Sample Motors Test

what is the purpose of a single-phase alternator?

convert mechanical energy into single-phase electrical energy (AC power).

what is the purpose of overcurrent protection in a motor circuit?

To prevent damage from excessive current by interrupting the circuit.

What is the most common design of an induction motor rotor?

squirrel cage rotor, which consists of laminated iron cores and conductive bars connected at the ends.

By what means is the power factor of an industrial facility typically increased?

capacitors

Wound-rotor motor starters use timers for removing what? [from the circuit?]

Rotor resistance

Left hand coil rule

• Fingers curl in the direction of current flow.

• Thumb points toward the coil’s north pole.

function of a centrifugal switch

To disconnect the starting winding from the circuit once the motor reaches a predetermined speed

what makes a compound-wound generator different from other types?

It has both series and shunt field windings

The maximum torque req'd to accelerate a synchronous motor into sync at the rated voltage and frequency is known as?

Pull-in torque

what's da purpose of a motor bearing?

To support the motor shaft and allow it to rotate with minimal friction

What is the purpose of interpoles in a DC motor?

To improve commutation and reduce sparking at the brushes

what is the purpose of the stator in an alternator?

To produce the electrical output by housing the stationary windings where voltage is induced.

Which type of motor uses a centrifugal switch to disconnect a start-capacitor at 60-80% speed?

Capacitor-start motor

how many overcurrent protection devices for a 3-phase circuit?

3

Left Hand Conductor rule

Index finger: magnetic field direction

Middle finger: current direction

Thumb: force/motion direction

How is voltage imbalance measured on a 3-phase circuit/motor?

Measure the voltage between each pair of phases, then use the average voltage to calculate the percentage voltage imbalance.

The synchronous speed is based on

Frequency and the number of poles

Combined magnetic fields in a motor interact to produce what?

Torque

what does the service factor represent

The motor’s allowable overload capacity under specified conditions.

what is the role of the drum switch in a wound rotor motor?

To connect and disconnect the rotor resistance in steps during starting

the Locked Rotor indicating code letter on a nameplate is abbreviated as

CODE

Closed-circuit transistion is preferable to open-circ transistion; because the closed-circuit method does not cause _ ?

A momentary interruption of power to the motor

what's the method of rotor braking that results in high line current and heat

Plugging (countercurrent braking)

what is the characteristic of a short-circuit (it takes the shortcut!!)

Low resistance, which causes a very high current to flow

Reversing which type of motor is very different from reversing a single-phase motor because it involves removing & turning the rotor?

Shaded-pole motor

How do electromagnetic overload relays operate

by using the magnetic field produced by motor current to trip the overload relay when the current becomes excessive

what should be done before re-marking the leads of a dual-voltage motor?

Disconnect the motor from the power source and verify it is de-energized.

what's da purpose of the exciter generator in a synchronous motor?

To supply DC current to the rotor field winding, creating the magnetic field needed for synchronous operation.

what does an infinite resistance reading mean between terminals S1 and S2 in a DC series motor?

An open circuit in the series field winding.

What can excessive torquing during bolt tightening cause in machinery alignment?

Misalignment — excessive torque can distort the machinery or mounting surfaces.

time delay fuses are also known as?

Dual-element fuses

BLANK torque is torque required to produce the rated power at full speed

Full-load

which motor type has a start winding that is automatically removed by a centrifugal switch as the motor accelerates?

Single-phase induction motor — specifically, a split-phase motor

what is the function of a commutator in a dc generator

To convert the AC induced in the armature into DC output.

what does the synchroscope indicate when the needle is stationary at the 12 o'clock position?

The incoming generator is in phase with the bus and at the correct frequency for synchronization.

how does the rotor of a wound-rotor motor differ from that of a squirrel-cage motor?

It has a three-phase insulated winding connected to slip rings, rather than shorted rotor bars.

what is the condition where substantially all of the magnetic domains in a magnetic core are aligned with the field

Magnetic saturation

what material can hold its magnetism for a long period?

Hard magnetic material (such as steel)

what is the purpose of the rim and face alignment method?

To align the shafts of two machines so they are collinear.

the type of motor that can operate on single-phase AC or DC?

Universal motor