Abstract: A temperature pickup for an oil-filled transformer or tap changer has within a resistance thermometer standard housing, the circuitry for duty-factor-modulated output of a measurement signal, interference circuitry which can slur the resulting wave form and an interface circuit which subjects the output signal to polarity reversal to produce an output symmetrical with respect to ground potential. This enables zero crossings to be detected and the time lapse between zero crossings or passages to be ascertained and the temperature calculated from the duty-factor ratio.

Abstract: A tap selector for a power transformer switchable under load is monitored by detecting the effective values of current and voltage of the drive motor of the tap changer. The power is calculated and from that the instantaneous torque and the latter is compared with setpoint values either of the torque and position of the tap selector or in terms of characteristic segments of the torque versus time graph with normalized segments of a setpoint graph so that, with serious deviation an immediate shutdown of tap selector operations is ensured or information can be generated as to trends or the need for maintenance.

Abstract: A motor-driven step switch for step transformers includes a drive motor connected to the step switch, display, input, and control units, a controller for actuating the drive unit in accordance with rotation direction, an information unit which obtains and transmits the step position and which is connected with the controller which delivers commands for controlling the drive motor and a switching operation, and an electrical connection between the controller and display, input, and control units. In accordance with this invention the information unit has a sensor for determining the absolute value of the actual position of the step switch, a nonvolatile memory unit for storing the position of the step switches with a range of step positions, and a unit for determining an end position of the step switch.