Metal-enclosed switchgear is a type of electrical equipment that consists of an earthed metallic enclosure that houses various components such as circuit breakers, switches, fuses, bus bars, and current transformers. Metal-enclosed switchgear is widely used for medium-voltage applications in utility distribution systems and commercial and industrial facilities. In this article, we will explain what metal-enclosed switchgear is, how it works, what are its advantages and disadvantages, and what are the different types and designs of metal-enclosed switchgear.
What is Metal Enclosed Switchgear?
Metal enclosed switchgear is defined as a switchgear assembly that is completely enclosed on all sides and top with sheet metal (except for ventilating openings and inspection windows) and containing primary power circuit switching or interrupting devices, or both, with buses and connections. Metal-enclosed switchgear is designed to provide protection, control, and isolation of electrical circuits and equipment.
Metal-enclosed switchgear can be classified into two main categories: metal-clad switchgear and compartmented switchgear. Metal-clad switchgear has metal partitions between the compartments that are intended to be earthed, while compartmented switchgear may have one or more nonmetallic partitions. Both types of switchgear have the following features:
- They have three main compartments: the front compartment for the circuit breaker, the top compartment for the bus bar assembly, and the rear compartment for the current transformer and cable connection.
- They have interlocking mechanisms between the components to ensure safe and proper operation. For example, the circuit breaker cannot be removed or operated unless it is in the OFF position, and the bus bar cannot be isolated unless the circuit breaker is in the OFF position.
- They can be easily operated, maintained, inspected, and replaced. All the components are accessible from the front of the switchgear.
Metal-enclosed switchgear has several advantages over other types of switchgear, such as:
- It has a low initial cost compared to metal-clad switchgear, as it has simpler construction and installation requirements.
- It has a low maintenance cost compared to metal-clad switchgear, as it does not require adjusting, programming, or dielectric testing of the switches and fuses.
- It has high reliability and performance compared to other types of switchgear, as it uses fuses that offer faster clearing time and reduce system stress compared to circuit breakers.
- It has a high customization potential compared to pre-engineered metal-enclosed switchgear, as it can be tailored to meet specific system or application needs.
However, metal-enclosed switchgear also has some disadvantages, such as:
- It has a larger footprint compared to gas-insulated switchgear, as it requires more space for ventilation and clearance.
- It has a lower arc-fault protection compared to metal-clad switchgear or gas-insulated switchgear, as it does not have arc-resistant enclosures or arc-extinguishing devices.
- It has lower environmental protection compared to gas-insulated switchgear or outdoor-type switchgear, as it is more susceptible to corrosion, dust, moisture, and vermin.
Types and Designs of Metal Enclosed Switchgear
There are various types and designs of metal-enclosed switchgear available for different voltage levels and applications. Some of the common types and designs are:
Metal Enclosed Indoor Switchgear
Metal-enclosed indoor switchgear is designed for indoor installation in buildings or substations. It can be either vertical isolation and horizontal draw-out type or horizontal isolation and horizontal draw-out type. The former type has a vertical isolating unit that separates the circuit breaker from the bus bar when it is withdrawn from its service position. The latter type has a horizontal isolating unit that slides along with the circuit breaker when it is withdrawn from its service position.
Metal-enclosed indoor switchgear typically has a low-voltage chamber attached to the main gear housing that contains the metering and relay panel. The withdrawal portion with the circuit breaker has three positions: service, test, and isolated. The service position allows the circuit breaker to be connected to the bus bar and operate normally. The test position allows the circuit breaker to be tested without disconnecting it from the auxiliary circuit. The isolated position allows the circuit breaker to be disconnected from both the bus bar and the auxiliary circuit.
Gas Insulated Medium Voltage Switchgear
Gas-insulated medium voltage switchgear is a fixed type metal-enclosed design that uses sulfur hexafluoride (SF6) gas as an insulating medium. It does not have any withdrawal portion. It mainly has two compartments: the circuit breaker compartment and the bus bar compartment. The circuit breaker compartment contains three interrupters that are usually of vacuum type. The bus bar compartment contains a three-position switch that can connect the bus bar to either the service position, the isolated position, or the earthed position.
Gas-insulated medium voltage switchgear has several advantages over other types of medium voltage switchgear, such as:
- It has a smaller footprint compared to metal-enclosed switchgear or metal-clad switchgear, as it requires less space for insulation and clearance.
- It has a higher arc-fault protection compared to metal-enclosed switchgear or metal-clad switchgear, as it uses SF6 gas that can quench arc effectively.
- It has higher environmental protection compared to metal-enclosed switchgear or metal-clad switchgear, as it is sealed from external influences such as corrosion, dust, moisture, and vermin.
However, gas-insulated medium voltage switchgear also has some disadvantages, such as:
- It has a higher initial cost compared to metal-enclosed switchgear or metal-clad switchgear, as it requires more sophisticated design and manufacturing.
- It has a higher maintenance cost compared to metal-enclosed switchgear or metal-clad switchgear, as it requires regular monitoring and servicing of SF6 gas pressure and quality.
- It has a higher environmental impact compared to metal-enclosed switchgear or metal-clad switchgear, as SF6 gas is a potent greenhouse gas that contributes to global warming if leaked.
Metal Enclosed Outdoor Type Medium Voltage Switchgear
Metal enclosed outdoor type medium voltage switchgear is similar to metal enclosed indoor type medium voltage switchgear except for its external housing. The external housing is made of welded sheet steel with a slanting roof and rain shields. The housing is designed to withstand outdoor conditions such as weathering, UV radiation, humidity, temperature variations, etc. This type of design of medium voltage switchgear is not commonly used except for some special utilities such as city distribution networks with underground cable systems.
Unitized Power Centers
Unitized power centers are a type of metal-enclosed low voltage (600 V) distribution equipment that combines transformers (dry-type or liquid-filled), secondary main breakers (molded case or insulated case), feeder breakers (molded case), metering devices (current transformers), protective relays (electromechanical or solid-state), control wiring (terminal blocks), grounding devices (ground bars), etc., in one compact enclosure. Unitized power centers are designed for indoor or outdoor installation in commercial or industrial facilities where space is limited or where multiple services are required.
Unitized power centers have several advantages over conventional low-voltage distribution equipment, such as:
- They reduce installation time and cost by eliminating separate transformer rooms, switchboards, panelboards, metering cabinets, etc.
- They improve reliability by reducing wiring errors, loose connections, and voltage drops.
- They enhance safety by providing arc-resistant enclosures, ground fault protection, and lockout/tagout provisions.
- They increase flexibility by allowing easy reconfiguration, expansion, or relocation of loads.
- They optimize efficiency by reducing losses, harmonics, and power factor penalties.
OEM Medium Voltage Switch Components
OEM medium voltage switch components are modular components that can be used by original equipment manufacturers (OEMs) to build custom metal-enclosed medium voltage switches according to their specifications. OEM medium voltage switch components include load interrupter switches (single-phase or three-phase), power fuses (SM or SML), electronic power fuses (Fault Fiter®), fuse mountings (clip-on or bolt-on), fuse holders (single-phase or three-phase), fuse pullers (manual or motorized), etc. OEM medium voltage switch components are designed for indoor or outdoor installation in utility distribution systems or commercial and industrial facilities.
OEM medium voltage switch components have several advantages over other types of medium voltage switching devices, such as:
- They provide high customization potential by allowing OEMs to choose from various ratings, configurations, and options
- They offer high performance by using proven technology, quality materials, and rigorous testing
- They ensure high compatibility by complying with industry standards, codes, and regulations
- They support high customer satisfaction by providing technical support, warranty service, and spare parts availability
Conclusion
Metal-enclosed switchgear is a type of electrical equipment that consists of an earthed metallic enclosure that houses various components such as circuit breakers, switches, fuses, bus bars, and current transformers. Metal-enclosed switchgear is widely used for medium-voltage applications in utility distribution systems and commercial and industrial facilities. Metal-enclosed switchgear can be classified into two main categories: metal-clad switchgear and compartmented switchgear. Both types of switchgear have the following features:
- They have three main compartments: the front compartment for the circuit breaker, the top compartment for the bus bar assembly, and the rear compartment for the current transformer and cable connection.
- They have interlocking mechanisms between the components to ensure safe and proper operation.
- They can be easily operated, maintained, inspected, and replaced.
Metal-enclosed switchgear has several advantages over other types of switchgear, such as:
- It has a low initial cost and maintenance cost compared to metal-clad switchgear.
- It has high reliability and performance compared to other types of switchgear.
- It has a high customization potential compared to pre-engineered metal-enclosed switchgear.
However, metal-enclosed switchgear also has some disadvantages, such as:
- It has a larger footprint compared to gas-insulated switchgear.
- It has a lower arc-fault protection compared to metal-clad switchgear or gas-insulated switchgear.
- It has lower environmental protection compared to gas-insulated switchgear or outdoor-type switchgear.
There are various types and designs of metal-enclosed switchgear available for different voltage levels and applications. Some of the common types and designs are:
- Metal enclosed indoor switchgear, which can be either vertical isolation and horizontal draw-out type or horizontal isolation and horizontal draw-out type.
- Gas-insulated medium voltage switchgear, which is a fixed type metal-enclosed design that uses SF6 gas as an insulating medium.
- Metal enclosed outdoor type medium voltage switchgear, which is similar to metal enclosed indoor type medium voltage switchgear except for its external housing.
- Unitized power centers are a type of metal-enclosed low-voltage distribution equipment that combines transformers, breakers, metering devices, relays, etc., in one compact enclosure.
- OEM medium voltage switch components, which are modular components that can be used by OEMs to build custom metal enclosed medium voltage switches according to their specifications.
In this article, we have explained what metal-enclosed switchgear is, how it works, what are its advantages and disadvantages, and what are the different types and designs of metal-enclosed switchgear. We hope that this article has helped you to understand the basics of metal-enclosed switchgear and its applications. If you want to learn more about metal-enclosed switchgear or other electrical equipment, you can visit electrical4u.com for more information and resources. Thank you for reading this article, and have a great day!
