2-42
888-2586-001
9/15/06
WARNING: Disconnect primary power prior to servicing.
Platinum Z16HD+
Section 2 Installation & Initial Turn-On
2.11 Power Distribution for Optimum
Transmitter Performance
This section is applicable to the three phase supplies only, as well as other three phase
equipment. For many years HARRIS engineers have recommended that the three phase
power distribution system should be either a closed delta or WYE configuration to
provide better radio and television transmitter performance by helping prevent line
unbalance. Operation with substantial voltage unbalance from line to line results in
higher than normal signal-to-noise ratio in the transmitter output signal, increased three
phase transformer heating, and hot three phase motors.
2.11.1 Overheating from Line Unbalance
Even a device as simple as a three phase motor should be operated from a power line in
which the voltage is balanced within 1%. It takes only a 3.5% line unbalance to produce
a 25% increase above normal temperature. A 5% unbalance will cause destructive
temperature rises of 50% greater than normal!
Similar characteristics can be expected in the windings of a three phase power
transformer down inside the cabinet of your transmitter. Transformers and motors can
be designed with extra safety features where thermal rise is limited to acceptable levels;
however, in this case, other transmitter parameters cannot be made acceptable at a
reasonable cost.
2.11.2 Transmitter Noise Performance
The most difficult parameter to meet with power line unbalance is transmitter noise
performance. Most large transmitters use six-phase or twelve-phase high voltage power
supplies. The energy storage capacitors are expensive to install and large stored
energies make destructive faults inevitable. A good design will have sufficient energy
storage capacitors to meet the specified signal-to-noise but not much more. When the
equipment is then operated from an unbalanced line, the power supply ripple frequency
will be twice the line frequency instead of six to twelve times. It becomes obvious that it
would take three times as much energy storage to achieve the original performance
goal.
2.11.3 The Causes of Line Unbalance
How does a line unbalance occur? It is a rare case in which a large commercial power
producer would generate unbalanced voltage, so we must look elsewhere in the system.
When you have large single phase power users on a power line this can cause uneven
distribution of the line currents in the system. Uneven currents through balanced
impedances will result in line-to-line voltage unbalance.
Summary of Contents for Platinum Z16HD+
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