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• Test (can verify self-check and perform functional
test)
The display will be blocked momentarily, every
minute, for the purpose of self-check; this will not af-
fect the relay protection function.
1.3.7 Power Supply Module
The Power Supply module (see Appendix G) is avail-
able in three ranges:
• 38 - 70 Vdc
• 88 - 145 Vdc
• 176 - 290 Vdc
Provides isolation from station battery; includes
overcurrent and overvoltage protection. Status mon-
itoring and loss-of-power indication are accom-
plished via a failure-alarm relay (on the Interconnect
module). Relay is normally picked up, but the pro-
cessor deenergizes it when a problem is found. Total
power loss also drops-out the relay. Front-panel test
points provide access to power-supply output voltag-
es for test purposes:
• +12 Vdc
• -12Vdc
•
-24 Vdc
• + 5 Vdc
1.3.8 Contact Outputs
• 4 make contacts (2 trip, 2 BFI); 8 additional op-
tional contacts when single pole trip option is
used.
• Single pole reclose initiate (2 Form A)
• Three pole reclose initiate (2 Form A)
• Reclose block (2 Form A)
• General Start (1 Form A)
• System failure alarm (1 Form C)
• Trip alarm (1Form C; 1 Form A is available if SBP
is not used).
1.4
TEST ACCESSORIES
The MDAR may be tested with two devices:
• Inner Chassis Test Fixture.
This device is similar to the outer chassis, and in-
cludes a Backplane and Transformer assembly.
• Extender Board
This device includes two small pc boards with two
ribbon cables. The inner chassis can be tested out-
side of the outer case by means of the Extender
Board.
(5/92)
1.5
FAULT DETECTION SOFTWARE
MDAR fault-detection software operates in two
modes:
• Background mode
• Fault mode
The MDAR relay normally operates in the "Back-
ground mode" where it looks for phase current or
phase voltage disturbances. Once a phase distur-
bance is detected, the relay enters the "Fault mode".
During non-fault operation (in the Background
mode), the MDAR Microprocessor (U100) used its
spare time to check its hardware, service the opera-
tor panel, and check for a disturbance in voltage or
current which indicates a possible fault. If a distur-
bance is seen, the programs switch to the Fault
mode, for several power cycles or longer, to perform
phase and ground unit checks for each zone and
function.
1.5.1 Background Mode
During the background mode, the seven inputs (cur-
rents and voltages shown in Figure 1-4) are sampled
to test for line faults. These currents and voltages
are sampled and converted into digital quantities and
input to the Microprocessor where all signal process-
ing takes place. (MDAR detects faults by digital com-
putation; not by analog.) The system continuously
takes 8 samples per cycle. The components of the
signals which are power system frequency are ex-
tracted.
The MDAR software which does the sampling has 8
states; these states correspond to the sampling rate
(8 samples per cycle). Movement from state to state
is controlled by a timer. The timer is loaded with a
state time at the beginning of the state. The code ex-
ecuted within a state should be completed before the
timer expires. The software then waits for the timer
to time out.
The MDAR relay program functions are included in a
flow chart loop (shown in Figure 1-5), which the
Microprocessor repeats 8 times per power cycle.
Most functions are performed all of the time, in the
background mode, as shown. An important detail
(not shown in Figure 1-5) is that many of the checks
are broken into small parcels, so that the whole com-
plement of tasks is performed over a one-cycle
period (eight passes through the loop). Some of the
checks are performed more than once per cycle.
I.L. 40-385.1B
1-3
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