Design Overview
The GC3 consists of a micro-processor based control circuit as well as separate independent protection circuits for fail-safe operation.
Fail-safe operation simply means that when failure does occur in the generating system, it shall shutdown safely and
the fault shall be contained - not spread to other areas of the aircraft.
For reliability and a long service life the GC3 is built with only solid-state components.
It does not contain any moving parts such as relay contacts found on others.
Also, when we designed the GC3, we designed it with simplicity in mind,
specifying the components conservatively and using redundancy in specific areas.
Our micro-processor architecture makes for more intelligent control and protection.
The GC3 is able to track the state of the generating system much more closely, making it for example better at detecting
and quicker at reacting to faults.
To remain operational for longer, the GC3 can adapt to a fault should it have a backup such as a redundant circuit available.
Should there be no backup, the GC3 will take the generator off-line and even shutdown completely
to prevent damage to a generating system component or a device on the load bus.
The architecture makes it possible for the GC3 to inform you about the integrity of external wiring.
Should certain wires not be connected properly, the GC3 will inform you about them.
The GC3 promises to be especially useful on new installations where it can assist you to sort out those early snags.
Illustrated below is the basic wiring diagram of the GC3.
Not shown are the RS232 and CAN bus interfaces that may be used to communicate with other devices in the aircraft.
The GC3 can for example be linked with another GC3, a VR-3PD display unit or various other devices via CAN bus.
Compatibility
As the above diagram illustrates, the GC3 is compatible and interchangable with other generator controllers that control
MIL-G-6162 starter/generators.
You can replace the current GCU in your aircraft with ours either by replacing the mating connector in your harness,
or by inserting a short inline harness that adapts your current mating connector to the GC3's connector.
POR Redundancy
One way the GC3 makes power generation more reliable is through fault tolerance or redundancy.
Should the point-of-regulation (POR) signal become disconnected (break) during operation,
an ordinary GCU will cause an over-voltage condition by inadvertently over-exciting the generator field.
This eventually leads to generator shutdown as the protective over-voltage circuit pops (opens) the generator circuit-breaker.
The bottom-line is that the generator is down.
The GC3 on the other hand will detect the POR breakage and adapt by using the BUS and GEN-ON signals for operation instead.
The generator will thus remain operational and continue undisturbed.
At the end of such a flight, as you switch-off the generator, the "GEN OFF" annunciator will then flash a certain code to
inform you about POR signal fault.
INHIBIT Redundancy
Another way our GC3 makes starter/generator operation safer is with INHIBIT redundancy.
Should the INHIBIT signal become disconnected,
an ordinary GCU will not disable the generator shunt field during the start with the generator switch on,
which will result in reduced torque to the starter motor and possible temperature exceedence on a turbine.
The GC3 on the other hand will firstly inform you at power-up should the INHIBIT signal be disconnected by flashing
a certain code on the "GEN OFF" annunciator.
Secondly, should you in any case proceed with a start, the GC3 would be able to recognize the start through alternative means and still
disable the generator shunt field.
Over-Voltage Protection
The GC3 incorporates an over-voltage protection circuit similar to other GCU's, which is independent and distinct from the
micro-processor based control circuit.
The protection circuit uses a "crowbar" circuit which once triggered not only pops (opens) the external
generator circuit-breaker, but also de-energizes the generator shunt field and opens the line-contactor to
remove the over-voltage condition and force the generator off-line.
Reverse Current Protection
Another independent protection circuit is the one handling reverse generator current. In this case the line-contactor
latches open when the current reverses inside the generator (generator becomes a motor). The current is measured by
monitoring the voltage on the GC3's SENSE pin which is connected to the D-terminal of the starter/generator.
Load Current Limiting
The GC3 can limit the current to the load bus by reducing the generator voltage.
In some cases this is done to prevent damage to the starter/generator when it's rated current is exeeded for too long a peroid of time.
Load current limiting is also employed on twin-engined aircraft so that the load can be shared equally among the two generators.
On twins the GC3 can additionally perform cross start current limiting to assist in the start of the second engine.
For multi-engine installations the GC3 units are typically linked via CAN bus.
Under-Voltage Protection
Should the generator voltage reach the under-voltage limit, which could happen when load current limiting is active,
the GC3 will pop (open) the generator circuit-breaker thereby shutting down the generating system.
In cross start situations the under-voltage limit is typically lowered.
Open FIELD Protection
The GC3 is able to detect whether both the FIELD output and RETURN wires are connected to the starter/generator.
These lines must be connected for proper operation of the generating system, thus the GC3 will restrain from generating
power, but flash out a code on the "GEN OFF" light identifying the cause.
Different flash codes are used for FIELD output fault and for field RETURN fault.
Open SENSE Protection
The SENSE input pin should be connected to the D-terminal on the starter/generator and is used to measure the load current.
It is essential to have it connected properly.
If not connected at power-up, the GC3 will flash a certain code out through the "GEN OFF" light to identify the SENSE pin disconnect.
Load Current Feedback
The GC3 is able to measure the generator current (load) through the SENSE pin when starting and when generating.
This as well as other information is made available to external devices, such as EFIS systems.
The GC3 provides this data via RS232 and CAN bus interfaces.
"GEN OFF" Annunciation
This annunciation light not only informs the pilot to the state of the generating system, but provides for
installers and servicing personnel means of identifying a system fault.
It flashes a particular code that tells you where to look for a wiring fault, or if the unit itself needs repair.
Connecting to a Laptop / PC
A laptop PC and USB-to-serial adapter (such as the Bafo BF-810) may be connected to the GC3
in order to make adjustments to settings as well as to troubleshoot the system.
This is mostly required only during the installation phase to properly configure the GC3.
It provides the means to for example change the "generator voltage" setting in a stand-alone application.
For special troubleshooting support this software is also useful to record the working of the GC3.
These recorded operations are stored in files and may even be emailed to VR Avionics should you require special support.
All are done through our System Link software which may be downloaded from this webpage (see right-hand column).
Availability
The GC3 have taken a long time to develop and we hope it will be worth the wait.
You may register your interest by contacting us so we will be able to keep you informed as to the progress
of this product and when it will become available. You are also very welcome to ask questions or make suggestions regarding the product.
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