Study Guide 168 questions Flashcards
How does a tap changer work?
It works by adding or subtracting a part of the primary coil, therefore changing the turn ratio.
What is the first thing to do after hanging a transformer on the pole?
Connect grounds neutral.
What is impedance range when banking transformers?
They must be within 10% of each other (because the can with the least impedance will tend to hog the load).
What is the range of most transformer tap changers?
95% to 105% (to increase voltage, lower the taps; to decrease the voltage, raise the taps.)
What 3 protective devices do CSP transformers have?
Circuit breaker on the secondary side, protective link on the primary, lighting arrester mounted on outside of can.
What are the dangers of banking CSP (completely self protected) transformers?
Over voltage on one of the lighter legs would occur if the secondary breaker opens so you would still have 240 volts across the secondary. This would cause the customers lights to burn out.
How would you treat secondary breakers on a CSP?
Treat it as it were energized. (Because you cannot physically open or close in the transformer).
How would you treat a floated neutral?
As if it were a primary voltage.
What is the most important thing on a transformer?
The name plate.
What is the purpose of a current transformer (CT)?
It is used to reduce amperage to a suitable range for metering. (It is connected to line in series).
What is the purpose of a potential transformer (PT)?
It is used to reduce voltage to a suitable range for metering. (It is connected to the line parallel).
What is the safety factor of new rope compared to the old rope?
New rope is 5 to 1, old rope is 10 to 1 (6 months is considered old).
What 3 things do you look for in an injured person?
Response, bleeding, pulse.
How is pole strength determined?
The classification from 1 to 10 determines the strength to resist loads applied 2 ft from the top of the pole.
What 3 things determine pole depth?
Soil conditions, height of the pole, and location.
Can porcelain withstand more compression or tension?
Compression
What is the main advantage of pin type insulators?
It is cheaper and requires a shorter pole for the same overhead clearance.
What is the main purpose of a distribution transformer (DT)?
To step down voltage of the primary mains to a useable voltage in the secondary mains.
What are the 3 main parts of a transfomer?
The core, the coil, and the can.
Most distribution transformers have no load tap changers. What does this mean?
It means that the tap changers must be changed only when the can is taken out of service.
What is the difference of a conventional and CSP transfomer?
A conventional needs separate cutouts, arresters; a CSP has both built in.
What is a fuse cutout and its purpose?
It is a protective device for equipment against overload.
What is a lightening arrester and its purpose?
It is the horn gap connected in series with a resistor. It protects electrical equipment from over voltage surges.
What is voltage regulator and how does it work?
It is an electrical apparatus used to regulate voltage at 10% or above or 10% below line voltage at 32 steps of 5/8%. (The high side is connected in parallel and the secondary is connected in series.)
What is the purpose of a capacitor?
To improve power factor.
What determines capacitance?
The area of the conductors, the distance between the conductors, and the type of insulating material.
What are the oil switches used for?
To bread load, the switch is under oil to help break the arc.
What is the purpose of bundling conductors?
To increase current carrying capacity.
Define corona?
It is where electrons have a tendency to leave the line at a high voltage (cutouts, nuts, bolts).
What must you do before phasing and tying two lines together?
Make sure both lines are energized.
What does Ohms law state?
E = I times R
Define a watt.
The power of one amp flowing under the pressure one volt.
Define capacitance.
It is the ability of a magnetic field to induce a voltage in a conductor and it is measured in farads.
Define inductance.
It is the ability of a magnetic field to induce a voltage in a conductor and it is measured in henrys.
What does a red light on a CSP transformer indicate?
It indicates that an over load has existed.
What is a constant current transformer used for and what things must you remember about them?
It is used for series street lighting. You must connect the secondary side first, it has a moveable secondary coil.
What are the parts of a rope?
The fibers, the yarns, and the strands.
What are 3 types of line faults?
Short circuit, open circuit, and ground.
What is the most common reason for transmission line failure?
Flashover on insulators.
When banking cans of different KVA rating, what is the maximum safe rating?
3 times the KVA rating of the smallest can.
How would you connect the secondary side of a can to get a 5% and 10% boost?
5% parallel, 10% series. (To change to a buck, change X1 and X3).
Can a line without a load still carry a current?
Yes, it can carry a charging current of as much as 20 amps.
Define fault current.
The amount of current that will flow when the line is shorted across.
Why do reclosers hold the line open longer on the third and fourth operations?
To give the sectionalizer time to operate. (Remember a recloser must always be backed by a sectionalizer and that sectionalizer only operates under no current conditions).
What does KVAR mean?
Kilo volt ampere reactive.
What is power factor?
The ratio of true power to apparent power.
What is a counterpoise?
it is a grounding grid for a sub station or a footer on a transmission line.
How does capacitor time switching work?
It adds capacitors to the line when the load is heavy, and takes them off when the load is light.
What fuzzing insulators, do you go by length of the arc or by intensity of the sound?
Intensity of the sound.
What device breaks the arc on air breaker switches?
Arcing horns.
Where is the fault current greater?
Near the sub station.
What is line loss?
The amount of voltage lost by pushing current through a resistance.
In general, the maximum bending radius of cable is how many times the diameter of the cable?
8 time and should not be bent when temperature is below 14 degrees F.
Which windings of the induction regulator is mounted so it can rotate on its’ axis?
Shunt windings.
What is the maximum ground resistance that a structure can have?
25 ohms
Define a vector
It is a line having a definite length and direction. (direction and magnitude.)
What will happen to a transformer if you give it more voltage than the smallest name plate voltage?
You will burn up the transformer.
Is system voltage always a phase to phase reading?
Yes
When the system voltage matches the smallest name plate voltage, what do you connect?
The high side delta.
On the secondary side, if the name plate reads 120/240 or 240/480, how do you get both to be 120/240 or 240/480?
Series the inside of the can (delta connection).
What is a wild leg on a delta connected secondary and where will it be?
A 208. It will always be the furthest leg from the grounded transformer. ( 1-1/2 coils out.)
What are substations used for?
To change voltage from one value to another.
Heavy loaded lines are protected by the use of _____.
OCB (OCR), sectionalizers, and fuse cutouts.
Sagging charts are used to show what 2 things for spans to a line where tension is used?
Distance and temperature.
What is a snatch block?
A closed sheave.
What are dampers used for?
To deaden vibrations and prevent conductor damage.
What 2 things should be checked before final sag is started?
Anchors and guys.
What is bus work in a substation?
Aluminum or copper bars that connect equipment together.
In a standard distribution transformer, are the primary and secondary coils physically connected together?
No. (magnetically coopled)
How are straight line poles generally set?
Gain to gain or back to back.
Is a series street line connected in line?
Yes
When placing a pole in a hot line, what should you wear when handling the butt of the pole?
Rubber gloves.
What are capacitors used for?
To correct power factor
What is the force which makes electricity flow?
Electromotive force (EMF).
In a series street lighting circuit, what type of transformer is used? What happens when one bulb goes out?
Constant current transformers. The transformers secondary windings is moveable, so when one light burns out, it moves, adjusting the voltage. (amps stay the same)
How many lumens are in one candle power?
12.57
A shock victim received several burns, but was not killed. What would you suspect, considering the amount of current drawn by his body?
Under .2 amps
How far must unqualified employees stay away from apparatus energized up to 5000 volts?
10 feet.
What are the 4 basic steps in pole top rescue?
Evaluate the situation, provide for your protection, climb to rescue position, and determine injuries and conditions.
NJATC stands for what?
National Joint Apprenticeship and Training Committee
How many current paths does a series circuit have?
One.
How are primary and secondary windings of a transformer coupled?
Magnetically coupled through mutual induction.
Adding parallel loads to a circuit will _____ total circuit resistance and _____ the total circuit current.
Decrease, increase.
What is the polarity of electrons when they enter a load? When they leave?
Negative, positive.
How does an analog meter operate?
On the magnetic principal that like poles repel each other.
List the 3 steps that should be followed when reading a multimeter.
Determine what the meter indicates, determine the full scale value of the meter, read the meter.
What are the 2 basic types of analog ohmmeters?
The series and the shunt.
Name 2 advantages for 4 wire feeders over 3 wire feeders.
Cheaper to build, more efficient.
Most electrical power generated today is ____ power.
Three phase
A three phase generator producers what kind of voltage?
Three equal voltages that are 120 degrees out of phase.
What is created whenever current flows through a conductor?
A magnetic field is created.
List 3 factors which determine the amount of voltage that will be induced in a transformer?
The number of turns of the wire, the strength of the magnetic field, the speed of the cutting action.
Upon what principal does a transformer operate?
Mutual induction.
Where is the secondary circuit breaker on a CSP transformer located?
Inside the tank between secondary bushings and secondary coil.
How many primary phases are used to connect a single phase distribution transformer on a 3 phase 3 wire circuit?
Two
In a delta connection, the phase voltage is ____ the line voltage and the phase current is ____ the line current by the factor of 1.73.
The same; less than
What is the current in a transformer winding when connected in delta?
Windings current = line current / 1.73
Name 3 important factors in determining the size of line conductors.
Line voltage, the amount of power to be transmitted, mechanical strength.
List 5 of the most common shapes of stranded conductors.
Concentric round, compact round, compact sector, annular, segmental.
What are the best ways to locate a fault in the shortest amount of time?
With the use of faulted circuit indicators, patrolling the line, customer calls in.
What is a cable fault?
When the insulation on the wire or cable does not sufficiently confine the voltage.
What rule must be observed when hauling dynamite and the caps in the same truck?
In separate containers, in separate compartments.
What is a megger?
An ohm meter that measures high resistance.
The most common defect in insulators are _____?
Cracks in the porcelain.
What is the national electrical code definition of medium voltage ranges?
From 2001 volts to 3500 volts.
Define a splice.
The joining of two or more conductors.
List the 3 major components of an implosive compression splice for an ACSR conductor.
Steel sleeve inner, aluminum sleeve outer, aluminum sleeve.
What happens if a lead wire supplying one lamp in a series circuit is borken?
It interrupts the entire circuit.
Define lumen.
One unit of light output.
What is a reflector?
It is a surface that stops light ray and redirects it in a desired direction.
What are reflectors made of?
Porcelain, metal, silvered glass.
Gaseous conduction lamps have circuit limiting devices called ______.
Ballasts (choke coil)
A florescent lamp requires a _____ to limit circuit during operation.
Ballast.
Name 3 devices that are used to protect lines for abnormal voltages.
Surge arresters, shield wire, protector tubes.
A transformer is usually loaded to what percent of the name plate voltage rating?
125 to 150% for 1 to 2 hours at a time.
How is phase sequence designated?
Clockwise or counterclockwise. (123 or 321)
Which direction will the motor turn if a phase sequence of a 3 phase system is a 321?
Counter-clockwise.
How can you best protect yourself from back-feed?
Treat everything as if it is energized at full primary voltage (or ground it).
What is the maximum resistance that a ground should have?
25 ohms
When using a test instrument to measure resistance, what 3 factors effect the amount of resistance?
Resistance of the electrode, the contacts of resistance between electrode-earth, resistance of the surround earth.
How many indicating pointers does a maximeter have?
Two
Can a maximeter be removed from a conductor, reset to zero, and immediately be placed on another conductor?
No, it must be allowed to cool.
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.
Alternating circuit loads are generally described as being?
Resistive, inductive or capacitive loads.
List 3 factors which determine the amount of voltage that will be induced in a conductor.
The size, type, and length of the conductor.
What 3 factors determine the capacitance of a capacitor?
The area of plates, the distance between the plates, the type of dielectric used.
List 4 type of controls that are used with capacitors.
Time switched, time-temp, voltage, current.
List 5 factors which effect the amount and type of capacitor banks installed on distribution circuits.
Length of the circuit, residential lines, rural lines, commercial lines, inductrial lines.
What do you do when you size up a distribution job?
Identify all the hazards on the pole.
Name 3 types of wire tong saddles.
Pole type saddles, cross arm saddles, tower saddles.
When does a recloser usually lock out?
After 4 operations.
Name 3 types of substations.
Transmission, distribution, sub-transmission.
Name the 3 basic safety practices that you can follow to avoid many safety hazards.
Planning jobs, inspecting job sites, and wearing PPE.
Electrical fires are classified as what type of fires?
Class C fires.
Can a primary cell be recharged?
No.
List 4 factors that determines a cell’s circuit capacity.
The type of cell, rate of current flow, voltage, and length of time involved.
List 3 types of air switches.
Circuit breaker, air break, disconnect.
name 3 types of overhead line faults.
Short circuit, open circuit, and ground.
Why are capacitors less flexible in controlling voltage than other voltage regulating equipment?
They are switched on and off in the circuit.
Describe the appearance of a capacitor which would be installed on a distribution circuit.
A long rectangle box with 1 or 2 high voltage bushings, containing no secondary connections and has no moving parts.
List the 3 most common size of capacitors.
100, 150, and 200 KVA .
Why do most underground distribution circuits use looped cable routes?
To permit the lineman to isolate the faulted cable between 2 transformers and restore electrical to the service customer.
Which type of control is usually provided at a sub-station?
Local control.
Define harmonic.
A vibration whose frequency is an integer multiple of fundamental frequency.
How are harmonics created?
By non-linear loads on the power system.
In new 3 phase installations, what will help eliminate harmonic problems?
Balancing loads or providing oversized neutral conductors.
A typical crystalline silicon cell produces how much power?
Approximately 1 watt of power.
When connecting closed wye close wye, why do you always connect the primary and the secondary neutrals together?
To prevent fluctuating voltage on the secondary side.
What is the procedure to take out a transformer?
Make sure the remaining transformer will hold the load, then take out hot sec legs and tape. Take off high side, then remove neutral and tank grounds.
What is the laminated core of a transformer made of?
Steel
Explain the procedure for paralleling 2 transformers.
Check to make sure that they have the same phase and voltage rating, be within impedance percentage and polarity. If OK, then hook grounds and neutral, then primary side, then phase in secondary side with the voltmeter. Conductors are phased in when voltmeter reads zero.
What do you test blasting caps with before using them?
A galvanometer.
What do you do if a blasting cap misfires?
Wait 1/2 hour before investigating. Then dig next to the cap, set another charge to set it off.
What is the current limiting properties of an inductor called?
Inductive reactance.
Rubber glove cuffs are rated at what KVA?
10,000 volts per one inch.
What is the purpose of rubber gloves sticking gout of the protectors?
To protect against flash over.
What is the advantage of a wye over a delta system?
A wye can carry 73% more load current than a delta and provides a balanced load.
How do you determine the mechanical advantage using block and tackle?
Count the number of lines not to include the fall line to determine the mechanical advantage.
What is a semicon for?
Dispenses eddy currents.
What are the 4 ways of sagging?
Dynamometer, transit with targets, sagging with a stop watch, unsagwatch.
What is the primary reason for transposing of a transmission line?
To balance the line. Cut down on ratio & telephone interference.
Why is it dangerous to a lineman to open a primary neutral?
It may cause a fire because the neutral carries the unbalanced load of all single or 3 phase circuits.
In common distribution transformers, the tap changer is located in which coil?
The primary.
Explain the procedure for mouth to mouth respiration and closed chest heart massage.
Two short breaths to 15 chest compressions.
What is used when paralleling 2 secondary circuits?
Voltmeter
Can the distribution transformer used in a 2400 volt, 3 wire delta system be used in a 3 phase, 4 wire, 4160 volt wye system?
Yes.
What is the procedure for tagging?
Identify, test, isolate, ground.
TRUE OR FALSE? A transformer whose secondary voltage rating is 240/120 volts has two independent coils, each rated 120 volts.
False.
TRUE OR FALSE? A transformer bank whose secondary voltage readings to ground read - 120, 120, 208 is wye connected.
False.
TRUE OR FALSE? Single phasing occurs when one fuse blows on a wye-delta bank with the primary neutral bus grounded.
True.
TRUE OR FALSE? Two wires of a delta primary feeder can be used to supply 3 phase to a customer.
False?
TRUE OR FALSE? When the secondary breaker is opened on a CSP transformer, the primary becomes de-energized.
False.
TRUE OR FALSE? A 4160 volt transformer when used on 2400/4160 volt systems requires only one cutout and arrester.
False. (delta)
TRUE OR FALSE? A subtractive polarity transformer cannot be used in a bank of additive polarity transformers.
False.
TRUE OR FALSE? A single bushing transformer can be used on a delta primary system.
True.
