DE10056988A1 - Voltage divider arrangement employing capacitors has measurement amplifier supplied by separate capacitor section of divider of tubular design - Google Patents

Abstract

The divider is in two parts. A tubular capacitor arrangement with hv terminal in a cast resin dielectric on the surface of which are two tubular plates. The terminal forms with one plate an upper divider capacitor (C2) and with the second capacitor (C1) to provide power for a voltage signal amplifier (6). The second capacitor ( C3) forming the divider is housed in the measurement amplifier case and has a dielectric of the same material as the first.

Description

The invention relates to a voltage divider arrangement for Measurement of high and medium voltages, with one off an upper capacitor and a lower capacitor best capacitive voltage divider and one with the Voltage divider connected and spatially connected arranged measuring amplifier, the one with the measuring voltage connected supply capacitor with elec trical energy is supplied.

It is known for voltage measurement of high and with to use capacitive voltage dividers. These have the compared to inductive voltage dividers Advantage of the simple and inexpensive construction. Capacitive voltage dividers still have one more favorable behavior towards higher frequencies. It is also known between low-voltage side Tapping the capacitive voltage divider and the intended use an output signal Provide amplifiers through which a retroactive effect of the output connected different Cable lengths or burden resistances on the Output signal can be prevented.

Finally, the supply energy for is also known the amplifier itself from the measurement signal. Known voltage divider arrangements, however, still have a relatively high sensitivity of the output signal against external influences such as temperature changes or electric fields in the close vicinity of the chip divider.

The object of the invention is to provide a voltage divider order to specify, which with a simple structure a high Measurement accuracy allows.

The inventive solution to this problem exists in that at least one for connection to the or medium voltage certain high voltage electrode, one intended for connection to the measuring amplifier Sensor electrode and one for supplying the measuring ver stronger supply with electrical energy electrode in a concentric arrangement to a condenser sator unit are connected.

These measures result in a voltage divider arrangement created between the high voltage electrode and the sensor electrode forms a capacitance that acts as an upper capacitor of a capacitive voltage divider is used while at the same time one between the high span voltage electrode and the supply electrode existing Capacity a supply capacitor for the elec trical power supply of the measuring amplifier forms. All electrodes can advantageously be cast resin be connected to a unit, so that the installation in an associated housing is eliminated or greatly simplified becomes.

It must be taken into account that the dielectric Properties of capacitors strongly on the temperature depend. Because this temperature influence does not even is linear, the compensation would be temperature-related capacity changes electronically consuming.

A full compensation of the nonlinear Temperature influences can be reached if a Sub located outside the capacitor unit capacitor of the capacitive voltage divider  Dielectric made of the same material as that Condenser unit.

In a preferred embodiment, the sub capacitor from a conductive surface, preferably a copper-coated circuit board as the first Electrode with a cast resin layer as Dielectric and one on the cast resin layer brought copper varnish layer as the second electrode of the Sub-capacitor is provided. The cast resin layer consists of the same material as that Dielectric of the top capacitor.

In a further simple embodiment, the Arrangement from a tubular, one-sided closed rod dielectric, the inside one Contains rod-shaped electrode that is made at one end protrudes from the dielectric and the high voltage is connected while the other end is through the Bottom of the rod dielectric isolated from the outside is completed.

Outside there will be two next to each other on the dielectric separated annular electrodes brings, preferably the larger the supply electrode and preferably the smaller the sensor elec trode represents.

On the one hand, this arrangement is easy to manufacture and on the other hand, not very sensitive to electromagnetic External influences when one is connected to ground Shield electrode over the sensor electrode (isolated) covers.

With one on the electrical connection between the Upper capacitor and the lower capacitor of the capacitive Voltage divider connected to the measuring amplifier Possibility to compare amplitude and phase  and a low source impedance of the output signal generated.

To shield against disturbing environmental influences the sub-capacitor and the measuring amplifier preferably housed in a shielding metal housing.

An embodiment of the invention is as follows explained in more detail with reference to the drawings.

Show it:

Fig. 1 is a schematic diagram of a voltage divider arrangement of the invention;

Fig. 2 is a schematic representation of the spatial arrangement of the subject invention;

Fig. 3 is a simplified circuit diagram of the voltage divider arrangement according to the invention.

In Fig. 1 you can see an upper capacitor C2 and egg NEN capacitor C3, which are connected in series between a connection 1 with a medium or high voltage U1 and a connection 2 connected to earth potential 3 . A connecting line 4 between the upper capacitor C2 and the lower capacitor C3 is connected to the input 5 of a measuring amplifier 6 , at the output 7 of which an output voltage U2 which is proportional to the high voltage U1 is present.

The power supply of the measuring amplifier 6 takes place from the high voltage U1 by means of a supply capacitor C1.

In Fig. 2 you can see a rod-shaped high-voltage electrode 8 and an annular supply electrode 9 , which is arranged around a tubular dielectric 12 and together with this and the high-voltage electrode 8 forms the supply capacitor C1.

Furthermore, one can also see a ring-shaped sensor electrode 10 , which is arranged adjacent to the supply electrode 9 on the dielectric 12 and together with the high voltage electrode 8 represents the upper capacitor C2, which together with the lower capacitor C3 forms the capacitive voltage divider. Around the sensor electrode 10 around a shield electrode 11 connected to the ground potential 3 is arranged, which is separated from the sensor electrode 10 by insulation 14 .

The components 8 to 10 and 12 mentioned form a capacitor unit 13 which has a high-voltage connection at its upper end. An amplifier unit has a metal housing 17 in which the measuring amplifier 6 and the sub-capacitor C3 are accommodated. The sub-capacitor C3 has a dielectric which consists of the same material as the dielectric 12 of the capacitor unit 13 .

The power supply for the operational amplifier 18 can be seen in FIG. 3. The alternating current flowing from the high voltage U1 flowing through the supply capacitor C1 is rectified via the diodes D1 and D2 (two-way rectification) and slightly smoothed by the capacitors C4 and C5. A Zener diode D5 limits the supply voltage for the operational amplifier 18 . The two high-resistance resistors R10 and R12 prevent the supply voltage from drifting away from the lasse 3, so that it is always in the middle between positive voltage + V and negative voltage -V.

The voltage connections + V and -V are connected to the corresponding connections of the operational amplifier 18 , which is preferably programmable in terms of its current consumption.

The supply voltage + V and -V follows the signal symmetrically in common mode. This signal-dependent reference of the supply voltage to ground 3 has many advantages. On the one hand, smaller charging capacitors C4, C5 are possible, so that a quick supply build-up takes place. Secondly, input protection can be omitted at the operational amplifier input 5 because the measuring voltage never increases above the supply voltage anyway. Finally, the slew rate of operational amplifier 18 may be less than the slew rate of the signal.

The smoothing capacitors C4 and C5 in voltage supply must be opposite the supply capacitor C1 are in the right ratio. That relationship makes itself felt when the input voltage is just is so small that the circuit works. Are the Smoothing capacitors C4 and C5 too large, it takes Charging too long and the circuit is not running right away on. If the smoothing capacitors C4 and C5 are too small, cannot be buffered enough and the ripple the supply voltage becomes too large.  

LIST OF REFERENCE NUMBERS

1

Connection

2

Connection

3

Ground / earth

4

connecting line

5

entrance

6

measuring amplifier

7

output

8th

High-voltage electrode

9

supply electrode

10

sensor electrode

11

shield grid

12

Cast resin / dielectric

13

condenser unit

14

isolation

17

Metal housing / Shielding

18

operational amplifiers
C1 supply capacitor
C2 upper capacitor
C3 sub-capacitor
C5 capacitor
D1 diode
D2 diode
D5 Zener diode
R1 resistance
R10 resistance
R12 resistance
U1 high voltage
U2 output voltage
+ V voltage connection
-V voltage connection

Claims (9)

1. Voltage divider arrangement for measuring high and medium voltages, with one from an upper capacitor (C2) and one. Sub-capacitor (C3) existing capacitive voltage divider and a measuring amplifier ( 6 ) connected to the voltage divider, which is supplied with electrical energy via a supply capacitor (C1) connected to the measuring voltage (U1), characterized in that at least one for connection to the high - Or medium voltage (U1) certain high-voltage electrode ( 8 ), one for connection to the measuring amplifier ( 6 ) certain sensor electrode ( 10 ) and one for supplying the measuring amplifier ( 6 ) with electrical energy certain supply electrode ( 9 ) in a concentric arrangement to a capacitor unit ( 13 ) are connected. 2. Voltage divider arrangement according to claim 1, characterized in that it has a tubular, one-sided rod dielectric ( 12 ) which contains a rod-shaped high-voltage electrode ( 8 ) which can be contacted at the open end with the high voltage, while the other End through the bottom of the rod dielectric ( 12 ) is closed to the outside, and on the outside of the dielectric ( 12 ) a, preferably larger and ring-shaped supply electrode ( 9 ) and a, preferably smaller and ring-shaped, sensor electrode ( 10 ) is applied. 3. Voltage divider arrangement according to claim 1 or 2, characterized in that it is connected by casting with casting resin to form a compact, mechanically stable and protected against external influences unit ( 13 ). 4. Voltage divider arrangement according to claim 2, characterized in that a shield electrode ( 11 ) to be connected to ground completely surrounds the sensor electrode ( 10 ) in an insulated manner. 5. Voltage divider arrangement according to one of the preceding claims, characterized in that an outside of the capacitor unit ( 13 ) arranged sub-capacitor (C3) of the capacitive voltage divider has a dielectric made of the same material ( 12 ) as the capacitor unit ( 13 ). 6. Voltage divider arrangement according to one of the preceding existing claims, characterized in that the Sub-capacitor (C3) made of a conductive surface, preferably a copper-coated circuit board consists of a cast resin layer and a attached to the cast resin layer Copper lacquer layer is provided. 7. Voltage divider arrangement according to one of the preceding claims, characterized in that the sub-capacitor (C3) and the measuring amplifier ( 6 ) are placed in a shielding metal housing ( 17 ). 8. Voltage divider arrangement according to one of the preceding claims, characterized in that the supply voltage (+) generated by the supply electrode ( 9 ) Ver (+ V / -V) of the associated amplifier arrangement in synchronism with the sensor signal changes to the ground potential ( 3 ), so that no protective measures against overvoltages from the high voltage side are required for the measuring amplifier input ( 5 ). 9. Voltage divider arrangement according to one of the preceding claims, characterized in that an adjustable / changeable operational amplifier ( 6 ) is used in its current consumption.