Page 281 - Introduction to Marine Engineering

Electrical equipment 255

The compound wound generator has two sets of field coils (Figure
14.1 (a)). The shunt coil has many turns of fine wire and the series coil
has a few turns of heavy wire. The shunt field produces full voltage on
no-load which falls off as the load current increases. The series field
creates an increase in voltage as the load increases. Properly combined
or compounded the result is a fairly constant voltage over a range of
load (Figure 14.1(b)).

Variattie
resistsnee
— » ft
I. |N
V

Voltage from
compound field
Voltage
{volts)
' Rated voltage
Voltage from
shunt field

Voltage from
series field

Full load
! current
Load current (amperes)
(b)
Figure 14.1 Compound wound d.c. generator, (a) field connection; (b) characteristic
curves

Direct current distribution
The generated supply is provided to conductors known as 'bus-bars'
which are located behind the main switchboard. The supply then passes
through circuit breakers to auxiliaries directly or to section or
distribution boards. A circuit breaker is an isolating switch. A section
board is a grouping of electrical services fed from the main board. A