What Is a Pad-Mounted Transformer Load Break Switch? A Must-Read Selection Guide

Basics of Load break switch

1.1 Definition of Load break switch

The load break switch in the three-phase pad-mounted transformer is a switching device used to connect and disconnect circuits in the load state. It is usually installed on the high-voltage side of the pad-mounted transformer and is used to control the incoming and outgoing line circuits, protect the equipment, and ensure the reliability and safety of the system.

1.2 Function of Load break switch

• Connecting and disconnecting load current：Load switches are mainly used to connect or disconnect the power supply under normal load conditions. Unlike circuit breakers, they are not designed to cut off fault currents.
• Isolation function：It can provide physical isolation during maintenance or repair, disconnecting the downstream equipment from the power supply, ensuring operational safety.
• Operating method：It can usually be operated manually, or remotely controlled or automated, in order to respond quickly to the demands of the power distribution system.

1.3 Installation position of Load break switch

Load switches are typically installed on the high-voltage side of pad-mounted transformers, near the high-voltage bushing of the transformer, and are used for switching on and off the transformer or for isolating during maintenance. They are suitable for loop feed systems, such as 4-Position LBS which supports dual power switching. The pad-mounted transformer is designed compactly, and the structure of the load switch also tends to be modular to save space. The load switch is an important component of the pad-mounted transformer, and its design and selection are crucial for the safety and reliability of the distribution system.

Type of Load break switch

2 position load break switch

Two states:

3.1 The 2-position load break switch has two operating positions, namely “closed” and “open”. It can only perform the basic operations of connecting and disconnecting the circuit.

3.2 Two-position load break switch schematic diagram (loop feed, 3 two-position load break switches)

3.3 Two-position load break switch schematic diagram (loop feed, 3 two-position load break switches)

3.4 Two-position load break switch schematic diagram(radial feed, 1 two-position load break switches)

3.5 Actual nameplate display 1(loop feed, 3 three-phase 2-position load break switches)

3.6 Actual nameplate display 2 (loop feed, 3 three-phase 2-position load break switches)

4 position load break switch

3.1 The 4-position switch is used for pad mounted transformer allows for four different switch settings:

Position 1: Source A&B tap off

Fully disconnect the high-voltage power supply and cut off the connection between the transformer and the power grid. This is the safe position for the load switch during maintenance or in case of a fault.

Position 2: Source A tap on

Connected to “Feed Line A” or input line A. The transformer obtains power from the power grid through “Feed Line A”.

Position 3: Source B tap on
Connected to “Feed Line B” or input line B. The transformer obtains power from the power grid through “Feed Line B”. This position is usually used as a backup or as a backup power source.

Position 4: Source A&B tap on

Both AB roads are connected, forming a loop network

3.2 four-position load switch principle

3.3 nameplate display (loop feed, 1 three-phase 4-position load break switches)

Common combinations