GB2100929A - Series linked capacitors - Google Patents

Abstract

Series linked capacitors for use in capacitative voltage dividers are formed from a rod 11 of high permittivity ceramic material having a slot or slots 12 through the rod transverse to the axis of the rod. The end surfaces of the rod and surface of the slot or slots are metalled to form capacitor electrodes. <IMAGE>

Description

SPECIFICATION Series linked capacitors This invention relates to electrical capacitor com ponents, in particular for capacitors used in capacitative voltage dividers.

In some countries it is the practice to provide electrical distribution switchgear of 3-phase operating voltage which devices the function of which is to show that the switch is live by illumination of a neon lamp or lamps, usually one for each of the three phases. The same type of circuit can also be used to provide signals for automatic equipment to switch in alternative power supplies, or to detect inadvertent phase reversal on power system supplies which are to be connected together.

The method used for such live line detection is to feed a neon lamp or other indicating or sensing load from a capacitative voltage divider. Usually a high voltage capacitor element is contained within an insulator which serves also as one of the mechanical supports of a bus bar. The high voltage capacitor element is usually a high permittivity ceramic rod or block having metallised end faces to form electrodes, and the support insulation is made from an epoxy resin or other moulding material having good adhesion to the capacitor element surface. This adhesion enhances the resistance to surface breakdown of the capacitor. The low voltage capacitor is usually remote from the high voltage capacitor and in a seperate box in which the neon lamps or other loads are contained.

This invention provides a capacitor component comprising a body of high permittivity ceramic material with terminal surfaces thereof metallised to form electrodes, characterised in that the ceramic body also has at least one intermediate metallised surface to form, with the terminal surfaces, two or more capacitors in a single body.

The invention is illustrated by way of example with reference to Figs. 1 to 4 in which: Fig. I shows a pairs of capacitors C1 and C2 linked in series between a high voltage line Land earth E. A load represented by a resistance R and noen light N is joined in parallel with C2. For capacitances C1 = 150 pF and C2 = 5850 pF and a high voltage line at 15 kV, V2 will be - 350 V.

Fig. 2 shows a sectional view of a known capacitor 1 equivalent to C1 in Fig. 1, mounted in a support insulator 2 and connected at one end through a metal rod 3 and screw-threaded terminal block 4 to a high voltage bus bar (not shown). The capacitor is connected at the other end, through a metal rod 5 and flexible lead 6 to one terminal of both a low voltage t-350 V) capacitor 7 (equivalent to C2 in Fig.

1) and a neon lamp 8. The other terminals of both the capacitor 7 and neon lamp 8 are connected to earth atE Fig. 2 also shows the two other capacitors 9 and neon lamps 10 required for 3-phase live-line indication.

Fig. 3 shows a capacitor component according to one embodiment of the present invention. This consists of a prismatic rod 11, in this case of hexagonal cross section, having a slot 12 cut transversely through the rod near one end. The end faces 13, 14 of the rod and the interior surface of the slot 12 are metallised to form the electrodes of two capacitors, respectively a high voltage capacitor between the slot 12 and end face 13, being equivalent to C, of Fig.

1, and a low voltage capacitor between the slot 12 and end face 14, being equivalent to C2 of Fig. 1. A suitable material for such a capacitor element is a barium titanate type, or other ceramic dielectric materials of permittivity value over 1000, an example of which is FARADEX 3000/1 ceramic manufactured and soldin the United Kingdom by Steatite and Porcelain Products Limited. FARADEX is their registered trade mark for a range of ceramic dielectric materials.

As one example a rod of this material of length = 65 mm and cross-sectional area 300 mm2 and having a slot of 4 mm width cut near one end within 1.5 mm of that end will provide a pair of capacitances approximately in accord with those stated for Fig. 1.

Fig. 4 shows a sectional view of a capacitor component 15 according to the present invention mounted in a moulded support insulator 2 and connected to a high voltage bus bar (not shown) through a metal rod 3 and screw-threaded terminal block 4. A metal rod 5 and flexible lead 6 connects to one terminal of a neon lamp 8 and earth at E. A force fitting clip or other connector (not shown) connects the slot electrode 12 in a terminal block 16 and flexible lead 17 to the other terminal of the neon 8. Fig. 4 also shows the two other means 10, required for 3-phase live-line indication.

Capacitor components made according to the invention have the major advantage that, being of the same material, the capacitors C1 and C2 have the same temperature, voltage, and frequency sensitivity of capacitance and so enable the ratio V1N2 to be maintained.

1. A capacitor component comprising a body of high permittivity ceramic material with terminal surfaces thereof metallised to form electrodes, characterised in that the ceramic body also has at least one intermediate metallised surface to form, with the terminal surfaces, two or more capacitors in a single body.

2. A capacitor component as claimed in claim 1 characterised in that an intermediate metallised surface is provided on a recess or opening in the body.

3. A capacitor component as claimed in claim 1 characterised in that the terminal surfaces are end surfaces of a ceramic rod and an intermediate surface is the surface of a slot through the rod and transverse to the longitudinal axis of the rod and located at such distance from the end surfaces respectively as to provide therewith given capacitance ratios.

4. A capacitative voltage divider comprising a capacitor component as claimed in claim 1, mounted in an insulating support, and with terminals provided for connection to a high voltage line, earth, and a sensing or indicating device.

5. A capacitor component as claimed in any of claims 1 to 3 with reference to the accompanying

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Series linked capacitors This invention relates to electrical capacitor com ponents, in particular for capacitors used in capacitative voltage dividers. In some countries it is the practice to provide electrical distribution switchgear of 3-phase operating voltage which devices the function of which is to show that the switch is live by illumination of a neon lamp or lamps, usually one for each of the three phases. The same type of circuit can also be used to provide signals for automatic equipment to switch in alternative power supplies, or to detect inadvertent phase reversal on power system supplies which are to be connected together. The method used for such live line detection is to feed a neon lamp or other indicating or sensing load from a capacitative voltage divider. Usually a high voltage capacitor element is contained within an insulator which serves also as one of the mechanical supports of a bus bar. The high voltage capacitor element is usually a high permittivity ceramic rod or block having metallised end faces to form electrodes, and the support insulation is made from an epoxy resin or other moulding material having good adhesion to the capacitor element surface. This adhesion enhances the resistance to surface breakdown of the capacitor. The low voltage capacitor is usually remote from the high voltage capacitor and in a seperate box in which the neon lamps or other loads are contained. This invention provides a capacitor component comprising a body of high permittivity ceramic material with terminal surfaces thereof metallised to form electrodes, characterised in that the ceramic body also has at least one intermediate metallised surface to form, with the terminal surfaces, two or more capacitors in a single body. The invention is illustrated by way of example with reference to Figs. 1 to 4 in which: Fig. I shows a pairs of capacitors C1 and C2 linked in series between a high voltage line Land earth E. A load represented by a resistance R and noen light N is joined in parallel with C2. For capacitances C1 = 150 pF and C2 = 5850 pF and a high voltage line at 15 kV, V2 will be - 350 V. Fig. 2 shows a sectional view of a known capacitor 1 equivalent to C1 in Fig. 1, mounted in a support insulator 2 and connected at one end through a metal rod 3 and screw-threaded terminal block 4 to a high voltage bus bar (not shown). The capacitor is connected at the other end, through a metal rod 5 and flexible lead 6 to one terminal of both a low voltage t-350 V) capacitor 7 (equivalent to C2 in Fig. 1) and a neon lamp 8. The other terminals of both the capacitor 7 and neon lamp 8 are connected to earth atE Fig. 2 also shows the two other capacitors 9 and neon lamps 10 required for 3-phase live-line indication. Fig. 3 shows a capacitor component according to one embodiment of the present invention. This consists of a prismatic rod 11, in this case of hexagonal cross section, having a slot 12 cut transversely through the rod near one end. The end faces 13, 14 of the rod and the interior surface of the slot 12 are metallised to form the electrodes of two capacitors, respectively a high voltage capacitor between the slot 12 and end face 13, being equivalent to C, of Fig. 1, and a low voltage capacitor between the slot 12 and end face 14, being equivalent to C2 of Fig. 1. A suitable material for such a capacitor element is a barium titanate type, or other ceramic dielectric materials of permittivity value over 1000, an example of which is FARADEX 3000/1 ceramic manufactured and soldin the United Kingdom by Steatite and Porcelain Products Limited. FARADEX is their registered trade mark for a range of ceramic dielectric materials. As one example a rod of this material of length = 65 mm and cross-sectional area 300 mm2 and having a slot of 4 mm width cut near one end within 1.5 mm of that end will provide a pair of capacitances approximately in accord with those stated for Fig. 1. Fig. 4 shows a sectional view of a capacitor component 15 according to the present invention mounted in a moulded support insulator 2 and connected to a high voltage bus bar (not shown) through a metal rod 3 and screw-threaded terminal block 4. A metal rod 5 and flexible lead 6 connects to one terminal of a neon lamp 8 and earth at E. A force fitting clip or other connector (not shown) connects the slot electrode 12 in a terminal block 16 and flexible lead 17 to the other terminal of the neon 8. Fig. 4 also shows the two other means 10, required for 3-phase live-line indication. Capacitor components made according to the invention have the major advantage that, being of the same material, the capacitors C1 and C2 have the same temperature, voltage, and frequency sensitivity of capacitance and so enable the ratio V1N2 to be maintained. CLAIMS

1. A capacitor component comprising a body of high permittivity ceramic material with terminal surfaces thereof metallised to form electrodes, characterised in that the ceramic body also has at least one intermediate metallised surface to form, with the terminal surfaces, two or more capacitors in a single body.

2. A capacitor component as claimed in claim 1 characterised in that an intermediate metallised surface is provided on a recess or opening in the body.

3. A capacitor component as claimed in claim 1 characterised in that the terminal surfaces are end surfaces of a ceramic rod and an intermediate surface is the surface of a slot through the rod and transverse to the longitudinal axis of the rod and located at such distance from the end surfaces respectively as to provide therewith given capacitance ratios.

4. A capacitative voltage divider comprising a capacitor component as claimed in claim 1, mounted in an insulating support, and with terminals provided for connection to a high voltage line, earth, and a sensing or indicating device.

5. A capacitor component as claimed in any of claims 1 to 3 with reference to the accompanying description and with particular reference to Fig. 3.