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Power topic #6008 | Technical information from Cummins Power Generation A Comparison of Generator Excitation Systems

■ White Paper By Greg Laliberte, Sales Application Engineering Group Leader, Cummins Power Generation

Generator set manufacturers offer Four Generator different options for providing power to Excitation Methods the automatic voltage regulator (AVR), and selection of the proper option is Excitation methods include: important to ensure correct operation n Self-Excited (Shunt) of the generator set. While there are n Excitation Boost System (EBS) multiple options available for excitation n Permanent Generator (PMG) systems, each has its own unique n Auxiliary Winding (AUX) features that provide benefits for different applications. This is generally Each method has its advantages. This paper describes each method including the construction, driven by the electrical characteristics operation and the appropriate types of applications of the loads and the short circuit for each. performance requirements. This paper The process flow for the and AVR goes discusses four methods of excitation, as follows: the advantages and disadvantages of n AVR voltage sense lines are connected to the each method, and recommendations main stator and are used to control the field for selecting the right method, based strength of the alternator to maintain a constant voltage on the output of the generator set under on the requirements of the application. varying conditions by the AVR

n Input power to the AVR is received through one 5823 of the many methods described in the paper

n The input power is used by the AVR to supply a DC output to the exciter stator and the voltage level sensing is used to determine the level at which the AVR induces an AC signal on the Power Topic # Topic Power |

exciter  07 02 | Power Topic #6008 Figure 1: Figure troubleshooting. when easier be can and wiring or parts additional no alternator. excite the requires It to properly requires AVR the power input necessary the to providing approach effective cost and simple avery is This 1). Figure (see exciter of the input the for required voltage the regulating properly to continue output alternator the sensing for used is output same This to AVR. the input the for power to stator derive main Shunt (self-excited) excitation uses the output of the Shunt the excitation type. impact on system in conjunction performance with an have can type construction Each Transistor (FET). Silicone-Control-Rectifier (SCR)and Field-Effect are discuss we will Two of construction input. types power and sensing voltage the on based excitation which will impact their to ability provide appropriate well, as construction different have AVRs can alternator. in the field of to loss due down to system shut the or damage potential causing to start to motorstruggling the lead could This condition. fault or amotorstart during voltage to recover able be not may system the power of source astrong Without situation. atransient in especially needed, when current of excitation amount appropriate the for allow will that source power strong AVRa have the to must work, process this For n load output output load for stator main onto the induced ultimately and rotor alternator of the main into the output a DC to rectified then is rotor exciter AC output The Shunt Excitation. Excitation System (EBS) Boost provide appropriate output power. AVR of the to ability the limit can which variation input to power the due is This system. excitation ashunt for achallenge be also can load of non-linear powering to the due Harmonics collapse. may alternator the in field main the as faults downstream to clear enough long voltage the to support capability the have not AVR the may case this In collapses. voltage the where fault circuit of ashort case the in especially achallenge AVRbecome the can powering frequency, and voltage input reduced With voltage. the support to current excitation more AVR drive the must and drop will frequency and voltage the downstream, appears afault or connecting/starting to aload due occurs atransient When downstream. powering is alternator the loads by the impacted AVR directly is to the quality power input the since drawback biggest The simplicity of Shunt excitation also leads to its not providing excitation. is it but time, this at potential avoltage producing is EBG The run-up. voltage excessive to prevent off switched is EBS the start-up, generator During situations. output shorter for intended AVR is the and to output power continuous for rated not is system, to a permanent magnet generator (PMG) excitation appearance in similar while EBG, The recovery. voltage the drive amotorand up to pick generator the enable or afault remove can breaker adownstream until load the supporting system, excitation generator’s the feeds power to EBC. the This a command through needed AVR by the when engaged is 2) and Figure (see lines AVR output exciter typical the with parallel in is EBG the from output power additional The system. of the needs the on depending current excitation of increased levels varying to engage AVR the ability the to AVR gives the and connected is module control This shaft. alternator of the end to non-drive the added (EBG) generator boost excitation small and module (EBC) control boost excitation an includes to AVR also the and input power and sensing voltage for excitation shunt of the setup same the follows system of this construction The system. self-excited to typical the a “boost” provides which of excitation form another is EBS n n n situations such as: loading non-linear and motorstarting both for of benefits anumber has system excitation PMG The system. aself-excited in a problem been havemay distortion waveform voltage significant to AVR the where input power isolated reliable provides PMG AVR. of the The power to input the disturbances any preventing thereby turning, is shaft alternator the as long as waveform 3phase uninterrupted a clean, produces and alternator the from output main the on disturbances the from isolated is output generator magnet 3). permanent AVR the This for Figure (see power to produce alternator of the end non-drive the an additional small permanent magnet generator at places actually method This PMG. or excited separately the is of excitation forms well-known most of the One (PMG) Generator Magnet Permanent motorstarting. improved and current circuit short 300% of providing needs the meets still that option smaller and expensive aless is it usage, non-continuous for rated being EBG the With PMG. from different EBS makes what is This situations. circuit short and motorstarting in response dynamic a for allows system EBS of the construction The Figure 2: of relying on residual . magnetism. residual on of relying instead start-up initial on up build voltage Powerful to exciter. the power provide to ability the on impact no have loads Non-linear to clear. downstream faults for allows and collapsing during fault conditions which prevent the fieldfrom Provides circuit (SSC) sustained short current EBS Excitation. n due to non-linear loads. loads. to non-linear due harmonics and output power sustainable with have can Shunt issues the avoids and alternator of the end the on PMG aseparate for need the eliminates This the main stator the alongside main output winding. separate single-phase winding which is into inserted a is stator. the on winding The winding a separate the for through power AVR generate to field main the AUX uses of the construction The installations. larger in practical more becomes and technology anew not is it of excitation, type used commonly aless is it While industrial. and marine including of applications types many on years many for used been has that excitation of form adifferent is (AUX) winding auxiliary The (AUX) Winding Auxiliary and non-linear loads. coordination selective motorstarting, for requirements system for applications with high performance excitation used commonly most the is it systems, AUX and EBS, to Shunt, the compared as complexity and weight, length, adds systems PMG Although PMG 3: Excitation. Figure up to speed quickly. quickly. toup speed motorto the get for torque ultimately and voltage to recover excitation full to provide AVR ability its in the limit would otherwise which situations starting motor in conditions transient high from Isolation

03 | Power Topic #6008 can be affected to a certain extent by the power power by the extent to acertain affected be can to AVR the input voltage its While systems. PMG with compared when to install equipment less is there as costs, production reduced and set generator of the length axial a shorter in results it that are winding of the AUX benefits Some AUX 5: Winding Excitation. Figure 10 for seconds. current 300% to provide needed is what beyond conditions, SSC and motor starting during response astrong for allows harmonics two of the usage balanced This AUX winding. the from theharmonic becomes dominant source for power field 3rd increasing rapidly the conditions, SSC and AVR. the for However, motorstarting under power generate to harmonic field first the use will unit the load) to full (no load operations normal 4). Figure in Under (shown series in connected being coils the all with coils three involves The Cummins Power Generation construction Winding. Auxiliary 4: Figure on power.cummins.com.) Topic Power #6014 reference please information more (For condition. fault over-speed afalse drive and sensing frequency improper cause also can It of excitation. amount appropriate the delivering in to system struggle the cause which points crossing zero- additional cause can 7) Figure in (shown the harmonic distortion and induced “notches” as loads non-linear with troubling especially be can governor. This electronic the to adjust used be also be may and firing SCR of the timing the impacts This used. not is pickup amagnetic when frequency system the to determine lines these on zero-crossings the 6). uses also It Figure in (shown to exciter the sent being of power amount the determines on is switch the of time length The zero-crossing. the called zero, otherwise based on when the voltage waveform reaches off turn will switch the and on turned be should switch the when to determine loop a feedback as used is level voltage The off. turned be will it when and on to turned is be switch the when both determine must It SCR. of the firing the time to level this uses and alternator of the output the on level voltage the senses system type SCR The AVR SCR set. generator the of to performance the important is that lines sense voltage and circuit power the with deal systems two the how is It loads. connected by customer voltage feedback signal from caused harmonics adistorted in result can which stator main the from pulled are lines sense voltage the systems excitation four all In circuits. sense voltage and power input independent have systems Both type. FET and type SCR of AVR construction: types two discuss We will circuits. of excitation types of these each of ability on the impact significant a have can of AVR construction type The AVR Construction demanding applications. for options suitable are AUX winding the and PMG Both AVR performance. affect not will loads non-linear from winding main the in distortions waveform the to this due and minimized is winding design, the mutual inductance with the main By of failure. incidents low with solution robust avery provides set.also It of the performance the on impact anegligible has it generated, being (over)

04 | Power Topic #6008 05 | Power Topic #6008 off” power to the exciter too soon. too exciter to the power off” AVR to ‘switch the causes notching waveform but time, correct the at on turns trigger single the that Note Waveform. Voltage Input Distorted with System Excitation 7. Sub-Controlled Figure used). is pick-up mag no (if readings frequency inaccurate and excitation improper drive still will crossings zero- the as voltage adistorted with problematic be still will lines sense voltage the early, but off to SCR shut the causing zero-crossings improper no be will there so power input to cleaner due improvement an be AUX will or of PMG use The excessive. becomes distortion the before linear non- being alternator of25% the rating base of the about handle can system the that is loads linear non- powering when systems two these for thumb of rule The systems. excitation EBS or Shunt with load of non-linear amounts large for recommended AVR not is type SCR an reasons these For level. voltage output generator to maintain energy of level proper the get not does exciter the so time, incorrect the at off to switch AVR the in SCR the causes notching waveform the loads, linear non- with applied is regulator that When off. it turns crossing AC voltage the power, and excitation the on” “turns input trigger asingle that Note System. Excitation SCR-Controlled 6. Figure

completely eliminated. were systems type SCR on limitations few the AUX systems or PMG the with and eliminated, mostly are loads to non-linear due harmonics for concerns the system, excitation EBS or a Shunt With significant. is AVRs discussed different the of AVR each with type aFET of using effect The loads. to non-linear due information frequency false only, preventing signal this from frequency the derives and speed engine for pick-up magnetic a AVRuses also type FET The system. of the capability excitation the on impact an having from quality power the prevents This to signal. aDC rectified and filtered is and output excitation for used only is waveform input power The cycle. duty the adjusting and pulsing by constantly excitation of amount the impacting from notch or event asingle dictating from zero-crossings prevents method 8). This Figure in (shown applied being of excitation amount the ultimately and signal PWM of the cycle duty the dictates signal translated The output. excitation the for circuit (PWM) modulated width apulse to drive translated and measured are lines sense AVR, voltage the FET of the case the In distortion. potential and loads to non-linear relating when performance improved for systems excitation four all for suited are that advantages many AVR has system type FET The FET AVR excitation regardless of level of waveform distortion. waveform of level of regardless excitation of levels proper provide output pulsed and triggers Multiple Pulse 8. Width Modulated (PWM) ExcitationFigure System. locate your distributor, visit power.cummins.com distributor, visit your locate distributor. To Generation Power Cummins local For additional technical support, please contact your circuit capability.and sustained short motor starting strong providing still while set of the size the to reduce generator the within harmonics inherent of the advantage takes AUX winding The output. power constant provides and output alternator the from AVR source the power isolates generator magnet of apermanent use The needs. application’s the meet to evaluated be should systems excitation winding AUX and PMG the faults, large during capability non-linear load and sustained short-circuit demands capability, motorstarting improved motor starting, For the most demanding applications requiring large PMG. than cost alower at and situation, demanding more slightly this in needed excitation of level the provide will system excitation EBS the circuit forshort capability selective coordination, sustained for requirements to and/or meet starting, motor to motors, improved have multiple to start need the dictates application the Once demanding. less are applications the as generators smaller for suitable the appropriate choice. be This willmore typically be may excitation Shunt loads, non-linear or motors few with solution cost alow requiring applications provide benefits forapplications. different Forsimple that features unique has each systems excitation for available options multiple are there While Summary high-horsepower generator set design. In his included experience previous His America. ApplicationSales Engineering group for North 2011 the since leads currently Generation and Power Cummins with been has He engineering. electrical in degree abachelor’s with Minnesota, of University of the agraduate is LaLiberte Greg author the About . the United States, Canada and Caribbean. and Canada States, United the in teams distribution to support content training technical provided he and program, training customer Seminar Power in the engaged actively is He issues. specific and distributors with technical guidance on application- clients assisting is focus Greg’s primary position, current GLPT-6008-EN (10/14) Generation. Power Cummins of atrademark is you.” for working energy “Our Inc. Cummins of trademarks registered are Cummins and Generation Power Cummins reserved. rights All Inc. Generation Power ©2014 Cummins power.cummins.com

06 | Power Topic #6008