Description

Coaxial design for secondary unit The invention relates to the technical field of RC voltage dividers .

Conventional RC voltage diver solutions use a flat arrange ^¬ ment of secondary components on a printed circuit board. This results in limitations in accurate measurement of frequencies above 3kHz. Other solutions with inductive or capacitive voltage transformers have even narrower limitations in band ^¬ width .

However, for power quality measurements it is important to achieve a linear response, high frequency bandwidth and accu ^¬ racy of voltage measurement over a wide voltage range. It is therefore the objective of the invention to satisfy this need .

This objective is solved by the measures taken in accordance with the independent claims. Further advantageous embodiments are proposed by the independent claims. According to an aspect, an RC voltage divider is proposed. The RC voltage divider comprises a secondary part connected to a primary part. The secondary part comprises a coaxial build up. In the following the invention is described on the basis of embodiments illustrated by the figures.

Figure 1 shows a block diagram of an RC voltage divider ac ^¬ cording to an embodiment of the invention.

Figure 2 shows a side view of an interior part of a single coaxial secondary part of the RC voltage divider of figure 1. Figure 3 shows a top view of the single coaxial secondary part of figure 2.

Figure 1 shows a block diagram of an RC voltage divider 1 ac- cording to an embodiment of the invention. The RC voltage di ^¬ vider 1 comprises a primary part 3, and a secondary part 2. The secondary part 2 is connectable to measurement equipment 9. The secondary part 2 comprises a metallic housing 6, and an outer housing 7. The secondary part 2 is connected to the primary part 3. The secondary part 2 comprises a coaxial build up. The outer housing 7 is for protecting the RC voltage divider 1 against external mechanical influences. The me ^¬ tallic housing 6 serves as an electrical shield for protect ^¬ ing the RC voltage divider 1 against electromagnetic influ- ences, such as induction, and is connected to ground.

Figure 2 shows a side view of an interior part of a single coaxial secondary part 2 of the RC voltage divider 1 of fig ^¬ ure 1 in more detail. Figure 3 shows a top view of the single coaxial secondary part 2 of figure 2. The secondary part 2 comprises a tap conductor 4, and electronic secondary compo ^¬ nents 5a-5j . Secondary components 5a-5j are arranged coaxial- ly around the tap conductor 4. The advantage of a coaxial build up is a well equalized arrangement that allows a good linearity over a large frequency spectrum.

The secondary components 5a-5j comprise a selection of capac ^¬ itors 5a-5e and resistors 5f-5j . Apart of capacitors and re ^¬ sistors, the secondary components can comprise other elec- tronic elements. Of course, also any other number of capaci ^¬ tors and/or resistors than the one used in the shown embodi ^¬ ment can be used and arranged coaxially.

As can be best seen in figure 3, the secondary components 5a- 5j are arranged symmetrically around the tap conductor 4. In this embodiment, there are several rotation symmetries around the tap conductor 4. In other embodiments the secondary components can be arranged according to other symmetries, such as e.g. mirror symmetry in respect of the conductor tap. The advantage of symmetries is that they often result in an equalized arrangement, allowing a good linearity over a large frequency spectrum. However, symmetries are not necessary for the invention. The secondary components can even be arranged coaxially, without complying with a symmetry scheme.

As can be best seen in figures 1, the tap conductor 4 and the secondary components 5a-5j are arranged within the electrical shield 6. This allows protection of both, the tap conductor and the secondary components 5a-5j against inductive influ ^¬ ences from outside. Since the electrical shield 6 is connect ^¬ ed to ground, an additional conductor for the ground can be avoided. The electrical shield 6 is preferably made of alumi- num. Other metals or alloys can also be used, but aluminum has the advantage of being inexpensive, mechanically robust, and insusceptible against corrosion.

The frequency dependent influence of an inductance of the secondary part 2 is reduced by an equalized arrangement of secondary components 5a-5j around the tap conductor 4.

According to an embodiment, a sufficient reduction of the in ^¬ ductance can be achieved by a coaxial compact build up and the use of low inductance secondary components, such as ca ^¬ pacitors as well as resistors.

In the center, the tap conductor 4 connects the active prima ^¬ ry part with the measurement equipment 9. The secondary com- ponents are arranged coaxial in a circle around the conductor one side on ground potential and one side on tap voltage po ^¬ tential. An earthed shield (metallic housing) 6 surrounds the arrangement of the all secondary components 5a-5j reducing the influence of external electromagnetic disturbance.

The frequency dependent influence of the inductance is re ^¬ duced by an equalized arrangement of capacitors and resistors around the outlet of the primary capacitance 3 (effect like coaxial shunt) . Shielding prevents influence of external electrical fields.