A
The voltage produced by a generator is zero for some period of time for the ? -phase power system. The voltage falls to zero ? each cycle.
Single and Twice
the line voltage is higher than the phase voltage by a factor of 1.73 on what connection
(Wye) also The system has a common connection for all three windings.
The line current is equal to the phase current.
If phase (A) has 120v and 35A ON A Delta xfmr what is line current
60.55 or 61
(I)line = (I)winding x 1.73
Which winding on a generator induces voltage?
Armature
generator are devices that turn _ energy into _ energy
mechanical and electrical
A single coil generator spinning in a magnetic field will produce a full sine wave for every ? of rotation.
360 degrees
An amusement park has a delta connected , 3 phase , 480 volt service with a balance load of 224A and a power factor of 86%. How much power in Kw is being consumed?
3 phase kw= (E line * I line * 1.73 * Pf) / 1000
159.96 kw
160 kw
What are the two basic styles of generators?
revolving armature and revolving field
what is one half cycle of a sine wave called
Alternation
test instruments
Any time a three-phase current unbalance exceeds ? %, electricians must test for voltage unbalance.
10
test instruments
what controls the number of times the solid-state switches in the inverter section of a Pulse Width Modulated (PWM) variable frequency drive turn on and turn off per second?
Carrier Frequency
A 4-pole generator will be supplying several loads that are designed for 84 hertz. At what speed does the generator need to be driven?
S(speed)= (120*F)/ # OF POLES
2520 RPM
What are the three factors that determine the output of a generator
The number of turns in the armature
The strength of the magnetic field
The speed of the armature
What is the time displacement between voltages on a 3-phase generator if the frequency is 72 hertz?
time period= 1/f
time vd(voltage drop)= time period/ # of phases
4.63 ms
.004629
The source for mechanical motion supplied to a generator is referred to as the ? .
prime mover
if a 3-phase resistive load is connected to the generator, what is the total power supplied?
240V 20A Delta
(POWER)three phase = (E)line x (I)line x 1.73
8304
how many poles are required for a generator that is 60hz at 3250 rpm
P= (f*120)/S
2.215 p
2 poles
what are the two types of rotating field construction generators
SALIENT POLE ROTOR and ROUND ROTOR
salient poles are pole face that are very pronounced and jut out
round rotor uses a smooth, longer, and narrower construction to minimize wind resistance and centrifugal forces
When is an armature called a stator
When the revolving field AC generator has its armature windings positioned around the generator housing.
or when the armature is stationary
If the only criterion for power factor correction were to reduce the utility bill, the capacitors would most likely be connected at the main service in order to achieve a lower priced installation.
true or false
True
which two ways can a transistor be used
amplifier and switch
what does the decibel scale on a multimeter indicate
the comparison between two or more signal powers or voltages.
a rotating exciter that is on the same shaft as the main generator is called a?
brushless exciter
exciters are made stationary or rotating
what are the three types of armature windings found in generators
1. frog leg ; are middle of the road type windings. most common configuration, moderates voltage and current found in large dc equipment
2. Lap wound ; designed for high voltage low current usually larger wire
3. Wave wound ; designed for high current low voltage usually smaller wire
A 3/0 AWG copper feeder conductor is tapped with 20 feet of 2 AWG conductor. What is the maximum OCPD size allowed at the termination of the tap conductors installed in a fused switch or circuit breaker? (All conductors and terminations are rated 75°C.)
110A
240.6(A)
TABLE 310.16
240.21(B)
240.4(B)