arc suppression coils
DESCRIPTION
ElecticalTRANSCRIPT
Arc Suppression Coils
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The most common type offailure in an electrical powerdistribution network is a singlephase-to-earth fault. Manyutilities are successfullymitigating the effects of thistype of fault by the use ofearthfault compensationsystems.
Introduction
In this scheme the systemneutral is earthed through ahigh impedance reactor, a socalled arc suppression coil(Petersen coil), which isadjusted to the earthcapacitance of the network.
By utilizing continuouslyvariable arc suppression coils,ideal compensation of theearthfault current, and there -fore optimal efficiency of theresonant earthing techniquecan be achieved.
Fig. 1 20 kV Arc Suppression Coils
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Arc Suppression Coil(ASC)
Since the topology of anelectrical power distributionnetwork is subject to dynamicchanges, the inductance ofthe arc suppression coil usedfor neutral earthing must bevariable.Two basic principles to varythe inductance exist:
• by performing switchingoperations on the reactorwhereby coil sections areconnected or disconnected(step coil), or
• by continuous variation ofthe reluctance of themagnetic circuit by means ofa mechanical drive (plungercore coil).
The earthfault protection systemdeveloped by Trench Austriafavours the plunger core coilcompared to a reactor which isadjustable in finite steps, as
• no switching operations forinductance variation arerequired (preferable sinceswitching can easily lead tonetwork perturbationsduring earthfault) and
• plunger core coils can betuned precisely to minimumcurrent at the fault locationdue to their continuousvariability.
Based on years ofexperience in the
construction of arcsuppression coils, the
coil design concept wasthoroughly reviewed,resulting in a new and
improved series of ASCswhich meet today’srequirements for
earthfaultcompensation. Bymeans of modern
planning andproduction processes
substantial cost savingsfor plunger core coilswere also achieved.
The plunger core coilapproach provides thefollowing advantages:
• continuously variable (in on-load condition) by means ofvariation of the air gap
• the adjustment is accom -plished by means of a motordrive unit which may beeither locally or remotelycontrolled
• automatic tuning to theactual network condition viaan earthfault compensationcontroller
• as current regulation is not
achieved by connecting ordisconnecting windingsegments, the core inductionis practically constant withinthe whole regulation rangeand slightly below satur -ation. As a consequence,overvoltages in the systemare limited.
• compact construction
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Principle Construction
Fig. 2 Principle construction of an arc suppression coil
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Technical Data
power range 200 kVAr – 35 MVAr
voltage range up to 145/√3 kV
insulation levelrated voltage up to 36 kV fully insulated or graded insulatedrated voltage > 36 kV graded insulation
duty • 2 hours short time duty• continuous duty
current regulation range 10 % – 100 %
rated frequency 50 Hz (60 Hz on request)
cooling method ONAN (self cooling)
installation indoor or outdoor
Fig. 3 20 kV Arc Suppression Coil
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Standard Design /Equipment
- iron cored, oil insulated coilwith continuously variable airgap adjustment in on-loadcondition by means of aplunger core
- suitable for automaticearthfault compensation viathe Trench Austria earthfaultcompensation controllerEFC50/EFC50i (see accessories)
- motor drive unit: TrenchAustria model DMA,230/400 V, 50 Hz, (control-voltage 230 V, 50 Hz),mounted on top of the tank,with hand-crank for emer -gency service and potentio -meter for remote positionindication, with separatecontrol cabinet mounted onthe side wall of the tank atoperational height
- in oil-filled corrugated steeltank with air cushion
- oil-filling: mineral oil onnaphthenic basis, PCB-free,accord. to IEC 60296 : 2003
- mobile base with bi-directional rollers
- porcelain bushings as per DIN;for Um > 36 kV condenserbushings
- protective cap over lowvoltage bushings
- voltage measuring winding100 V/3 A
- power auxiliary winding (500 V, 5 % of coil power,30 s short time duty) forcurrent injection used for theTrench Austria earthfaultprotection system EPSY (for adetailed description refer toour brochure EPSY EarthfaultProtection System)
- one additional pocket for oiltemperature indicator as perDIN 42554
- oil gauge without indicatingcontacts
- dehydrating silicagel breather
- surface treatment with zincprimer and multiple coating,top coat colour grey as perRAL 7033
Routine Tests
- measurement of windingresistance
- measurement of current overthe whole adjustment range
- measurement of voltage ratiobetween main winding andsecondary windings
- separate-source power-frequency voltage test
- induced overvoltage test
- operation tests of core airgap mechanism
Type Tests
on request, as per agreement
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Special Designs /Optional Equipment
- steel tank with flangemounted radiators
- with detachable oilconservator (OC)
- double float Buchholz relay as per DIN 42566 (only withOC)
- various insulating fluids
- current transformer
- power auxiliary winding(with extended power rating,continuous or short timeduty)
- devices for temperaturesupervision
- minimum oil level indicatorwith indicating contacts(without OC)
- magnetic type oil levelindicator with/withoutindicating contacts(only with OC)
- plug-in cable terminationsystem
- surge arrester
- different motor drive types
- alternative motor voltages
- devices for remote indication
- supplementary resistormounting brackets/hardware(only in connection with acorresponding power auxiliarywinding)
Abb. 4 077/√3 kV, 31500 kVAr, short time duty 2h
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Special ASC Designs
- air insulated resistor forresistive residual currentincrease (see accessories)
- skid base
- hot galvanized
- paint/colour as per customer’sspecification
Sliding Core ASC
Simplified design for a powerrange within 200-1250 kVAr,current regulation range 1:5with hand or motor drive.Optional equipment as perplunger core ASCs.
Neutral EarthingAggregate
Compact construction of anarc suppression coil and acorresponding earthingtransformer, housed in acommon oil-filled steel tank.For a detailed description referto our brochure NeutralEarthing Aggregates.
Fixed Core ASC
Iron core coil with multiplesub-divided air gap forcompensation of invariablenetwork sections, withoutadjustment device.
Technical Data
power range up to 1250 kVAR
voltage range up to 10 kV
insulation level graded insulated to 1 kV
max. BIL 60 kV
duty • 2 hours short time duty
• continuous duty
current regulation range 10 % – 100 %
rated frequency 50 Hz
cooling method AN
installation indoor
Dry Type ASC/Neutral Earthing Aggregat
Design with epoxy resignimpregnated windings.
Fig. 5 Dry Type Neutral Earthing Aggregate 6 kV / 400 kVAR
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Accessories
Shunt Resistor
In order to eliminate earthfaultsrapidly, the faulty feederhas to be detected quickly andselectively.
One approach for detection oflow-ohmic earthfaults is therecognition by means ofwattmetric directional relays.When this approach is used it issometimes necessary to
increase the residual earthfaultcurrent via a low voltage shuntresistor connected to thepower auxiliary winding of theASC.
Fig. 6: air cooled resistor in stainless steel
enclosure, protection class IP23,
built on to the ASC base,
electrically connected to the power
auxiliary winding, including
contactor and thermal overload
protection.
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ElectronicResistor Control EZA3
The electronic resistor controlEZA3 is used for controlling alow voltage shunt resistorwhich is connected to thepower auxiliary winding of thearc suppression coil. It alsoprotects the resistor and thepower auxiliary winding of theASC from thermal overload.
Earthfault Compen sationController EFC50
When changes occur in thenetwork topology the arcsuppression coil must be
Fig. 8 Resistor control EZA3
Fig. 7 Earthfault Compensation Controller EFC50
immediately adjusted to themodified network. This task isachieved by the Trench Austriaearthfault compensationcontroller EFC50 throughadjustment of the inductance
of the ASC to the actual sys -tem earth capacitance. For adetailed description refer toour brochure Earth-FaultCompensation ControllerEFC50 / EFC50i.
Subject to change without notice04.11
E 670
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