US2066955A - Distance relay for the protection of electric plants - Google Patents

Description

Jan. 5, 1937.

R. WIDERGE 2,066,955

DISTANCE RELAY FOR THE PROTECTION OF ELECTRIC PLANTS Filed May 2, 1934 2 Sheets-$heet l l?- h iole r66,

Jan. 5, 1937. R. WIDEROE 2,066,955

DISTANCE RELAY FOR THE PROTECTION OF ELECTRIC PLANTS Filed May 2, 1934 2 sheets-sheet 2 Patented Jan. 5, 1937 UNITED STATES DISTANCE RELAY FOR THE PROTECTION OF ELECTRIC PLANTS Rolf Wideriie, Vinderen, near Oslo, Norway Application May 2, 1934, Serial No. 723,571 In Norway May 9, 1933 18 Claims.

Electric plants are frequently protected against short-circuitings by relays, wherein the time-lag of release increases proportionally to the impedance, reactance or resistance of the shortcircuiting circuit. Such relays, distance-relays, yield a very effective protection. They cut out the short-circuiting place selectively and with a very short time-lag of release.

However, it must be considered a very essential drawback in the distance relays made hitherto that the member determining the timelag of release is of a very complicated kind. Usually a plurality of meter devices, ohmmeters, clock works or the like connected together is used with a great number of movable parts. These relays are therefore very sensitive apparatus which require a frequent inspection, lubrication and cleaning. Therefore they in no way fulfil the requirements as to robustness and constant qualities made by the superintendents, and they have therefore been restricted hitherto to special, important transmission plants. The present invention has for its object a distance relay fulfilling all requirements as to the characteristic of the time-lag of release, has a minimum number of movable parts and is built up in a particularly simple and robust manner.

Fig. 1 shows the principle of the relay.

Figs. 2 and 3 show modifications.

Figs. 441 show several devices and further modifications which may be used in connection with the present distance relay.

The relay is illustrated diagrammatically in the drawings. a and b represent the conductors to be protected. The current flows from the current transformer 26 through an ordinary over-current magnet I over a pair of contacts 2 and back. In case of over-current or shortcircuiting in the plant the armature? of the over-current magnet is attracted. The contact at 2 is opened, and current now flows over the primary coil of a current transformer 4 and back. The secondary coil 5 of the current transformer i is series-connected with a bimetal 5 whicnwill be heated. To this bimetal is attached a latch l maintaining in open position an arm 8 with the releasing contact 23. However, the releasing motion of the bimetal is prevented by a voltage magnet 9 exerting an attracting force on an armature it! connected mechanically with the bimetal. This magnet 9 is over a voltage transformer 21 connected to the voltage U of the short-circuiting circuit a, b or a certain fraction thereof, and it prevents the motion of the bimetal latch I, aslong as the force produced by the voltage U on the armature I0 is greater than the force exerted by the curved bimetal 6. By means of iron saturation in the magnet circuit of the current transformer 4 (by the reduced iron cross sections II) and iron saturation in the magnet circuit (armature and core) of the voltage coil 9 it may be obtained that the current intensity in the bimetal isproportional to whereas the attracting force of the voltage coil v is proportional to U. (J and U are virtual values of current intensity and voltage of the circuit a, b).

In this case the force it; exerted by the bimetal will increase proportional to the time and the current intensity k1=ci.-t-.i. The relay releases, when this force k; rises beyond the force k2=c2-U produced by the voltage coil 9. Consequently, it may be put up for release Islic, or C1-T-J=O2-U, giving The time lag of release will therefore be direct proportional to i. e. to the impedance of the short-circuiting circuit a, b. In order that the time-lag of release be not dependent upon the temperature of the environs a bimetal i2 is arranged in known manner outside the circuit and heated only by the surrounding air to curve at temperature variations opposite to the bimetal 6 heated by the current, said bimetal I 2 being connected with the latter through a link l3. If the two bimetals produce equal and oppositely directed -iorces, the influence of the temperature of the environs will be quite equalized. In order to prevent the voltage coil 33 from becoming too hot and to reduce its constant voltampere consumption, it

may be suitable to supply full voltage to the coil the contact 24 of the over-current magnet l as indicated in Fig. 1.

For control the series resistance may also consist totally or partly of a milliamperemeter 2| or another current meter, whereby faults in the voltage circuit may be easily substantiated.

In case a. short-circuiting takes place in the plant a, b under control, it will be suitable to prevent the bimetal 6 irom becoming overheated or heated excessively. For this purpose the arm 4 when passing to releasing position after the release of the latch I may close a pair of contacts 25 which short-circuit the transformer 4. This is of special importance in case the opening time of the interrupters be comparatively long or the interrupters might be unsafe.

The air gap 22 oi the voltage magnet may be adjusted by a non-magnetic adjusting screw l4, so that in a simple manner the steepness of the characteristic of release may be altered.

In order to adjust the relay to the most favorable current interval in the input circuit, it may be suitable to divide the current coil i or 4 into two or more sections 43 and 44 which by the adjustment once for ever may be series or parallel-connected as shown in Fig. 2.

The relay described above has no special member for energy direction control. Such control may be obtained, as indicated in Fig. 1, by con necting the releasing contacts 23 in series with the contact 28 of a direction-relay. The current from the battery 30 therefore may act upon the releasing coil 29 of the interrupter only, when both contacts 23 and 28 are closed.

In order to make the relay insensitive to mechanical blows and shocks, it may be suitable that also the over-current magnet l locks the releasing contact 8 mechanically, for instance by moving an arm 42 (Fig. 1). In such case the relay will operate only, when the armature 3 of the over-current magnet is attracted. When the armature 3 returns, the arm 42 opens the releasing contacts 23.

The relay described hereinbefore will operate quite independently of the phase angle between current and voltage of the circuit a, b. If a certain phase-dependency is desired (for instance in certain angle intervals an approximate reactance-dependency), this may be obtained by a portion 34 of the windings of the voltage magnet 9 being a current coil under the influence of the short-circuiting current (Fig. 2) and by a suitable phase displacement between the two energizing currents of the voltage magnet being effected by means of an adjustable ohmic resistance as shown at 35.

The embodiments described above are suitable particularly in case a simple construction of the relay is of the greatest importance, whereas the exactness of the time-lag of release is of subordinate importance. As the voltage coil 33 (Fig. l) is energized by alternating voltage, vibrations of the armature l0 cannot be avoided, and these vibrations may under certain conditions cause an unexactness (of some tenth of a second) in the time-lag of release.

Hereinafter some embodiments are described, having for their purpose to avoid these vibrations and opening still further possibilities for increasing the efliciency of the relay.

As shown in Figs. 3, 4 and 5 the vibrations are suitably avoided by the use of rectified currents. The voltage coil 33 of the distance relay is connected over a. rectifier IE to the voltage transformer 21.

During one of the half cycles an exciting current flows over this rectifier and the current also in the second half cycle will flow further over the rectifier I6 on account of the self-induction of the magnetic circuit.

The magnetic flux thereby will be subjected. only to small variations. The attracting force on the armature III is practically constant and no detrimental vibrations can arise. As the wattless component of the exciting current and also the total losses of the magnetization are abolished the energy consumption of the voltage coil is so much reduced that it may also be connected to capacitive voltage members I! (condenser bushings etc.), when no voltage transformer is present. Figs. 4 and 5 illustrate two further examples of the diagram of the rectifier. In Fig. 4. the rectifier I8 is operative during one half cycle, the voltage being then connected to the upper half 45 of the voltage coil. In the other half cycle the rectifier I9 is operative, while the voltage forces the exciting current through the lower half 46 of the voltage coil. Consequently the connection has the same action as a double wave rectifying arrangement, and thereby produces a special constant magnetic flux. According to Fig. 5 the usual bridge arrangement of the rectiflers 51 is used. The arrangement also in this case is double-acting. This connection has the advantage that the total voltage coil is connected durably to the exciting voltage. Thereby a very small energy consumption is obtained.

In Fig. 2 is shown that the voltage magnet 9 of the relay may be acted upon by voltage and current by two coils 33, 34. This connection may be used advantageously in case the voltage magnet be excited by rectified currents. The advantages reside on the one hand in the additional load of the current transformer being very small by this additional excitation, and on the other hand it is possible to obtain by direct current excitation that the operation of the relay is independent of the phase relation between current and voltage.

In the following Fig. 6 shows a principal connection of this kind. Fig. '7 shows a charactcristic operation of these connections. Figs. 8-l1 show several embodiments.

In Fig. 6 2! denotes the terminals, to which the voltage transformer supplying the net work voltage to the distance relay is connected. The winding of the voltage coil proper is made in two halves 45 and 46, the one end of the voltage coil windings being connected together over two rectifiers l8 and I9 connected in series. The other ends are connected to an impedance 52. denotes the secondary coil of an auxiliary transformer whose primary coil bears auxiliary current corresponding to the net work current. The rectificrs 4"! and 48 serve to rectify the voltage supplied from the secondary coil 50. This connection operates in the manner that through the impedance 52 a current flows which is supplied from the secondary coil 50 and rectified by the rectiflers 41, 48. This current produces a voltage drop at this impedance. The current supplied at the terminals 21 from the voltage transformer and rectified by the rectifiers I8, l9 and flowing through the coils 45, 46, can commence to flow only, when the voltage at the terminals 21 has become high enough relatively to the said voltage drop. The characteristic of the relay, however, will consequently occupy the position shown in Fig. 7 by the straight line a, whereas a relay as described above has a charaooao'u 3 acterlstic according to the straightv line b in Fig. 'I

It will be shown in the following by means of a short calculation that by means of the connection according to Fig. 6 it will be possible easily to obtain locations of the characteristic according to the dotted straight lines c. For' Ki=ci-J-t 01 being a constant, J the net work current and t the time. The two voltage coils 45, 46 bear not only a current corresponding to the voltage at the terminals 21, but also a current corresponding to the voltageat the secondary coil 50 of the auxiliary transformer. If U means the voltage at the terminals 21 and c, and c3 two constants, and if further K2 means the force exerted by the voltage coil on the armature, then we have:

K2=C2-U+0a-J I As mentioned above, the distance relay releases, when the force exerted by the bimetal strip on the armature increases beyond the force exerted by the voltage coil. For the time-lag of release t then applies:

The last equation corresponds to the dotted straight line in Fig. 7.

A characteristic according to line 0 in Fig. '7 may also be obtained in other manners. Figs. ll-ll. show some connections for this purpose. In Fig. 8 the contacts49, encircled by dotted lines, are to be imagined-as short-circuited. The voltage coil of the relay has again two windings 45 and 46 which are connected in some other manner than that shown in Fig. 6. The partial winding 45 is supplied over the rectifiers I8, I!) from the voltage transformer connected to the terminals 2?. The partial winding 46 is supplied from the auxiliary transformer, whose secondary coil is again denoted 50. The rectifiers 41, d8 serve to rectify the currents of the auxiliary transformer. Another connection is shown in Fig. 9. The voltage coil of the relay consists, contrary to Figs. 6 and 8, of one winding only provided withanintermediate tapping so as to form two sections 65, 56. The secondary winding 50 of the auxiliary transformer is in series with a single rectifier ll".

The arrangements shown in Figs. 8 and 9 all operate in the manner that in addition to the direct current corresponding to the net-work voltage, also a direct current corresponding to the net-work current will flow through the voltage coil oi the relay respectively through the second winding. Therefore, as will appear from the above calculation, all these arrangements are suitable to impart to the distance relay a characteristic according to the straight line 0 in A further development of the inventive thought consists in connecting contacts of a wattmetric relay into the circuit over which the voltage coil of the relay or a part of this coil is supplied by a direct current, corresponding to the net-work current. Thereby may be obtained that the distance relay at one energy direction obtains a characteristic according to the lines a, b or to the'dotted line it in Fig. '7, whereas at the other energy direction an auxiliary supply of the voltage coil is obtained corresponding to the net-work current and produced by the wattmeter contacts, so that the relay characteristic at this reversed energy direction, obtains the location of the line 0 in Fig. 7, or is displaced still more upwards. The time to is then to be so dimensioned that it will be greater than the maximum timelag of release applying for the first named energy direction.

In Fig. 8 is indicated how the contacts 49 of the wattmetric relay may be connected.

Instead of this connection the contacts 49 may also be so arranged that they short circuit the primary or the secondary coil 50 of the auxiliary transformer at the energy direction imparting to the relay the characteristics a, b, d in Fig. 7 and again interrupt this shortcircuiting at the reversed energy direction, at which the characteristic c is desired.

Fig. 10 shows the complete distance relay diagram when using a direct current supply of the voltage coil corresponding to the network current, this supply serving to impart to the relay a different characteristic at different energy directions.

In Fig. 10 53 denotes the network conductors to be protected and which are combined with a current transformer 26 and a voltage transformer 21. In series with the primary coil of the intermediate transformer 4 are connected the current coils 54 of the wattmetric relay and the primary coil 54 of the auxiliary transformer 56. Therefore these coils are normally not excited and are supplied with current only at the attraction of the over-current magnet l and opening of the contacts 2. The contacts of the wattmetric relay are shown at 49. As a control of the voltage circuit of the relay a neon lamp 55 is indicated. Besides, all parts are denoted with the same letters as used in the foregoing figures. According to the energy direction the relay will show the characteristic 2) or c of Fig. 7.

Fig. 11 shows an arrangement of a polyphase relay. For the supply of each phase the arrangement of Fig. 8 is used. The contacts 49 are used only once and operate all three phases simultaneously.

If now, as the present invention proposes, the energy-direction-sensitive element is caused to influence upon the distance relay characteristic the advantage is obtained that the very weak contacts of the wattmetric relay are loaded only with a very low current, viz: with the direct current of the voltage coil corresponding to the net-work" current. This arrangement is therefore more advantageous than that, in which, as made hitherto in distance relays, the wattmeter contacts are connected into the releasing circuit for the oil switch. At this latter place the contact load will always be much higher than at the place proposed according to this invention. As a consequence most relay combinations working in this manner are using special intermediate relays to close the tripping contacts of the oil circuit breakers.

The invention is also greatly advantageousfor the protection of the electric equipment in the station in case a short-circuiting occurs between the sections to be protected by the relays (for instance on the bussbars). In this case the power flow will be directed against the bussbars and all the wattmetric relays will go into the blocked position. If now the contacts of the wattmetric relays are arranged in the tripping circuit of the oil circuit breakers, the whole protective system will be completely blocked, and there exists no bussbar protection. But according to the present invention the releasing of the distance relays will not be blocked but only delayed with the time to. This will therefore also be the tripping time for a short-circuiting on the bussbars, giving a very good bussbar protection.

In all connections described above all rectiflers are preferably dry rectiflers, for instance cuprous oxide or selenium-iron rectiflers.

I claim:--

1. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent on the current in said circuit and causing in case of shortcircuiting a heating of the thermal element, means dependent on the voltage of said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces so as to be actuated only when the influence of the force produced by the thermal element predominates that of the voltage-dependent force.

2. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a bimetal arranged for creating, when heated, a mechanical force increasing with the time, means dependent on the current in said circuit and causing in case of shortcircuiting a heating of the bimetal, means dependent on the voltage of said circuit, and causing an instantaneously acting force counteracting the force produced by the bimetal, and releasing means arranged to cause, when actuated, the release of current interrupter for said circuit and being under influence of the said two forces so as to be actuated only when the influence of the force produced by the bimetal predominates that of the voltage dependent force.

3. A distance relay for protecting an alternating current electric circuit in case of a short circuiting, comprising a bimetallic strip arranged for creating, when heated, a mechanical force increasing with the time, a transformer with primary and secondary coil, means dependent on the current in said circuit and connected to the primary coil of said transformer so as to cause in case of short-circuiting a current in said coil, a connection between the secondary coil and the bimetal to cause by the current produced in the secondary coil a heating of the bimetal, a voltage dependent electromagnet, means for supplying thereto a current dependent upon the voltage of said circuit and producing in the magnet an instantaneously acting force counteracting the force produced by the bimetal, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces so as to be actuated only, when the influence of the force produced by the bimetallic strip predominates that produced by the magnet.

4. A distance relay for protecting an alternating current electric circuit in case of a short-circuiting, comprising a bimetallic strip arranged for creating, when heated, a mechanical force increasing with the time, current supply means dependent on the current in said circuit, a transformer with primary and secondary coil, the primary coil being connected to said current supplying means and the secondary coil connected to the bimetal, the transformer being so saturated as to cause in case of short-circuiting a current in said coils proportional to the square root of the current to be controlled and heating the bimetal, a voltage electro-magnet, means for supplying thereto a current dependent upon the voltage of said circuit, the magnetic iron circuit of said magnet being so saturated that the current produces in the magnet an instantaneously acting force proportional to the voltage of said circuit and counteracting the force produced by the bimetal and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces so as to be actuated only when the influence of the force produced by the bimetal predominates that produced by the magnet.

5. A distance relay as set forth in claim 4, wherein the primary transformer coil is normally short-circuited by a pair of closed contacts, an electro-magnet operatively connected with a bridge-piece for said contacts, means dependent upon the current in the circuit to be controlled and supplying to said magnet under normal conditions a current insufiicient to cause the bridgepiece to open the contacts but causing in case of over-current the opening of the contacts and connecting thereby the primary coil to the last named means so as to supply the coil with current.

6. A distance relay as set forth in claim 3, wherein a second bimetallic strip not heated by current is so operatively connected with the current-heated bimetal as to produce at variations in the ambient temperature a force opposite to that produced simultaneously by the current-heated bimetal, in order to compensate the influence of such variations.

7. A distance relay as set forth in claim 4, wherein the primary transformer coil is normally short-circuited by a pair of closed contacts, an electro-rnagnet operatively connected with a bridge-piece for said contacts, means dependent upon the current in the circuit to be controlled and supplying to said magnet under normal conditions a current insufficient to cause the bridge-piece to open the contacts but causing in case of over-current the opening of the contacts and connecting thereby the primary coil to the last named means so as to supply the coil with over-current, normally open releasing contacts for closing current to release the current interrupter for the circuit being under control, and mechanically connecting means between the releasing contacts and said bridge-piece so as to maintain the releasing contacts in open position, as long as the bridge-piece is in position to maintain its contacts opened.

8. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent on the current in said circuit and causing in case of shortcircuiting a heating of the thermal element, means dependent on the voltage of said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces so as to be actuated only when the influence of the force produced by the thermal element predominates that of the voltage dependent force, the said voltage dependent means 'being a voltage coil combined with rectifiers-causing a direct current to magnetize said coil.

9. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent upon the current in said circuit and causing in case of shortcircuiting a heating of the thermal element, an electromagnet arranged to be magnetized by direct current dependent upon the voltage and the current of said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces, so as to be actuated only when the influence of the force produced by the thermal element predominates that of the counteracting force.

10.'A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent upon the current in said circuit and causing in case of shortcircuiting a heating of the thermal element, an electromagnet arranged to be magnetized by direct current dependent upon the voltage and the current of said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces, so as to be actuated only when the influence of the force produced by the thermal element predominates that of the counteracting force, said electromagnet being provided with coils supplied through rectifiers with direct current in such a manner that the current flowing in said coils depends not only upon a direct current corresponding to the voltage of the circuit under control but also upon a direct current corresponding to the current of said circuit.

11. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent on the current in said circuit and causing in case of shortcircuiting a heating of the thermal element, means dependent on the voltage of said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces so as to be actuated only when the influence of the force produced by the thermal element predominates that of the voltage dependent force, the said voltage dependent means being a voltage coil combined with rectifiers causing a direct current to magnetize said coil,

an impedance, further rectifiers, means for supplying current corresponding to the network voltage, and means for supplying current corresponding to the network current, the said rectiflers, impedance and current supplying means being so connected together that a voltage-dependent direct current flowing through said coil flows also through the impedance and a current-dependent direct current flows through the same impedance.

12. A distance relay as set forth in claim 11, wherein the voltage-dependent means being a magnet energized by two separate coils connected between the ends 01 the impedance, two series-connected rectifiers inserted between the other ends of the magnet coils, the lead connecting the rectiflers being connected to one terminal of the means supplying current proportional to the network voltage whose other terminal is connected to a middle tapping of thesaid impedance, two series-connected rectifiers connected between the ends of the impedance, and a supply coil supplying current corresponding to the network current and connected between the above-mentioned middle tapping and the lead connecting the two last-mentioned rectifiers.

13. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a

mechanical force increasing with the time, means dependent on the current in said circuit and causing in case of shortcircuiting a heating of the thermal element, means dependent on-the voltage of said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces so as to be actuated only when the influence of the force produced by the thermal element predominates that of the voltage-dependent force, the voltage-dependent means being a magnet coil which consists of two separate parts, one coil part being combined with two series-connected rectifiers inserted between the ends of said coil part, means for supplying current corresponding to the network voltage being connected between a middle tapping of the said coil part and a lead connecting both rectifiers, the second coil part being combined with two further oppositely arranged rectifiers and a supply coil which is in series with these rectifiers and arranged for supplying current corresponding to the network current, the second coil part being inserted in a conductor between a middle tapping of the said supply coil and a lead connecting the last-named rectifiers.

14. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent upon the current in said circuit and causing in case of shortcircuiting a heating of the thermal element, an electromagnet, rectifier means for energizing said electromagnet by direct current from said alternating current circuit in dependence upon the voltage and the current of said circuit and for causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the

release of a current interrupter for said circuit and being under influence or the said two forces, so as to be actuated only when the influence of the force produced by the thermal element predominates that of the counteracting force, a wattmetric relay being arranged to control the current-dependent parts or said magnetizing means and being itseli energized by the current and voltage of the circuit under control so as to bring said current-dependent magnetizing means into action, when the powerflow in the circuit under control has a special direction.

15. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent on the current in said circuit and causing in case of short-circuiting a heating of the thermal element, means dependent on the voltage 01' said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release or a current interrupter for said circuit and being under influence of the said two forces so as to be actuated only when the influence of the force produced by the thermal element predominates that of the voltage-dependent force, the voltage-dependent means being a magnet coil which consists of two parts, one coil part being combined with two series-connected rectiflers inserted between the ends oi said coil part, means for supplying current corresponding to the network voltage being connected between a middle tapping of the said coil part and a lead connecting both rectiflers, the second coil part being combined with two further rectiflers and a supply coil which is in series with these rectifiers and arranged for supplying current corresponding to the network current, the second coil part being inserted in a conductor between a middle tapping of the said supply coil and a lead connecting the last-named rectiflers, the said conductor containing between the supply coil and the last-named middle-tapping contacts of a wattmetric relay.

16. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent on the current in said circuit and causing in case 01' shortcircuiting a heating of the thermal element, means dependent on the voltage of said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two iorces so as to be actuated only when the influence oi the force produced by the thermal element predominates that of the voltage-dependent force. the voltage-dependent means being a coil combined with a current supply coil which is in series with a rectifier and arranged for supplying current corresponding to the network current, the exterior terminal of the supply coil and that of the rectifier being connected to the respective ends of the magnet coil, two seriesconnected rectiflers being also connected between the said external terminals, means for supplying current corresponding to the network voltage being connected between a middle-tapping oi the magnet coil and a lead connecting the two last-named rectitlers.

17. A distance impedance time relay for protecting an alternating current electric circuit in case of shortcircuiting, comprising a thermal element arranged for creating, when heated, a mechanical force increasing with the time, means dependent on the current in said circuit and causing in case of shortcircuiting a heating of the thermal element, means dependent on the voltage of said circuit and causing an instantaneously acting force counteracting the force produced by the thermal element, and releasing means arranged to cause, when actuated, the release of a current interrupter for said circuit and being under influence of the said two forces so as to be actuated only when the influence of the force produced by the thermal element predominates that of the voltage-dependent force, the voltage-dependent means being a coil combined with a current supply coil which is in series with a rectifier and arranged for supplying current corresponding to the network current, the exterior terminal oi the supply coil and that 01 the rectifier being connected to the respective ends of the magnet coil, two series-connected rectifiers being also connected between the said external terminals, means for supplying current corresponding to the network voltage being connected between a middle trapping of the magnet coil and a lead connecting the two last-named rectifiers the device comprising the current supply coil and the rectifier containing in series also contacts of a wattmetric relay.

18. A relay as characterized in claim 13, arranged in more than one phase of a three-phase network to be controlled, the devices consisting of rectiflers, supply coil and the magnet coil connected to the lead between the rectiflers, being connected in parallel with each other and with a pair of contacts arranged to be actuated by a common wattmetric relay to control the power direction in the said three phases.

ROLF WIDERDE.

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