Global Power Technologies
1120 - Class I, Division 2, Group D, T3
The hot junction of the thermocouples is maintained at a high temperature (538ºC or 1000ºF) by
a burner which operates on gaseous fuels such as propane or natural gas. The cold junction of
the thermocouples is maintained at a lower temperature (163ºC or 325ºF) by an array of cooling
fins which transfer the heat to ambient air by natural convection. The thermocouples are con-
tained in a hermetically sealed enclosure because they are adversely affected when exposed to
air at operating temperatures. They are surrounded by thermal insulation to minimize heat loss.
Maximum power is delivered to the load when: (a) the load voltage is one-half of the open circuit
voltage and (b) the load resistance is equal to the internal resistance. This condition is called
the matched-load power (also maximum efficiency) when the load voltage is slightly higher than
one-half (approx. 55%) of the open circuit voltage.
The TEG is supplied with a precision load resistor that provides a known load. This resistor
is used both in adjusting the TEG for proper operation and in evaluating its performance. The
fuel flow to the burner is adjusted so that the proper voltage exists across this precision resistor.
At this condition the TEG is operating at the intended junction temperature and is delivering
maximum power.
The TEG is supplied with a protective device which prevents its output voltage from rising
beyond 11.4 Volts. This is required because under extended open circuit (or slightly loaded)
conditions the hot junction temperature could increase beyond the safe operating range.
The burner operates at moderate pressures from 28 to 70 kPa (4 to 10 psi). The gas is
expanded through an orifice and then flows through a venturi where it draws in air needed for
combustion. The fuel flow is controlled by a pressure regulator and is adjusted by the operator
to obtain the desired power output.
In summary, the TEG produces electrical power when a temperature difference is maintained
between the hot and cold junctions of the thermoelectric materials. The temperature difference,
and therefore the amount of power produced, depends on the rate at which fuel is supplied to
the burner. The operation of the TEG is simply the control of the fuel pressure to the burner
which results in the desired power output.
1 .4 Physical Description
Figure 2 shows the generator in its normal operating position.
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