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What are Voltage Fluctuations?

Under voltages and over voltages are caused by faults on power lines, and the subsequent actions of fault clearing devices. High current loads which temporarily exceed the FLA of a transformer, such as across the line motor starts or contactor soil energiztion, can cause voltage drops of 20% or more. This can result in expensive and time consuming errors, loss of information, downtime, recovery and rerun costs and possible equipment damage. Voltage fluctuation on the input of a transformer or autotransformer will be passed through to the secondary.

These high inrush currents need to either be mitigated (e.g. reduced voltage starters) or have the transformer sized large enough to handle. Control transformers are recommended for loads with magnetic coils such as contactors.

Snubber circuits should be considered in medium voltage applications which also use vacuum breakers.