Tapchanger Controls
App Tip #5
Application Tip
How to Obtain
“No Intentional Time Delay” Voltage Control
In some applications, it is desirable to initiate immediate tapchanger action without any
intentional time delay. However, the normal operation with a voltage control time delay of 0
seconds would allow numerous undesirable tap changes due to spurious, transient conditions.
One application for such an operation is that of a generating station reserve auxiliary transformer
where the load can instantaneously go from nearly zero to full load with the operation of an
automatic throw-over scheme. The immediate effect of the substantial voltage drop in the
transformer may cause undesirable effects on other equipment and motor operation before the
tapchanger can correct the voltage level.
Different solutions are possible using the Beckwith Electric M-2001B Tapchanger Control
with voltage reduction capabilities, depending on the resultant desired operation.
Solution - Initial conditions/settings: (Pre throw-over bus voltage held at maximum allowable
level)
•Light initial load
•Voltage setpoint - maximum allowable voltage level (nominal +5%?)
•Bandwidth setpoint - normal (1.5-2.5 volts?)
•Time delay setting - normal (15-30 seconds?)
•Sequential operation - no time delay between tapchanges
•Voltage Reduction #1 setting - results in desired operating voltage (-5%?)
•No voltage reduction invoked
Operation: The bus voltage is initially at nominal voltage +5% (+/-) ½ bandwidth setting.
•The automatic throw-over initiation transfers the load and closes a contact across the
appropriate Beckwith Electric control panel terminals to invoke the voltage reduction.
•The setpoint immediately is changed to the voltage reduced setting (nominal?).
•If required to maintain the new voltage operation, the tapchanger control will operate
without a time delay as many taps as necessary to establish in-band operation.
•After the voltage is established in-band, the time delay will become effective for
further tapchanger operations.
•Up to 5% of the new load voltage drop in the transformer is compensated for by the
pre-throw-over voltage level.
Other arrangements are possible depending on the desired result. For instance, if an application
exists where a higher (rather than lower) operating voltage is required after an event, the control
could be normally operating in voltage reduction mode which would be removed upon the
event. This would result in a higher operating voltage level that was invoked without any time
delay as described above.
For more information, contact:
E-mail: support@beckwithelectric.com
Phone: 727-544-2326
Online: www.beckwithelectric.com
APTP05-06-03
© Beckwith Electric Co.
Printed in the U.S.A.