Method and system for measuring electrical quantity in electrical network
A method and system for measuring an electrical quantity in an electrical network. The system is configured to obtain samples of the electrical quantity through measurements at different feeders or locations in the electrical network. The measurements are taken in turns and at different time instants, such that a value sequence is created on the basis of the measured samples.
1. A method for measuring an electrical quantity in an electrical network including at least a substation, the method comprising:
receiving, via at least two intelligent electronic devices, an input or measurement signal describing or corresponding the electrical quantity to be measured;
measuring samples of the electrical quantity, via each of the at least two intelligent electronic devices, respectively at the different feeders or locations of the electrical network in turns at different feeders or locations one sample at a time and at different time instants such that after a sample of the electrical quantity is measured at a respective feeder or location and at a respective time instant, a next sample of the electrical quantity is measured at a different feeder or location at a next time instant, wherein the measuring of samples of the electrical quantity at other feeders or locations being idle at each time instant the electrical quantity is measured via a respective one of the at least two intelligent electronic devices at the respective feeder or location,
creating, in one of the at least two intelligent electronic devices a value sequence on the basis of the measured samples, at least one individual value of the value sequence corresponding to a measured sample, or a value calculated on the basis of at least one measured sample, wherein the at least one individual value in the value sequence is arranged in an order corresponding to a chronological order of the measured samples; and
performing, in one of the at least two intelligent electronic devices a transient analysis on the value sequence to determine a fault location in the electrical network,
wherein a sampling frequency of the electrical quantity being measured in the network is multiplied by a total number of different feeders or locations at which a sample is measured.
2. The method according to claim 1 , wherein
at least two sample sequences of a same electrical quantity are measured such that samples of each sample sequence are measured at a different feeder of the electrical network than the samples of any other sample sequence, and, the samples of different sample sequences are measured in turns one sample at a time at different time instants, and
the value sequence is created on the basis of the samples of the at least two sample sequences, the at least one individual value of the value sequence corresponding to a sample of one of the at least two sample sequences or a value calculated on the basis of at least one sample of the at least two sample sequences, wherein the values of the value sequence are arranged in an order corresponding to a chronological order of the samples of the at least two sample sequences.
3. The method according to claim 1 , wherein the electrical quantity to be measured is a phase voltage or a zero voltage and the individual values of the value sequence correspond to samples of the measured phase voltage or zero voltage.
4. The method according to claim 1 , wherein the electrical quantity to be measured is a phase current or a zero current and the individual values of the value sequence correspond to a value calculated on the basis of one actually measured phase current value at one feeder or location and a calculated or estimated phase current value in at least one other feeder or location of the electrical network.
5. The method according to claim 4 , wherein the calculated or estimated phase current value is determined by linear interpolation, and a starting value of the linear interpolation is a last actually measured phase current value at a corresponding feeder or location.
6. The method according to claim 1 , wherein measurement errors due to gain, offset, or timing mismatches in the sampling of the electrical quantity are compensated between different feeders or locations of the electrical network.
7. The method according to claim 6 , wherein the sampling of the electrical quantity at one feeder or location of the electrical network is synchronized to take place after a time offset relative to the sampling of the electrical quantity at another feeder or location of the electrical network, wherein the time offset minimizes the timing mismatches of the sampling of the electrical quantity.
8. The method according to claim 7 , wherein measurement errors in the sampling of the electrical quantity between different feeders of the electrical network due to gain mismatches are compensated on the basis of the fundamental frequency value of the electrical quantity at the different feeders.
9. The method according to claim 6 , wherein measurement errors in the sampling of the electrical quantity between different feeders of the electrical network due to gain mismatches are compensated on the basis of a fundamental frequency value of the electrical quantity at the different feeders.
10. The method according to claim 1 , wherein the sampling of the electrical quantity at one feeder or location of the electrical network is synchronized to take place after a time offset relative to the sampling of the electrical quantity at another feeder or location of the electrical network and after a number of feeders or locations of the electrical network where the sampling takes place is changed due to network topology changes.
11. The method according to claim 1 , comprising:
analyzing the value sequence for a transition among the electrical quantities measured at the different feeders; and
identifying a fault location in the electrical network based on the analysis so that outage time of a respective feeder can be minimized.
12. A system for measuring an electrical quantity in an electrical network including at least a substation, the system comprising:
at least two intelligent electronic devices arranged at different feeders or locations of the electrical network, the at least two intelligent electronic devices being configured to measure the electrical quantity of the electrical network and each intelligent electronic device is configured to measure samples of the electrical quantity in turns at different feeders or locations one sample at a time and at different time instants such that after one sample of the electrical quantity is measured at a respective feeder or location at a respective time instant by an associated intelligent electronic device, a next sample of the electrical quantity is measured at a different feeder or location at a next time instant by another intelligent electronic device associated with the different feeder,
the intelligent electronic devices at other feeders or locations are idle at these time instants when considering the measuring of samples of the electrical quantity, and
one of the intelligent electronic devices is arranged to create a value sequence on the basis of respective measured samples, an individual value of the value sequence corresponding to a measured sample or a value calculated on the basis of at least one measured sample, the values in the value sequence being arranged in a chronological order according to the measured samples; and
one of the intelligent electronic devices is arranged to perform a transient analysis on the value sequence to determine a fault location in the electrical network,
wherein a sampling frequency of the electrical quantity being measured in the network is multiplied by a total number of different feeders or locations in the network at which a sample is measured.
13. The system according to claim 12 , wherein:
the one intelligent electronic device is configured to measure samples of the electrical quantity in turns one sample at a time and at different time instants with respect to other intelligent electronic device of the electrical network,
the one intelligent electronic device is configured to create a sample sequence on the basis of the measured samples, the sample sequence including the measured samples in a chronological order, and
the one intelligent electrical device is configured to create the value sequence on the basis of the samples of the sample sequences, an individual value of the value sequence corresponding to a sample of one of the sample sequences or a value calculated on the basis of at least one sample of at least one sample sequence, the values in the value sequence being arranged in an order corresponding to the chronological order of the samples of the sample sequences.
14. The system according to claim 12 , wherein the electrical quantity to be measured is a phase voltage or a zero voltage and the individual values of the value sequence correspond to the samples of the measured phase voltage or zero voltage.
15. The system according to claim 12 , wherein the electrical quantity to be measured is a phase current or a zero current and the individual values of the value sequence correspond to a value calculated on the basis of one actually measured phase current value at one feeder or location and a calculated or estimated phase current value in at least one other feeder or location of the electrical network.
16. The system according to claim 15 , wherein the calculated or estimated phase current value is arranged to be determined by linear interpolation, a starting value of the linear interpolation being the last actually measured phase current value at a corresponding feeder or location.
17. The system according to claim 12 , wherein the system is arranged to compensate measurement errors due to gain, offset, or timing mismatches in the sampling of the electrical quantity between intelligent electronic device arranged in the electrical network.
18. The system according to claim 17 , wherein the system is configured to synchronize the sampling of the electrical quantity by one intelligent electronic device to take place after a time offset relative to the sampling of the electrical quantity by another intelligent electronic device for minimizing the timing mismatches of the sampling of the electrical quantity.
19. The system according to claim 18 , wherein the system is arranged to compensate measurement errors in the sampling of the electrical quantity between different feeders of the electrical network due to gain mismatches on the basis of the fundamental frequency value of the electrical quantity at different feeders.
20. The system according to claim 17 , wherein the system is arranged to compensate measurement errors in the sampling of the electrical quantity between different feeders of the electrical network due to gain mismatches on the basis of a fundamental frequency value of the electrical quantity at different feeders.
21. The system according to claim 12 , wherein the system is arranged to synchronize the sampling of the electrical quantity by one intelligent electronic device to take place after a time offset relative to the sampling of the electrical quantity by another intelligent electronic device after a number of the intelligent electronic devices arranged to take samples changes due to a change in network topology.
22. The system according to claim 12 , wherein the one intelligent electrical device is configured to create the value sequence is configured to analyze the value sequence for a transition among the electrical quantities measured at the different feeders and identify a fault location in the electrical network based on the analysis so that outage time of a respective feeder can be minimized.