Trade Concepts Flashcards
What is the formula to find circumference?
2•pi•r
What is the formula for CMA?
diameter^2
d is mils. Mils is 1/1000
What is the formula for SMA?
L•W or CMA•0.7854
What is resistance when given CMA?
R = K•L / CMA
K is constant
L is measured in feet
What is the constant resistance value for copper?
10.4
What is the constant resistance value of aluminum?
17
What is the conversion for ft to meter?
1 foot = 0.305 meters
What is for formula to find P, when given I and R?
I^2•R
What is the formula to find I when given P and R?
Square root of P/R
What is the formula to find voltage when given P and R?
Square root of P•R
What side of a diode is more positive?
Triangle side
What side of a diode is more negative?
Flat side
How is a diode connected in reverse bias?
When the anode (triangle side) is connected to negative.
When a diode is acting as an open switch, it is in what bias?
Reverse
What will a voltmeter read on an open in a series circuit?
Source
When a diode is in forward bias, what will be the voltage drop across it?
0.7V
What does an ohmmeter read on a diode when it is in reverse bias?
High resistance
What does an ohmmeter read on a diode when it is in forward bias?
Low resistance
How will a diode be connected in a circuit when it is in forward bias?
The cathode (flat part) will be connected to negative.
In a transistor, the lead associated with the arrow is the ______
Emitter
In a transistor, the lead associated with no arrow is the _____
Collector
In a transistor, the arrow points towards the ____
N in a PNP or NPN junction
In a transistor, the load is connected to the _____
Collector
In a transistor, which is the common?
Emitter
In a transistor, the base is the _____
Control
What is the formula to calculate beta?
I collector / I emitter
What is saturation?
Max output
What is cut-off?
No output
The scale of a hysteresis loop measures what?
Retentivity
What are the characteristics of core material?
- high resistance
- high permeability (easier to conduct lines of flux)
- low reluctance
- laminated
A large hysteresis loop would be what kind of material?
Iron or carbon steel
A small hysteresis loop would be what kind of material?
Soft iron
What is the formula for L regarding flux magnetism?
L = n^2•permeability•Area
What is the formula for C regarding flux magnetism?
C = 8.85 x 10^-12 x area / d
For an inductive circuit, what happens when the switch closes?
All voltage will be seen across the inductor, as time goes by voltage will be seen across resistor again and none on the inductor
In a capacitive circuit, what happens when the switch is closed?
Instantly all current is at a max and charges the capacitor. Once capacitor is charged there is no more current flow, all voltage is dropped across the capacitor and 0V across the resistor.
A scalar has _____
Magnitude only (weight)
A vector has _____
Velocity and direction
Phasors are _______
Electrical vectors
What is effective AC resistance?
DC resistance plus all other things that oppose current (hysteresis losses, skin effect)
What are the characteristics of a HV winding?
Smaller conductor, thicker insulation
What are the characteristics of a LV winding?
Larger conductor, thinner insulation
What does the short circuit test measure?
Copper losses and impedance
What does the open circuit test measure?
Core losses
What would happen to the power of a wye or delta connection if it was reconnected in the other configuration?
Reconnected in delta - power would increase by 3x
Reconnected in wye - power would decrease by x3
How is an alternator different from any other three phase connections?
The phase values stay the same if it was reconnected in wye or delta, and the line voltages change
What is the only connection type that the 1, 2, root3 triangle cannot be used?
Delta open in phase or wye with neutral
When doing a voltmeter test on a wye secondary, what will the voltages read if connected properly?
X1 to X2 will read phase voltage, measuring any two lines will read line voltage (phase • root3)
When doing a voltmeter test on a wye secondary, what will the voltages read if connected improperly?
There will be two measurements of line voltage and the third measurement will be root3 higher
When doing an open delta test, what will the voltmeter read if connected properly?
Close to zero
When doing an open delta test, what will the voltmeter read if connected improperly?
Double the line voltage
What are the uses for an auto transformer?
- Buck/boost for a single piece of equipment
- Motor starters
What are the conditions needed for an SCR to conduct?
- forward bias
- must be triggered
What are SCRs used for mainly?
Phase control
A resistive triggering circuit will trigger ______
0 - 90°
An RC triggering circuit will trigger ______
0 - 180°
What are voltage sensitive switches?
Diacs
What are polarity sensitive switches?
Diodes
What are the characteristics of a wye - delta start?
- 1/3 the starting torque
- six conductors between starter and motor
- six or 12 lead motors
- Overloads are sized to phase currents
Which timers change state instantly?
NOTO, and NCTC
(Arrows pointing down)
What is the major pro of shunt generators?
Deliver constant speed
What is the standard output of a PT?
120V
What is the standard output of a CT?
5A
If a three phase instrument transformer only had one wattmeter, what can be said about the circuit?
That the loads are balanced. Wattmeter reading must be divided by 3
What is the formula to find sync speed in an AC motor?
120 x f / P
(P is number of poles per phase)
What is the formula for slip %?
sync speed - rotor speed / sync speed
What is the formula for finding rotor frequency?
f = P x Sr / 120
P is number of stator poles, Sr is the slip speed
What is the formula for finding efficiency of a transformer?
Power out / Power out - power losses
How do you find horsepower of an AC motor?
HP = Torque x speed / constant
Constant is 5252
What is conductivity?
Measurement of material that describes how easily that material will conduct current
What is DC resistance?
Opposition to current flow where heat is dissipated (skin effect, hysteresis, eddy currents)
What is the formula for work?
Force • d
What are the five main divisions of construction?
Architectural, Steuctural, Mechanical, Plumbing, Electrical
The speed of a synchronous motor depends on:
Number of poles and supply frequency
What is the torque angle of a sync motor?
Stator pole and rotor pole
What is the torque angle affected by?
Load
What are skewed armatures used for?
Used to reduce vibration
Direction of rotation of a three phase induction motor is determined by:
Same direction of the rotating magnetic field
How can the direction of a split phase motor be changed?
Interchanging the start OR run winding leads
Why does the capacitor start motor have higher starting torque than a split phase motor?
More displacement between start and run winding currents
Which DC motor has the best speed regulation?
Shunt motor
What is the formula for Charge?
Q = V • C
When there is an open in the line in a delta, what will power be at? What will voltage across the open read?
Power will be at 50%
Voltage will read root 3 of half the original line voltage (1,2,root3 triangle)
When there is an open in the phase of a delta, what happens to power and what does the voltmeter read?
Power is 2/3
Voltmeter reads 0V
When there is an open in the line of a wye with a neutral, what happens to the power? What does the voltmeter read?
Power will be 2/3
Voltmeter will read 0V
When there is an open in the phase of a wye with a neutral, what happens to power? What does the voltmeter read?
Power is 2/3
Voltmeter reads phase voltage
When there is an open in the line or phase of a wye with no neutral, what happens to power? What would the voltmeter read?
Power is 50%
Voltmeter will read 1, 2, root3 triangle
