Hobart 60PL20 Operation And Maintenance Manual page 25

Trip values for protective circuits are as follows:
Overvoltage trips at 130 V to 134 V
Undervoltage trips at 102 V or below
Overfrequency trips at 415 Hz to 425 Hz
Underfrequency trips at 390 Hz to 395 Hz
Undervoltage time delay (adjustable)
Overload circuit trips at any value over 125% rated load capacity.
Trip values are adjustable, however, adjustments should be made ONLY under laboratory
conditions.
See Para 6,H, (3) for more specific and detailed information regarding overload device.
(b) Memory and time delay module
The memory and time delay module (7) 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 (4, 5, and 6) . 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. The module relay will remain energized (OPEN) and the light will remain
ON until the reset switch (17, Fig. 6) is pushed to break the module 12-V DC cirucit, and allow
the relay to return to normal, CLOSED position. All circuits, except the undervoltage circuit,
function immediately to open the load contactor. A time delay system is designed into the un-
dervoltage circuit to prevent nuisance opening of the contactor under conditions of momen-
tary undervoltage in the generator 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 (10, 11, 12, 13 and 14) which is turned on when a fault occurs.
(c) Excitation-deenergization relay
The purpose of this relay (1) is to allow automatic excitation to be connected to the exciter
field only when engine speed is being controlled by the electric governor.
(d) Plug-interlock relay
The function of the plug interlock relay (2) is to cause the output load contactor to open in the
event the cable plug connector becomes accidentally disconnected from the aircraft during
power delivery, or if an attempt is made to deliver power when the output cable is not con-
nected to the aircraft. Twenty-eight-volt, direct current for operation of the relay is supplied
from the aircraft either through an on-board transformer-rectifier, or from a twenty-eight-volt,
electrical system. Connection from the aircraft to the interlock relay is made through termi-
nals E and F on the output cable plug connector.
(e) Test-bank switch
A spst, toggle switch (19) provides a means of bypassing the plug interlock relay (2) when
supplying power to a load bank or to an aircraft not equipped with a plug interlock system.
(f) Resistor
A 100-ohm, 25-watt resistor (18) is connected in series with the plug interlock relay to protect
the relay in the event that phase C contacts in the load contactor should fail to close when the
generator ON switch is operated.
December 31/91 Revised
OM-2053
1-1
Page 11