Application Note Sine Wave Filter Solutions For Motor .
Application Note1Sine wave filter solutions formotor drive applications
Note: This document is in Contenttended to support designers,installers, and applicationengineers with sine wave1. Technical background 32. Motor drives output phenomena 4filter selection, installation,application and maintenance2.1 Excessive dv/dt 42.2. Peak- and overvoltage 5In order to get the maximum2.3 Additional losses in the motor 6benefit out of the Schaffner2.4 Cable shields and parasitic earth currents 6filters, please also consult2.5 HF electromagnetic noise in the motor cable 7“Basics in EMC and Power2.6 Bearing currents 8Quality”, published in2.7 Acoustic motor noise 9in motor drives applications.the download section ofwww.schaffner.com.3. Output filter solutions for motor drives 10These additional guidelines3.1 dv/dt reactor 10provide helpful hints for HF-3.2 dv/dt filter 11grounding, shielding, prop 3.3 Sine wave filter 12er cable routing including a3.3.1 Symmetrical sine wave filter 13chapter “Output solutions for3.3.2 Sinus plus symmetrical and asymmetrical sine wave filter 14motor drives”.4. Sine wave filter selection 16Schaffner will not assume4.1 Current and voltage rating 16liability for any consequential4.2 Frequency 17downtimes or damages4.3 Required drives settings 18resulting from use or appli 4.4 Voltage drop considerations 20cation of this document and/or installation of Schaffnersor any other sine wave filter.5. Application examples 215.1 Motor drive with long motor cable 215.2 Motor drive with multiple motors in parallel 215.3 Retrofit installations with motor drives 215.4 LV motor drive with MV-motor/ 22step-down / step-up transformer application 6. Mounting and installation guidelines 2226.1 Important safety considerations 226.2 General application notes 236.3 General installation notes 246.4 Mechanical mounting 256.5 Wiring and cabling 25
1. Technical backgroundWhenever electricity is used to drive an equipment, in particular when amotor drive is controlling the speed of an electric motor special attentionof the noises generated by the motor drives need to be taken into considerations along the entire electric power line from the source to the load.This guideline is intended to describe why and when to use which type ofmotor drive output filter. Nevertheless, following overall view of the noisepotential around the motor drive, which can cause equipment to malfunction or be damaged, is shown as follow:Overview of noise potential around a motor driveFor cancellation of the unwanted noises and fulfilment of the norms onthe line side, Schaffner offers a complete range of EMC filter– and harmonicfilter solutions for any applications, enabling cost effective standard andcustomized solutions to cancel or reduce the voltage and current noisesto the levels required.For 3-Phase motor drive applications, following filter combinations are appropriate to be considered:In this application and selection guide the output filters and in particularthe sine wave filters will be described in detail.3
Motor drives (frequency inverters) are among the most widely used piecesof equipment for AC motor control. Nowadays, they are found in virtuallyevery area of industry, in applications as diverse as pumps, air conditioningsystems, elevators and cranes, conveyors, machine tools, renewable electricity production and in a vast array of other industrial and domestic automation. In the quest for ultra-compact, efficient power conversion, motordrive manufacturers employ high-speed semiconductor (IGBT ) switchesand pulse width modulation (PWM) techniques to generate fast rise timevoltage pulses of the appropriate duration and polarity. Unfortunately, thiscreates a considerable number of problems for OEMs and system integrators, from purely functional difficulties to very severe motor damage. Hereis a brief summary of the most significant problems and phenomena:Motor drive input:Motor drive output:EMC problemsExcessive dv/dtHarmonicsPeak– and overvoltageCommutation notchesParasitic earth currentsInrush & peak currentsEddy current losses in the motorLow-frequency interferenceDisplacement currents in the coilsMotor drive DC link:Bearing currentsDC link capacitor stressAdditional inverter pulse loadsHarmonicsAcoustic motor noiseOther interference problemsEMC problemsWhole system:Low efficiency/low power factorUncertain system immunityUnacceptable interference emissionsUncertain service security & reliability2. Motor drives output phenomena/influenceMotor drives are known sources of interference and are therefore usuallyequipped with an input filter. However, the problems generated on theoutput side of the motor drives where the converter supplies the motorwith a modulated rectangular PWM signal (a switching frequency dependent series of trapezoidal pulses with variable width) have to be taken intoadditional consideration as described in following chapters.2.1 Excessive dv/dt voltageTo keep the losses in the frequency converter low, the aim is to keep theswitching times of the power semiconductors as short as possible. The result of this is that with the newest generation of IGBTs, rise times of sometimes more than 12 kV/us can be measured, whereas – depending on themotor – a dv/dt of around 1000 V/us is considered permissible. The IEC60034-17 standard does define the voltage peak limits in relation to the rise4
time for general purpose 500 VAC motors when fed by motor drives andIEC 60034-25 specifies the limits for motor drive rated 500 VAC and 690 VACmotors. For US applications the NEMA MG1 standard shows the limit fordefinite purpose motor drive fed motors.VtdvtdtDefinition of dv / dt: PWM-Signal and single pulse at the inverter outputIn the case of short motor cables (up to about 20 m), these rise times – owing to the small line impedance – act fully on the insulation of the motorwindings. Depending on the structure of the motor coils, wires that carrythe full voltage are situated immediately in parallel and next to each other.Since even very short parallel-laid wires have a capacitive action, the permanent potential jumps result in pole reversal losses across the windinginsulation. Now, if the enamel insulation is impure even to a very minorextent, this results in hot-spots, and hence, sooner or later, to a destructionof the winding insulation. In any case, this dv/dt stress leads to prematureaging and thus to a reduction in the life of the motor, in particular when anolder motor is fed by a motor drive.2.2 Peak- and overvoltageVoltage overshoots and voltage peaks can come with high dv /dt valuesbut are also a problem on their own. Due to the structure of the windings, amotor acts like a capacitor in the equivalent circuit diagram – owing to thefast voltage pulses of the switching frequency – and not as an inductance,as is the case in normal 50 Hz applications. With every additional meter ofmotor cable, more wire inductance is added to this structure. This inductance acts like a choke according to the energy storage principle. If chokesare subject to voltage pulses, voltage peaks occur every time switchingon or off takes place. The higher the energy content (inductance) of thechoke, the higher these voltage peaks become. In other words, the longerthe motor cable, the higher the maximum voltage amplitudes.VInv.tVMot.VInv.VMot.InverterMotor cableMotor10m cable / 100m cableSimplified equivalent circuit diagram of shielded cables (only 2 phases areshown) and theoretical single pulse at 10 m and at 100 m motor cable length5
These amplitudes can, in turn, reach values that cause a stress situation inthe winding insulation of the connected motor. Owing to the cable impedance, the dv/dt stress – in the case of longer motor cables – is reducedto less problematical values. On the basis of the line theory, however, peakvalues of 1600 V or more (depending on the DC link voltage) can occur dueto cable reflections, which can have very steep dv/dt values. According toIEC 60034, peak values of around 1000 V are recommended. In cases theresulting voltage peak and rise time exceed the standard limits an outputfilter should be used for protecting the motor winding insulation. Despitethe reduced dv /dt owing to the cable impedance, there is no significantstress relief for the motor, since now the increased voltage amplitudes represent the dominant stress factor.2.3 Additional losses in the motorApart from protecting the winding insulation against unacceptable voltagepeaks, the steep switching edges create another phenomenon of harmonics of the output signal. By applying Fourier analysis, it can be mathematically proven that the harmonic spectrum of the motor currents becomeswider with the steepness of the pulses which means that the harmoniccontent increases. The current ripple (PWM and harmonics) results in additional magnetic losses in the motor. The life of the motor is sensitivelyshortened owing to the permanently increased operating temperature.2.4 Cable shields and parasitic earth currentsFrom the standpoint of EMI suppression, shielded motor cables are required to avoid back-coupling of radiated interference to the mains cablein the frequency range from about 1 to 30 MHz. This measure of the EMCcan, however, only be considered to be efficient if the ends of the cableshield of the motor cable are put in contact with the ground of the motorand the frequency converter – if possible, at HF low impedance and overas large an area as possible. This ensures that the interference currents canmostly flow back to the source by the shortest route. Frequency converters normally work in grounded networks and do not have any potentialseparation. The geometric expansion of the frequency converter, motorand this shielded motor cable therefore form parasitic capacitances of theelectrically conducting components with respect to the ground potential.If the available DC voltage is chopped in the frequency converter, thenduring the potential jumps of the voltage, considerable pulse currents flowacross the parasitic capacitances to the earth. The level of the interferencecurrents on the cable shield depends on the dv/dt as well as the valueof the parasitic capacitances (I C * dv/dt). With a motor cable length ofabout 100 m, peak values of the pulse currents of 20 amperes and more arenot unusual, regardless of the power rating class of the drive.The harmonic spectrum of these currents can reach a range of severalMHz. The shield of the motor cable, owing to the existing braiding, offers avery large surface area and a sufficient cross-section to carry these currents.As a result, the impedance of the shield across a broad frequency range isof a very low-impedance nature. Losses due to the skin effect are limitedto a minimum because of the large surface area. Inadequate ground connections of the cable shield (the so-called “pigtails”), on the other hand,are highly resistive for the frequency range under consideration and oftennullify the desired shielding effect.6
If there are parallel-laid control cables or electronic components in the vicinity of the motor cables, pulsed HF currents flow across their geometricexpansion and the resultant parasitic capacitances, which in turn couldhave an impermissible influence on neighbouring equipment through capacitive coupling.If neighbouring components are located in the immediate vicinity of themotor cable, the conductor loops and the high di / dt values of the shieldcurrents also result in a magnetic coupling that can also lead to impermissible influencing.Parasitic capacitances in a drive systemThe currents flowing across the shield must be supplied by the frequencyconverter as well. They are not dependent on the rating of the drive butonly on the geometric expansion of the structure. With small power ratings, the result of this, especially in case of long motor cables, can be that afrequency converter of the next higher rating has to be used that is able tosupply both the currents required by the load and the parasitic currentsvia the earthing. The operation of several motors connected in parallel onone frequency converter is problematic. The parallel connection of severalshielded cables results in a relatively high total capacitance and thus correspondingly high shield currents. The parallel connection of several drives,however, is accompanied by even more issues to be solved. Parasitic currents across the motor and the installation can considerably affect the re liability of the entire system. refer also application examples in chapter 52.5 HF electromagnetic noise in the motor cableThe high frequency noise is caused by the switching frequency of thesemiconductors. The source occurs due to the pulse voltage overshoot atthe motor terminal. With the use of a dv/dt filter the frequency of the ringing oscillation is only reduced below 150 kHz compared with a sine wavefilter eliminating the pulse voltage overshoot completely by feeding themotor with a sine wave phase-to-phase voltage.7
The noise coupling between the unshielded motor cable with the line cable or other sensitive cables (sensors, encoder etc.) can be reduced whenusing sine wave filters in combination with EMC line filters.Line conducted noise without (left) and with sine wave filter (right)2.6 Bearing currentsA general distinction has to be made between two different physical occurrences: The shaft voltage (or rotor voltage) is an inductive voltage that is inducedin the motor shaft owing to the differences in the flux densities of thestator and rotor. Above all, it is influenced by the length of the motor. Aslong as the lubricant film in the bearing is intact, the voltage builds upuntil, finally, a compensating current flows towards the earth. In this case,the path of least resistance is through the motor bearings. This bearingcurrent (I 1), over a long period of time, usually results in drying out thebearings and thus create a mechanical motor failure, acoustic noise anda possible break-down. It is possible to counter this phenomenon to acertain degree through the use of ceramic bearings. The bearing voltage is an asymmetric (common-mode) voltage that occurs because of capacitive coupling between the motor housing, thestator and the rotor (C 1, C 2, C 3) and results in dv/dt and electrostaticdischarge currents (I dv/dt and I EDM) across the bearing (C Bearing, UBearing). To be more accurate, this bearing voltage results in two different currents: in the first minutes of operation, as long as the lubricant inthe bearing is cold, currents in the range of 5 to 200 mA (I dv/dt) flowthrough C Bearing because of the dv/dt. These rather negligible currentsgenerally do not result in any bearing damage. After a little while, whenthe lubricant film has heated up, peak currents of 5 to 10 A and morecan be measured (IEDM). These flashovers leave behind small pits on thesurface of the bearing. The running of the bearing becomes increasinglyrough because of the damaged surface and the life is thus considerablyshortened. Typically, the bearing voltage is between 10 and 30 V. Butsince it is directly dependent on the mains supply voltage, bearing damage increases over proportionally at higher supply voltages.In the case of the use of unshielded motor cables, the cable capacitance(C Cable) and hence the current (I Cable) is relatively small. The parasiticcapacitances on the inside of the motor dominate. Ideally, the parasitic currents flow through the motor housing to the ground (I C1).8
IC1Motor cableMotorLineInv.I1C1C3C2uninsulated MRotor shaftCCableICableRotorCopper coilsC1StatorMetal frameIC1IBearingImp.However, if the grounding of the motor is inadequate, an additional impedance (Imp.) is limiting the current (I C1). As a result of the additional impedance, the potentials at C 2, C 3 and C Bearing increase sharply. The values of the bearing currents also increase massively and flow fully throughthe bearings to the earth (I Bearing); in that case, the life expectancy of theball bearings, and hence of the entire motor, is reduced to a few hours.120I e [A]100806040200500 kW motor A500 kW motor B110 kW motor A110 kW motor Bmotor earth current with out filtermotor earth current with sine wave filtermotor bearing current with out filtermotor bearing current with sine wave filter2.7 Acoustic motor noiseCompared to the previously described issues, the whistling noises of themotor – caused by the pulse width modulated (PWM) switching frequency –would appear to be negligible. However, in applications related to heating,ventilation and airconditioning technology (HVAC), the noise is distributedand may be amplified in the entire building through air ducts or heating pipes. For acoustic noise sensitive applications, often the motor driveswitching frequency is set to 16 kHz, since this audible frequency noiselevel is less noticeable by humans. This generates higher IGBT switchinglosses, higher heating, higher leakage currents and therefore a corresponding derating of the motor drive need to be taken into consideration.Three main acoustic noise sources are generated by motors:Motor core magnetic noise, through magnetostrictionMotor bearing noiseMotor ventilation noise9
6 Sine Wave Filter - Application and SelectionIn order to eliminate or reduce unwanted acoustic noise levels, a sine-wavefilter can be used. This will filter the pulse shaped voltage from the frequency converter and provide a smooth sinusoidal phase-to-phase voltage atthe motor terminals.3. Output filter solutions for motor drivesFor reasons of cost, time and space, an attempt is generallyfirst made to overcome the motor drives issues without addi3.Output filter solutions for motor drivestional components. However, the subsequent costs that canresult from motor or system failures are often entirely out ofproportionto cost,the farlowerof preventiveoutputfilter toFor reasons oftimeand initialspace, costsan attemptis generallyfirst mademeasures.the decisionis madein favourof componentstoHowovercometheIf motordrives issueswithoutadditionalcomponents.increasethe reliability,safetyandthe installaever,the subsequentcoststhethatoperationalcan result frommotoror systemfailures tercompooften entirely out of proportion to the far lower initial costs of preventivenents haveestablishedto solvethe majorapplica- tooutputfilter measures.If thethemselvesdecision is madein favourof componentstion requirements:increasethe reliability, the operational safety and the installation lifetimeWith Schaffnerreduction of higcan be achieveshaped generaIt protects the mdestruction andtric motors. dv/tor cables. Thepends mainly ovoltage. The vaderating curvethe following types of passive output filter components have establishedI dv/dt reactors (increase inductivity, signal smoothing)themselves to solve the major application requirements:I dv/dt filters (low inductance, hardly any reduction in the condv/dtreactors (increase inductivity, signal smoothing)troldynamic) dv/dt filters (low inductance, hardly any reduction in the control dynamic)I Sinusoidaloutput filters (high L and C for optimizing the out Sinusoidal output filters (high L and C for optimizing the output signal,putsignal, but also not universally applicable)but also not universally applicable)Locations of filters around motor / power drivesLocations of filters around motor/power drives3.1 dv/dt reactorReactors can be used in various locations in a power drive system: as line3.1 dv/dtreactorreactor,in theDC link between the rectifier and capacitor (DC link choke)and at the drive output to the motor (dv/dt reactor). A reactor at each ofReactors can be used in various locations in a power drivesystem: as line reactor, in the DC link between the rectifier andsive.capacitor (DC link choke) and at the drive output to the motor(dv/dt reactor). A reactor at each
3.3 Sine wave filter 12 3.3.1 Symmetrical sine wave filter 13 3.3.2 Sinus plus symmetrical and asymmetrical sine wave filter 14 4. Sine wave filter selection 16 4.1 Current and voltage rating 16 4.2 Frequency 17 4.3 Require
output generated: modified sine wave, and pure sine wave1. A modified sine wave can be seen as more of a square wave than a sine wave; it passes the high DC voltage for specified amounts of time so that the average power and rms voltage are the same as if it were a sine wave.
4. Advantages of a Pure Sine Wave Inverter Today s inverters come in two basic output waveforms: modified sine (which is actually a modified square wave) and pure sine wave. Modified sine wave inverters approxi
encodes a sine wave. The duty cycle of the output is changed such that the power transmitted is exactly that of a sine-wave. This output can be used as-is or, alternatively, can be filtered easily into a pure sine wave. This report documents the design of a true sine wave inverter, focusing on the inversion of a DC high-voltage source.
Again modified sine wave inverters are named after their output waveform. The output of the modified sine wave inverter cycles through positive, ground and negative voltage as shown in the diagram above, to give a similar output waveform to pure sine wave. Modified sine wave inverters are a much cheaper alternative to pure sine wave inverters .
800VA Pure Sine Wave Inverter’s Reference Design Sanjay Dixit, Ambreesh Tripathi, Vikas Chola, and Ankur Verma ABSTRACT This application note describes the design principles and the circuit operation of the 800VA pure Sine Wave Inverter. The pure Sine Wave inverter has various applications because of its key advantages such as operation
medium voltage cables. All VLF test units from Megger can also be used for sheath testing and sheath fault pin-pointing. TECHNICAL DATA VLF Sine 34 kV VLF Sine 45 kV VLF Sine 62 kV VLF test voltage 0 to 34 kV peak 0 to 45 kV peak 0 to 62 kV peak Frequency 0.01 to 0.1Hz 0.01 to 0.1Hz 0.01 to 0.1Hz Wave form Sine Sine Sine Testing cable capacitance
a pure sine wave output signal. We are looking to fill a current niche on the market and supply a possible low cost design that also has an appropriate sine wave output signal. Our circuit will not have a sine-wave reference signal in order to reduce cost. It will be able to transform DC to aFile Size: 299KB
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