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Construction Electrician Basic - Electricity handbook for electricians | Next
Inspection of the Generator |
3. Insert the load cables through the protective
sleeve. Attach the cables to their respective load
terminals, one cable to each terminal, by inserting the
cable in the terminal slot and tightening the terminal nut
with the wrench that was clipped to the transparent
cover. Install the wrench on the cover and install the
cover.
4. Tighten the drawstring on the protective sleeve
to prevent the entry of foreign matter through the hole
around the cable.
You may convert the voltage at the load terminals to
120/208 volts or 240/416 volts by properly positioning
the voltage change board (fig. 3-9). The board is located
directly above the load terminal board.
The procedure for positioning the voltage change
board for the required output voltage is as follows:
1. Disconnect the transparent cover by loosening
the six quick-release fasteners.
2. Remove the 12 nuts from the board. Move the
change board up or down to align the change board
arrow with the required voltage arrow. Tighten the 12
nuts to secure the board.
3. Position and secure the transparent cover with
the six quick-release fasteners and close the access
door.
PHASE SEQUENCE INDICATORS
The phase sequence indicator is a device used to
compare the phase sequence of three-phase generators
or motors. Examples of its use are as follows: to
Figure 3-9.—Voltage change board.
compare the phase rotation of an incoming alternator
that is to be operated in parallel with an alternator
already on the line or to determine the phase rotation of
motors being put into use for the first time.
One type of phase sequence indicator is a tiny three-
phase induction motor. The three leads of the motor are
labeled "A," "B," and "C," as shown in figure 3-10. The
insulating hoods over the clips are of different colors:
red for A, white for B, and blue for C.
The rotor in the instrument can be observed through
the three ports as it turns so that you can note the
direction in which it rotates. The rotor can be started by
means of a momentary contact switch: it, stops again
when you release the switch.
You also may use a solid-state phase sequence
indicator with two lights. Whichever light is on
indicates the phase sequence of the voltage in the
conductors that the instrument is connected to; for
example, the light labeled "ABC" indicates one phase
sequence, while the other light, labeled "BAC,"
indicates another. If you are working with three-phase
conductors (all of the same color) that are installed but
not labeled, you may connect the phase sequence
indicator to the three conductors, turn on the power,
check the phase sequence of the conductors as
connected to the instrument, and turn off the power.
You may then label the conductors with numbers,
letters, or colored marking tape.
You also may check the phase sequence of an
incoming alternator before paralleling it with an
operating load-side alternator. Connections must be
made so that the phase sequence of the two generators
will be the same.
Figure 3-10.—Phase sequence indicator.
3-13
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