INDEX
Introduction
2
Electrical substation
2
Elements of a substation
2
Transmission substation
3
Distribution substation
4
Grid Substation ±Horana
5
Substation main equipment
6
Surge Arresters
6
Substation Current Transformers
8
Circuit breakers
9
Types of insulations used in Overhead lines
10
Insulators and Fittings
11
Conductors
12
Cut out fuse
13
Aerial Aerial Bundled Conductors
14
Minimum Factor of Safety
15
1
Introduction
We were trained last two month in CEB, at Horana Area office and Construction Branch at Panadura. We mainly studied about Distribution System and Transmission System and about construction.
Electrical substation An electrical substation is a subsidiary station of an electricity generation, generation, transmission and distribution system where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several substations between generating plant and consumer, and may be changed in voltage in several steps.
A substation that has a step-up transformer increases the voltage while decreasing the current, while a step-down transformer decreases the voltage while increasing the current for domestic and commercial distribution. distribution. The word substation comes from the days before the distribution system became a grid. The first substations were connected to only one power station where the generator was housed, and were subsidiaries of t hat power station.
Elements of a substation Substations generally have switching, protection and control equipment and one or more transformers. In a large substation, circuit breakers are used to interrupt any short-circuits or overload currents that may occur on the network. Smaller distribution stations may use re closer circuit breakers or fuses for protection of distribution circuits. Substations do not usually have generators, although a power plant may have a substation nearby. Other devices such as capacitors and voltage regulators may also be located at a substation. Substations may be on the surface in fenced fenc ed enclosures, underground, or located in specialspecial purpose buildings. High-rise buildings may have several indoor substations. Indoor substations are usually found in urban areas to reduce the noise from the transformers, for reasons of appearance, or to protect switchgear from extreme climate or pollution conditions.
2
Transmi Transmissi ssi n substati substati n
At
i i
subst subst ti
connect connec ts t o or more transmi ransmissi ss ion lines. s impl mplest est case is lines. The si
where all a ll transmi ransmissi ssion lines lines have the same volt voltage. age. In such cases, the subst substation tion cont contains high-volt gh-voltage age swit switches ches that hat allow llow lines lines to be connect connected or isol solated for fault fau lt clearance or mai maintenance. A transmi ransmissi ssion station between two tion may have transformers to conver t bet transmi ransmissi ssion volt voltages, ages, volt voltage age cont control/ rol/ power power fact factor correcti correction on devi devices such as capacit capac itors, ors, react reactors or st static tic VAr compensat compensa tors and equi equ i pment pment such as phase shi sh if ting ting transformerst ransformerst o cont control rol power f low bet between two adjacent adjacent power syst systems.
Transmi Transmissi ssion subst substations s impl mple to compl complex. A small sma ll "swit "switch chiing station" tions can range from si tion" may be little p lus some ci c ircuit rcu it breakers. The largest argest transmi ransmissi ssion little more than a bus pl 3
subst substations tions can cover a large area (several (severa l acres/ acres/hect hectares) wit with h multi multi pl ple volt voltage age level evels, many ci circuit rcu it breakers and a large amount amount of prot prot ecti ection on and cont control rol equi equi pment pment (volt (voltage age and current current transformers, rel relays). Modern subst subs tations tions may be impl mplement ement ed usi using Int Internati ernationa onall Standards such as IEC IE C
str ibut butii Distri
.
n substati substati n
A distr i buti bution on subst substation tion transfers power from the transmi ransmissi ss ion syst sys tem to the distr i buti bution on syst system of an area. It I t is uneconomi uneconomical cal to di directl rectly y connect connect elect ectr icity ity consumers to the hi h ighvolt voltage age mai ma in transmi ransmissi ssion net network, unl unless they use large amount amounts of power, so the distr i buti bution on st station tion reduces volt vo ltage age to a val va lue suit suitab ablle for l for local ocal distr i buti bution. on.
The input nput for a di distr i buti bution on subst substation tion is typi ypicall cally y at least east two transmi ransmissi ssion or sub transmi ransmissi ssion lines. lines. Input Input volt voltage age may be, for exampl examp le, 33kV, or what wha tever i ever is common in the area. The out ou t put put is a number of feeders. Di D istr i buti bution on volt voltages ages are typi ypicall cally y medi medium volt voltage, age, bet between 230V dependi depending on the size ize of the area served and the practi practices ces of the local ocal utility. tility.
4
The feeders will will then run overhead, al a long st street reets (or under st s treet reets, in a cit c ity) y) and event eventuall ually y power t power the di distr i buti bution on transformers at a t or near t near the cust customer premi premises. Besi esides changi changing the volt voltage, age, the job of the distr i buti bution on subst substation tion is to isol solate fault faultss in either ither the transmi ransmissi ss ion or di distr i buti bution on syst systems. Di Distr i buti bution on subst substations tions may al a lso be the poi points of volt voltage age regul regulation, tion, alt a lthough hough on long di distr i buti bution on circuit rcu itss (several (severa l km/ km/ miles), iles), volt voltage age regul regulation tion equi equi pment pment may al a lso be inst nstalled lled al along the line. line.
Compli omplica catted distr i buti bution on subst substations tions can be found in the downt downtown areas of large citi cities, es, with ith high-volt gh-voltage age swit switch chiing, and swit switch chiing and backup syst sys t ems on the low-voltage ltage si side. More typi ypical cal distr i buti bution on subst substations tions have a swit sw itch, ch, one transformer, and mi minimal mal faciliti facilities es on the low-volt ow-voltage age si side.
Gri
Substati Substati n ±Horana
Mathugama Substation Horana Grid
Substation
8*33Kv Feeders
Pannipitiya Substation
Ace Power Plant
Horana Gr id Subst Substation tion pl placed bet between Panni Panni piti pitiya ya and Mathugama subst substations. tions.IIt¶s t¶s 132Kv si s ide is a out outdoor Gr id and 33Kv si s ide is a indoor syst system. Whol Whole syst sys tem is full fully y comput computer cont control rol and al a lso manuall manua lly y cont control rol. There were two mai main transformers and those are on load tap changi changing machi machines. Rat Rated power i power is 31500 KVA .
5
Substati Substation mai main equip equipment ment
Surge Arresters
The Back f lash On
shi shielded transmi ransmissi ssion lines under-bu ilt distr i buti bution on ci circuit rcu its, s, the arrest arrester prevent prevents lines or under-built
ower-to-phase insul nsulator back-f lashovers dur ing a ligh str ike. On unshi unshielded sub tower-t lighttning st transmi ransmissi ssion or di distr i buti bution on ci circuit rcu its, s, the arrest arrester prevent prevents phase-t phase- to-ground f lashovers.
6
How
Transmission Line Arresters Work
Transmission Line Surge Arresters conduct lightning surges around the protected insulator so that a lightning flashover is not created. They are designed to be installed functionally in parallel with the line insulator. The arrester conducts the lightning surges around the protected insulator so that a subsequent 60 H fault on the circuit is not not created. The arrester becomes a low ohmic path for the surge as voltage across it increases. When the voltage returns to normal, the arrester once again returns to a high ohmic device with only micro amps of leakage current.
Ca
acitor acitor voltage voltage transform transformer er
A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay. In its most basic form the device consists of three parts: two capacitors across which the transmission line signal is split, an inductive element to tune the device to the line frequency, and a transformer to isolate and further step down the voltage for the instrumentation or protective relay. The device has at least four terminals: a terminal for connection to the high voltage signal, a ground terminal, and two secondary terminals which connect to the instrumentation or protect ive relay. I here CVT is used for for communication system . CVTs in combination combination with wave traps are used for filtering hi gh frequency communication signals from power frequency. This forms a carrier communication network throughout the transmission network. 7
Substati Substation Current Transformers
Current urrent transformers in el elect ectr ical cal subst substations tions measure the syst system current currents at at predet predetermi ermined measur ing poi points of t of the swit switchgear chgear wit with h a cer tain measurement measurement inaccuracy. The measur ing poi points are typi ypicall cally y locat ocated at a t all incomi ncoming and out ou tgoi going lines lines and possi poss i bl bly al a lso wit with hin the syst system, e.g. for the busbar prot protecti ection. on. The current current measurement measurement signal gnals are usedfor prot protecti ective ve functi functions, ons, for monit monitor or ing the subst substation, tion, for cal ca lcul culating ting performance dat da ta for operati operating ng purposes or for consumpti consump tion on billi b illing ng and for t for the represent representation tion on a di displ splay. The out out put put of t of the current current transformer provi provides a represent representation re nt f lowi owing through tion of the curren the assembl assembly that hat is bei being monit monitored. ored. Associ Associated monit monitor or ing and cont control rol inst nstrument rumentation tion in combi combinati nation on with ith the current current transformer may provi prov ide cr itica iticall syst system functi functions ons such as over load prot protecti ection on and power usage monit mon itor or ing. Elect ectr ical cal power di distr i buti bution on syst systems may requi requ ire the use of a var iety of ci circuit rcu it conditi condition on monit monitor or ing devi devices to facilit facilitaate the det detecti ection on and locati ocation on of syst system mal ma lfuncti functions. ons. Current urrent transformers and current curren t sensors are well well known in the f ield of el elect ectroni ronic circui rcuti breakers, provi providing the general genera l functi function on of power ing the elect ectroni ronics with ithin the circuit rcu it breaker tr i p p unit unit and sensi sens ing the circuit rcu it current current with ithin the prot protect ected circuit rcu it.. Ground fault fau lt circuit rcu it breakers for alt alterna ernati ting ng current current distr i buti bution on circuit rcu itss are commonly used to prot protect ect peopl people agai against nst dangerous shocks due to line line-to-ground current current f low through someone's body. Ground fault fault circuit rcu it breakers must mus t be abl able to det detect ect current current f low bet between line line conduct conductors and ground at a t current current level evels. Upon det detecti ection on of such s uch a ground rou nd fau lt current current, the cont contact acts of the circuit rcuit breaker are opened to de energ energiz izee the circuit rcuit.. Current urrent transformers are an integral egral par t of ground fault fault circuit rcu it breakers. 8
Circu rcuiit breakers
Elect ectr ical cal power transmi ransmissi ssion net networks are prot pro tect ected and cont control rol ed by hi high-volt gh-voltage age breakers. The def inition ition of hi high volt voltage age var ies but but in power transmi ransmissi ssion work is usuall usua lly y thought hought to be 11 kV or hi h igher. Hi High-volt gh-voltage age breakers are near ly al a lways sol solenoi enoid-operat d-operated, with ith current current sensi sensing prot prot ecti ective ve rel relays operat operated through current curren t transformers. In subst subs tations tions the prot protecti ective ve rel relay scheme can be compl comp lex, prot protecti ecting ng equi equi pment pment and busses from var ious types of over load or ground/ ground /ear th fault fault.. High-volt gh-voltage age breakers are broadl broad ly cl classi ass if ied by the medi medium used to exti extingu nguiish the arc. y y y y y
Bulk oil oil Min Minimum oil oil Air bl blast ast Vacuum SF6
High-volt gh-voltage age ci circuit rcu it breakers used on transmi ransmissi ssion syst sys tems may be arranged to allow llow a singl ngle pol po le of a three-phase line line to tr i p, p, inst nstead of t of tr i ppi pping all a ll three pol poles; for some cl c lasses of fault faultss this improves the syst syst em st stabilit ability y and avail ava ilab abilit ility. y.
Main
Fail Failure ure Probl Problems.
y
ghtning Light
y
Insul Insulation tion Damages
y
Falli Falling ng trees
y
Shor t circuit rcu it probl problems
y
Acci Accident dents
9
Types Types of insulations used in Overhead lines
Overhead line insulators, as the name suggests, suggests, are used to t o electrically insulate pylons from live electrical cables. Overhead line insulators may consist of a string of insulator units, depending on insulator type and application. application. The higher the line voltage voltage insulated, the more insulator insulator units used in the string. Different types of line insulators are used, depending on voltage and mechanica l strain (tension) requirements. require ments. The more widely used types are as follows. Disc typ typee
where insulation discs (also called insulation units) are strung together depending on the insulation level desired. Each disc is typically rated at 10-12kV, 10-12kV, with a capacitance of 30-40pF . Discs are strung together via their caps and pins. Locking Locki ng mechanisms may be ball-socket ball-socket or clevis-tongue type. The cap is insulated insulated form the pin via via the porcelain (or (or glass) disc which adheres to the cap and pin via adhesive cement. Long rod typ typee
These may also be strung together for higher insulation and may have similar ball-socket and clevis-tongue locking mechanisms used among the disc types . Their longer length makes them applicable for phase-to-phase insulation to reduce line galloping during strong winds . Both disc disc and long rod-type rod-type insulators are commonly commonly used in suspension or strain (tension) insulator applications .
10
Pin
typ typee
Pin types are screwed onto a bolt shank secured on the cross-arm of the transmission pole or pylon. The pin type does not take main transmission transmiss ion line strain strai n (tension) (tensi on) ,and functions as a j a jumper umper line insulator. Shackle
typ typee
insulators. insulator s. These are mostly applied to support line strain strai n (tensi (tension), on), such as at changes of of transmission line direction. Insulators and Fittings y
132 kV Line - 400mm2 ACSR ACS R
y
Suspension Insulator Discs, 120kN
y
Jumper Suspension Insulator
y
Suspension Insulator Hardware
y
Tension Insulator Discs, 160kN
y
Tension Insulator Hardware
y
Suspension Clamps - Conductor
y
Tension Clamps ± Conductor
Discs,70kN
11
Most
used LT LT conductors in CEB
y
Fly
7/3.40 mm
y
Wasp
7/4.39 mm
y
AAAC
7/4.25 mm
y
AAAC
7/3.10 mm
Most
used LT LT conductors in CEB
y
AAAC (ELM) 19/3.76 mm
y
ACSR ACSR ((R acoon) acoon) 7/4.09 mm
Earth Conductors
y
Steel Wires 7/3.25mm
y
Stranding Steel Wires 7/3.25mm
Earth conductor fittings
y
Clamps
y
Tension Clamps
y
Mid-span Joints
Line Conductor fittings y
Mid-Span Joints - Conductor
y
Repair Sleeves
y
Vibration Dampers
12
Cut
out fuse
In electrical distribution, a fuse cutout or cut-out fuse is a combination of a fuse and a switch, used in primary overhead feeder lines and taps to protect stepdown transformers from current surges and overloads.A cutout consists of three ma j ma jor or components:
* The cutout body, an open "C"-shaped frame that supports the "fuse holder " and a porcelain insulator that electrically isolates the conductive portions of the assembly from the support to which the insulator is fastened.
* The fuse holder, often called the "fuse tube" tube" or "door ", which contains the interchangeable fuse element and also acts as a simple knife switch. When the contained fuse operates or blows, the fuse holder will drop open, disengaging the knife switch, and hang from a hinge assembly. This hanging fuse holder provides a visible indication that the fuse has operated a nd assurance that t he down-stream down-stream circuit is electrically electrica lly isolated.
* The fuse element, or "fuse link ", is the replaceable portion of the assembly that operates due to high electrical currents.
The fuse elements, or fuse links used in most distribution cutouts are tin or silver alloy fuse links that melt (or operate) when exposed to high current conditions. Ampere ratings of fuse elements vary from 1 ampere to 200 amperes. a mperes. 13
Aerial Bundled Conductors
Aerial bundled cables (also aerial bundled conductors) are overhead power lines using several insulated phase conductors bundled tightly together, usually with a bare neutral conductor. This contrasts with the traditional practice of using uninsulated conductors separated by air gaps.
In moister climates, tree growth is a significant problem for overhead power lines. Aerial bundled bundled cables cabl es will not arc over if touched by tree bra nches. Although persistent rubbing rubbing is still a problem, tree-trimming costs can be reduced.
Note that bundled cables are used only for low volta ges (1000 V or less), in the distribution portion of the electrical grid, as the required insulation thickness would be impractical at higher voltages
i) Number of strands 12 or 19 ii) Nominal cross sectional area 70 sq. mm iii) Max. linear resistance at 20°C 0.443 Ohms/Km iv) Minimum breaking strength 840 da N v) Diameter of compacted bare conductor Max. 10.2mm Min. 9.7mm vi) Thickness of insulating sheath Max. 1.8mm Min. 1.52mm at 1 point vii) Insulated cable outside diameter diamet er Max. 14.2mm Min. 13.3mm
One, two, and three R ibs ibs to distinguish the three phase cores from each other and the neutral shall be plain without any R ibs ibs.
14
Minimum Factor of Safety
Description
y
Factor of Safety
Conductors, Conductors, Earth wires and OPGW at Maximum Working Tension based on Ultimate Strength
y
Conductors and Earth wires at Everyday Temperature still Air Tension, based on Ultimate Strength
y
3.0
Straight Line Supports and Foundations under Normal Working Loads
y
0.95
Insulator Strings and Fittings at Maximum Working Tension based on Failing Load
y
4.5
Anchor Clamps and Mid-span Joints, based on Ultimate Strength of Conductor Conductor and Earth wire
y
2.5
2.0
Angle, Section and Terminal Supports and Foundations under Normal Working Loads
2.5
y
Towers under Broken Wire Loads
1.25
y
Foundations Foundations under Broken Wire Loads
1.5
y
Cross arms of straight line support support under under broken wire condition
2.0
y
Cross arms of angle, section and terminal support under broken wire condition
2.5
15
