
194 Shipboard Electrical Power Systems
is for low voltage systems to which the lamps can be directly connected. The lamp
A will turn dark if line A gets grounded, which can again be ascertained by pressing
the pushbutton on and off. The scheme (c) is for high voltage systems, where a single
lamp is connected inside the ∆ of secondary coils of a suitable step-down transformer.
When all phases are healthy, the phasor sum of all phase voltages in the ∆ is zero,
keeping the lamp dark. If phase C on the primary side gets grounded, the phase C of
the secondary side also loses the voltage, and the phasor sum of the remaining two
voltages in the ∆ ...