FR2470466A1 - Mains overvoltage protector - uses magnetic core balance operated by break-over devices connected to earth and coil detecting resulting core flux - Google Patents

Abstract

The relay is connected between the incoming supply and the consumers installation. Both incoming and return wires are connected to coils (GA,GB) wound on a closed magnetic circuit (MG) so that when both currents are equal there is no net flux in the magnetic circuit. Beyond the coils, a circuit including two break over devices (TN1,TN2) is connected with one end of each device on incoming and return wires and the other connected via resistors (VR1,VR2) to a common earth point. Should an over voltage occur one of the break over devices will conduct to earth, setting up an imbalance between incoming and return currents resulting in a magnetic flux appearing in the third winding (GF) on the magnetic circuit (MG). This induces in the third winding an emf which is rectified (FR) and applied to the coil (RY) of the circuit breaker, which operates contact (ry1,ry2) in both lines. A capacitor (CP) across the circuit breaker coil provides a delay in operation to avoid short transients opening the circuit.

Description

The present invention relates to a device for protection against overvoltages and, more particularly, to a device intended to ensure the protection of the most sensitive sections of an electrical subscriber installation against accidental overvoltages.

 In fesïostallatiens; Elsetrics of subscriber, it can happen that the lines of the distribution network introduce overvoltages of atmospheric origin (lightning) or others (inductions for example -). Such overvoltages are in the form of pulses with a more or less steep front, the voltage level of which can reach, in the case of lightning for example, a very high value, the duration of this pulse being able to be relatively long in the overvoltages due to inductions for example.

 Subscriber equipment generally comprises two types of device: electromechanical devices with high insulation such as motor, heating and lighting devices, capable of withstanding instantaneous overvoltages without deterioration; and devices with semiconductor or solid state components such as television receivers, high-fidelity channels and devices for controlling microprocessor-based household appliances, which are particularly vulnerable in the presence of overvoltages, even instantaneous .

The same is true in industrial installations where the electrical installations include both apparatuses capable of withstanding very high instantaneous overvoltages without deterioration (manufacturing machines in general) and particularly fragile apparatuses (management or control computers). control of said machines, laboratory apparatus).

The protection devices currently used mainly include, at the private subscriber, a differential circuit breaker connected immediately at the output of the meter, as well as fuses each associated with a part of the stations of the installation and each intended to isolate from the rest of the installation the associated part in which a short circuit occurs. These devices are totally ineffective when an accidental overvoltage appears. In fact, they generally have a response time much longer than the duration of the overvoltage pulses. On the other hand, to avoid untimely and continuous operation of the residual current device caused by inevitable leaks from the various devices of the equipment supplied, the the tripping threshold of this circuit breaker is arbitrarily chosen at an average value (750 mA for example3 taking into account the sum of the estimated leaks of all the devices that the subscriber's equipment may include. It follows that this threshold of particularly high tripping, associated with the relatively long response time, removes the RCD much of its power to protect users against said leakage currents.

In some industrial installations, surge protection devices are connected to the output of the circuit breaker. These devices essentially comprise a discharge tube connected between each conductor and the earth. When an overvoltage of amplitude greater than the starting voltage of the argue tube appears, the latter starts and ensures the earthing of the electrical conductor connected at one of its ends. The installation is short-circuited and the circuit breaker undergoes a strong overcurrent circuit breaker. Resetting the circuit breaker after disappearance of the overvoltage returns to normal operation. Thus, in this type of protection, the appearance of an overvoltage brings the total stop of the supply of electrical energy to the entire installation and the return to normal operation of the entire installation na can take place if during the operation described above any of the discharge tubes accidentally short-circuited. In addition, as in the previous type of installation, the tripping threshold of the circuit breaker provided for the entire installation does not provide any protection for the user.

The present invention therefore relates to a protection device which overcomes the drawbacks of known devices. I1 makes it possible to ensure the protection of the user against accidental leaks in the devices used, as well as protection of these devices against overvoltages of any origin whatsoever while ensuring the continuity of the supply of the device (s) devices capable of withstanding these overvoltages without deterioration.

 The protection device of the invention is essentially characterized by the fact that it comprises, for each unit of equipment to be protected, a differential circuit breaker connected, relative to the energy source, downstream of this equipment, and a circuit with disruptive elements connected between the differential circuit breaker and the equipment unit.

The various objects and characteristics of the invention will now be explained in more detail in the description which follows, given by way of nonlimiting example, with reference to the appended figures which represent
- Figure 1, the block diagram of the device
protection of the present invention
- Figure 2, the detailed diagram of an example of
realization of the circuits DD and PF of the device of FIG. 1.

We will describe first, referring to the diagram of
principle of Figure 1, the protection device of this
invention.

The block diagram of Figure 1 represents in particular
a subscriber CD counter-circuit breaker set connected to two L1 wires
and L2 for transporting electrical energy. The different equipment
of the subscriber are then supplied via two wires
supply L1 'and L2'.

According to the invention, the power inputs of these
equipment, such as inputs C and D of a unit of equipment UD,
are connected respectively to respective connection points
A and B of the supply wires L1 'and L2' through a device
protection composed of a DD differential circuit breaker and a circuit
disruptive elements PF.

The unreferenced inputs of the DD RCD
are respectively connected to connection points A and B by
through two secondary supply wires L3 and L4, the
non-referenced outputs of the circuit of disruptive elements PF being
respectively connected to inputs C and D of the equipment unit.

This unit of equipment includes one or more devices which
must be the subject of individual protection.

The DD differential circuit breaker is designed in particular for
detect an imbalance between the currents flowing respectively ~ on the supply wires connected to its outputs and greater than
a predetermined threshold. The only circuits powered across the
DD RCD being those of the UD equipment unit, this
threshold is fixed according to the leakage currents tolerated in this
unit of UD equipment, i.e. without taking currents into account
of leakage existing in the other equipment units UD ', UD "of
the installation connected to the supply wires L1 'and L2', or
directly, or through another circuit breaker. The threshold
tripping of the DD circuit breaker is therefore relatively low, of the order of -10 mA for example, that is to say less than the maximum limit
bearable for the user of the UD equipment unit.

The circuit of disruptive elements PF includes elements
which can be, for example, known type discharge tubes, or semiconductor elements such as Zener diodes; these elements are connected respectively between each of the secondary supply wires L3 and L4 and the earth potential.

In normal operation, the electrical energy supplied by the wires L1 and L2 is retransmitted to the inputs C and D of the equipment unit UD.

When an anomaly occurs in this equipment, an accidental connection between one of the inputs e and D of this equipment and its structure normally connected to the reference potential
(ground) for example, there is an imbalance between the currents flowing respectively at these inputs. This imbalance is detected by the differential circuit breaker DD as soon as its amplitude reaches the tripping threshold, 10 mA according to the example chosen. This circuit breaker switches and cuts the power supply to the UD equipment unit.

 It can therefore be seen that, by means of the differential circuit breaker DD, the device of the invention provides protection for the user of the equipment unit UD.

 It is now assumed that an accidental overvoltage, caused for example by known induction phenomena, appears on the wire L1 and / or the wire L2. This overvoltage is retransmitted by the counter-circuit breaker CD assembly on the wire L1 'and / or the wire L2' and also on the secondary supply wires L3 and / or -L4.

This overvoltage therefore appears at the input terminals of the circuit with disruptive elements PF and makes the disruptive element connected between the earth potential and the wire where this overvoltage appears conductive. As a result, this overvoltage is not retransmitted 9 - the equipment unit UD. As soon as the tension on the wire considered becomes normal again, that is to say lower than the starting tension of the disruptive element, the latter no longer conducts and the operation of the system continues normally.

 The device of the invention therefore effectively protects the unit of equipment UD against overvoltages.

In the previous example, the initiation of the disruptive element is accompanied by an imbalance between the currents flowing respectively on the two secondary supply wires L3 and L4.

However, the DD differential circuit breaker which, to ensure effective protection of the user of the unit of equipment UD against leakage currents, is a fast circuit breaker with a response time of the order of ten milliseconds. This time is very much greater than the duration of the accidental overvoltage pulses which is of the order of a few tens of microseconds for overvoltages of atmospheric origin for example. The differential circuit breaker DD therefore does not intervene in the operation of the protection device of FIG. 1 when a brief accidental overvoltage appears.

If the duration of the overvoltage appearing on the wire L1 and / or the wire L2 is sufficiently long or if this overvoltage is in the form of a series of short pulses sufficiently close together the duration of conduction of the disruptive element concerned becomes prohibitive and this may result in a definitive short-circuiting of this element. A judicious dimensioning of the differential circuit breaker and of the circuit breaker avoids this drawback: the response time of the differential circuit breaker is chosen so that when the duration of the overvoltage is such that the circuit breaker risks being damaged , this circuit breaker switches and no longer retransmits to the PF circuit and to the UD equipment unit the electrical signals supplied on its inputs.

The device of the invention therefore also provides protection for the disruptive elements of the PF circuit against overvoltages the duration of which exceeds a determined threshold.

 Despite these precautions, it is still possible for a disruptive element to short-circuit definitively as soon as the first overvoltage appears. It is obvious that, in the absence of the differential circuit breaker DD, everything would then happen as if the connection points A and B of the wires L1 'and L2' were short-circuited.

The serrated circuit breaker of the CD assembly would detect this short circuit and interrupt the supply of all the equipment in the installation.

 The introduction of the DD differential circuit breaker avoids this drawback: it detects the imbalance caused by the permanent short-circuiting of the disruptive element of the PF circuit and then cuts the supply of the circuits located downstream, this is ie only from the PF circuit and from the UD equipment unit, the other equipment units of the installation being normally supplied.

We will now describe, referring to Figure 2; an exemplary embodiment of the differential circuit breaker DO and of the circuit with disruptive elements PF of the protection device of FIG. 1.

The DD differential circuit breaker includes in particular a magnetic toroid with three windings GA, GB and GF, a rectifier bridge with diodes FR, a capacitor CP and a bistable high-impedance relay RY whose contacts ry1 and ry2 are respectively connected in series on the wires L3 and L4.

The windings CA and GB are respectively connected in series on the secondary supply wires L3 and L4.

The ends of the GF detection winding are respectively connected to the alternating inputs of the rectifier bridge
FR.

The capacitor CP and the excitation winding of the relay
RY are connected between the continuous outputs of the rectifier bridge FR.

When the currents flowing respectively on the wires
L3 and L4, therefore in the windings CA and GB are of the same amplitude, no induced voltage appears at the terminals of the detection winding GF therefore at the inputs of the rectifier bridge FR. The excitation winding of relay RY is not supplied. Relay RY is at rest and its contacts ry1 and .y2 are in the closed position as shown in the figure.

When the current flowing on the wire L3 (therefore in the winding GA) and the current flowing on the wire L4 (therefore in the winding GB) are of different amplitudes, an induced voltage, the amplitude of which is a function of the difference in amplitude of these currents, appears at the terminals of the detection winding CF and at the alternative inputs of the rectifier bridge FR. This bridge then supplies a DC voltage across the capacitor CP which charges.

When the charge of the capacitor CP is sufficient, the relay RY is energized: it switches to the working position and its contacts ryl and ry2 open. The circuits located downstream of the differential circuit breaker DD are no longer supplied by the secondary supply wires L3 and L.

The circuit with disruptive elements PF of FIG. 2 essentially comprises two disruptive elements TN1 and TN2 and four varistors UR1 to UR4.

The disruptive element TN1, which can for example be a discharge tube, is connected between the wire L3 and the first end of the varistor VR1, the other end of which is connected to the earth potential.

Similarly, the disruptive element TN2 is connected between the wire L4 and, via the varistor VR2, ie potential of, the earth.

 Varistors VR2 and VR4 are connected in series between wires L3 and L4, downstream of the disruptive elements TN1 and TN2. The midpoint of the varistors VR3 and VR4 is connected to the potential of the mound.

When the voltage of the supply wire L3, for example, increases and reaches the value of the ignition voltage of the disruptive element IN1, the latter. starts and ensures the flow of this overvoltage to earth through the varistor VR1, A constant potential difference of the order of 15 V is then established at the terminals of the element TN1 supposed to be a discharge tube of known type. A current of up to several kiloamperes can thus be flowed through the discharge tube and the varistor between the terminals of which there appears a substantially constant potential difference depending on the type of varistor used, This potential difference allows increase the line voltage for which the tube is defused and which would be equal to 80 V in the absence of the varistor VR1.

Varistor VR3 is used to dampen the overvoltage pulse and, consequently, the tube having a non negligible response time although reduced (a few tens of milliseconds for example) to prevent the line voltage from becoming too much higher at the tube start voltage
In the preceding description, the nature of the supply wires L1 and L2 and therefore of the wires L1 'and L2' and of the wires L3 and L4 has not been specified. It is obvious that they can be, one a phase wire, the other the neutral wire or else both of-n phase wires.

Likewise, only the case where an overvoltage appears on a single wire has been considered. When an overvoltage appears on the two wires, the operation of the protection device described is identical
Indeed, this overvoltage is not equal on the two wires and, in all cases, one of the disruptive elements of the PF circuit always starts having, the other so that an imbalance etr, e the currents circulating on these wires still exists. In all cases, the differential circuit breaker therefore works.

It is obvious that the above description has been given only by way of nonlimiting example and that numerous variants can be envisaged without departing from the scope of the invention. Numerical details in particular have been provided only to facilitate dsscriptinn and may vary with each application case.

Claims (5)

1. Device for protecting a subscriber's electrical installation against overvoltage, characterized in that it comprises, for each unit of equipment to be protected, a differential circuit breaker connected, with respect to the energy source, in downstream of the connection points of this equipment to this source, and a circuit with disruptive elements connected between the residual current device and the individual equipment.  2. Protection device as defined in 1, characterized in that the differential circuit breaker comprises in particular a magnetic circuit comprising a first and a second winding connected respectively in series in the supply wires of the equipment unit and a detection winding, a rectification circuit whose inputs are connected to the terminals of the detection winding, a capacitor connected between outputs of the rectification circuit, and a high impedance electromagnetic relay whose excitation winding is connected in parallel with the capacitor and two contacts of which are respectively connected in series on the supply wires.  3. Protection device as defined in 1 or 2, characterized in that the circuit with disruptive elements comprises, for each of the supply unit supply wires, a disruptive element of which a first end is connected to the supply wire and the second end of which is connected to the earth potential.  4. Protection device as defined in 3, characterized in that the circuit with disruptive elements also comprises, for each of the supply unit supply wires, a first varistor connected between the second end of the disruptive element and the earth's potential. 5. Protection device as defined in 3 or 4, characterized in that the circuit with disruptive elements further comprises, for each of the supply unit supply wires, a second varistor, a first end of which is connected at a point of said wire located between the point of connection of the disruptive element to this wire and a corresponding input of the equipment unit, and the second end of which is connected to the earth potential.