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LV switchgear layout: Design & Size

Low voltage (LV) switchgear is a broad terminology that includes a wide range of equipment like circuit breakers, switches, offload isolators, MCCBs, etc. within the 1 kV rating required to protect the LV system. The most common use of LV switchgear is in the LV distribution board which further comprises multiple segments like the main incomer, sub-incomers, feeders, etc. the size, configuration, and physical layout for switchgear vary as per specific requirements and standards.

My experience in drafting the layout of an LV switchgear (equipment, inside installations)
My experience in drafting the layout of an LV switchgear (equipment, inside installations)

In this article, we will discuss multiple factors to consider for sizing and designing the layout of LV switchgear for real-world application. The design engineer must go through various phases and iteration before finalizing the layout, which later is realized physically.

Original Equipment Manufacturers (OEMs) and independent manufactures produce thousands of LV switchgear assemblies each year, and properly designed layouts are mandatory to ensure that it meets the requirements.

Table of Contents:

  1. Classification and critical features
  2. LV switchgear introduction and functionality
    1. What differentiates switchgear from switchboards, MCCs, and PBDs?
  3. Layout design and construction details
    1. Factors to consider while designing the switchgear layout
      1. Prevalent standards
      2. Component selection and clearance
      3. Temperature control and ingress protection
      4. Safety factors
    2. Power flow, interlink, and placement of components
      1. Placement of circuit breakers
      2. Provision for terminations, anchoring, and bends
    3. Housing, frameworks, and dimensions
    4. Single-line diagram to switchgear assembly, the final layout
      1. Taking a base of the single line diagram
      2. Determining the make and model of components
      3. Additional ancillary components
  4. Bonus – AutoCAD drawings and pictures

1. Classification and critical features

The switchgear is of different type based on the voltage level at which it operates. HV switchgear operates at a voltage level of above 33 kV. MV switchgear operates at the voltage level of 33 kV and below. Likewise, LV switchgear operates at the voltage level of 1.1 kV maximum.

Irrespective of particular voltage levels, switchgear are known for their complete reliability, quick operation, and absolute isolation compared to other similar devices.

Figure 2 – MV switchgear cubicle (Left) and LV switchgear cubicle (right) inspection

MV switchgear cubicle (Left) and LV switchgear cubicle (right) inspection
Figure 1 – MV switchgear cubicle (Left) and LV switchgear cubicle (right) inspection

Figure 1 displays the internals of cubicles of typical MV and LV switchgear. Physically, higher voltage creates extra complexity because of the higher risk of arc flashes and insulation failures. Apart from that, MV and LV switchgear shares a lot of similarities in terms of design and construction.

There has been substantial advancement in technology which started from the simplest form of switchgear, like a tumbler switch used widely for controlling small lights and household circuitry.

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Bishal Lamichhane

Electrical Engineer (B.E Electrical, M. Sc Engineering) with specialization in energy systems planning. Actively involved in design and supervision of LV/MV substations, power supply augmentations and electrification for utilities and bulk consumers like airports and commercial entities. An enthusiast and scholar of power systems analysis.

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