Maintenance
For an in-phase, real load, this I4 R8 voltage drop
shortens vector 01' but lengthens vector 02' (dashed
lines). The average of the three vectors remains
The static regulator has no moving parts. Its
essentially constant. However, for a reactive load the I4
components are extremely rugged; therefore, little
R8 voltage drop lengthens vectors 01' and 02' (dashed
maintenance besides preventive maintenance is
lines) and increases the average of the three vectors.
required. Some of the actions you should take are as
The regulator senses this higher voltage and reduces the
follows:
generator voltage. It does this by giving the generator
a drooping characteristic for reactive loads. Since the
Ensure that the regulator is kept clean and
average of the three vectors 01', 02', and 03' did not
internal connections remain tight.
change for a real load, the generator output should
Protect all parts from moisture-this is an
remain essentially constant.
essential action, especially when selenium rectifiers are
The amount of reactive droop can be increased by
involved. Exposure to moisture or mercury compounds
increasing the resistance of resistor R8. You should
will destroy selenium cells.
make sure that the resistance is 2 ohms or more.
When you replace new rectifier units in CR4,
CR5, or CR6, don't overheat their leads when soldering.
Manual Operation
To prevent overheating, use a low-temperature solder
(rosin core). Attach a small heat sink, such as an
To start the static excitation and voltage regulation
alligator clip or long-nosed pliers, between the rectifier
system equipment to run in manually, you should use
and the attached lead where the soldering occurs. This
the following procedure:
will prevent damaging heat from reaching the rectifier
cell.
1. Set the manual control rheostat R7 for minimum
volts (fully counterclockwise).
If it is necessary to apply a high-potential test to
2. Set the control switch S1 on MANUAL.
out all rectifiers with clip leads. High-potential tests are
3. Hold the FLASHING SWITCH S2 in the
discussed in the NSTM, chapter 300.
FLASH position until the generator starts to
build Up.
4. Adjust the manual control rheostat R7 to obtain
SPR-400 LINE VOLTAGE
the proper generator voltage.
REGULATOR
The SPR-400 line voltage regulator (fig. 8-20) is a
Automatic Operation
general-purpose, automatically controlled ac line
regulator. It ensures precision voltage regulation for
To operate the system in AUTOMATIC, bring the
line, load, frequency, and power factor variations in
system up in MANUAL control as just described, then
single or three-phase (delta or wye connection) circuits.
proceed as follows:
There are several designs of line voltage regulators
1. Turn the control switch S1 to the AUTO position
available. The operation described in the next section
will cover a typical design. The line voltage regulator
2. Adjust the voltage-regulating rheostat R11 to
is designed around the use of the silicon controlled
obtain the proper voltage.
rectifier (SCR). The SCR acts as a switch when a
NOTE: Never leave control switch S1 in an
control voltage is applied to it.
intermediate position between MANUAL and
AUTOMATIC.
OPERATION
The control switch S1 has an emergency shutdown
feature when placed in its OFF position. This can be
The voltage regulator is installed in series with the
used to quickly de-energize the generator in case of an
load, which requires a precise] y regulated power supply.
emergency.
8-27
