US3617807A - Current-limiting switch employing low-temperature resistor - Google Patents

Current-limiting switch employing low-temperature resistor Download PDF

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Publication number
US3617807A
US3617807A US39040A US3617807DA US3617807A US 3617807 A US3617807 A US 3617807A US 39040 A US39040 A US 39040A US 3617807D A US3617807D A US 3617807DA US 3617807 A US3617807 A US 3617807A
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Prior art keywords
resistor
switch
main switch
temperature
current
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Expired - Lifetime
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US39040A
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English (en)
Inventor
Fritz Kesselring
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Siemens AG
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Siemens AG
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/02—Details
    • H02H3/021—Details concerning the disconnection itself, e.g. at a particular instant, particularly at zero value of current, disconnection in a predetermined order
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
    • H01H33/002—Very heavy-current switches
    • H01H33/004—Very heavy-current switches making use of superconducting contacts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
    • H01H33/02—Details
    • H01H33/04—Means for extinguishing or preventing arc between current-carrying parts
    • H01H33/16—Impedances connected with contacts
    • H01H33/161—Variable impedances
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
    • H01H33/02—Details
    • H01H33/28—Power arrangements internal to the switch for operating the driving mechanism
    • H01H33/285—Power arrangements internal to the switch for operating the driving mechanism using electro-dynamic repulsion
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
    • H01H33/02—Details
    • H01H33/04—Means for extinguishing or preventing arc between current-carrying parts
    • H01H33/16—Impedances connected with contacts
    • H01H33/161—Variable impedances
    • H01H2033/163—Variable impedances using PTC elements

Definitions

  • This invention relates to circuit interrupters, and more specifically relates to circuit interrupters in which a currentlimiting resistance having a positive temperature coefficient of resistance is inserted into the circuit being protected during interruption of the circuit.
  • resistors which are inserted into a circuit to limit the current to be interrupted are well known, where such resistors can be inserted in the vicinity of a current zero in the circuit to be interrupted, Such resistors have been inserted into the circuit and their value increased as by a sliding contact arrangement which gradually inserts additional resistance to limit the current to be interrupted.
  • resistors have also been made of a material which has a high positive temperature coefficient of resistance, so that their resistance will automatically increase due to the heat generated in the resistor when the resistor is inserted in the circuit, thereby reducing or limiting the current in the circuit to be interrupted; Chemically pure iron has been used for such resistors and these resistors will exhibit an increase in resistance of aboutl2 times.
  • U.S. Pat. No. 3,495,056 illustrates an interrupter using a pure iron resistor where the resistor is heated from room temperature to a calculated temperature which the resistor can safely withstand during current-limiting operation.
  • the principle of the present invention is to cool the resistor which is to be inserted into a circuit which is to be interrupted to a temperature of from 4 K. to 80 K., but above the critical temperature at which the resistor material becomes superconductive and to heat this resistor to a temperature of about 373 K. during current-limiting operation.
  • the present invention is based, in part, on the discovery that the above-noted expression is followed only for temperatures down to about 70 C. Below -70 C., however, the resistivity changes according to a different and nonlinear relationship which is:
  • T 273 K. and ,1.
  • tungsten p. is about equal to 3.
  • the second discovery leading to the present invention is that the specific heat c decreases below -70 C. with the square of the absolute temperature, and, at very low temperatures, with the third power of absolute temperature.
  • k is a constant having a characteristic value for different materials. This constant and the relationship above permits the calculation for a resistor for a given application as will be later described. Typical values for the constant K are approximately as follows:
  • Tungsten K 0. 1 X10 Iron: 10.09Xl0' Copper: K OJZXIO' It can be shown that the absolute temperature T reached by the resistor after a time t is:
  • S is the current density in the resistor.
  • the resistor should be dimensioned such that reaches the highest possible value during the current-limiting interval in which current flows in the resistor so that the resistor will be heated to its maximum temperature T (and thus undergo a maximum resistance change). If r is the time permitted for current limiting action, then the resistor should be designed for an effective current density S which is:
  • the above integral can then be computed from the predicted wave shape of the current in the resistor and the cross section of the resistor wire can be computed.
  • An important aspect of the present invention is that' useful current-limiting resistors can be designed despite the low specific heat of the resistance materials at the low initial temperature since the heat produced in the low temperature region is slight.
  • there is a matching between the specific heat c' and resistivity P so that there is a relatively gradual increase in the temperature of the resistor, rather than a rapid increase which could cause an explosive evaporation of the cooling liquid surrounding the resistor.
  • Materials useful for the resistor are preferably extremely pure metals including tungsten, iron and copper.
  • FIG. 1 schematically illustrates an interrupter constructed in accordance with the present invention.
  • FIG. 2 illustrates the operation of the interrupter of FIG. 1 under short-circuit conditions on the line being protected.
  • FIG. 3 illustrates the operation of the interrupter of FIG. 1 with the contacts being synchronously operated to insert the resistor at a current zero.
  • FIG. 4 shows an interrupter arrangement which can be synchronously operated as illustrated in FIG. 3.
  • DESCRIPTION OF PREFERRED EMBODIMENTS tainer 4 is surrounded in known manner by a covering 7 which reflects the heat rays.
  • the leads 8 and 9 to the resistor 3 may also be cooled so that the heat loss by thermal conduction is as small as possible.
  • the design of resistor 3 can be determined as follows:
  • the peak let-through current i should not be greater than about (2-3) I
  • the time 1' of flow of current in the case of short circuit at 50 cycles is about ms. and at 60 cycles is about 4.5 ms.
  • the slope of the current i is known, the course of the reduced current i can be approximately determined. Ifq in cm. is the still-unknown cross section of the variable resistor wire, then by squaring and dividing by q it is possible to calculate the value:
  • FIG. 3 shows a short-circuit current i in the circuit, and its wave shape if undisturbed by the resistor.
  • the auxiliary switch 2 Shortly prior to the time current i, reaches a current zero N, the auxiliary switch 2 is closed and the main switch 1 is opened by means of a suitable synchronous control.
  • the cold resistor r connected in parallel with the main switch 1 is now so dimensioned that the rise of the recovery voltage (m /d1). is substantially reduced.
  • the value k which is controlling for this is defined by:
  • T is the arc time-constant.
  • the current zero N (FIG. 3) the current flows through the cold resistor 3, the resistance of which is thereupon increased by several orders of magnitude so that at the next current zero N the driving voltage u and the very small reduced current i, pass through zero simultaneously. Therefore, the reduced current i, can be easily interrupted. Since in the case of the reduction switch, following the techniques of FIG. 3, the energy conversion is much less than in the case of the switch operating, as shown in FIG. 2, the current limiting resistor 3 will be correspondingly smaller and simpler.
  • the maximum current slope is thus:
  • the final temperature T is:
  • the total resistance ratio is:
  • variable resistor 3 must have approximately the value r, at the start of an interruption. This result is obtained by closing the auxiliary switch 2 of FIG. I
  • the resistor r is preferably made of thin wires or thin strips connected in parallel. With a diameter of the wire of, for instance 0.3 mm., cooling times of fractions of a second can be obtained.
  • the use of thin wires and strips is also advantageous with respect to the skin effect, since the resistivity I in a cooled condition is vary small.
  • the interrupter is to be capable of several operations within a very short time interval, it is preferable to provide at least two circuits in parallel to the main switch 1, each consisting of a resistor 3 and auxiliary switch 2 in series therewith. These circuits are alternately connected whereby the resistor being connected on subsequent operations will have been cooled to the desired low temperature.
  • FIG. 4 One illustrative embodiment of such an arrangement is shown in FIG. 4.
  • temperature-dependent resistors 11 and 12 are cooled to a low temperature, as described above.
  • Main interrupter switch 13 is then provided with an electrodynamic drive consisting of a stationary coil 14 and a movable metallic plate 15 which is rigidly connected with the movable bridge contact 16.
  • Auxiliary switches 17 and 18 are provided for resistors 11 and 12, respectively, and are each provided with electrodynamic drives consisting of stationary coils l9 and 20, respectively, and the conductive bridge contacts 21 and 22 which simultaneously serve as secondary coils of their electrodynamic drive system.
  • Movable conductive contact discs 23 and 24 are provided which are connected with the pistons 25 and 26 of the delay pumps 27 and 28.
  • Contacts 23 and 24 are also adapted to be accelerated to the right responsive to energization of coils 19 and 20.
  • the contacts 23 and 24 are connected via a balance beam 29 with a freely movable fulcrum 30 to which a lever 31 is rigidly fastened.
  • Contacts 23 and 24 cooperate with stationary contacts 33-36 and 34-35, respectively.
  • Springs 37 and 38 are received in cylinders 27 and 28 and bias the pistons 25 and 26, respectively, to the left.
  • An auxiliary DC power source is then provided (not shown) which charges capacitor 39.
  • a three-electrode spark gap 40 is then provided in series with a capacitor 39 and can be fired in known manner upon the occurrence of a fault current.
  • Springs 41 and 42 are provided to bias open the auxiliary switches 17 and 18, respectively, so that these contacts will reopen some predetermined time after they are closed by their electrodynamic system.
  • the trigger electrode of spark gap 40 is energized from a suitable zero current anticipating circuit 40a, which is suitably coupled to the line being protected, as shown by dotted lines.
  • Circuit 40a may be any conventional type in which an output pulse is generated at some predetermined time prior to a current zero. Note, however, that the circuit of FIG. 4 could be operated outside of the current region, as described in FIG. 2.
  • the spark gap 40 fires and the capacitor 39 discharges through coil 14 of the main switch 13 and through coil of the auxiliary switch 18.
  • Auxiliary switch 18 closes and main switch 13 opens, whereby the current i is switched to the resistor 12.
  • the sequence of the closing of the auxiliary switch 18 and of the subsequent opening of the main switch 13 can be controlled by proper design of the movable masses of the switches. With the excitation of the coil 20, the contact 24 is accelerated toward the right and the piston 26 is also pushed to the right in opposition to the spring 38.
  • Auxiliary switch 18 then opens under the influence of the spring 42 and after a predetermined period of time, whereupon the resistor current is interrupted at the subsequent current zero.
  • FIG. 4 assume that an interruption occurred prior to the interruption described above, using resistor 11 and auxiliary switch 17.
  • a second switching operation using resistor 11 is possible only after the resistor 11 has cooled down approximately to the cold value r,,. This could be done by providing a conventional temperature-measuring device which prevents operation of switch 17 (and switch 18) until the temperature T, is reached.
  • FIG. 4 illustrates a lockout arrangement for switches 17 and 18 which uses damping pumps.
  • the auxiliary switch 18 is closed and the piston 26 moves to the right together with the disc 24.
  • the balance beam 29 rotates to a perpendicular position and the lever 31 reaches a horizontal position.
  • the piston 25 moves toward the left and-since the piston 26 is still approximately in the right-hand position-pushes the lever 31 and the insulating disc 32 downward.
  • the contact 23 engages contacts 33, 36, whereby the auxiliary switch 17 is again ready for operation.
  • the closing of the auxiliary switch 18, however, is prevented by the downwardly displaced insulating board 32 so that only auxiliary switch 17 can be actuated upon the next disconnection.
  • the resistivity of resistors is slightly increased by the magnetic field traversing the resistor material. This slight increase in resistance is generally unimportant to the use of the resistors in accordance with the invention.
  • the magnetic field strength can, however, be reduced to harmless values without difficulty by known magnetic shielding screening.
  • An arc interrupting device for an electrical circuit comprising at least one main switch and at least one resistor electrically connectable in parallel circuit therewith whose resistance increases with temperature and to which current flowing through said main switch is shifted upon the opening of said switch, characterized by means being present to cool said resistor under normal operating conditions to a temperature between 4 K. and K. and higher than the critical temperature of the material from which said resistor is constructed, and that as said circuit resistance material there is used a material having a resistivity which increases by at least times with a temperature increase'over the range of 20 K. to 373 K.
  • the arc interrupting device of claim 1 having at least one auxiliary switch in parallel connection to said main switch and in series connection with said resistor, characterized by means for opening said auxiliary switch under normal operating conditions when said main switch is closed and for closing said auxiliary switch upon directed opening of said main switch, and just prior to said main switch opening.
  • the arc interrupting device of claim 2 further characterized by means for closing said auxiliary switch substantially only when said resistor has cooled to a predetermined temperature.
  • the arc interrupting device of claim I particularly for use where high magnetic fields are present, characterized by magnetic screening means being present to shield said resistor from the effects of said fields.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Emergency Protection Circuit Devices (AREA)
  • Arc-Extinguishing Devices That Are Switches (AREA)
US39040A 1969-05-23 1970-05-20 Current-limiting switch employing low-temperature resistor Expired - Lifetime US3617807A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE1926972A DE1926972C3 (de) 1969-05-23 1969-05-23 Schalteinrichtung zur Strombegrenzung

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CH (1) CH509004A (de)
DE (1) DE1926972C3 (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5250508A (en) * 1990-09-14 1993-10-05 Gel Alsthom Sa Superconductor current-limiting apparatus
US5373205A (en) * 1992-12-29 1994-12-13 Cincinnati Milacron Inc. Method and apparatus for limiting motor current
US20080100974A1 (en) * 2006-11-01 2008-05-01 Rolls-Royce Plc Electrical current limiter

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2647590A1 (fr) * 1989-05-26 1990-11-30 Alsthom Gec Transformateur-limiteur de courant supraconducteur
FR2657194B1 (fr) * 1990-01-17 1993-12-31 Gec Alsthom Sa Disjoncteur de reactance a faibles surtensions.
DE19756624A1 (de) * 1997-12-19 1999-07-01 Abb Research Ltd Vorrichtung zur Überstrombegrenzung

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5250508A (en) * 1990-09-14 1993-10-05 Gel Alsthom Sa Superconductor current-limiting apparatus
US5373205A (en) * 1992-12-29 1994-12-13 Cincinnati Milacron Inc. Method and apparatus for limiting motor current
US20080100974A1 (en) * 2006-11-01 2008-05-01 Rolls-Royce Plc Electrical current limiter

Also Published As

Publication number Publication date
CH509004A (de) 1971-06-15
DE1926972B2 (de) 1974-12-19
DE1926972A1 (de) 1970-11-26
DE1926972C3 (de) 1975-07-24

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