• Reactive LTC uses reactors to limit current during switching; because reactor can be designed as permanently loaded with trough-current of LTC, one may use bridging position to double the number of steps in LTC • Typically, reactive-type LTC uses two reactors (two parallel branches), two by-pass switches, selector switch with two contacts and vacuum interrupter; also reversing switch is used to double the number of steps • the entire tap changer mechanism is enclosed in the oil-tight compartment, separated from main transformer tank Transformer Consulting Services Inc. Transformer Design: Tap changers - LTC with reactors
Transformer Consulting Services Inc. Transformer Design: • Typically a center-tapped reactor (or preventive autotransformer) is used to prevent excessive current flow between taps • Continuous operation in a bridging position is possible, which results in fewer leads Tap changers - LTC with reactors
Transformer Consulting Services Inc. Transformer Design: LTC with reactors - MR RMVII Typical RMV -II winding layout (L.T.C. on position 16 L) Tap change sequence from position 16 L to 15 L
Transformer Consulting Services Inc. Transformer Design: Tap Changer: Schematic and Connection Chart
Transformer Consulting Services Inc. Transformer Design: RCBN or FCBN? • RCBN – reduced capacity below nominal – MVA is reduced in lower voltage tap positions; current can not be greater then nominal voltage position – used mainly for LTC taps in LV i.e. +/- 10% LTC • FCBN – full capacity below nominal – MVA is constant in lower voltage tap positions; current can be greater then the nominal voltage position – always the case for DTC taps and HV LTC i.e. +/- 5% DTC
Transformer Consulting Services Inc. Q&A?