What is a Medium Voltage Modular Cell (MV Cell)?
Medium voltage (MV) switchgear, also known as modular switchgear, is a compact and safe switchgear equipment used in power distribution systems up to 36 kV for switching, protection, and measurement operations. It is used in numerous applications, including transformer substations, industrial facilities, and step-down and step-up substations.
These switchgear integrates many components, including MV circuit breakers, disconnectors, load disconnectors, current and voltage transformers, protection relays, busbar systems, and cable connection points. Their compact design saves space, while their modular structure facilitates system expansion. Generally maintenance-free, these structures prioritize user safety and offer ease of operation.
MV Cell Types: Air and Gas Insulated MV Cells
MV switchgear is classified into two main groups according to its insulation type:
Air-insulated MV switchgear: Busbars are insulated with air. Circuit breakers and disconnectors may be located in tanks filled with SF6 gas. These types of switchgear are generally larger in volume but offer advantages in terms of maintenance.
Gas-insulated MV switchgear (GIS): All active parts are located in a metal enclosure insulated with SF6 gas. Thanks to its compact design, it offers an ideal solution for applications with space constraints. These types of switchgear are commonly known in the industry as RMU (Ring Main Unit).
MV switchgear contains many different elements such as busbar systems, disconnectors, grounding disconnectors, MV circuit breakers, protection relays, surge arresters, MV fuses, indicator lamps, lighting equipment, and measuring transformers. The contents may vary depending on the switchgear type and function.
OG Cell Structure and Classifications
MV modular switchgear is structurally classified according to different criteria:
- Compartment Type
PM (Metal Compartment): Components under voltage are separated by grounded metal compartments with open access areas.
PI (Insulating Compartment): This separation is achieved with insulating materials. Generally, they stand out due to their lower cost and lighter weight.
- Internal Arc Resistance (IAC Classes)
A: Only authorized technical personnel can access.
F: Access is possible from the front surface.
L: Side surface access is possible.
R: Access is possible from the rear surface.
- Service Continuity (LSC Classes)
LSC-1: All components in the switchgear are in a single compartment; the entire system must be de-energized for any intervention.
LSC-2A: Intervention on other components is possible while the busbars are energized.
LSC-2B: Access to switching elements is possible while both the busbar and cable compartment are energized.
OG Cell Rating Values and Sizing
Commonly used medium voltage (MV) switchgear in Turkey has a rated voltage of 36 kV, a continuous current carrying capacity of 630 A, and a short-circuit breaking capacity of 16 kA. The physical dimensions of these switchgear vary depending on the voltage they carry. In an air-insulated 36 kV switchgear, an average spacing of 36 cm should be left between the busbars for safe insulation. This calculation is based on the dielectric strength of air, which is approximately 1 kV/cm, and directly affects the physical dimensions of the switchgear.
The superior insulation properties of SF₆ gas allow for the construction of a structure that occupies less space at the same voltage in gas-insulated switchgear. Therefore, these switchgears are frequently preferred in confined spaces.
TEDAŞ-type medium voltage switchgear used in Turkey.
In our country, MV switchgear is manufactured according to TEDAŞ standards based on project requirements:
Switchgear to be used in SF6 gas systems must fully comply with TEDAŞ-MYD/95-002.B; air-insulated metal-enclosed switchgear must comply with TEDAŞ-MYD/95-007.E.
MV switchgear can be manufactured according to different protection classes such as IP 3X, IP 4X, IP41. The most common switchgear types are:
Load disconnect switchgear (input/output)
Fused transformer protection switchgear
Switchgear (input/output)
Switchgear (input/output)
Switchgear (transformer protection switchgear)
Coupling switchgear
Cable connection switchgear
Measuring switchgear (current/voltage)
Applications of OG Cells
MV modular switchgear is widely used in many areas such as:
Urban distribution centers
Organized industrial zones
Renewable energy power plants
Industrial facilities
Low and medium voltage transformer substations
They save space and offer high personnel safety. Thanks to their compact structure, the system can be easily expanded. MV switchgear is a modular switching element that offers high safety, ease of operation, and long service life in energy distribution facilities. Properly selected MV switchgear increases facility safety and guarantees system continuity.