LT and HT Switchgear - Why Both?

Those breakers are there for all around protection and operations; for the Generators, for the tranformer(s) and the Grid. Damaging electrical faults can occur in any of the components that make up this system; Generator> Transformer > Grid; in addition to the need to occasionally shut down and/or isolate the generators or the transformer from the grid for maintenance or rest. In addition, as part of the protection scheme there will be controls to properly synchronize each component, the breakers play an important role in that function.

If the power plant is connected to a grid, then power could flow in either direction. The grid need to be protected from a transformer fault, hence the fuses on the HT.

Think about what the circuit breakers are protecting and you'll have your answer!

Note that the transformer is inbetween LT and HT side.It has primary(coil)winding LT and secondary(coil)winding HT.The primary side takes care of the LT circuitry and associated circuits while the secondary side takes care of the HT circuitry and other associated circuits.Just as you are aware of faults on the HT side and the need for its protection,so are faults on the LT side and the need for its protection using LT circuit breakers.Recall that when loads are switched,there is current flow from primary LT to the secondary HT or vice-versa through the Transformer(ie-Transformation principle).If fault occurs on primary side,it can damage devices,components and or equipment on the primary circuit,if there is no protective device on the LT side.Note also that the LT breaker has a different current trip setting from the HT current trip setting due to current and voltage differential values on both sides.Apart from the above reasons,the LT and HT breakers also provide isolation(Break in Contuinity) to enable work to be done by personnel on either side for safety of life and property.

Note that the Transformer is inbetween LT and HT side.It has primary(coil)winding LT and secondary(coil)winding HT.The primary side takes care of the LT circuitry and associated circuits while the secondary side takes care of the HT circuitry and other associated circuits.Just as you are aware of faults on the HT side and the need for its protection,so are faults on the LT side and the need for its protection using LT circuit breakers.Recall that when loads are switched,there is current flow from primary LT to secondary HT or vice-versa through the transformer(ie Transformation principle).If fault occurs on primary side,it can damage devices,components and equipment on the primary circuit if there is no protective device on the LT side.Note also that the LT breaker has different current trip setting from the HT breaker current trip setting due to current and voltage differential values on both sides.Apart from the above reasons,the LT and HT breakers also provide isolation(Break in Contuinity) to enable work to be done by personnel on either side for safety of life and property.

Patrick Whowha