Abstract: There is disclosed herein a method for locating a ground fault in an energy storage system comprising a plurality of parallel strings. A string comprises a plurality of energy storage units connected in series and an energy storage unit includes one or more energy storage modules and a bypass circuit. The method comprises for each string of said energy storage system, identifying an energy storage unit candidate as a potential ground fault location based on a number of energy storage units in the string, a pole unbalance voltage and an energy storage system voltage, and determining in which string the ground fault is located by successively bypassing, one string at a time, at least some of the identified energy storage unit candidates and identifying the string for which a deviation from an expected behaviour is measured.

Abstract: There is disclosed herein a method for detecting a ground fault in an energy storage system comprising at least one string having a plurality of energy storage modules. The string is connected between a first direct current (DC) pole and a second DC pole. The first DC pole and the second DC pole are connected to an AC side through a respective converter. The method comprises determining a first co-phasal harmonic component based on at least one phase-to-ground voltage measured at the AC side, determining a second co-phasal harmonic component based on at least one pole-to-ground voltage measured at the DC side, and determining presence of a ground fault if the first co-phasal harmonic component increases and/or the second co-phasal harmonic component decreases. There is also disclosed herein a control unit and an energy storage system.

Abstract: A protection device for a power network performs a method to align measuring times of first and second measurements of an electric quantity, taken at different ends of a power network line transmitted with measuring times via a telecommunication network. In the method, a send transmission time from the local to remote end of the line and a receive transmission time from the remote to local end of the line are determined based on time signals from internal clocks. After a global time reference to synchronize the internal clocks is lost, a clock drift is determined between the internal clocks. The measuring times of the first and the second measurements are aligned using the send and receive transmission times as well as the clock drift. A sudden change in the clock drift is determined in order to recognize a route switching in the telecommunication network and the clock drift is corrected.

Abstract: A protection device for a power network performs a method to align measuring times of first and second measurements of an electric quantity, taken at different ends of a power network line transmitted with measuring times via a telecommunication network. In the method, a send transmission time from the local to remote end of the line and a receive transmission time from the remote to local end of the line are determined based on time signals from internal clocks. After a global time reference to synchronize the internal clocks is lost, a clock drift is determined between the internal clocks. The measuring times of the first and the second measurements are aligned using the send and receive transmission times as well as the clock drift. A sudden change in the clock drift is determined in order to recognize a route switching in the telecommunication network and the clock drift is corrected.

Abstract: A device for determining the location of a fault at a fault position (F) on a power transmission line between two stations (P, Q), and in which the power transmission line has an unknown conduction impedance (Z.sub.PQ), wherein, at one of the stations (P), capacitive voltage measuring transformers measure the phase voltage (U.sub.PM) and the phase currents (I.sub.P) or changes in the phase currents (.DELTA.I.sub.P) are measured on the occurrence of a fault. The phase voltage, phase currents or changes in the phase currents are low pass filtered; and the filtered phase voltage, phase currents or the change in the phase currents are converted from an analog to instantaneous digitized phase voltage, phase currents or changes in phase current values, respectively.The fault distance .alpha. and a value of an apparent fault resistance R.sub.F at the fault location are calculated, using linear regression, on the basis of the relationship:U.sub.PM =.alpha.Z.sub.PQ I.sub.P +R.sub.F I.sub.P +.DELTA.U.sub.CVT ;where .