MX321 AUTOMATIC VOLTAGE REGULATOR SPEClFlCATION

General description

MX321 is a three phase sensed Automatic Voltage Regulator and forms part of the excitation system for a brush-less generator. Excitation power is derived from a three-phase permanent magnet generator (PMG), to isolate the AVR control circuits from the’ effects of nonlinear loads and to reduce radio frequency interference on the generator terminals. Sustained generator short circuit current is another feature of the PMG system.
The AVR senses the voltage in the main generator winding and controls the excitation to maintain the generator output voltage within the specified limits, compensating for load, speed, temperature and power factor of the generator. Three phase RMS sensing is employed for superior voltage regulation.
Adjustable Soft start circuitry is included to provide a smooth controlied build up of generator output voltage.

A frequency measuring circuit continually monitors the shaft speed of the generator and provides under-speed protection of the excitation system by reducing the generator output voltage proportionally with speed below a pre-settable threshold. A further enhancement of this feature is an adjustable volts per Hertz slope and voltage recovery time, to improve the response of turbo charged engines.

Current limiting may be included to allow control over the amount of sustained short circuit current.Maximum excitation is limited to a safe period by internal shutdown of the AVR output device. This condition remains latched until the generator has stopped.

The AVR includes an over-voltage protection feature with internal shutdown of the AVR output device, plus the ability to trip an optional excitation circuit breaker if required.

Provision is made for the connection of a remote voltage trimmer, allowing the user fine control of the generator’s output. An analogue input is provided allowing connection to a Newage Power Factor controller or other external device with compatible output.

The AVR has the facility for droop CT connection, to allow parallel running with other similarly equipped generators.

NOTES

1.Derate linearly from 3.7A at 50*C to 2.7A at 70°C
2.The stated voltage regulation may not be maintained in the presence of certain transmitted radio signals. Any change in regulation will fall within the limits in Criteria B of BS.EN.61000-6-2 : 2001.
3.After 10 minutes. 

4. Applies to Mod status Eonwards. Generator de-rate may apply. Check with factory. Factory set, semi-sealed, jumper selectable.
5. Any device connected to the analogue input must be fully floating (galvanically isolated from ground), with an insulation strength of 500V ac.
6.Non condensing.

Technical specification

SENSING INPUT
Voltage 190-264V ac max, 2 or 3 phase
Frequency 50-60 Hz nominal

OUTPUT
Voltage max     120 V de
Current            continuous 3.7 A (see note 1)
                       Intermittent 6A for 10 secs.
Resistance       15 ohms minimum

SOFT START RAMP TiME
0.4 – 4 seconds


TYPICAL SYSTEM RESPONSE
AVR response 10 ms
Filed current to 90% 80 ms
Machine Volts to 97% 300 ms

UNIT POWER DISSIPATION
18 watts maximum
ANALOGUE INPUT
Maximum input +/- 5 Vdc (see note 6)
Sensitivity 1 v for 5

OVER VOLTAGE DETECTOR INPUT
Set point: 300v. Time delay: 1 Sec (fixed)
CB trip coil volts: 10-30 vdc
CB trip coil resistance: 20-60 ohms
OVER EXCITATION PROTECTION
Set point 75 V de
Time delay 8-15 seconds (fixed)

POWER INPUT (PMG)
Voltage 170-220V ac max, 3 phase, 3 wire
Current 3A/phase
Frequency 100-120 Hz nominal

REGULATION
+/- 0.5% RMS with 4% engine governing (see note 2)


THERMAL DRIFT
0.02% per deg. C change in AVR ambient (note 3)

EXTERNAL VOLTAGE ADJUSTMENT
+/-10% with 5 k ohm 1 watt trimmer (see note 4)


UNDER FREQUENCY PROTECTION
Set point 95% Hz (see note 5) Slope 100-300% down to 30 Hz
Max. Dwell 20% volts/S recovery

QUADRATURE DROOP INPUT
10 ohms burden
Max. sensitivity: 0.22 A for 5% droop 0PF
Max. input: 0.33 A


CURRENT LIMIT INPUT
10 ohms burden
Sensitivity range: 0.5 – 1A

ENVIRONMENTAL Vibration 20-100 Hz 100Hz-2kHz Operating temperature Relative Humidity 0-70°C Storage temperature

The main functions of the AVR are:

Potential Divider and Rectifier takes a proportion of the generator output voltage and attenuates it. The potential divider is adjustable by the AVR Volts potentiometer and external hand trimmer (when fitted). The output from the droop CT is also added to this signal. A rectifier converts the a.c. input signal into a d.c. signal representing generator voltage.

The DC Mixer adds the Analogue input signal the generator voltage signal.
The 3 Phase Rectifier converts the output of the current limit CT’s into a de signal representing generator current

The Amplifier (Amp) compares the generator voltage or current signals to the Reference Voltage and amplifies the difference (error) to provide a controlling signal for the power devices. The Ramp Generator and Level Detector and Driver infinitely control the conduction period of the Power Control Devices and hence provides the excitation system with the required power to maintain the generator voltage within specified limits.

The Stability Circuit provides adjustable negative ac feedback to ensure good steady state and transient performance of the control system.
The Power Supply provides the required voltages for the AVR circuitry.

The 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. The Dip and Dwell circuits provide adjustments for greater voltage roll off and recovery time. A Light Emitting Diode gives indication of underspeed running.

The Synchronising circuit is used to keep the Ramp Generator and Low Hz Detector locked to the Permanent Magnet Generator waveform period.

Power Control Devices vary the amount of exciter field current in response to the error signal produced by the Amplifier.

The Circuit Breaker provides circuit isolation of the control system in the event of an over excitation or over voltage condition.

The Over Excitation Detector continuously monitors the exciter field voltage and turns off the power device if this rises above the reference leve.l for greater than the stated time period. An external signal is also provided to trip the Circuit Breaker

The Over Voltaoe Detector continuously monitors the generator stator voltage and turns off the power device if this rises above the reference level, for greater than the stated time period. An external signal is also provided to trip the Circuit Breaker

FITTING AND OPERATING (Refer to generator wiring diagram for connection details)

SUMMARY OF AVR CONTROLS

CONTROL

FUNCTION

DIRECTION

VOLTS

TO ADJUST GENERATOR OUTPUT VOLTAGE

CLOCKWISE INCREASES OUTPUT VOLTAGE

STABILITY

TO PREVENT VOLTAGE HUNTING

CLOCKWISE INCREASE THE DAMPING EFFECT

UFRO

TO SET THE UFRO KNEE POINT

CLOCKWISE REDUCES THE KNEE POINT FREQUENCY

DROOP

TO SET THE GENERATOR DROOP TO 5% AT OPF

CLOCKWISE INCREASES THE DROOP

TRIM

TO OPTIMISE ANALOGUE INPUT SENSITIVITY

-CLOCKWISE INCREASES THE GAIN OR SENSITIVITY

EXC

TO SET THE OVER EXCtTATION TRIP LEVEL

CLOCKWISE INCREASES THE TRIP LEVEL

DIP

TO SET THE HZ RELATED VOLTAGE DIP

CLOCKWISE INCREASES THE DIP

DWELL

TO SET THE HZ RELATED RECOVERY TIME

CLOCKWISE INCREASES THE RECOVERY TIME

I LIMIT

TO SET THE STATOR CURRENT LIMIT

CLOCKWISE INCREASES THE CURENT LIMIT

OVER V

TO SET THE OVER VOLTAGE TRIP LEVEL

CLOCKWISE INCREASES THE TRIP LEVEL

RAMP

TO SET THE NO LOAD VOLTAGE RAMP UP TIME

CLOCKWISE INCREASES THE VOLTAGE RAMP TIME

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 and 2 on the AVR will be fitted with a shorting link if no hand trimmer is required.

WARNING! Do not increase the voltage above the rated generator voltage. If in doubt, refer to the rating plate mounted on the generator case.
WARNING! Do not ground any of the hand trimmer terminals, as these could be above earth potential. Failure to observe this could cause equipment damage.

If a replacement AVR has been fitted or re-setting of the VOLTS adjustment is required, proceed as follows:
1.Before running generator, turn the 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. Continued.

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