Bbc Brown, Boveri & Company, Limited

Bbc Brown Boveri Ag

Georg Mastner

Martin Maschek

Otto Lanz

Thomas Dobler

Urs Ammann

Branko Tomic

Measurement value signals (S1), for example from a signal transmitter which is located at high-voltage potential, which are transmitted by a signal transmitter (1) with a transmit diode (6) on the high voltage side via an optical waveguide (8) to a signal receiver (9) with a photodiode (10) at ground potential, are subject to an optical signal attenuation along the way. To ensure automatic attenuation compensation both for alternating and for direct voltage measurement signals (S1), a reference direct current (I.sub.REF) is fed back to the transmit diode (6). The transmission system is calibrated before each measurement. During this process, the input of an amplifier (4) of the signal transmitter (1) is connected to reference potential (U0) via a switch (3) and the gain factor of the signal receiver (9) is controlled in such a manner that its output signal (S9) is equal to a predeterminable reference voltage (U.sub.REF). The output signal (S14) of a differential amplifier (14) is supplied via a lowpass filter (16) and a 1st post amplifier (17) to an instantaneous-value memory (18), the output signal (S18) of which controls the gain factor. After the calibrated state has been reached, the closed-loop control circuit is interrupted so that the gain factor remains constant until a new calibration is performed. The gain factor can be adjusted via electrically, electromechanically or optically controllable resistances or a multiplier or via the bias voltage of an avalanche photodiode (10).

Method and device for automatic compensation of the attenuation of a

A system for the automatic identification of the type of measuring head (1) of a fiber optic measurement value acquisition and transmission device which exhibits a measurement signal fiber (3) and a control signal fiber (4), in which the measuring head (1) can be remotely operated from a control unit (2) by means of control signals which are transmitted via the control signal fiber and, in particular, can be caused to emit a calibration signal. According to the invention, calibration signals of different frequencies are provided for various types of measuring heads. Using the frequency of the calibration signal, the control device is capable of identifying in each case the measuring head connected to it.

Method for the automatic identification of the type of measuring head of

In a high-voltage-conducting assembly (10), such as, for example, the current transducer arrangement for a high-voltage outdoor installation, measurement information items are transmitted via optical waveguides from high-voltage potential to ground potential. To reduce the voltage gradient along the optical waveguide, the latter is spirally conducted along an optical waveguide carrier (7) between the high-voltage side (9) and the ground potential side (5) of a high-voltage insulator (6). The optical waveguide support (7) can be a self-supporting plastic coil (7) or the outer layer of the insulator tube of fibre-glass-reinforced plastic of the high-voltage insulator (6) or its silicon layer applied on the outside or its silicon shield tape. In this arrangement, the surface leakage path of the optical waveguide support is greater than 1.5-times, preferably greater than 5-times the height (h) of the high-voltage insulator (6). The optical waveguide can be wound at a steep pitch onto the coil or arranged in a U-shaped groove of the coil or in the hollow space of a hose-spaced coil.

Optical waveguide arrangement for a high-voltage insulator

To increase the availability of current transducers for outdoor high-voltage installations, an electronic signal processing device for the measurement signal of the current transducer is arranged above the current transducer as a block which can be removed from above within a transducer head casing which is painted on the outside. The electronic signal processing device is attached to a coverplate, which is aligned parallel to a primary conductor of a magnetic shield casing, which is surrounded by an electrical shield casing. The signal processing device consists of low-power electronics below and power electronics above the coverplate; it converts analog signals of the current transducer into digitized and encoded signals for serial transmission by means of a fibre-optical line. The power electronics are in good thermally conducting contract with the coverplate of the electrical shield casing via a metal plate. Lower and upper ventilation slots are provided at the transducer head casing. To keep any temperature increase due to solar irradiation low, radiation reflectors of polished and degreased aluminium are located at a distance of 3 cm between transducer head casing and electrical shield casing.

Current transducer arrangement for outdoor high-voltage installations

To improve the heat protection of an electronic device (7) in the case of heat radiation coming from the outside, for example solar rays, lateral radiation reflectors (12, 13; 16, 17) of 1 mm-thick aluminium plate polished on both sides and degreased are arranged between the electronic device and the walk (20, 21) of a heat protection casing (1) which laterally surrounds the electronic device. In addition, upper radiation reflectors (14, 15) are provided between the coverplate of the electronic device (7) and a coverplate (4) of the heat protection casing (1), a ventilation opening (18) remaining to the lateral radiation reflectors. In the sidewall of the heat protection casing (1), lower and upper ventilation slots (5,6) are arranged by means of which a chimney effect is achieved in the interior of the heat protection casing. In addition, a bottom plate (2) of the heat protection casing (1) can exhibit cooling openings (3).

Heat protection casing

A circuit arrangement for converting an input voltage into a proportional ouput signal, including a converting resistance which is followed by operational amplifier having a feedback resistance. For the purpose of stabilizing the gain of the circuit arrangement with respect to changes in the converting resistance, the latter is formed by connecting two branch resistances in parallel with each other. These branch resistances are series-connected in a bridge circuit to which a direct voltage is supplied from a voltage source. The bridge circuit also includes an operational amplifier and high-quality film resistors and a variable balancing resistance which includes, in series, another film resistor and a field effect transistor. An integrator automatically balances the bridge circuit by controlling the field effect transistor. The balancing resistor. The feedback resistance operational of the amplifier contains, in series, a film resistor which corresponds to the film resistor in the balancing resistance and a field effect transistor which is matched to the field effect transistor (13) in the balancing resistance. The field effect transistors are controlled in parallel by the integrator. The circuit arrangement can be used for processing the output signal of a capacitive voltage transducer.

Circuit arrangement for converting an input voltage into a proportional

Analog output signals from decentralized transducers for current and voltage are sampled with timing patterns generated at a decentralized location and are transmitted to a central evaluating facility in the form of digitally encoded data streams (D.sub.UR, . . . ). For the purpose of generating data sets which are each based on one sampling of each analog output signal, such that the relative time displacement of the samplings should not exceed a predetermined value which corresponds to the maximum (.DELTA.) of the data-refresh intervals, latch commands (L) are generated at greater intervals in the central evaluating facility, following which in each case the digitized sampled value arriving next of each data stream (D.sub.UR, . . . ) is temporarily stored. After the temporary storage has taken place, in each case a 'Ready' signal (B.sub.UR, . . . ) is set. The 'Ready' signals (B.sub.UR, . . . ) are combined in a logical AND operation to form a 'Data set ready' signal (DB) which is transferred to a computer which interrogates the temporarily stored data (Z.sub.UR, . . . ) via a databus.

Method for processing analog output signals from current and voltage

A shunt arrangement for processing the output current of an inductive current transformer having a wide dynamic range in which, in order to provide high-precision conversion with smaller currents, a power shunt is connected in series with a precision shunt which is connected in parallel with an overvoltage protection circuit containing a switchable semiconductor rectifier and a control circuit. The rectifier changes to a conductive state if the voltage at the precision shunt reaches a limit value. The control circuit contains a symmetric voltage limiting element which is constructed as a pair of limiting diodes or as a fullwave rectifier, the output of which is connected to a reference diode. In order to check the switching state of the overvoltage protection circuit, the series circuit including the power shunt and the precision shunt is connected in parallel with a series circuit consisting of a first bridge resistor and a second bridge resistor which, together with the shunts, form a balanced bridge circuit whereby, when the overvoltage protection circuit is inhibited, bridge circuit is monitored by a window discriminator.

Shunt arrangement with power overload protection by a voltage responsive

A thyristor circuit including a primary winding and at least one secondary winding and first and second bipolar thyristor switches connected across respective connections of the secondary winding. The first bipolar thyristor switch bridges N.sub.1 turns of the secondary winding, while the second bipolar thyristor switch bridges N.sub.2 turns of the secondary winding, wherein N.sub.2 is less than N.sub.1. The product between the maximum forward current of the second bipolar switch and the number of turns N.sub.2 is greater than the product between the latching current of the first bipolar thyristor switch and the number of turns N.sub.1 thereof. The second bipolar thyristor switch thus makes it possible to short-circuit the portion of the secondary winding bridged thereby, for operation as a switchable choke, e.g. in a reactive compensator, or as a variable power supply when supplemented by additional components. The second bipolar thyristor switch which bridges a smaller number of windings than the first bipolar thyristor switch expands the operational range of the thyristor circuit and finds particular utility in providing a regulated d.c. power supply.

Thyristor circuit for current regulation

The voltage present at an input is chopped by a switch which is actuated by a pulse-width modulator controlled by the output voltage and is smoothed at least by a low-pass filter, consisting of an inductance and a capacitance, at the output. In order to reduce to a minimum the delay between the time an input voltage is applied and the time a rated value is at least approximately reached by the output voltage, the inductance is bypassed by a bypassing circuit which has a low inductance and which conducts if the output voltage is below a minimum voltage and in other cases is turned off. It contains, for example, a switch which is constructed as a switchable current source and which is actuated by a comparator comparing the output voltage with a reference voltage. In transformer-coupled embodiments, isolation between the output and the input is possible. The supply unit is suited, for example for supplying auxiliary devices of an instrument transformer from the current of the power-line to be monitored.

Switching power-supply unit with improved start-up behavior

In this voltage transformer for compressed-gas insulated high-voltage systems, between a straight internal conductor (1), which is located in a gas space (4) and forms a high-voltage electrode, and a low-voltage electrode (3) surrounding the internal conductor in the gas space (4) a measuring electrode (5) is arranged at which an output voltage is tapped off and fed to a signal processing system (6). In order to reduce the dependence of the output voltage on tolerances and fluctuations of geometric parameters, a guard electrode (7) is arranged between the low-voltage electrode (3) and the measuring electrode (5) and a plate capacitor (11), which is located in insulating gas, is placed between the measuring electrode (5) and earth. Between the guard electrode (7) and earth a supplementary capacitor (13) is also placed which is dimensioned in such a way that the capacitive voltage dividers formed by the internal conductor (1), the measuring electrode (5) and earth, on the one hand, and the internal conductor (1) the guard electrode (7) and earth, on the other hand, have approximately the same transformation ratios. The guard electrode (7) is earthed via a compensating device (14) the impedance of which is dimensioned in such a way that the time constants for the discharges of the measuring electrode 5 and the guard electrode 7 are approximately equal.

Capacitive voltage transformer

A digital integrator (1) having a 16-bit output is followed by a first 12-bit digital/analog converter (2a) which is supplied with the output bits 1-11 and 16 of the integrator (1) and which forms a first tracking loop with a first subtracter (3a), which forms a first difference signal from the output signal, proportional to the input signal of the analog/digital converter, of a first amplifier (4a) and the output signal of the first digital/analog converter (2a), and a tracking circuit (6) which generates tracking signals for the integrator (1) on the basis of the difference signal. To extend the dynamic range, a second 12-bit digital/analog converter (2b) is present which is supplied with bits 5-16 from the output of the integrator and which forms a second tracking loop with a second subtractor (3b) and a second amplifier (4b), the gain factor of which is 1/16th of the gain factor of the first amplifier (4a), to which loop a control logic (15) switches over when the range which can be covered with the first digital/analog converter (2a) is exceeded. Switching back takes place at the next zero crossing, that is to say change of the most significant bit. The digital/analog converter is particularly suitable for processing the output signal of a current or voltage converter.

Analog/digital converter

An analog/digital converter wherein an analog input signal is applied to a variable gain input amplifier which has an output connected to a subtractor. Also connected to the subtractor is the output of a D/A converter, the input of which is connected to the output of an integrator. The subtractor forms from the output signal of the input amplifier and that of the D/A converter a difference signal which is used by a tracking circuit for generating tracking signals for the integrator. For the purpose of widening the dynamic range, the input amplifier contains four scaling amplifiers, one of which is connected by a selection switch to the output of the input amplifier. The scaling factors of the second, third, and fourth scaling amplifiers are 1/4, 1/16, and 1/64, respectively, of that of the first scaling amplifier. If the output of the integrator exceeds predetermined limits, a control logic circuit sets the selection switch to the scaling amplifier having the next-smaller scaling factor, effects a resetting of the output signal of the integrator which corresponds to a division by four of this signal when it exceeds one of the limits of the output range and indicates the respectively valid scaling factor. Switching operations into the other direction take place at zero crossings of the output signal of the integrator. The analog/digital converter is particularly suitable for processing the output signal of a current or voltage converter.

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Niederrohrdorf, Switzerland

Georg Mastner