Application Note EX-SCTPPT Offers Basler’s New Solutions for Aging SCT/PPT Voltage Regulators

In the 1970s main field static excitation systems became increasingly popular for medium and large synchronous machines used with gas and steam turbine generators. Due to their isolated locations, many of these systems were designed with the ability to maintain fault current into the system or bus voltage support during a system fault.

These systems, trade name SCT/PPT, utilized a combination of linear reactors, saturable power current transformers, and a power potential transformer that had outputs connected together to provide an ac voltage into a rectifier bridge to supply power for the main generator field. The generator voltage was regulated by an automatic voltage regulator via a control winding embedded in the saturable power current transformer. SCT/PPT systems were popular with the pulp and paper industry, municipals and utility power plants.

Today, these systems have become hard to maintain as worn-out mechanisms such as open potentiometers, shorting transformers, failing semiconductors, and defective motor-operated potentiometers have turned into an unpopular frustration.

Application Note EX-SCTPPT provides solutions to the aging voltage regulator situation, where obsolescence of parts has made it difficult to achieve reliable operation.