Hobart 90CU24, Руководство по эксплуатации и обслуживанию

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8.
400 Hz. Output Module Panel Assembly Single Output 500392-001 (See Fig. 9)
The output module panel assembly, sometimes referred to as the contactor panel, is located at the left
front of the machine under the control box. It is accessible by opening the left front door and then
removing the clear lexan and steel panels below the control panel. 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).
a. Load contactors
The load contacts (5) contains a magnetic operating coil and four sets of contacts. The three larger
conduct three-phase AC generator output. A small 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 generator output power is conducted to the load contactor by 2/0
cables which pass through two sets of current transformers
.
b. Current transformers
(1) Line-drop current transformers
Items 2 and 3 (Fig. 9) are line-drop current transformer-burden resistor combinations. They work
in conjunction with one another to detect the magnitude 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 required to maintain a constant predetermined voltage at the load.
(2) Generator ammeter and overload current transformers
Three overload current transformer-burden resistor combinations (4 and 6) work in conjunction
with one another, to convert a current signal to a voltage signal which is sent to the ammeter and
to the overload sensing board. The ammeter is really a voltmeter graduated and numbered in
amperes to show current proportional to the voltage signal received. This ammeter is so
graduated and numbered that, when cables running through the current transformers carry a
current of 260 amperes (rated load), 6.67 volts is sent to the ammeter. The ammeter will indicate
it as 260 amperes.
c. Overload Conditions
When an overload condition develops, wherein load exceeds 325 amperes (125% of rated load) the
overload sensing board (1) sends a signal to the memory and time delay PC board (4, Fig. 6). This
signal, which is the same one used in the ammeter circuit, interrupts the load contactor circuit to
open the load contactor.
(1) Generator overload module
When there is load on the generator set, and an overload condition exists which exceeds 125%
of the generator’s rated load)
, this solid-state overload module (1) interprets a signal from the
generator overload current transformers (3) and sends a signal to the memory and time delay
PC board (4, Fig. 6).
To do this, the overload module is equipped with a hermetically-sealed, reed-type relay. Relay
contacts are normally open. The solid-state circuitry is designed to close relay contacts when
output current reaches 125% of normal rated output capacity. The closed relay sends a signal to
the protective monitor. This signal gates the overload SCR (silicon-controlled rectifier) in the
protective monitor and opens the contactor(s) (5).
The following is a list of overload module characteristics:
•
At 125% load the module will function in 5 minutes.
•
At 150% load the module will function in 16 seconds.
•
AT 200% load the module will function in 4 seconds.
NOTE: The overload protective system will function when any phase carries 123% to 127% of rated
load. All times are plus or minus 25% and are adjustable.
OM-2084 / Operation and Maintenance Manual
90CU24 / Series 500392 Generator Sets
Chapter 1-1 November 27/1997
Page 18