General Description
The AS480 is a half wave phase controlled AVR which forms part of the excitation system of the brushless generator. The design employs Surface Mount Technology (SMT), custom mouldings and heatsinks to produce a compact AVR assembly.
The AVR also incorporates an interface to the optional Excitation Boost System (EBS) for use where short-circuit current maintenance is required.
The AVR is linked with the mainstator windings and the exciter field windings to provide closed loop control of the output voltage with load regulation of +/- 1.0%. The AVR voltage sensing terminals continuously sample 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 withinthe specified limits, compensating for load,speed, temperature and power factor of the generator.
Positive voltage build up from residual levels is ensured by the use of efficient semiconductors inthe power circuitry of the AVR.
A frequency measuring circuit continually monitors the generator output frequency and provides under-speed protection of the excitation system. Thisis done by reducing the output voltage proportionally with speed belowa pre-settable threshold.
A manual adjustment is provided for factory setting of the under frequency roll off point, (UFRO). This can be changed to 60Hz (or 50Hz) in the field by push-on link selection.
A wide range of stability settings are available to compensate for machine sizes and applications. A ‘slow’ setting is available for applications involving single/twin cylinder engines and where lamp-flicker could be a problem.
Provision is made for the connection of a remote voltage trimmer, allowing the user fine control of the generator’s output voltage.
Operation with 110Vac sensing is possible, replace the hand trimmer link with fixed resistor. The hand trimmer option cannot be used in this configuration.The generator overload capability is reduced in 110V operation.
The AVR has the facility for droop CT connection, to allow parallel running with other similarly equipped generators.
Over excitation conditions are limited to a safe period by a protection circuit within the AVR. Once activated by a sustained over-excitation condition, the generator voltage is reduced to a low level until reset. Stopping the generator or removing power from the AVR will perform the necessary reset.
Connections are provided to interface to the optional Excitation Boost System. This incorporates a small externally mounted rotary power supply which providesexcitation power in the event of heavy overloads or short circuits. The EBS is short term rated and responds to signals from the AVR to deliver excitation power when required. A separate overload protection system within the EBS electronic module protects the generator against sustained overloads.