For Reference Purpose Only SS440 AUTOMATIC VOLTAGE ...

1 SS440 AUTOMATICVOLTAGEREGULAT OR (AVR)SPECIFICATION, INSTALLATION AND ADJUSTMENTSGENERAL DESCRIPTIONThe SS440 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 volt age, the AVR circuit ryincludes underspeed and sensing loss protection to ensuresafe, reliable control of the generator. Excitation power isderived directly from the generator ti ve VOLTAGE build up from residual levels is ensured by th euse of efficient semiconductors in the power circuitry of AVR is linked with the main stator windings and the exciterfield windings to provide closed loop control of the output volt agewith 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, temperatureand 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). This can easily be changed to50 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?

3 S 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 dcTransient 6 A for 10 secondsField Resistance15W 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 W trimmerUNDER FREQUENCY PROTECTIONSet Point (See Note 3)95%HzSlope170% down to 30 HzUNIT POWER DISSIPATION12 watts maximumBUILD UP Vac @ AVR terminalsACCESSORY INPUT+/- 1V = +/- 13% change in output voltsQUADRATURE DROOP SENSITIVITYM aximum sensiti vi ty(10W Burden) for 5% droop @ Hz50mm/sec100 Hz-2 kHz3.

4 3gRelative Humidity0-60 C95%OperatingTemperature-40 C to + 70 CStorageTemperature-55 C + 80 CNOTES1. With 4% engine governing2. External trim range is reduced to +/- 5%with 1 K W trimmer when 3 phase sensingis Factory set, semi-sealed, jumper Reference Purpose OnlyDESIGN 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 . 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 .

5 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 trimmer 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 generator voltagewithin the specified limits. The "Stability circuit" providesadjustable negative ac feedback to ensure good steady stateand transient performance of the control Hz detector measures the period of each electrical cycleand causes the Reference VOLTAGE to be reduced approximatelylinearly with speed below a presettable threshold. A lightemitting diode gives indication of underspeed 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 severely 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 main components are included to prevent sub cyclevoltage spikes damaging the AVR components and also toreduce the amount of AVR thyristor noise on the main terminalsof the Supply components consist of zener diodes withdropper resistor and smoothing to provide the required voltagesfor the integrated circuits and Reference AVR is fully encapsulated to ensure long trouble-freeoperation. It is usually fitted on a panel of the terminal box.

8 Itcan also be separately fitted in a AND OPERATINGADJUSTMENT 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 & 2on 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,refer to the rating plate mounted on thegenerator a replacement AVR has been fitted or re-setting of the VOLTS adjustment is required, proceed as follows:-1)Before running generator, turn VOLTS control )Turn remote volts trimmer (if fitted) to midway )Turn STABILITY control to midway )Connect a suitable voltmeter (0-300V ac) acrossline to neutral of the )Start generator set, and run on no load at nominalfrequency 50-53Hz or )If the red Light Emitting Diode (LED) is illuminated,refer to the Under Frequency Roll Off (UFRO) )Carefully turn VOLTS control clockwise until ratedvoltage is )If instability is present at rated VOLTAGE , refer to stabilityadjustment, then re-adjust VOLTAGE if ) VOLTAGE adjustment is now !

9 A separate 3 Phase Sensing unit isneeded. Do not connect as shownunless a 3 Phase Sensing unit isfitted. (See sheet 5515)Warning !SUMMARY OF AVR CONTROLSCONTROLFUNCTIONDIRECTIONVOLTSSTA BILITYUFRODROOPV/TRIMTO ADJUST GENERATOR OUTPUT VOLTAGETO PREVENT VOLTAGE HUNTINGTO SET UNDER FREQUENCY ROLL OFF KNEE POINTTO SET GENERATOR OR DROOP TO 5% AT FULL LOAD 0 PFTO MATCH AVR INPUT TO ACCESSORY OUTPUTCLOCKWISE INCREASES OUTPUT VOLTAGECLOCKWISE INCREASES STABILITY OR DAMPING EFFECTCLOCKWISE REDUCES THE KNEE POINT FREQUENCYCLOCKWISE INCREASES THE DROOPCLOCKWISE ALLOWS THE ACCESSORY MORE CONTROL OVER AVR STABILITY ADJUSTMENTThe AVR includes a stability or damping circuit to provide goodsteady state and transient performance of the correct setting can be found by running the generator atno load and slowly turning the stability control anti-clockwiseuntil the

10 Generator VOLTAGE starts to become optimum or critically damped position is slightly clockwisefrom this point (i. e. where the machine volts are stable but closeto the unstable region).OPTIMUM RESPONSE SELECTIONThe "jumper" selector lead should be correctly linked (A,B,C atthe bottom of the board) for the frame size of the generator(See diagram).UNDER FREQUENCY ROLL OFF (UFRO) ADJUSTMENTThe AVR incorporates an underspeed protection circuit whichgives a volts/Hz characteristic when the generator speed fallsbelow a presettable threshold known as the "knee" red Light Emitting Diode (LED) gives indication that theUFRO circuit is UFRO adjustment is preset and sealed at the works andonly requires the selection of 50/60Hz using the jumper optimum setting, the LED should illuminate as the frequencyfalls just below nominal, 47Hz on a 50Hz system or 57 Hzon a 60Hz ADJUSTMENTG enerators int ended for parallel operation are fitted with aquadrature droop which provides a power factor dependentsignal for the AVR.