GB2305316A

GB2305316A - A protection arrangement for overvoltage suppressor

Info

Publication number: GB2305316A
Application number: GB9619090A
Authority: GB
Inventors: Monika Makowski
Original assignee: Schupa Elektro & Co KG GmbH
Current assignee: Schupa Elektro & Co KG GmbH
Priority date: 1995-09-15
Filing date: 1996-09-12
Publication date: 1997-04-02
Anticipated expiration: 2016-09-12
Also published as: GB9619090D0; GB2305316B; IT1284501B1; DE19534273A1; FR2738962A1; FR2738962B1; ITMI961858A1

Description

2305316 1 A protection arranqement for overvoltage suppressor The present

invention relates to a protection for overvoltage suppressors, whereby the protection is a suppressor isolating switch, which comprises a through which the external conductors leading to the suppressor and the neutral conductor are taken arrangement arrangement transformer overvoltage and that a tripping relay is provided which operates the interrupting contacts in the feed circuit to the overvoltage suppressor via a switching mechanism.

Overvoltage suppressors using varistors as voltage limiting elements are frequently used as protection against damage from overvoltage. In these the varistors are connected both between the connecting terminals for the neutral and external conductors on the one side and the connecting terminals of the earthed conductor on the other side as well as between those for the neutral and external conductors.

In the normal operating condition a varistor carries only a very small leakage current. If it is however overloaded by many small pulse currents, it becomes irreversibly damaged and the leakage current rises. The leakage current causes a heating of the varistor, which depending on the damage to it can become so great, that an acute danger of f ire arises from it. It is therefore absolutely necessary, that overvoltage suppressors with a high leakage current are immediately isolated from the mains. The state of the technology has it that overvoltage suppressors are connected in series with, for example, fuses with a rated 2 current In < 10A. It should be noted however that a fuse, conditioned by its characteristic, is not suited to solving this problem, since it responds to every loading with a rated surge current (5 kA, 8/20 As) and thus the connected installation is often without overvoltage protection. Apart from this, the varistor is only isolated from the circuit in the event of a defect caused by a very high leakage current, so that the risk of fire already mentioned exists.

It is proposed in EP-A-0, 350, 477 that a suppressor isolating switch, whose contact is arranged in the earthed conductor path can be connected after the overvoltage suppressor. This suppressor isolating switch is essentially a pulse current tolerant defect current protection switch. The isolation of the suppressor only occurs when the leakage current in the ground circuit exceeds a certain value. All the varistors arranged between the neutral conductor and the external conductor are not controlled. But even the isolation of the varistors between neutral and external conductors and the earthed conductor is insufficient since the overvoltage suppressor is isolated only from the grounded conductor, but not from the supply network. Thereby it is possible for an unacceptably high leakage current to flow through the varistors even after the suppressor isolating switch has operated. If a varistor connected between an external conductor and the grounded conductor becomes conductive as a result of overload, the suppressor isolating switch isolates the overvoltage suppressor from the earthed conductor. This has the result that the remaining varistors connected between an external conductor and the earthed conductor are overloaded, since they remain at the external conductor voltage. The leakage current which is necessarily formed must then be disconnected by the input fuses. Unacceptable heating of the overvoltage suppressor is thereby pre-programmed.

Arrangements are also proposed in EP-A-0,385,832, in which the overvoltage protection is installed after a selective, surge current tolerant defect current protection switch. Under this neutral and external conductors are taken through the transformer of the defect current protection switch in the same sense. But this arrangement is also unsuitable for controlling varistors connected between neutral and external conductors.

Further to this, arrangements are proposed in DE-A-41 27 457, in which the suppressor isolating switch and the varistors are contained in one housing. Here too the suppressor isolating switch is essentially a defect current protection switch. Since, however, only the overvoltage protection elements have to be exchanged as a result of aging, the solution is not sensible. That apart, this known arrangement does not protect varistors connected between neutral and external conductors due to the similar sense of the primary windings in the transformer of the neutral and external conductors.

The aim of the present invention is to develop a protection arrangement based on a suppressor isolating switch, which not only protects the varistors connected to the grounded conductor PE but also the varistors between the neutral conductor and the external conductors.

Accordingly the present invention is directed to a protection arrangement as described in the opening paragraph of the present specification, in which the wiring of the primary winding of the transformer in the suppressor isolating switch to which the neutral conductor is connected, is in opposite sense to the wiring of the windings to the external conductor.

Preferably the suppressor isolating switch is suitable both for connection to a single phase and to a three phase supply.

Advantageously the overvoltage suppressor is provided with varistors as overvoltage elements, which are exchangeable as a module.

An example of a protection arrangement made in accordance with the present invention is shown in the accompanying drawings and is described in greater detail hereinbelow in connection with the previously proposed circuit engineering characteristics, in which:

Figure 1 is a schematic circuit diagram of a previously proposed overvoltage suppressor for three-phase mains; Figure 2 is a schematic circuit diagram of a previously proposed overvoltage suppressor for single phase mains; and Figure 3 is a schematic circuit diagram of a protection arrangement according to the present invention of a 4pole suppressor isolating switch with overvoltage suppressors.

Figures I and 2 show overvoltage suppressors or diverters 10 with varistors 11, 12 as voltage limiting elements, which - overvoltage suppressors are often used as protection against overvoltage damage. These varistors 11, 12 are connected both between the connecting terminals for the neutral conductor 1 and external or outer conductor 2, and the earthed conductor 13 and also between those for the neutral and external conductors 1, 2. As can be seen from Figure 3, an isolating switch 6 serves as protection facility for an overvoltage suppressor 10, which operates on the previously proposed principle of a delayed surge current tolerant defect current protection switch. It comprises a transformer 7 through which the neutral conductor 1 and the external conductor 2 are taken. A tripping relay 5 is connected with a delay circuit 8 to the secondary winding 9 of the transformer 7. The tripping relay 5 operates a switching mechanism 4, which opens all the interrupting contacts 3 simultaneously. The neutral conductor 1 is led through the transformer 7 in opposite sense to the external conductors 2. Then, whenever the leakage current through any of the overvoltage protection elements, varistors 11, 12, becomes greater due to the onset of irreversible damage to the varistors 11, 12, caused by overloading or frequent loading with small surge currents this increase in the leakage current is detected by transformer 7 as a difference. A voltage is induced by this in the secondary winding 9, which causes the tripping relay 5, delayed by the time element 8, to operate and activate the switching mechanism 4 and isolate the overvoltage suppressor 10 from the mains. Since the suppressor isolating switch 6 operates for a leakage current of at least 30 mA, unacceptable heating of the overvoltage 6 suppressor 10 is avoided. Since the neutral conductor 1 is taken through the transformer 7 in opposite sense to the external conductors, as previously mentioned, not only the varistors 12 connected to the earthed conductor 13, but also the varistors 11 connected between the neutral conductor 1 and the external conductors 2, are controlled by the suppressor isolating switch 6 described here. Unacceptable heating of the overvoltage suppressor 10 after the operation of the suppressor isolating switch 6 is not possible because of the arrangement according to the present invention, since the overvoltage suppressor 10 is isolated from the supply network at all poles LI, L2, L3 and N.

The delay circuit 8 ensures that the tripping relay 5 only operates after a preset pulse duration, so that the suppressor isolating switch 6 does not isolate the overvoltage suppressor 10 f rom the mains on short term current peaks, but only on increased continuous leakage current.

7

Claims

Claims overvoltage wirina of 1. A protection arrangement for overvoltage

suppressors, whereby the protection arrangement is a suppressor isolating switch, which comprises a transformer through which the external conductors leading to the overvoltage suppressor and the neutral conductor are taken and that a tripping relay is provided which operates the interrupting contacts in the feed circuit to the suppressor via a switching mechanism, in which the the primary winding of the transformer in the suppressor isolating switch to which the neutral conductor is connected, is in opposite sense to the wiring of the windings to the external conductor.
2. A protection arrangement according to Claim 1, in which the suppressor isolating switch is suitable both for connection to a single phase and to a three phase supply.
3. A protection arrangement according to Claim 2, in which the overvoltage suppressor is provided with varistors as overvoltage elements, which are exchangeable as a module.
4. A protection arrangement substantially as described herein with reference to Figure 3 of the drawings.