and automation requirements. Start with the rated voltage (for example, 24 kV or 36 kV) and the rated current of the busbars and feeders. Then establish the system's short-circuit level: the panel's rated short-time withstand current (in kA, for a stated duration) must be at least equal to it. If these three values are set wrong, the switchgear will either be undersized or needlessly oversized.

Next, choose the functional type (incoming/outgoing, transformer protection, metering, bus coupler), the insulation type (air or gas) and the safety classes (LSC, IAC, PM/PI) to suit the project. The installation location is just as critical: available space, pollution class, humidity and altitude all directly influence the panel type. On coastal or dusty industrial sites, gas-insulated solutions have a clear advantage.

Finally, define the protection and automation requirements: relay type, communication protocol and SCADA integration for remote monitoring should be built into the switchgear design from the start. Evaluating all of these criteria together, in line with TEDAŞ specifications and IEC standards, eliminates the re-manufacturing and delays caused by wrong selections.

Miratek Elektrik manages design, switchgear supply, installation and commissioning end to end for medium-voltage systems from 1 kV to 35 kV, with 48 MV switchgear panel (cubicle) installations completed. In transformer substation projects, the switchgear is selected through engineering calculations based on transformer rating, short-circuit data and the site's environmental conditions, producing a solution that fits the site and fully complies with the standards.

Beyond switchgear installation, the same team integrates protection relay coordination, grounding, cable connections and, where needed, SCADA-based remote monitoring. Carried out under ISO 9001:2015, ISO 14001:2015 and ISO 45001:2018 management systems, this work prioritizes full standards compliance at commissioning and a reliable, uninterrupted supply.

To have your transformer substation or MV switchgear project assessed, contact the Miratek engineering team: +90 541 359 72 58 · miratek@miratekelektrik.com.