DE355310C - Overcurrent switch to protect motors - Google Patents

Description

GERMAN EMPIRE

ISSUED JUNE 24, 1922

REICH PATENT OFFICE

PATENT LETTERING

- JVe 355310 - CLASS 21c GROUP 50.

Fried. Krupp Akt-Ges. in Essen, Ruhr.

Overcurrent switch for protecting motors.

Patented in the German Empire on December 31, 1920.

The invention relates to overcurrent switches for protecting motors by means of Starting resistor are started, and the purpose of an overcurrent switch of this type to create, the sensitivity of which is low at the beginning of the tempering and when Starting automatically increased.

In the drawing the invention is on

three embodiments in schematic

ίο illustration illustrates, namely show Fig. Ι the first,

Fig. 2 the second and

Fig. 3 and 4 the third embodiment.

The first embodiment will be explained first.

In the armature circuit of a main current motor BB ¹ fed by a direct current network A , there are a starting resistor C as well as the interruption point consisting of two carbon contacts DD ¹ and the main current release coil D ^{2 of} the overcurrent switch provided with two release coils, the second release coil D ^{s of} the overcurrent switch.

ters is connected at one end to the end of the main current release coil · D ² connected to the positive pole of the network A; its other end is connected with the interposition of a Vorschältwiderstandes F by a line B with the with the field winding B ¹ of the engine BB ¹ conductively connected to the end of the starting resistor C, at the other end to an empty contact c ¹ for the ίο switch crank c ² desAnl'assers is located. The tripping ^{coil D s} and the Yorschaltharz F are dimensioned so that on the one hand, in any position of ^{the crank c 2} on the starting resistor C, the tripping ^{coil D 3 is} sufficiently excited to open the overcurrent switch against the action of a spring (not shown) in its hold Öffnungsstellüng, and on the other hand, when short-circuiting the starting resistor C and closed line circuit breaker, the magnetic tensile force thereof so veritärkt that the overcurrent switch according loading \ termination of cranking at a current ^intensity: triggers in the main circuits, which makes up a predetermined fraction of that current, wherein the overcurrent switch in the absence of the second trip ^! coil Z3 ^a , so ttunter the action of the main current coil D ² would trigger alone.

The mode of operation of the overcurrent switch described is explained using an example will.

A normal operating current of 40 amperes is assumed for the motor BB ^1.

men, and it is stipulated that the overcurrent switch trips at 60 amperes in normal operation and at 120 amperes in the starting period. If the main current coil D ″ of the overcurrent switch is now designed with 100 turns and the second tripping coil D ⁸ with 1500 turns, and the resistance values of the tripping coil D ^s and the pre- switching resistor F ; are dimensioned so that the mains voltage in the current |

+5 circuits of this second trip coil causes a current j strength of 4 amperes, then with j short-circuited starting resistor C the contribution of the second trip ^{coil D 2} to the excitation of the magnetic circuit of the overcurrent switch 4 X 1500 = 6000 ampere win- 1 fertilize, while the main current coil D ^{2 is} able to develop an exciting force of 120 X 100 = 12,000 ampere turns j at the start of starting. If the overcurrent switch is always to trip at a total ^{excitation of 12,000 ampere-turns, its main current coil P 2} only needs to contribute 6,000 ampere-turns when the starting resistor is short-circuited. From-

go solution is then thus already at a current of 6, 000: 100 = 60 amperes in the main circuits, that is, ι ¹ /, times the operating current of the motor, and thus the over-current switch has at shorted _t senem occasion resistance twice as high sensitivity to Start of starting, where only three times the operating current causes tripping.

In the first moment of the starting period (1st i.e. when the crank c- comes into contact with the first contact c ^{3 of} the starting resistor C , the stationary motor BB ¹ does not develop any counter-electromotive force, so that the entire mains voltage in the starting resistor C is consumed , and the second trip coil D ^z remains unexcited. As the speed of the motor BB ¹ increases when starting, the excitation current in the trip coil D ^{3 also increases} . The trip ^{coil D 8} thus makes a gradually increasing contribution to the excitation of the magnetic circuit of the overcurrent switch, so that its sensitivity increases accordingly until it reaches twice the value as at the beginning of starting when the starting resistors are short-circuited, i.e. at full engine speed.

Is it a matter of the ratio of the sensitivities that the circuit breaker has when the engine is at a standstill and when it is running, it is sufficient in many cases to to change the size of the pre-peeling resistance F accordingly.

The embodiment illustrated by Fig. 2 differs from the one described only in that the motor BB ^{1 is} a shunt motor, the field winding S ¹ with its one end to an armature brush b ² and with its other end to the first contact c ^{3 of} the starting resistor C is connected so that the motor field is fully excited when the crank ^{c 2} passes to the first contact c ^{3 of the starting resistor.} The mode of operation is essentially the same as that of the first exemplary embodiment.

In the third embodiment (Fig. 3 and 4) are held by the overcurrent switch one engine two engines of a vehicle, e.g. B. a tram, to protect, the for the purpose of economical speed control both in series connection (Fig. 3) as well as in parallel connection (Fig. 4).

In the series connection (Fig. 3), the main current release coil G ^{2 of} the overcurrent switch is conductively connected at one end to the contact wire T ₁ via a pantograph H ~ with its other end to one, G, of the two contacts GG _{1 of the overcurrent switch.} To the other contact G ¹

the two main current motors MM ¹ and NN ¹ and the starting resistor P, to which a crank p ¹ connected to earth belongs, are connected in series. One end of the second trip coil G ³ is connected to the current collector H. connected; the other end is connected to the junction of the second motor NN ¹ with the starting resistors P via a series resistor Q. Between the second trip coil G ³ and the contact G ^{1 of} the overcurrent switch, a resistor R is connected, which is dimensioned so that the trip coil G ³ when the over-

t5 current switch a sufficiently strong excitation current receives to hold the switch against the action of a spring (not shown) in the open position. It is taken into account that the full starting resistor P may be switched on can be!

The parallel connection (Fig. 4) differs from the circuit according to Fig. 3 only in that the two motors MM ¹ and NN ^{1 are} now connected in parallel to one another instead of one behind the other, while maintaining the connection between the field winding M ¹ of one and the other of the armature winding N of the other motor so far with the starting resistor P conductively connected end of the line 6 * containing the resistor Q is connected to the contact G ^{1 of} the overcurrent switch.

The mode of operation of the exemplary embodiment illustrated by FIGS. 3 and 4 corresponds in the circuit according to FIG. 3 with regard to the processes during starting completely to that of the first exemplary embodiment (FIG. 1), as can be readily seen. By moving the connection of the resistor Q from the starting resistor P to the contact G ¹ at the transition to the circuit according to Fig. 4. "The coil G ³ loses its property as a tripping coil, since the voltage feeding it is almost zero when the overcurrent switch is closed the sensitivity of the overcurrent switch now goes back to the value determined solely by the tripping coil G ^2. However, this is the same value that existed in the circuit according to Fig. 3 at the start of starting.

In the parallel connection of the motors shown in Fig. 4, the line 5 ¹ containing the series resistor Q is connected to the terminal of the motor armature M which is conductively connected to the contact G ^{1 of} the overcurrent switch, without the connection between the line 6 ¹ and the circuit shown in Fig. 3 connected to the starting resistor P terminal of the field winding N ¹ had to be released beforehand. This circuit brings z. B. in trams the V orteil with it that the associated drive switch does not require a special busbar and brush for connecting the line 5 ", but that any existing drive switch set up for series parallel connection can be used when it comes to the subject of the Invention forming overcurrent switch to be installed.

Claims (3)

Patent Claims: 1. Overcurrent switch for contactors of motors that are started by means of a starting resistor, characterized in that the overcurrent switch (DD ¹ D ² D ^s or GG ¹ G ² G ³ ) except one with its interruption point (DD ¹ or GG ¹ ) in series lying main current coil (D ² or G ^{2 ) has a second trip coil (Z? 3} or G ³ ) which also serves to prevent the overcurrent switch from being switched on again and which is connected in parallel to one of the parts of the armature circuit containing the interruption point (D D ¹ or GG ¹⁾ and in series connection with the effective part of the starting resistor (C or P). 2. Overcurrent switch according to claim 1 for protecting motors that can be connected either in series or in parallel, characterized in that the series-connected second trip coil (G ³ ) with a series resistors (Q) after the transition from the series to Parallel connection of the motors (MM ^x and NN ¹ ) is connected to two points of the armature circuit, between which there is only a negligibly small voltage when the overcurrent switch (GG ¹ G ² G ^{3) is closed.} 3. Overcurrent switch according to claim i ° 5 for two main current motors, characterized in that in the series connection of the two motors (MM ¹ , NN ¹ ) with the starting resistors (P) connected current outlet point of a ^lx ° motor (NN ¹ ) and one at this connected line (S ) containing the series resistor (Q) is connected to the current inlet part of the other motor (MM ¹ conductive "5) when the motors are connected in parallel. 1 sheet of drawings.