Nautel NX5 AM, Руководство по предварительной установке

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NX5 PRE-INSTALLATION MANUAL ELECTRICAL REQUIREMENTS
VERSION 0.1 2015-08-01 PAGE 1.5.9
Generator Considerations
NX transmitters have several characteristics that make operating on a generator non-trivial. An
incorrectly selected generator could cause transmitter and/or generator instability and a degradation in
transmitter performance. Consider the following factors when selecting a generator:
 The source impedance of the generator will be significantly (typically 10x or more) higher than that
of the normal power utility ac supply. This factor could impact the performance of the generator
and the transmitter in a few ways:
 With the main load being an SCR rectifier, the voltage distortion at the output of the
generator will increase significantly due to a phenomenon called "line notching". This
notching could cause instability in the voltage regulation circuitry at the output of the
generator, and could cause the SCR controller to switch the SCRs at the incorrect time, either
in the transmitter, or the control SCRs in the generator.
 The increased line reactance could cause a significant drop in the output voltage of the
transmitter's SCR rectifier. In an AM transmitter, this would result in a reduction in peak
modulation capability and digital transmission performance.
 Because of the nature of an AM transmitter, the power being drawn from the generator varies
drastically with modulation. As the load on the generator changes, the frequency of the
generator's output voltage changes with it. This could cause stability issues for two reasons:
 The generator's control system may not be fast enough to follow the constantly changing
load.
 The transmitter’s SCR rectifier controller has limitations on the input frequency slew rate for
which it is capable of compensating.
 The transmitter's control system will maintain a constant power output from the transmitter
regardless of ac voltage fluctuations. This means that as the ac voltage to the transmitter
increases, the ac current drawn by the transmitter decreases, presenting a negative incremental
resistance load to the generator, which is opposite to what the generator's control system might
expect. This characteristic could interfere with the generator's control systems.
The high source impedance characteristic of the generator may be mitigated by over-sizing the
generator to minimize the reactance of the windings. There may also be different winding
configurations that could help to reduce reactance, depending on the manufacturer of the generator. In
addition, there are generator control systems and configurations that are more compatible with the
above mentioned transmitter characteristics than others, and selecting a generator with control
circuitry that is not affected by the line notching is also recommended.
Nautel recommends you consult with the generator manufacturer to carefully select and configure the
correct generator to ensure successful operation of the transmitter.