Fault current filter
AssigneeAsea Brown Boveri AG
InventorsLeif Eriksson, Murari M. Saha
Life of this patent
Estimating the term…
Abstract
A method and a device for determining the fault current which occurs in case of a fault through a short circuit between phases or from phase/phases to ground. A measure of the fault current can be obtained by a linear combination of the sum of measured current samples for each phase at two adjacent points in time and in which each of these sample values is multiplied by a coefficient which is chosen such that the fault current gets into phase with the positive- and negative-sequence current changes.
Claims4
A method for determining the fault current I.sub.F resulting from a fault on a multi-phase transmission line upon a short circuit between at least one of the phases of said multi-phase transmission line and ground, comprising the steps of:
- measuring the respective phase currents;
- low-pass filtering the respective measured phase currents;
- sampling the respective filtered phase currents;
- multiplying two continuously and consecutively measured sampled phase currents for each phase, namely I.sub.R1, I.sub.R2, I.sub.S1, I.sub.S2, I.sub.T1, I.sub.T2, by a predetermined coefficient k.sub.R1, K.sub.R2, k.sub.S1, k.sub.s2, k.sub.T1, k.sub.T2, which are selected so that the fault current is brought into phase with the positive-sequence and negative-sequence components of the measured phase currents;
- and
- obtaining the fault current by forming the sum I.sub.F =k.sub.R1 .multidot.I.sub.R1 +K.sub.R2 .multidot.I.sub.R2 +k.sub.S1 .multidot.I.sub.S1 +k.sub.S2 .multidot.I.sub.S2 +k.sub.T1 .multidot.I.sub.T1 +k.sub.T2 .multidot.I.sub.T2.
Apparatus for determining the fault current I.sub.F resulting from a fault caused by a short circuit on a multi-phase transmission line between at least one phase of said multi-phase transmission line and ground, comprising:
- means for measuring the phase currents;
- means for low-pass filtering the measured phase currents;
- means for continuously and consecutively providing sampled measured values I.sub.R2, I.sub.S2, I.sub.T2 of the low pass filtered phase currents;
- means for time-delaying sampled measured current values I.sub.R1, I.sub.S1, I.sub.T1 at least one sampling interval earlier than said sampled measured current values;
- means for multiplying both the sampled measured values and the time-delayed sampled current values by respective coefficients k.sub.R1, K.sub.R2, k.sub.S1, k.sub.s2, k.sub.T1, k.sub.T2, which are selected so that the fault current is brought into phase with the positive-sequence and negative-sequence components of the measured phase currents to generate the product of the respective coefficients and the sampled measured values and the time-delayed sampled current values;
- and
- means for summing said product to obtain a signal corresponding to the fault current I.sub.F =k.sub.R1 .multidot.I.sub.R1 +K.sub.R2 .multidot.I.sub.R2 +k.sub.S1 .multidot.I.sub.S1 +k.sub.S2 .multidot.I.sub.S2 +k.sub.T1 .multidot.I.sub.T1 +k.sub.T2 .multidot.I.sub.T2.
Dependencies are inferred from the claim text.