Voltage Regulator - Hobart 90 C 20 Operation And Maintenance Manual

OM-2031
G. Voltage Regulator
Mag-Amp type, Hobart Part No. 430391C, See TM-759 in Chapter 6 of this manual.
Solid-State type, Hobart Part No. 489812A, See OM-2020 in Chapter 6 of this manual.
H. Power Module Panel Assembly
The power module panel assembly (Fig. 10) sometimes referred to as the "contactor panel",
is located 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 cir-
cuit 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 oc-
curs. Three-phase, 400-Hz generator 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 (250-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 magni-
tude and power factor of current flowing from generator to load. They feed a signal to the voltage regula-
tor which interprets the signal and alters the exciter field current as required to maintain a constant
predetermined voltage at the load (see Voltage Regulator Manuals 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).
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April 30/96 Revised