cst tech role study guide

For a journal bearing design, the clearance ratio ("clearance") should be approximately considered as:

0.001

A v-belt drive has just had its belts replaced. What must be checked/done as a first precaution before running the drive?

The belts are placed over the sheaves and in the grooves without forcing

The bimetallic circuit breakers, used in the motor, control circuit's __________ and breaks if the __________ on/of the bimetallic strip is increased.

current, temperature.

Breakdown maintenance cost ___________________ with the increase in preventive maintenance cost.

decreases

____________ is zero in transformers even at full load:

friction loss, Friction losses are zero in transformers. A transformer is composed of a core, primary and secondary windings. Eddy current loss and hysteresis loss depend upon the magnetic properties of the material used for the construction of the core.

The cross-sectional area of a copper wire ____________ related to its resistance.

inversely, The resistance is inversely related to the cross-sectional area. Increasing the area decreases the resistance of the wire and vice versa

a solenoid

is an electromagnetic circuit component that actuates its mover to open or close a valve.

To prevent a bolt from rotating loose, we may use a

lock washer

An instrument is measuring a physical quantity which is changing frequently with time. The instrument should have _____________ damping.

low damping, Damping in instruments is caused by the resistance or the friction in the measuring elements. Higher damping causes slow responses which are not desirable for systems with higher response rates. In order to measure the physical quantity at higher rates, the instrument should have less damping.

The two most important qualities for a flywheel are:

low moment of inertia, low friction

The benefit/benefits of dynamic balancing are:

low vibration, low noise, and higher bearing life

zero-film are sliding bearing which are _____________.

lubrication-free

Which of the following lubrication system is used in two stroke engines?

mist system

The average value of AC voltage and current is _________.

zero, The positive and negative cycle of a typical AC wave is shown in the figure below. The sum of the positive and negative values is zero.

The method can be used to detect material wear in the machinery is:

Ferrous Concentration, The ferrous wear concentration test is not subject to such limitations and gives us an accurate measure of the ferrous metals in your oil

Power transmitting sprockets need a chain wrap of approximately: A. 90 deg. B. 180 deg. C. 115 deg. D. 270 deg.

180 deg.

The amperemeter reading will increase, the voltmeter reading will not change

A circuit consists of a battery, two light bulbs, an amperemeter and a voltmeter is connected as shown below (black). After adding another light bulb as shown in gray:

a rectifier

A rectifier is a diode or combination of diodes which is/are used in AC to DC voltage conversion power supply.

The field windings of a DC shunt motor are burnt. The cause of this can be:

AC voltage applied to the winding, this will cause the windings to heat up and burn eventually.

A voltage of 12 V is applied to a resistance to produce 1 A current. What should be the value of resistance to twice the current with the same amount of voltage?

According to this law, the relationship between current and resistance is inversely proportional. Therefore, the resistance should be halved if the current is required to be doubled at a fixed amount of voltage.

____________ ultrasound technology is used for compressed air leak detection.

Air borne

____________ load is acting on the plane of the bearings' axis of rotation.

Axial, Thrust bearings are used to support an assembly in the axial direction and to avoid axial misalignment.

Which of the following can be used to measure speed of a DC motor?

Back-emf, The speed of a DC motor is directly proportional to the back-emf produced in the windings. Back-emf is the voltage produced in the windings to oppose the rotation of the armature due to the laws of magnetism. Back-emf is higher for higher speeds of the armature.

Where is a torque limiting clutch placed in the motor-gearbox-load chain?

Between the gearbox and the load

A short circuit will happen in the reverse starter circuit if ____________________.

Both buttons are pressed simultaneously

Both of the terminals of a DC motor are connected to only negative or only positive terminals of a battery. This will cause:

Braking, Since DC motors are reversible electrical machines, when the voltage and current are applied to motor windings, the rotor rotates and vice versa. Connecting both of the terminals to the same potential (voltage) eliminates the possibility of a current flowing through the motor windings. Consequently, the rotor locks, and this is called braking

How is the frequency of a secondary winding voltage changed in a transformer?

By changing the frequency of the primary winding.

Which of the following is NOT a procedure for surface and edge wear inspection of a belt?

Confirm that belt can be moved laterally of the drive/idle shaft.

Oil (lubricants) foaming in gear mechanism is caused by:

Contamination of lubrication with water

Coolant leakage into the engine cylinders is most likely to occur because of defective:

Cylinder head gasket

In order to remove a bearing from a steel shaft, ___________ can be used without damaging the bearing or the shaft. A. High impact hammer B. Dry ice C. Liquid Nitrogen D. Both B and C

D. both B and C

Bearing failure in motors can be caused due to wrong selection of bearings. A motor mounted horizontally or vertically needs _____________ types of bearings.

Different, A motor mounted horizontally or vertically encounters different types of loading. A vertically mounted motor would undergo axial loading. Whereas a horizontally mounted motor undergoes radial loading. Therefore, each mounting would require a unique type of bearing according to its application.

Which of the following is a fault that is caused by the rotor of a synchronous motor?

Eccentricity, Eccentricity is defined as the offset between the rotor and stator centers.

When current flows in a wire, the _______ of the metal are moving

Electrons

Oil contamination can be measured by:

Fourier transform infrared (FTIR) spectroscopy, Acid number, viscosity

____________ diode is used to protect the motor from the sudden voltage spikes when the current is instantly changed.

Freewheel

A full-wave rectifier is subjected to a 50 Hz AC voltage. What is the frequency of the output voltage?

Frequency is measured by how frequently the period is completed in one second. A Time period (denoted by 'T' ) is the time needed for one complete cycle of vibration to pass in a given point. The output signal completes a period twice as fast as the input frequency. T = T/2 so frequency f=2f

Which of the following is used for a dielectric withstand test?

Hipot tester, The Hipot test stands for high potential test and is used to measure the dielectric strength between the high potential line and the ground lines.

High voltage circuit breakers provide insulation of _________ Mega Ohms.

In high voltage circuit breakers, insulation resistance of 100 Mega Ohms is provided.

4 and 6

In the motor control circuit shown, at what points should the voltmeter probes be placed to check the limit switch? A 2 and 6 3 and 6 4 and 6 D 4 and 5

Which of the following instruments can be used to measure the alternating current?

Induction meter

_____________ cause overheating in the bearing and reduces the bearing life.

Insufficient lubrication and speed

In the case of a short circuit:

Voltage is high, resistance is low

Discharge corona is an undesirable effect because:

It is a waste of energy and it may lead to corrosion

If the main electricity supply is AC 110 V, it means that the 110 V is: A. The highest voltage supplied B. The lowest voltage supplied C. The constant voltage supplied D.The RMS of the voltage supplied

The RMS of the voltage supplied.

Which one of the following CANNOT be used as self-lubricating bushings? A. Graphite B. Copper C. Bronze D. None of the above

None of the above

The inductance of an iron-core coil decreases if

Number of turns is decreased, A greater number of turns of wire in the coil results in greater inductance due to a greater magnetic field force, while fewer turns of wire in the coil results in less inductance.

Hydrostatic bearing usually use __________ as lubricant.

OIL, Hydrostatic bearings use highly pressurized oil bearings controlled with an electromechanical pump. Grease is a viscous material and cannot be used for such a system.

Impedance is measured in:

Ohms

A bimetallic strip in motors is used to prevent:

Overload, A bimetallic strip is a simple strip that consists of two different metals on top and bottom. When subjected to heat the metals expand at different rates, causing the strip to bend. That mechanism is used mostly to break or make circuits in overload devices.

Oil whirl in journal bearing can be prevented by ________

Providing an obstacle to whirling fluid, and/or providing stabilizing load to minimize whirl.

The current and voltage passing through resistance are doubled. The power will be:

Quadrupled, the power of the resistance is a product of voltage and current. if both the voltage and current are doubled, the power of the resistor will be quadrupled.

The imaginary part of the impedance of an AC circuit is known as:

Reactance, Impedance is defined as the total opposition to current flow in AC circuits. Impedance is the sum of the resistance and reactance. Resistance is the real part and reactance is the imaginary part of the Impedance.

The cause of creep in belts is due to:

Unequal tension in tight and slack sides of the belt

Which one is NOT true for under tension belts:

Reduce bearing and belt life, The under tension in belt mechanisms does not affect the bearing and belt life.

The transformer core is laminated rather than a solid core as shown in the figure below. This is to:

Reduce eddy current

Which is NOT a benefit of Predictive Maintenance?

Reduce uptime

An electrical 60 Hertz (Hz) sine wave will have a _________ than a 50 Hz wave.

Shorter period

____________ roller bearings are available in cylindrical, barrel and taper shaped rollers.

Staggered

Select a bearing to sustain axial as well as radial loads:

TAPER roller bearing, Tapered roller bearing can provide radial loads as well as uni-directional thrust loads.

Which of the following can provide bi-directional thrust load?

THRUST ball bearing

A sag in an overhead power line is required to reduce

Tension in the line

line current, line voltage, and power and power factor. The coils shown in the three-phase lines are measuring the current of the respective load line. Each node voltage information is provided to the instrument as well. Instrument X can measure line voltage as well as the line current. Since the instrument is sensing both current and voltage, it can estimate the power as well as power factor.

The instrument X that is shown in the power distribution schematic can measure _________.

When two different metals are connected together, a temperature function electromotive force (voltage) is generated. This phenomena physical principle is called ____________.

Thermoelectric effect,

A snubber circuit is used across inductive loads to:

To suppress voltage spikes, The property of an inductor is that it does not allow a change in its current. Since inductive loads do not allow a change in current (current transients), voltage spikes are produced. In order to avoid these spikes, a snubber circuit is used. The snubber circuit is a series R-C network connected in parallel to the motor as shown in the figure below.

Using ___________ makes it possible to reduce the wire size of power distribution lines:

Transformers

A DC stepper motor is taking one step ahead and one step backward. What can be the possible cause of the behavior?

Wrong sequence of windings, In stepper motors, less current or voltage or higher load will stop the motor. The mentioned behavior in the stepper motors can only be because of the wrong sequence of energization of the coils. Since the stepper motor contains stator coils and they should be powered up in a special sequence to produce forward or backward motion.

When saturated, the resistance of a transistor is (theoretically):

Zero

The frequency of DC current is defined as:

Zero, The frequency of a current is how many times per second it changes its direction (or polarity). That definition is actually relevant only for AC (alternating current) since DC (direct current) is constant and does not change polarity.

A rotary switch that is used in electrical machines to reverse the direction of the current in the rotor coil is _________.

a commutator, A commutator is a rotary switch used in the rotor electrical machines, which reverses the current direction.

What is the aim of flexible couplings?

allow shaft misalignment

induction motors are what kind of motor

asynchronous motors, principle of induction which is inducing a current in the rotor by changing the magnetic field of the stator

What stresses are generated in a piping system?

axial, hoop, and expansion stress

Removing dirt from the motor winding is a preventive maintenance procedure. The dirt on motor windings cause:

block the ventilation process

Which sleeve bushing would be selected for an operation at temperatures higher than 1500°C.

ceramic, The only bushing that can be used at such temperatures is ceramic bushings because of their higher thermal properties.

Which one is NOT a regulating valve?

check valve, Check valves are used in the pneumatic systems to avoid the reverse flow and they are a type of one-way valve. Since it can only open or closed based on the flow-direction and geometry, they are not regulating valves.

The purpose of a cylindrical roller bearing is to _________.

contain radial motion of the shaft, The purpose of a cylindrical roller bearing is to react against radial forces and to contain the radial motion of the shaft.

Which of the following is NOT suitable for the core material in electromagnetic devices?

copper, Copper is not a magnetic material, and its relative permeability is around 1 which is closer to air.

Which of the following wear type occurs the least in a bearing when used in a turbine?

corrosion, Corrosion rarely occurs in turbine bearings because of the controlled moisture content. However, local wears, cracks, and cavitation occur in them due to heavy vibrations and insufficient supply of oil.

Thrust ball bearing are used to __________.

counteract axial force

Which of the following can be used to measure the torque of a DC motor?

current, The torque of a DC motor is directly proportional to the current of the windings.

What happens if two of the voltage lines of a three-phase motor are reversed?

motor runs in the opposite direction, A three-phase motor requires a particular voltage and phase to produce a rotating magnetic field in the stator to rotate the armature. If two wires of the three-phase are reversed, it will change the direction of rotation only, but the motor will work totally fine.

The number of discs in a multi-disc clutch is 6.Calculate the number of contacting surfaces.

number of contacting surfaces = (number of disks) -1=6-1=5.

Also called eccentrically loaded bearing is:

offset bearing, The load is eccentric when the line of action is not passing through the axis of the central column. Offset bearing is loaded eccentrically as shown in the figure below.

A braking resistor prevents _________.

overvoltage supply to the DC buss of a (VFD), Tripping of a VFD, Back energy drive from motor to VFD while decelerating.

Before the piston is removed, we must remove the:

piston rings

The distance between two sprocket teeth is called _______.

pitch

What is the advantage of bushing?

self-lubrication, less noise, and less vibration

Which of the following configurations provide better torque characteristics in a DC motor?

series winding

In induction motors, the difference between the synchronous and asynchronous speed of the rotor is referred to as

slip,

Which of the following is an overload relay type?

solid state, thermal and inductive, and electromagnetic

When the motor stalls, the _____________ is maximum. This sudden change is controlled by protection relay devices.

stator winding current, When the motor is unable to start (stalls) due to heavy loads, the amount of stator winding current is maximum. This is a known phenomenon that the load torque is directly proportional to the winding current. That is the reason the starting torque requires more current at the beginning which is controlled by protection relay devices that allow a particular amount of current, normally up to 2 sec.

V-belts are superior to flat belts because ________.

the belt does not slide away and slip-off from the pulley

When pressing a bearing into the housing, you should press against _________. A. the inner race only B. the outer race only C. both the inner and outer races. D. the seal

the outer race only

A transformer is used to transform an AC voltage. What would be the output if the applied voltage is DC as shown in the figure.

the voltage would be zero, a DC voltage is applied in this case that means there will be no change in a magnetic field and consequently no output current in the secondary coil.Transformers are used to transform AC voltage because the working principle of the transformer is a change in voltage. When a voltage change (sinusoidal) is applied at the input (primary coil), the magnetic field that is produced inside the core is changing as well. This change produces a current in the output windings (secondary coil).

The interlock device connected in-between the two contactors to reverse the phase of the motor terminals is used _________.

to avoid both contractors turning on at the same time. Main-line contactors are electrical relays that switch the line ON/OFF when power is applied to the coil. One contactor is used for this relay operation in one line. In order to reverse the direction of the current, a similar contactor should be added with an interlock device in-between them. The interlock device prevents both devices from turning ON at the same time.

Which of the following is NOT a predictive maintenance procedure on electrical systems?

ultrasonic analysis,ultrasonic analysis is used in mechanical systems to detect cracks and leakage in compressed gas pipelines.

A snubber circuit is used in DC motor control circuits to prevent _________.

voltage transients, Since the motor windings do not allow a change in current (current transients), voltage spikes are produced. In order to avoid these voltage spikes, a snubber circuit is used. The snubber circuit is a series R-C network connected in parallel to the motor