GARYLAND M/C QUIZ #6

When the motor reaches the ____________________ stage, it is connected directly to the power line and the autotransformer is completely disconnected from the circuit.

Run

If the motor is to be operated on the higher voltage, the stator leads will be connected in ____________________.

Series

In a delta connection, the phase current will be less than the line current by a factor of the square root of ____________________.

Three

When the coil of S contactor energizes, all S contacts ____.

change position

Most autotransformer starters use two transformers connected in ____________________ delta.

open

Three-speed consequent pole motors can be wound to produce constant horsepower, constant torque, or ____________________.

variable torque

If the stator windings of a motor are connected in delta during the starting period, the starting current will be ____ times the value if the windings were connected in wye.

Three

Closed transition starting is generally used on starters size 6 and larger.

True

What are the two factors that determine the synchronous speed of an AC motor?

1. Frequency of the applied voltage 2. Number of stator poles per phase

What are the two requirements that must be met before wye-delta starting can be used?

1. The motor must be designed for the stator windings to be connected in delta during the run period. 2. All stator windings leads must be accessible.

Part winding starting reduces the normal locked rotor current to approximately ____ percent of the value if both windings are connected during starting and the torque is reduced to approximately 50%.

50%.

What is open transition starting and when is it used?

Open transition simply means that there is a brief period of time when the motor is disconnected from power when the start contactor opens and the run contactor closes. Open transition starting is generally used on starters of size 5 and smaller.

Can any dual-voltage motor be used for part winding starting?

Some, but not all, dual-voltage motors may be used for part winding starting. The manufacturer should be contacted before an attempt is made to use a dual-voltage motor in this application. Delta-connected dual-voltage motors are not acceptable for part winding starting. When dual-voltage motors are used, the motor must be operated on the low voltage setting of the motor. A 240/480-volt motor, for example, could only be operated on 240 volts.

A two-speed motor will contain six T leads in the terminal connection box.

True

Autotransformer starters increase the amount of inrush current by reducing the voltage applied to the motor during the starting period.

False

Part winding starting is another method of increasing the starting current of squirrel-cage induction motors.

False

The thermal capacity of the stator windings greatly expands the length of starting time for a part winding motor.

False

One advantage of part winding starters is that they provide ____ starting.

Closed transition

What is one advantage of consequent pole motors over some others types of variable speed alternating current motors?

Consequent pole motors have an advantage over some others types of variable speed alternating current motors in that they maintain a high torque when speed is reduced.

Discuss the use of taps in autotransformer starters.

Many autotransformer starters contain taps that can be set for 50 percent, 65 percent, or 80 percent of the line voltage. Reducing the voltage applied to the motor not only reduces the amount of in-rush current, but also reduces the motor torque. If 50 percent of the normal voltage is connected to the motor, the in-rush current will drop to 50 percent also. This will produce a torque that is 25 percent of the value when full voltage is connected to the motor. If the motor torque is insufficient to start the load when the 50 percent tap is used, the 65 percent or 80 percent taps are available.

A three-phase two-pole motor contains ____ actual poles.

Six

What is open transition starting and how does it differ from closed transition starting?

Open transition starting means that the motor is disconnected from the power line during the transition from wye to delta. This may be objectionable in some applications if the transition causes spikes on the power line when the motor changes from wye to delta. Another method that does not disconnect the motor from the power line is called closed transition starting. Closed transition starting is accomplished by adding another three-pole contactor and resistors to the circuit.

As a general rule, a time delay of two to three seconds is common before the second winding is connected in ____________________ with the first.

Parallel

What are some typical part winding applications?

Part winding starting is typically used for motors that supply the moving force for centrifugal pumps, fans, and blowers. They are often found in air conditioning and refrigeration applications. They are not generally employed to start heavy inertia loads that require an excessive amount of starting time.

In a wye-connected load, the line current and phase current are the same.

True

Two-speed consequent pole motors contain one reconnectable stator winding.

True

Wye-delta starting is accomplished by connecting the motor stator windings in wye, or star, during the starting period and then reconnecting them in delta during the run period.

True

Consequent pole motors that are intended to operate with three speeds contain ____________________ separate stator windings.

Two

Motors that are intended to operate on two voltages, such as 240 or 480 volts, contain ____ separate windings for each phase.

Two

To help prevent damaging the first winding, some circuits contain a timer that disconnects power to the motor if the second winding is not energized within a predetermined time. This timer is often called a(n) ____________________ timer.

Watchdog

Autotransformer starters are generally employed to start ____ -type motors.

squirrel-cage

Consequent pole motors intended to operate with four speeds use ____ windings.

two reconnectable