power distribution - Siemens

TransformersSentron Harmonic Mitigating Transformers (HM1 & HM2)Descriptionthe 3 rd , 9 th and 15 th harmonic currentsare canceled as previously described,The Sentron Harmonic Mitigatingand additionally the 5Transformers (HMTs) are designed toth and 7 th harmoniccurrents are cancelled in the electricalmeet the needs of modern powersupply common to both transformersdistribution systems that contain a largedue to their relative 30° phase shift.percentage of non-linear equipment thatproduces harmonics. Some examples of If a single harmonic mitigatingthis type of equipment are computers, transformer (0°) is used in an existingprinters, fax machines, scanners, copiers, or new system utilizing standarduninterruptible power supplies, ballast delta-wye transformers (-30°), the 5 thand variable frequency drives (VFD).and 7 th harmonic currents originatingThis type of equipment generatesfrom the HMT transformer (0°) willharmonic voltages and currents because attempt to cancel the 5 th and 7 ththey contain AC to DC power conversion harmonic currents originating from therectifiers. Harmonic voltages andstandard delta-wye transformer (-30°).currents can cause a variety of problems This reduces the overall 5 th and 7 thranging from poor power factor, voltage harmonics present in the system, withdistortion, capacitor resonance and motor the actual reduction dependent on thefailures to overloaded transformers and magnitudes of the secondary loads.conductors.Double-Output Harmonic MitigatingThe Sentron HMTs are specially designed Transformer (0° and -30°, -15° and -45°,to operate under high non-linear load or +15°and -15° primary-secondaryconditions and have the additional benefit angular displacement)of improving the overall power system The primary of this transformer has areliability.delta connection and its secondary hasApplicationdouble-output, special double windingconnections with 30° phase shiftOne of the most effective ways tobetween outputs. This arrangementeliminate power system harmonics is tocancels the 3use a technique known as “phaserd , 5 th , 7 th , 9 th , and 15 thharmonics at very low impedanceshifting.” In this method power systemon the secondary side. This greatlyharmonics are eliminated by pairingimproves voltage distortion for thetogether harmonics that have 180°loads and the primary power factor.relative angular displacement, whichThe advantage of this arrangementcauses them to cancel one another out.is that the reductions of harmonicThis can be accomplished by a varietycurrents are achieved with oneof means:transformer creating a 12 pulse load.Single Output HarmonicIf two of these transformers are used,Mitigating Transformerwith the primaries of each phase(0° or -30° primary-secondaryshifted 15° with respect to oneangular displacement)another, then cancellation of harmonicsThe primary of this transformer has a up to the 19 th are achievable creatingdelta connection and its secondary has a 24 pulse load.a special double winding connection.BenefitsAlthough there is only one secondarythree phase output, the 3 rd , 9 th and 15 th Elimination of undesirable harmonics byharmonic currents are prevented from using the Siemens Sentron HMTs is ancirculating in the primary windings by effective solution to the power qualitycanceling their magnetic fluxes at low problems encountered by today’s powerimpedance with the double winding system professionals. By treating thesecondary, reducing voltage distortions harmonics at their source, usingto the loads.advanced technology, installationproblems can be avoided and overallWhen two transformers with thissystem reliability improved. The Sentrontype of connection, 0° and -30°HMT product line provides many fardisplacement, are used in parallel,Selectionreaching benefits such as loweroperating cost, improved operatingefficiency, reduced down-time due tooutages caused by nuisance tripping,and increased equipment life due tolow voltage distortions.Design and ConstructionFeaturesThe Sentron Harmonic MitigatingTransformers comply with all applicableANSI/IEEE standards includingC57.12.91, C57.96, C57.110, CSA #C22.2 No. 47 (CUL), UL506, UL1561 aswell as NEMA ST-20. The design life is25 years at 130 degree C rise, 30 yearsat 115C rise and 40 years for 80C risemodels. Approvals and listings includeUL, CSA. with CE approval availablewhen requested. The Sentron HMTshave capability up to the load capabilityup to K-20, which is achieved byharmonic cancellations in the secondaryand low flux density design forprotection against heat in place ofdesign enlargement protection only.Copper coil windings with full widthcopper foil electrostatic shield arestandard and additional shield optionsare available for higher noise attenuationrequirements. All HMTs have 130C risewith optional 115C and 80C winding risedesigns available. All designs includevacuum impregnated polyester resinencapsulation of windings and NEMA 3Renclosures. A neutral sized at 200% ofthe ampacity of the secondary phaseconductors for extra protection againsttriplens and unbalanced single phaseloads. The Sentron HMT designs haveTP1 energy efficient rating equal to thatof a non K-Factor rated transformer andhave the Energy Star emblem displayed.Siemens HMT designs have TP1 efficiencylevels at 35% load @ ref temp. 75degree C and also retain TP1 efficiencylevels at 65% load @ referencetemperature 85C. A ten-year pro-ratedwarranty with standard liabilitylimitations applies to all Sentron HMTs.7 TRANSFORMERSSiemens Power Distribution & Control, SPEEDFAX 2007-2008 Product Catalog 7-15