Switch S2 is an assembly of 18 contacts (fig. 8-12,
The control switch (S1) in figure 8-12, view B, has
three positions-OFF, MANUAL, and AUTOMATIC.
view C). They are connected in series, operate
The setting of this switch determines the type of
simultaneously, and function as a single ON-OFF
operation to be used. The OFF position can be
device. Again, the function (using many contacts)
used to quickly de-energize the generator in case
serves to break a long arc into several smaller arcs and
of an emergency. With the switch in the OFF
produce longer life for the heat-dissipating contacts.
position, four sets of contacts (sets P, Q, R, and S)
are closed. Contacts P, Q, and R "short circuit" the
Static Exciter
potential winding of the three potential transformers.
They are identified as T1, T2, and T3 in figure
As you read this section about the static exciter,
8-12, view A. They remove rectified current
refer to figure 8-13. The static exciter consists of a
from the exciter. Concurrently, contact S (upper
three-phase rectifier; CR1, three linear inductors, L1,
right, fig. 8-12, view A) functions to trip the main
L2, and L3; and three transformers, T1, T2, and T3.
breaker.
The transformers are alike and interchangeable.
An analysis of the contact arrangement (fig. 8-12,
Each transformer has four windings (figure 8-13 shows
view B) in switch S 1 shows 32 contacts are placed (four
only the three windings that perform in the basic exciter
per pole) on 16 poles. The first four poles produce 8
circuits). The first winding is the potential or primary
single-pole-single-throw contact switches (each SPST
(P2) winding, the second winding is the secondary (S-2)
identified by 8 letters, A through H). These 8 have 12
winding, and the third winding is the current winding.
terminals (identified further by 12 numbers, 1 through
12).
The fourth winding is the control winding, which is
discussed later. Each transformer is identified as a
The fifth pole (No. 5 in fig. 8-12, view B) has
saturable current potential transformer (SCPT).
only two numbered terminals (13 and 14) to identify
switch section I. Its two SPST contacts are arranged in
The primary windings of T1, T2, and T3 are
series. The function of this series arrangement is
Y-connected through the linear inductors L1, L2, and L3
twofold:
by conductors 13, 14, 15, and 23.
1. It provides two contacts that can open fast
The secondary winding is delta connected to diodes
and wide, preventing excessive arcs
(A, B, C, D, E, and F) of rectifier CR1 by means of
produced (in an inductive-reactance circuit)
conductors 16, 17, and 18. Rectifier CR1 delivers de to
during the OFF "break" of the switching
conductors 11 and 9, which supply the generator field.
action.
The current in the control windings CW1, CW2, and
2. It provides optimum cooling of heated contacts
CW3 (fig. 8-12, view A) controls the output of the SCPT
that become hot from arcing.
secondaries and thus the output of the static exciter. The
The remaining 11 poles of switch S1 are arranged
control windings are supplied by the voltage regulator
with series assemblies like switch section I. They
output as discussed later. Load current flowing in the
are identified by letters J through T, with their
current windings (I1, I2, and I3 in fig. 8-12, view A)
terminals numbered 15 through 36. Switch section
compensates for changes in the generator load.
T is a spare. The letter X denotes those contacts that
FIELD-FLASHING CIRCUIT.-- The static
are closed and letter 0 denotes those contacts that
exciter cannot supply field current until some ac voltage
are open when the switch is put into a selected
has built up on the 400-kW generator. DC power is
position of OFF, MANUAL, or AUTOMATIC. S 1 is
temporarily provided by a 50-kW dc generator
shown in the AUTOMATIC position in figure 8-12,
delivering 120 volts.
view A.
8-20
