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.2.
, 2010
1. Unit 1. 5
2. Unit 2. 10
.3. Unit 3. 15
4. Unit 4. 21
5. Unit 5. 26
6. Unit 6. 33
7. Unit 7. 38
8. Unit 8. 43
9. Unit 9. 50
. 10. Unit 10. 53
1.
. 67
2.
. 74
1. UNIT 1.
1. ,
.
oper a tion el e ctric s y stem c o mplex
b a sic eff e ctively eff i ciently o perate
altern a ting n e cessary e lectr i city gr o ss
ch a nge personn e l b u siness bec au se
displ ay ed exc e ss i ndustries o pposite
s a me st ea dily del i very acc o mmodate
w ay eff e ct fac i lities v o ltage
m a de m ea surement d i gitally f o llowing
sh a pe r ea dily compos i tion w a tt
disp a tch f u ndamental prov i de ret ur ned
m a gnet c u stomer l i ght c ir cuit
underst a nding c u rrent appl i ed p er
m a ximum o ne p i pe t er med
g a llons d oe s t y pe c er tain
b a ttery cond u ctor rise th er mocouple
a tom res u lt t i me ref er
m a nner o ther s i ze transf er
ch a racteristics s u bstance pr i me conv er t
compl e ting u sed ent ire s our ce
rep ea ted u nit sc ie nce a lternating
m e ter c u bic w ire c a lled
ea ch f ew h igher f or m
f ee t prod u ce des i rable c au se
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m ea ns u tilize env i ronment f or ce
ea sily rev iew requ i red au tomatic
h ea t f u el f i re a ll
imm e diately u sually violent imp or tant
air p ower g oa l ap ar tment
comp are d our h o me pl a nt
v a rious hour fl ow ing ch ar ge
th ere t ower l oa d br a nch
th eir fl our l ow f ar
v a ry fl ower c oa l p a ss
c are ful s our bel owar ticle
w here sh ower kn ow n h ar mful
b are p ower ful contr o l adv a ntage
2. .
to operate , , ;
to dispatch ;
a business , ;
to complete , ; ;
unidirectional ();
to rise , , ;
to increase , ;
to decrease , ;
by means of , ;
in the same manner ;
a junction ;
to turn on / off / , ;
a means of .
3. 1. Fundamentals of Electricity, ( ), ( ), ( ). .
TEXT 1. FUNDAMENTALS OF ELECTRICITY
The operation of an electric system is not complex. To effectively and efficiently operate and dispatch in an electric system, a fundamental understanding of basic electricity is necessary.
Electricity is used to light homes, businesses and operate industries. When a water delivery system has water flowing, the water flows to the customers by pipes. The excess water is not returned directly to the source. In electrical systems, electricity flows to the customers by wire. In an electrical system, the current is returned to the source, completing the circuit. There are two types of electric current: direct current (DC) and alternating current (AC).
Direct current is so called because it flows directly to the load and returns to the source. It is unidirectional by character.
Alternating current does not immediately change its direction. The change rises to a maximum flow in one direction, and then it decreases to zero. Next it rises to a maximum flow in the opposite direction, and then decreases to zero. This entire sequence is called a cycle. In power systems, the frequency of complete cycles is repeated 60 (sixty) times each second.
Current flow is expressed in units termed amperes (amps). This is similar to the measurement of the water flow by units called cubic feet per second or gallons per second. Amperes are read by means of ammeters or displayed digitally.
All substances do not accommodate electrical current flow in the same manner. Materials which readily allow current flow are termed conductors. Materials which do not readily allow current flow are termed insulators.
There are six main ways to produce electricity. Electricity may be produced by means of friction. Friction is used to produce electricity by rubbing two materials together. Electricity may be produced by pressure. Pressure can be utilized to produce electricity by applying pressure to a crystal of certain materials. The crystal is placed between two metal sheets with pressure being applied. Then voltage can be registered between the two plates. Certain crystals which possess this particular characteristic are quartz and tourmaline. Electricity may be produced by heat. This is exhibited in the form of a thermocouple. A thermocouple uses two dissimilar metals. The two metals are subjected to the direct action of heat and can cause electricity at the junction of these two metals. Electricity may be produced by chemical reaction. The current delivered by batteries is termed DC. Electricity may be produced by light. Light may be used to produce electricity in the action of light striking photosensitive materials. The photovoltaic effect is used in the form of a light meter which utilizes a selenium alloy iron and a transparent material. Photocells used in turning on and off lighting systems also utilize this means of producing electricity. Electricity may also be produced by magnetism. Magnetism may be used to produce electricity by utilizing the relative movement of a magnet and a wire. This will result in the cutting the lines of force. Anytime the lines of force are cut by a conductor, electricity is produced.
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4. , :
1) , work, operation, job
2) , delivery, transfer, flow
3) buyer, customer, operator
4) , customer, load, wire
5) , wire, line, circuit
6) current, customer, conductor
7) line, load, flow
8) frequency, voltage, current
9) frequency, voltage, current
10) photoactor, photocathode, photocell
5. .
1)
2)
3)
4)
5)
6) ,
7)
8)
9)
10)
6. .
1) Where is electricity used?
2) What types of electric current are there?
3) What is the basic difference between direct current and alternating current?
4) What units are used to measure current?
5) Is there any difference between conductors and insulators?
7. .
8. .
2. UNIT 2.
1. ,
.
c onsidering c ircuit surrounding s flu x
c urrent s in c e flow s ma x imum
cir c uit c ycle si z e e x plain
magneti c s ine increa s ing basi cs
c an c ertain oppo s e s e x cess
cy c le resi s tan c e re si stive mi x ing
c ause s ame z ero e x press
pea k re c eive ri s e e x change
che ck lo ss degree s a x ial
effi c iency direc tionwh ich v oltage
accompli sh alterna tionw ill de v ice
sh ape situa tionw ave v alue
ra ti o opera tionwh ere wa v e
poten t ial induc tionw ould v oltmeter
ter t iary connec tionwh en relati v e
establi sh sec tionw ire subdi v ision
pre ss ure transmi ssionw ound v ery
sh ould propor tionw inding di v ide
be h ind ch ange e qu ip ma g netic
h inder ac t ually e qui pment ma g nitude
h ave rea ch e qu al la g
h igh ch eck re qu ire de g ree
h andle mu t ual e qu ivalent re g ard
wh o combus tio n qu ick fi g ure
wh ose fea t ure s qu are to g ether
wh ole struc t ure qu ality ne g ative
wh om manufac t ure qu antity lan g uage
volta g e bo thth en alternati ng
lar g e some th ing th ere surroundi ng
ener g y th ird th at si ng le
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ener g ize th rough th ey ba n k
g enerator no th ing th is windi ng
dama g e me th od th ese meteri ng
in j ury streng th ano th er relayi ng
a dj ustable th ick wi th in readi ng s
chan g e ma th ematics wi th out stre ng th
2. :
an alternating current circuit ;
a magnetic field ;
inductance ; , ;
both the current and the voltage , ;
magnitude ;
to lag behind , ;
an induction motor ;
a transformer ;
a reactor () ; ;
to energize () ; ;
to de-energize , ; ;
;
a collapsing field (.)
to flash over ; ;
a circuit breaker ;
a field breaker ;
a coil (); (); ;
;
a turn ; ;
spacing ; ; ;
a winding ;
power operations personnel ;
to transfer power ; ;
a core ; ;
mutual inductance ;
self-inductance , ;
3. 2. Inductance,
, , . . , -.
TEXT 2. INDUCTANCE
In considering alternating current circuits, remember anytime current flows, a magnetic field surrounds the conductor. That flux (magnetic field) surrounding it is relative to the direction of current flow in the conductor. Since the alternating current circuit entails the alternation of the current flow first in one direction and then in another, the flux is also increasing and decreasing. As the current flow changes direction, the direction of the flux surrounding that conductor also changes.
In order to fully understand alternating current circuits well consider certain other phenomena. The first of which we will term inductance. Inductance is the property of an electrical circuit which opposes the change of current. In an alternating current circuit both the current and the voltage alternate in magnitude and polarity (direction). Since the current and voltage alternate, the phenomenon of inductance retards the rate at which the current can change. It does not hinder the changing of the voltage. In a 60 (sixty) cycle system, if there is inductance in a circuit, the inductance actually retards and causes the current to lag behind the voltage sine wave.
In simple terms, the effect of inductance upon an AC circuit is that the inductance retards the current sine waves and causes them to lag behind the voltage sine waves. If there is no inductance in a circuit and it is purely resistive, the current and the voltage change at the same rate. They reach maximum at the same time and they reach zero at the same time. When inductance is introduced into a circuit, the inductance causes the current sine wave to lag behind that of the voltage sine wave. When inductance is introduced into a circuit, the current and the voltage do not rise to maximum at the same time, nor do they fall to zero at the same time. They peak and reach zero at different times. A complete cycle is said to be 360 electrical degrees.
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The maximum amount that inductance can cause current to lag behind the voltage would be 90 (ninety) electrical degrees. This is evident in any electrical circuit where there is a large number of induction motors. A large size or number of induction motors, transformers, reactors or other equipment which introduces inductance into an electrical circuit causes the current to lag behind the voltage.
Any time the current and the voltage do not peak at the same time, there is a loss of efficiency. This means that it requires more current to do the same amount of work as would have previously been accomplished if the current and the voltage were both in phase. The efficiency of the equipment operation is less if the current and the voltage do not peak or reach zero at the same time.
Inductance in a direct current (DC) circuit is significant when there is a great increase or decrease of current flow in that circuit and upon energizing or de-energizing that circuit. When a DC system is de-energized rapidly the collapsing field in the DC circuit produces a very high induced voltage. This induced voltage is relative to the rate at which the lines force collapse and to the strength of the magnetic field. Actually this can be so great in magnitude as to flash over certain pieces of equipment. This induced voltage in a situation like this can be many times that of the normal circuit voltage. This may be evidenced on the opening of the generator field breakers.
Inductance of a circuit is measured in units of measurement termed Henries. A Henry is used to measure the inductance of a coil. Inductance can not be measured in ohms. A simple resistor can be checked with an ohmmeter. The inductance of a circuit is dependent on a number of factors. It is dependent upon the number of turns, the spacing between the turns, the shape of the coils, the diameter of the coil, the core material, the wire size, the number of layers of windings and the manner in which it is wound. Each of these things is involved in determining the inductance of a circuit. The calculation of the circuit inductance is something which is not ordinarily calculated by power operations personnel. However, inductance is a very important factor with regard to the operation of power systems. The operation of transformers is directly attributable to inductance.
Inductance is the ability to transfer power from one conductor to another conductor without a direct electrical connection. In a transformer, two conductors are wound around a common core. Because the flux is rapidly expanding at the rate of 60 cycles per second, inductance is present between the two coils. The secondary winding of the transformer has a voltage induced therein. If the secondary circuit is completed, current will flow.
Energy can be transferred from one circuit to the other by induction. This is commonly termed mutual induction. That is a transfer of power or voltage from one circuit to the other without a direct electrical connection. Self-inductance is another term which refers to the induction within one circuit.
4. ,
:
1) alternating current circuits
2) a current flow
3) a voltage sine wave
4) an induction motor
5) equipment operation
6) generator field breakers
7) the circuit voltage
8) the core material
9) the wire size
10) the circuit inductance
11) power operations personnel
12) power systems
5.
:.
| 1) field 2) flux 3) current 4) circuit 5) voltage 6) degree 7) equipment 8) magnitude 9) breaker 10) turn 11) core 12) winding 13) coil 14) conductor 15) transfer | 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) , 13) , 14) 15) |
6.
:
1) , ;
2) , ;
3) , , ;
3) , ;
4) () , , ;
5) ;
6) ;
7) , ;
8) , ;
9) , ;
10) ;
11) ;
12) , ;
13) () , ;
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14) ;
15) .
7.
.
8. .
3. UNIT 3.
1. ,
.
Ref er, c er tain, c ir cuit, t ur n, th ir d, t er tiary, s er ve, comm er cial, p ur pose.
Pr e viously, betw ee n, f ie ld, m ean s, incr ea se, decr ea se, k ee p, m e tering,
ea sily.
Fl u x, cond u ctor, c u rrent, ind u ction, o ne, but, en ou gh, m u ch, n o thing.
Prev a lent, b a sis, ch a nge, gr ea t, a ble, s a me.
Compr i se, w i nding, beh i nd, l i kew i se, h i gh, wh y, pr i mary, c y cle, suppl y.
V i c i n i t y, cons i der, s i ngle, s i gn i f i cance, equ i pment, ab i l i t y, s y stem.
S our ce, m ore, c au se, c a ll, sm a ll, imp or tant.
Prod u ce, m u t u al, distrib u tion, n eu tral, val ue, u se, ind u ced.
R a pidly, b a nk, v a lue, cap a city, m a nner t a p.
Am ou nt, h ow, f ou nd, d ow n, n ow,r ou nd.
Des ire d, requi re d, h igher, w ire.
Reg ar d,ret ar d, f ar, ex a mple.
Transform er, whenev er, rel a tive, second a ry, a noth er, prop er ty.
2. .
a bank ;
losses ;
to step up ();
to step down ();
a transmission system ;
a tertiary winding ;
an instrument transformer ;
a current transformer ;
a potential transformer ;
a distribution transformer ,
;
a power transformer () ;
a one-to-one transformer
, ;
potential , , ;
metering equipment , ;
relaying equipment ;
the primary ;
the secondary ;
opposition ; ;
a stack , ; , ;
capacitance ; ;
resistance () ; ;
impedance ;
billing ; ;
utilities () ;
a tap changer ( );
a load tap changer ( )
;
excitation ; ;
to shut down ; ; ;
setting .
3. 3 Transformers.
-. , - 1) , 2) . .
TEXT 3. TRANSFORMERS
Part I
To understand the operation of a transformer, one must refer to certain basics which were previously explained. Voltage is produced whenever there is relative motion between a magnetic field and a conductor. Whenever current flows in a conductor, a magnetic field (flux) is established surrounding that conductor. The magnetic field (flux) is most prevalent in the vicinity of that conductor.
These basics are the basis for transformation of currents and voltages. A transformer may be defined as a piece of apparatus without continuously moving parts which by electromagnetic induction transforms alternating voltage and current in one winding into alternating voltage and current in one or more other windings, usually at different values of voltage and current. It consists essentially of an iron core on which are wound the primary and the secondary windings. The core comprises the means by which the flux is concentrated. The rapidly changing alternating current produces rapidly changing flux. As this flux increases and decreases, there is relative motion between flux from windings of the source side of the bank and the secondary windings. This produces mutual inductance. Mutual inductance is the ability to transfer energy from one circuit to the other circuit without a direct connection.
Transformers do not produce electricity. They merely transform it from one level to another. The total amount of power does not increase. There are losses which are associated with transformers. Anytime the voltage is stepped down, the current is stepped up by the same ratio. Likewise, when the voltage is stepped up, the current is stepped down by the same ratio. This is why transmission systems utilize high voltage. The higher the voltage the less the current for a given value of power. Less AC decreases losses.
The winding of a transformer which is electrically connected to the source of power is called the primary winding. The load side winding of a transformer is termed the secondary winding. Transformers with a third winding require a term other than primary and secondary. The third winding of a power transformer is termed the tertiary winding. A transformer may be used to step the voltage up or down. It may also serve to step the current up or down.
Let us consider the basic types of transformers. First, instrument transformers are of significance. Current transformers and potential transformers are instrument transformers. Instrument transformers transform potential or current to values which can be easily used on metering and relaying equipment. The potential transformer transforms voltage from a high value to a lower value, the most common of which is 120 volts AC. The potential transformer is similar to a power transformer, but can only handle small volt-ampere values. The load of a potential transformer must be considerably less than that normally found on a power transformer. A potential transformer will transform voltage. It can only handle enough current for metering and relaying.
Another type of instrument transformers is the current transformer. The current transformer transforms current from higher values to lower values. High values cannot easily be used in metering and relaying circuits. Low values may easily be used in metering and relaying circuits. The current transformer is rated in ratio of, for example 600:5. MR represents a multi-ratio current transformer. The 5 is not the maximum of current that can flow in the secondary, but is an easy reference to what is commonly referred to as a full scale deflection on an ammeter. Unlike a potential transformer a current transformer is a very low impedance device. The secondary of the current transformer offers very little opposition to the current flow. The primary may be the conductor and the secondary may represent a number of turns around that conductor. The current flow through the primary establishes flux. Based upon the number of turns, the secondary produces a current flow proportional to but much less than the primary current.
If the current is stepped down, the voltage must be stepped up. Anytime the current is stepped up, the voltage must be stepped down. The voltage is stepped down on a potential transformer and the current is stepped up. On a current transformer, the current is stepped down and the voltage is stepped up.
There is very little voltage associated with a CT secondary voltage. This is true because the primary of that current transformer is actually nothing more than one phase of the conductor itself. The voltage across two points on one phase of the primary is no more than millivolts.
4. ,
, :
1) , ;
2) , ;
3) , - ;
4) ;
5) , ;
6) ;
7) , ;
8) , ;
9) ;
10) ().
5.
.
6. .
4. UNIT 4.
1. ,
:
/ Λ / an o ther, , , ;
/ ju: / distrib u tion, , , ;
/ : / p ur pose, , , ;
/ i / s y stem, , , ;
/ ai / suppl ie s, , , ;
/ i: / ea sily, , , ;
/ ð / th ey, , , ;
/ ∫n / distribu tion, , , ;
2. :
a lightning arrestor ;
lightning surges () ;
to extinguish the arc () ;
a surge crest voltage ;
; ;
to bypass (.) ;
a surge discharge ;
an outage , ; ,
(); ;
a failure ( ); ; ; ;
a circuit breaker bushing ;
to furnish a path , ;
to cease to conduct (); . ;
rated voltage () ;
an insurance ;
severity ;
to break down ; ;
to fail ; ; ;
;
ratio .
3. 4. Transformers, Part 2. -
. , - . .
TEXT 4. TRANSFORMERS
Part 2
Another type of transformer is the distribution transformer. A distribution transformer is a transformer with a capacity much less than the power transformer. It is normally used for the purpose of providing service to customers. We see distribution transformers on poles or on concrete pads for industrial or commercial application. They provide power for certain services in our systems.
The power transformer is considered a major transformer which is normally of a substantial capacity. A power transformer would be the definition assigned to the transformer which supplies power transforming voltage levels. The utility power transformer would be utilized to transform voltages from high voltage transmission levels to lower levels such as from 230 (two hundred and thirty) kV to 69 (sixty nine) kV or 115 (a hundred and fifteen) kV.
If the purpose of a transformer is to step the voltage down, it could be termed a step-down transformer. A step-down transformer is one that has a secondary voltage lower than the primary voltage.
A step-up transformer is used in conjunction with power generation equipment. After the power is generated, for example at a level of 13.8 (thirteen point eight) or 25 (twenty five) kV, it is stepped up to higher values which more easily permit transmission to distant locations with minimal losses. The power transformers that generation units utilize are of the step-up type.
Tap changers allow change of transformer ratio to give versatility required for utility system operation. Operating at low voltages is not desired. Operation at high voltage can result in over excitation of the transformer, increased noise levels, and greater excitation loss in terms of economics. Simply, it pays to operate at the best ratio for excitation conditions. Load tap changers allow for changing taps under full load conditions.
The type of tap changer which is also common is the no load tap changer. In order to operate this no load type, the transformer must be completely de-energized. It may be necessary to shut down, de-energize or change taps several times a year. If conditions remain stable, no changes may be required. As a general rule, voltage levels should be near the tap setting for the best economic considerations. It is possible; however, that other criteria may outweigh the economic considerations in arriving at a tap setting.
Lightning arrestors protect transformers from lightning surges. The purpose of lightning arrestors is similar to that of a safety valve on a boiler. The safety valve relieves a high pressure by permitting the escape of steam. When the pressure is reduced to normal, the valve closes and it is again ready to protect against another abnormal condition. Lightning arrestors operate in a similar manner. When a voltage much higher than normal voltage exists on a line, the arrestor immediately breaks down and furnishes a path to ground. As soon as the voltage returns to normal, the arc is extinguished, the arrestor ceases to conduct and the line returns to normal. Lightning arrestor equipment then must limit the surge crest voltage which may be applied to the apparatus it protects and bypass the surge to ground. The arrestor must be able to withstand its rated voltage and must be capable of extinguishing any power arc which follows the surge discharge.
Application of lightning protection equipment is an insurance against outages and equipment failure. ***The amount and kind of protection needed are influenced by the frequency and severity of storms in the area, the importance of reducing line outages due to lightning and the risk of failure of the equipment used. Generally, the insulation level of the line in the vicinity of the station, within the insulation level of the equipment in the station, should be considered in such a way that the line insulation would break down before the insulation in the station equipment would fail. Line insulators are cheaper and easier to replace than transformers and circuit breakers bushings.
4. ,
:
a distribution transformer the definition assigned to the transformer
a power transformer versatility required for the operation
power transmitting voltage levels increased noise levels
the utility power transformer the rated voltage
voltage transmission levels protection needed
a step-down transformer the equipment used
power generation equipment power provided for certain purposes
generation units the utility power transformer utilized to
utility system operation transform voltages
excitation conditions the power generated
load tap changers changes required
a no load type the apparatus applied
a lightning arrestor line insulators replaced
a lightning surge
a safety valve
lightning arrestor equipment
the surge crest voltage
the insulation level
the line insulation
5. :
1) ( );
2) ;
3) ;
4) , ;
5) ;
6) ;
7) , ;
8) ;
9) ().
6. Transformers
.
7. .
8. ***.
.
5. UNIT 5.
1. . ,
.
Des i gned, l i ne, t i me, t y pe, c y cle, f i ve, pr i marily, h y draulic, h i gh, i dentif ie d,
dev i ce, util i ze, w i nd, f i nd, l i ght.
Interr u pt, c u rrent, p u mping, n u mber, m u st, s u ch, d o ne, o ther, f u nction,
th o roughly.
Au tomatically, or der, c au se, dr aw, au xiliary, c au tion, rest ore, n or mal, m ore,
s our ce, c a lled, a lternating.
Thr ou gh, m o ve, r ou tine, l oo p, s oo ty, t wo, evol u tion, gr ou p, c oo led, r u le,
rem o val, m o vement.
C ir cuit, subm er sed, t er med, ref er, c er tain, w or k, em er gency, det er mine,
transf er, th er mal, conv er t.
Ar c, reg ar d, bl a st, p a ss, l ar ge, ar mature, ch ar ge, disch ar ge, ar ticle, h ar mful,
adv a ntage.
Circ ui t, e qu i pment, wh i ch, transm i ssion, d i str i bution, s y stem, capab i l i t y,
s i ngle, volt a ge, b e g i n, tr i p, unt i l, t y p i cal, cons i der, c y l i nder.
P ie ce, cont i nuous, m e tering, r ea ch, m ea ns, ea ch, th e se, rel ea se, rout i ne,
compl e te, h ea t.
C a pability, autom a tically, c a rrying, cap a city, d a mage, v a lue, g a s, v a cuum,
m a nner, disp a tch.
Distrib u tion, v iewe d, pn eu matic, u tilize, u se, c u bicle, prod u ce, s ui t, u nit,
f ew, f u el, u sually.
Break er, reclos er, typic a l, mod er n, medi u m, c o nsid er, vari ou s, o p e rat or,
c o ntin uou s, c o mpress or.
F ou nd, with ou t, n ow, h ow, ou t, all ow, ab ou t, ou tside, surr ou nd, am ou nt,
ar ou nd.
Br ea ker, m ay, r a ted, rel ay, th ey, b a sis, enc a sed, s a fety, b a sic, r ai se, d ay,
demonstr a te.
Cl o se, m o st, fl o w, contr o l, m ou ld, o pen, g oa l, h o me, l oa d, kn ow, bel ow,
c oa l, f o ld, bl ow.
Che ck, c lose, c ubi c le, brea k er, cir c uit, cy c le, c onfuse, c an, pneumati c,
c ontrol, c are, c apable c hemistry, ar ch ive, ar ch eology, s ch ool.
C ell, s pring, thi s, c ircuit, s afety, c ylinder, c ycle, s uit, re c eive, s earch,
sc ienti s t, sc ien c e, ne c e ss ary.
Whi ch, ch eck, swi tch ing, dis ch arge, combus tio n, ques tio n, na tu ral, su ch,
ea ch, ch ose.
Volta g e, dama g e, char g e, dischar g e, in j ury, ener g ize, emer g ency, g eneral,
sub j ect, lar g e, arran g e, ma j or, g enerate, sta g e, leaka g e.
Provi sion, deci sion, confu sion.
Mea sure, plea sure, u su ally.
W e, w ill, w ithin, wh ich, wh en, wh ere, wh y, w ith, o ne, wh ether, w ork,
wh ile, wh at, w ire, w ind.
S qu are, qu ick, qu arter, subse qu ent, qu ality, qu antity, qu estion, re qu ire,
conse qu ently, e qu ipment, ade qu ately, li qu id.
Th rough, th oroughly, th ink, th eory, th ermal, me th od, th ree, th irty,
ma th ematics, leng th.
Th is, th ey, wi th, wi th in, wi th out, th ereon, whe th er, al th ough, ano th er, th ere,
th at, th eir.
Fla sh, sh all, sh ould, ma ch ine, espe c ially, spe c ial, pre ss ure, effi c iency,
suffi c ient, accompli sh.
Applica tion, genera tion, ac tion, posi tion, loca tion, direc tion, men tion,
suc tion, fric tion.
Y es, y ou, y oke, y oung, y et, y ellow.
Wh o, wh ose, h ow, wh ole, wh om, h ello, H enry, h ere, h igh, h ydraulic, h ard.
Wr ite, wr ong, cu rr ent, ca rr ying, r elative, r ating, r ight, r ound, vi r us, t r ouble.
2. :
a circuit breaker ;
fault current , ;
to be rated , , ;
a rating , , , , ,
, ;
interruption , , , ;
to interrupt , , ;
a trip coil , ;
a series trip coil ;
a circuit recloser ;
;
a fault , , , ,
to close , ,
an arc () ;
to be submersed , ;
an oil circuit breaker ;
an air circuit breaker ;
an air blast circuit breaker ;
a gas blast circuit breaker ;
a vacuum circuit breaker ;
an operator , ;
a spring operator ;
a motor operator ;
a closing coil ;
to trip , ;
a latch , -, -, ,
;
a trip latch , ;
an armature ,
to charge , ;
to discharge , , , ,
, ;
a cubicle , , ;
a cell , , ;
a metal clad switch gear
;
a flash suit ;
switching , , , ,
;
emergency ;
a tank ;
a control valve ;
a piston ;
a failure ( ), , , ;
to reset , , ,
;
3. 5 Circuit Breakers, Part 1.
. - , . .
CIRCUIT BREAKERS
Part 1
A circuit breaker is a piece of equipment which is designed to interrupt fault current automatically. Circuit breakers may be found on generation, pumping, transmission and distribution systems. Circuit breakers are rated in a number of ways: circuit breakers are rated in momentary and continuous current carrying capability. Breakers are also rated as to voltage, KVA and MVA, and interruption times.
The interruption time is the time from the point the current begins to flow through the trip coil (or the current value in the series trip coil of a current recloser reaches the trip value) until the breaker interrupts the fault. Closing time is a time between the point when closing is actuated and the circuit is closed through that breaker.
There are five basic types of circuit breakers used on power systems. They are the oil circuit breaker, the air circuit breaker, the gas blast circuit breaker and the vacuum circuit breaker. In each case the five terms designate the means which is used to interrupt the arc in the breaker. We will consider primarily the circuit breaker with applications of the air or magnetic air circuit breaker and the oil circuit breaker.
Circuit breakers are also identified by various means used to close them. A circuit breaker may be closed by a number of means. The device used to close a circuit breaker is called the operator. The various types of operators we might find on a power system could include the spring operator, the solenoid operator, the pneumatic operator, the hydraulic operator, the motor operator, and the neudraulic (hydropneumatic) operator. Each of these may be utilized in order to close a circuit breaker.
We should also consider the solenoid type operator, the spring type operator and the pneumatic operator. The solenoid type operator closes the circuit breaker merely by magnetic action produced by passing a large current flow through the closing coil. This causes the armature to close the circuit breaker in which position it is latched. If the trip latch is released it allows the breaker to trip. The spring type operator is one which utilizes an AC or DC motor to charge a closing spring. Most circuit breakers use a spring to assist in the tripping of the circuit breaker. The reference to a spring operator refers to the device used to close that circuit breaker. This is in addition to the spring used to trip the breaker. A DC motor is utilized to charge (wind) the spring, and the spring is used to close the circuit breaker. In closing, this large spring discharges and in closing the circuit breaker it latches it into position. As the circuit breaker closes it charges the tripping spring.
Breakers which have the spring operator must be checked upon drawing them out to be certain that this closing spring has discharged upon drawing the breaker from the cubicle or cell. In checking this closing spring, discharged when the breaker is open and drawn out of the cell, it is important to prevent personal injury to the personnel working thereon. Anytime switching is done on energized enclosed areas, such the cells of the metal clad switch gear, the flash suit should be worn for safety. Carelessness cannot be tolerated in any high voltage switching, whether routine or emergency applications are involved.
A pneumatic operator uses an air compressor, air storage tank, and a pneumatic cylinder to close a circuit breaker. A control valve allows air into the cylinder. The subsequent piston operation causes the operating rod to close the circuit breaker. The air is used to close the circuit breaker. Pneumatic operators are used on many types of oil circuit breakers. Do not confuse the operator type with the circuit breaker type.
All personnel should know how to trip a circuit breaker manually where that opportunity is provided in the event of an electrical trip failure. Know the location of the manual trip lever. If the breaker fails to trip electrically, then it would not trip upon any electrical initiation whether it be from the control center or from the plant local breaker control. When breakers are out for maintenance one should observe on the breaker whether it indicated a charge-discharge state of the closing spring. If it is a spring type operator, one should be capable of telling whether it is charged or discharged upon making up an inspection. One should be capable of examining the contacts internally on the circuit breaker when apart and be able to tell what the various functions would be on that circuit breaker. One should be capable of telling exactly how a breaker could be tripped in an emergency if there is a manual trip and if that manual trip must be mechanically reset before the breaker could be closed again.
4.
:
- , ;
- ;
- , ;
- ;
- ;
- ;
- ;
- ();
- , ;
- ();
- ;
- .
5. ,
, , .
6.
.
7. .
6. UNIT 6.
1. :
a specific current , , ;
a short-circuit current ;
a rupturing capacity , ;
a blowout , ;
to extinguish the arc , ;
switch blades , ;
to bridge contacts , ;
a push button ;
a remote control type ;
an arc extinction chamber ;
a toggle mechanism ;
a transformer bank ;
sulphur hexafluoride (SF6) ;
an arc quenching quality ;
to exhaust , ;
to liquefy () ;
a puffer technique ;
a clogging effect ;
sweeping of the arc ;
exhausts , ;
to energize ;
against the opposition of ;
pressure ;
a disconnecting switch , ,
.
2. 6 Circuit Breakers, Part 2.
, .
CIRCUIT BREAKERS
Part 2
A circuit breaker is a switch designed to interrupt a specific current at a specific voltage. The specific current is always the maximum short circuit current that the breaker may be required to interrupt in the particular application under consideration. A three-phase circuit breaker consists of three single-pole switches arranged to operate simultaneously. The interrupting or rupturing capacity of a three-phase breaker is expressed in kilovolt-amperes, and is equal to √3 EI/1,000, where I is the maximum short-circuit current that it can interrupt, and E is the normal line voltage.
Air-break circuit breakers with magnetic blowout are available in various designs for d.c. voltages up to 3 kv and for a.c. voltages up to 34.5 kv. Their rupturing capacities range up to 2.5 million kva, three phase.
Oil circuit breakers have their contacts immersed in oil which helps to extinguish the arc which always forms as the contacts separate. For voltages up to 14.4 kv, the three poles are usually enclosed in a single tank. The three switch blades remain horizontal at all times. When they are raised, they close the three circuits by bridging the stationary contacts. The opening of the breaker therefore produces two arcs in series at each blade. In all cases the breaker is closed against the opposition of a spring and is held closed by a latch. This latch may be tripped by means of a trip coli, energized either automatically by one or more relays or by means of a push button located at any convenient place. When voltage or required rupturing capacity is high, a separate tank is provided for each pole.
The larger circuit breakers are all of remote-control type and are closed by means of a small motor or a solenoid or by compressed air acting on a piston. Small breakers are also often remote-controlled. Oil circuit breakers were at one time standard for all voltages above 600 volts, but new indoor installations are usually air-break up to 34.5 kv and air-blast above 34.5. Oil circuit breakers are still used extensively for outdoor installations, but air-blast circuit breakers are competing successfully in this field.
Air-blast circuit breakers rely mainly on a violent blast of compressed air to extinguish the arc. These breakers require a continuously available supply of compressed air at pressures ranging to 800 lb per sq. in. This supply of compressed air is used not only to blow out the arc but also to operate opening and closing mechanisms.
The circuit breaker is opened by sending a powerful blast of air into the arc extinction chamber. The tube like moving contact is blown to the left against the opposition of a spiral spring, and the arc that forms as the contacts separate is blown out through the hollow contact. The duration of the air blast is only a fraction of a second, and at its conclusion the spiral spring slams the contacts closed again. In the brief interval of time during which the contacts are open, a coordinated toggle mechanism opens the external disconnecting switch, so that the reclosing of the contacts in the arc extinction chamber does not reestablish the circuit.
The 230 kv air-blast circuit breakers at one of the hydroelectric plants have eight of these arc extinction chambers connected in series in each of the three conductors. Since the eight chambers operate simultaneously, it follows that with ideal operation only one-eighth of the voltage appeared across the chamber. The air-blast breakers do not make use of coordinated disconnects.
As soon as the arc is extinguished, the exhausts are closed and the air-blast pressure is maintained so as to hold the moving contacts open.
Disconnecting switches. Knife switches () are used at all voltages and currents, but except when the power is very small they must not be opened while current is flowing. They are used to isolate apparatus after the circuit has been opened by a circuit breaker. Switches that are used in this way are called disconnecting switches, or isolating switches, or disconnects. In general, every important piece of equipment, such as a circuit breaker or a transformer bank, has a three-pole disconnect on each side of it, so that maintenance and repairs can be carried out in safety. The smaller disconnecting switches are opened and closed by means of a long wooden stick with a hook attached to one end, the larger ones by a motor-driven mechanism.
3. :
1) excellent (qualities) a) very poor
b) very good
2) advanced (technology) a) technology that is new
b) technology that is widely used
3) to obtain a) to connect
b) to get, to receive
4) to restore a) to make, to produce
b) to make normal again, to
