DE593513C - Protective device for portable electrical apparatus - Google Patents

Description

The invention relates to a protective device for portable electrical apparatus the kind in which the apparatus is powered by a trailing cable and by a main switch is controlled using a two-wire control circuit for the double Purpose of grounding the frame of the portable device and monitoring the activity of the main switch from the end of the cable attached to the device. In arrangements of this type, it is common practice to provide devices to enclose to prevent the main switch in the event of an interruption in the control circuit, however the known arrangements do not provide adequate protection against a short circuit (particularly one that has substantial resistance) between the two Control circuit wires. It is further

zo desired to provide devices to switch the main switch in the event of failure of the To open the current and to prevent it from automatically closing again, if the power supply starts again.

The object of the invention is primarily a protective arrangement of the type described, in which a sufficient protection against the effects of errors of all kinds in the Control circuit is achieved. The invention also makes it possible to reduce the risk of damage of the apparatus to avoid resulting from the absence and subsequent recurrence of the current from the main power source.

In the arrangement according to the invention, the main switch is through a differential relay controlled, which the current that flows -in the control circuit, with that, which in a Comparison circuit flows, compares and in this way closes the main switch prevented if the control circuit is not OK. The comparison circuit is expediently parallel to the control circuit switched and has an impedance which corresponds to that of the control circuit, wherein the differential relay, the two coils of which are connected in series with respect to the two Circuits are arranged in such a way that the main switch can only be closed if the currents flowing in the two circuits are exactly the same and with respect to the phase are consistent.

In order to switch off the disturbances which result from the failure of the comparison circuit, a relay is preferably switched on in this comparison circuit, which works in such a way that it prevents the main switch from closing if the comparison circuit is not sufficiently energized. This further relays can be combined with the differential relay and thus become a single relay with it Form relay. If two separate relays connect

^ ψ

are used, they can be mechanically entangled to reduce the risk of a Prevent damage to the controlled apparatus resulting from failure and subsequent recurrence of power from the main power source.

The invention can be carried out in various ways. Some expedient practical Arrangements in which the invention ίο for the protection of a portable three-phase coal cutting machine, which is fed by a trailing cable with the interposition of a limit switch, application finds are shown for example in the drawings.

Fig. Ι shows a circuit diagram of a simple one Arrangement.

Fig. 2 shows a similar scheme of a particularly useful arrangement. Fig. 3 shows an appropriate type of relay, which in the circuit according to Fig. 2 Find use.

Figs. 4 and 5 represent sections through the construction according to Fig. 3, namely according to lines 4-4 and 5-5.

Fig. 6 shows schematically another particularly useful arrangement.

In the arrangement according to FIG. 1, the cutting machine A is fed by the towing cable A ¹ from a three-phase power supply system B under the control of the limit switch C , the latter being actuated ^{by a coil C 1.} The control circuit DD ¹ is fed with single-phase current from the network B through a step-down transformer B ¹ , B " . One side of the secondary winding B ^ of the transformer is grounded and the other side is connected to the two coils EE ^{1 of} a differential relay. One of the coils E of this relay is connected in series with a control line D and the second coil e ¹ via the two control lines DD ¹ in series with an impedance F, the second control line D is grounded. ¹ at the opposite end, the two control lines DD ¹ together by a control switch G and a further impedance H, respectively. the values of the impedances F and // are chosen so that normally flow of the differential relay during operation of the apparatus equal currents through the two coils EE ^1. the operating coil C ¹ for the limit switch C is under the control of the contacts E ^{2 of} the differential relay EE ¹ , the arrangement being such that the contacts E ² open when different currents flow in the coils EE ^{1 of} the relay and in this way ^{de-energize the actuating coil C 1} for the limit switch.

In this way, when the control switch G is open at the opposite end, the secondary current flows from the transformer B ¹ , B- only through the comparison circuit in which the second coil E ^{1 of} the differential relay is located, which consequently keeps its contacts E ″ open When the control switch G is closed , current also flows through the control circuit, and the two coils EE ¹ also become live, so that the contacts E ' ¹ close and ^{energize the work coil C 1} , which now closes the limit switch C.

If the control circuit is interrupted, the comparison circuit alone is excited and the differential relay prevents the limit switch C from closing, or it triggers this switch when it is closed. In addition, a short circuit between the control lines DD ¹ , regardless of whether it is a direct one or one with a relatively high resistance, would disturb the state of equilibrium in the coils EE ^{1 of} the relay, which therefore keep their contacts E- open and that Closing of the limit switch C would prevent.

It is evident that this simple arrangement has the effect that if there is no current from the network B, both coils of the differential relay are de-energized and when the current returns, the coils would be energized again evenly if the control switch G is closed at the opposite end is left, with the result that the end switch C would close again and now perhaps set the apparatus A unexpectedly into operation. In order to prevent this, the impedance H in the control circuit at the opposite end can be designed in the form of a holding winding for the control switch G , which can only be switched on by hand. Here, a Stromloswerden the control circuit DD ¹ would be from the main network forth effect the opening of the control switch G due to absence of the current, so that now the apparatus A can be started only by operating the Kontrpllschalters G by hand. However, this modified embodiment requires the arrangement of a special apparatus next to the cutting machine A, which is exposed to the unfavorable vibration effects. Another disadvantage of this arrangement arises from the fact that the differential relay EE ¹ allows the switch C to close when its armature drops out. In order to avoid these disadvantages, the preferred arrangement according to Fig. 2, which will be described later, has been developed.

This preferred arrangement differs from the simple one described above in that the impedance in the dummy circuit is designed as an auxiliary relay / whose contacts J ¹ in series with those of the

Differential relay EE ^{1 are connected} in the control circuit for the actuating coil C ^{1 of} the limit switch C , the relays being mechanically interlocked with one another in such a way, as indicated at K , that the auxiliary relay / its contacts J ¹ cannot close when the contacts E ^{2 of} the differential relay are already closed.
A suitable practical design for the mutual entanglement is shown in Figs. 3 to 5. In this design, the differential relay with its coils EE ¹ , its contacts E ² and its armature E ^a and the auxiliary relay with its coil /, its contacts J ¹ and its armature / ² are attached to a frame L next to one another. The entanglement, which is indicated at K in Fig. 2, is effected with the aid of a hook member M , which is hinged at L ² to a bracket L ¹ on the frame L and has a protruding arm M ¹ which, under the action of a spring M ² stands. This spring normally acts to urge the hook member M into the path of a projection / ³ on the armature / ^{2 of} the auxiliary relay. A head start i? ⁴ on the armature E ^{3 of} the differential relay acts on the hook arm M and holds the hook M outside the path of the projection / ³ when the armature Ε ^{Ά of} the differential relay is attracted.

A very slight delay is provided for the dropping of the differential relay armature E ^{z in} order to create time for the auxiliary relay to lift its armature / ² before the hook member M has fallen into its path.

5 In this way, provided that the cutting machine A is in operation and the control switch G and the contacts E ² and J ^{1 of the} two relays are closed, failure of the power supply from the network B will de-energize both relays and the limit switch C open, the hook member M being actuated by its spring M ^2. When the power supply returns, if the control switch G is still closed, the same current flows through the coils ES ^{1 of} the differential relay, and its armature E ³ therefore remains down. The auxiliary relay / tries ^{to close its contacts / 2} , but it is prevented from doing so by the hook member M , which makes an undesired automatic reclosing of the limit switch C impossible. In order to be able to close this switch C , the operator must now open his control switch G first. As a result, the control circuit DD ^{1 is} de-energized, so that. the differential relay EE ¹ opens its contacts E ² and so 'the hook member M is removed. The auxiliary relay / now picks up its armature / ² because the dummy circuit is now live, but the limit switch C cannot close because the differential relay contacts E ^{% are} open until the operator closes his control switch D again. As soon as it does this, the equilibrium state is restored in the differential relay and its contacts E ² close and at the same time cause the limit switch C to close.

The control switch G in the control circuit can, if desired, be designed as an auxiliary switch for a controller G ¹ , which regulates the power supply from the network via the towing cable A ^x to the cutting machine A , the arrangement being such that the control circuit DD ¹ only is closed when the main conductors of the trailing cable A ^{x are connected} to the cutting machine.

In a further modified embodiment, shown in Fig. 6, the differential relay and the relay in the comparison circuit are connected to one another and thus form a single relay. Here, the contact member of the combined relay can consist of a rotatably hinged bar N on which opposing closing and opening forces are exerted. The closing force »is derived from a single coil O , which is located in the comparison circuit and corresponds to the auxiliary relay / in the previous arrangement, while the opening force is only derived from the differentially arranged coils PP ¹ , which are the two coils EE ^{1 of} the differential relay correspond to the previous arrangement, is derived. The relay is arranged so that its contacts N ¹ can only be closed when the working coil O is energized and the two differential opening coils PP ^{1 are} equally energized. With this arrangement, in order to prevent the risk of damage as a result of the failure and subsequent recurrence of the current from the main power source, the control switch G can be provided at the opposite end with a holding winding Q , which is in series with the control circuit DD ¹ in the above-described Way is switched.

Of course, the above arrangements are only described as examples, and the invention can be carried out in other ways. no

Claims (5)

Patent claims: i. Protective device for portable electrical apparatus or machines, which the current is fed through a trailing cable with the interposition of a main switch using a two-wire control circuit to ground the frame of the portable machine and to control the main switch from the on-set end of the Cable to cause a control switch, characterized in that the main switch is controlled by a differential relay (EE ¹ ) , which compares the current flowing in the control circuit with that which flows in a comparison circuit and in this way a closing of the Main switch (C) prevents if the control circuit is not live. 2. Protection device according to claim i, characterized in that the comparison circuit is connected in parallel with the control circuit and has an impedance (F) which corresponds to the impedance of the control circuit, the two coils (EE ¹ ) of the differential relay in series with the two circuits are switched and arranged so that closing the main switch (C) is only possible if the currents flowing in the two circuits are exactly the same size and phase. 3. Protection device according to claim 1, characterized in that the track circuit contains a relay (/) which is used to prevent the main switch (C) from closing, if not the Comparison circuit is under sufficient voltage. 4. Protection device according to claim 1 and 3, characterized in that the two relays (EE ¹ ^ J) are mechanically interlaced with one another. 5. Protection device according to claim 1 and 3, characterized in that the two relays (EE ¹ , J) are combined to form a single relay (PP ¹ , O). 1 sheet of drawings