M-0067E Tapchanger Control

General Purpose LTC Transformer Control or Replaces Westinghouse SVC and SVR Controls.

  • Adaptable to any LTC Transformer — old or new
  • Meets ANSI Class 1 (1%) Accuracy Requirement
  • Now in Use by Leading Manufacturers as Standard Equipment


Line Drop Compensation, Non-Sequential and Sequential modes of operation, and manual voltage adjustment capability is included.


Power: A two wire input, requiring less than 3 W at 90 to 140 V ac, provides all power requirements. The unit should be powered from a potential transformer or from the voltage to be controlled.

Line Current: Line drop compensation is provided by a CT input with a 0.2 A nominal full scale rating. The burden imposed by this input on the current source is 0.03 VA. A Beckwith Electric model M-0121 (5 A to 0.2 A) or M-0169 (5 A or 8.66 A to 0.2 A) Auxiliary Current Transformer is available when required.

Circulating Current: Parallel operation of transformers is provided by a second CT input with a 0.2 A nominal full scale rating. The burden imposed by this input on the current source is 0.005 VA. A paralleling input with a 0.2 A full scale rating gives approximately 24 V correction at approximately 90° for parallel operation with other transformers.

Front Panel Controls

VOLTAGE CENTER OF BAND: The center of the control band may be set to any voltage from 105 to 135 V ac. The scale calibration accuracy is ±0.5 V at 120 V ac.

TOTAL BANDWIDTH: The bandwidth control can be adjusted from 1.0 to 6.0 V. The scale calibration accuracy is ±0.3 V.

TIME: The timer is adjustable from 0 to 120 seconds, with a scale calibration accuracy of ±10% of setting or ±2 seconds, whichever is greater. The timer starts when the voltage goes outside the band and resets within a few milliseconds upon return to the band or when reset by an external contact in the Non-Sequential mode.

LINE DROP COMPENSATOR: The resistance compensation provides 24 V compensation for 0.2 A input in phase with the input voltage. The reactance compensation provides 24 V compensation for 0.2 amps input at a phase angle of ±90° as chosen by the DIRECT/REVERSE switch. The magnitude and angle of each circuit is individually set by a pair of trimpots to any accuracy limited only by the instruments used in setting. The factory setting of magnitude will be within ±5% and the phase angles within ±2%. The voltage and two current circuits are isolated from each other and do not interact.

TEST/OPERATE: When this switch is in the TEST position, the Line Drop Compensator is deactivated and the voltage may be raised and lowered by means of an uncalibrated voltage control. An external voltmeter with a burden of 500 Ω per V or higher can be connected to test the band limits by observing when the RAISE and LOWER LEDs light. No special test voltage source required.

Modes of Operation

Either of the following modes are available as determined by the presence or absence of a cam switch which is closed while the LTC is in transition.

  • Non-Sequential Mode: The timer resets after a tapchange, regardless of voltage.
  • Sequential Mode: The timer resets only after the sensed voltage is back within the control band.