Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1996-11-12
1998-01-20
Hofsass, Jeffery
Communications: electrical
Condition responsive indicating system
Specific condition
340646, 324127, 361 76, 361 94, 364483, 364572, G08B 2100
Patent
active
057105421
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
Method of measuring an AC current in a conductor in an AC power transmission network.
BACKGROUND INFORMATION
It is known (see, for example, "etz" vol. 114 (1993) no. 18, pages 1122-1127) that the current in a conductor of an a.c. power transmission network can be measured by means of a current transformer whose primary winding has current flowing through it in the conductor and whose secondary winding is connected to a device for measuring the current. Such a conventional device may be a measuring device or a protective device such as those conventionally used for detecting and localizing short circuits in a.c. power transmission networks. It is also known that a measurement quantity which is provided by the secondary winding of the current transformer and is proportional to the current can be processed digitally, which presupposes that digital samples are formed from the measurement quantity by means of a sampling device (with an analog-digital converter). These digital samples are then processed further in a digital measuring device or a digital protective device.
SUMMARY OF THE INVENTION
The present invention is based on a method of measuring the a.c. current in a conductor of an a.c. power transmission network where a measurement quantity proportional to the current is obtained by means of a current transformer and digital samples are formed from the measurement quantity by means of a sampling device. An object of the present invention is to provide the ability to differentiate, with regard to a secondary current, whether the current measured is based on a current flowing in the conductor of the a.c. power transmission network in the primary circuit or on a decaying d.c. current component caused by the current transformer when the current in the conductor is interrupted.
The above object is achieved according to the present invention in that two initial auxiliary measurement quantities normal to one another are formed from the samples by means of at least two FIR filters; firstly, in an analyzer, an absolute value signal corresponding to the amplitude of the first measurement quantity and secondly an angle signal whose value depends on the phase difference between the first measurement quantities and older measurement quantities determined by complex division of a vector obtained from the first samples by another vector obtained with the older samples are generated from the two initial auxiliary measurement quantities and two additional auxiliary measurement quantities that are normal to one another and are obtained from older samples formed from an older measurement quantity obtained earlier by a quarter period of the current to be measured; and in an evaluation device an output signal is generated from the absolute value signal and the angle signal if these signals exceed preset threshold values. FIR filters are finite-impulse-response filters described in Elektronik 2, Jan. 23, 1987, pp. 89-96, for example.
Furthermore, the method according to the present invention can also be carried out with auxiliary measurement quantities that are not normal to each other. However, much greater effort is then required to carry out the method.
One of the advantages of the method according to the present invention is that it is possible to ascertain at any time whether a current measured in a secondary circuit is to be attributed to a current through the conductor of the a.c. power transmission network or to the decaying d.c. current component of the current transformer when the current flow in the conductor is actually interrupted.
With the method according to the present invention it is advantageous that if a filtered measurement quantity is formed from the samples in a digital high-pass filter first and if the two auxiliary measurement quantities that are normal to one another are formed from the filtered measurement quantity by means of at least two FIR filters. Forming a filtered measurement quantity has the advantage that the decay due to the current transformer can be limited i
REFERENCES:
patent: 5115226 (1992-05-01), Schweitzer, III
patent: 5309312 (1994-05-01), Wilkerson et al.
patent: 5592393 (1997-01-01), Yalla
Lemmer et al., "Distanzschutz mit Signalprozessortechnik fur die Hochspannungsebene", Etz, vol. 114 (1993) No. 18, pp. 1122-1127.
Bastard et al., "The Technique of Finite-Pulse-Response Filtering applied to Digital Protection and Control of Medium Voltage Power Systems", IEEE Transactions on Power Delivery, vol. 7, No. 2, Apr. 1992, pp. 620-622.
Weighardt et al., "Im Blickpunkt: Digitale Signalverarbeitung", Elektronik 2, Jan. 23, 1987, pp. 89-96.
AEG--Betriebsanleitung fur Distanzschutz PD511.
Hofsass Jeffery
Mannava Ashok
Siemens Aktiengesellschaft
LandOfFree
Method of measuring the A.C. current in a conductor in an A.C. p does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of measuring the A.C. current in a conductor in an A.C. p, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of measuring the A.C. current in a conductor in an A.C. p will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-728719