Ripple Regulator Circuit Card Al 1; Fuse Alarm Circuit - Marconi LORAIN RHM800E50 Manual

6.25 This circuit card continuously monitors the ripple
current Mrough the rectiiier DC output filter capacitors.
within the adjustable limits set by the ripple regulator cir-
cuit card and no output signal is provided. However, if
one AC input phase is lost or another failure occurs
which results in a high output ripple condiiin exceeding
the ripple current setting of circuit card Al 1, the ripple
regulator provides a positive output signal. This signal
is applied to the regulation circuitry of Regulator and
Alarm circuit card A7 causing a subsequent reduction in
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rectifier output voltage until the ripple current through
the filter capacitor is reduced to normal limls.
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626 Current transformer T2 senses the ripple current
through the DC filter capacitor and applies a voltage to
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input is rectffied by diodes CR1 through CR4 and fiC
voltage is applied through resistor R5 to the non-invert-
ing input of comparator Al. The variable input at the
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non-inverting input of Al is compared to a reference
voltage applied at the inverting input of Al The refer-
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resistor R4. and is adjustable depending upon the set-
ting of potentiometer R3. This reference input deter-
mines the value of ripple current at whidr the ripple
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cuitry on circuit card A7. When the ripple current
the
of potentiometer R3, comparator Al provides a positive
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output signal through diode CR5 to Me regulator and
627 This positive signal is applied to the inverting
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input of voltage follower A18 on circuit card A7 tii
generates a negative error signal of equal amplitude but
opposite polarity. The resulting positive and negative
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error signals are men applied to me pulse generation
circuitry previously described.

Fuse Alarm Circuit

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626 The fuse alarm circuit initiates rectiiier shutdown
and provides visual indication of an open fuse ii any
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fuse in the rectffier. wfth the exception of fan fuses F5
and ffi. opens. The DC output and filter fuses are con-
nected to associated alarm fuses FlA. F3A. and F4A.
An alarm type fuse, F2, pmtects the negative battery
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input circuits u&ed for control purposes. If any of these
fuses open, me alarm contact of me fuse connects neg-
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me ripple
FUSE ALARM light emitting diode. The LED illuminates
and contacts of K4 open which deenergizes Kl and K2.
When K2 releases, its contacts open which interrupt AC
input power to the rectifier. This automatic shutdown
6.29 This rectifier is equipped with cooling fans and
fan faifure and temperature sensors. The fan fail sen-
mounted beneath each heatsink fan while the tempera-
ture sensors S3 and S4 are mounted at the approximate
center of the heat sinks. The fan fail circuits contfnu-
ously monitor the presence of air flow across the heat
sinks while temperature sensors S3 and S4 continu-
ously monitor the temperature of the heat sinks. If the
air flow ceases, relay KS releases and, in addition, illu-
minates indicator FAN FAILURE. If the air flow ceases
or the temperature of the heat sink reaches +65'C
vate an external rectifier fail alarm. if connected.
6.30 Fan fail circuit cards A12 and Al3 and tempera-
ture sensors 53 and S4 are connected in series with the
coil of relay K3. In addition. fan fail circuit cards A12
and Al3 are connected in series with the coil of relay
K5. During normal operation. the temperature sensors
and fan fail monitors are closed which energizes the coil
of K3. Contacts of relay K3, energized, provide closed
circuits between J4 pins 11 to 12 and J2 pin 14 to J5 pin
11 of circul card A7. The closed circul across J4 pins
11 to 12 bypasses resistor A7-R17 in the current limiting
voltage divider circuit, while the closed circuit across JZ-
14 to JS-11 supplies voftage to hold rectifier fail relay Kl
on afarm interface assembly A9 energized. This inhibits
the external rectifier fail alarms. Wii resistor A7-R17
bypassed in the voltage divider. the current limiting cir-
cuit is adjusted by potentiometer A7-R23 to provide full
rated output current. During a fan failure condiiion. relay
K5 releases and, through normally closed contacts,
causes indicator FAN FAILURE to illuminate. During a
fan failure or overtemperature condition, relay K3 is
R17 in the current lift cinuil and opening the coil cir-
cuit of relay Kl on A9. Addition of resistor A7-R17 into
the cunent limit voltage divider alters the voltage in the
divider which results in reducing the current limff setting
of potentiometer A7-R23. Insertion of resistor A7-R17
results in limiting oufput cunent at approximately 66% of
full load. This prevents damage from overheating the
rectifier during a fan failure. Opening the coil path of
Section 4397
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