Hobart Brothers 6910, Operation And Maintenance Manual With Illustrated Parts List

Page: 35 / 206

G. Power Module Panel Assembly
The power module panel assembly (Fig. 10) sometimes referred to as the “contactor panel”, is lo-
cated at the right rear of the machine behind the control box. On all models except the tow tractor
mounted unit, it is accessible by removing rear access-vent cover
(2, Fig. 1) on the canopy. The
panel assembly provides sensing and overload protection for the output circuit and provides a means
of connecting and disconnecting generator output to and from the load
(aircraft).
(1) Load contactor
The load contactor
(6, Fig. 10)
is a sealed unit which contains a magnetic operating coil and four
sets of contacts. The three larger contacts conduct three-phase AC generator output. A smaller
contact set is connected in the protective monitor circuit and supplies 12-V DC power used by
sensing relays to signal the protective monitor when a fault occurs. Three-phase, 400-Hz gener-
ator output power is conducted to the load contactor by 2/0 cables which pass through 3 sets of
current transformers
(3, 4, and 9).
NOTE : This contactor may be replaced by the old style contactor used in previous 60-KVA machines.
This note is for the benefit of those users who may have old style contactors Part number 75GH-566
(Hartman No. A-874C) in stock.
(2) Current transformers
(a) Ammeter current transformers
Three current transformers (4) lower the output load current to a lesser value of definite ratio
(500-A to 5-A) which will operate the ammeter (4, Fig. 9) movement without damage. The
ammeter dial scale is graduated and numbered so that the ammeter pointer will indicate the
true load current value rather than the meter movement current.
(b) Line-drop current transformers
The three line-drop current transformers (9), in conjunction with burden resistors (8), detect
the magnitude and power factor of current flowing from generator to load. They feed a signal
to the voltage regulator which interprets the signal and alters the exciter field current as re-
quired to maintain a constant predetermined voltage at the load
(see Voltage Regulator Manu-
als No. TM-759 for a Mag-Amp type or OM-2020 for a Solid-State type regulator).
(c) Overload current transformers
Three overload current transformers (3), in conjunction with burden resistors (1), monitor the
output load current in each of the three output phases, and supply a reduced value current
signal to the overload module
(7).
OM-2028
May 1/91 Revised 1-1
Page 21