–2–
M-0329B Backup Control
The M-0329B LTC Backup Control provides the extra protection that can save your customers from the hazards
and inconvenience of excessively high or low voltage. Defective LTC tapchanger controls can cause either too
high or too low a voltage along the line, possibly damaging customers' motors, computers or televisions. Even
when the control is operating properly, customers close to the transformer may receive dangerously high voltage
as the line drop compensator attempts to maintain a constant voltage under heavy load at a central point on the
distribution line. The Beckwith Electric M-0329B LTC Backup Control can be installed as a solution to both of
these problems.
The LTC Backup Control will prevent a defective LTC tapchanger control from running the voltage outside the
upper and lower voltage limits and, in addition, will prevent the line drop compensator from raising the voltage too
high under full load or overload conditions. Setting the voltage bands on the M-0329B slightly wider than the
transformer control limits will assure that a failed control will not result in a runaway LTC transformer. Under full
or overload conditions, the control automatically takes over as an upper voltage limit control, not affected by load
current, to prevent damage to equipment close to the transformer. While the Block Raise contact prevents a raise
operation, a Lower contact forces the tapchanger down if the primary voltage should subsequently rise.
Features
Block Raise and Block Lower voltage levels are set by accurately calibrated
BANDCENTER
and
BANDWITH
controls, similar to those found on LTC transformer controls.
BLOCK RAISE/LOWER
and
LOWER
LEDs indicate backup control status.
Block Raise, Block Lower, Lower
and Alarm
contacts provide outputs to drive external components.
Inputs
Power
: 90 to 140 V ac, 50/60 Hz, 2 W at 120 V ac
Voltage
: Less than 0.2 VA burden at 120 V ac input
Front Panel Controls
BANDWITH VOLTS:
An accurately calibrated dial adjusts the bandwidth between Block Raise and Block Lower
from 6 V to 24 V for 120 V ac.
BANDCENTER VOLTS:
An accurately calibrated dial adjusts the Bandcenter from 100 V rms to 140 V rms
which allows the M-0329B to operate with most transformer controls.
TIME DELAY SECONDS:
Adjustable from 1 to 30 seconds. If voltage remains above the maximum (Block
Raise) voltage by the selected amount for longer than the time set on the timer delay control, the M-0329B will
initiate a tapchanger operation to lower the voltage.
Selectable Deadband:
The deadband is the voltage range above the Block Raise Level where no tap changer
operation takes place. In the M-0329B, it is selectable as 1, 2, 3, or 4 V rms. Measured voltages above the Block
Raise Level plus the deadband will cause the control to immediately issue a Lower command.
Terminals:
Barrier Strip with 8 to 32 screws
LED Indicators
The
BLOCK RAISE/LOWER
LED will light to indicate when the voltage is outside the band.
The
LOWER
LED will light when the voltage exceeds the Block Raise level for an adjustable time period.
Output Contacts
Output Contacts:
Contacts are rated at 2 A at 120 V ac.
Blocking Contacts:
Contacts will operate within 0.2 seconds after a voltage excursion to prevent the transformer
control from causing another tapchange.
Alarm Contacts:
After a fixed 3 minute time delay, if the voltage excursion is still present, the alarm is activated
to indicate control failure.
