Transformer BushingANSI Standard

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Application

Trench bushings, Type COTA, aredesigned for application on liquidfilled power transformers. Theyare used to connect the powertransformer to overhead lines orexposed bus in either outdoor orindoor conditions.

Connection to the transformerwinding leads can be accom-plished by one of three methods:

Bottom connected via a fixed copper conductor.

Connected via a copper draw leadcable(s) supplied with the powertransformer.

Bottom connected via Trench's allcopper "Split-Conductor" drawlead.

The method selected depends onvoltage rating, maximum throughcurrent or user preference. Connection to the power system isaccomplished with an industrystandard threaded top terminal.

Applicable Standards

Trench, Type COTA, bushings aredesigned to meet or exceed thefollowing industry standards forpower transformer applications:

ANSI/IEEE Standard C57.19.00-1997IEEE Standard General Requirementsand Test Procedure for OutdoorPower Apparatus Bushings

ANSI/IEEE Standard C57.19.01-1997IEEE Standard Performance Characteristics and Dimensions forOutdoor Apparatus Bushings

IEEE Standard C57.19.100-1995IEEE Guide for Application ofPower Apparatus Bushings

Active Part

The active part of the COTA bushingis constructed of oil-impregnatedpaper with layers of aluminumfoil. The position of the foil layersis computer optimized to ensure ahomogenous electrical field, radiallyand axially controlled, providingextremely high dielectric resistance.

Depending on the rated current,the active part is wound on eitheran aluminum central tube or afixed copper conductor.

Housing

The housing is constructed of ahead, outdoor insulator, mountingflange, ground sleeve (COTA 250and above) and epoxy insulator,held together by either a centralaluminum tube or a fixed copperconductor. Pre-tensioned conespring washers provide mechanicalstability over the entire temperaturerange, ensuring a leak free bushingwith the highest possible mechani-cal strength. COTA bushings aresealed exclusively with 0-Ring gas-kets and each bushing is hermeti-cally sealed with its own indepen-dent oil reservoir. The interior ofaluminum castings are painted.

Design

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Head

The cast aluminum head containsan oil expansion chamber with anoil level indicator. The design ofthe head allows the bushings tobe shipped and stored horizontallyand mounted as follows:

COTA 150 and COTA 200 Fixedconductor models: vertical or hori-zontal.

COTA 150 and above draw leadmodels and fixed conductor modelsabove COTA 200: vertical to amaximum inclination of 40º.

For greater inclination, contactTrench for special instructions andlimitations.

Outdoor Insulator

The outdoor insulator is either ahigh-grade electrotechnical porcelainor a composite insulator constructedfrom a explosion-resistant fiber-glass epoxy resin tube with moldedsilicone rubber sheds.

Porcelain Insulators

The standard porcelain insulatoron COTA bushings is ANSI No.70,light gray. Brown porcelain is avail-able upon request. When theheight of the bushing makes itnecessary to use more than oneporcelain element, Trench uses aspecial gluing procedure devel-oped to ensure that the porcelainelements will exhibit the samelevel of performance as a singleporcelain element. On bushingstyle COTA 250 and above, theporcelain insulator is cemented tothe mounting flange using specialcement and sealed with an 0-Ringgasket. To protect against corro-sion, the mounting flange surfacethat is in contact with the cementis treated with a special coating,ensuring a trouble free interface.

Composite Insulators

Composite insulators used by Trenchare specifically designed for use onhigh voltage bushings. The com-posite insulator demonstrates superior electrical and mechanicalcharacteristics not found in othertypes of insulators. The physicalproperties of the silicone rubberprovide many advantages overconventional porcelain insulators.The composite insulator hasdemonstrated superior perfor-mance in earthquake prone areas.

Porcelain insulatorTypical design COTA250 ... COTA900

Alternative sheds

Porcelain insulator

Portland cement

Mounting flange

O-Ring gasket

Mounting flange

Fiberglass-reinforcedepoxy resin tube

Silicone rubber sheds

Composite insulatorTypical design COTA550 ... COTA900

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Epoxy Insulator

The lower end of the COTA bush-ings (COTA 200 and below) areprotected by a fiberglass-reinforcedepoxy-resin tube or (COTA 250and above) by a cone shaped vacu-um molded epoxy resin insulator.The epoxy insulator is designed tobe installed during the in-tank dryingprocess of the active part of thetransformer and can withstandtemperatures up to 130ºC.A special aluminum electrode isembedded into the end of theepoxy-resin insulator providingcontrol of the electrical fieldstrength in this area of the bushing.

Mounting Flange

The mounting flange is a highquality aluminum casting, ma-chined to exact dimensions, ensur-ing an excellent seal between thebushing and the transformer.

Integrated into the mountingflange of COTA bushings through69 kV are test taps. Above 69 kVthe mounting flange is equippedwith a voltage tap

Test Tap, COTA150 ... COTA 350 Voltage Tap, COTA 550 and above

Epoxy Insulator

Design

Current Path

Two current path options are available:

Fixed conductor

Current path via a copper conductorthat is fixed in place has the activepart wound on the conductor. Thefixed conductor is either solid copperor a copper tube, depending onthe specific bushing design.

Draw lead

Current path via the transformer’scopper cable(s) to a silver-platedcopper terminal through multispring contacts to the copper-alloy

top terminal. Or via Trench’s copper”Split-Conductor” draw leadthrough multi spring contacts tothe copper-alloy top terminal.

Both current path options areavailable, depending on the appli-cation, on all COTA bushings.

Sealing cap

Multiple spring contactfor grounding

Sealing cap Oil plug

Multiple spring contactfor grounding

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Fixed Conductor

When a fixed conductor bushing isselected the connection to thetransformer winding leads will beat the bottom of the bushing. Theterminal configuration at the bot-tom a fixed conductor bushing willdepend on the current ratingand/or the desired application andthe requirements of the ANSI/IEEEStandards. Refer to the TechnicalOrdering Data for standard andoptional bottom terminals.

Draw Lead Cable(s)

When a draw lead application isselected, and the through currentallows the use of flexible coppercable(s), a draw lead cable termi-nal must be selected from theTechnical Order Data. The limitingfactor in determining if a flexiblecopper cable(s) can be applied isthe inside diameter of the bushing’scentral tube. For most applicationsthrough 69 kV, up to 700 amperescan be carried by cable(s). Above69 kV, up to 800 amperes can becarried by cable(s).

When applying draw lead cable(s)on bushings with a vacuum mold-ed epoxy resin insulator, the em-bedded end shield provides for asimple, space-saving assemblywithout additional shielding orbarriers. Recommendations aremade in this catalog for applyinginsulated leads from the trans-former windings.

“Split-Conductor” Draw Lead

When a draw lead application isselected, and the through currentexceeds the capability of flexiblecopper cable(s) a ”Split-Conduc-tor” will be provided with thebushing to meet the requiredthrough current. ”Split-Conduc-tors” are capable of carrying be-tween 1,400 and 3,000 amperesdepending on the BIL rating of thebushing. (See the COTA TechnicalSpecification Sheet for available”Split-Conductor” ratings)

For ”Split-Conductor” applicationthe termination of the transformerwinding leads will be at the bot-tom of the bushing. The type oftermination required will dependon the maximum through current,operating voltage and mountingposition. Additional measures(shielding, barriers, etc.) may berequired. Contact Trench for avail-able terminals and shields for yourspecific application of the ”Split-Conductor”.

Split-ConductorCOTA150 ... COTA900

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Top terminal

Multiple spring contact

Retaining pin with locking device

Central tube

“Split Conductor” upper part

Mounting flange

Gasket surface flange

“Split Conductor” lower part

Epoxy insulator

End-shielding

Bottom terminal

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Top Terminal

The top terminal assembly of aTrench COTA draw lead bushing isdesigned to provide maintenancefree termination of the overheadline or bus. To ensure that the topterminal will not become loose inservice it is bolted to the head ofthe bushing, sealed with an 0-Ringgasket. The top terminal is designedto accept either a draw lead termi-nal or Trench's ”Split-Conductor”.

Standardization

Trench COTA bushings were devel-oped to promote the concept of”standardization”. The designsdetailed in this catalog will covernearly 100% of the bushing requirements for liquid filled powertransformers rated through 100 MVA, 900 kV BIL. All COTAbushings are designed for operation,without de-rating, to an altitudeof 10'000 feet. COTA bushings(COTA 200 and above) have asstandard, ”extra-creep” porcelain

in accordance with the Heavy con-tamination level as described inthe IEEE Guide for Application ofPower Apparatus Bushings,C57.19.100-1995.

COTA bushings present a level ofstandardization that will reduce inventories while meeting the mostdemanding requirements.

Top TerminalCOTA Draw Lead Bushings

Top terminal

Draw lead stud

Multiple spring contact

Retaining pin with locking device

4 Fixing screws

O-Ring gasket

Terminal ID

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Bushing head

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Top terminal

Multiple spring contact

Draw lead stud

Cone spring washers

Oil level indicator

Head

Outdoor insulator

Active part

Central tube

Mounting flange

Volt tap (COTA 550...COTA 900

Ground sleeve

Epoxy insulator

End-shielding

Test tap (COTA 150...350)

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Top terminal

Cone spring washers

Oil level indicator

Head

Outdoor insulator

Active part

Test tap

Mounting flange

Fixed conductor

Fiberglass-reinforcedepoxy resin tube

Bottom terminal

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Cut Views

Typical designCOTA 150 and200 (fixed conductor)

Typical designCOTA 150 ... 900(draw lead)

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Technical Ordering Data

Trench has developed a technicalordering data system that is ”userfriendly”. It is designed to allow youto build your own bushing from aselection of standard accessoriesand options that meet your specificapplication requirement.

The technical ordering data systemis made from three components,the bushing Type, the bushing Stylenumber and the bushing Options.On the next page are tables thatlist the available options and acces-sories.

Type COTACOTA, which stands for CondenserOil Transformer bushing designedaccording to ANSI Standards.

Style NumberThe style number is made up ofseven sets of numbers and/or lettersthat will provide specific informationabout the bushing.

The first set of three numbers statesthe BIL (Basic Insulation Level) ofthe bushing. Style Code 1 lists thestandard levels available.

The next set of 1 letter and 3 num-bers state the maximum throughcurrent rating of the bushing. Theletter designates the current pathoption, F for fixed conductor or Hfor draw lead. The numbers desig-nate the through current for thebushing x100. (Example 015 =1,500 amperes) Style Code 2 liststhe available current ratings by cur-rent path.

The next set of two numbers statethe CT pocket length. The lastgrounded foil layer of the bushing’sactive apart determines the CTpocket length. Style Code 3 liststhe available CT pocket lengths byvoltage class.

The next letter code states themounting flange configuration. TheIEEE/ANSI Standards dictate themounting flange configuration formost bushings, however, there area number of exceptions that mustbe considered when applying bush-ings. The table for Style Code 4 willprovide the specific letter codedesignation for each availablemounting flange configuration bybushing style.

The next letter code states the out-door insulator material and color.There are 3 options available forthe outdoor insulator and are listedin the table for Style Code 5.

The next letter code states the out-door insulator’s minimum creepdistance in accordance with thefour contamination levels listed inthe IEEE Guide for Application ofPower Apparatus Bushings, C57.19.100-1995. The next two numbers are a Trenchfactory code designation that isused by Trench to determine aspecific bushing's compatibility withother bushings within the samestyle number.

OptionsThe last four letters are the OptionCodes. The option codes are theaccessories that are added to abasic bushing to suit the specificrequirement or application. Theseoption codes will not appear onthe bushing nameplate but willappear on the bushing outlinedrawing and the specific outlinedrawing number will appear onthe bushing nameplate. There arepresently 4 sets of options avail-able for Trench COTA bushings

When Code Z appears it indicatessomething special is required. If aspecific requirement is not coveredby the above codes the letter Z canbe used in the option code. Therequired special option or accessorymust be fully detailed and reviewedby Trench before an order is accepted. If a Z option code doesnot appear in a specific option codetable there can not be a special requirement for the option or ac-cessory.

If a bushing is ordered with or with-out a draw lead terminal or drawlead adapter the option codes willnot appear on the outline drawing.These option codes will appear onthe order acknowledgement if orderwith the bushing.

Example

COTA 900-H016-26-AG3-01

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Style Code 1, Basic insulation level

Code Description

150 25.0 kV Bushing, 150 kV BIL200 34.5 kV Bushing, 200 kV BIL250 46.0 kV Bushing, 250 kV BIL350 69.0 kV Bushing, 350 kV BIL550 115.0 kV Bushing, 550 kV BIL650 138.0 kV Bushing, 650 kV BIL750 161.0 kV Bushing, 750 kV BIL900 230.0 kV Bushing, 900 kV BIL

Style Code 2, Maximum current rating

Code Description Available onH014 1,400 A COTA 250...750H015 1,500 A COTA 150...200H016 1,600 A COTA 900HO20 2,000 A COTA 250...350H030 3,000 A COTA 150...200F020 2,000 A COTA 550...900F023 2,350 A COTA 200F027 2,700 A COTA 150FO30 3,000 A COTA 550...900

Style Code 3, CT pocket lengthCode Description

10 10 Inch CT pocket, through 34.5 kV16 16.5 Inch CT pocket, through 69 kV21 21 Inch CT pocket, through 69 kV23 23 Inch CT pocket, through 230 kV26 26.75 Inch CT pocket, 230 kV

Style Code 4, flange configuration

kV COTA Code Class Bushing Flange

A 25 150-H015 71/4” – 4 HoleA 25 150-F027 71/4” – 4 HoleA 34.5 200-H015 71/4” – 4 HoleA 34.5 200-F023 71/4” – 4 HoleB 34.5 200-H030 71/4” – 4 HoleC 34.5 200-H030 81/4” – 4 HoleD 34.5 200-H030 91/4” – 6 HoleA 46 250-H014 81/4” – 4 HoleA 69 350-H014 91/4” – 6 HoleA 69 350-F030 101/4” – 6 HoleA 115 550-H014 131/4” – 6 HoleA 115 550-F030 131/4” – 6 HoleA 138 650-H014 141/4” – 6 HoleA 138 650-F030 141/4” – 6 HoleA 161 750-H014 151/4” – 8 HoleA 230 900-H016 21” – 12 HoleA 230 900-F030 21” – 12 HoleA 230 900-F050 21” – 12 Hole

Style Code 5, outdoor insulator

Code Description

G #70 gray porcelainB brown porcelainC #70 gray composite insulator

Style code 6, min insulator creep distance

Code Description1 28mm/kV (optional)2 35mm/kV (optional)3 44mm/kV (standard)4 54mm/kV (optional)

Option code 8, top terminal plating

Code DescriptionA Silver platedT Tin platedN no plating

Option code 9 draw lead connection when option code 10 = R, crimp type terminal

Code Description Cable size mm2

H ID = 0.433" 1/0 50J ID = 0.500" 2/0 70K ID = 0.625" 4/0 95L ID = 0.720" 300 KCMIL 150N ID = 0.830" 400 KCMIL 185Z SPECIAL

Option code 9, draw lead connection when option code 10 = W, braze type terminal

Code DescriptionM 0.315" pilot holeP SpadeZ Special size

Option code 9, bottom connection when option code 10 = T, special threads

Code DescriptionX 11/2" - 12 UNF threadsK 2" - 12 UNF threadsL 3" - 12 UNF threadsZ Special plate

Option code 9, bottom connection when option code 10 = P, plate

Code DescriptionD ANSI FIG. 2E ANSI FIG. 3F ANSI FIG, 4Z Special

Option code 9, bottom connection when option code 10 = S, spade

Code DescriptionY 2 Hole spadeX 4 Hole spadeZ Special spade

Option code 10

Code DescriptionP Bottom terminal is a plateR Crimp type draw lead terminalS Bottom terminal is a spadeT Bottom terminal is a threaded studW Braze type draw lead terminalZ Special

Option code 11 and 12 (Assigned by Trench)

Minimum distanceCOTA 150 ... COTA 900

Recommendations forCOTA 550 ... COTA 900

R min.

(mm) (inch)

COTA 150 65 2.56

COTA 200 75 2.95

COTA 250 85 3.35

COTA 350 120 4.72

COTA 550 145 5.71

COTA 650 180 7.09

COTA 750 225 8.86

COTA 900 270 10.63

Oil conditions

Oil mineral

Water < 15 ppm

Particles max. 39'630 each US gal.

size 59 to 2362 µinch

Oil strength >70 kV per 0.1 inch(degassed)

Minimum Distance toGrounded Parts

Recommendations forInsulated Draw Lead Application

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Epoxy insulator

End-shielding

Dimensions seeoutline drawing

Cable insulation

Cable

COTA Technical Specification Sheets

Type COTA COTA COTA COTAStyle Number 150-H015-21-AG2-01 150-F027-21-AG2-01 200-H015-21-AG3-01 200-F023-21-AG3-01Drawing Number 025D001A 025F002A 035D001A 035F001ACurrent Path (copper) draw lead fixed draw lead fixedInsulation Class (kV) 25 25 34.5 34.5Max. Line to Ground Voltage (kV) 16 16 22 22BIL (kV) 150 150 200 200Max. Current Rating (A) 1'500 2'700 1'500 2'350CT Pocket Length (inches) 21 21 21 21Min. Creep Distance (inches) 21 21 34.5 34.5Min. Arcing Distance (inches) 9.25 9.25 13.4 13.4Withstand 60 Hz60 s dry (kV) 60 60 80 8010 s wet (kV) 50 50 75 75Mounting vertical vert./horiz. vertical vert./hori.Max. Altitude (feet) 10'000 10'000 10'000 10'000Color of Porcelain gray gray gray grayApproximate Weight (lbs) 40 90 66 93

Type COTA COTA COTA COTAStyle Number 200-H030-21-CG3-01 250-H014-21-AG3-01 350-H014-21-AG3-01 550-H014-23-AG3-03Drawing Number 035S004A 046D001A 069D002A 115D002ACurrent Path (copper) draw lead draw lead draw lead draw leadInsulation Class (kV) 34.5 46 69 115Max. Line to Ground Voltage (kV) 22 29 44 88BIL (kV) 200 250 350 550Max. Current Rating (A) 3'000 1'400 1'400 1'430CT Pocket Length (inches) 21 21 21 23Min. Creep Distance (inches) 34.5 46 69 115Min. Arcing Distance (inches) 13.4 18 27 42.1Withstand 60 Hz60 s dry (kV) 80 105 160 26010 s wet (kV) 75 95 140 230Mounting vertical vertical vertical verticalMax. Altitude (feet) 10'000 10'000 10'000 10'000Color of Porcelain gray gray gray grayApproximate Weight (lbs) 128 84 110 270

Type COTA COTA COTA COTAStyle Number 650-H014-23-AG3-01 750-H014-23-AG3-01 900-H016-26-AG3-01 900-H016-23-AG3-01Drawing Number 138D002A 161D001A 230D001A 230D003ACurrent Path (copper) draw lead draw lead draw lead draw leadInsulation Class (kV) 138 161 230 230Max. Line to Ground Voltage (kV) 102 146 146 146BIL (kV) 650 750 900 900Max. Current Rating (A) 1'430 1'430 1'660 1'660CT Pocket Length (inches) 23 23 26.75 23Min. Creep Distance (inches) 138 161 230 230Min. Arcing Distance (inches) 50 59 84.7 84.7Withstand 60 Hz60 s dry (kV) 310 365 425 42510 s wet (kV) 275 315 350 350Mounting vertical vertical vertical verticalMax. Altitude (feet) 10'000 10'000 10'000 10'000Color of Porcelain gray gray gray gray

Approximate Weight (lbs) 315 360 660 630

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Subject to change without notice04.2000

E 322.73

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Trench LimitedCoil Product Division71 Maybrook Drive, ScarboroughOntario, Canada M1V 4B6Phone (416) 298-8108Fax (416) 298-2209E-Mail sales@ca.trenchgroup.com

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