Newage SX440 Quick Start Manual

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

GENERATOR

SUPPRESSION

CURRENT

INPUT

VOLTAGE

SENSE

VOLTAGE

TRIM

ACCESSORY

INPUT

SEN SING

LO SS D ETE C T O R

DROOP

SENSING

RESISTORS

POWER

SENSING

DC MIXER

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.

LOW

Hz DETECTOR

REFERENCE

VOLTAGE

MAIN COMPARATOR

AM PLIFIER

STABILITY

CIRCUIT

SYNCHRONISING

CIRCUIT

PEDESTAL AND

RAMP CIRCUIT

LOW PASS

FILTER

POWER
SUPPLY

LEVEL DETECTOR

AND DRIVER

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.

POWER

CONTROL

DEVICES

EXCITER
STATOR

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.

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.