Motors 2

By connecting the motor directly to the power

How is Across-the-line Starting accomplished?

Connected to stator winding in wye during the starting period and then reconnecting them in delta for normal operations

How is wye delta starting accomplished?

True

In an inductive circuit, the current must rise at an exponential rate?

Series, Shunt, and Compound

Three basic types of direct current motors

True

Wound rotor type motors and synchronous motors generally use autotransformer starters?

Soft

Wye delta starting is sometimes called ________ starting

Autotransformers

________ starters are generally employed to start squirrel cage type motors

True

Shunt field windings exhibit a much higher resistance than series field windings

Holding Coil and Pick up Coil

Some DC contactors contain two separate coils, describe the coils.

Motor

Some control circuits sets __________ speed to determine when to shunt the resistors out of the power line?

Connecting resistance in series with the stator winding during the starting period

The thermal capacity of a stator winding, generally limits the length of the starting time for a part winding motor. How do you overcome this problem?

Normal

When full line voltage is applied to both the armature and shunt field, the motor is said to operate at ____________ speed

True

Compound motors contain both a series and shunt field

5

Open transition starting is generally used on starters size _____ and smaller

This is accomplished by tapping the resistor or reactor to provide different values of resistance or inductive reactance

Some resistor and reactor starters use multiple steps for starting, how is this accomplished?

True

The closed transition starting does not disconnect the motor from the power line

Watchdog Timer

To help prevent damaging the first winding, some circuits contain a timer that disconnect the power to the motor if the second winding is not energized within a predetermined time. This timer is called _______

False

For closed transition starting, four separate start contactors are used?

False

Frog leg wound armatures are most often used in small machines?

False

Delta connected dual voltage motors are acceptable for part winding starting

Speed regulation

Differential speed from no load to full load is to refer to as _________

Load

Direct Current motors require only one _____________ contact to connect or disconnect them to the power line and one overload sensing device.

True

Dual voltage motors designed for wye delta starting will supply all 12T leads at the terminal connection box

True

Dual voltage motors not intended for wye delta connections will have certain terminals tied internally

Thermal

Each winding in motor design for part winding started is individually protected by _________ overload heaters

Timer

Figure 24.1 (Uses ______ to shunt the resistors out of circuit after some period of time?)

Motor coils energizes and closes all contacts. The M contacts connect the motor to the resistors and resistors to the line.

Figure 24.1 (What happens right after the start button is pressed?)

False

Figure 24.4 (The current Sensor contacts are normally open?)

Basic control circuit for wye delta starter

Figure 26.9 (what does it show)

so it will disconnect both motor windings

Figure 27.2 (Why are both overload relays connected in series)

A circuit is completed, energizing CR causing all CR contacts to close

In an autotransformer starter, what happens when the start button is pressed?

reducing the voltage applied to the motor during the starting period

How do autotransformer starters reduce the amount of in rush current

50 percent

If 50 percent of the normal voltage is connected to the motor the in rush current will drop to _________

Open Delta

Figure 25.1 (Transformers are connected in?)

Stator windings connected in delta

Figure 26.1 (what does this show)

3

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

Delta

If the stator windings are connected in __________, the voltage across each phase will be 480 volts because the line voltage and phase voltage in _______ connection

Pick Up

In a DC contactor with 2 coils, the __________ coil is intended for momentary duty and not continuous operation.

Ungrounded

In a grounded system the current sensing device must be in the __________ conductor.

False

In a wye connection the line current and the phase current are not the same

Windings

Motors are intended to operate on two voltages such as 240 or 480, volts contain two separate ________ of each phase

Wye or Delta

Motors designed to be used for part winding starting contains two separate stator windings. What are they?

Lap, Wave, and Frogleg

What are the three basic types of armature windings?

Reduce in rush current and starting torque

What are the two effects of reducing the voltage applied to the motor?

Motor must be designed for stator windings to be connected in delta and all stator winding leads must be accessible

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

Resistive and reactive starting

What are two of the most common methods to reduce the amount of starting current

Use multiple contacts

What do DC starters and contactors that do not utilize arc suppressors or magnetic blow out coils use to break the circuit?

The first winding can be severely damaged

What happens if the second winding is not connected to the power line within a short period of time?

Start contactor opens and the run contactor closes

What is meant by open transition starting?

Inductive

Autotransformer starters are __________ type loads and will effect the power factor during the starting period

True

Autotransformer starters provide greater starting torque per amp drawn from the line than any other type of reduced voltage starter?

True

Compound motors generally employ a Field Loss Relay that is intended to disconnect the motor from the power line in the event that shunt field current should be interrupted or drop below the acceptable level

Transformers

Current ________ are used to sense the amount of motor current?

Reduce the current to a level that common overload heaters can be used to protect the motor

In closed transition starting what is the role of three current transformers (CT) being used in the circuit?

Resistance of the windings

In direct current motors, by what is the in rush current limited?

True

In part-winding starting. Neither of the two windings is individually capable of withstanding the starting current for more than a few seconds

Locked Rotor

In rush current is referred to as ____________ current

True

Many transformer starters contain taps that can be set for 50, 65, or 80 percent of the line voltage?

Part winding

Method of starting in which only half the motor winding is used during the starting is called ________ starting

Armature

Most common way of reversing the direction of the rotation of a direct current motor is to reverse the direction of the current flow through the _________?

Too much torque or current

Name two conditions where it is not possible to start a motor across the line?

Attraction and repulsion of magnetism

On what principle do series motors operate?

Closed Transition

One advantage of part winding starting is that they provide _________ starting because the motor is never disconnected from the power line during the starting time

True

One way of determining when to shunt the resistors out of the circuit, is by sensing motor current?

False

Open transition starting means that the motor is connected to the power line during the transition from wye to delta

Constant speed

Shunt motors are also called ___________ motors

True

Part winding starters provide closed transition starting?

True

Part winding starting is typically used for motors that supply the moving force for centrifugal pumps, fans, and blowers

Inductive reactance

Reactors limit to in rush current with ________ instead of resistance?

True

Resistors connected in series with the motor, limit the amount of in rush current?

False

Series field windings are marked F1 and F2 in the thermal connection box?

They have no upper speed limit if they have no load

Series type motors have one undesirable characteristic, what is it?

Making the actual load connections to the motor

What is the most critical part of connecting a wye delta starter

Connected in cumulative or differential compounding

When compound motors are installed, what should they be tested for?

False

When dual voltage motors are used, the motor must be operated on the high voltage setting of the motor

Low Inertia

Why is it that small DC motors can be started by using Across-the-Line starting?

Simple and inexpensive

Why is the time delay one of the most popular methods to determine when to connect the motor directly to the power line

Overheat

With part winding starting the first winding will _______ rapidly if the second winding is not connected within a very short period of time

Torque

Wye delta starting is often used with large horsepower motors to reduce in rush current the starting period and reduce starting ________

Compounding

_____________ is the term used to indicate the relative strength of a series and shunt fields