study guide, notes Flashcards
1
Q
why is a closed Y closed delta bank primary neutral floated?
A
to prevent balance or bank action - to prevent burning out the two remaining transformers when on fuse blows and creates an open, the bank continues to provide 3 phase power using two transformers instead of 3. Also to prevent back-feeding the line when a line becomes de-energized, or to prevent backfeeding the hi side of the transformer if the fuse becomes blown.
2
Q
why is a forth cutout installed on the primary neutral of a closed wye closed delta bank?
A
to prevent ferroresonance - when you lose your 3rd potential, your reactance and capacitance in the bank can build up to 10X the normal voltage, closing the 4th cutout (connecting the primary neutral bus to the system neutral or ground) will balance the voltage on the neutral bus preventing ferroresonance.
3
Q
on an open bank what KVA capacity do you have of the two transformers being used?
A
86.6%
4
Q
what must be done before climbing above a de-energized transformer?
A
isolate the secondary leads or ground with approved equipment.
5
Q
what do you need to do on a closed wye closd wye transformer bank?
A
tie the primary and secondary neutral bus to prevent high secondary voltages.
6
Q
what purpose does the case ground serve on a transformer?
A
to ground the case of the transformer and acts as your neutral on a single bushing transformer
7
Q
how do you find full load current?
A
KVA divided by primary or secondary voltage used. On primary use the voltage the transformer is using. On secondary use larger voltage supplied, if paralleled use paralleled voltage.
8
Q
how do you size two transformers to carry 3 phase balanced load?
A
multiply the 3 phase load by 57%. This would be the load on each transformer. The single phase load is added only to the “lighter transformer”
9
Q
how to fuse wye connected primary
A
KVA divided by primary voltage used, multiplied by design factor of 2 (utility spec will vary) round to nearest fuse size
10
Q
how to fuse closed delta connected primary
A
KVA divided by primary voltage used multiplied by 1.73, multiplied by design factor of 2 (utility spec will vary) round to nearest fuse size.
11
Q
how to fuse open delta primary
A
cutout with 2 bushings attached: KVA divided by primary voltage used multiplied by 1.73, multiplied by designed factor of 2 (utility spec will vary) round to nearest fuse size.
cutout with 1 bushing attached: KVA divided by primary voltage used, multiplied by designed factor of 2 (utility spec will vary) round to nearest fuse size
12
Q
transformer core; how does it work, what is made of
A
the core is the part of the transformer in which the magnetic field oscillates. it consists of laminated steel, insulated, and wound to a desired shape for the coils. the purpose of this thin sheet is to reduce the core loss and the heating produced in the core by insulating each sheet from the other.
13
Q
coils; what do they consist of, size
A
the coils consist of an insulated wire or bus bar wound around a wooden block to fit the core; the fewer the turns, the larger the wire. the insulation on the wire depends upon the voltage to be supplied to the coils. the two coils are referred to as an input and output coil. There is no electrical connection between the primary and secondary coil in a distribution transformer.
14
Q
how to get turns ratio of a transformer
A
primary voltage used divided by highest secondary voltage used. if paralleled use paralleled voltage
15
Q
describe transformer tank
A
the tank is used as a means for enclosing the assembled core and coils. it acts as a protective barrier for the high voltage and current carrying parts, and holds the coolant or transformer oil.
16
Q
transformer bushings; what are they used for, what are they made of?
A
used to bring the high and low voltage leads from the coils to the outer edge of the tank. the bushings are made of a strong wet-process porcelain which insulates the line leads form the tank.
17
Q
what are the 3 main parts of a CSP transformer?
A
circuit breaker on secondary side; external tank mounted lightning arrestor; internal high voltage fuse mounted in the primary bushing
18
Q
what are the two basic types of lightning arresters?
A
expulsion and valve
19
Q
what are the two main enemies of transformers?
A
high voltage surges and heating caused by overloading
20
Q
on a CSP transformer what coil is the circuit breaker on?
A
secondary
21
Q
transformer taps are used for what two purposes
A
to correct low primary voltage and to control voltage to a customer ( raise and lower voltage)
22
Q
standard taps for transformers are what?
A
5 taps total, middle tap 100%, then 4 - 2.5% taps, 2 - above 100%, 2 - below 100%
23
Q
when changing taps on a transformer, which coil are you affecting? primary or secondary?
A
primary
24
Q
what happens to the primary coil when changing the taps?
A
increasing the tap adds to the number of turns of the primary coil; therefore, lowering the secondary voltage and lowering the taps reduces the number of turns of the primary coil raising the secondary voltage.
25
when determining what tap to select on a transformer tap changer, what formula can be used?
actual voltage divided by desired voltage
26
what determines the amount of voltage drop when a transformer is fully loaded?
impedance
27
impedance must be how close when paralleling or banking transformers?
plus or minus 10%
28
how much capacity would you gain from using a closed delta bank instead of an open delta bank?
42.3%; 100% minus 57.7%
29
open wye - open delta or open delta - open delta bank KVA ratings Rules of thumb.
86. 6% of the two transformers
| 57. 7% of the initial three (if going form closed to open)
30
how to size the transformers on a open wye - open delta or open delta - open delta bank
multiply the 3 phase load by 57%, this is the load on each transformer. the single phase load is added only to the lighter transformer.
31
in closed wye - closed delta or closed delta - closed delta banks how is the load split between the transformers
the lighter pot carries two-thirds of the single phase load and each power pot carries one-third of the single phase load the 3 phase load splits one-third on each transformer
32
conditions exist on a wye-delta closed bank if the primary neutral bus is tie to the system neutral and one or two primary fuses are blown?
if a primary fuse is blown:
- the bank capacity is reduced to 57% of bank rating, possibly causing overloaded and transformer failure.
- also, the voltage measured on the neutral bus is on half the phase to ground voltage or when two primary fuses are blown, voltage on the neutral bus is at full phase to ground voltage (these two conditions also exits every time a closed wye-delta bank is energized or de-energized)
33
in open banks can CSP transformers be used
yes if future plans do not call for the closing of the delta
34
in wye-delta and delta-delta closed banks can CSP transformers be used
yes; only on 240 volt and 480 volt 3 phase 3 wire only. if used on for wire systems and the secondary breaker of the CSP opens it would act as an open neutral causing high secondary voltages.
35
in wye-wye closed banks can CSP and single bushing transformers be used?
yes
36
in delta-wye closed banks can CSP and single bushing transformers be used?
only two bushing transformers can be used, 2 bushing CSP transformers can be used
37
what are the five types of stranded conductor shapes?
concentric round, round, compact round, compact sector, annular, segmental
38
how are rubber gloves rated; phase to phase or phase to ground?
phase to phase
39
what type of hard hat is worn by electrical workers? how many volts are they tested to?
class E, 20,000 volts
40
what is the minimum size of protective grounds?
equipment must be capable of conducting the maximum fault current that could flow, for the time necessary to clear the fault, grounds must have ampacity greater than or equal to that of no. 2 awg
41
what 5 steps are taken for proper grounding?
need a low-resistance path to earth, clean connections, tight connections, connections made at proper points, adequate current carrying capacity or grounding equipment
42
what sizes do capacitors come in?
15, 25, 50, 150 and 200 KVA with the 100, 150 and 200 sizes most common
43
what is the proper procedure for pole top rescue?
```
call loudly to the injured employee
call for help
evaluate the situation
plan the rescue
climb to the proper rescue position
asses the casualties condition
rig the rescue rope or handline
lower victim to the ground
administer first aid/cpr
```
44
formula for peak value
1.414 x RMS
45
formula for RMS value
.707 x peak
46
RMS is also known as what?
effective voltage
47
what are the six types of substations?
```
step-up transmission
step-down transmission
distribution
industrial
customer owned
converter
```
48
what is a permanent fault?
where the circuit cannot be automatically reclosed, a line crew is needed to repair and re-energize the circuit
49
what is line loss? and formula
the amount of voltage lost by pushing current through resistance. I2XR
50
what are harmonics?
AC and voltage disturbances that can be represented by sine waves, but are at different frequencies of the fundamental 60 hertz sine wave: 30, 120 - 2nd harmonic, 180 - 3rd harmonics
51
how much more load can a wye system handle over a delta system?
73% more
52
a fire extinguisher used in an electrical environment must have what rating?
must be a C rated in combination with another rating
53
what is the purpose of transpositions?
to cancel out induced voltages and reduce electromagnetic fields that interfere with open wire telephone circuits
54
what type of transformer is used on series street lighting? why?
a constant current transformer, it is used to raise and lower the voltage automatically, depending on the number or street lights in the circuit. a constant current has to be maintained because if one lamp burns out the total resistance of the circuit becomes smaller and current would tend to increase.
55
what are the two basic distribution voltage regulators
induction and step
56
an induction voltage regulator is connected how with the load?
series
57
induction regulators as a rule have two series coils, by operating the coils in series how will they be rated? when the coils are paralleled?
+-10%, when in series, +- 5% when in parallel but carry twice the amperage
58
the step voltage regulator is basically what?
an auto transformer
59
the step voltage regulator is connected how with the line?
series
60
can the step voltage regulator coils be paralleled?
no
61
what do the load bonus settings do on a voltage regulator?
they are mechanical stops on the position indicator dial. allows the regulator to handle larger amounts of current, used when the voltage regulator becomes overloaded.
62
is external fuse protection required for voltage regulation
no, a regulator can be connected and disconnected form the power lines using a regulator by-pass switch
63
what must be done before the by-pass switch is operated on a regulator?
the voltage regulator indicator must be in the neutral position
64
should surge arrestors be installed on voltage regulators?
yes on the source and load side
65
T/F, two cutouts and arresters are needed on a wye connected transformer
false
66
T/F, series can happen when you contact two current carrying sources at the same time
false - second point of contact
67
T/F, if you have high primary voltage on a transformer your secondary voltage will be low
false
68
T/F, name plates are only needed if you don't know your phase to phase voltage
false
69
T/F, low voltage rubber gloves are needed if you are checking voltage on a new transformer
false
70
T/F, a 250 KVA transformer would have a additive polarity
false, below 200 KVA or 8660 volts is additive all others are subtractive
71
T/F you can connect the H2 bushing on a single bushing transformer only to the neutral
false, case ground and secondary neutral tie strap is considered the neutral and should be tied down.
72
T/F, a transformer can usually only be connected to one circuit voltage on the primary side
true
73
T/F, a delta connection will allow you to balance the system voltage better than a wye connection
false
74
T/F, the unlike bushings are connected together to make a wye connection
false
75
T/F, you must always use the same phase and bushing when paralleling transformers
false, same phase not same bushing
76
T/F, a transformer whose primary voltage rating is 4160/7200 volts can be used on a 7200/12470 system
false
77
T/F, a transformer whose secondary voltage rating is 277/480 has two secondary bushings
true
78
T/F, a 250 KVA transformer whose secondary voltage rating is 120/240 volt has three secondary bushings
false, transformers 100KVA and over have 4 secondary bushings
79
what are the two basic function of oil in a transformer?
cooling and insulation
80
underground loop fed transformers are connected through
a buss bar
81
how many phases of a feeder must be present to connect the open delta-delta bank?
must have 3 phases
82
what are the three most important things that should be considered from the nameplate of a transformer before installing it in a transformer bank
impedance, polarity, voltage
83
how are the internal secondary leads connected in parallel on a conventional transformer?
AC-BD, alley cat-bad dog, head to head-tail to tail
84
in common distribution transformers the tap changer is located in which coil?
primary coil
85
what is the main advantage of a wye secondary over a delta secondary?
efficiency - because the load is balanced
86
two 50 KVA transformers are connected open-delta/open-delta. what is the capacity of the bank?
50 KVA x 2= 100 KVA, X 86.6%, 100 x .866=
| 86.6 KVA
87
what types of transformers are used for primary metering?
current and potential
88
transformers are additive polarity if their KVA rating is less than?
200 KVA
89
transformer tap changers are located where?
located in the oil on the primary coil and the control handle is located above the oil
90
how are lightning arrestors connected?
in series with a resistor
91
what 3 advantages does bundling conductors have?
cuts down on corona loss, lower line loss, 50% of the reactance of a single conductor
92
define corona
an electrical discharge at the surface of a conductor accompanied by the ionization of the surrounding atmosphere. it can be accompanied by light and audible noise.
93
when banking transformers, what's a rule of thumb for the max safe rating for the bank?
three times the KVA of the smallest can
94
what is the element in apparant power that does not do any work?
KVAR
95
1 watt equals?
one amp flowing under pressure of 1 volt
96
how many watts equal on horsepower?
746 watts
97
define impedance
total opposition to flow of current in AC circuit, measured on ohms
98
define inductance
ability to induce a magnetic field on a conductor measured in Henery's
99
what type of transformer is used for series street lighting?
constant current transformer
100
3 types of faults?
open circuit, short circuit, grounded fault
101
what's the most common reason transmission line failure?
insulation flashover
102
vector is what?
line having definite length and direction
103
how is a current transformer connected?
series
104
how is a potential transformer connected?
parallel
105
define circular mil
a circle with a diameter of one one-thousandth of an inch
106
volts and amps are ________ proportional
inversly
107
what percent of electrical contractors worked in the electrical field beforehand?
83%
108
3 main causes of accidents
human element, acts of nature, mechanical failure
109
natural enemy of rubber gloves
oil and grease
110
how often are hot sticks tested?
every 2 years
111
what would you use to cover a primary insulator?
rubber hood
112
max exposure for rubber goods is?
36KV
113
an enclosed space at 5 feet requires what?
mechanical retrieval device, (tripod)
114
oxygen level in an enclosed space: max, normal, minimum
23. 5 max
20. 8 normal
19. 5 minimum
115
what's the greatest risk of bloodbourne pathogen?
hepatitis B
116
minimum overlap distance of an extension ladder is
3 feet
117
what's the safe distance from machinery for swing radius
6 feet
118
what is found in PVC that can cause cancer
carcinogens
119
how many IBEW vice presidential districts
11
120
order that union meeting is conducted
Roberts Rules of order
121
type of light is used in fiber optic
infrared
122
extra high voltage is considered what range
34KV and up
123
how long (in cycles) does a recloser hold the line open for?
60 cycles, a second
124
a 3 phase line can use wire __% smaller and hold the same load as 1 phase 2 wire system
75%
125
defibrillation can occur from how much current for how long?
1 amp for .01 of a second
126
how often to test ground cables?
every 2 years
127
how many feet to keep away from lines in a sub
15 feet
128
turns ratio and voltage ratio are _______ proportional
directly
129
power factor =
true power divided by apparent power
130
when do you test rubber blankets and sleeves
every 12 months
131
what type of device is a transformer?
an electromagnetic device
132
what size hole for a 5/8" bolt
11/16"
133
why do we put aluminium over copper?
salts in the copper will corrode the aluminium
134
percent efficient of knots, hitches and splices?
knots 50%
hitches 75%
splices 85%
135
how many lumens = one candle power?
12.57
136
where should capacitors be installed
near the customer
137
which way does a capacitor improve power factor in line, towards the sub or away
from the point installed back to the sub or source
138
in capacitors what gives them more capacitance?
the size of the plate, larger the plate the more capacitance, the closer the plates the more capacitance
139
what does a capacitor consist of?
two thin pieces of metal or foil separated by a dielectric or insulator, and is generally rolled or folded. it is then inserted in a metal case along with a discharge liquid. at the top are one or two high voltage bushings
140
transformers work on the principal of
mutual induction
141
what does KVAR stand for?
kilo volt amps reactive
142
what is polarity in a transformer?
direction of current flow between the primary and secondary
143
what do you use when raising conductor to prevent conductor from falling to other side
holding tong
144
what determines the strength of magnetic field when current flows through a conductor
amount of current
145
OSHA Transmission and Distribution is covered under what article
1910.269
146
OSHA new construction is covered by
1926 of standard 29 CFR and 1926.957 (a)(1)
147
formula for fall line load
weight of object + (10% weight of object X # of sheaves
rope passes over )
___________________________________________
mechanical advantage
148
T/F, horizontal axis is a group that modern wind turbines fall into
true
149
T/F in an inductive circuit, the voltage leads the current by 90 degrees
true, ELI the ICE man
150
T/F the external air gap of a distribution class surge arrester is designed to prevent sparkover by normal system voltage if the lightning arrestor fails
true
151
T/F if lightning arrestor connections are too long, too much resistance might force high voltage surges into the transformer.
true
152
T/F, in wiring the arrestor connections, the wire must be smaller than the primary drop
false
153
what is the safety factor of new rope compared to old rope
new rope is 5 to one, old rope is 10 to one (6 months is considered old)
154
what three things do you look for in and injured person?
response, bleeding, pulse
155
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.
156
what 3 things determine pole depth?
soil conditions, height of pole, and location
157
can porcelain withstand more compression or tension
compression
158
what is the main advantage of pin type insulators?
cheaper and requires a shorter pole for the same overhead clearance
159
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 at 32 steps of 5/8%. (the high side is connected in parallel and the secondary is connected in series)
160
what is a constant current transformer used for and what things must you remember about them?
it is used for street lighting. you must connect the secondary side first, it has movable secondary coil
161
what are the parts of a rope?
the fibers, the yarns, and the strands
162
can a line without a load still carry a current?
yes it can carry a charging current of as much as 20 amps
163
why do reclosers hold the line open longer on the third and fourth operations?
to give the secionalizer time to operate.
164
a recloser must always be backed up by what?
a sectionalizer.
165
a sectionalizer only operates under what
no current conditions
166
what ratio makes up power factor?
true power to apparent power
167
what is a counterpoise?
grounding grid for a sub station or a footer on a transmission line
168
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.
169
when fuzzing insulators do you go by length of arc or by intensity of sound?
intensity of sound
170
what device breaks the arc on air break switches?
arcing horns
171
what is line loss?
the amount of voltage lost by pushing a current through a resistance.
172
in general, the maximum bending radius of cable is how many times the diameter of the cable?
8 times and should not be bent when temperature is below 14 degrees F
173
which windings of the induction regulator is mounted so it can rotate on its' axis?
shunt windings
174
what is the maximum ground resistance that a structure can have?
25 ohms
175
heavy loaded lines are protected by the use of
OCB (OCR), sectionalizers, and fuse cutouts
176
sagging charts are used to show what 2 things for spans to a line where tension is used?
distance and temperature
177
what is a snatch block?
a closed sheave
178
what 2 things should be checked before final sag is started?
anchors and guys
179
what is bus work in a substation?
aluminum or copper bars that connect equipment together
180
in a standard distribution transformer, are the primary and secondary coils physically connected together?
no. they are magnetically coupled together
181
how are straight line pole generally set?
gain to gain or back to back
182
is a series street line connected in line
yes
183
what is the force which makes electricity flow?
EMF electromotive force
184
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 movable, so when one light burns out, it moves, adjusting the voltage. (amps stay the same)
185
how far must unqualified employees stay away from apparatus energized up to 5,000 volts
10 feet
186
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
187
adding parallel loads to a circuit will ________ total circuit resistance and ________ the total circuit current.
decrease, increase
188
what is the polarity of electrons when they enter a load? when they leave?
negative, positive
189
how does an analog meter operate?
on the magnetic principal that like poles repel each other
190
list the 3 steps that should be followed when reading a multimeter.
determine what the meter indicates, determine the full scale value of the mater, read the meter.
191
what are 2 basic types of analog ohmmeters?
the series and the shunt
192
name 2 advantages for 4 wire feeders over 3 wire feeders
cheaper to build, more efficient
193
what is created whenever current flows through a conductor?
a magnetic field is created
194
list the three 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.
195
how many primary phases are used to connect a single phase distribution transformer on a 3 phase 3 wire circuit?
two
196
what is the current in a transformer winding when connected in delta?
windings current = line current/1.73
197
name 3 important factors in determining the size of line conductors
line voltage; the amount of power to be transmitted; mechanical strength.
198
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 .
199
what is a cable fault?
when the insulation on the wire or cable does not sufficiently confine the voltage.
200
what rule must be observed when hauling dynamite and the caps in the same truck?
in separate containers, in separate compartments.
201
what is a megger?
an ohm meter that measures high resistance.
202
the most common defect in insulators are
cracks in the porcelain.
203
what is the national electrical code definition of medium voltage ranges?
from 2001 volts to 3500 volts
204
define a splice
the joining of two or more conductors
205
list the 3 major components of an implosive compression splice for an ACSR conductor.
steel sleeve inner. aluminum sleeve outer, aluminum sleeve.
206
what is a reflector?
it is a surface that stops light ray and redirects it in a desired direction.
207
what are reflectors made of
porcelain, metal, silvered glass
208
gaseous conduction lamps have circuit limiting devices called
ballasts (choke coil)
209
name 3 devices that are used to protect lines from abnormal voltages
surge arresters, shield wire (static wire), protector tubes.
210
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
211
how is a phase sequence designated?
clockwise or counterclockwise: (123 or 321)
212
what is the maximum resistance that a ground should have?
25 ohms
213
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 surrounding earth.
214
how many indicating pointers does a maximeter have?
two
215
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
216
what is the RMS value of AC equal to?
.707 times the peak value
217
what is the peak value of AC equal to?
1.414 times the RMS value
218
alternating circuit loads are generally described as being?
resistive, inductive or capacitive loads
219
list the 3 factors which determine the amount of voltage that will be induced in a conductor.
the size, type and length of the conductor
220
what 3 factors determine the capacitance of a capacitor?
the area of plates, the distance between the plates, the type of dielectric used.
221
list 4 type of controls that are used with capacitors
time switched, time-temp, voltage, current
222
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, industrial lines
223
what do you do when you size up a distribution job?
identify all the hazards on the pole.
224
name 3 types of wire tong saddles
pole type saddles, cross arm saddles, tower saddles
225
when does a recloser usually lock out?
after 4 operations
226
name the 3 basic safety practices that you can follow to avoid many safety hazards
planning jobs, inspecting job sites, and wearing PPE
227
electrical fires are classified as what type of fires?
class C fires
228
can a primary cell be recharged?
NO
229
list 4 factors that determines a cell's circuit capacity.
the type of cell, rate of current flow, voltage, and lingth of time involved.
230
list 3 types of air switches
circuit breaker, air break, disconnect
231
name 3 types of overhead line faults
short circuit, open circuit, and ground
232
why are capacitors less flexible in controlling voltage than other voltage regulating equipment?
they are switched on and off in the circuit
233
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.
234
list the 3 most common sizes of capacitors
100, 150, and 200 KVA
235
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 service to the customer
236
which type of control is usually provided at a sub-station?
local control
237
define harmonic
a vibration whose frequency is an integer multiple of fundamental frequency
238
how are harmonics created?
by non-linear loads of the power system
239
in new 3 phase installation, what will help eliminate harmonic problems?
balancing loads or providing oversized neutral conductors
240
a typical crystalline silicon cell produces how much power?
approximately 1 watt of power
241
what is the laminated core of a transformer made of?
steel
242
what do you test blasting caps with before using them?
a galvanometer
243
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.
244
what is the current limiting properties of an inductor called?
inductive reactance.
245
rubber glove cuffs are rate at what KVA?
10,000 volts per one inch
246
what is the purpose of rubber gloves sticking out of the protectors?
to protect against flash over.
247
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.
248
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.
249
what is a semicon for?
dispenses eddy currents
250
what are the 4 ways of sagging?
dynamometer, transit with targets, sagging with a stop watch, unsagwatch
251
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
252
what is used when paralleling 2 secondary circuits?
voltmeter
253
what is the procedure for tagging
identify, test, isolate, ground
254
single phasing occurs when one fuse blows on a wye-delta bank with the primary neutral bus grounded.
false, when one fuse blows and the primary neutral bus is grounded, the bank continues to operate as before except at 57% capacity. that is one reason we float the primary neutral on a wye delta bank.
255
explain the procedure of paralleling an additive and subtractive transformer
ground the cans, install both neutrals, heat up top side of one can, install the secondary , heat up the other can and phase the secondary with a meter
256
define transformer
an electrical apparatus that changes electrical energy from one potential to another potential
257
can you ground a transformer in a delta power bank?
yes only one can
258
what are four ways to cool transformers?
air oil fans fins
259
what function does oil have in an transformer?
to cool and insulate
260
explain the procedure for paralleling 2 transformers
select can with proper voltage impedance and check polarity, hang can connect all grounds and the neutral, connect primary to same phase, phase secondary legs with volt meter and make proper connection
261
when working in an unknown area on a distribution line, low do you verify for yourself what the primary voltage of the line is?
check the name plate on the transformer or with phasing sticks
262
what are the dangers of using electronic blasting caps under a circuit?
the caps could be set off by induction or by communication interference or the blast could blow lead wires into primary
263
primary metering requires what kind of transformers?
potential transformer and current transformer
264
mechanical jumpers should be checked for what 3 things?
good insulation, proper wire size (adequate current carrying capacity and tight (clean) connection
265
when ground framing H structures, what must be done before putting on knee braces and X braces
make sure the structure is square
266
what precaution should be taken when de-energizing pole top termination coming from underground?
to eliminate capacitance form the underground feed
267
why does underground cable rated above 5 KVA require a grounded sheild?
to bleed off capacitance
268
when 3 transformers are banked together closed wye closed wye why is the midpoint on the primary side grounded?
to prevent excessive and fluctuating voltage on the secondary side
269
what is the advantage of a 3 phase wye secondary?
more efficient, you can supply single phase and 3 phases, more balanced load
270
on an open wye open delta, what will occur if the primary neutral becomes disconnected from the system neutral?
one half of the phase to ground primary voltage will be present
271
name 3 devices that are used to protect lines from abnormal voltage?
surge arresters, shield wire, protector tubes
272
a transformer is usually loaded to what percent of the name plate voltage rating?
150% to 150% for 1 to 2 hours
273
how is phase sequence designated?
clockwise or counter - clock wise (ABC CBA)
274
how to find right tap when using tap changers?
find turns ratio, primary rating divided by secondary rating divide actual primary voltage by the turn ratio, gives you 100% voltage then divide by that by all percentages, or actual voltage divided by desired voltage
275
what does the term frequency mean in relation to AC current and voltage?
the number of complete cycles that occurs in a given time measured in hertz
276
what is the maximum resistance that a ground should have?
25 ohms
277
what is the purpose of the internal discharge resistor installed in a capacitor unit?
will reduce voltage 50 volts or less within 5 minutes
278
list for reasons why capacitors may be installed on a distribution circuit with a lagging power factor?
reduces lagging components of circuit current
increase voltage level at the load
increase power factor of the source generator
reduce investments in the system facilities
279
alternating circuit loads are generally described as being
resistive, inductive or capacitive loads
280
list 3 factors which determine the amount of voltage that will be induced in a conductor
the size, type and length of conductor
281
what 2 things must be checked when selecting a pulling grip for use?
correct size (diameter) and correct type of wire
282
on a 25 KVA transformer nameplate rating 7620/120/240 volt what would the amperage values on the secondary side be?
KVA/voltage on secondary side 25000/120= 208.33, 25000/240= 104.16 (if question doesn't specify if the secondary coils are series or paralleled give both)
283
what is the difference between 3 wire single phase and 3 phase secondary?
2 phases and a neutral, 3 phases and a neutral
284
how do you field test a phase set?
test by battery or or on an energized line phase to ground voltage and phase to phase voltage.
285
what is the purpose of a stress cone?
to dissipate eddy currents
286
what is as autotransformer?
it is a one-winding transformer the same winding is used for both the primary and secondary small-efficient transformer
287
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
288
if a line is balanced with 10 amps on A phase, and on B phase, and on C phase, how many amps are on neutral?
Zero (0) amps, well balanced
289
what does getting in series mean?
it is getting between the line and load or between the line and ground or between the line and the line in essence becoming a human mack
290
how would you check rubber gloves in the field?
check the voltage rating the last inspection date give rubber gloves visual and air test give a visual check for cuts and embedded materials on protectors
291
what is a 3 phase transformer?
3 single phase transformers in one can using one core
292
if one circuit is regulated (with a voltage regulator) and the other unregulated can they be tied together without other immediate action?
no the circuit that is regulated must be set to zero before they can be tied in with a phasing set
293
explain the procedure for removing grounds on a distribution or transmission line
furthest to nearest then ground
294
in a wye underground system shielded cable requires the installation of a neutral where concentric cable does not
cable that does not come with a built in concentric cable requires a neutral be laid next to it
295
how do you determine the rotation of motors from the given phase sequence?
write the sequence out 3 times if ABC shows up then its CW if not then CCW
296
resistance to the flow of current in a conductor is governed by what?
the size of the conductor, length of the conductor, type of material, and the temperature
297
formula for power factor
kW(true power)
_______________________________________
kVA(apparent,available power) X Pf(power factor)
298
why must transformers that are being banked have almost the same impedance?
the transformer with the least impedance will carry most of the load
299
what are Eddy currents?
low voltage, short circuited currents which are caused to flow in various areas of the core by the magnetic lines of force cutting across the core in varying intensities.
