Hydropower Plant,Substation/Electrical Machine Repair and Maintenance

Alternator Static Excitation System

Residual voltage transformer (RVT): RVTs
are used for residual earth fault protection
and for discharging capacitor banks. The
secondary residual voltage winding is
connected in open delta. Under normal
conditions of operation, there is no voltage
output across the residual voltage winding.
When there is an earth fault, a voltage is
developed across the open delta winding
which activates the relay. When using a
three phase RVT, the primary neutral
should be earthed, as otherwise third
harmonic voltages will appear across the
residual winding. 3 phase RVTs typically
have 5 limb construction.