SX440 AUTOMATIC VOLTAGE REGULATOR (AVR) - …

1 SX440 AUTOMATIC VOLTAGEREGULATOR (AVR)SPECIFICATION, INSTALLATION AND ADJUSTMENTSGENERAL DESCRIPTIONThe SX440 is a half-wave phase-controlled thyristor typeAutomatic VOLTAGE REGULATOR (AVR) and forms part of theexcitation system for a brushless addition to regulating the generator VOLTAGE , the AVRcircuitry includes underspeed and sensing loss protection toensure safe, reliable control of the generator. Excitation poweris derived directly from the generator VOLTAGE build up from residual levels is ensured bythe use of efficient semiconductors in the power circuitry ofthe AVR is linked with the main stator windings and theexciter field windings to provide closed loop control of theoutput VOLTAGE with load regulation of +/- 1%.

2 In addition to being powered from the main stator, the AVRalso derives a sample VOLTAGE from the output windings forvoltage control purposes. In response to this sample VOLTAGE ,the AVR controls the power fed to the exciter field, and hencethe main field, to maintain the machine output VOLTAGE withinthe specified limits, compensating for load, speed,temperature and power factor of the frequency measuring circuit continually monitors thegenerator output and provides output underspeed protectionof the excitation system, by reducing the output voltageproportionally with speed below a presettable threshold. Amanual adjustment is provided for factory setting of the underfrequency roll off point, (UFRO).

3 This can easily be changedto 50 or 60 Hz in the field by push-on wire link caused by open circuit sensing terminals areavoided by sensing loss detection circuitry which reduces thegenerator terminal VOLTAGE to a safe fixed is made for the connection of a remote voltagetrimmer, allowing the user fine control of the generator' are available for this AVR. Please refer to factoryfor further SPECIFICATIONINPUTV oltage170-250 V ac maxFrequency50-60 Hz nominalPhase1 Wire2 OUTPUTV oltagemax 90 V dc at 207 V ac inputCurrentContinuous 4 A dcTransient6 A for 10 secondsField Resistance15 minimumREGULATION(See Note 1) +/- 1%THERMAL DRIFT(after 10 min)1% for 40 C change in AVR ambientTYPICAL SYSTEM RESPONSEF ield current to 90%80msMachine Volts to 97%300msEXTERNAL VOLTAGE ADJUSTMENT (see note 2)+/- 8% with 1 K trimmerUNDER FREQUENCY PROTECTIONSet Point (See Note 3)

4 95% HzSlope 170% down to 30 HzUNIT POWER DISSIPATION12 watts maximumBUILD UP Vac @ AVR terminalsACCESSORY INPUT+/- 1V = +/- 13% change in output voltsQUADRATURE DROOP SENSITIVITYM aximum sensitivity (10 Burden) for 5% droop @ Hz 50mm/sec100 Hz-2 Humidity0-60 C95%Operating Temperature-40 C to + 70 CStorage Temperature-55 C + 80 CNOTES1) With 4% engine governing2) External trim range is reduced to +/- 5% with 1 K trimmer when 3 phase sensingis ) Factory set, semi-sealed, jumper DETAILSThe main functions of the AVR are:Sensing Resistors take a proportion of the generator outputvoltage and attenuate it. This input chain of resistors includesthe range potentiometer and hand trimmer which adjust thegenerator VOLTAGE .

5 An isolating transformer allows connectionto windings of different polarity and phase. An operationalprecision rectifier converts the ac sensing VOLTAGE into dc forfurther droop circuit converts the current input into avoltage, which is phase mixed with the sensing VOLTAGE . Theresult is a net increase in the output from the sensing networkas the power factor lags, causing the reduction in excitationneeded for reactive load sharing of parallelled generators. Atrimmer allows control over the amount of droop loss detector is an electronic changeover switchwhich normally connects the main comparator/amplifier to the"input sensing" network, and automatically changes over tothe "power sensing" network when the normal sensing voltageis Mixer provides an interface between the AVR andaccessories and allows the generators excitation to becontrolled by adding or subtracting the accessory dc outputvoltage to the AVR rectifier sensing Comparator/Amplifier compares the sensing VOLTAGE tothe "reference VOLTAGE " and amplifies the difference (error) toprovide a controlling signal for power devices.

6 The "pedestaland ramp" circuit and "level detector and driver" provide themeans to infinitely control the conduction period of the outputdevice over each half cycle (phase control), and provide theexciter with the required power to maintain the generatorvoltage within the specified "Stability circuit" provides adjustable negative acfeedback to ensure good steady state and transientperformance of the control Hz detector measures the period of each electrical cycleand causes the reference VOLTAGE to be reducedapproximately linearly with speed below a presettablethreshold. A light emitting diode gives indication ofunderspeed circuit provides a short pulse at the zerocrossing of each cycle and is used to synchronise theunderspeed and pedestal and ramp circuit to the generatorwaveform.

7 The circuit is preceded by a "low pass filter" toprevent false zero crossing pulses caused by severelydistorted Devices are configured as half-wave thyristor andfreewheel diode to vary the amount of exciter field current inresponse to the error signal produced by the components are included to prevent sub cyclevoltage spikes damaging the AVR components and also toreduce the amount of AVR thyristor noise on the mainterminals of the Supply components consist of zener diodes withdropper resistor and smoothing to provide the requiredvoltages for the integrated circuits and reference AVR is fully encapsulated to ensure long trouble-freeoperation.

8 It is usually fitted on a panel of the terminal box. Itcan also be separately fitted in a DETECTORSYNCHRONISINGCIRCUITPOWERSUPPLYP OWERCONTROLDEVICESSUPPRESSIONEXCITERSTAT ORGENERATORSENSINGRESISTORSPEDESTAL ANDRAMP CIRCUITLEVEL DETECTORAND DRIVERMAIN COMPARATORAM PLIFIERLOW PASSFILTERVOLTAGESENSEVOLTAGETRIMPOWERSE NSINGCURRENTINPUTDC MIXERDROOPACCESSORYINPUTSEN SINGLO SS D ETEC TO RFITTING AND OPERATINGSUMMARY OF AVR CONTROLSCONTROLFUNCTIONDIRECTIONVOLTSTO ADJUST GENERATOR OUTPUT VOLTAGECLOCKWISE INCREASES OUTPUT VOLTAGESTABILITYTO PREVENT VOLTAGE HUNTINGCLOCKWISE INCREASES STABILITY OR DAMPING EFFECTUFROTO SET UNDER FREQUENCY ROLL OFF KNEE POINTCLOCKWISE REDUCES THE KNEE POINT FREQUENCYDROOPTO SET GENERATOR OR DROOP TO 5% AT FULL LOAD 0

9 PFCLOCKWISE INCREASES THE DROOPV/TRIMTO MATCH AVR INPUT TO ACCESSORY OUTPUTCLOCKWISE ALLOWS THE ACCESSORY MORE CONTROL OVER AVRADJUSTMENT OF AVR CONTROLSVOLTAGE ADJUSTMENTThe generator output VOLTAGE is set at the factory, but can bealtered by careful adjustment of the volts control on the AVRboard, or by the external hand trimmer if fitted. Terminals 1 &2 on the auxiliary terminal block inside the generator terminalbox will be fitted with a shorting link if no hand trimmer not increase the VOLTAGE above therated generator VOLTAGE . If in doubt, referto the rating plate mounted on thegenerator a replacement AVR has been fitted or re-setting of theVOLTS adjustment is required, proceed as follows.

10 -1) Before running generator, turn VOLTS control fully ) Turn remote volts trimmer (if fitted) to midway ) Turn STABILITY control to midway ) Connect a suitable voltmeter (0-300V ac) across line toneutral of the ) Start generator set, and run on no load at nominalfrequency 50-53Hz or ) If the red Light Emitting Diode (LED) is illuminated, referto the Under Frequency Roll Off (UFRO) ) Carefully turn VOLTS control clockwise until rated voltageis ) If instability is present at rated VOLTAGE , refer to stabilityadjustment, then re-adjust VOLTAGE if ) VOLTAGE adjustment is now separate 3 Phase Sensing unit isneeded.