Continental Electronics 816R - Page 29

TECHNICAL INFORMATION LETTER
October 30, 1991
THREE PHASE TRANSMITTER PRIMARY POWER SOURCE
The purpose of this Information Letter is to describe the primary power source for
Continental transmitters that require Three Phase Primary Power. Our
specification sheets, instruction manuals, and sales brochures state the primary
power requirements for individual transmitters but do not state reasons for
exempting certain types of power sources. Questions have come to our attention that
indicate a need for us to express our concern about the use of Open Delta power
sources for radio transmitters and to make recommendations.
The Open Delta three phase connection is sometimes referred to as "Phantom three
phase" connection or "V-V" connection. The only reason that this configuration is
ever used is to reduce power line and transformer costs to the power company which
may be passed on to the subscriber. This configuration requires two transformers
instead of three and one less power transmission wire to the subscriber's location.
Non-sinusoidal phase voltage, excessive third harmonic content, susceptibility to line
and switching transients, and imbalance of phase voltages are problems inherent
with the Open Delta connection. Because of this lack of stability, peak ratings of
power supply components may be exceeded, resulting in frequent power supply
component failure and impaired performance. For these reasons, the open Delta
connection must be avoided as a primary power source for transmitters.
Conventional WYE and Closed Delta are the only acceptable power sources for
three phase transmitters. Both offer acceptable phase to phase voltage and phase
characteristics under changing load conditions. Lightning and transient protection
devices can perform their function when used with either type and a proper ground
system. The WYE configuration is prefered when there is a choice between WYE
and Closed Delta.
This is not to say that a transmitter will not function with other types of primary
power configuration, but reliability and performance will likely be affected by using
another type.
For further information or if there are questions, please contact our Field Service
group at (214) 388-5800.
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