Multiphase fault protection circuitry with variable functional level detection

Circuitry for generating tripping and blocking signals for the protection of electrical components in an electrical power supply network as a result of the occurrence of faults therein, comprising:

• means for generation of respective tripping signals and blocking signals for each phase of the electrical power supply network in dependence on whether the fault lies ahead or behind the electrical component to be protected, respectively, in response to measurement of the voltage and current associated with transient waves generated by faults in each phase of the electrical power supply network;
• detection means having a predetermined operating level, for determining the presence of a first tripping signal resulting from the occurrence of a single phase fault and the presence of a second tripping signal resulting from the occurrence of a fault in another phase, and means for changing the operating level for detection of said second tripping signal upon detection of the first tripping signal;
• and
• means responsive to said detection means for generating respective tripping and blocking outputs for each phase of said electrical power supply network, whereby double or triple pole tripping is prevented unless the presence of said second tripping signal is detected.