Demystifying Switchgear Classification

By Amol Surendra Patharkar

While many of us possess a general understanding of switchgear, newcomers in the industry often find it challenging to grasp various terms associated with switchgear.

In our engineering curriculum, we receive a broad education on switchgear, but there's often a gap between what's taught and current industry standards. With this in mind, I'd like to contribute a brief overview of switchgear and its various facets, drawing from my experience.

This article aims to explore the fundamental categorization of switchgear. But first let's see what a switchgear is:

Definition - A switchgear can be defined as an equipment which can carry, make & break the current under normal as well as certain abnormal conditions, thus isolate the healthy section of the system from the faulty portion and save the human life and property from any damage.

Classification of Switchgear

Switchgear can be broadly classified in different ways as below:

1. Voltage Class Broadly switchgears are classified on the basis of voltage rating.

Low Voltage (LV) Switchgear – Low voltage switchgear is mostly used in power electronics circuit that deals with the voltage level below 1 kV, few examples of LV switchgear are switch fuse unit, HRC fuses, Air circuit breakers), miniature circuit breakers), molded case circuit breakers (MCCB) etc.

Medium voltage switchgear – Practically speaking as per IEC, any switchgear including and above 1 kV is classified as high voltage switchgear, but for commercial purpose this is further classified as medium voltage switchgear i.e between voltage class including and above 1kV up to 33 kV, few examples of MV switchgear are Bulk oil circuit breaker ( BOCB), Minimum oil circuit breaker ( MOCB) , Sulphur hexa- fluoride circuit breaker ( SF6) , Vacuum circuit breaker ( VCB ), SF6 Free circuit breakers.

High Voltage Switchgear – Switchgears between voltage level 33 kV up to 220 kV are classified as HV switchgear. Further these HV switchgears are classified as Extra HV (EHV) i.e., between 220 kV to 760 kV & Ultra High Voltage (UHV) i.e. voltage level above 800 kV.

2. Installation

Indoor Type Switchgear – Switchgears used inside an enclosed room are termed as indoor type of switchgear. Usually, indoor switchgears have ingress protection class ranging from IP 1X to IP 6X.  Further indoor type switchgears are classified as:

Metal enclosed indoor switchgear – In this type of the switchgear is enclosed on all sides with metal sheets containing primary interrupting device and fuses, and all the piece of equipment is encased in a central assembly.

Metal clad indoor switchgear. – This type of switchgear is compartmentalized in nature which typically has various compartments such as circuit breaker compartment, LV compartment for relays and meters which is isolated by grounded metal barriers separately.

Thus, all metal clad switchgears are metal enclosed, but all metal enclosed switchgears are not metal clad switchgear. The metal enclosed switchgear of same voltage rating as that of metal clad switchgear is of simpler construction.

Few examples of indoor type switchgear are indoor isolator, indoor SFU, Indoor VCB, indoor RMU etc.

Advantages of using indoor switchgear are it is more reliable and safer, takes less space, easy maintenance, low operating cost, more secure and less prone to harsh environmental conditions.

Limitation of using indoor switchgear is higher initial cost.

Outdoor Type Switchgear - Switchgears that are installed in open environment such as switchyards are called as outdoor type of switchgears. This type of switchgear shall provide protection against water droplets and water submersion in addition to protection against dust particles.

This type of switchgears are bulky and requires more space as compared to indoor type switchgear, mostly HV, EHV and UHV switchgear can be found installed in outdoor application.

Few examples of outdoor type switchgear applications are – Porcelain Clad Vacuum Circuit Breaker (PCVCB), Outdoor type VCB Kiosk (line up Kiosk & roof bushing Kiosk), outdoor isolator, outdoor SFU, Outdoor type Ring Main Unit (RMU), Compact secondary substation (CSS) or Unitized substation (USS).

3. Insulating Medium 

Insulating medium refers to the medium in which switchgear is enclosed. Insulating medium protects the switchgear from any unexpected arching event. Air is the most common insulating medium, but air has low dielectric strength as compared to solid insulators, gases like SF6 and liquid like mineral oil & insulating oil. Depending upon the type of insulation is used switchgears can be broadly classified as: 

Air Insulated Switchgear – Air Insulated Switchgear (AIS) is a switchgear that is encapsulated in a metal frame that houses different electrical devices such as circuit breaker, disconnector, earth switch all these devices are surrounded by natural air that is used as dielectric / insulating medium between the phases and between phase to earth. In case of a circuit breaker the closing & opening contacts are inside a vacuum interrupter (which provides high dielectric strength), while for disconnector or a load break switch the closing - opening contacts are in natural air. Since the dielectric strength of air is less as compared to solid or gas (SF6) the physical footprint of the switchgear is larger compared to others. 

Oil Insulated Switchgears – Compared to natural air, oil insulated switchgear will have better dielectric strength with additional cooling effect. Although oil used must be fire resistant and should not pollute the environment. Also due to large volumes of oil used the switchgear becomes quite bulky and requires more space & maintenance.

Solid Insulated Switchgear - Solid insulated Switchgear broadly means an epoxy insulated Switchgear, where all the bus bar, current transformer, potential transformer, cable termination are enclosed in an epoxy insulation. Although there are few advantages of solid insulated switchgears such as compact dimensions & environmental friendliness, but the insulation can have defects arising during production process such as internal air gaps or cracks, defects during assembly such as dust or any foreign substance introduce during manufacturing, during operation due to mechanical forces etc.

Gas Insulated Switchgear – Gas Insulated Switchgear drastically improves the dielectric strength compared to natural air. The most used gas as an insulating medium is SF6 (Sulphur Hexa Fluoride). Closing and opening contacts are enclosed and sealed in a tank with pressurized SF6 gas. Due to compactness the overall footprints of the switchgear are small. Although there are many adverse effects of SF6 gas on the environment if it is leaked out in the environment, the same we have discussed in previous article. There are many new technologies coming up as an alternative to SF6, one of the most popular and reliable technology is use of climate friendly dry air. 

Climate Friendly Dry Air Insulating Switchgear or SF6 FREE Switchgear – This type of switchgear replaces SF6 gas in switchgear, which is the strongest greenhouse gas with climate friendly dry air. This is achieved while maintaining the benefits of SF6 gas i.e.  Compact dimensions, high reliability & maintenance free design. Thus, the user gets both the benefits of AIS as well as GIS in this type of the switchgear. At Nuventura, NU1 falls under this category, it is an IEC certified medium voltage (up to 36 kV) single busbar GIS for primary distribution. Nuventura is the only company in world to offer 36 kV SF6 Free GIS.

 4. Network Position

This refers to the position of switchgear, accordingly, can be classified as primary or secondary switchgear.

Primary Switchgear – Primary switchgears are positioned in network where the switchgear must deal with higher fault current rating typically above 20 kA, higher normal current rating normally equal to or above 630 A, generally close to HV transformer. This switchgear provides full voltage and current protection based on load and application i.e Transformer, motor, capacitor protection & feeder protection. Major interrupting device in primary switchgear is circuit breaker.

At Nuventura, NU1 falls under this category, it is an IEC certified medium voltage (up to 36 kV) single busbar GIS for primary distribution. Nuventura is the only company in world to offer 36 kV SF6 Free GIS in this segment. 

Secondary Switchgear – Secondary switchgears are the switchgears which comparatively handle lower fault & normal current i.e. less than 20 kA & less than 630 A respectively and are installed near to the LV transformer. Due to low value of normal & fault current main interrupting devices used are fuse, load break switch & circuit breakers.

With this information, I trust that the diverse classifications of switchgear are now evident, providing valuable insights for making informed choices in selecting the appropriate switchgear.

Amol Surendra Patharkar

Technical Manager – Sales & Marketing

Email: amol.patharkar@nuventura.com