Transformers Flashcards
Distribution voltages range from what to what?
2400-34400V
Secondary Voltages include?
120,208,240,277,347,480 and 600
What are the main parts of transformer?
Core
Coil or winding
Bushings
Tank
What are two types of transformer losses?
Iron - no load losses, caused by magnetic hysteresis (happen regardless of load) opposition of atoms to align
Copper - caused by resistance in transformer losses when current flows.
The Power Triangle consist of these factors.
Real Power - Metered
Apparent Power - Generated
Reactive - Used to build inductive and capacitive fields
What Does ELI ICE stand for
In a capacitive circuit, current leads voltage by 90°
In an inductive circuit, current lags voltage by 90°
Power Factor is a ratio between what and what?
Real Power divided by apparent power
How does a power company fix the power Factor?
Install capacitors to bring current and voltage sign waves in sync.
ICE
Current leads voltage
I - Current
C - capacitive Circuit
E - Voltage
ELI
Current lags voltage by 90°
E - Voltage
L - Inductive
I - Current
0 values on sine waves
0,180,360 degrees
How many taps are on primary windings of transformer equiped with tap changer?
- 2 up and 2 down. Come in 2.5% steps
What is the impedance range when banking transformers?
They must be within 10% of each other. Can with lowest impedance carries a majority of the load.
How does a tap changer work?
By adding or subtracting coils on the primary side.
What is the range on a transformer with tap changer?
95% to 105% works in 2.5% increments.
To increase voltage lower the taps, to decrease voltage raise the taps.
How would you treat secondary breakers on a CSP can?
Treat as if energized. You cannot physically open or close them in a transformer.
Three things to note on transformer nameplate?
Voltage, Impedance, and polarity.
What protective devices are located on a CSP can?
Secondary circuit breaker, primary fuse and exterior mounted arrestor.
What is the purpose of a lightning arrestor?
Protects line equipment from over voltage/voltage surges.
What is the purpose of a fused cutout?
To protect a device from dangerous overload.
Define Corona
The tendency of electrons to leave the line at high voltage.
Define Ohms Law
Ability of 1 volt to push 1 amp through 1 ohm of resistance.
Define circular mil
A circle with a diameter of one, one thousandth of an inch.
Source side equals
Line side
Customer side equals
Load side
What is the purpose of transposing?
To help reduce the electromagnetic field.aroumd conductors.
What are the 3 types of faults?
Open circuit, short circuit and ground fault
What is CT and how is it hooked up?
Current transformer, reduces amperage to safe levels for metering. Connected in series.
What is a PT?
Potential Transformer, reduces voltage to safe levels for metering. Hooked up parallel.
Ladder safety specs.
4 to 1 ratio when setting up and needs to be extended 3 feet above the object.
What is Roberts Rule of Order?
The order in which a union meeting is conducted.
What is impedance?
The total opposition to current flow in a transformer. Made up of resistance, inductive reactance and capacitive reactance
What relationship does inductive and capacitive reactance share?
Oppose one another. Balancing this helps prevent ferroresonance.
How many degrees in a sine wave?
- With 0, 180 and 360 representing 0
What determines capacitance?
Surface area of conductor, distance between conductor and type of insulation.
What is line loss.
Amount of voltage lost pushing current through a resistance.
Can porcelain withstand more compression or tension?
Compression
What is a voltage regulator and how does it work?
It is an electrical apparatus used to regulate voltage at 10% above or 10% below line voltage. Works in 32 steps of 5/8%. The high side is connected in parallel and the secondary is connected in series.
I²R, measured in watthour meters, what the customer is billed for.
Real Power
Does not do any work, used to build magnetic fields.
Reactive Power
Power generated by utility, how distribution transformers are rated.
Apparent Power
Distro circuits are almost always more (capacitive/inductive) due to the presence of windings in motors and transformers.
Inductive
This apparatus is installed on the line to combat inductive reactance on the line.
Capacitor
Not tying the neutral down in a Wye/Wye bank will cause what?
A boost in the secondary Voltages.
Having more than one ground strap on a grounded delta bank results in what?
It creates a phase angle with a difference of potential. Produces a fault which will blow the ground strap.
Impedance is made of what?
Resistance and Reactance - (inductive and capacitive)
What are some ways to prevent ferroresonance?
Utilize a gang operated switch to prevent back feed onto UG cable creating capacitive reactance.
Increase the inductive reactance by adding load to the transformer. At least 15% rated capacity.
What percentage of load should a mack carry before opening a jumper?
33%
What range are rubber gloves rated for?
5 to 34,500V
What are some common problems to look for with rubber gloves?
Cracking or cutting - from storing rubber folded or pinched.
Checking - caused from UV Light or sunlight exposure.
Embedded wood or metal splinters - from climbing poles or over fences with gloves on.
Punctures - from any sharp objects one comes in contact with.
Swelling - caused by exposure to petroleum based products.
Name the various glove ranges and their colors.
00 Beige
0 Red
1 White
2 Yellow
3 Green
4 Orange
Name voltages for each class of glove.
00 - 500/750
0 - 1000/1500
1 - 7500/11250
2 - 17000/25500
3 - 26500/39750
4 - 36000/54000
AC/DC
If a transformers secondary rating is represented with the big number first, what does that indicate?
240/120 vs typical 120/240
If the larger number precedes the smaller it means the coils in the transformer cannot be altered. No option to parallel for capacity.
Maintain ____ feet of clearance from lines in a substation.
15
Describe delta configuration laws.
Voltage across coil/winding = voltage across line.
Current through the coil/winding X 1.73 = the current through the line.
Describe Wye Laws of a system.
Voltage across the coil/winding X 1.73 = voltage across the line.
Current through the coil/winding = current through the line.
How many lumens in 1 candle power?
12.57 lumens
What size capacitors are the most common?
100, 150, 200
- Typically a bank of three so total capacities are 300/450/600.
Are capacitors installed near the customer or near the sub?
Capacitors are installed near the customer and fix Power Factor back to the substation/source.
How do you take a capacitor out of service?
De-energize then wait five minutes to bleed voltage, test and shunt secondaries.
Transformers work on the principle of?
Mutual Induction
Voltage and current are _______ proportional.
Inversely
What kind of transformer is used on street lighting?
Constant current transformer.
Produces 6.6 amps constantly.
How do you hook up a transformer with a nameplate of 7200/12470Y?
Phase to phase on a delta system or phase to ground on a wye system.
How do you know which tap setting to use on a transformer?
Measured voltage divided by desired voltage.
What’s the difference between a 120/240 and 240/120 can?
120/240 is typically an overhead can with the availability to parallel the coils.
240/120 is typically an underground can with permanent 240 coil with a center tap.
What is the laminated core of a transformer made of?
Steel
What is the current limiting property of an inductor called?
Inductive Reactance
What is the purpose of rubber glove sticking out of the protectors?
To protect against flashover.
What is the advantage of a Wye over a Delta system?
A Wye system can carry 73% more load current and provides a balanced load.
What are the 4 ways of sagging wire?
Dynamometer, transit with targets, cornfield, return wave.
What is the primary reason for transposing a transmission line?
To balance a line also to cut down on radio and telephone interference.
Electrical fires are classified as what type?
Class C
List three types of air switches.
Circuit breaker, disconnect and air break.
Which type of control is usually provided at a substation?
Local Control
Define harmonic.
AC and voltage disturbances that can also be represented by sine waves but are at different frequencies than the fundamental 60 Hz.
Harmonic frequencies include?
30
120 Second Harmonics
180 Third Harmonics
What is affected by harmonics?
When harmonics become distorted and severely distorted it affects sensitive electronic equipment.
How are harmonics created? And what produces them?
Non linear loads on the power system.
Produced by transformers, arc furnaces, arc welders, lighting ballast, converters.
What will help eliminate harmonics on new three phase installations?
Balancing loads, or providing oversized neutral conductors.
What determines the strength of the magnetic field in a circuit?
The amount of current that flows through a conductor.
What is the RMS value of AC equal to?
.707 times the peak value.
What is the peak value of AC equal to?
1.414 times the RMS value.
List three factors which determine the amount of voltage that will be induced in a conductor.
The size, type and length.
When does a reclosure usually lock out?
After 4 operations.
Define lumen.
One unit of light output.
A transformer is usually loaded to what percentage of the nameplate voltage rating?
125 to 150 percent for 1-2 hrs at a time.
How is phase sequencing designated.
Clockwise 1 2 3 or counterclockwise 321
What is the maximum resistance that a ground should have?
25 ohms.
List three factors which determine the amount of voltage that will be induced in a transformer.
The number of turns of wire, the strength of the magnetic field, the speed of the cutting action.
Upon what principle does a transformer operate?
Mutual Induction.
What is a snatch block?
A closed sheave.
What are dampers used for?
To deaden vibrations and prevent conductor damage.
Are the primary and secondary coils of a transformer physically connected?
No Magnetically Coupled
What is the force that makes electricity flow.
Electromotive Force (EMF)
What is a Megger?
A device that measures high resistance.
What is a cable fault?
When the insulation on the wire or cables doesn’t sufficiently confine the voltage.
What are the most common stranded conductor shapes.
Concentric round, compact round, compact sector, annular, segmental
What is a counterpoise?
A grounding grid for either a substation or a footer on a transmission line.
What device breaks the arc on air break switches?
Arcing horns
Line loss as an equation.
IR²
Define a vector.
A line having definite length, direction and magnitude.
What are the efficiencies of Knots, hitches and splices?
Knots 50%
Hitches 75%
Splices 85%
Impedance is represented by ____ and measured in ____.
Z
Ohms
What is PCB and what was it used for and where found?
Poly chlorinated Biphenyl
And insulating and cooling medium in transformers.
What is SF6, and where is it utilized.
Sulfur hexafluoride. It is used as a arc snuffing gas in switches.
Describe Lenz Law
An induced electromotive force always tends to oppose the force that causes the induction.
How do you find a conductors size?
Measure the diameter of a conductor in mils, and then square it.
What is BIL and what does it stand for?
Basic Impulse Level
It is the voltage level that can flash over the leakage distance of an insulator. The longer distance over the outside of an insulator is the leakage distance.
What is the name of the line above a substation or transmission structure?
And what is its function?
Shield Wire, Ground Wire, Static Wire
It acts as a more attractive path to ground for lightning strikes.
What are the various cutout fuse speeds?
K link - fast
T link - slow
Solid Material
What are the various fuse types used in utility applications?
Expulsion - cutout fuse links
Under oil expulsion - bayonet style
Solid Material filled -
Non expulsion
Under Oil backup
Liquid Filled
Fault Tamers - think giant plastic star wars
Who was the first president of the IBEW?
Henry Miller
What are the two types of cover up?
Rigid (plastic) and Rubber
How are rubber and rigid cover up rated differently?
Rubber parallels that of rubber gloves where as rigid is based on air space, and goes up to class 6 72.5 phase to phase.
Is rubber or plastic cover up rated higher?
Plastic
What are the testing intervals on gloves, sleeves, blankets and hoses/Insulator covers?
Gloves 6 months, sleeves and blankets each year, hoses, cover etc upon unsatisfactory inspection.
What are some things to look for with hot sticks?
Surface scratches and deformed/popped rivets.
Loose or popped rivets can cause what _____ in hotsticks?
Moisture
Hollow hotline tools are more susceptible to ________ and may need more frequent ______.
Moisture, testing
If accidental energization occurs, currently flowing through worker must be below _____?
10mA
Grounds should be applied in this type pattern to ensure quickest lockout of protective devices.
T
________ provide a major short circuit when the circuit becomes energized accidentally.
Grounds
What is the purpose of protective grounds?
To prove isolation.
What are the two ways of working with energized lines?
Insulation or isolation.
In a Wye-wye system what connection is made first with grounds?
Neutral
In a Delta System how are grounds applied?
Phase to phase to phase then to a ground rod in the earth. To prove isolation.
The allowable tension on a link stick depends on diameter.
1.25?
1.5?
1.25 - 3500lbs
1.5 - 6500 lbs
What is the working load limit for a roller link stick?
1.25 - 1000lbs
What is the minimum distance between saddles on a pole for a vertical lift?
5 feet
What is a three phase vertical lifting assembly called?
Kite
The maximum height a conductor can be lifted is?
When the belly reaches adjacent structures. That’s when the conductors weight has doubled.
How to calculate the WLL of wire tongs?
When calculation WLL on wire ton. For tension or top tong multiply length times total weight divided by saddle distance. And for compression multiply bottom tong length times total weight divided by saddle difference.
List some hazards involving hot line tools.
Encroaching on the minimum approach distances. Using a contaminated work glove will leave residue. Lifting tongs can slide through saddles when weight/load is applied.
When the larger number comes first on the transformer primary. What does it mean?
12470/7200
It means it’s a CSP transformer.
How to calculate three phase bank capacity?
Always 3 times the rating of the smallest can.
What is an open bank capacity?
86.6% of the two remaining transformers or 57.7% of the original three pots.
What does a red light on a CSP transformer indicate?
That an overload situation has occurred.
What are three methods to cool a Transformer?
Oil, air, water
Why is the neutral floated on the primary side of a closed eye closed Delta Bank?
So you wouldn’t have a back feed condition if you were to lose one of the cans.
How do you obtain the full potential of a transformer?
Put the coils in series
How do you obtain the full capacity of a transformer?
Put the coils in parallel.
Describe the primary coils of a transformer.
More turns of wire, smaller wire and higher insulation.
Describe the secondary coils of a transformer.
Less turns of wire, larger wire and less insulation.
What is frequency?
The number of cycles per second.
What does the internal discharge resistor of a capacitor do?
Once the capacitor has been de-energized it reduces the voltage to 50 volts or less within 5 minutes.
Do capacitors have voltage ratings?
Yes
Name four types of controls that are used with capacitors.
Time, temperature, voltage, and current
Induced voltage is always opposite of ?
Applied voltage
What is permeability?
The ease in which an iron core conducts lines of force.
Why is a fourth cutout installed on the primary neutral of a closed Wye closed Delta bank?
To prevent ferroresonance, when you lose your third potential reactance and capacitance in the bank can build up to 10X the normal voltage. This 4th cutout will drain this excess voltage.
