Devices for monitoring and protecting power circuits

A method for measuring current by means of a device for monitoring and protecting equipment powered by at least one solid-state power controller called SSPC, said device including at least one current measurement circuit comprising:

• a current measuring transformer comprising a primary through which at least three phases of a three-phase power supply of the equipment or at least the phase of a single-phase power supply of the equipment pass and provided at a secondary with at least two measurement windings for measuring the current at the primary,
• a measuring and testing module including a measuring and testing controller provided with at least one analog input connected to at least one of said measurement windings by a measurement channel for measuring a current at the secondary, representative of a differential current Id at the primary and provided with a measurement program and a digital channel for communication with said SSPC for controlling a switch of said SSPC in the event that said current Id exceeds a given threshold;
• wherein said module includes a channel for injecting current into said transformer, said channel comprising a current Iinj generator controlled by an output of the measuring and testing controller and connected to an injection winding on said transformer, said injection winding including a number of turns Ninj adapted so that the current Iinj produces in said measurement windings a test current Im of said secondary in the absence of current at the primary and said module includes a test program adapted to control a current injection in parallel with a current measurement;
• and wherein said at least two measurement windings at the secondary are such that a first measurement winding is adapted for a measurement of a leakage current at the primary in a range 0 to 100 milliamps and a second measurement winding is adapted for a measurement of a leakage current at the primary in a range of 0 to 2 amps, the method comprising:
• a self-test sequence for which at least one injection of current representative of one or more given primary current threshold(s) on said injection winding, for which a measurement of the currents at each of said first measurement winding and second measurement winding is carried out and in that the measuring and testing module emits an order for switching off the switches of the SSPC module(s) in case of non-detection of a measurement current on at least either one of said first measurement winding and second measurement winding during said current injection.