Digital safety system against short circuit, overcurrent etc. - uses short circuit data in digital memory and comparison with actual values of digitalised phase currents

摘要

The control of the safety system transmits digital words and control clock pulses. The system comprises a data input panel, a zero passage detector, and a comparator, supplied with a voltage from a D/A converter and with rectified voltages of a measured value generator, derived from the phase currents. The system is completed by a logic for the control. In order to detect a short circuit current, short circuit switching values (X, IN) and preset angular short circuit constants (KW1-KW6) from a digital memory (22) are compared with actual values of digitalised phase currents (IR,IS,IT). For overcurrent detection, each detected highest phase current (IM) is supplied as a digital word, together with heating-cooling model constants, given by each load type (23), to a computer which detects the highest heating factor for the given load. The latter is compared with a digital heating maximum for possible disconnection, on exceeding the given limit.