Q7-16. Which of the following is NOT a voltage
protection function of a mobile electric power
plant?
1.
AC overvoltage
2.
DC undervoltage
3.
Underfrequency
4.
Phase sequence
MOBILE ELECTRIC POWER PLANTS
(MEPP)
LEARNING OBJECTIVE: Identify the
A
components of mobile electrical power plants
(MEPP).
A mobile electric power plant (MEPP) is a power
generating unit. Some models can be driven under their
own power; others must be towed. An operator's
license is required to drive a MEPP and to operate the
generators.
There are many types of MEPPs available. Some
are designed for universal use, while others can be used
only on specific aircraft.
NC-2A MOBILE ELECTRIC POWER
PLANT
The NC-2A (fig. 7-39) is a self-propelled, diesel
engine-powered service unit. It is front-axle driven,
B
steered by the two rear wheels, and readily
ASf07039
maneuverable in congested areas. The front axle is
Figure 7-39.--NC-2A mobile electric power plant.
driven by a 28-volt dc, reversible, variable-speed
motor that is capable of propelling the unit up to 14
mph on level terrain. The unit has a turning radius of
The dc generator is an aircraft generator with an
approximately 11 feet.
output of 28 volts and up to 500 amperes at a maximum
speed of 6,300 rpm. Table 7-3 lists the leading
The primary source of power is a three-cylinder,
particulars for the NC-2A.
water-cooled diesel engine, which drives the ac and dc
generators through a speed-increasing transmission.
Governors
All propulsion and electrical power controls are
available to the operator on three panels located in the
When an electrical load is placed on a generator,
front and to the right of the operator's seat.
the prime mover speed decreases. When the load is
The power plant is designed for air transport; it is
removed, the prime mover speed increases. In a dc
provided with two tie-down rings each on the front and
generating system, the prime mover has to drive the
the rear bumpers. Forklift channels are located
generator within a certain speed range (depending on
between the front and rear axles, providing safe lifting
the particular generator) to maintain the required
points for the unit.
voltage, even though the system has a voltage
regulator. In an ac generating system, speed is far more
The ac generator is an aircraft-type, single-
critical because it also determines the output
bearing, synchronous, 115/200 volt, 400-hertz,
frequency. Unless some means is used to regulate the
three-phase, four-wire wye, brushless generator with
speed, engines will over speed. A manual throttle is
an output of 30-kVA at 6,000 rpm.
7-31
