AU2015344910B2 - Electromagnetic actuator with multiple windings - Google Patents

Abstract

A line protection electromagnetic actuator, comprising several windings surrounding a movable magnetic core capable of moving from a rest position to an actuating position under the effect of the magnetic field created by the windings, and comprising: - a differential winding (2) generating a magnetic field in response to a differential fault on the current line to be protected; - a magnetic winding (1), engaged with the differential winding (2), and generating a magnetic field in response to a short-circuit fault on the current line to be protected. This electromagnetic actuator is characterised in that it also comprises a third winding (3) wound in a short circuit and engaged with said differential winding (2) and magnetic winding (1), generating a magnetic field opposed to the magnetic field created by the magnetic winding (1).

Description

PCT/FR2015/053039

ELECTROMAGNETIC ACTUATOR WITH MULTIPLE WINDINGS

FIELD OF THE INVENTION The present invention relates to an electromagnetic actuator whose immunity to electric shocks has been enhanced. It relates in particular to electromechanical actuators which are used in conjunction with triggering locks of electric line protection devices, for example differential and / or voltage dependent disjunction devices.

These devices must trigger under very specific conditions, typically when an imbalance occurs between the sum of the incoming currents and the sum of the outgoing currents of the line protected by the device in question, which corresponds is to a "differential" protection due to a differential fault, or when the current is abnormally high, which corresponds to a "magnetic" protection following a short circuit fault.

An actuator conventionally comprises coils surrounding a movable magnetic core capable of moving from a rest position to an actuating position under the effect of the magnetic field created by the coils. More specifically, it comprises:

• A coil said to be "differential" generating a magnetic field in response to a differential type fault on the current line to be protected;

• A coil said to be "magnetic" generating a magnetic field in response to a short circuit type fault on the current line to be protected.

It is in fact a multi-winding actuator which consists of a compact solution making it possible to provide different types of protection with the same actuator.

BACKGROUND OF THE INVENTION The problem which this invention proposes to solve is as follows: the circuits protected by electrical devices such as those mentioned above undergo tests and are subjected to electromagnetic compatibility (EMC) tests in order to check whether they are sufficiently immune to disturbances from other equipment, or more generally from the environment.

These tests are standardized, and consist in sending several waves of current 8/ 2 0 ps, then a voltage wave 1.2/50ps in the electrical device. The device must not trip under these conditions. This means that by applying the above mentioned surges there must be no dielectric breakdown or damage to the component inside the device.

It is customary for such an actuator to be piloted by a control element, for example a thyristor, which is itself activated when the detection circuit of the device detects a fault. A varistor protects the control element in case of an overvoltage surge such as a 1. 2 /50ps voltage surge. This varistor becomes conductive beyond a defined voltage threshold and thus makes it possible to limit the voltage at the terminals of the control element to a value lower than the breakdown voltage of the control element.

When a 1. 2 /50ps voltage wave circulates in the differential coil, it can cause the device to unwantedly trip at 2kV, whereas the standard requires that the actuator be able to withstand shocks without triggering below 2kV.

When an 8/ 2 0ps current surge flows in the magnetic coil and the windings of the differential coil are imbricated with the windings of the second magnetic coil, an electromagnetic coupling causes a large induced voltage across the terminals of the first differential coil, which causes dielectric breakdowns with destruction of the differential protection.

To overcome these two problems, the solution at present consists of placing an additional varistor at the terminals of the differential coil. This solution makes it possible to avoid 8/20ps current surge breakdowns, but has the disadvantage of increasing the voltage (of the order of 100OV) across the terminals of the control element during a voltage surge 1, 2 / 5 0 ps because of the very strong current (of the order of 1000A) drained by the two varistors in series. The control element, so as not to degrade prematurely, must therefore be able to withstand such load. It will thus consist, for example, of a thyristor 1200V or an IGBT, that is to say a relatively expensive component.

It is possible to add a resistor upstream of the differential coil in order to limit the current which passes through the varistors, but this calls into question the compactness of the actuator and the control element will still be chosen from expensive components to withstand both the 1, 2 /50ps surges and the 8/ 2 0ps current surges.

The current solution is therefore relatively expensive.

It is therefore desirable to develop an electromagnetic actuator capable of withstanding shocks caused by short over-voltages not caused by a malfunction of the circuit itself, without inducing a triggering of the apparatus in which the actuator is integrated. It is further desirable that the manufacture of such an electromagnetic actuator is simple to implement and inexpensive.

OBJECT OF THE INVENTION It is an object of the invention to substantially overcome or at least ameliorate one or more of the aforementioned problems, to meet one or more of the above desires, or to provide a useful alternative.

SUMMARY OF THE INVENTION One aspect of the present disclosure provides an electromagnetic line protection actuator comprising a plurality of coils surrounding a movable magnetic core capable of moving from a rest position to an actuating position under the effect of the magnetic field created by the coils and comprising: a differential coil generating a magnetic field in response to a differential type fault on the current line to be protected; a magnetic coil characterised in that said magnetic coil is imbricated with the differential coil and generates a magnetic field in response to a short-circuit type fault on the current line to be protected, and in that the electromagnetic actuator also comprises a third coil wound in a short circuit and imbricated with said differential coil and said magnetic coil, generating a magnetic field opposite to the magnetic field created by the magnetic coil.

3a

In a preferred embodiment, the electromagnetic actuator comprises, conventionally:

• A differential coil generating a magnetic field in response to a differential type fault on the line of current to be protected;

• A magnetic coil imbricated with the differential coil and generating a magnetic field in response to a short circuit fault on the current line to be protected.

This actuator also comprises a third coil wound in a short circuit and imbricated with the said differential and magnetic coils, generating a magnetic field opposite to the magnetic field created by the magnetic coil.

The main idea of this invention is to provide an additional short-circuited coil instead of an additional varistor as was the case in the prior art. This solution is as economically advantageous, since a coil is less expensive than a varistor, and from the compactness aspect, because the additional coil is imbricated in the volume defined by the existing coils, it does not take up any additional space.

When the magnetic coil is crossed by an 8/2 0ps current surge, it generates a magnetic field. The short-circuited coil picks up this magnetic field by virtue of its positioning in the vicinity of the magnetic coil and created naturally by magnetic coupling, an induced a current which passes through it in the opposite direction to the current flowing in the magnetic coil. This induced current then creates a magnetic field which is opposed to that created by the magnetic coil. The resulting magnetic field is markedly less than that initially created by the magnetic coil, which makes it possible to reduce the induced voltage on the differential coil.

This configuration avoids the breakdown caused by current surges 8/20ps, without influencing the correct operation of the actuator during a 1.2/50ps voltage surge.

Moreover, since the voltage induced on the differential coil is reduced, the components situated downstream, ie the varistor at the terminals of the control element and the is control element, can be selected in a lower range and thus less costly.

The invention is based on the fact that the three coils are located in the same defined space in order to have a magnetic coupling between them. The three coils can even be coaxial in order to simplify their winding and their positioning within the actuator. This configuration ensures maximum compactness of the actuator.

According to one possibility, the third short-circuited coil and the differential coil have a common point regarding the winding, for example at a spindle of a cylindrical sleeve around which the windings of the two coils are wound simultaneously during manufacture of the actuator. This common point thus makes it possible to facilitate the simultaneous winding of the two coils and the integration of the short-circuited coil within the actuator.

In general, the short-circuited coil is dimensioned so that it does not interfere with the normal operation of the magnetic and differential coils.

The invention also protects an electrical line protection device comprising an electromagnetic actuator as described above.

The present invention will be better understood from the following detailed description and the accompanying drawings, which are provided byway of illustration only, without limiting the present invention.

s BRIEF DESCRIPTION OF THE FIGURES The invention will now be described in more detail with reference to the attached drawings, in which:

Figure 1 shows a schematic view of the actuator according to the invention;

Figure 2 is a graph showing the evolution of the induced voltage measured on an actuator during a 8/ 2 0ps current wave.

The actuator of the invention as illustrated in Figure 1 comprises a magnetic coil (1) is and a differential coil (2) connected in parallel in the protected line, that is to say typically between Ph and neutral phase N. This actuator is placed classically upstream of a load present on the line to be protected.

These coils (1, 2) surround a movable magnetic core (not shown) movable from a rest position to an actuating position under the effect of the magnetic field created by the coils (1, 2), so as to close or open the contacts (8) positioned upstream of the load.

This actuator is driven by a control element (5), a thyristor in this case, itself activated when the detection circuit (not shown) of the device detects a fault. This thyristor (5) is placed downstream of the differential coil (2) between the phase Ph and the neutral N.

A varistor (4), connected in parallel to the thyristor (5), protects the latter in the event of an overvoltage surge.

This actuator further comprises a short-circuited coil (3) on itself. The three coils (1, 2, 3) are separated from one another in Figure 1, but are in fact imbricated with one another so as to generate a magnetic coupling.

Because of its short-circuit formation, the coil (3) will always generate a magnetic field opposite to the field generated by the magnetic coil (1) during a current surge 8/20ps, whatever the winding direction. Consequently, the voltage at the terminals of the differential coil (2) is reduced, thereby avoiding dielectric breakdowns and deterioration of the adjacent varistor and thyristor.

The short-circuited coil (3) and the differential coil (2) can be connected to a common point (7), which is then at the phase potential. The connection is shown in dotted lines in Figure 1. It serves as an anchor point for the simultaneous winding of the two coils (2,3).

Figure 2 illustrates the reduction of the voltage induced on the differential coil during a current surge 8/ 2 0ps of 3000A. In this example, the magnetic coil comprises 7 turns, and the differential coil comprises 1000 turns.

The curve (10) shows the evolution of the induced voltage measured on an actuator of the prior art as described above, without additional varistor. The induced voltage has a peak which rises above 12000V.

The curve (11) shows the evolution of the induced voltage measured on an actuator according to the invention, with a third coil having 100 turns short-circuited and imbricated with the other two coils. With respect to the curve (10), the induced voltage is divided by 3, and rises to a maximum of 4000V.

Finally, the curve (12) shows the evolution of the induced voltage measured on an actuator according to the invention, with a third coil having 200 turns short-circuited and imbricated with the other two coils. The increase in the number of turns in short circuit also makes it possible to reduce the induced voltage, and the latter amounts to less than 3000V.

The configurations shown in the aforementioned figures are only some possible, non limiting, examples of the invention which, on the contrary, encompasses variants of forms and designs within the scope of those skilled in the art.

Claims (4)

1. Electromagnetic line protection actuator comprising a plurality of coils surrounding a movable magnetic core capable of moving from a rest position to an actuating position under the effect of the magnetic field created by the coils and comprising: a differential coil generating a magnetic field in response to a differential type fault on the current line to be protected; a magnetic coil wherein said magnetic coil is imbricated with the differential coil and generates a magnetic field in response to a short-circuit type fault on the current line to be protected, and wherein the electromagnetic actuator also comprises a third coil wound in a short circuit and imbricated with said differential coil and said magnetic coil, generating a magnetic field opposite to the magnetic field created by the magnetic coil.

2. Electromagnetic actuator according to the preceding claim, wherein the three coils are coaxial.

3. Electromagnetic actuator as claimed in any one of the preceding claims, wherein the short-circuited third coil and the differential coil have a common point for the winding.

4. Electric line protection device comprising an electromagnetic actuator as described in any one of the preceding claims.

Hager-Electro SAS By Patent Attorneys for the Applicant ©QCOTTERS Patent & Trade Mark Attorneys