GB1586235A

GB1586235A – Electric circuits incorporating non-linear resistors
– Google Patents

GB1586235A – Electric circuits incorporating non-linear resistors
– Google Patents
Electric circuits incorporating non-linear resistors

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Publication number
GB1586235A

GB1586235A
GB2658177A
GB2658177A
GB1586235A
GB 1586235 A
GB1586235 A
GB 1586235A
GB 2658177 A
GB2658177 A
GB 2658177A
GB 2658177 A
GB2658177 A
GB 2658177A
GB 1586235 A
GB1586235 A
GB 1586235A
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GB
United Kingdom
Prior art keywords
resistor
resistors
voltage
series
electric circuit
Prior art date
1978-05-23
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)

Expired

Application number
GB2658177A
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AEI

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AEI
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1978-05-23
Filing date
1978-05-23
Publication date
1981-03-18

1978-05-23
Application filed by AEI
filed
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AEI

1978-05-23
Priority to GB2658177A
priority
Critical
patent/GB1586235A/en

1981-03-18
Publication of GB1586235A
publication
Critical
patent/GB1586235A/en

Status
Expired
legal-status
Critical
Current

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Classifications

H—ELECTRICITY

H03—ELECTRONIC CIRCUITRY

H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS

H03H5/00—One-port networks comprising only passive electrical elements as network components

H03H5/12—One-port networks comprising only passive electrical elements as network components with at least one voltage- or current-dependent element

Description

(54) ELECTRIC CIRCUITS INCORPORATING NON-LINEAR RESISTORS.
(71) We, ASSOCIATED ELECTRI
CAL INDUSTRIES LIMITED, of 1
Stanhope Gate, London W1A 1EH, a British Company, do hereby declare this invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:
This invention relates to non-linear resistors and in particular to their application to voltage limiting electric circuits.
The relationship between applied voltage
V and current flow I for a non-linear resistor is conveniently expressed by the equation: I = (V/C) a, where C is a coefficient of the resistance, and a an index of the non-linearity of the resistor.
Obviously, this equation reduces to Ohm’s law, i.e. to a linear relationship between V and I, in the case of a = 1.
The voltage hereinafter referred to as the threshold voltage of a non-linear resistor shall be that voltage at or below which, if applied to the resistor, the current flow through the resistor is practically negligible, being in the order of 10-4A or less. It will be obvious from the characteristics of nonlinear resistors, that this threshold voltage is not an absolute quantity, but must be defined in relation to the required circuit parameters.
In certain application, e.g. voltage limitation, it is desirable to use non-linear resistors having a high a-value, i.e. a 2 15. One such use of high-a resistors, i.e. that of shunt resistors in electric circuit breakers for limiting voltage surges due to switching operations, is disclosed in the co-pending patent application No. 13108/77 by the present applicants.
The use of high-a resistors has hitherto been severely restricted because of the difficulties encountered in matching the current-voltage characteristics of two or more such non-linear resistors sufficiently well over a large enough range of voltages to ensure adequate load sharing between such resistors when they are connected in parallel.
This difficulty, due in the main to manufacturing tolerances, is most prominent in the high current region of the current-voltage characteristic, i.e. when appreciable arnounts of energy are dissipated.
A further problem associated with this region is the rapid increase of current broughtabout by only minor increments in the applied voltage, and the consequent risk of destruction of the resistor concerned.
It is an object of this invention to provide a solution to these problems, and thus widen the field of application of high-a non-linear resistors.
In accordance with the invention, an electric circuit incorporates at least one series resistor chain comprising at least one resistor of a first kind and at least one resistor of a second kind, each resistor having a value of resistance coefficient C appropriate for the voltages to be applied thereto in use, wherein each resistor of the first kind is a non-linear resistor with a non-linearity index a equal to or greater than 15, and wherein each resistor of the second kind is a resistor with a nonlinearity index a less than 15 and equal to or greater than 1.The incorporation of one or more resistors of the second kind of appropriate a value provides for variability of the current-voltage characteristic of said series resistors chain, and thereby allows in use two or more of said resistor chains to be connected in parallel and/or provides for a limitation of the current flow through each series resistor chain.
Preferably, the index measure of nonlinearity of each resistor of the said first kind is of the order of 30.
Each resistor of the second kind may be a linear resistor, or alternatively a non-linear resistor with a < 7.. Conveniently, the coefficient of resistance C of resistors of the said first and second kind respectively may, for each series resister chain, be such that at or below a suitable threshold voltage the voltage drop across the or each said series resistor chain is substantially the voltage drop across its resistor or resistors of the first kind, and at a selected higher voltage is shared substantially equally between its resistors of the first kind and its resistors of the second kind thereby to limit the current flow through the or each said series resistor chain. Alternatively, for each series resistor chain, the coefficient of resistance C of its resistor or resistors of the second kind may be such that the voltage drop across said resistor or resistors is over a large range of voltages about the threshold voltage appreciably less than the voltage drop across the respective resistor or resistors of the first kind, the resistor or resistors of the second kind serving mainly to provide for variability of the current-voltage characteristics of the corresponding series resistor chain so as to allow parallel connection of two or more series resistor chains. Thus an electric circuit in accordance with the invention may incorporate at least two parallel branch circuits each consisting of a series resistor chain comprising at least one resistor of the first kind and at least one resistor of the second kind, with the parallel branch circuits having substantially matching current-voltage characteristics. Each series resistor chain may comprise two or more resistors of the first kind in series connection, with each such resistor having a non-linearity index a 2 15. Each series resistor chain may comprise two or more resistors of the second kind connected in series, with each such resistor having a non-linearity index a < 15. Conveniently, an electric circuit according to the invention may form a voltage limiting circuit. An electric circuit in accordance with the invention may be connected in series or in parallel with one or more suitably dimensioned spark gaps to form a voltage limiting circuit. An electric circuit in accordance with the invention may be connected in parallel with at least one contact pair of an electric circuit breaker. The invention will be further described by way of example only and with reference to the accompanying drawings, of which: Figure 1 shows a graph of different current-voltage characteristics of non-linear resistors as used hitherto; Figure 2 illustrates current-voltage characteristics of different electric circuits in accordance with the invention; Figure 3 shows, in diagrammatic form. a typical application of the present invention to a voltage limiting spark gap; Figure 4 illustrates the current-voltage characteristics of the arrangement of Figure 3; and Figure 5 shows the application of the present invention to an electric circuit breaker. Referring at first to Figure 1, curve 11 represents the current-voltage characteristics of a non-linear resistor with a = 5, drawing a current of 2.5A at an applied voltage of 1500 V. If the applied voltage is reduced to 1000V, the current flowing through the resistor is still approximately 0.3A, with the threshold voltage, producing a current flow of the order of 10 A being about 200V. In contrast, curve 12 represents a non-linear resistor having an a-value of 25. The current passing through this resistor at 1500V is again 2.5A, but the threshold voltage is approximately 1000V, the current flow at this voltage level being 1.0 x 10-4A.Increasing the voltage from 1 500V to 1 600V increases the current flow from 2.5A to 12.6A, the resistor being useable as a shunt resistor for a circuit breaker in accordance with the invention described in patent application 13108/77. However, a simple calculation shows that a resistor with the same a = 25, but a coefficient of resistance C only 1 % less than that of the illustrated resistor, draws an approximately 28% higher current, which demonstrates the difficulties in matching two or more such resistors sufficiently well to achieve adequate load sharing in parallel connection. Curve 13 represents, for comparison, a linear resistor. Curves 21, 22 and 23 of Figure 2 show different current-voltage characteristics of resistor chains in accordance with the present invention, dimensioned such that an applied voltage of 1500V results in a current flow of 2.5A. Curve 21 represents a series connection of a non-linear resistor with a = 30 (curve 25) and a linear resistor, chosen so as to result in the voltage drop across the linear resistor being equal to that across the nonlinear high-a resistor at approximately 1500V, and it can be clearly seen that as the voltage falls below 1500V, the voltage drop across the resistor chain is increasingly dominated by the non-linear, high-a resistor, while for voltages above 1500V, the linear resistor provides an efficient current limitation. The same applies to the resistor chains represented by curves 22 and 23, curve 22 illustrating a series chain of two non-linear resistors, one having an a-value of 30 (see curve 25) the other of a = 5, the voltage drop at 1500V being again approximately equally shared by both resistors. In contrast, curve 23 represents a combination of resistors, in which the low-a, or linear resistor serves mainly to adjust the characteristics of the resistor represented by curve 24. It is to be understood, that the examples given here are, for the sake of clarity and simplicity, restricted to one high-a and one low-a/linear resistor, but similar results can, of course, be achieved by combining two or more high-a and/or low-a resistors in series, and connection of such resistance chains in parallel. Figure 3 shows a circuit diagram of a voltage limiting circuit, comprising a spark gap 33, and two series resistance chains 35, 36 and 37, 38 respectively in parallel with the spark gap 33. Each of the high-a resistors 35, 37 is made up of three high-a resistors 351, 352, 353, and 371, 372, 373, while the low-a resistors 36 and 38 comprise each two resistors 361, 362 and 381, 382. Referring now also to Figure 4, a voltage V applied to terminals 31 and 32 will cause a negligibly small current flow through resistors 35, 36 and 37, 38 as long as the threshold voltage Vt is not exceeded.If the applied voltage rises above Vt, the current flow I will increase rapidly, with the voltage drop across the resistors 35 and 37 staying very nearly constant (see also e.g. curve 25 of Figure 2), while the voltage drop across the low-a resistors 36 and 38 becomes increasingly larger as the applied voltage between terminals 31 and 32 increases. The maximum voltage, which can safely be applied repeatedly to these terminals is indicated by Vm, and in this example the respective resistors 35 and 36, and 37 and 38 are chosen such, that the voltage drop Vh across the high-a resistors equals the voltage drop V1 across the low-a resistors at Vm. Only when the voltage across the terminals 31, 32 rises to Vg, i.e., when the energy to be absorbed exceeds a predetermined value, will flash over occur between the electrodes 331 and 332 of the spark gap 33. Similarly, such a voltage limiting circuit may comprise only one series resistor chain in accordance with the invention, or three or more of these sexes resistor chains connected in parallel, the number being determined largely by the amount of energy to be dissipated. A further application of non-linear resistors in accordance with this invention is illustrated in Figure 5, which shows a single gap circuit breaker comprising terminals 51 and 52, a fixed contact 55 and a movable contact 56 mounted on a stem 59 of conducting material associated with means (not shown) for moving the movable contact 56 and stem 59 towards or away from the fixed contact 55. In the closed state, as shown in the Figure 5, the electric current path between terminals 51 and 52 is completed through fixed contact 55, movable contact 56. the conducting stem 59 and a suitable sliding contact arrangement as indicated schematically at 58. The shunt resistor 54 is connected in parallel with the breaker assembly 55, 56, 58, 59 at its terminals 53 and 57.The use of a non-linear resistor circuit in accordance with the present invention allows auxiliary contacts for disconnecting the shunt resistor after opening of the circuit breaker contacts to be dispensed with. The invention can of course equally well be applied to multigap circuit breakers. The shunt resistor 54 consists in this example of one single chain of resistors, 541, 542 and 543 being the high-a resistors, and 544 being the low-a component, but two or more parallel chains, each consisting of series connected high-a and. low-a resistors, and having closely matched current-voltage characteristics could alternatively be used. WHAT WE CLAIM IS: 1. An electric circuit incorporating at least one series resistor chain comprising at least one resistor of a first kind and at least one resistor of a second kind, each resistor having a value of resistance coefficient C appropriate for the voltages to be applied thereto in use, wherein each resistor of the first kind is a non-linear resistor with-anon- linearity index a equal to or greater than 15, and wherein each resistor of the second kind is a resistor with a non-linearity index cr less than 15 and equal to or greater than 1. 2. An electric circuit as claimed in claim 1, wherein at least one resistor of the first kind has a non-linearity index a of the order of 30. 3. An electric circuit as claimed in any preceding claim wherein at least one resistor of the second kind is a non-linear resistor having a non-linearity index a less than 7. 4. An electric circuit as claimed in any preceding claim, wherein the coefficient of resistance C of the resistors of the first and second kind respectively is, for the or each series resistor chain, such that at or below a suitable threshold voltage the voltage drop across the or each said resistor chain is substantially the voltage drop across its resistor or resistors of the first kind, and at a selected higher voltage is shared substantially equally between its resistor or resistors of the first kind and its resistor or resistors of the second kind thereby to limit the current flow through the or each said series resistor chain. 5. An electric circuit as claimed in claims 1 to 3, wherein the coefficient of resistance C of the resistors of the first and second kind respectively is, for the or each series resistor chain, such that over a large range of voltages above the threshold voltage the voltage drop across its resistor or resistors of the second kind remains appreciably less than the voltage drop across its respective resistors of the first kind, its resistor or resistors of the second kind serving mainly to provide for variability of the current-voltage characteristics of the respective series resistor chain so as to allow parallel connection of two or more series resistor chains. 6. An electric circuit as claimed in any **WARNING** end of DESC field may overlap start of CLMS **. Claims (12) **WARNING** start of CLMS field may overlap end of DESC **. It is to be understood, that the examples given here are, for the sake of clarity and simplicity, restricted to one high-a and one low-a/linear resistor, but similar results can, of course, be achieved by combining two or more high-a and/or low-a resistors in series, and connection of such resistance chains in parallel. Figure 3 shows a circuit diagram of a voltage limiting circuit, comprising a spark gap 33, and two series resistance chains 35, 36 and 37, 38 respectively in parallel with the spark gap 33. Each of the high-a resistors 35, 37 is made up of three high-a resistors 351, 352, 353, and 371, 372, 373, while the low-a resistors 36 and 38 comprise each two resistors 361, 362 and 381, 382. Referring now also to Figure 4, a voltage V applied to terminals 31 and 32 will cause a negligibly small current flow through resistors 35, 36 and 37, 38 as long as the threshold voltage Vt is not exceeded.If the applied voltage rises above Vt, the current flow I will increase rapidly, with the voltage drop across the resistors 35 and 37 staying very nearly constant (see also e.g. curve 25 of Figure 2), while the voltage drop across the low-a resistors 36 and 38 becomes increasingly larger as the applied voltage between terminals 31 and 32 increases. The maximum voltage, which can safely be applied repeatedly to these terminals is indicated by Vm, and in this example the respective resistors 35 and 36, and 37 and 38 are chosen such, that the voltage drop Vh across the high-a resistors equals the voltage drop V1 across the low-a resistors at Vm. Only when the voltage across the terminals 31, 32 rises to Vg, i.e., when the energy to be absorbed exceeds a predetermined value, will flash over occur between the electrodes 331 and 332 of the spark gap 33. Similarly, such a voltage limiting circuit may comprise only one series resistor chain in accordance with the invention, or three or more of these sexes resistor chains connected in parallel, the number being determined largely by the amount of energy to be dissipated. A further application of non-linear resistors in accordance with this invention is illustrated in Figure 5, which shows a single gap circuit breaker comprising terminals 51 and 52, a fixed contact 55 and a movable contact 56 mounted on a stem 59 of conducting material associated with means (not shown) for moving the movable contact 56 and stem 59 towards or away from the fixed contact 55. In the closed state, as shown in the Figure 5, the electric current path between terminals 51 and 52 is completed through fixed contact 55, movable contact 56. the conducting stem 59 and a suitable sliding contact arrangement as indicated schematically at 58. The shunt resistor 54 is connected in parallel with the breaker assembly 55, 56, 58, 59 at its terminals 53 and 57.The use of a non-linear resistor circuit in accordance with the present invention allows auxiliary contacts for disconnecting the shunt resistor after opening of the circuit breaker contacts to be dispensed with. The invention can of course equally well be applied to multigap circuit breakers. The shunt resistor 54 consists in this example of one single chain of resistors, 541, 542 and 543 being the high-a resistors, and 544 being the low-a component, but two or more parallel chains, each consisting of series connected high-a and. low-a resistors, and having closely matched current-voltage characteristics could alternatively be used. WHAT WE CLAIM IS: 1. An electric circuit incorporating at least one series resistor chain comprising at least one resistor of a first kind and at least one resistor of a second kind, each resistor having a value of resistance coefficient C appropriate for the voltages to be applied thereto in use, wherein each resistor of the first kind is a non-linear resistor with-anon- linearity index a equal to or greater than 15, and wherein each resistor of the second kind is a resistor with a non-linearity index cr less than 15 and equal to or greater than 1. 2. An electric circuit as claimed in claim 1, wherein at least one resistor of the first kind has a non-linearity index a of the order of 30. 3. An electric circuit as claimed in any preceding claim wherein at least one resistor of the second kind is a non-linear resistor having a non-linearity index a less than 7. 4. An electric circuit as claimed in any preceding claim, wherein the coefficient of resistance C of the resistors of the first and second kind respectively is, for the or each series resistor chain, such that at or below a suitable threshold voltage the voltage drop across the or each said resistor chain is substantially the voltage drop across its resistor or resistors of the first kind, and at a selected higher voltage is shared substantially equally between its resistor or resistors of the first kind and its resistor or resistors of the second kind thereby to limit the current flow through the or each said series resistor chain. 5. An electric circuit as claimed in claims 1 to 3, wherein the coefficient of resistance C of the resistors of the first and second kind respectively is, for the or each series resistor chain, such that over a large range of voltages above the threshold voltage the voltage drop across its resistor or resistors of the second kind remains appreciably less than the voltage drop across its respective resistors of the first kind, its resistor or resistors of the second kind serving mainly to provide for variability of the current-voltage characteristics of the respective series resistor chain so as to allow parallel connection of two or more series resistor chains. 6. An electric circuit as claimed in any previous claim incorporating at least two parallel branch circuits each consisting of a series resistor chain comprising at least one resistor of the first kind and one resistor of the second kind, with the parallel branch circuits having substantially matching currentvoltage characteristics. 7. A voltage limiting circuit incorporating at least one electric circuit as claimed in any preceding claim. 8. A voltage limiting circuit as claimed in claim 7. wherein at least one said electric circuit is connected in parallel with one or more suitably dimensioned spark gaps. 9. A voltage limiting circuit as claimed in claim 7 or 8 connected in parallel with one or more breaker contact pairs of an electric circuit breaker. 10. An electric circuit wherein the or each series resistor chain has a currentvoltage characteristic substantially as described with reference to, and as shown in Figures 2 and 4 of the accompanying drawings. Ii. A voltage limiting circuit substantially as described with reference to, and as illustrated by Figure 3 of the accompanying drawings. 12. An electric circuit breaker incorporating a voltage limiting circuit substantially as described with reference to, and as illustrated by Figure 5 of the accompanying drawings. GB2658177A 1978-05-23 1978-05-23 Electric circuits incorporating non-linear resistors Expired GB1586235A (en) Priority Applications (1) Application Number Priority Date Filing Date Title GB2658177A GB1586235A (en) 1978-05-23 1978-05-23 Electric circuits incorporating non-linear resistors Applications Claiming Priority (1) Application Number Priority Date Filing Date Title GB2658177A GB1586235A (en) 1978-05-23 1978-05-23 Electric circuits incorporating non-linear resistors Publications (1) Publication Number Publication Date GB1586235A true GB1586235A (en) 1981-03-18 Family ID=10245884 Family Applications (1) Application Number Title Priority Date Filing Date GB2658177A Expired GB1586235A (en) 1978-05-23 1978-05-23 Electric circuits incorporating non-linear resistors Country Status (1) Country Link GB (1) GB1586235A (en) Cited By (1) * Cited by examiner, † Cited by third party Publication number Priority date Publication date Assignee Title US4799125A (en) * 1986-09-05 1989-01-17 Raychem Limited Circuit protection arrangement 1978 1978-05-23 GB GB2658177A patent/GB1586235A/en not_active Expired Cited By (2) * Cited by examiner, † Cited by third party Publication number Priority date Publication date Assignee Title US4799125A (en) * 1986-09-05 1989-01-17 Raychem Limited Circuit protection arrangement US4807081A (en) * 1986-09-05 1989-02-21 Raychem Limited Circuit protection arrangement Similar Documents Publication Publication Date Title WO2007131762A2 (en) 2007-11-22 Power circuit with short-circuit protective circuit FR2655188B1 (en) 1992-02-07 HIGH VOLTAGE CIRCUIT BREAKER AT VARISTANCES. DE2060483A1 (en) 1972-06-15 Electric motor protection device EP0350825A3 (en) 1991-04-17 Electrical switch gear US3504233A (en) 1970-03-31 Electric circuit interrupting device with solid state shunting means US20200127453A1 (en) 2020-04-23 Dc high-voltage electrical installation and method for controlling a cut-off apparatus in such an installation GB1586235A (en) 1981-03-18 Electric circuits incorporating non-linear resistors WO1999017415A1 (en) 1999-04-08 Power breaker for power supply and distribution DE2522525A1 (en) 1976-12-02 Load disconnector with arc quenching in vacuum chamber - appropriate for operation in medium voltage range EP1449299A1 (en) 2004-08-25 Circuit arrangement for the reliable switching of electrical circuits DE1154555B (en) 1963-09-19 Electrical switchgear working with contacts DE102016213875A1 (en) 2018-02-01 Residual Current Device DE3317942C2 (en) 1987-07-23 DE2751451A1 (en) 1979-05-23 ELECTRIC SWITCHING DEVICE DE2702181C3 (en) 1980-03-27 Short-circuit protection circuit for devices that can be switched on or off via semiconductor switches, in particular for light control devices US2586544A (en) 1952-02-19 Variable impedance device DE2933399A1 (en) 1980-02-28 PERFORMANCE INTERRUPTER DE2320075A1 (en) 1974-11-07 PROTECTIVE CIRCUIT FOR ELECTRONIC EQUIPMENT AND COMPONENTS US3214677A (en) 1965-10-26 Circuit for controlling transient voltages to prevent premature triggering of semiconductors DE2552356B2 (en) 1978-07-20 Link circuit in integrated field effect transistor circuit technology GB858095A (en) 1961-01-04 Improvements in or relating to tap-changing switches DE4116948C2 (en) 2002-11-07 relay circuit GB1589071A (en) 1981-05-07 Electric circuit breakers SU148140A1 (en) 1961-11-30 Auto Multiband Bridge AT286460B (en) 1970-12-10 Diverter switch for a transformer Legal Events Date Code Title Description 1981-06-03 PS Patent sealed 1985-01-23 PCNP Patent ceased through non-payment of renewal fee
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