Ramp test development and data acquisition

Since the late 1960s Manitoba hydro has been making high direct-voltage ramp tests to detect defects in the groundwall insulation of the stator windings of generators and motors. At first an electrostatic generator was used to obtain the necessary voltage regulation and an operational amplifier was added to the control circuitry to produce the desired ramp function in the output voltage. In the 1980s a much smaller solid state supply was introduced in which the high voltage transformer operates >40 kHz. This high voltage supply has superior voltage regulation and it was modified to provide the desired ramp function output voltage. Until recently the measured current was plotted on the vertical axis of an X-Y recorder while the horizontal axis indicated either time (for the initial polarization index step) or voltage (for the ramp test). However there has been increasing difficulty in maintaining the X-Y recorder in reliable condition. New recorders of this type are no longer available from most suppliers. To overcome these problems a data acquisition system was introduced which allows the current and voltage data to be logged on a laptop PC. Identification and temperature data are keyboard entered. Once stored securely the data can be displayed in different formats. This greatly increases the flexibility of the record system