Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of ground fault indication
Patent
1995-04-19
1996-09-24
Wieder, Kenneth A.
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of ground fault indication
324650, 324521, 307 29, 361113, G01R 3100
Patent
active
055594395
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to electrical distribution networks of the compensated type, that is to say that they comprise a compensation coil or Petersen coil which makes it possible to compensate for the capacitive current due to capacitances distributed in the line; the compensation coil makes it possible to obtain balance, that is to say perfect compensation for the capacitive impedances of the line.
The subject of the invention is, more particularly, a method and a device making it possible to measure the detuning of the compensation of the network; in fact, when the intrinsic capacitive impedance of the network varies, as a result, for example, of connecting or disconnecting high-load-factor consumers, the compensation coil is detuned, that is to say that it no longer exactly compensates for the overall capacitance of the network. In such a case it is advantageous to vary the value of the impedance of the compensation coil so as to reestablish balance.
It has already been proposed, in order to detect and measure the imbalance in the compensation of a network, to inject an electric current into the neutral circuit, the frequency of which current is slightly different from the frequency of the network; as a result of the appearance of a beat phenomenon, it is then possible to detect and measure the imbalance of the network. This method is relatively complex and requires a significant amount of equipment, in particular a generator having a different frequency from that of the network. Furthermore, this type of operation requires long adjustment and measurement periods.
It has also been proposed, as described in European Patent 235,145, to provide a device which makes it possible to add a supplementary reactance between the neutral and the earth of the network and subsequently to calculate the attenuation, asymmetry and imbalance parameters of the network. Connecting a supplementary reactance between the neutral and the earth can be done by impedance switching in parallel or in series with the compensation coil or even, in the case when the network comprises a variable compensation coil, by acting on the compensation coil itself.
This method has the drawback that the response time of the measurement thus carried out is high, and may be of the order of several minutes; the accuracy of the measurement is not very good, especially if the asymmetry is low, and this method cannot function reliably under all operational conditions of a network.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method and a device for measuring the imbalance in the compensation of an electrical distribution network compensated by a compensation coil, which have a short response time, which have a low cost price and which function under all circumstances independently of the natural asymmetry of the network.
To this end, the subject of the invention is a method for measuring the compensation imbalance of an electrical distribution network comprising a compensation coil, characterized in that an auxiliary measurement signal is injected into the neutral circuit of the network, in that the variation in the homopolar voltage induced by the said auxiliary signal injection is measured and in that an impedance measurement is carried out by comparison, in amplitude and in phase shift, of the variation in the homopolar voltage with the auxiliary measurement signal.
This is a measurement comprising an active system, the response time of which is significantly less than solutions employing neutral impedance variations. Furthermore, this method can be employed simply.
According to a first embodiment, an auxiliary measurement voltage is injected in series with the compensation coil.
Advantageously, the auxiliary measurement voltage is injected by means of a transformer, the secondary of which is connected in series to the compensation coil.
According to another embodiment, a current is injected in parallel into the neutral circuit.
Advantageously, the auxiliary measurement current is injec
REFERENCES:
patent: 4368498 (1983-01-01), Neuhouser
patent: 4472676 (1984-09-01), Eichmann
patent: 4857830 (1989-08-01), Matsuno
Electricite De France Service National
Solis Jose M.
Wieder Kenneth A.
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