In the field of multi-terminal electrical power network protection, a protection apparatus comprises a measurement apparatus to measure the respective terminal current (I.sub.L, I.sub.R1, I.sub.R2, I.sub.R3, I.sub.R4, I.sub.R5) flowing at each terminal (L, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5) in a multi-terminal network that includes a plurality of electrically interconnected terminals (L, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5). The protection apparatus also includes a control unit that is programmed to process the measured terminal currents (I.sub.L, I.sub.R1, I.sub.R2, I.sub.R3, I.sub.R4, I.sub.R5) to obtain first and second summed values (I.sub.POS(n), I.sub.NEG(n)). The first summed value (I.sub.POS(n)) is the sum at a given time (n) of the or each terminal current (I.sub.L, I.sub.R1, I.sub.R2, I.sub.R3, I.sub.R4, I.sub.R5) flowing in a first direction (D.sub.1) relative to a corresponding terminal (L, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5) and the second summed value (I.sub.NEG(n)) is the sum at the same given time (n) of the or each terminal current (I.sub.L, I.sub.R1, I.sub.R2, I.sub.R3, I.sub.R4, I.sub.R5) flowing in a second direction (D.sub.2) opposite the first direction (D.sub.1) relative to the corresponding terminal (L, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5). The control unit is further programmed to compare the phase of the first summed value (I.sub.POS(n)) with the phase of the second summed value (I.sub.NEG(n)) to determine whether a fault in the multi-terminal network is internal or external to the multi-terminal network and thereafter to produce an internal fault output signal upon the determination of an internal fault.

A method may include receiving, via at least one processor, a first set of data indicative of a fault being present and send a first signal to a breaker based on the first set of data. The first signal may cause the breaker to open a plurality of poles of the breaker. The method may then involve receiving a second set of data indicative of the fault being cleared and sending a second signal to the breaker based on the second set of data. The second signal may cause the breaker to close a first pole of the plurality of poles at a first time and close a second pole of the plurality of poles at a second time different from the first time.

A fault protection system is configured to detect a fault in an electric power system. The fault protection system obtains a differential measurement signal. The differential measurement signal may, for example, indicate, as a function of time, the difference between currents or voltages measured at two or more terminals or boundaries of a fault protection zone of the electric power system. Regardless, the fault protection system generates a fault detection signal by cross-correlating the differential measurement signal with a reference signal. The reference signal may for instance be the differential measurement signal that is expected upon occurrence of a fault. The fault protection system performs fault detection, for detecting a fault internal to the fault protection zone, as a function of the fault detection signal.

According to one embodiment, an excitation inrush current suppression device for suppressing excitation inrush currents flowing through a breaker of the three-phase collective operation type for opening and closing connection is configured to measure a three-phase AC voltage of the power supply bus bar to calculate prospective magnetic fluxes of the transformer, and to measure a three-phase AC voltage on the transformer side to calculate residual magnetic fluxes of the transformer after shutoff, so as to set the breaker closed when polarities of the prospective magnetic fluxes respectively agree with polarities of the residual magnetic fluxes in all of the phases respectively.

The invention relates to a method of differential protection in the power distribution networks based on phase difference principles. The method comprises the following steps: collecting the current and voltage signals of each loading switch; calculating phase difference between the corresponding currents at two adjacent loading switches, wherein at least one of the two adjacent loading switches accords with I.sub.max>n.Math.I.sub.T+I.sub.dz; tripping the two adjacent loading switches if the phase difference corresponding to the two adjacent loading switches being greater than a threshold then a section between the two adjacent loading switches being determined as a fault section. The method only needs to calculate the phase difference between the corresponding currents at the two adjacent loading switches, and achieves the fault determination according to the phase difference being greater than the threshold. The method has low data synchronizing requirements, and processes the fault determination according to the collected signals. The time required for the entirely determining process is short, and a fast protecting response is achieved, thus the problem of slowly protecting response in the existing relay-protection method for the power distribution networks is solved.