Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an arrangement for potential-ree
measurement of currents or voltages in high-tension installations, having a
transformer at a high voltage potential which picks up the magnitude to be
measured, and having an optical transmitter whereby the measurement informa-
tion is passed from a high to a low voltage potential, the said transformer
and/or transmit~er being fed from an auxiliary power source. An arrangement
o this kind is knot~n from German Patent 1,283,364.
The source of auxiliary power in this connection is a constant-
voltage source not described in detail. If, for example, a battery is used
for the purpose, a replacement is often necessary, due to use and age, and
this involves shutting down the high-tension installation. In practic~,
therefore, the auxiliary power for the transformer and transmitter is usually
drawn from the high-tension network (German Patent 1,264,606). It is also
conceivable, however, to obtain this auxiliary power from isolating-
transformers and capacitors, but such types of power supply are costly and
complex.
It is the purpose of the invention to reduce the cost and complexity
o~ the circuitry required for providing this auxiliary power3 without the
need for periodic shut-downs of the high-tension installation.
According to the invention, this purpose is achieved in that the
auxiliary power source is in the form of a battery adapted to be charged
while the unit is in operation. Since the ba~tery is being continuously
recharged, it is unnecessary to shut the installation down in order to replace
the auxiliary power source. Abo~e all, however, the cost of the circuitry is
low.
According to a further development of the invention, the battery is
charged by sunlight, or by photovoltaic elements irradiated by artificial
light sources and/or the energy of the harmonic oscillations of the magnitude
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to be measured.
Thus, in accordance with the invention, there is provided
an arrangement for the potential-free measurement in high-voltage
power plants of a direct current affected by harmonic oscillations,
having
a transformer at a high voltage potential which detects
the direct current to be measured,
an optical transmitter over which measurement information
is conducted from a high to a low potential,
a battery at high-voltage potential as an auxiliary
voltage source feeding the transformer and/or transmitter,
characterized in that
the battery can be charged by two charging generators at
high voltage potential, decoupled by means of diodes,
the one charging generator is in the form of a photo-
voltaic element irradiated by sunlight or artificial light sources,
and
the other charging generator consists of a transformer
which uses only harmonic oscillations present in the measured
current,
The invention is explained hereinafter in greater detail
in conjunctLon with the example of embodiment illustrated in the
drawing attached hereto, wherein:
Figure 1 is a wiring diagram of a high-tension installat-
ion in which three-phase current is transformed into direct current,
and
Figure 2 illustrates a device for measuring the high-
voltage direct current.
Figure 1 shows two current-converter groups 1, 2 which
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feed a direct-current double conductor (+ and - potentials)
symmetrical with ground potential, for example from a three-phase
~ high-tension networ~ RST, for the purpose of transmitting high-
- tension direct current.
The direct currents are measured by two transformers,
usually so-called Kramer transformers or transformers which, in
conjunction with parallel resistors, transform the voltage at the
resistors into an alternating or direct voltage, or transformers
based upon the Hall generator principle.
The alternating currents are dealt with by alternating-
current transformers 5.
Figure 2 shows in greater detail the measuring device
fitted to transformer 3. Current I to be measured is picked up
; in transformer 3 and is transformed, by a light-emitting element,
not shown, into a light signal. A light-sensitive diode 9 is
controlled by a light conductor (light-pipe) 8 to divide the
potential, so that, with the aid of a digital signal, the intensity
of the current may be measured there at a low potential. The
auxiliary power for transformer 3 is supplied by a battery 6 which,
in turn, is recharged by a photovoltaic element 7 and/or by the
~- harmonic oscillations of current I.
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Two diodes 10, 11 prevent battery 6 from being discharged. Ir
normal operation, i.e. when the high-tension installation is functioning, the
alternating-current part of the direct current containing harmonic oscilla-
tions is rectified and used to recharge the battery. If transformer 5, on
the alternating-voltage side, is used instead of transformer 3 ~or 4), on the
direct-voltage side, for measuring the current, the current may be a pure
alternating current. Thus battery 6 is discharged only if no current I is
. flowing. In the case of lengthy shut-downs, battery 6 is charged by the
~hotovoltaic element. Sinc~ transformer 3 requires little power, recharging
battery 6 with current I may, if necessary, be dispensed with. Where little
power is required, the light energy made available by the sun to photovoltaic
element 7 is normally sufficient ~even in the shade). If longer periods of
darkness are to be expected, ~he source of light may be artificial.
; As already indicated, the advantage of the circuit is to be
perceived in its very low cost. Transformer 3, for example, may consist of
a shunt, a simple vibrator, and an amplifier for control of the light-
emitting element (a gallium-arsenide diode or a laser element). As the
photovoltaic element passes from monocrystalline to polycrystalline
structures, a very economical source of power becomes available. For
~ 20 instance, a power output of 1 W requires a crystal surface of only about 1
;~ dm .
In addition to the current measurements described above, it is
easy to measure volta~es and voltage commands to high-tension circuit
elements, e.g. to the valves of rectifier groups 1, 2.
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