Gerrish Book Flashcards
A __________ is used to maintain a constant direction of current from the armature.
Commutator or split rings
Difference between slip rings & split rings;
Slip rings are __C and split rings are __C.
Slip rings are in _______ contact with brushes, Splits are ____.
Slips, ______ changes; Splits, the AC in the armature is changed to a __________ DC.
AC, DC
Constant, not
Polarity, pulsating
Name 3 types of generator losses.
- I (squared) R
- Eddy Currents
- Hysterisis
I (squared) R losses is when resistance _______ and power loss _________.
doubles
quadruples
Eddy currents = alternating currents flowing in ____, caused by _______ voltages and ________ by laminations.
core
induced
decreased
Hysteresis = internal molecular ________ between ________ particles that creates a ____ loss. Decreased by _______ steel.
friction
magnetic
heat
silicon
Generator output is determined by what two items?
- Strength of magnetic field
2. Speed of rotation
What kind of generator requires an external power source to provide voltage to the field windings: A. Series generator B. Compound generator C. Shunt generator D. Separately excited field generator
D. Separately excited field generator.
This generator is considered a constant voltage device: A. Series generator B. Compound generator C. Shunt generator D. Separately excited field generator
C. Shunt generator
This generator has both series and shunt windings in the field. A. Series generator B. Compound generator C. Shunt generator D. Separately excited field generator
B. Compound generator
State the mathematical equation for regulation of a power source.
E (no-load) - ( full load ) / E (full load) x 100 = % regulation
What is meant by three-phase power.
Each phase develops positive and negative peaks at different times that are120 degrees apart.
A delta connected generator has its winding connected in series or parallel?
Series
A three-phase power generator supplied 120/208 volts, would it most likely be from a delta or wye connection generator?
Wye
What three characteristics must match before you can connect two generators in parallel?
- Frequency
- Voltage
- Instantaneous polarity
What are the three major causes of generator failure?
- Excessive brush wear.
- Excessive bearing wear.
- Electrical overload.
How may a self excited generator lose its residual magnetism?
Heat from excessive overload.
The motor is used to convert _________ energy into __________ energy.
electrical
mechanical
Outline how a simple dc motor operates.
A external power source energizes an armature coil which rotates a commutator that cuts the magnetic field inducing the energy.
The turning power of a motor is called the ______.
torque
How is counter emf generated in a dc motor?
If the motor were connected to a prime mover & rotated in the same direction as the dc motor, it would produce a voltage with the opposite polartity.
What is the recommended maximum fuse size for a dc motor?
A fuse that is no more than 150% of the full load current.
An ________ is a smaller field pole placed midway between main field poles.
Interpole
Give the formula to find percent of speed regulation.
Speed no-load - Speed full load / Speed full load x 100% = % of speed regulation
