The development was as old as the development of electricity generation. The initial developments in switchgear are very simple which are wall fixed and then upgraded to mount on wooden boards. Later on, the wooden boards were substituted by marbles and slate materials. And this is directed for further enhancement.
The first easiest development of this was a tumbler switch which was utilized for controlling and safeguarding lights in houses and others. So, this is a brief history of switchgear advancement and now the article focuses on explaining switch gear functionality, what are the components involved, types, and features.
What is SwitchGear?
Switchgear is the device, which is used for regulating, monitoring, and switching ON or OFF the circuit in an electrical power system. This is a system that has a direct connection with the supply system and is located in both the HV and LV sides of the transformer.
These devices mainly consist of switching and protection equipment like circuit breakers, regulating panels, fuses, potential transformers, isolators, switches, current transformers, lightning arrestors, and other related devices.
Few of the devices are intended to function in both unusual and normal scenarios, whereas few are designed only for switching purposes but not for observing the faulty conditions. For the normal operating condition, it allows ON and OFF distributors, generators, transmission lines, and other devices. Whereas in the faulty condition such as in short-circuited scenario, there will be a huge amount of current flow through the devices thus creating damage for the device and causes interruption for customers.
So, this is the device useful for finding faults and then separates the fault section from the system. Along with these few of the other components of switchgear are:
Bushings – When a conductor with a high voltage level flows across the metal sheet that is placed at earthing potential, then the required protection is offered to it using bushings.
Bus bars – The current transporting equipment in a circuit-breaking device is included with both moving and constant contacts. The conductors that have a connection with the bus bars are externally located to the circuit breaker.
When the switchgear is of the external type, the bus bar connections have a direct connection with overhead lines, whereas, for internal type switchgear, the bus bards are connected to the conductors that are incoming for the breaker.
Functions of Switchgear
The crucial functional aspects of the device are mentioned as follows:
- It has to play the functionality of transporting, either creating or disconnecting the normal load current such as how the switch performs
- This device should support the functionality of protecting devices from overload faulty current conditions. For sensing appliances such as potential and current transformers and relays, this operation has to be provided.
- Also, the requirement for regulating, metering the data is the one functionality in which multiple devices are utilized for accomplishing the switching operation.
- It even consists of the combination of various switching equipment along with measuring, regulation, controlling and protection devices.
- The device along with the above equipment is utilized in various purposes like distribution, generation, and transformation of electrical energy. These devices are also used for regulating huge current flow thus protecting the equipment from damage.
- The other functionality is to de-energize the equipment for testing purposes and so clear the fault.
There are mainly three switchgear types depending on the level of voltage and each of those is clearly explained in the below section.
Low Voltage Switchgear
This type of switchgear is usually used for the voltage range of 1000V and 1500V DC current. In general, the low voltage type consists of HRC fuses, small circuit breakers, ACBs, circuit breakers of molded type, off-road isolators, and other related equipment for safeguarding the system.
The main usage of this type is in the low voltage distribution boards.
Medium Voltage Switchgear
This type of device is usually used for the voltage range of 3.3kV to 33kV. This type of switchgear is essentially utilized for the supply of electrical energy that has a connection with multiple networks. They consist many of substation devices like a vacuum, minimum and heavy oil circuit breakers, vacuum, air, and gas-shielded type. The below picture is the medium voltage switchgear diagram.
This MV switchgear can be of metal-covered indoor and outdoor types, and also can be outdoor type having no metal shield. In these, the interruption medium might be SF6, air, or oil.
The essential constraint of a medium voltage type of device is to disrupt the current flow when there happens incorrect condition regardless of the kind of CB in the system. Along with these, an MV device should hold the ability to:
- Perform switching activities such as ON/OFF
- Providing interruption during short-circuit conditions
- Switching of capacitive/inductive currents
- And few other special functionalities.
High Voltage Switchgear
This type of switchgear is usually used for the voltage range beyond 36kV. As the level of voltage is more, the arcing generated while switching functionality also becomes high. So, additional consideration is needed while constructing the HV switchgear devices.
In high voltage switchgear devices, the essential component is the HV circuit breaker and because of this, the device must hold special characteristics for smooth and consistent functionality. Defective tripping and switching functionality of this HV switchgear are relatively rare than LV and MV switchgear devices. In many of the situations, the HV circuit breakers persist to be in an ON state and might be functioned after a very long period. So, it is needed that circuit breaker should hold an extensive level of reliability to make sure of protected functionality.
Switchgears are also categorized as indoor and outdoor devices.
For the voltage level less than 66kV, switchgear is usually placed internal to the device due to economical concerns. It is of a metal-clad kind and in the designing phase, almost all the live components are shielded in a metal case that is of earthed type. The major objective behind this is for exact localization and limitation of any damage.
The outdoor switchgear is used above 66kV level of voltages because for this voltage level the clearances in between the conductors and the space necessary for transformers, switches, circuit breakers, and other related devices turn to be great which seems to be not inexpensive to locate inside the system.
This section explains on essential features of switchgear and those are:
Enhanced Reliability – Because of the progression of interconnection and the enhanced capacity of developing stations, the requirement for reliable type switchgear holds more prominence. When there is any damage in the power system, these switchgear devices should be able to separate the damaged part from the rest of the circuit.
Fast Operation – When there is any damage to the power system, these devices should be able to respond quickly so that it shows no harm for devices like transformers, isolators, generators, and other related devices.
This is on the whole about switchgear device. This article has provided complete data on switchgear functionality, features, types, and its components. Furthermore, know what is the switchgear and protection it shows for other kinds of electrical devices?