Power supply circuit for on board energy source or storage device and particularly for super-capacitor storage unit

1. A power supply circuit for an on board energy source or storage device, and particularly for a super-capacitor storage unit having a plurality of super-capacitors interconnected to one another and a first and a second terminal, the power supply circuit comprising:

a positive bus connecting the first terminal of the super-capacitor storage unit to a positive pole of a DC high voltage feeding source;

a negative bus connecting the second terminal of the super-capacitor storage unit to a negative pole of the DC high voltage feeding source, the negative bus being connected to ground at a grounding point downstream of the DC high voltage feeding source; and

a disconnecting device configured to disconnect the super-capacitor storage unit from the DC high voltage feeding source in response to detection of fault current circulation due to insulation losses to the ground of the super-capacitor storage unit,

wherein the disconnecting device comprises a high speed circuit breaker and a differential relay which are connected in series only along the negative bus, and

wherein, between the second terminal and the grounding point, the differential relay is further connected in series in the positive bus and is configured to generate an activation signal of the high speed circuit breaker in response to the fault current circulation detected by measuring differences in currents in the positive and in the negative bus.

2. The power supply circuit according to claim 1 , further comprising a second disconnecting device on the positive bus which is configured to disconnect the super-capacitor storage unit only from the positive pole of the DC high voltage feeding source.

3. The power supply circuit according to claim 1 , further comprising a first device configured to detect fault currents having an intensity higher than a predetermined threshold and a second device configured to detect fault currents having an intensity lower than a predetermined threshold, the first and second devices configured to detect fault currents driving the high speed circuit breaker when a fault current is detected.

4. The power supply circuit according to claim 3 , wherein the first device configured to detect fault currents comprises a tripping device of the high speed circuit breaker, and wherein the second device configured to detect fault currents comprises a differential relay driving the high speed circuit breaker.

5. The power supply circuit according to claim 1 , further comprising:

a positive and a negative input terminal for the DC high voltage feeding source; and

the positive and the negative bus connecting the DC high voltage feeding source to the first and to the second terminals of the super-capacitor storage unit,

wherein, on the negative bus, the negative input terminal is connected to the ground and to a first input of the differential relay, and the positive input terminal is connected to a second input of the differential relay, and

wherein a negative output of the differential relay is connected to the high speed circuit breaker interposed between the differential relay and the second terminal of the super-capacitor storage unit.

6. The power supply circuit according to claim 5 , further comprising a charging/discharging unit interposed between the differential relay and the high speed circuit breaker on the negative bus.