New Age SX440 Manuale utente

SX440 AUTOMATIC VOLTAGE

REGULATOR (AVR)

SPECIFICATION, INSTALLATION AND ADJUSTMENTS

GENERAL DESCRIPTION

The SX440 is a half-wave phase-controlled thyristor type

Automatic Voltage Regulator (AVR) and forms part of the

excitation system for a brushless generator.

In addition to regulating the generator voltage, the AVR

circuitry includes underspeed and sensing loss protection to

ensure safe, reliable control of the generator. Excitation power

is derived directly from the generator terminals.

Positive voltage build up from residual levels is ensured by

the use of efficient semiconductors in the power circuitry of

the AVR.

The AVR is linked with the main stator windings and the

exciter field windings to provide closed loop control of the

output voltage with load regulation of +/- 1%.

In addition to being powered from the main stator, the AVR

also derives a sample voltage from the output windings for

voltage control purposes. In response to this sample voltage,

the AVR controls the power fed to the exciter field, and hence

the main field, to maintain the machine output voltage within

the specified limits, compensating for load, speed,

temperature and power factor of the generator.

A frequency measuring circuit continually monitors the

generator output and provides output underspeed protection

of the excitation system, by reducing the output voltage

proportionally with speed below a presettable threshold. A

manual adjustment is provided for factory setting of the under

frequency roll off point, (UFRO). This can easily be changed

to 50 or 60 Hz in the field by push-on wire link selection.

Overvoltages caused by open circuit sensing terminals are

avoided by sensing loss detection circuitry which reduces the

generator terminal voltage to a safe fixed level.

Provision is made for the connection of a remote voltage

trimmer, allowing the user fine control of the generator's

output.

Accessories are available for this AVR. Please refer to factory

for further details.

TECHNICAL SPECIFICATION

INPUT

Voltage 170-250 V ac max

Frequency 50-60 Hz nominal

Phase 1

Wire 2

OUTPUT

Voltage max 90 V dc at 207 V ac input

Current Continuous 4 A dc

Transient 6 A for 10 seconds

Field Resistance 15 Ω minimum

REGULATION (See Note 1) +/- 1%

THERMAL DRIFT

(after 10 min)

1% for 40°C change in AVR ambient

TYPICAL SYSTEM RESPONSE

Field current to 90% 80ms

Machine Volts to 97% 300ms

EXTERNAL VOLTAGE ADJUSTMENT (see note 2)

+/- 8% with 1 K Ω trimmer

UNDER FREQUENCY PROTECTION

Set Point (See Note 3) 95% Hz

Slope 170% down to 30 Hz

UNIT POWER DISSIPATION

12 watts maximum

BUILD UP VOLTAGE

3.5 Vac @ AVR terminals

ACCESSORY INPUT

+/- 1V = +/- 13% change in output volts

QUADRATURE DROOP SENSITIVITY

Maximum sensitivity (10 Ω Burden)

0.07A for 5% droop @ 0p.f.

ENVIRONMENTAL

Vibration 20-100 Hz 50mm/sec

100 Hz-2 kHz 3.3g

Relative Humidity 0-60°C 95%

Operating Temperature -40°C to + 70°C

Storage Temperature -55°C + 80°C

NOTES

1) With 4% engine governing

2) External trim range is reduced to +/- 5% with 1 K

Ω trimmer when 3 phase sensingis fitted.

3) Factory set, semi-sealed, jumper selectable.

DESING DETAILS

The main functions of the AVR are:

Sensing Resistors take a proportion of the generator output

voltage and attenuate it. This input chain of resistors includes

the range potentiometer and hand trimmer which adjust the

generator voltage. An isolating transformer allows connection

to windings of different polarity and phase. An operational

precision rectifier converts the ac sensing voltage into dc for

further processing.

Quadrature droop circuit converts the current input into a

voltage, which is phase mixed with the sensing voltage. The

result is a net increase in the output from the sensing network

as the power factor lags, causing the reduction in excitation

needed for reactive load sharing of parallelled generators. A

trimmer allows control over the amount of droop signal.

Sensing loss detector is an electronic changeover switch

which normally connects the main comparator/amplifier to the

"input sensing" network, and automatically changes over to

the "power sensing" network when the normal sensing voltage

is lost.

DC Mixer provides an interface between the AVR and

accessories and allows the generators excitation to be

controlled by adding or subtracting the accessory dc output

voltage to the AVR rectifier sensing voltage.

Main Comparator/Amplifier compares the sensing voltage to

the "reference voltage" and amplifies the difference (error) to

provide a controlling signal for power devices. The "pedestal

and ramp" circuit and "level detector and driver" provide the

means to infinitely control the conduction period of the output

device over each half cycle (phase control), and provide the

exciter with the required power to maintain the generator

voltage within the specified limits.

The "Stability circuit" provides adjustable negative ac

feedback to ensure good steady state and transient

performance of the control system.

Low Hz detector measures the period of each electrical cycle

and causes the reference voltage to be reduced

approximately linearly with speed below a presettable

threshold. A light emitting diode gives indication of

underspeed running.

Synchronising circuit provides a short pulse at the zero

crossing of each cycle and is used to synchronise the

underspeed and pedestal and ramp circuit to the generator

waveform. The circuit is preceded by a "low pass filter" to

prevent false zero crossing pulses caused by severely

distorted waveforms.

Power Devices are configured as half-wave thyristor and

freewheel diode to vary the amount of exciter field current in

response to the error signal produced by the main

comparator.

Suppression components are included to prevent sub cycle

voltage spikes damaging the AVR components and also to

reduce the amount of AVR thyristor noise on the main

terminals of the generator.

Power Supply components consist of zener diodes with

dropper resistor and smoothing to provide the required

voltages for the integrated circuits and reference voltage.

The AVR is fully encapsulated to ensure long trouble-free

operation. It is usually fitted on a panel of the terminal box. It

can also be separately fitted in a switchboard.

STABILITY

CIRCUIT

REFERENCE

VOLTAGE

LOW

Hz DETECTOR

SYNCHRONISING

CIRCUIT

POWER

SUPPLY

POWER

CONTROL

DEVICES

SUPPRESSION

EXCITER

STATOR

GENERATOR

SENSING

RESISTORS

PEDESTAL AND

RAMP CIRCUIT

LEVEL DETECTOR

AND DRIVER

MAIN COMPARATOR

AM PLIFIER

LOW PASS

FILTER

VOLTAGE

SENSE

VOLTAGE

TRIM

POWER

SENSING

CURRENT

INPUT

DC MIXER

DROOP

ACCESSORY

INPUT

SEN SING

LO SS D E TEC TO R

FITTING AND OPERATING

SUMMARY OF AVR CONTROLS

CONTROL FUNCTION DIRECTION

VOLTS TO ADJUST GENERATOR OUTPUT VOLTAGE CLOCKWISE INCREASES OUTPUT VOLTAGE

STABILITY TO PREVENT VOLTAGE HUNTING CLOCKWISE INCREASES STABILITY OR DAMPING EFFECT

UFRO TO SET UNDER FREQUENCY ROLL OFF KNEE POINT CLOCKWISE REDUCES THE KNEE POINT FREQUENCY

DROOP TO SET GENERATOR OR DROOP TO 5% AT FULL LOAD 0 PF CLOCKWISE INCREASES THE DROOP

V/TRIM TO MATCH AVR INPUT TO ACCESSORY OUTPUT CLOCKWISE ALLOWS THE ACCESSORY MORE CONTROL OVER AVR

ADJUSTMENT OF AVR CONTROLS

VOLTAGE ADJUSTMENT

The generator output voltage is set at the factory, but can be

altered by careful adjustment of the volts control on the AVR

board, or by the external hand trimmer if fitted. Terminals 1 &

2 on the auxiliary terminal block inside the generator terminal

box will be fitted with a shorting link if no hand trimmer is

required.

Do not increase the voltage above the

rated generator voltage. If in doubt, refer

to the rating plate mounted on the

generator case.

If 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 fully anti-

clockwise.

2) Turn remote volts trimmer (if fitted) to midway position.

3) Turn STABILITY control to midway position.

4) Connect a suitable voltmeter (0-300V ac) across line to

neutral of the generator.

5) Start generator set, and run on no load at nominal

frequency e.g. 50-53Hz or 60-63Hz.

6) If the red Light Emitting Diode (LED) is illuminated, refer

to the Under Frequency Roll Off (UFRO) adjustment.

7) Carefully turn VOLTS control clockwise until rated voltage

is reached.

8) If instability is present at rated voltage, refer to stability

adjustment, then re-adjust voltage if necessary.

9) Voltage adjustment is now completed.

A separate 3 Phase Sensing unit is

needed. Do not connect as shown

unless a 3 Phase Sensing unit is

fitted. (See sheet 5515)

STABILITY ADJUSTMENT

The AVR includes a stability or damping circuit to provide

good steady state and transient performance of the generator.

The correct setting can be found by running the generator at

no load and slowly turning the stability control anti-clockwise

until the generator voltage starts to become unstable.

The optimum or critically damped position is slightly clockwise

from this point (i.e. where the machine volts are stable but

close to the unstable region).

OPTIMUM RESPONSE SELECTION

The "jumper" selector lead should be correctly linked (A,B,C

at the bottom of the board) for the frame size of the generator

(See diagram).

UNDER FREQUENCY ROLL OFF (UFRO) ADJUSTMENT

The AVR incorporates an underspeed protection circuit which

gives a volts/Hz characteristic when the generator speed falls

below a presettable threshold known as the "knee" point.

The red Light Emitting Diode (LED) gives indication that the

UFRO circuit is operating.

The UFRO adjustment is preset and sealed at the works and

only requires the selection of 50/60Hz using the jumper link.

For optimum setting, the LED should illuminate as the

frequency falls just below nominal, i.e. 47Hz on a 50Hz

system or 57Hz on a 60Hz system.

DROOP ADJUSTMENT

Generators intended for parallel operation are fitted with a

quadrature droop C.T. which provides a power factor

dependent signal for the AVR. The C.T. is connected to S1,

S2 on the AVR.

The DROOP adjustment is normally preset in the works to

give 5% voltage droop at full load zero power factor.

Clockwise increases the amount of C.T. signal injected into

the AVR and increases the droop with lagging power factor

(cos Ø).

If a three phase sensing unit is fitted droop adjustment is

made on this separate unit.

With the control fully anti-clockwise there is no droop.

TRIM ADJUSTMENT (V/TRIM)

An auxiliary input is provided to connect to the VAr/PF

controller, (A1,A2). It is designed to accept dc signals up to +/-

5 volts.

The dc signal on this input adds to or subtracts from the AVR

sensing circuit, depending on polarity.

The V/Trim control allows the user to adjust the sensitivity of

the VPF controller.

With V/Trim fully anti-clockwise the VPF controller has no

effect. Clockwise it has maximum effect. Normal setting is

fully clockwise.

TD_SX440.GB_09.02_01

8511 NW 61st Street, Miami, FL 33166

Tel: 305-592-6800 •Fax: 305-592-5900

Website: www.gopower.com

Reprinted with permission of N.I. only.

Printed in England.

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