Why has metal-clad switchgear remained the industry’s go-to switchgear for medium voltage applications? There are three key drivers that make metal-clad the dominant choice: 1) customization capabilities, 2) ease of maintenance, and 3) enhanced safety features.
Customization: One of the most attractive benefits of metal-clad switchgear is its ability to be fully customizable, based upon customers’ specifications. Customization is based on how intricate the system application must be. But what does customization really mean?
Metal-clad switchgear provides basic load protection; it operates based on the instructions of the relay that is installed. Therefore, the selection of the relay adds to the level of customization that is specified. For basic applications, the relay will usually contain minimal ANSI functions that typically include overcurrent, under voltage, overvoltage and tripping the circuit breaker. Demanding or complex applications, e.g., zone selective interlocking may include current, voltage, and frequency protection features such as direction ground fault and phase overcurrent. Additional customization applications might require phase sequence and phase balance. As more advanced relay schemes are required, the relay size may change, directly affecting the amount of wiring detail that is required.
Customization not only affects the relay/wiring schemes but the structure of the switchgear, as well. Different layout options allow metal-clad circuit breakers to be stacked one on top of another based upon the ampere of the switchgear. This usually provides adequate space for customization in the low voltage compartment, such as laying out additional switches, lights, alarm signals, racking ports, plugs, communication ports and so on.
Ease of Maintenance: Maintenance needs vary based on customer application requirements. Some applications call for reduced switching of the equipment. Its main purpose is to function as a disconnect that continually operates in the ‘on’ position except for a yearly shutdown. Other applications require the equipment to switch from an ‘open-to-close’ or ‘on-to-off’ state more frequently. For these frequent switching applications, customers prefer equipment that can handle the constant use to operate the loads that are fed.
MastercladTM medium voltage metal-clad switchgear from Schneider Electric is tested to all IEEE requirements listed in the C37.20.2 (up to 10,000 operations). With the testing requirements set in place, Masterclad has quickly become a favorite in the switchgear industry. The ability to withdraw the circuit breaker from its compartment allows the electrical and mechanical parts to be monitored and maintained on a more frequent basis. A metal-clad circuit breaker has withdrawable finger clusters that allow the circuit breaker to be racked out of its compartment with the push of a button or racking handle. With the withdrawable feature, there is no requirement to provide a visual means of disconnect.
Enhanced Safety: Metal-clad switchgear has enhanced safety features that are not mandatory in traditional metal-enclosed switchgear. For example, metal-clad is fully compartmentalized, which means the low voltage compartment is accessible without allowing access to any other live parts in the switchgear. The main bus and incoming bus are also separated. It is a fully grounded unit with grounded barriers, mechanical interlocks, circuit breaker shutters and fully insulated bus, which keeps operators segregated from the medium voltage sections.
Another safety feature is the remote circuit breaker racking option. Racking operations can be performed by an operator up to 50 feet away via a push button, removing personnel from direct contact with the equipment. Finally, Arc Terminator, an active arc extinguishing system, is available upon request.
For an in-depth look at Schneider Electric’s medium voltage product offering, visit www.schneider-electric.us/mediumvoltage.