TM 9-6115-669-13&P
1.14.2 PDU Electronics Group Monitoring Circuit.
The PDU electronics group N6 (figure 1-9) performs two functions:
Main power cutout if a limit value is exceeded on a phase line.
Detecting voltage and frequency synchronization at EPP III PDU bus bars and commercial
power converter bus bars if the converter is used.
Main power cutout
The main power cutout system consists of four identical plug in boards. Operation will be described
using the example of power contactor K6, which is cut out by relay K19.
If an overload at any of current transformers T10, T11, or T12 causes the voltage at input 4JR, 4JS,
or 4JT to exceed its limit value, time relay K19 at output J4 is set, and cuts out contactor K6 in the
main power circuit (figure 1-8). The contactor is not switched back on until relay K19 is reset by
pressing the OVERLOAD RESET pushbutton switch S4 on the control panel (figure 1-9).
Overload triggering is preset at the factory, by means of resistors R30, R31, and R32 and three
potentiometers on the PDU electronics group N6, to the following levels:
Cutout at 1.2 times rated value J = 156 A, with a delay less than (<)2.5 seconds.
Cutout at 1.8 times rated value J = 234 A, with a delay less than (<)1.5 seconds.
These settings cannot be changed by the customer.
Synchronization
Pressing PARALLEL OPERATION ON pushbutton switch S2 (figure 1-10), on the control panel
energizes relay K12 (figure 1-9), and initiates sychronization testing. +24 VDC voltage is delivered
to PDU electronics group N6 input +S, activating synchronization.
In this process, the R and S phases of generators 1 and 2 of the EPP III, and phases R (L1) and S
(L2) (R'/S') of the commercial power converter, are evaluated by the synchronization plug in board.
When voltage and frequency synchronization criteria have been met, time relay K13 is energized,
emitting a 0.5 seconds wipe pulse which triggers the appropriate generator change over process
(paragraph 1.14.3).
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