ITMI981824A1 - CIRCUIT FOR THE CREATION OF CURRENTS FOR THE ANALYSIS OF THE FUNCTIONALITY OF DIFFERENTIAL SWITCHES - Google Patents

Description

DESCRIPTION

Technical problem

The invention solves the technical problem of creating the forms of current prescribed by the standards for the analysis of the functionality of RCDs in the simplest and least expensive way possible.

State of the art

The differential switch (figure 1) is used to protect appliances and in particular users from the dangerous contact voltage, which arises in the event of a short circuit of the phase voltage to the protective conductor E. The differential switch must interrupt the circuit protected immediately when the difference in currents between branches L (phase) - 1 and N (neutral conductor) - 2 increases up to values between 0.5 ΙΔΝ and 1.4ΔΝ, where ΙΔΝ represents the nominal current sensitivity of the differential switch. According to the standard, the nominal values of ΙΔΝ are: 10 mA, 30 mA, 100 mA, 300 mA and above, but RCDs with the maximum value of ΙΔΝ equal to 500 mA are used in domestic systems.

Depending on the many different users of electrical energy, different forms of residual current currents can be had, so that also in practice, residual current devices are used which are sensitive to different forms of residual currents. Therefore, the test in alternating current regime is not sufficient, but it is necessary to analyze the functionality also with half-wave pulsating current, superimposed on a rectified direct current with a maximum value of 6 mA and with smoothed direct current. The verification requests are contained in the standards IEC 755/1983, IEC 755 Annex 1/1988, IEC 755 Annex 2/1992, IEC 1009-1 / 1996, DIE IEC 1557, 1. and 6. Party.

Several solutions are known for the formation of test currents. So eg. the functional analyzer for RCCBs from the manufacturer Edgcumbe - Instruments - N.E.I. Electronics (Bothwell-Glasgow, England) contains a circuit, shown schematically in fig. 3. The circuit has a commutator with numerous resistors and an electronic switch, which makes it possible to analyze functionality in alternating and pulsating direct current conditions, but not in direct and changing current conditions. The circuit used by the manufacturer Norma Messtechnik, Optik, Elektronik GmbH (WR.Neudorf, Austria) is shown in fig. 4 and has a power transistor in the rectification bridge, where the transistor is guided so that the alternating current at the output is of the desired shape and intensity. The mentioned circuit makes possible the independence of the amplitude of the measurement current from the mains voltage and makes it possible to change the intensity of the analysis current during the test, but does not make it possible to analyze with direct current.

Description of the new solution

The substance of the new solution contained in the present invention lies in the rectification bridge divided by switches S1 and S2, in the guided current dispersion unit P (Current Sink) and in the smoothing unit F. By means of the switches SI and S2 in the split rectification bridge it is possible to create a form of both alternating and direct half-wave current as well as rectified direct current of the desired direction. The intensity of the current and also the shape (alternating or continuous half-wave) is determined by adjusting the current dispersion element P. The new solution will be explained in particular with the aid of the figures which illustrate:

Figure 1 schematic connection of the differential switch in the electrical network;

figure 2 - schematic illustration of the leakage element of the test current

figure 3 - solution according to the state of the art (Edgcumbe Instruments)

figure 4 - solution according to the state of the art (Norma);

figures 5 to 10 - illustration of the elementary form of the test currents;

figure 11 - illustration of the circuit object of the invention.

Figure 1 shows the connection of the differential switch. Normally the current present in branch L - 1 is equal and of opposite direction to that in branch N - 2. Their contribution to the magnetic flux in the core of the RCD is therefore zero. In the event of a short between phase L and the protective conductor E, part of the current flows from contact 1 through Rp into contact 3. As a result, a difference in currents arises in branches L -l and N - 2. The current in branch L - 1 is greater for the current flowing from 1 through Rp to 3. A sufficiently large difference in currents must cause the RCD to operate.

Figure 2 shows the tester as a unit of dispersion of the current P - constant alternating current, with which, through the line K, the intensity and shape of the current are determined.

Since only the difference between the currents in the branches L - 1 and N - 2 affects the operation of the differential switch, this test method is satisfactory.

Figures 5 to 10 illustrate the forms of current for analyzing the functionality of RCCBs and precisely in Figure 5 the alternating test current ia is illustrated, in 6 also the alternating current ia, but this begins with a phase shift equal to 180 °. Figure 7 illustrates the pulsating direct current ic with a weak rectified direct current component Ib. Figure 8 illustrates the pulsating direct current ic with a weak rectified direct current component Ib, both in the opposite direction to those of Figure 7. Figures 9 and 10 illustrate the direct currents Id, where the current Id of Figure 10 has opposite direction of the current of Figure 9.

All the forms of current, illustrated in Figures 5 to 10, are created by means of the circuit object of this invention, illustrated in Figure 11. The elements of the circuit are the rectifying diodes D1, D2, D3 and D4, the switches Si and S2, the smoothing unit F and the current leakage unit P regulated through the line K. All these elements are known and included in the state of the art, while their mutual connection is new.

The circuit object of this invention is composed as follows:

Contact 1 is connected to the cathode of diode D1 and to the anode of diode D2; contact 2 is connected to contact 11 of switch SI and to contact 14 of switch S2; contact 3 is connected to the cathode of diode D3 and to the anode of diode D4; The anode of the diode D1 is connected to the contact 12 of the switch S1; the cathode of diode D2 is connected to contact 13 of switch S2; the anode of the diode D3 is connected to the contact 5 of the current leakage unit P, to the contact 7 of the switch Si and to the contact 15 of the switch S2; the cathode of the diode D4 is connected to the contact 4 of the current leakage unit p, to the contact 8 of the switch S2 and to the contact 10 of the switch S1; the contact of the smoothing unit F is connected to the contact 6 of the switch S1, while the contact of the unit F is connected to the contact 9 of the switch S2.

In the context of the current dispersion unit P, by contact 4 is meant that in which the current flows, while by contact 5 that from which the current flows. The current leakage unit is regulated via the K line.

During the test the contacts 1,2 and 3 are connected with the contacts of the differential switch marked in the same way (figure 1).

The smoothing unit F consists of a capacitor and a resistor connected in parallel.

The current leakage unit P acts as a test current regulator. Basically it is composed of a power transistor and the regulation electronics. In our case, the regulation voltage is supplied by a microprocessor through a digital analog converter.

Switches S1 and S2 are independent of each other and both have two possible positions, therefore four possible combinations, of which only three are used, namely:

1. YES in position I (contacts 6-11 and 7-12 closed) and S2 in position I (contacts 8-13 and 9-14 closed). The circuit in this case supplies alternating current ia. During the positive half-period (contact 1 is positive with respect to contact 2) the alternating current flows from the phase conductor L through the branch L - 1 and passes through the diode D2, the current leakage unit P, the diode D3 and therefore through contact 3 back into the neutral conductor N (contact 3 is connected to the protective conductor E, which has a ground connection and is connected to the neutral conductor N) See figure 1. During the negative half-period, alternating current flows from the neutral conductor N through contact 3, through the diode D4, the current leakage unit P, the diode DI and then through the branch L - 1 back into the phase conductor. Alternating current flows through branch L - 1, while pulsating direct current (unidirectional half-wave alternating current) flows through the current leakage unit. The amplitude of the alternating test current ia is maintained at the pre-selected value by the current leakage unit P, adjusted by unidirectional sinusoidal pulses. The regulation pulses are in phase with the applied alternating voltage (voltage between contacts 1 and 2). The start of the current can also be determined by adjusting the current leakage unit P.

2. SI in position II (contacts 6-10 closed) and S2 in position I. In this case, the circuit supplies both pulsating direct current ic superimposed on a weak direct component Ib (figure 7) and smoothed direct current Id (figure 9 ), depending on the setting of the current leakage unit P. During the positive half-period (contact 1 is positive with respect to contact 2) the pulsating direct current ic flows from the phase conductor L through the branch L - 1 (in the direction from L to 1), through the diode D2, the current leakage unit, through the diode D3 to contact 3 and from there into the neutral conductor N. The current leakage unit P during the positive half-period is regulated as in the case of alternating current and provides a normal sinusoidal form of half-wave of current ic, while during the next half-wave the microprocessor drives the regulation so that the current leakage unit P supplies current Ib. In this period the source for the current Ib is the capacitor of the smoothing unit F, which during the second half period discharges in the ring starting from the contact of the smoothing unit F, continues through the current dispersion unit P , up to diode D3, to contact 3, to neutral conductor N, through branch N 2 and closes on contact - of the smoothing unit F. During the second half-period the current Ib does not flow in branch L - 1, but in the N - 2 branch, but has the same direction as that of the current ic through the L - 1 branch during the first half period, so its effect on the magnetic flux in the RCD core is exactly the same as that which would arise if the current flowed in the same direction in the branch L - 1. When the test with smoothed direct current Id is carried out, the capacitor of the smoothing unit F represents the internal source for the test current Id, while the unit current leakage is adjusted to a constant value of the preselected intensity of the current Id. The current Id flows in the same circuit as the current Ib.

3. YES in position I and S2 in position II (contacts 9-15 closed). In this case, the circuit delivers pulsating direct current ic superimposed on a weak component Ib (figure 8) or smoothed direct current Id (figure 10), depending on the regulation of the current leakage unit P, in which case the currents ic , Ib and Id have the opposite direction to the previous ones. During the negative half-period (contact 2 positive with respect to contact 1) the pulsating direct current ic flows in the circuit from the neutral conductor N to through the contact 3, the diode D4, the current leakage unit P, the diode DI and through the branch L - 1 returns to the phase conductor L. The unit of dispersion of the current P during the negative half-period is regulated as for the alternating current and supplies a current ic with a half-wave having a normal sinusoidal shape.

During the following half-period the microprocessor guides the regulation so that the dispersion unit P supplies current Ib. In this period the current source Ib is the capacitor of the smoothing unit F, which during the second half-period discharges in the ring that starts from the contact of the smoothing unit F, flowing through the branch N - 2, the conductor of neutral N, contact 3, diode D4, the current leakage unit P and returns to the contact - of the smoothing unit F. During the second half-period the current Ib does not flow in branch L -1, but in branch N - 2, but it has the same direction as that of the current ic through the branch L - 1 in the first half period and its effect on the magnetic flux in the core of the RCD is exactly the same as it would if it flowed in the same direction through the branch L - 1. The smoothing unit capacitor F discharges with current ic even during the first half period, when the voltage across the smoothing unit capacitor is greater than the voltage between contacts l and 2.

When the test is carried out with continuous smoothed current Id, the capacitor of the smoothing unit F represents the internal source of the test current Id, while the leakage unit P is regulated at a preselected constant value of intensity of the current Id. La current Id flows in the same circuit as current Ib.

When the leakage current unit P operates under test with smoothed current Id in constant current regime, through the correct sizing of the smoothing unit F no wavy test current Id is generated, despite the relatively undulating voltage on the capacitor of the smoothing unit F. In order to simplify the description of the circuits, I assumed that the protective conductor E is at the potential of the neutral conductor N (fig. 1). In practice, small potential differences may arise, which however do not disturb the leakage current unit P, which maintains the delivery efficiency of the prescribed intensities of the individual test currents.

The switches SI and S2 are usually relays which are activated by the microprocessor and are in position I if the relay is not activated.

The direct current Ib, which is added to the half-wave current ic, is used to ascertain the disconnection of the differential switch. If the disconnection detection is carried out in some other way, this current is not necessary. The half-wave test current ic can also be supplied when switches SI and S2 are in position I, if the leakage current unit P is properly adjusted.

The current leakage unit P (Current Sink) is included in the state of the art and is described e.g. in the "Application Notes" of the company National Semiconductor GmbH (Fürstenfeldbruck, Germany) of 1973.

The circuit object of this invention is inexpensive. In case of continuous test current Id supplies, to a capacity of the smoothing unit equal to 47 / xF and to the power supply voltage 230 Vef, at least 800 mA. In this case, the leakage unit P is regulated for a constant current.

Claims (1)

CLAIM Circuit for the creation of currents for the analysis of the functionality of RCCBs, consisting of directional diodes (DI), (D2), (D3), (D4), circuit breakers (SI), (S2), smoothing (F), by the adjustable current leakage unit (P), characterized by the fact that the contact (2) is connected to the contact (11) of the circuit breaker (SI) and to the contact (14) of the circuit breaker (S2 ), that the contact (3) is connected to the cathode of the diode (D3) and to the anode of the diode (D4), that the anode of the diode (D3) is connected to the contact (7) of the switch (51), to the contact (5) of the leakage current unit (P) and to the contact (15) of the switch (52), that the contact (4) of the leakage current unit (P) is connected to the cathode of the diode (D4), to the contact (8) of the switch (S2) and to the contact (10) of the switch (SI), that the anode of the diode (DI) is connected to the contact (12) of the switch (SI) , that the cathode of the diode (D2) is connected to the contact or (13) of the switch (S2), that the contact (+) of the smoothing unit (F) is connected to the contact (6) of the switch (SI) and finally that the contact (-) of the smoothing (F) is connected to the contact (9) of the switch (S2).