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Home / Download Center / Electrical Engineering Books and Technical Guides / Relay control and protection guides / Design control and protection for medium voltage switchgear

Purpose and Objective

The purpose of this thesis has been to plan and commission necessary drawings for switchgear according to my commissioner’s demands. The drawings were used for a project. The project is an engine that is not on the production line yet. The purpose is to test the engine before it will reach Wärtsila engine portfolio.

Design control and protection for medium voltage switchgear
Design control and protection for medium voltage switchgear (photo credit:

It needed to be tested in different kinds of loads and frequencies. This was done with load banks. It is not possible to test the engine on grid operation with another frequency than (50 Hz).

Operating the switchgear from the control room had to be realized. The positions in which the breakers are in the switchgear were to be visible on the indicators. The infrastructure needed to be established. The infrastructure means making switchgear as safe as possible. This was realized with protection relays. Energy measurement was necessary, so that the efficiency would be visible.


The switchgear needs to be able to break and connect generators to load banks or to the grids. Open switchgears are big and they needed a lot of equipment. The switchgear is going to be a GIS (Gas Isolated Switchgear). This will be 10-15% smaller than an open switchgear.

GIS are used where you cannot use an open switchgear, which may be because of the environment or because of the size of the switchgear. Switchgears are cabinets with breakers inside.

With breakers in different positions the energy can be transported to load banks, transformers or to the grid. With the switchgear you can control high voltage transportation.

Switchgear cabinets
Switchgear cabinets

Control panel (Mimic)

In order to control the switchgear you need a different panel. The switchgears are made so that you can disconnect breakers from the switchgear room, but you cannot connect them. To be able to control the different switchgear cabinets a control panel had to be designed.

This panel needed to be simple to understand and have the different switches in the correct order so that there won’t be any misunderstanding in which position any breaker is in. To see what positions breakers are in there are indicators that show if a breaker is connected, unconnected or outside the cabinet.

The Mimic consists of several indicators and switches where you can control the switchgear. The indicators will flip to another position depending on breaker position.

Control for switchgear
Control for switchgear

Switchgear protection

Switchgear protection has been around for as long as we have had switchgears. The idea of the protection is that when we have an overcurrent or overvoltage, a relay will notice it and react. The relay opens the breaker to avoid damage to the equipment. If the breaker is unable to break the circuit, then the feeders to that switchgear have to break the main breaker. That is how the infrastructure is established with switchgear protection.

To get the relays to work properly different trip times for the relays were made. These have been calculated so that the correct relay trips at the right time.

Title:Design control and protection for medium voltage switchgear – Bachelor’s Thesis by Carl-Johan Nylund at University of Vaasa, Department of electrical engineering and energy technology
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Design control and protection for medium voltage switchgear
Design control and protection for medium voltage switchgear

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