APPLICATION SELECTOR...BURNDY® Products Substation — Welded/EHV US: 1-800-346-4175 Canada: 1-800-387-6487 Throughout the catalog you will notice blue highlighted items. These are
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Throughout the catalog you will notice blue highlighted items. These are the most frequently ordered BURNDY® Products.
M-3
Connectors for use in EHV Substations mustmeet essentially the same electrical andmechanical requirements as those for otherpower connectors. However, operation atextra high voltages imposes an importantadditional requirement. They must not pro-duce corona discharges that interfere withradio reception and cause energy loss.
Corona forms when the voltage gradient atthe surface of a conducting material exceedsa critical value and ionizes the surroundingair. For conductors, the four basic factorsthat determine surface voltage gradient aredistance from ground, conductor diameter,phase spacing and voltage.
In A.C. circuits, there are two basic kinds ofcorona. Negative corona forms during thenegative half cycle, and positive corona dur-ing the positive half cycle. Negative coronagenerally appears as a glow on conventionalconductors at about 20 kV rms/cm. Its ampli-tude is relatively low and causes no signifi-cant radio interference. Positive coronaappears as a plume at above 30 kV rms/cm.Its amplitude is about 50 times higher thanthat for negative corona and is the majorcause of radio interference.
BURNDY® EHV Connectors are designed sothat under fair weather operating conditions,the voltage gradient at the connector surfacewill be at a level that will not cause coronaand the resultant radio interference. (RIV)
BURNDY® DESIGN CRITERIACable ConnectorsFor reasons of economy, EHV systems usingstranded conductor are generally designedto operate at voltage gradients close to thenegative corona onset level. It is essential,therefore, that connectors provide corona-free performance superior to that of thecable. So our design criterion calls for thevoltage at which corona extinguishes fromthe connector to be higher than the voltageat which it extinguishes from the cable. Thiscriterion is met by eliminating all projectionsand by providing smooth contours on all sur-
faces. On compression elements, the endsare especially critical. Carefully designedtapers are provided to keep the voltage gra-dient at a level lower than that on the con-ductor. Of course, it is still necessary duringinstallation to smooth crimped elements.
On accessories, like spacers for bundledlines, the critical areas are those at the edgesof the bundle. The bundle itself generallyshields those parts that fall within it. Manyprojections that would cause corona on asingle conductor line are quiet when they fallwithin the shielding influence of a bundle.However, those parts that fall at the edgesare carefully finished at the factory to insurecorona-free operation.
Tubular Bus ConnectorsStation designers choose tubular bus sizeson the basis of mechanical rather than elec-trical requirements. For instance, stationsthat only need 4" IPS to meet electrical andcorona requirements often have 6" IPS asmain buses. The resultant voltage gradienton these buses is very low, perhaps only 10kV rms/cm, well below the corona onsetlevel.
It is impractical, therefore, to require thatconnectors operate quieter than the busregardless of voltage. Under some circum-stances, it might be impossible to meet suchcriteria. In most cases, it would be prohibi-tively expensive to do so.
Of course, theoretically optimum connectorscould be designed for each application,based on the design voltage gradient forindividual stations. However, in most caseseven differences as great as that between345 and 500 kV don’t have a meaningfulimpact on connector costs. So, from a prac-tical point of view, it is feasible to designmost connectors for 500 kV operation. Thismakes it more convenient for station design-ers to select and order connectors.
Bus connectors are designed to providecorona-free performance under conditions ofactual operation. This is done by calculatingthe voltage gradient on the surface of the bus
at 500 kV, using the phase spacing andground distance typical for this voltage.Connectors are then designed to operatecorona free when the voltage gradient on thebus is 10% above this value.
The exceptions to this rule are the flexibleexpansion connectors. Those designed for345 kV are self-shielding. Those for 500 kVhave separate shielding rings. Experimentalwork on self-shielding 500 kV expansionconnectors indicates that the margin of safe-ty is too small to justify recommending themfor this voltage.
CONTROLLING CORONASince corona is caused when the voltagegradient at the surface of a conducting mate-rial reaches a level that causes the surround-ing air to break down, then obviously, theway to prevent corona is to keep the gradientbelow this critical level.
From the point of view of the connectordesigner, this can be accomplished in three ways:
1. By providing generous radii on all out-side surfaces to keep the voltagestresses to a minimum.
2. By providing shielding rings.3. By placing the connector within the
shielding influence of some part of thebus structure.
Since it is impossible for the connectordesigner to know the exact configuration ofevery bus system where the connectorsmight be used, the third approach is notpractical. So, for purposes of developing astandard line, we concentrate on the firsttwo.
Whenever possible, connectors are designedto be self-shielding. This approach leads toless costly and less obstrusive designs. Onlyin the case of complicated connector config-urations do BURNDY® EHV designs usecorona rings. Examples of such applicationsare disconnectable equipment taps, expan-sion couplers and equipment terminalswhich often have configurations that pre-clude the use of self-shielding designs.
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M-4
NOMOGRAM FORDETERMINING THEEQUIVALENT
HEIGHT (he) OF A THREE PHASE LINE
Nomogram for determining the equivalentheight of a single conductor line having thesame average voltage of gradient as theCENTER conductor of a horizontally spaced
d-Phase To Phase Spacing
h-Th
ree
Pha
se L
ine
Hei
ght
Ab
ove
Gro
und
Example:
For a three phase line height, (h), of 60 ft. and a phase spacing, (d),of 40 ft., the equivalent height, (he), is 19 ft.
hdhe = ——————
(4h2 + d2)
three phase line, with the same line to groundvoltage and the same conductor size. Alldimensions measured in the same units.
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M-5
The use of the laboratory is based on the factthat it is the surface voltage gradient thatcauses corona. Although most systems con-sist of 3 phase conductors and a groundplane, it is a rather simple matter to duplicatein the laboratory the conductor surface volt-age gradient as it exists on any of thesephase conductors with a single conductorand a ground plane.
The following formula and nomograms givethis three phase to single phase equivalency.Because this conversion is possible, all EHVtesting is done single phase; and there is nonecessity for 3 phase testing with its highcost in terms of equipment and space.
Since voltage gradient is the significant fac-tor, the single phase test does not have to bedone at the full voltage of an operation
system. By setting up the test closer to theground plane, the operation voltage gradientcan be obtained with a lower test voltage.There is a limit, however, below which theheight cannot be lowered lest corona onsetand flashover occur simultaneously.Generally, the minimum test height should beabout 10 times the diameter of the test conductor.
GRADIENT CALIBRATORNormally, the conductor surface voltagegradient at the extinction of corona in thelaboratory is calculated using the accompa-nying equations. However, for test setupsinvolving unusual conductor configurations,the conductor gradient cannot be readily cal-culated. In these cases, a gradient calibrator
may be used. This is a small sphere mount-ed on the conductor. It has previously beencalibrated for each conductor size to estab-lish the surface voltage gradient that startspositive corona on the sphere. With it testscan be duplicated in any number of laborato-ries. The applied voltages and ground dis-tances could all be different. But the voltagegradient on the surface of the conductorwhen the corona occurs on the sphere willalways be the same. The calibrator providesa convenient bench mark for measuring thecorona performance of connectors.
In use, the sphere is mounted on the con-ductor in a connector test setup. The voltageis raised until there is a corona on the sphere.We already know from previous calibrationwhat the voltage gradient on the surface ofthe conductor is at this point.
The sphere is removed and the voltageraised until there is a corona on the connec-tor. Since the voltage gradient increasesdirectly with increases in applied voltage, thegradient on the conductor at this point canbe readily calculated.
It is important to note that the significantparameter is the voltage gradient on thesurface of the conductor. It is not necessary
to know the gradient on the connector. Theconductor gradient in any given substationis controlled by its design parameters andmay be calculated using the followingformulae and nomograms. Once thegradient is known, it is unnecessary to haveany other information to design connectors.As long as connectors are corona-free at aconductor voltage gradient higher than thatplanned for the conductor, the connector
will be corona-free under fair weatheroperating conditions.
There may on occasion be unusual situationswhere choice of conductor, station geometryor clearance problems cause the need forconnectors of special design. Where this isthe case, BURNDY® is prepared to designcorona-free devices to operate under such conditions.
The center conductor has a gradient about 5% higher than the outside conductors. The gradient on the center phase may be calculated using the formula for the single conductor.Single phase system and substituting (he) from the following formu-la or attached nomograms for the height above ground (h). For the center phase:
Bundled Conductor - Three PhaseThis case may be reduced to the single bundled conductor case by replacing h with he in the equation.The definition of he is identical to that given for the single conductor –– three phase situation.
The maximum gradient (Em) occurs on the side facing the groundplane.
Formula for Determining The Voltage GradientNotations Used
h = line to ground distance (cm) he = equivalent single phase line to ground distance (cm)r = radius of the individual conductor (cm) re = equivalent single conductor radius (cm) of bundleds = conductor spacing in the bundle (cm) conductorsd = phase to phase spacing of the line (cm) n = number of conductors in the bundleV = line to ground voltage (kV)Ea = average gradient at the surface of the conductor (kV/cm)Em = maximum gradient on the surface of a single conductor
It should be noted that he is somewhat smaller than
The value of � � is unity for 1-, 2-, and 3- conductor bundles and1.12 for 4- conductor bundles.
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M-7
NOMOGRAM FOR FINDINGTHE AVERAGE CONDUCTOR-SURFACEVOLTAGE-GRADIENT FROM LINE DIMENSIONSAND VOLTAGE.
Example: For a 30 ft. high single phasebus* of 4" diameter, V/E = 30. At 450 kVto ground the average conductor-sur-face voltage-gradient is 15 kV RMS/CM.
* For the equivalent single phase height(he) of a 3 phase bus arrangement seepage 5.
There is serious question as to whethermeasurement of RIV on connectors makes ameaningful contribution to quieter stationoperation.
Under test conditions, there is generally nosignificant indication on the radio noisemeter until the onset of visible positive coro-na. At this point, the RIV reading goes intothe hundreds of thousands of microvolts.The effect of this phenomenon is to provide avisibly discernable point at which RIV willbecome excessive. It eliminates the necessi-ty to make, record and plot RIV measure-ments. Where there is no corona, there is noRIV. So our test criterion calling for no visiblecorona insures that there will be no radiointerference generated by the connectorunder operating conditions.
EFFECT OF CONDUCTORSIZE ON TESTINGConductor diameter has a significant effecton potential corona problems. The larger thediameter, the lower the surface voltage gradi-ent for a given test voltage. This means thatsmaller conductors produce corona at lowervoltages than larger ones.
Many connector designs have the samebasic configuration for various conductorsizes. The only difference being the size ofthe attaching elements. This is particularlytrue for many of the welded type connectors.Where this is the case, it is often sufficient totest the connector only on the smallest con-ductor, since it yields the lowest coronaextinction voltage. When there is any doubt,each size is tested.
CONTAMINATIONMuch work has been done to establish therelationship between the corona onsetvoltage for contaminated as compared toclean hardware. Experiments in the
BURNDY® laboratory indicate that this valuecan be reduced to half of the voltage forclean hardware. However, the relationshipvaries with the kind of contamination, atmos-pheric condition and type of connector.
There have been a number of attempts toproduce artifical contamination and atmos-pheres in laboratories. However, there is asyet no clearly established relationshipbetween the corona performance of hard-ware contaminated in the laboratory. Untilsuch a relationship is established, the onlytesting that provides comparable data is onclean hardware under fair weatherconditions.
CONCLUSIONFor more than 80 years, BURNDY® has beendesigning connectors for the industry’s mostcritical applications. Connectors for EHV arean outgrowth of this tradition. Whether yourneed is for catalog items or special designs,you can count on electrical, mechanical andcorona-free performance, commensuratewith the application.
2300 kcmil through 2156 kcmil through 84-19 1.741 1.875 2.62 4.00 4.25 1.84 3.31 7.50 1.12 1.12SWA486A-44N
2500 kcmil 2300 kcmil 96-19 [44] [48]1
[67] [102] [108] [47] [84] [191] [28] [28]
NOTES:1. Dimensions in brackets [ ] are in millimeters.2. DOES NOT INCLUDE SHIELDING CAPS. For EHV
applications, shielding caps are required. Order separately(type) shown on page 32 or ADD SUFFIX “STS” to catalognumber (example: SWA54R-44NSTS), includes oneshielding cap.
3. One surface of pad finished. For finished pad on bothsides add SUFFIX “Q” to the catalog number (example:SWA22A-44NQ).
4. For 45 or 90 degree angle add SUFFIX “45” or “90” tocatalog number (example: SWA54R-44N90).
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M-11
WELDED TERMINALCONNECTOR
SWAC-A-N
Weld typeApplication: Bus to Two or Four
Hole Pad (center formed)
EHV RATED: UP TO 550 kVwhen used withShielding Caps
Material: Cast 356 Aluminum Alloy
NOTES:1. Dimensions in brackets [ ] are in millimeters.2. Conductor smaller than 3 inch bus size not recommended
for 550 kV.3. DOES NOT INCLUDE SHIELDING CAPS. For EHV
applications, shielding caps are required. Order separately(Type STS) shown on page 32 or ADD SUFFIX “STS” toCatalog Number (example: SWAC22A44NSTS), includestwo shielding caps.
4. Pad surface finished on both sides of tongue.5. For six hole NEMA pad contact factory.
Catalog Number Conductor Fig. Dimensions In./[mm]IPS (Sch. 40) EHPS (Sch. 80) IPS A No. B L T
NOTES:1. Dimensions in brackets [ ] are in millimeters.2. “G” dimension conforms to NEMA standards.➂ Cap mounting (galvanized steel) hardware supplied as
standard. For Base Mounting hardware add SUFFIX “B” tocatalog number (example: SWOH22A-5B).
4. Conductors smaller than 3 inch bus size notrecommended for 550 kV.
NOTES:1. Dimensions in brackets [ ] are in millimeters.2. “G” dimension conforms to NEMA standards.➂ Cap mounting (galvanized steel) hardware supplied as
standard. For Base Mounting hardware add SUFFIX “B” tocatalog number (example: SWSUH22A-5B).
4. Conductors smaller than 3 inch bus size notrecommended for 550 kV.
➄ Four aluminum alloy bushings are supplied for slip fitinstallations.
Throughout the catalog you will notice blue highlighted items. These are the most frequently ordered BURNDY® Products.
M-21
WELDED RIGID ORSLIP FIT BUSSUPPORT
SWHRH-A
Welded typeApplication: Fixed or Slip Fit Bus
Support to Insulator.
EHV RATED: SELF-SHIELDINGUP TO 550 kV—When used oncorona free PostInsulators.
Material: Cast 356 Aluminum Alloy
NOTES:1. Dimensions in brackets [ ] are in millimeters.2. G dimension conforms to NEMA standards.3. Cap mounting (galvanized steel) hardware supplied as
standard. For Base mounting hardware add SUFFIX “B’” tocatalog number (example: SWHRH22A-5B).
4. Conductors smaller than 3 inch bus size not recommend-ed for 550 kV.
AluminumCatalog Number Catalog Number Conductor 3� Bolt Circle 5� Bolt Circle3� Bolt Circle 5� Bolt Circle IPS/EHPS “A” Dia. G H K L W K L W
Cable Range Cable Dia.Catalog Number A.A.C. A.C.S.R. Min. Max. “J” Dia.
2000 kcmil 91 Str. (1.630 Dia.) 1890 kcmil 84/19 Str. (1.650 Dia.) 1.632 1.737 5/8”-11 � 2” LG.S3GBP483A
2250 kcmil 91 Str. (1.729 Dia.) 2167 kcmil 72/7 Str. (1.737 Dia.) [41] [44] Alum. Alloy
NOTES:1. Dimensions in brackets [ ] are in millimeters.2. For stainless steel hardware add SUFFIX “SS” to catalog
number (example: S3GBP48ASS).3. For variations in cable spacing contact factory.4. Not recommended for overhead transmission lines.5. For four hole straight pad tap or 90° version or bus sup-
port three bundled cable spacer, contact the factory.