DE1042085B - Relay arrangement for monitoring small overcurrents - Google Patents

Description

For the operation of transformers, motors or other electrical system parts, a sensitive display and, if necessary, a switch-off in the event of a relatively very low overload of an inadmissible period of time is often desired or necessary. For this purpose relays, e.g. B. overcurrent relays, with a particularly small hold ratio are required so that the signaling or disconnection of a low overload is reversed when the load drops to rated load and a possibly started timing relay can be made to drop out again for delayed tripping. However, as is well known, simple, inexpensive and reliable overcurrent relays can only be built with a holding ratio of at least 1.1 to 1.2. Achieving a much smaller value deviating only very little from the holding ratio value 1.0 is, however, not previously possible under the conditions mentioned
for monitoring small overcurrents

Applicant:

LICENTIA Patent-Verwaltungs - G. mbH _r Hamburg 36, Hohe Bleichen 22

Heinz Gutmann and Dipl.-Ing. Hans Diehl,

Heiligenhaus (District Düsseldorf),
have been named as inventors

been.

The subject of the invention is a relay arrangement for monitoring small overcurrents of impermissible duration, where a commercially available relay with a relatively large one is used as the monitoring relay Hold ratio is used; According to the invention, this relay operates an auxiliary relay arrangement which in turn short-circuits the monitoring relay, so that this and then also the auxiliary relay arrangement itself to fall again and in this way a periodic poll of the measured variable by the monitoring relay as long as the overcurrent is greater than the response value of the monitoring relay is. By a second working contact of that auxiliary relay of the arrangement, that actuates the bridging contact of the monitoring relay, a signal lamp can be actuated, which is shown in in this case flashes periodically as long as the response value is exceeded.

If you don't just want to signal the electricity, you want to switch it off automatically after a certain time carry out the endangered part of the system, you can make contact, which is periodic Of course, the auxiliary relay arrangement also has an additional auxiliary relay with a suitable drop-out delay convert into a continuous pulse for the continuous running of a timing relay.

Finally, you can also use the start system of the timer itself, for. B. its electromagnetic Drive or release system for the passage of time, with means known per se, a suitable one Grant decay delay without departing from the scope of the present invention.

Embodiments of the invention are shown in the drawing. Fig. 1 shows the basic circuit diagram a single pole embodiment of the relay arrangement according to the invention. In the course of line 1, via which an electrical part of the system is fed,

ao Is the monitoring relay A, z. B. an ordinary overcurrent relay, with a hold ratio of about 1.3. If this relay is to respond at an overcurrent of 5%, ie 1.05 times the value of the nominal current / ", it would only react again at 1.05 / 1.3 /" = 0.81 / "according to its holding ratio go back to the rest position and thus falsely report an overload even if the current has meanwhile fallen by up to 19% below the nominal value. In order to avoid this, according to the present invention, the contact α of the monitoring relay A is not used directly for signaling or for starting a timing relay, but rather to excite a downstream auxiliary relay arrangement. This consists initially of an auxiliary relay Z, which z. B. may be a capacitor connected in parallel. If necessary, a series resistor can also be provided to achieve a certain response delay. The contact s of the auxiliary relay Z in turn actuates another auxiliary relay H, whose contact Zi _{2 is used} to signal the overload condition and whose contact h _t short-circuits the monitoring relay A so that it drops out and opens its contact α again. Thus, after a certain delay, the auxiliary relays Z and H also drop out again; the short-circuit of the monitoring relay A is thereby canceled again, and the relay A responds again, etc., if an overload still exists. However, if the load drops to at least 1.04 I _n and the current in conductor 1 falls below the response value of relay A, it no longer responds again and the entire arrangement goes back to the normal rest position.

309 660/233

It is now not absolutely necessary to use two auxiliary relays Z and H. The contacts Zi ₁ and Zi ₂ can also be accommodated on the auxiliary relay Z without changing the basic mode of operation, thus making the auxiliary relay H unnecessary. This can be quite useful in the single-pole arrangement shown. It should be borne in mind, however, that the increased number of contacts of the auxiliary relay Z also makes correspondingly larger capacitors necessary in order to achieve a certain drop-out delay. Therefore, at least in the case of multi-pole protective devices, in which overload relays have to be short-circuited in several conductors and accordingly more contacts are required, the arrangement shown in FIG. 1 with two separate auxiliary relays will be more expedient. In principle, the delayed relay Z will be equipped with only a single contact, if possible, and all the contacts that are otherwise required will be conveniently placed on the downstream auxiliary relay H.

Since a message or shutdown should not be initiated with every brief overload, is it is usually necessary to equip the relay Z with a longer response delay. To the resulting To keep the cost of capacitors low, it can be useful to use an additional auxiliary relay converting the response delay into a dropout delay in a known manner; an embodiment for the circuit then required is shown in FIG.

In the event of an overcurrent in line 1, relay A responds and closes its contact a. As a result, the release delayed relay Z is immediately made to respond via contact V _1. Its contact Z switches on another auxiliary relay V , whereby with its contact V ₁ the relay Z is again separated from the voltage and the relay V itself is made self-holding. After the delay time of relay Z has elapsed, contact ζ returns to the position shown and allows relay H to respond via contact v _2, which was previously closed by relay V. This relay fulfills the tasks of the output relay described in FIG. 1, ie it short-circuits relay A with its contact U ₁ and actuates contact Zi ₂ to periodically report the overcurrent. By opening the contact α relay V immediately drops back and interrupts via its contact _v.sub.z the circuit of the relay H. This is but a drop delay of a few tenths of a second to the short circuit of relay A sure until this relay his new Has clearly taken a position. After the delay time of relay H has elapsed, the short circuit of relay A is canceled and it responds again, etc., if the overcurrent is still greater than the response value of the monitoring relay. As in the arrangement according to FIG. 1, a signal lamp is made to flash via the contact Ji _%. If a continuous message is to be given in addition to the flashing signal, this can be achieved by another contact v _s on relay V. The downstream relay W, which is connected to voltage via this contact, must then receive a dropout delay that is slightly greater than that of relay H. The contact w then remains closed as long as there is an overcurrent in the line, regardless of how the fall time of relay Z is large. ~

The described arrangements naturally also come into operation when high short-circuit currents flow in the monitored part of the installation. In this case, the auxiliary relay contacts Ji ₁ are subjected to an undesirably high load. Where such conditions can occur, the overcurrent elements need not be completely short-circuited. Rather, as indicated in FIG. 1, a limiting resistor can be switched on in series with the contact Ji ₁ , which is dimensioned so that when the contact Ji ₁ closes the partial current flowing through the relay A is definitely less than that Holding current of this relay.

Instead, however, a weak auxiliary winding arranged on the overcurrent elements can also be used short-circuit using additional auxiliary contacts. The counter-AW occurring in this auxiliary winding can also be used to bridge the holding ratio. One achieves through this measure not only the advantage that the alternating currents to be switched by the auxiliary relay contacts are transformative Can be reduced in size, but can also be an effective limitation of these currents through the saturation properties of the overcurrent element.

Finally, there is the possibility of simply protecting the device against damage by the short-circuit currents by means of simple short-circuit release systems that are usually present. If the short-circuit system U shown in Fig. 2 works, for example, directly on tripping, the short-circuit current is switched off before the response of the relay H and thus the short-circuiting of the system A through the contact Ji _{1 is} no longer initiated. But if the over-current in the relay A will not reported, the relay U can vary depending on the value of its holding ratio of the relay A will be set to three to four times the value of the operating current, and its contact α then bypassed at high currents, the contacts α and V ₁ . As a result, the relay Z is connected to voltage until the current in the line 1 has fallen below the holding current value of the relay U. The contact u thus prevents the relay Z from dropping out, and the relay H can not respond, so that the relay A is also not caused to drop out when high short-circuit currents flow. On the other hand, the relay V and via the contact v _s also the relay W remain addressed and initiate a trip if the high overcurrent does not decrease beforehand.

Claims (10)

Patent claims: 1. Relay arrangement for monitoring low overcurrents of impermissible duration, in which the monitoring relay (A) used commercially available relays with a relatively large holding ratio, characterized in that the monitoring relay actuates an auxiliary relay arrangement when the response value is exceeded, which in turn short-circuits the monitoring relay, so that this and then the auxiliary relay arrangement itself will drop out again, the latter possibly with a certain time delay, so that the monitoring relay will periodically query the measured variable as long as the overcurrent is greater than the response value of the monitoring relay. 2. Relay arrangement according to claim 1, characterized by the use of an auxiliary relay (H) , which is actuated via the make contact (a) of the monitoring relay (A) directly or with the interposition of one or more additional auxiliary relays, whereby a make contact (H ₁ ) assigned to it temporarily bridges the winding of the monitoring relay, while other assigned make contacts (e.g. h ₂ ) activate an optical or acoustic signaling device. 3. Relay arrangement according to claim 1 and 2, characterized in that the normally open contact _{(H 1} ) of the auxiliary relay (H) bridges an auxiliary winding of the monitoring relay. 4. Relay arrangement according to claim 1 and 2, characterized in that an ohmic resistor is connected in series with the winding of the monitoring relay (A) bridging working contact Qi ₁ ) which is dimensioned so that at the maximum possible current in the monitoring relay (A) after the contact is closed, the partial current still flowing through the monitoring relay is lower than the holding current of this relay. 5. Relay arrangement according to claim 1 to 4, characterized in that for converting the periodically occurring contact of the auxiliary relay arrangement in a continuous pulse an additional Auxiliary relay is arranged with a correspondingly dimensioned dropout delay. 6. Relay arrangement according to Claim 1 to S, characterized in that the auxiliary relay (H) has a drop-out delay and is actuated directly via the normally open contact (a) of the monitoring relay (A) . 7. Relay arrangement according to claim 6, characterized in that the auxiliary relay also is delayed. 8. Relay arrangement according to claim 1 to 5, characterized in that the auxiliary relay (H) works without a time delay and is actuated via the normally open contact (2) of a drop-out and optionally also delayed-on intermediate relay (Z), which in turn is actuated via the normally open contact (a) of the monitoring relay (A) is switched on (Fig. 1). 9. Relay arrangement according to claim 1 to 8, characterized in that a further relay (V) is arranged to achieve a response delay of the auxiliary relay (H) , which via the changeover contact (2) of the upstream and via the normally open contact (a) of the monitoring relay ( A) actuated drop-out delayed relay (Z) is switched on without delay, holds itself via its own changeover switch _{contact (^ 1} ) with simultaneous interruption of the circuit of the drop-out delayed relay (Z) and prepares the response of the auxiliary relay (H) via a further normally open contact (v ₂ ) (Fig. 2). 10. Relay arrangement according to claim 1 to 9, characterized in that the relay of the auxiliary relay arrangement actuated via the make contact (α) of the monitoring relay (A) is made to respond directly via a make contact (u) of the relay (U) which responds in the short circuit. Considered publications:
German patent specification No. 889 790. 1 sheet of drawings ® -80 & 660/233 10.58