Generator Control Box Interior Components (Figure 7); (A) Sensing Modules; (B) Memory And Time Delay Module - Hobart 140GT17P Operation And Maintenance Manual With Illustrated Parts List

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(2) Generator Control Box Interior Components (Figure 8)
Mounted on the generator contrl box interior are electrical and safety devices designed to protect
the aircraft electrical system against damage which could result from overvoltage, undervoltage,
overfrequency, or underfrequency. Also on this panel are devices for the protection and control of
the generator output electrical system.

(a) Sensing modules

The voltage sensing module (17) and frequency sensing module (18) are connected to the
generator output leads between the generator and the load contactor. These solid-state mod-
ules sense any abnormal condition of voltage or frequency and signal the solid-state circuitry
of the memory and time delay module (19) to open the load contactor and disconnect output
to the aircraft. Trip values are adjustable, however, adjustments should be made ONLY under
laboratory conditions.
Solid-state overload signaling devices (one for each output, and located on the power module
panel assembly) are also connected to the protective monitor module and perform a function
similar to the voltage and frequency sensing modules.
Trip values for protective circuits are as follows:
• OVERVOLTAGE trips at 130V to 134V
• UNDERVOLTAGE trips at 102V or below
• OVERFREQUENCY trips at 415Hz to 425Hz
• UNDERFREQUENCY trips at 390Hz to 395Hz
• UNDERVOLTAGE time delay (adjustable)
• OVERLOAD circuit trips at any value over 125% rated load capacity

(b) Memory and time delay module

The memory and time delay module (19) is sometimes called the protective monitor module.
It is a solid-state device with a hermetically-sealed, reed-type relay. The printed circuit board
or "card" includes five memory circuits and a time delay circuit. Each circuit is connected to a
corresponding sensing circuit in the sensing modules (17 and 18) . All memory circuits are
connected to the module relay coil, and any one of the circuits can energize the coil to open
the relay contacts. Thus, when a sensing device energizes any one of the module circuits, the
module relay is also energized to break the load contactor holding circuit and allow the load
contactor to open. All circuits, except the undervoltage circuit, function immediately to open
the load contactor. A time delay system is designed into the undervoltage circuit to prevent
nuisance opening of the contactor under conditions of momentary undervoltage in the gener-
ator output. An undervoltage condition which continues uninterrupted for a period of 4 to 12
seconds (adjustable) will cause the time delay circuit to open the load contactor. Each of the
five circuits is connected to a corresponding indicating light (9, 11, 14, 15 and 16) which is
turned on when a fault occurs.
The module relay will remain energized (OPEN) and the light will remain ON until the reset
switch (5) is pushed to break the module 12-V DC circuit, and allow the relay to return to nor-
mal, CLOSED position.
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July 27/90 Revised