DE2510322A1 - Cold conductor structural element - contg. current-conducting body of vanadium sesquioxide doped with preg. chromium oxide or aluminium oxide - Google Patents

Abstract

Passive, electrical cold-conducting structural element with 2 terminals and a +ve resistance temp. coefft., contains a current-conducting body (1) of V2O3 doped with 0.1-5 mol.% of another metal oxide. Pref. (1) has nominal compsn. (V1-xCrx)2O3 where 0.005 = x =0.02, or (V1-yAly)2O3 where 0.005 = y =0.02, and in an esp. cylindrical or prismatic sinter-body, esp. having density >3 g/cm2 and wt. 1-20 g. Structural element is pref. used as heat-controlled overcurrent fuse element at current conducting body temp. of 20-200 degrees C, esp. with a switch in series or in parallel. Transmission values 1000-17000 A2 sec can be achieved when using structural element at current 15-100 A and operating voltage 220 v. Transmission integral 12(t).dt of power pack protected for temp.-dependent resistance for 6-100 A, 50-400 v, short circuit efficiency factor cos circle with radical sign is nearly equal 0.85 is 17000 A2 sec (where to is moment of current rise, ta is moment of current path disconnection and 1(t) is line current).

Description

PTC thermistor component The invention relates to a passive electrical Component with two connections and a positive temperature coefficient of resistance, as well as a process for its production and a special use thereof, Components of the type mentioned are as. PTC thermistor known (e.g. DT-OS 2'242'767). They are good conductors at low temperatures and bad conductors at higher temperatures. They are used, for example, as temperature sensors or, for example, in switchgear to support the mechanical switch when a circuit is interrupted used (e.g.

US-PS 2,978,505 for BaO and BaTiO3, DT-AS 1,204,302).

It is known from basic research (e.g. J. Phys.

(Paris) 32, 1971, pp. C1-1079 to C1-1085, Phys. Rev. Lett.

23 (15 Dec. 69), 1384-1387, Phys. Rev. B 7 (1 March 1973), 1920-1931), that chromium-doped vanadium sesqui9xide of the nominal composition (V0.99Cr0.01) 2O3 at about minus 1000C from an isolating, antiferomagnetic state by leaps and bounds passes into a metallically conductive state, and from this metallically conductive State at around room temperature into a magnetically disordered isolator state.

However, this material could still be used in technical components today Not used.

In general, however, none of the known PTC thermistor components has yet been able to do so where higher rated currents and / or outputs are used successfully to influence, in particular to switch. This is mainly due to the fact that the known PTC thermistor components even in their "good" conductive state have such a large resistance value that when loaded with the rated current they become unbearable Losses result. In addition, the voltage resistance of the well-known PTC thermistor components only slightly.

On the other hand, there has long been a great need for inexpensive ones and space-saving electrical components with a positive temperature coefficient for larger N.nnstrflwts and / or services, for example instead of or together with conventional fuses or automatic circuit breakers ensure such a network protection that in the event of a short circuit on the one hand the Passage value is as low as possible, but on the other hand the response characteristic so that there are no intolerable switching overvoltages and the possibility of a Selective protection exists.

It is the object of the present invention to create a component which remedies the above need, the component in particular to be used as an overcurrent fuse element, and in particular small ones Passage values are aimed for, as well as great flexibility in terms of adjustment the operating data and the network protection selectivity. This task is carried out according to the invention solved in that the electrical component of the type mentioned the current-carrying body made of vanadium sesquioxide (V203) with an addition of 0.1-5 Mól-t consists of another metal oxide.

Preferably the current-carrying body should have the nominal composition (Vl-xCrx) 2O3 with 0.005 # x # 0.02 and a sintered body with a density of more than 3 g / cm, the one with two large metal electrodes ohmic (lock-free) is contacted.

Such a component has a steep rise in electrical Resistance increases with increasing temperature. If this increase is at a medium Temperature Tc takes place, then Tc for x # 0.005 is about 80 C and for xh 0.0i at 0 about 0 C. Tc shifts to smaller values with increasing chromium doping. On the other hand, the electrical resistance of such a component is at rated current load sufficiently low.

If such a component at rated currents of about 15 A to about 100 A, and operating voltages around 220 V are used, they are in fact forward values from 1000-17'000 A² sec can be achieved, which was previously not possible. With the aforementioned Operating data is the permeability value of a conventional automatic circuit breaker ("Deion" switch) at around 30,000 A2sec.

The component is placed in the current path of the power supply unit to be protected switched, and the cooling of the element and the element itself are designed in this way and dimensioned so that, in the event of overcurrents, the resulting heat loss hits the component before half a period of the supply voltage has elapsed to a temperature above Tc brings.

Further features and advantages of the invention emerge from the following Exemplary embodiments explained with reference to drawings. It shows: Fig. 1 shows a component according to the invention in longitudinal section, FIG. 2 shows the specific resistance 'of a component according to the invention as a function of the temperature T of the current-carrying Body, Fig. 3 the idealized course of the electrical resistance R of a lying in a current path component according to the invention as a function of the time t when a short-circuit current occurs, Fig. -4 a cascade circuit three differently dimensioned components according to the invention with associated R (t) curve in the event of a short circuit, FIG. 5 shows a component according to the invention with a trapezoidal shape Longitudinal section and associated R (t) curve in the event of a short circuit, FIG. 6 shows a component according to of the invention with a concave face and associated R (t) curve in the event of a short circuit, 7 shows a component according to the invention with a convex end face and associated R (t) curve in the event of a short circuit, FIG. 8 shows a component according to the invention in series with a switch, FIG. 9 shows a component according to the invention with a serial counter and a parallel fixed resistor, FIG. 10 shows a component according to the invention with a series switch and a parallel switch, and FIG. 11 shows a component according to the invention with a parallel fixed resistor and a parallel lying switch, as well as a serially lying switch.

The component shown in Fig. 1 according to the invention has a current-carrying body 1, which consists of sintered (VO 995 Cr) 20 powder, has a cylindrical shape., and 0.005 3 on both end faces over the entire surface with, metal electrodes 2 and 3 is contacted ohmically or without blocking.

The electrodes 2, 3 are made of copper or also hard solder. they are alloyed onto the sintered body 1. It is between the sintered body 1 and the Electrodes 2,3- a thin layer of titanium is applied, e.g. by vapor deposition of Titanium on the sintered body. This results in the alloy at the contact point a titanium oxide-containing vanadium oxide layer between the electrode and the sintered body, which conducts well. Instead of evaporating the titanium in metallic form, it can can also be applied to the sintered body in the form of titanium hydride, TiH2, which decomposes to titanium when the electrodes are alloyed.

Instead of alloying the electrodes 2, 3 on the sintered body 1, you can they are also soldered, pressed, sprayed or vapor-deposited in a known manner Always make sure that they work well with the sintered body form conductive ohmic contact. Nickel-chromium is also advantageously used for vapor deposition 60/40 used as electrode material.

The sintered body 1 has an insulating surface on its outer surface Protective layer 4, e.g. made of epoxy resin.

In intimate contact with the electrodes 2,3 are heat sinks 5,6 e.g. made of copper or aluminum. Cooling plates are also used for smaller components or cooling fins a suitable coolant, e.g. water.

d2 # Both the area F = of the cross section of the sintered body 4 1, as well as its length 1 are of great importance for the response characteristics of the component. The ratio 1 / F determines the resistance of the component in the cold state, while the product 1.F determines its mass at a given density and thus determines its thermal inertia.

For small values of l / F, the component is in the cold state a small resistor so that the power dissipation under current load is low. However, when a short-circuit current starts, the element only switches relatively slowly to higher resistance values, so that the achievable conduction value is still is relatively large.

For large values of 1 / F, on the other hand, there is the electrical resistance and thus the power loss resulting from the current load is greater, but switches the element much faster, and extremely small transmission values can be achieved.

Regardless of cold resistance, the response speed and the resilience of the component. Change in mass at one for the practical constancy of the density, i.e. its volume, can be varied.

For low-voltage fuses, the mass of the sintered body is advantageously between 1 and 20 g.

The permeability values QO are defined as follows: where i (t) is the electrical current that passes through the sintered body 1 and is dependent on the time t, t0 is the point in time at which the short-circuit current begins, and t is the point in time at which the current path is interrupted, i.e. when i (t) = 0 .

Correspondingly, the response value Qa is defined as follows: where ta = time of onset of the change in resistance of the component.

In addition to 1 / F and 1.F, the type of cooling also has an influence Q and QO, also the shape of the sintered body 1, and the type of circuit in the current path.

The composition (Vl-xCrx) 2O3 with 0.005 # x # 0.02 is therefore particularly advantageous because it eliminates the components that are important for practice special cooling for lower temperatures can be generated.

Before, however, further electrical properties, effects and possible uses of the component according to the invention are given, two examples will first be given indicated for the advantageous production of two components according to the invention are: Example 1 A component is to be manufactured whose current-carrying Body 1 nominally consists of (V0.995Cr0.005) 203. Nominal means that the specified composition refers to the weighed amount.

For this purpose, vanadium pentoxide (V2 0) is used in a reducing atmosphere, 5 e.g. hydrogen atmosphere, heated and thus reduced to vanadium sesquioxide (V203). The temperature is initially 6000C for 2 hours, then 10000C for 6 hours.

The V203 powder obtained in this way becomes intimate with Cr203 powder to 0.5 nominal% mixed and ground wet in a ball mill.

The mixture obtained becomes hydrostatic or uniaxial to become circular-cylindrical Components of the desired cross-sectional area E and length 1 pressed, with Milling added polyethylene glycol ate the press additive the strength of the compact elevated.

The pressing is seen at a pressure of about 2-3 k-bar.

Thereafter, the compact is placed in a controlled atmosphere Oxygen partial pressure sintered at high temperature. Doing so, at the same time with sintering, a homogeneous distribution of the chromium is also achieved. For the sake of maintenance of a very small and constant partial pressure of oxygen becomes a compound Atmosphere is used, a gas mixture of H2 / H20 or CO / CO2 being advantageous has proven.

The sintering temperature is e.g. 1400 ° C and the sintering time is e.g. 24 h chosen. Under these conditions, vanadium sesquioxide is at partial pressures of oxygen stable between 10-6 and 10'15.5 atm.

In order to achieve high densities and good strength of the sintered bodies, the oxygen partial pressure is advantageously chosen so that it is only slightly greater is the low-oxygen limit of the stability range of V2O3 at the selected Sintering temperature. This is achieved, for example, by using pure hydrogen Water of temperature 0 0C is passed.

The high densities and strengths that can be achieved in this way make it possible at all only possible, the chromium-doped vanadium sesquioxide for a component in question standing type to use.

After completion of the sintered body 1, this, 2. B.

by alloying, as described above, with the large-area Metal electrodes 2.3 contacted.

Example 2 A component is to be produced whose current-carrying Body 1 nominally consists of (V0.992 Al0.008) 203.

To do this, proceed exactly as described in Example 1, only with the difference that a part of Al 203 is added to the V203 powder instead of Cr203 will.

Components according to the invention can be particularly advantageous than thermal Controlled overcurrent fuse elements are used, the temperature of the Sintered body 1 by appropriate control of the electric current (t) generated heat loss and adapted heat dissipation via the cooling device itself moved between 200C and 200 0C.

The dependence of the specific resistance> (#cm) on the temperature T (OC) of the sintered body 1 is shown in FIG. The sintered body is made here 1 from (V0.995Cr0.005) 2 ° 3 with a density of 5 g / cm³. T0 is the operating temperature at nominal current load and T is the mean temperature at c at which the element "switches".

In Fig. 3, the top is the circuit symbol of the component according to the invention shown is a non-linear resistance that changes in the same direction as the temperature. If this component is loaded with a nominal electrical current, which at the time t0 changes into a short-circuit current, the element speaks after a delay time t at time ta and switches - in the idealized case shown here -. by leaps and bounds from the nominal resistance RN to its short-circuit resistance RK The ratio RN / RK is referred to as the resistance stroke and is at the components in question between 20 and 1000.

- An adaptation of the components to the operating data (nominal current, Operating voltage), - a suitable response and switching characteristic for the purpose of avoidance of excessively large switching overvoltages and QO on-state values, and - the possibility selective protection are achieved - through the design and / or dimensioning of the sintered body 1, - the design and arrangement of the cooling., and / or - the Combination with ohmic resistances and / or switches.

With the exception of cooling, these possibilities are shown in the figures 4 to 11: In Fig. 4, a cascade circuit is made up of different Components shown according to the invention. The Elements are designed in such a way that they respond one after the other, as shown in the curve will. There is a temporal lubrication of the switching compared to the intrinsic Material properties achieved without, however, when fully switched through of all elements the total resistance stroke changes.

A similar time from lubrication of the switching results from a suitable shape of the sintered body 1, as shown in Figures 5 to 7 is shown. As can be seen, not only the duration of the connection can are influenced, but also the response characteristics in detail.

The sintered bodies shown in FIGS. 5 to 7 are these are disks designed as shown.

The resistance value RK that the component according to the invention at Short-circuit current is sufficient to briefly reduce the short-circuit current (within a half-wave). However, there can be no galvanic connection with the component Separation to be achieved. In addition, the residual current would continue to flow in the Rule of further, possibly impermissible heating of the structural element to lead.

In practice, the components are therefore used to protect the network used with switches.

In Figure 8, the component is in series with such a switch S. The use of the component R has the great advantage that the switch S is not designed as a circuit breaker with an arc extinguishing chamber has to be, but can be a simple blank switch. The component 'R ensures to ensure that the current flowing through the arc after the contact pieces have been separated is reduced very quickly- 'and the voltage that returns after the zero crossing cannot cause reignition, or in other words, the follow current at next zero crossing is interrupted.

A particularly preferred circuit form is shown in FIG. 9. In this, a fixed resistor R p is connected in parallel with the component R. To this Way is avoided that the component R after switching into the high resistance State is thermally overloaded. The switch S can, in turn, be designed in a very simple manner be.

In Fig. 10, instead of the parallel fixed resistor R, the p Fig. 9 a thermally or magnetically detachable switch 5 p is provided. To this In the case of nominal current, the component R does not carry any current at all. Only when In the event of a short circuit, the switch Sp is triggered, the current commutates to the element R which then increases its resistance value and a largely load-free switching of the switch S allows.

The cold resistance of the component R is chosen so that when Triggering the switch 5 in this no arc arises.

FIG. 11 shows a combination of the circuit forms from FIG.

9 and 10 shown.

In all of the embodiments of FIGS. 8-11, the switch S can also voltage-building, e.g. a Deion switch, and thus in the current-limiting process take part.

The circuit forms of FIGS. 9 and 11 are described below with reference to FIG Dimensioning examples further explained: Example A circuit as shown in Fig. 11 was dimensioned and operated as follows: Mains at nominal load: Ieff = 100 A, Veff = 220 V, f = 50 Hz N N Mains in the event of a short circuit: eff IK = 6000 A, cos # = 0.85, Rnet = 31.2 m a, Lnet = 61.5 H.

Trip integral switch Sp: Parallel resistance Rp = 1.0 # Switch S: Galvanic isolator, without voltage build-up Component R: Shape: Circular cylinder Density s = 5 g / cm³ Specific heat c = 0.8 Wsec / g grad Specific resistance at nominal current # N = 5 # 10 -2 # cm cross-sectional area F = 2.7 cm length 1 = 9.4 mm 3 volume V = 2.54 cm mass M = 12.7 g T0 # 200C (Tmax c Tc) / (Tc - To) = 5 with Tmax = maximum temperature, which the component is subject to a short circuit.

Cold resistance RN = 17.55 m resistance lift h = RKIRN = 25 No special Cooling.

E s was found to be the permeability value and as response value The example shown relates to symmetrical short-circuit phase angles, i.e. about the worst case. When switch 5 responds, the voltage drop is only p 20 V, so that no arcing occurs in this switch.

The example shows that with the given. Network the requirement QO = 17,000 A²sec with a resistance swing h = 25 through the circuit according to Fig. 11 can just be met. With a slightly larger stroke (about h # 30.) can however, the parallel resistor R can be omitted, as shown in p. 10, with the same QO.

Example B A circuit as in Fig. 9 was dimensioned as follows and operated: Mains at nominal load: eff = 16 A, Veff = 220 V, f = 50 Hz N N mains in the event of a short circuit: eff IK = 1000 A, cos d = 0.85, network - 187 m 1l, L network = 369 µH.

Parallel resistance R = 643 m ii p switch S: zero-crossing disconnector without stress build-up component R: shape: circular cylinder 3 density s = 5 g / cm specific Heat c = 0.8.Wsec / g grad Specific resistance at nominal current 9 N = 5 # 10 -2 # cm Cross-sectional area F = 1.25 cm length 1 = 4.38 mm volume V = 0.548 cm3 mass M = 2.74 g To # 500C (TmaX - Tc) / (Tc - T0) = 5 cold resistance RN = 17.53 resistance stroke h = 200.

E s resulted as the let-through value QO # 1000 A2²sec and as the response value Q: 500 A2sec.

a The power loss in element R at nominal current is NO = 4.5 W and must be derived from a cooling device so that the Temperature of the element not increased above T.

0 The example shows that with a resistance change of h = RK / RN = 200 for smaller rated currents <1N # 25A), i.e. for the majority of the Final fuses in distribution networks, an effective suppression of short-circuit currents can reach. The switch S has no other task than the interruption of the Follow current at the next zero crossing.

With a prospective short-circuit current, a half-wave has a QO = 10,000 A2sec. Prospective short-circuit current is the unimpeded short-circuit current according to the settling.

Example C A circuit as in Fig. 9 was dimensioned as follows and operated: Mains at nominal load: as in example B Mains in the event of a short circuit: Ieff = 6000 A, cos # = 0.85, K mains = 31.2 mA, L mains = 61.6 tH parallel resistance R = 280 m p switch S: as in example B Component R: shape, density, specific heat, specific resistance at nominal current, resistance swing and O ' (Tmax TC) / (Tc - To) as in example B-.

- 2 cross-sectional area F = 2.58 cm length 1 = 2.45 mm volume V = 0.63 cm3 mass M = 3.16 g cold resistance RN = 4.7.5 m The result was the permeability value QO L 16'140 A2 and as response value Qa = 11'000 A2 sec.

The power loss in element R at nominal current is NO = 1.2 W. and must be dissipated by a suitable cooling device to keep the temperature of the element is not increased to above T 0.

With a prospective short-circuit current, a half-wave has 360,000 A2sec.

Example D If higher power losses NO are permitted in element R. are, in this way the permeability value QO can be pushed down considerably further will.

This shows the following re-dimensioning of example C: parallel resistance R = 652 m p component R: cross-sectional area F = 1.40 cm2 length 1 = 2.67 mm 3 volume V = 0.374 cm Mass M = 1.87 g Ka; lt resistance RN = 9.5 (all values not mentioned are the same as in example C.) The result was 41s transmission value Q0 # 4565 Å sec and as response value Q = 4000 A sec.

The power loss in element R at nominal current is NO = 2.4 W. and must be dissipated by a suitable cooling device to keep the temperature of the element is not increased to above To.

As can be seen particularly from Examples C and D, can consistent. Network parameters through different dimensioning of the components R and R the response value a p and the conduction value QO vary over a wide range will.

This makes it possible to use different levels as shown in FIG. 9 to be connected in series with good selectivity, i.e. when a At first level, the others remain in charge. For this purpose, the let-through value QO becomes the response level made smaller than the threshold Q of the upstream stages. With larger ones Nominal currents IN> 25 A in circuits according to FIG. 9 with a resistance change h s 200 with a simple zero-crossing disconnector S is either the conduction value QO or the power loss Ng at rated current is impermissibly high. However, if instead If a voltage-building circuit breaker is used for the disconnector, see below this supports the current limitation effectively and thus relieves the element ' R. Such hybrid systems, which consist of resistance-building components according to the invention and voltage-building switches are composed, can be up to substantially Use higher rated currents successfully. In circuits as in Fig. 9 is the upper limit at about 100 A, with circuits as in FIG. 11 is a switching of several 1000 A possible in principle, with only switch S building up voltage is. Basically, there are two possibilities for mutual adaptation: - The component R responds first and the switch S then suppresses the follow-up current so that the element R is not thermally overloaded.

The switch S responds first and the element R supports afterwards the voltage build-up in switch S due to its resistance swing.

An optimal mutual support of the two elements S and R results from almost simultaneous response.

Claims (27)

Patent claims Passive electrical component with two connections and one positive Resistance temperature coefficient, characterized in that the current-carrying Body (1) made of vanadium sesquioxide (V203) with an addition of 0.1-5 M <i-% one-it- other metal oxide. 2. Component according to claim 1, characterized in that the current-carrying end Body (1) has the nominal composition (V1 xCrx) 2 ° 3 with 0.005 # x # 0.02. 3. The component according to claim 1, characterized in that the current-carrying Body (1) has the nominal composition (V1 yAly) 203 with 0.005 # y # 0.02. Ii. Component according to Claim 1, characterized in that the current-carrying Body (1) is a sintered body. 5. The component according to claim 11, characterized in that the sintered body has a cylindrical or prismatic shape, and the end faces on their metal electrodes (2, 3) are in contact over the entire surface without blocking. 6, component according to claim 5, characterized in that between the sintered body and the metal electrodes (2, 3) with heating at the contact surface of the sintered body (1) a highly conductive metal oxide-forming metal is provided is. 7. The component according to claim 6, characterized in that the metal titanium is provided between the sintered body and the metal electrodes (2, 3). 8. The component according to claim 1, characterized in that there is a Has cooling device (5, 6). 9. The component according to claim 4, characterized in that the density of the sintered body is greater than 3 g / cm³. 10. Component according to claims 2, 4, 5 and 9, characterized in that that the mass of the sintered body is between 1 and 20 g. 11. Component according to claims 4 and 5, characterized in that that the end faces of the sintered body (1) are not parallel to one another and / or none Levels are. 12. A method for producing a component according to claim 1, characterized in that Vanadiur-Sesqudoxid (V203) with the desired additive of the other metal oxide is ground, the mixture obtained is then pressed and sintered, and the obtained sintered body is then contacted with the metal electrodes will, 13. The method according to claim 12, characterized in that a V203 powder is generated by heating V205 in a reducing atmosphere, 14. Procedure according to Claim 12, characterized in that V O.3 and Cr 203 powder are intimately mixed and then ground 23 wet. 15. The method according to claim 14, characterized in that the Powder mixture together with a pressing additive, e.g. Polyethylene glycol, is pressed. 16. The method according to claim 14, characterized in that the press body in an atmosphere with controlled partial pressure of oxygen at one temperature is sintered at over 10000C for more than 0.5 h. 17. The method according to claim 16, characterized in that the oxygen partial pressure is little greater than the oxygen-poor T.imite of the stability range of V203 at the selected sintering temperature. 18. The method according to claim 17, characterized in that for the purpose Maintaining the very small, constant partial pressure of oxygen as a compound Atmosphere a gas mixture of IS2-H2O or CO-CO2 is used. 19. Use of a component according to claim 2 as a thermally controlled Overcurrent fuse element at temperatures of the current-carrying body (1) between 200C and 2000C. 20. Use according to claim 19, such that the component as an overcurrent fuse element in an alternating current network when the network current rises to the maximum short-circuit current a change in its effective resistance before half a period of the alternating voltage has elapsed by more than the PaktorPO. 21. Use according to claim 19, such that the passage integral of the power supply unit protected by the temperature-dependent resistor for nominal currents in the range of 6 - 100 A, operating voltages of 50 - 400 V, a prospective short-circuit current of maximum 6000 A and a short-circuit power factor cos # # 0.85 is less than 17000 A2 sec, whereby t0 = time of current increase, t = time of current path interruption, and 1 (t) 5 mains current. 22. Use of a component according to claim 19 together with one switch connected in series. 23, use according to claim 22 together with one for the component ohmic resistor connected in parallel. 24. Use according to claim 23 together with one for the component and the switch connected in parallel with the ohmic resistor. 25. Use according to claim 22 together with: one for the component switch connected in parallel. 26. Use according to claim 1Q in selective network protection. whereby the permeability integral 2 i2 (t) dt and the response integral J i (t) dt of the component by shaping and / or a Dimensioning of the insulating body is adapted to the selectivity requirements, where t = time of the current rise, t5 = time of interruption of the current path, ta = time of response of the component, and i (t) = mains current. 27. Use according to claim 23, wherein the switch is a voltage-building Switch is.