H A N S V O N M A N G O L D T A A C H E N

IRON-CORE REACTORSFOR DETUNING POWER

CAPACITORSIN MEDIUM AND LOWVOLTAGE NETWORKS

ED DTR 04.01

Harmonic networkdistortion and its effects

(background)

Electrical power supply to industrial networks isnowadays polluted to the same degree as the air webreathe in the major conurbations and large cities ofour planet. This is due to increasing application ofnon-linear loads, such as variable speed drives,frequency converters and rectifiers, but also theastronomically high number of electrical energyconsumers. The outcome is unusually high levels ofharmonic distortion, not only resulting in unnecessarylosses from transmission lines, but also in non-calculable resonances between network inductancesand power factor correction capacitors. This was previously not a major problem, because thedesign of capacitors for power factor correction(mixed dielectric and liquid impregnation containingPCBs) meant that such capacitors were relativelyinsensitive to line distortion. Following the world-wide banning of electrical components containingPCBs, this kind of capacitor had to be replaced. Overthe last twenty years, capacitors made of metallizedpolypropylene film have found application. This new capacitor design provides many advantages,chiefly very low loss dissipation and small volumecombined with low weight. However, advantagesoften go hand-in-hand with disadvantages and thisalso applies to metallized film capacitors: a distinctsensitivity to harmonic distortion, currently a familiarand increasing problem in industrial networks.

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Several phenomena associated with this problem canproduce substantial premature aging in fi lmcapacitors:

1. Harmonic distortion in extended networks inducesresonance between inductances of the networkand power capacitors, resulting in excessivecapacitor heating.

2. Harmonic currents over and above the funda-mental load result in voltage drops across thecapacitor elements which may exceed the voltagethe capacitor was designed for. This causes partialdischarge and results in extreme self-healing eventswithin the capacitor elements, liable to shortencapacitor life considerably.

3. Excessive harmonic currents can overload theinternal connections between the cables andcapacitor film, causing the arc-sprayed zinc layer tobe stripped off from the surface of the capacitorcoil

The problems discussed above are in no way re-stricted to low-voltage networks. Capacitor banks inmedium-voltage power supply systems are implicatedin the same way.

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in power factor correction equipment. In configurations of this kind, serial reactors areconnected to the capacitors. The serial reactorsdetune the circuit to a frequency below the 5th (or3rd) harmonic, which is the most significant in aharmonic-rich environment. In Europe, detuning by afactor of 3.78 times the line frequency is mostcommon, whereas in other parts of the world, inparticular in Asia, a factor of 4.08 is standard (Fig. 1).

The thinking behind this solution is quite simple: theimpedance of L/C resonance circuits is capacitivebelow the resonance frequency, and becomesinductive above this value. At line frequency thecapacitive load of the capacitor is thus dominant,enabling it to achieve a perfect power factor

Remedial measuresand what they can achieve

When film capacitors first started to be manu-factured, the only way of avoiding prematurecapacitor failure was over-dimensioning the thicknessof the capacitor film. This dealt with the excessiveovervoltages due to harmonic currents in a betterway. However, this method proved to be ratherexpensive and not very appropriate to withstandingresonance conditions, which in extended networksare difficult to plan for. This called for an effective and simple solution forextending the life-time of power factor correctionequipment, while at the same time eliminatingresonance amplification. Over the last couple of years, the use of detunedfilter circuits has proved to be a very reliable and safeway of avoiding premature failure or excessive aging

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Fig. 1: Common detuning factors and ordinal of resonance

correction (see Fig. 1). The fact that the L/C filter isinductive above its resonance frequency eliminatesthe occurrence of any resonance between cableinductances and power factor correction equipment.In particular, all harmonic currents above the tuningfrequency of the filter are limited to values whichdepend only on the voltage distortion in the relevantnetwork. Sensitive capacitors are thus spared anyunpredictable situations. Apart from this obviousadvantage, there are two other effects related todetuning power capacitors which should beremembered. As Graph shows in Fig. 1, theimpedance of an L/C filter relative to the fundamentalimpedance of the capacitor versus frequencyvariation starts at 1 and reaches its minimum atresonance frequency. Beyond this, impedance doesnot increase sharply, but steadily rises to infinity. Theresult of this is a harmonic filtering effect beyond theresonance frequency, which does however decreasewith the order of the harmonic frequency. Thus,capacitor detuning usually cleans the network ofharmonic distortion. A second advantageous effect is based on the laws ofphysics: the vector of the voltage across the reactorcorresponds to network voltage. This means that thisvoltage is added to line voltage, and the sum of thetwo is present at the capacitor terminals. Again, thelaws of physics tell us that the reactive power of acapacitor increases in proportion to the square of thevoltage increase. However, we have to rememberthat this increase is partly compensated for by thereactive power of the reactor. As a result, the gain ofreactive power due to the reactor is

___1___

which means that capacitance can be reduced byp(%) to arrive at 100 % NC in respect of the serialreactor. At the same time, care must be taken indealing with the extra voltage (Fig. 2).

Reactor designand technology

High demands are placed on reactors. Reactors areconnected in series with capacitors and thus need tobe able to withstand losses resulting from bothfundamental and other harmonic currents withoutthe temperature range of the insulation materialbeing exceeded under actual environmentalconditions. Moreover, inductance accuracy must beto within close tolerances, and sufficient core linearitymust obtain to withstand switching of capacitor stepswithout causing saturation problems in networks ofhigh harmonic distortion.

- 1 (%),___1001-

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Fig. 2: Gain of reactive power due to the detuning reactor

p

Expertise unique toMangoldt

The success that Mangoldt reactors have enjoyed isno miracle. Our achievement is the result of soundand detailed engineering (1), imaginativemanufacturing (2), uniquely innovative measuringequipment (3) and excellent support from our salesforce (4)

(1) The software we have developed enables ourdesign engineers to optimize reactor design toprovide customers with a tailor-made product, inwhich their requirements with regard to losses,dimensions and environmental conditions aregiven our full attention. To facilitate reactorinstallation in a given configuration, customerscan obtain CAD drawings as pdf files by e-mail(Fig. 3).

Fig. 3: CAD work station

In the case of medium-voltage reactors, otherrequirements, such as the capacity to withstandinduced overvoltage, fault level and BIL, have to beconsidered.Our company, Hans von Mangoldt, is able to lookback on more than 20 years experience insuccessfully handling such tasks. Starting withtransformer production only, Mangoldt decided inthe seventies to focus their future energies on thisgrowing filter market. Time has proved this decision asound one. Today, there are few countries aroundthe world where Mangoldt reactors are not inoperation. Typical industrial applications are cementand steel mills, furnace compensation, the chemical,petrochemical and rubber industries, car assemblyplants and public transportation systems, while otherapplications include high-rise buildings, hospitals,public water supply systems, flicker compensators,active filters, wind generators, motor starting devicesand dynamic compensation systems. Mangoldtreactors function in an unobtrusive and efficient way.The main downside of iron-core reactors is theirl imited linearity and the high cost in outdoorinstallations. Yet iron-core reactors are findingincreasing acceptance among expert consultants insituations where air-core reactors were previouslyused. This is because space available for reactorinstallation is limited and also because linearityis not a major concern. In applications like these,Mangoldt reactors, with a design which preventsmagnetic leakage and ensures low losses and noiselevel, provide the best solution. Mangoldt reactorscan be mounted within metal enclosures or in switchrooms, correctly observing clearances so as to obtainthe BIL level required and making sure that ventilationis sufficient for dissipation of reactor losses (specifiedin the quotation we give ahead of the customerspurchase order).

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(2) High-precision core lamination punching forelimination of inductance tolerances between thethree phases, or to enable accurate reactortuning. Applying copper or aluminum band coilsusing computer-controlled winding machineswhich use cold pressure welding for theconnection of copper bar terminals. Mountingcoils on multi-gap cores and impregnation of thecomplete unit under high vacuum andoverpressure with a high-grade thermosettingvarnish. All production phases have been fine-tuned to a standard of excellence, ensuring that

quality standards are maintained as demanded bythe DIN EN ISO 9001 specification (Fig. 4).

(3) Database-controlled test equipment is used forroutinely completed reactor testing at nominalcurrent. For type-testing Mangoldt has aunique three-phase harmonic generator rated atapprox. 0.9 MVAr, enabling to test reactors in arealistic environment, i.e. simultaneously loadedwith fundamental and specified harmonic currents(which can also be modified in respect ofamplitude and angle of shift). Thus heat-run andnoise dissipation tests are available, as well asinduced overvoltage tests for product reliabilitytesting (Fig. 5).

(4) As required, Mangoldt is able to supply clientswith high-grade measurement equipment, plusthe analytical expertise of a team experienced infinding solutions to low-voltage network tasks.

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Fig. 4: Assembly of a three phase iron cored reactor

Fig. 5: Harmonic generator for real load tests

Design Criteria

Since it is impossible to predict conditions prevailing in the network where the reactor will do its job, all reactorshave to be designed for a defined worst-case scenario, meeting all tolerances laid down by the internationalstandard IEC 60289. In the absence of an appropriate standard relating to network quality, this worst-casescenario had to be agreed between leading power factor capacitor suppliers and Mangoldt. These are thedesign criteria of proven reliability over a period of many years:

Tolerance for inductance: - 2 % ... + 3 % of LN

Fundamental current I1: 1.06 ICN or 1.10 ICN (for 6% or 10 % overvoltage respectively)

Assumed harmonic voltage distortion: UH3 = 0,5 %; UH5 = UH7 = 5,0 %; basing on UN

Thermal current Ith: 1.05 Irms (relative to worst-case tolerances and capacitor aging)

Limit of core linearity ILin: 1.20 I1...7 (relative to switching procedures at full harmonic load)

Assumed ambient temperature: 40 C

These design parameters remain unchanged for medium-voltage reactors

Against a background of deteriorating network quality, standards have now been launched, making correspondingadjustments to the Mangoldt design for low voltage reactors necessary as follows:

Tolerance of the inductance: 3 % of LN

Fundamental current I1: 1.10 ICN (for 10 % overvoltage)

Assumed harmonic voltage distortion: UH3 = 0.5 %, UH5 = 6.0%UH7 = 5.0 %, UH11 & UH13 = 3.5 % relative to UN

THD: limited to 8 %

Thermal current Ith: 1.0 Irms (neglecting tolerances and capacitor aging)

Limit of core linearity ILin: k ICN where k = f(p) (p = 5.0 / 5.67 / 6.0 / 7.0 / 12.5 / 13.0 / 14%)

Assumed ambient temperature: 50 C

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There is thus no question that reactors manufacturedby Mangoldt...

- ...are designed and manufactured according to theabove-mentioned specifications and under theconditions laid down by DIN EN ISO 9001(Registration No. 09 100 6544), and, as necessary, toUL File No. 173 113

Proof of load capacity as specified can be provided inthe form of a heat-run test report, available onrequest for a corresponding extra fee (Fig. 6).

- ...are multi-gap. The cores are punched out of cold-laminated steel to a standard of very high precision,thus ensuring low tuning tolerance (Fig. 7)

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Fig. 6: Heat-run test report

Fig. 7: Production of core laminations

- ...have wire wound coils, or aluminum or copperband coils. With aluminum band, the copper barterminals are welded to the aluminum by coldpressure welding (Fig. 8)

- ...are impregnated as a complete unit undervacuum and overpressure using thermosettingimpregnation varnish of temperature class H (Fig. 9)

- ...are measured at nominal current using data basetest equipment. If the inductance is outside thespecified tolerance, the equipment does not print thename plate and test report (Fig. 10)

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Fig. 8: Computer controlled winding machines Fig. 9: Vacuum/overpressure impregnation equipment

Fig. 10: Data base test equipment for routine tests

How to getthe reactor you need

Since Mangoldt reactors are currently exported tomore than 30 countries around the world, thepotential range of different networks is extensive.Mangoldt has therefore decided not to print adetailed catalog, but to make use of the Internet,thus enabling customers to identify the products theyrequire by using the Mangoldt website. On ourwebsite there is a menu to guide you through thecatalog pages on the site. Go to the website at

www.mangoldt.com

to find the reactor you are looking for. You will finduseful data about current values and losses (includingdiagrams). Prices are available on request. (In case ofproducts outside the scope of the above-mentionedspecification standard, we shall be happy to deal withyour direct inquiries).

Temperature monitoring

All low-voltage reactors can be fitted with atemperature control device in the center coil(available for all coils, if requested).Medium-voltage reactors are available withtemperature monitoring in the core only. The sensorscan be microswitches (normally closed or normallyopen), thermistors or PTC sensors.In addition, Mangoldt can provide low-voltagereactors including a retrofit device, i.e. the center coilincludes an insertion slot for later installation of atemperature sensor. This sensor can be supplied byMangoldt soldered to a screw terminal and is easyto fit.

Important: Please specify the reactor temperatureclass when ordering the retrofit set. Please alsoremember that when monitoring all coils, normallyopen switches must be connected in parallel,whereas normally closed switches are connected inseries.

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Mechanical design features

Low-voltage reactors come complete with mountingbrackets (and lifting devices if weight exceeds 35 kg).

Medium-voltage reactors are fitted with lifting eyesand can be supplied with an optional bidirectionalsub-assembly. All reactors of this type come mountedon mounting tracks including rubber/metal mountingfittings (standard feature). Terminals can be fitted onone or both sides of the reactor. If desired, supportinsulators at top of the reactor can be provided forfixing the copper bar terminals.

Where network voltages exceed 17.5 kV, single-phase reactors mounted on cast-resin insulators andrubber/metal mountings are the Mangoldtstandard. With reactors of this type, the core isconnected to the serial connection of the two coils.

All reactors can be supplied in a sheet-metal housing,as required.

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Hans von Mangoldt GmbH & Co. KG is appropriately equipped to meet the requirements which activity in theinternational market place and the occupation of a position of increasing importance in that market implies. Ahighly-motivated and experienced workforce make a vital contribution to the success of the company. The use ofstate-of-the-art production systems, together with self-defined high demands for quality and reliability allowcustomers to have absolute confidence and trust in the products they order. The management of HvM looks to

the future, firmly determined in maintaining its success in meeting this quality objective.

PRODUCTION RANGE:Single phase dry type transformers up to 400 kVAThree-phase dry type transformers up to 800 kVA

Transformer for special applicationRectifier transformersSmoothing reactors

Audio frequency blocking filtersFilter reactors for low and medium voltage power capacitors

Single phase magnetic voltage stabilizers up to 2 kVAElectronic voltage stabilizers up to 100 kVAPower electronics for special applications

H A N S V O N M A N G O L D T G m b H & C o. K GHergelsbendenstr.18

D-52080 Aachen Germany /AllemagneTelefon ++49 (0)241/1 66 07-0Telefax ++49 (0)241/1 6607-35

www.mangoldt.comE-Mail: info@mangoldt.comCertified to DIN EN ISO 9001Registration No. 091006544