Development of high power GTO inverter drives for low signalling interference currents

In industrial AC drives the main emphasis is on minimising the total harmonic distortion due to the harmonic currents in the motor so as to achieve an improved motor performance. It is the relatively unsophisticated power frequency (33-125 Hz) and the reed relay type of track circuits (typically 360-425 Hz) which cause the most concern. Apart from the higher amplitude of the low frequency harmonics generated by the equipment and the lower attenuation of the inverter input filter, these track circuits are usually not securely coded and therefore, pass band invasion represents a potential hazard rather than a `fail-safe´ situation