Electricity: power supply or regulation systems – In shunt with source or load – Using impedance
Patent
1980-09-23
1982-05-11
Shoop, William M.
Electricity: power supply or regulation systems
In shunt with source or load
Using impedance
361 17, G05F 160
Patent
active
043296386
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to capacitive voltage transformers.
FIG. 1 is a diagram of a conventional capacitive voltage transformer (TCT) with the representation in dotted line of a modification envisaged;
FIG. 2 is a graph representing the variations in the error voltage at the terminals of a transformer of the type represented in FIG. 1 at the time of the appearance of a fault on the line to which the TCT is connected;
FIG. 3 is a sectional elevation of a conventional TCT equipped in accordance with the invention;
FIG. 4 represents diagrammatically the circuit of the transformer as FIG. 3;
FIG. 5 is a vector diagram illustrating the relations between complex voltage signals capable of being present in the circuit as FIG. 4.
In FIG. 1 a line 11 is shown which has been brought to a high voltage with respect to the earth 12 for the conveyance of electrical energy. A conventional capacitive voltage transformer (TCT) 13 is connected between the line 11 and the earth 12 includes diagrammatically two capacitors C.sub.1 and C.sub.2 connected in series between a terminal 15 connected to the line 11 and a terminal 16 connected to earth. Between the point of join 18 of the two corresponding ends of the two capacitors C.sub.1 and C.sub.2 and the terminal 16 is connected a circuit 20 forming the medium voltage detector of the transformer for taking off the voltage at the terminals of C.sub.2. This circuit 20 includes essentially a transformer by induction which produces a lowering of voltage and galvanic insulation between the TCT and a load connected to the terminals 22 and 23 of its secondary winding 24, consisting of a device for utilization of the signal which is the image of the voltage of the line (not shown).
The primary winding 26 of this transformer is connected to the terminals 16 and 18 by way of a tuning coil 28.
Transformers of the type diagrammatically described with reference to FIG. 1 are well known and are employed at present for the reduction of the voltage of very high voltage lines providing the conveyance of electrical energy. By choosing suitably the transformation ratio of the circuit 20 and the values of the capacities of the capacitors C.sub.1 and C.sub.2 in order to obtain a division in a suitable ratio a voltage existing between the line 11 and earth one can reduce the primary voltage of the TCT which may, for example, be 220 KV/.sqroot.3 by passing through an intermediate voltage of 20/.sqroot.3 KV at the terminals of C.sub.2. By way of example the capacity of the capacitor C.sub.1 may be about 4400 pF and that of the capacitor C.sub.2 about 44000 pF. The output voltage from the medium voltage circuit 20 is in general employed for purposes of measurement for feeding pick-ups of 0.5% accuracy, reclosers, load protection, etc.
The interest of capacitive voltage transformers is in enabling the reduction in a very high line voltage to be obtained with a bulk and a price which is in general very much lower than that of conventional ordinary wound transformers. They lend themselves particularly well to the working out of a voltage which is an image of the line voltage for purposes of measurement which do not necessitate the transformation of the power conveyed by the line.
Amongst the applications which necessitate the putting into effect of a reduced voltage which is the image of that of the line 11 there is, however, one to which the conventional TCT do not lend themselves well: it is a question of the protection of the lines against insulation fault within times which become shorter and shorter. The appearance of a fault in an electrical line in general manifests itself by a sudden modification of an operational parameter of the line which is detected in order to trigger as rapidly as possible either an alarm or an interruptor device or more complicated devices. In the latter the line interruption is followed by a reclosure after a predetermined waiting time d with a view to restoring the voltage on the line containing the fault under the assumption that the fault has eliminated itself, or
REFERENCES:
patent: 2756414 (1956-07-01), Doremus
patent: 3401304 (1968-09-01), Woodworth
patent: 3517263 (1970-06-01), Okamura et al.
patent: 3947725 (1976-03-01), Lucas
Enertec
Gaudier Dale
Ishimaru Mikio
Shoop William M.
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