Device for testing the operation of a protection unit of an electrical network, said protection unit including: - a current transformer composed of a magnetic circuit positioned around at least one current conductor through which a primary current (Ip) flows forming a primary circuit, said transformer comprising a first secondary winding wound around the magnetic circuit; - a measurement circuit, connected to the first secondary winding, the measurement circuit including a second-order low-pass filter, and arranged to deliver, after filtering through the second-order low-pass filter, a signal that is representative of the primary current and a measurement of the primary current; and - a trip circuit, linked to the measurement circuit, including means for selecting a trip threshold, And said test device including: - a second secondary winding wound around the magnetic circuit; - a generator, linked to the trip circuit so as to acquire the selected trip threshold (Sd), and arranged to generate a pulse train in the second secondary winding according to a profile of frequencies such that the measurement of the pulse train after passage through the second-order low-pass filter is lower than the selected trip threshold (Sd); and - a processing circuit, connected to the measurement circuit and to the generator, arranged to identify a presence of the pulse train in the signal that is representative of the primary current. said protection unit including: - a current transformer composed of a magnetic circuit positioned around at least one current conductor through which a primary current (Ip) flows forming a primary circuit, said transformer comprising a first secondary winding wound around the magnetic circuit; - a measurement circuit, connected to the first secondary winding, the measurement circuit including a second-order low-pass filter, and arranged to deliver, after filtering through the second-order low-pass filter, a signal that is representative of the primary current and a measurement of the primary current; and - a trip circuit, linked to the measurement circuit, including means for selecting a trip threshold, - a current transformer composed of a magnetic circuit positioned around at least one current conductor through which a primary current (Ip) flows forming a primary circuit, said transformer comprising a first secondary winding wound around the magnetic circuit; - a measurement circuit, connected to the first secondary winding, the measurement circuit including a second-order low-pass filter, and arranged to deliver, after filtering through the second-order low-pass filter, a signal that is representative of the primary current and a measurement of the primary current; and - a trip circuit, linked to the measurement circuit, including means for selecting a trip threshold, And said test device including: - a second secondary winding wound around the magnetic circuit; - a generator, linked to the trip circuit so as to acquire the selected trip threshold (Sd), and arranged to generate a pulse train in the second secondary winding according to a profile of frequencies such that the measurement of the pulse train after passage through the second-order low-pass filter is lower than the selected trip threshold (Sd); and - a processing circuit, connected to the measurement circuit and to the generator, arranged to identify a presence of the pulse train in the signal that is representative of the primary current. - a second secondary winding wound around the magnetic circuit; - a generator, linked to the trip circuit so as to acquire the selected trip threshold (Sd), and arranged to generate a pulse train in the second secondary winding according to a profile of frequencies such that the measurement of the pulse train after passage through the second-order low-pass filter is lower than the selected trip threshold (Sd); and - a processing circuit, connected to the measurement circuit and to the generator, arranged to identify a presence of the pulse train in the signal that is representative of the primary current.