Week 5
How many leads does a phase rotation meter contain?
6
3-phase power is transmitted in phases that are ___ degrees apart.
120 degrees
T or F: 3-phase voltages are 180 degrees out of phase with each other.
F
T or F: another name for 3-phase connection is the star connection.
F
Some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the higher of the two voltages, the phase windings are connected in _____.
series
T or F: A phase rotation meter compares the phase rotation of two different three-phase connections.
T
T or F: In 3-phase systems, delivered power never falls to zero.
T
If the number of poles in a consequent pole motor is ___, the motor speed will be cut in half.
doubled
When a squirrel-cage motor is first started, current draw is ___.
high
3-phase watts can be calculated by multiplying the apparent power by the ___.
power factor
The operating principle for all 3-phase motors is ___.
rotating magnetic fields
The line current of a delta connection is higher than the phase current by a factor of ___.
square root of 3
A squirrel induction motor achieves maximum ___ when the phase angle between the stator and the rotor fields is zero.
torque
Line current and phase current are the same in the _____ configuration.
wye
Many of the three-phase motors used in industry are designed to be operated on how many voltages?
2
phase rotation meter
Compares the phase rotation of two different three phase connections. (determine the rotation of a motor).
In a balanced three-phase system, the conductors need to be only about _____ the size of conductors for a single-phase, two-wire system of the same kilovolt-ampere (kVA) rating.
3/4
Wye Connection
A method of connecting the windings on a three-phase transformer in which one end of all three windings is connected to a common neutral center point, forming a Y shape. It is also known as a star connection.
T or F: to reverse the direction of a 3-phase motor, reverse any of its lead.
F
The ___ must supply the line current for each load.
alternator
In a single-phase service, the ___ is connected to ground and becomes the neutral conductor.
center tap
If the service factor for a motor isn't give on the nameplate, what should you assume the service factor to be?
1
T or F: When calculating the power of a pure resistive load, the voltage and current are in phase with each other, and the power factor is 1.
T
T or F: the speed of rotation of the magnetic field is called synchronous speed.
T
An AC squirrel-cage motor has a ___ on its nameplate that indicates the type of bars used in the rotor.
code letter
In a three-phase connection, what is the voltage measured between the lines?
phase V
T or F: Line current and phase current are the same in wye configuration.
T
What item on a motor's nameplate is used to determine how much power a motor can safely produce above its rated output power?
service factor
In one of the three lines that supply power to a 3-phase motor should open, the motor will be connected to ___ power.
single phase
In a wye-connected system, the line voltage is higher than the phase voltage by a factor of _____.
square root of 3
