General Description
The AS480 is a half-wave phase-controlled Automatic Voltage Regulator (AVR) designed for brushless generators. It utilizes Surface Mount Technology (SMT), custom mouldings, and heatsinks for a compact assembly. The AVR includes an interface for the optional Excitation Boost System (EBS) to maintain short-circuit current. It operates by sensing the generator's output voltage via stator windings and controlling power to the exciter field to maintain voltage within specified limits, compensating for load, speed, temperature, and power factor.
Positive voltage build-up from residual levels is ensured by efficient semiconductors. A frequency measuring circuit monitors generator output frequency, providing under-speed protection by reducing output voltage proportionally with speed below a pre-settable threshold. The Under-Frequency Roll-Off (UFRO) point can be field-adjusted to 60Hz or 50Hz via a push-on link. Stability settings are available to compensate for various machine sizes and applications, including a 'slow' setting for engines prone to lamp flicker.
A remote voltage trimmer can be connected for fine control of the generator's output voltage. For 110Vac sensing, the hand trimmer link is replaced with a fixed resistor, which reduces generator overload capability. The AVR supports droop CT connection for parallel running with other generators. An over-excitation protection circuit limits over-excitation conditions to a safe period, reducing voltage to a low level until reset by stopping the generator or removing power. The EBS interface connects to a small, externally mounted rotary power supply that provides excitation power during heavy overloads or short circuits, with the EBS module protecting the generator against sustained overloads.
Technical Specification
| SENSING and POWER INPUT | |
|---|---|
| Voltage | 100-264 V ac 1 phase |
| Frequency | 50-60 Hz nominal |
| OUTPUT | |
|---|---|
| Voltage | 82 V d.c. @ 200 Va.c power input. 45 V d.c. @ 110 Va.c power input. |
| Current | continuous 5A (see note 1). transient 7.5A for 10 secs. |
| Resistance | 15 ohms min |
| REGULATION | |
|---|---|
| Voltage | ± 1.0% (see note 2) |
| THERMAL DRIFT | |
|---|---|
| 0.03% per deg. C change in AVR ambient (see note 3) | |
| TYPICAL SYSTEM RESPONSE | |
|---|---|
| AVR response | 20ms |
| Field current to 90% | 80 ms |
| Machine Volts to 97% | 300ms |
| EXTERNAL VOLTAGE ADJUSTMENT | |
|---|---|
| ±10% with 1 k ohm 1 watt trimmer (see note 4) | |
| Increasing resistance lowers voltage. | |
| Fixed 15kOhm resistor enables 110V sensing | |
| UNDER FREQUENCY PROTECTION | |
|---|---|
| Set point | 94-98% Hz (see note 5) |
| UNIT POWER DISSIPATION | |
|---|---|
| 12 watts maximum | |
| BUILD UP VOLTAGE | |
|---|---|
| 4 Volts @ AVR terminals | |
| QUADRATURE DROOP INPUT | |
|---|---|
| 10 ohms burden | |
| Max. sensitivity: 0.07 A for 5% droop OPF | |
| Max. input: 0.33 A | |
| OVER EXCITATION PROTECTION | |
|---|---|
| Set point | 67 Vdc ±3% (fixed) |
| Time delay | 10-15 seconds (fixed) |
| ENVIRONMENTAL | |
|---|---|
| Vibration | 20-100 Hz 50mm/sec |
| 100Hz-2kHz 3.3g | |
| Operating temperature | 0-70°C (note 6) |
| Relative Humidity | 0-95% (note 7) |
| Storage temperature | -55 to +80°C |
NOTES:
- De-rate by 20% if mounted external to generator.
- Inclusive of 4% engine governing.
- After 2 minutes warm-up.
- Generator de-rate may apply. Check with factory.
- Factory set, semi-sealed, jumper selectable.
- De-rate output current by 5% per deg. C above 60°C.
- Non condensing.
Block Diagram Description
The AS480 AVR block diagram illustrates the signal flow and component interactions within the voltage regulation system. Key functional blocks include:
- Sensing Voltage Divider/Adjust: Samples and attenuates the generator output voltage, incorporating droop CT input. A precision rectifier converts this AC signal to DC for further processing.
- Amplifier: Compares the sensed voltage to a reference voltage, amplifying any difference (error) to control power devices.
- Ramp Generator, Level Detector, and Level Shifter: These components control the conduction period of the AVR Output Power Control devices, providing variable power to the exciter field windings to maintain generator voltage.
- Stability Circuit: Provides adjustable feedback for stable steady-state and transient performance, with options to suit different generator frames and applications.
- Low Hz Detector: Monitors generator frequency and reduces reference voltage linearly with speed below a preset threshold, indicating low-speed operation with an LED.
- Synchronising Circuit: Locks the Ramp Generator and Low Hz Detector to the generator waveform period, with a Low Pass Filter preventing distorted waveforms from affecting control.
- AVR Output Power Control: Varies exciter field current based on the amplifier's error signal.
- Input Power Suppression: Protects AVR components from load-generated transients and reduces radio-frequency noise.
- Over Excitation Detector: Monitors exciter field voltage and collapses output voltage if an over-excitation condition persists for a set time.
- Power Supply: Provides necessary voltages for AVR circuitry.
- EBS Interface: Provides signals to control the Excitation Boost Generator (EBG), which supplies additional power during overloads.
Links and Adjustments
The AS480 AVR features several linking and adjustment points for configuration and operation. Refer to the generator wiring diagram for complete connection details.
Configuration Options:
- Excitation Boost Unit Connection: Terminals are provided for connecting the optional excitation boost unit.
- Stability Linking: Options include 'Link BC', 'Link BD', or 'No Link', selectable based on generator size (e.g., > 100kW, < 100kW) and desired response (Fast, Slow).
- UFRO Linking: A jumper link allows selection between 50Hz and 60Hz operation for the Under-Frequency Roll-Off feature.
AVR Board Layout and Controls:
The AVR board includes:
- VOLTS Terminal: For generator output voltage setting.
- DROOP Terminal: For voltage droop adjustment during paralleling.
- STABILITY Terminal: For output voltage stability adjustment.
- UFRO Terminal: For under-frequency 'knee' point adjustment.
- LED Indicator: Shows operational status, including under-speed or over-excitation conditions.
- F1, F2 Terminals: Connections for the exciter field windings.
- S1, S2 Terminals: Connections for the droop CT.
- Links: Various jumpers for configuration (e.g., 50/60Hz UFRO, stability settings).
- Hand Trimmer (optional): A 1kΩ, 1W trimmer for external voltage adjustment.
- Droop C/T (optional): Connection for the Current Transformer for droop compensation.
Specific adjustments are made via controls or links:
| Control | Function | Direction |
|---|---|---|
| VOLTS | Generator output voltage setting | Clockwise raises voltage |
| STABILITY | Output voltage stability | Clockwise increases stabilisation effect |
| DROOP | Voltage droop for paralleling | Clockwise increases drooping effect |
| UFRO | Under-frequency 'Knee' point | Clockwise decreases 'Knee' point |
| LED | Indicates under-frequency or over-excitation | N/A |
Note: For 110Vac operation, remove the link marked (*) before fitting and connect the 15kΩ/1W sensing link. The hand trimmer cannot be used in this mode, and overload performance is limited.
Adjustment of AVR Controls
Voltage Adjustment
The generator output voltage is factory set but can be adjusted using the VOLTS control on the AVR board or an external hand trimmer. Before adjusting, observe the following warnings:
- Warning: Do not increase voltage above the rated generator voltage.
- Warning: Do not ground external hand trimmer terminals to avoid equipment damage.
Adjustment Procedure:
- Before starting the generator, turn the [VOLTS] control fully anti-clockwise. Set the [STABILITY] control to its midway position and the external hand trimmer (if fitted) to its midway position.
- Connect a voltmeter (0-300Vac range) across the generator's Line and Neutral terminals.
- Start the generator and run it at no load at the nominal frequency (e.g., 50Hz or 60Hz).
- If the red LED is illuminated, refer to the Under-Frequency-Roll-Off adjustment section.
- Carefully turn the [VOLTS] control clockwise until the desired voltage is reached.
- If instability occurs at the rated voltage, refer to the Stability Adjustment section.
- Voltage adjustment is now complete.
Stability Adjustment
The AVR features an optimized stability circuit for good steady-state and transient performance. Linking options allow adjustment for different generator frames and applications. A 'slow' response setting is recommended for small generator sets and helps reduce lamp flicker.
To find the correct stability setting, run the generator at no load and slowly turn the stability control anti-clockwise until the generator voltage becomes unstable. The optimum position is slightly clockwise from this point, where the machine volts are stable but close to the unstable region.
Under-Frequency-Roll-Off Adjustment (UFRO)
The AVR includes under-speed protection that creates a volts/Hz characteristic when generator frequency drops below a preset threshold (the "knee" point). The red LED indicates when the UFRO circuit is active in the low-frequency region.
The UFRO adjustment is preset and sealed, requiring only the selection of 50Hz or 60Hz operation via a jumper link. For normal operation, the LED should illuminate as the frequency falls just below 95% of nominal (e.g., 47Hz on 50Hz systems or 57Hz on 60Hz systems).
Droop Adjustment
Generators for parallel operation require a quadrature droop CT connected to S1 and S2 on the AVR. This CT provides a power factor-dependent signal to the AVR voltage sensing circuit, controlling generator reactive current during parallel operation.
The DROOP adjustment is typically preset to provide 5% voltage droop at full load, zero power factor. Turning the control clockwise increases the CT signal injected into the AVR, thereby increasing voltage droop. With the control fully anti-clockwise, there is no droop.
Over Excitation Trip
The over-excitation trip level is factory set at 65Vdc and is not adjustable. An over-excitation condition is indicated by the LED (which also indicates under-speed running).
The over-excitation condition is permitted for approximately eight seconds to prevent nuisance tripping and support normal transients and short-term overloads. When the trip is activated, the generator voltage drops to low levels. The generator must be stopped to reset an over-excitation shutdown condition.
Excitation Boost System
There are no user adjustments required for the EBS module; simply connect the unit, and it is ready for use.
