Hobart 9OC24S Operation Manual page 215

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OPERATION, MAIN TENAN CE , AND OVERHAUL MAN UAL, TM-240A
SELF-PROPELLED GENERATOR SET, SPEC. NO. 5381A
(2) Fault sensing devices
(a) Fault sensing relays
Four fault sensing relays (OV, UV, OF, UF) are connected directly to
the generator output leads between the generator and the load contactor.
Each relay contains circuitry ,designed to sense a particular fault, and a
set of normally open contacts. When a faulty output condition is sensed
by one of the relays,
the contacts are automatically closed and a signal
is sent to the protective monitor module (PM) which responds to the signal
by causing the load contactor to open. Sensing relay trip values are
contained in 3-2, Para. 6.
(b) Overload sensing device
The overload sensing device consists of solid-state circuitry designed to
interpret input signals from load sensing transformers in the generator output
circuit, and to close a sealed, reed-type relay when generator output
reaches 125%, or more, of normal rated load. Since signals from each
of the three output phases are interpreted separately, an overload in any
phase will cause the overload device to function. The device is designed
to tolerate a load of 125% normal rated load for approximately 5 minutes.
As the overload increases the response becomes much faster so that a load
of 150% will cause the device to function in approximately 16 seconds.
When the solid state circuitry closes the relay, a signal is sent to the
protective monitor module. The signal causes the module to interrupt
the load contactor holding circuit and disconnect the output load.
(3) Protective monitor module
Ott 30/73
The function of the protective monitor module is to interrupt the load contactor
holding circuit upon signal from any one of the fault sensing devices. The
module consists of five memory circuits connected to a norma I ly closed,
reed-type relay. When triggered by a signal from a fault sensing device, any
one of the memory circuits can actuate the relay to open the load contactor.
Signals from the overload, overvoltage, overfrequency, and underfrequency
sensing devices cause the protective monitor to function instantly. The
undervoltage memory circuit includes a 5-second time delay system to pre-
vent nuisance opening of the load contactor under conditions of momentary
undervoltage. Each memory circuit is connected to an indicating light which
is turned ON when the circuit functions to open the relay. The operator is
able to immediately identify the fault which caused the load contactor to
open by noting which light was turned ON. The light (or lights) will remain
ON and the relay will remain open until the 12-V DC holding circuit is
opened by pressing the reset switch
(1PB) I ocated on the front
of the protective
re lay tray.
3-l
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