RU2342758C1 - Method of reducing capacitive enclosure leakage currents on power-line filters of radio interference - Google Patents

Abstract

FIELD: physics; radio.

SUBSTANCE: present invention pertains to transformation technology and can be used in power-line filters of radio interference. The technical outcome of the invention is the profound suppression of non-symmetrical electromagnetic interference with simultaneous meeting of electrical safety requirements on limiting capacitive leakage currents. Proposal is given of a method of reducing capacitive leakage currents on power-line radio interference filters, comprising one or more nodes, each of which is connected through a capacitor to the power-line filter lines and the case. The potential of one of the nodes is varied such that, the potential difference at low frequency between the given node and the case approaches zero. Potential of similar nodes of other sections of the filter are simultaneously controlled through chokes, decoupling at high frequency. As a result of reducing the potential difference at low frequency between the node and the case down to zero, all leakage currents on the case are practically eliminated. In particular, to implement the method, a signal is generated, proportional to the voltage between one of the indicated nodes and the case. That signal is applied to the input of a duo-directional amplifier, at the positive supply input of which a more positive voltage is applied through rectification, acting on the lines of the power-line filter at points of connection to capacitors of the given node. At the negative supply input of the duo-directional amplifier, a more negative voltage is applied through rectification from the same points of the lines of the power-line filter. Capacitors are re-charged by the output current of duo-directional amplifier and as a result, voltage between the given node and the case of the filter at low frequency is practically reduced to zero and consequently, all leakage currents on the case are eliminated.

EFFECT: reduced capacitive leakage currents of power-line filters of radio-interference.

2 cl, 3 dwg

Description

The invention relates to a conversion technique and can be used in surge suppressors for the deep suppression of asymmetric conducted noise while fulfilling electrical safety requirements for limiting capacitive leakage currents.

Known noise suppression filters [1], consisting depending on the required level of suppression, as well as on the impedance of the network and the load from the capacitors, or from capacitors and inductances according to the scheme of a L-shaped, U-shaped, T-shaped or n-link filter, in which inductors are included in the circuit of the linear wires, and capacitors connect the inductance leads to the filter housing. The disadvantage of such filters is the presence of capacitive leakage currents, which, according to safety conditions, are limited by the relevant regulatory documents, for example, GOST RV 20.57.310-98. In addition, the use of such filters degrades the operation of residual current devices (RCD), which respond to the appearance of leakage currents to the housing, and therefore the threshold of operation of such devices must be increased. This means that if a person gets under voltage, acting, for example, between the ground and the electrical installation case, the RCD will operate at a higher current flowing through the person than it would be without a radio interference filter. Obviously, the safety of the electrical installation is reduced.

The closest analogue is the radio interference filter [2], in which capacitors are connected to the housing with one output, and connected to the inductance outputs with the other output through a capacitive divider connected between the linear wires. The prototype has the same drawbacks as the analogue, and to ensure the necessary level of noise suppression, subject to safety standards, it is necessary to reduce the capacitance of the capacitors connecting the filter to the housing, and therefore increase the number of links and the inductance of the inductive elements of the filter, which leads to an increase mass and dimensions of the device.

The problem to be solved in the present invention is to increase the efficiency of suppressing conductive asymmetric noise in the filter and to reduce its overall dimensions by increasing the capacitance of case capacitors while observing electrical safety requirements for limiting capacitive leakage currents.

The technical result from the application of the invention is to reduce the capacitive leakage currents of the radio noise filter.

This object is achieved by the fact that a method for reducing capacitive leakage currents to the housing of the RFI network filters, containing one or more nodes, each connected via capacitors to the line filter lines and to the housing, is proposed, which consists in the potential of one of the nodes change in such a way that the potential difference at a low frequency between this node and the housing tends to zero, the potentials of similar nodes of other filter links are controlled simultaneously through decouples chokes with high frequency, as a result of reducing the potential difference at a low frequency between the nodes and the housing to zero, practically eliminate the leakage current to the housing at a low frequency.

In particular, in order to implement the method, a signal is generated proportional to the voltage between one of these nodes and the housing, it is fed to the input of a push-pull amplifier, the power of which is provided using a bridge rectifier, the input of which is connected to the line filter at the connection points of the capacitors of this link, the output the current of the push-pull amplifier, while recharging the capacitors, control the voltage of this node and through the decoupling high-frequency chokes the voltage of the nodes of other filter links in this way to reduce to zero the low-frequency signal at the input of the amplifier, and hence the low-frequency voltage between the housing and filter nodes, and as a result, leakage current to the housing is practically eliminated at a low frequency.

The essence of the invention is illustrated by the functional diagram shown in figure 1, as well as the measurement circuits of capacitive leakage currents in figure 2 and 3.

Figure 1 shows the radio interference filter 1, filter link 2, inductive elements 3, capacitors of capacitive dividers 4, housing capacitors 5, voltage sensor 6, push-pull amplifier 7, rectifier 8, decoupling inductor 9. Figure 2 shows the measurement circuit of capacitive currents filter leakage by the example of a single-link capacitive filter according to the structure of the analogue and prototype. In addition to these elements, figure 2 and 3 shows the EMF network 10, an ammeter for measuring leakage currents 11 and a limiting resistor 12.

The proposed method is illustrated by the example of a block diagram of a single-phase, two-link radio interference filter 1 (Fig. 1). The filter has two lines (according to the number of network lines) with inductive elements connected in series. The filter inputs L1 and L2 are connected to an alternating voltage network, and the outputs H1 and H2 are connected to a load (a device that generates interference). The input and output of the filter are connected through two series-connected links 2. Each link consists of an inductive element 3, two capacitors of capacitive dividers 4 connected to the input terminals of the inductive element 3 and a midpoint through the housing capacitor 5 to the housing. A voltage sensor in the form of a capacitive divider 6 is connected to the midpoint of the capacitive divider of the second link, the lower arm of which is connected to the housing, and the output is connected to the non-inverting input of the push-pull amplifier 8, the inverting input of which is connected to the output of the voltage sensor 6, and also with the output of the amplifier 8 and with the midpoint of the capacitive divider of the second link. The power of the amplifier 7 is provided by a bridge rectifier 8, the input of which is connected to the filter lines at the connection points of the capacitive divider of this link. Between the midpoints of the capacitive divider links included decoupling choke 9.

The principle of compensating for capacitive leakage current is that the voltage at the midpoints of the dividers (point A, Fig. 3) at the low frequency (mains frequency) is set equal to the voltage of the case, therefore an alternating low-frequency voltage and the low-frequency component of the leakage current are not applied to the case capacitors they do not leak.

The method is implemented as follows.

When a circuit occurs between one of the network lines and the housing (Fig. 1), the voltage on the housing will approach the voltage of this network wire and will begin to differ in frequency from the voltage of the midpoints of the dividers connected to each other by the inductor 9. This alternating voltage is supplied through the voltage sensor 6 to the non-inverting input of the push-pull amplifier 7, the output current of which is recharged by the capacitive dividers 4 by the principle of negative feedback so that the variable low-frequency component of the voltage between the inputs of the amplifier 7 tends to zero. In this case, the alternating LF component of the voltage of the case capacitors 5 will also tend to zero, which means that the capacitive leakage current at the network frequency will also tend to zero.

Bibliographic data

1. Sources of power supply of electronic equipment: Handbook / G.S. Nayvelt, K. B. Mazel, Ch. I. Khusainov and others; under the editorship of G.S. Naivelt. - M .: Radio and communications, 1985 .-- 576 p., Ill.

2. www.epcos.com. Filters for Converters in Traction Systems. Type B84142A * S002. Ordering code B84142A0250S002.

Claims (2)

1. The method of reducing capacitive leakage currents to the housing of the network noise filters, containing the number of links one or more nodes, each of which is connected through capacitors to the lines of the network filter and to the housing, characterized in that the potential of one of the nodes is changed so that the difference potentials at a low frequency between this node and the housing tended to zero, the potentials of similar nodes of other filter links are controlled simultaneously through high frequency decoupling chokes, as a result of the potential difference at a low frequency between the assembly and the housing to zero practically exclude low frequency leakage current to the body. 2. The method of reducing capacitive leakage currents according to claim 1, characterized in that they generate a signal proportional to the voltage between one of these nodes and the housing, feed it to the input of a push-pull amplifier, the power of which is provided using a bridge rectifier, the input of which is connected to the network lines filter at the connection points of the capacitors of this link, the output current of the push-pull amplifier, while recharging the capacitors, control the voltage of this node and through the decoupling high-frequency chokes the voltage of the nodes their filter links in such a way as to reduce to zero the low-frequency signal at the amplifier input, and hence the low-frequency voltage between the housing and filter nodes, and as a result, leakage current to the housing is practically eliminated at a low frequency.

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