The invention relates to a method for ascertaining an earth fault and the earth-fault direction in a three-phase network which is operated in a compensated manner or in an insulated manner. Value pairs of a zero voltage and a zero current are measured, the active or reactive energy is calculated, and a voltage flag and a current flag are combined by a Boolean link, wherein the presence of a earth fault is ascertained depending on the result, and a decision is made as to whether the earth-fault direction is signalled as “forward” or “reverse” at least on the basis of the sign of the active or reactive energy.
G01R 31/08 - Locating faults in cables, transmission lines, or networks
H02H 3/16 - Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to fault current to earth, frame or mass
H02H 3/38 - Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to both voltage and currentEmergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to phase angle between voltage and current
H02H 3/42 - Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to product of voltage and current
G01R 31/02 - Testing of electric apparatus, lines, or components for short-circuits, discontinuities, leakage, or incorrect line connection
H02H 1/00 - Details of emergency protective circuit arrangements
The invention relates to a method for ascertaining a ground fault and the ground-fault direction in a three-phase network which is operated in a compensated manner or in an insulated manner. Value pairs of a zero voltage and a zero current are measured, the active or reactive energy is calculated, and a voltage flag and a current flag are combined by a Boolean link, wherein the presence of a ground fault is ascertained depending on the result, and a decision is made as to whether the ground-fault direction is signaled as "forward" or "reverse" at least on the basis of the sign of the active or reactive energy.
H02H 3/16 - Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to fault current to earth, frame or mass
H02H 3/38 - Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to both voltage and currentEmergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to phase angle between voltage and current
H02H 3/42 - Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to product of voltage and current
G01R 31/08 - Locating faults in cables, transmission lines, or networks
3.
METHOD FOR PROTECTING AN ELECTRICAL SUPPLY NETWORK
The invention relates to a method for protecting an electrical supply network in the event of a fault (K). In this case, at least one electrical time-periodic signal (i(t)) from the supply network is measured and is transformed to the frequency domain. The complex variables are modified by means of modified filter coefficients (I1D) of the transformed time-periodic signal (i(t)) by combining imaginary part filter coefficients of the first and second harmonics (I1, I2). In a first alternative, a check is then carried out for each sample in order to determine whether the modified imaginary part (I1D) has the same sign as the imaginary part of the first harmonic (I1) and whether the magnitude of the modified imaginary part (I1D) is greater than the magnitude of the imaginary part of the first harmonic (I1). An output imaginary part (I1A) is then set equal to the modified imaginary part (I1D) if the conditions from step d1) are satisfied or is set equal to the imaginary part of the first harmonic (I1) if the conditions from step d1) are not satisfied. In a second alternative, a first impedance (Z1) is determined using the first harmonic (I1) and a second impedance (Z2) is determined using the modified imaginary part (I1D). Either the impedance having the smaller magnitude from the first and second impedances (Z1, Z2) or the impedance with the imaginary part having the smaller magnitude from the first and second impedances (Z1, Z2) is then selected and is set as the line impedance (ZL). The line impedance (ZL) determined is compared with at least one predefined value. Finally, a control signal (B) for an interruption component (2) of the supply network is output if the line impedance (ZL) is lower than the at least one predefined value.
H02H 3/40 - Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to ratio of voltage and current
H02H 3/46 - Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition, with or without subsequent reconnection responsive to frequency deviations
G01R 19/00 - Arrangements for measuring currents or voltages or for indicating presence or sign thereof
G01R 27/08 - Measuring resistance by measuring both voltage and current
G01R 27/16 - Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
H02H 1/00 - Details of emergency protective circuit arrangements
patents
