Switchgear, the combination of electrical disconnect switches, circuit breakers, and fuses that controls electrical equipment, has been a mainstay of the electric industry since the late 19th century.
Originally invented for use in motors and electric machines, switchgear technology has evolved and improved, providing reliability for the electricity supply, clearing faults downstream, and de-energizing equipment when work needs to be performed. Its primary function is protection: the interruption of short-circuit and overload fault currents without disturbing service to circuits that aren’t affected. It can also isolate circuits from power supplies and allow more than one source to feed a load, which improves a system’s performance.
How It Works
A switchgear assembly has two types of components:
- Power-conducting components such as switches, circuit breakers, fuses, and lightning arrestors that conduct or interrupt the flow of electrical power
- Control systems, such as control panels, current transformers, potential transformers, protective relays, and associated circuitry that monitor, control, and protect the power-conducting components.
Switchgear is located on the high- and low-voltage sides of large power transformers in substations and can be used with voltages up to 1,100 kV. Switchgear on the low-voltage side can be used in conjunction with medium-voltage (MV) circuit breakers for distribution circuits, metering, control, and protection equipment.
For example, the ZX2 switchgear from ABB offers protection and control devices or pure protection devices. The gas insulation with SF6 increases operator safety, as all MV parts are fully encapsulated, making contact with live parts impossible.
The switchgear consists of metal-partitioned circuit breaker and busbar gas compartments for double busbar and single busbar applications. The cables are accessible from the rear and all switching devices can be controlled remotely. It incorporates digital bay control technologies, conventional devices, and plug-in technology for easy installation.
A long service life is achieved through the use of the insulating gas sulfur hexafluoride, an inert gas that insulates and protects all the high-voltage components throughout the life of the switchgear.
ABB is a technology leader in power grids, electrification products, industrial automation, and robotics. Its customers include utilities, industry, transport, and infrastructure. The goal of the 130-year-old company is to bring electricity from any power plant to any plug.
How they do so is changing. “There are several new and exciting innovations regarding switchgear,” states Craig Wicker, global product marketing manager, ANSI LV and MV Switchgear. “The latest innovative solution in MV switchgear is digital, utilizing IEC61850 protocols with GOOSE messaging.” It provides simplified control schemes, reduced wiring, and flexible protection and control designs.
Medium voltage (MV) switchgear is considered a key element of the electrical energy distribution system. The digital switchgear concept, at the MV distribution level, offers operational advantages. It is based on the combination of technologies, such as current and voltage sensors and IEC 61850 incorporated into modern numerical IEDs. When these technologies are combined in an optimal way, the advantages of digital switchgear include increased safety and space, weight, and energy savings, flexibility toward changing load flows, the ability to more easily handle last-minute load changes, faster delivery times, and the possibility of customization.
Digital solutions include the use of voltage and current sensors, utilizing low-level millivolt outputs (as compared with the higher voltages seen with conventional instrument transformers), Wicker explains. They also require much less wiring, utilizing a single CAT5E cable from each device.
“Current sensors are based on the Rogowski coil design and have full linear operation, so there is no need to determine CT ratios: one size fits all,” continues Wicker. “Due to their linear functionality, they will not saturate during faults as conventional current transformers will.”
They are also:
- Smaller, requiring less space
- Lighter, requiring less support structures
- Safer—as opening the secondary connection will not result in high-voltage spikes like conventional CTs will
Voltage sensors are used to take the place of conventional PT drawout units, saving space and allowing the total number of frames to be reduced, Wicker explains. “They, too, are smaller and lighter, as well as safer to operate.”
The use of sensors, as opposed to conventional instrument transformers, also results in less watt losses during equipment operation, allowing more energy to be put toward the loads where it is actually needed. All this translates into improved safety and greater reliability, along with better efficiency and space savings.
Another significant advancement in MV switchgear involves new Circuit Breaker technology. This technology is known as magnetic actuation. Traditional MV breakers rely on springs to initiate and manage their functionality. “As we all know, springs can be prone to breakage and may develop a ‘memory’ as they age, resulting in less than optimum performance,” elaborates Wicker.
Magnetic actuation eliminates this issue and provides a much more reliable system with significantly fewer moving parts. “This allows recommended maintenance cycles to be extended from one year to every five years, while delivering a much more consistent performance, enhanced safety, and lower total cost of ownership.”
Magnetic actuation can be used “anywhere” and is particularly effective in applications where the extended maintenance cycles and reliability are able to offer more system uptime and lower total cost of ownership. These include any critical or continuous process applications. Because there is less need to be inside the equipment, safety is increased for operations and maintenance personnel.
ABB says it is responding to “new challenges” in distribution networks, including distributed generation of renewable resources, increased energy demand, and the need for reliability as well as availability in the energy supply.
Their quest led to a recent innovation for medium voltage switchgear called UniGear Digital. Based on an optimized integration of MV sensors for current and voltage measurement into the MV switchgear, combined with the most recent design of protection relays and utilization of IEC 61850 communication for signal distribution, it ensures uninterrupted power. It’s used to distribute electric power in a variety of applications, such as on offshore platforms, in container or cruise ships, in mines, and in utility substations, power plants, and chemical plants.
UniGear Digital is an air-insulated digital switchgear using compact current and voltage sensors, Relion protection relays, and IEC 61850 digital communication. Each panel can accommodate two sets of current sensors. The voltage sensors are integrated as part of support insulators housed into the cable compartment or built directly in the busbar compartment.
According to ABB, distribution networks face new requirements, challenges, and evolution, which, in turn, create demands for a safer, smarter, more reliable, more efficient, environmentally friendly, and easy-to-use MV switchgear. UniGear offers flexibility, increased process efficiency, reliability, safety, and lower cost of operation.
With UniGear Digital, there is flexibility of changing the loads without changing the transformer. Current and voltage sensors feature linear characteristics; they operate with a wide range of primary currents by modifying the parameters of the protection relay. This provides smart grid flexibility and cost savings.
Further cost savings are achieved because of its energy efficiency and reliability, which reduces the risk of outage and contributes to a worry-free electrical network. Current and voltage sensors use very little energy, so less energy is needed to operate the switchgear.
ABB offers several switchgear options, such as the Ability GIS for MV - ZX for medium-voltage switchgear. ZX0.2 Digital is an enhancement of the existing ZX0.2 gas-insulated switchgear portfolio for primary applications.
The ZX0.2 Digital concept relies on three main pillars: proven ZX0.2 switchgear (up to 36 kV, up to 2500A, up to 31.5 kA); state-of-the art sensor technology for current and voltage measurement; and advanced communication technology according to IEC 61850. Thanks to continuous supervision of communication on the redundant bus system, ZX0.2 Digital offers superior reliability in comparison to a conventional switchgear.
Key benefits include:
- Simplified planning of switchgear projects
- Shortened delivery time by up to three weeks
- Increased flexibility towards changes in projects
- Increased safety during commissioning and operation thanks to sensor technology
- Lower energy consumption by up to 250 MWh
Digital technology can be applied to virtually any market segment, and is especially effective for “fast-tracked” projects because it allows late-cycle customization, and because it’s quicker to install. Other benefits include safer operation and field flexibility to address load changes over the course of installation.