![background image](http://html1.mh-extra.com/html/tronair/11a6647-1000/11a6647-1000_operation-and-service-manual_1171190014.webp)
28.5 VDC Ground Power Unit
Models:
11A6647-1000/1010
11B6647-1000/1010
11C6647-1000/1010
11D6647-1000/1010
11A6647C1000/1010
11B6647C1000/1010
11C6647C1000/1010
11D6647C1000/1010
11A6655-1000/1020
11B6655-1000/1020
11C6655-1000/1020
11A6655C1000/1020
11B6655C1000/1020
11C6655C1000/1020
11D6655C1000/1020
11A6665-1000/1010
11B6665-1000/1010
11C6665-1000/1010
11A6666-1000
11B6666-1000
11C6666-1000
12/2006 - Rev. 04
- 8 -
3.6
CONTROL AND MONITORING (continued)
3.6.3
Converter Operation
As soon as mains incoming power is applied to the control logic the microprocessors commence
operating and the internal function becomes active. Initially their only function is a ‘watchdog
operation’ checking for faults within the converter and monitoring the incoming supply for voltage
and frequency deviations. Any faults or deviations detected, are reported internally at the System
Controller Board (A100) which in turn passes the information to a built-in Event Monitor. The red
Warning LED at the operator panel is lit if there is an outstanding “unacknowledged” alarm in the
Event Monitor.
If the converter is switched on using the AJ “I” and “Enable” buttons simultaneously, the thyristors
V1 to V3 are fired and the generated voltage is fed to output transformer T6. The power rectifier
A6, generates the DC output voltage immediately. section 5.0 “Operating instructions” gives a
detailed description of the operation sequence.
3.7
VOLTAGE REGULATION MODE
3.7.1
General
The unit supplies a load which requires a supply voltage with very little deviation. (Normally 28V
DC +/- 1%). If a very long cable is used between the converter and the aircraft (load), a voltage
drop will be created which might be greater than the acceptable voltage tolerance of the aircraft. If
this happens, it is no longer possible for many units on the market to provide an acceptable
voltage supply to the aircraft especially under all load conditions.
To overcome this problem, two possibilities are available:
1.
The cable between the converter and the load could be designed in such a way that the
voltage drop will be decreased so that the supply voltage is within tolerance range. The
amount of copper wires and/or size can be increased or parallel cables can be used.
However there comes a point where the size of the copper wires required could become
too heavy or costly, or if the length of run is so long, that increasing the amount or wire
size will still not be enough to keep the tolerance within the voltage range, for all load
conditions.
2.
The converter must incorporate a LDC (Line Drop Compensation) system that can
provide active compensation so as to automatically compensate for the voltage drop.
With very long cable runs, parallel cables will increase the wire investment costs dramatically and
if flexible aircraft cables are also used, then parallel cabling might not be possible or practical.
To ensure that the proper voltage is delivered to the aircraft plug under all load conditions, there
must be a means of measuring the voltage at the aircraft plug, and sending those voltage signals
back to the converter, so they can be analyzed and responded to. This requires that signal wires
be run between the plug and the converter unit, where again cost and practicality must be
considered. In many cases, where voltage sensing wires are not available, the active voltage
drop compensation provided by the I-Boost compensation function is the only practical method
available to overcome this voltage drop problem.