Medium voltage panels consist of various subsystems to fulfill their basic functions. One of these systems is switching devices. Thanks to these devices, electricity distribution can be made in a safe and controlled manner, electrical distribution networks are safely protected by cutting off the current in case of malfunctions and short circuits, or safe work areas are created when maintenance is required.
In this study, switching devices vacuum circuit breaker, separator, load disconnector And vacuum contactor has been examined.
Switching devices are devices designed to turn one or more electrical circuits on and off via detachable contacts. In medium voltage panels, switching devices are located in the medium voltage compartment of the panel, referred to as the switching device compartment.
Some critical parameters taken into consideration when selecting switching devices to be used in the relevant facility: voltage values, current values, ambient conditions, mechanical properties, assembly and layout, operating requirements, safety features, compliance with standards, economic factors, auxiliary equipment, special customer requirements, environmental effects, etc.
Vacuum circuit breakers are widely used in air-insulated medium voltage panels. Vacuum circuit breakers are a type of circuit breaker in which the contacts (electrical connection points) perform the opening and closing movement in a special chamber that is left airless (vacuumed). This type of breaker extinguishes the arc that occurs between the contacts in a short time within the vacuum system when the breaker contacts are separated.
Vacuum circuit breakers are a critical piece of equipment in protection circuits. In case of a fault in the operating line or a short circuit in the system, it can automatically cut off the current for line protection (with the protection systems in the low voltage cabinet). Vacuum circuit breakers are widely used in industrial areas, power generation stations, distribution substations, commercial and industrial buildings, airports, etc. They are used in many areas such as.
Vacuum Interrupter [4]
► Disconnector: They are mechanical switching devices that provide an isolation distance in the open position in accordance with the specified requirements. [5]. Disconnectors can carry rated currents under normal circuit conditions. These devices are subject to the IEC 62271-102 standard.
Disconnectors cannot dampen the arc and cannot open the circuit under rated current, if the current increases to a certain extent or in short circuit situations.
The main function of disconnectors is to safely isolate circuits that are not under load. In this way, a safe working environment is provided during works such as maintenance and repair.
► Switch Disconnector: In the open position, while ensuring the isolation distances specified for a separator [6]are devices that can turn on and off even under rated current.
Fuseless load disconnectors can open and close under rated current, but cannot interrupt short circuit currents. These devices are subject to the IEC 62271-103 standard.
Switch disconnectors, when combined with fusesFuse Switch Disconnector (switch-fuse combination)”. In these devices, short circuit protection is provided by a fuse (they cannot be combined with a relay (protection systems in low voltage cabinets).) When the fuse blows in the phase where the short circuit current occurs during a short circuit, the load disconnector opens in three phases. This is a process that takes place within the device itself. In the phase where the fuse blows, the load disconnector opens the circuit under load (there is no load left), and in the other two phases it opens the circuit under load. These devices comply with IEC 62271-105 They are subject to the standard.
– Load disconnectors are cost-effective products.
– Load disconnectors, like vacuum circuit breakers, can open and close under rated current. However, the current values at which load disconnectors operate are lower than vacuum circuit breakers.
– The fused switch disconnector trips faster and provides protection than the relay-breaker-current transformer combination. However, since the fuse in the fused switch disconnector will blow in the event of a short circuit, this fuse cannot be reused and the fuse must be replaced in the field. Vacuum circuit breakers can be controlled remotely.
Fuse Switch Disconnector [3]
► Vacuum Contactor (Vacuum Contactor):
They are switching devices with high mechanical strength, used in situations where contacts are opened and closed in a vacuumed environment and require frequent operations (on-off). Vacuum contactors can open and close under rated current. They are often used with a combination of fuses. In short circuit conditions, the interruption of short circuit current is provided by the fuse system. These devices are subject to the IEC 62271-106 standard.
Vacuum contactors are electromechanically operated switching devices. They can turn on and off under rated current with the protection control devices in the low voltage cabinet or by remote control.
Vacuum contactors are long-lasting, have low maintenance costs and are compact. These devices are used for switching of motors, switching of transformers, resistive consumers, capacitors, etc. They are used in areas that require frequent opening and closing, such as
– Vacuum contactors, like vacuum circuit breakers, can open and close under rated current and use a similar vacuum system. However, the current values at which vacuum contactors operate are lower than vacuum circuit breakers.
– Since the fuse in vacuum contactors will blow in the event of a short circuit, this fuse cannot be reused and the fuse must be replaced in the field. Vacuum circuit breakers can be controlled remotely.
– The electrical and mechanical life of vacuum contactors is much longer than vacuum circuit breakers.
Vacuum Contactor [3]
: Short circuit protection is provided by the fuse.(**): Commonly used values are indicated. The specifications of the relevant medium voltage panel brand should be checked.
(***): Evaluated very roughly. It would be meaningful to consider it together with investment costs.
Conclusion
Switching devices are of critical importance to ensure the security and continuity of electrical distribution systems. Switching devices to be used in air-insulated medium voltage panels should be selected appropriately according to the needs of the relevant facility. When making this selection, the features and operating principles of the switching devices should be evaluated and the facility should be configured according to need.