Ch25-33
If the motor nameplate indicates only the delta-comnected full load current, divide this value by___to obtain winding current
1.73
The slip at rated load may vary from 3 percent to ? for different types of motors
20%
The thermal capacity of the motor limits the length of acceleration on the first winding to approximately___seconds depending on the connected load
5
When full-voltage starting may cause serious line disturbances, reduced voltage starters may recommended for motors with ratings as small as
5 horsepower
Closed transition connections are usually found standard size ___and larger starters.
6
In an autotransformer-type starter, autotransformers supply___ of the line voltage to the motor.
65%
rotor winding consists of many copper or ? Bars into slots on rotor
Aluminum
correct rotational direction is indicated by___ on the driven machine
Arrows
The squirrel cage induction motor is a
Constant speed motor
In a two speed, reversing controller, an overload in either the low or high speed setting will de-energize the ___
Control circuit
Part winding starters are not suitable for use with delta-wound, ____motors
Dual voltage
Every function in solid-state starting units is illuminated with electronic LEDs.
False
In an automatic speed control for a two-speed, two-winding three-phase motor, the circuit is so designed that a certain amount of speed must be achieved before the motor can be changed from low to high speed
False
In an autotransformer-type starter the timing for the time-delay relay that controls the transfer from the reduced voltage
False
Locked rotor currents for different motor types vary from 10 to 20 times the full-load current of the motor.
False
Machines will not be harmed if the direction rotation is changed from that for which they are designed
False
Most motors are successfully started at 90% percent voltage.
False
Part winding motor windings intended operate in series.
False
Part winding motors are different in construction from standard squirrel cage motors.
False
Slip refers to the twisting or turning of the motor shaft.
False
Slow and continued speed transfers may activate the overload relays
False
Star-delta motor starting is sometimes called double-delta starting.
False
The energy- saving option, including a microcomputer, is activated before the motor is up to speed.
False
Three-speed, consequent pole have three windings.
False
With a compelling relay, the motor is started at low speed and is then accelerated automatically through successive speed steps until the seleted speed is reached
False
In addition to the greater noise immunity provided by integrated electronic circuits, the logic functions include additional
Filtering and buffering
The speed of a star-delta, squirel cage induction motor depends on the number of poles of the motor and supply line___
Frequency
Some starters have ___ compression disk resistors and are used for starting polyphase squirrel cage motora
Graphite
When selecting heater elements for the overload relays, the electrician should remember that each of the relays carries only ____of the motor current
Half
One disadvantage the two-step part winding starter is that
It is almost always an incremental start device
Solid-state provides a method for electrically controlling machines and different processes with _____elements and accessories
Logic
Star-delta motors are widely used on loads having high inertia and a___
Long acceleration period
The phrase pairs of poles is used to indicate that____poles are always in pairs
Motor
With primary resistor starters, the motor starts at a ___power factor than with other starting methods.
Much higher
Starting transformers momentarily affect the
Power factor
The inactive winding must be open circuited to ____circulating current due to transformer action between the idle winding and the energized winding
Prevent
Circuits for controlling a two speed consequent pole motor may use contactors with three load contacts because they are
Readily availabe
Four-speed consequent pole motors have two ____windings
Reconnectable
The most common function of reduced voltage starting devices is to_____the starting current
Reduce
The operating principle on which the squirrel cage motor is based calls for a rotor
Revolving with a stator
The fewer the number of poles established in the stator, the greater is the speed in ____ of the rotor
Rpm
A solid-state, reduced voltage motor starter uses___controlled rectifiers for power control
Silicon
Current transformers are used on large motor starters to step down the current so that a conventional overload relay and heater_____ may be used
Size
In the color coding LEDs , AMBER indicates -
Starting
Wye-delta starting is accomplished by connecting ___ in wye during the starting period and then reconnecting them in delta for normal run operation
Stator windings
Using the formula for speed, the___speed of a two-pole motor supplied by 60-hertz electrical energy is determined
Synchronous
When the starter is equipped with an accelerating relay
The final speed is determined by the button pressed
when a compelling relay is used
The motor must be started at low speed before a higher speed can be selected
In a standard starter, before change is made from a higher to a lower speed,
The stop button must be pressed
A thee phase squirel cage motor can be wound so that six leads are brought out.
True
By reducing the starting voltage, at the motor terminals, the starting torque is decreased.
True
Closed transition starting accomplished by adding another three pole contactor and resistors to the circuit
True
Compeling relays ensure that the motor starts at the lowest speed
True
De-energizing the transformers while in the running position is done to conserve electrical energy
True
Electromechanical devices are used provide interlocking methods and sequencing control.
True
Four speed, consequent pole, squirrel cage motors have two reconnectable windings and two speeds for each winding.
True
In a two speed, reversing controller, the circuit may provide automatic acceleration to high speed in either the forward or reverse direction
True
Magnetic overload relays are used on large reduced voltage starters.
True
Multispeed starters are provided with mechanical and electrical interlocking
True
Part winding starters are designed to be used with squirrel cage motors having two separate and parallel stator windings
True
Part winding starters can be used in many applications as other, more expensive types of reduced voltage starters.
True
Power-saving modules are available that detect idling or low-power periods of operation.
True
Primary resistor starters provide closed transition starting
True
Solid-state starters are available in ranges up to several hundred horsepower
True
Star delta motor are similar in construction to stand squirrel cage motors
True
Star-delta motors may be used where a reduced starting current is required.
True
Two-speed, consequent pole motors have one reconnectable winding
True
With impedance starting, reactors are used in series with the motor
True
primary resistance-type starter has a high power factor
True
primary resistance-type starter has a low initial cost.
True
In the part winding motor, the stator windings may be ____connected or delta connected, depending on the motor design
Y
With full-voltage starting:
b. a hand-operated or automatic starting switch throws the motor directly across the the line
Mechanical and electrical interlocking avoid the possibility of
connecting more than one speed winding at the same time
Starting compensators using a five-pole starting contactor are classified as
open transition starters
With part winding starting:
the stator windings of the motor are made up of two or more circuits
Primary resistor starters are used to start squirrel cage motors in situations where limited torque is required
to prevent damage to driven machinery
Primary resistor starters are used with limited current inrush
to prevent excessive power line disturbances
The design of the motor will determine the percentage of slip.
True
The squirrel cage induction motor is the most widely used industrial motor.
True
The starting transformers are inductive loads.
True
The use of an automatic starter and a control station gives greater operating efficiency.
True
Part winding starting has many applications in air-conditioning systems.
true
With an accelerating relay, the motor can be started only by pressing the low-speed push button.
False
With primary resistor-type starters, a resistor is connected in parallel in the lines of the motor
False
disadvantage of open transition starting is that it does not require accessory voltage reducing equipment.
False
primary resistor starters are available only with multi-points of acceleration.
False
Solid-state starters are an efecive choice in__applications.
Reduced voltage