RU2097894C1 - Ac mains electrical safety device - Google Patents

Abstract

FIELD: electrical engineering; automatic electrical safety devices for personnel. SUBSTANCE: newly introduced are resistors 9-11 and second voltage regulator diode 12 connected so that output of rectifier bridge 7 becomes connected via first resistor 9 to coil of output relay 4 and via second resistor 10, to base of transistor 3. EFFECT: improved noise immunity of device. 2 cl, 1 dwg

Description

 The device relates to electrical engineering, in particular to automatic devices for protecting people from electric shock. Protective shutdown devices (RCDs) are known and widely used, for example, RCD [1] RCD-V [2] RCD-B [3] and others containing a leakage current sensor 1, a semiconductor threshold element 2, a transistor switch 3, an output relay 4 , a zener diode 5, a filter capacitor 6, a rectifier 7 for powering a threshold element and a relay, and a current-limiting capacitor 8 in the rectifier's AC circuit. For all known devices, the output relay coil is connected via a key parallel to the power supply circuits of the threshold element.

 Closest to the technical nature of the proposed device is a device of types UZOSH, adopted by us as a prototype.

 Functional diagram of the prototype is shown in the drawing.

In the prototype, a voltage of 220 V through a current-limiting capacitor 8 with a large capacitance X _c is supplied to the bridge rectifier 7.

 The voltage rectified and smoothed by the filter capacitor 6 is supplied to two parallel branches: a relay coil 4 with a transistor switch 3 connected in series; voltage stabilizer on a zener diode 5 and a semiconductor threshold element 2.

The disadvantage of the prototype is the high power consumed from the AC network, and the lack of reliability of the device. This is because the device operates in two modes: mode A, in which the relay coil circuit is open and a current I _{A is supplied} from the network through a current-limiting capacitor 8, equal to the sum of the current I _pe passing through the threshold element and the current I _st.A , current through a zener diode in mode A (I _A I _pe + I _{st. A} ); In the mode in which the coil of the relay circuit is closed and the total current I _{A to} I over approximately a current value I _p of the relay coil (I = I _a + I _{Peh st.v} + I _p), where I _st.v new current value going through a zener diode in mode B.

Obviously, _with the current-limiting resistance X of the capacitor 8 must permit passage largest current corresponding to the mode B. In mode A will flow from the network to the circuit current I _{and in} ≈I, since the magnitude of this current is mainly determined by the resistance of the capacitor 8 _with X, and it is selected from the conditions of mode B. In this case, the current increment ΔI I _in -I _а ≈ I _р will be added to the current through the zener diode 5 and will cause its increased heating and, as a result, a decrease in the reliability of the entire device.

 Another serious common drawback of analogues and prototype is their low noise immunity, which is manifested in the fact that the device responds to electromagnetic waves that occur when sparking switched electrical appliances in parallel outlets, and gives false shutdowns. This reduces the reliability of the power supply of the protected electrical installation.

 The aim of the invention is to reduce the power consumed from the network, increasing the reliability and noise immunity of the device.

 This circuit is achieved by the fact that the first, second and third resistors and the second zener diode are additionally inserted into the device, so that the connection point of the first output of the filter capacitor with the output of the rectifier bridge is connected through the first input resistor to the output relay coil and through the second input resistor to the base transistor, the other end of the relay coil is connected to the first output of the first zener diode, parallel to the relay coil, taking into account the polarity, the collector and emitter of the transistor are connected, the base of which is attached One through series-connected the third resistor and a second zener diode to the output of the threshold element. Improving the noise immunity of the device is achieved by the fact that an additional capacitor is introduced, which is connected to the output of the threshold element with one output, and the other to one of the relay output contacts.

 The device, the circuit of which is shown in the drawing, contains a sensor 1, a threshold element 2, a transistor 3, a relay 4, a zener diode 5, a filter capacitor 6, a rectifier bridge 7, a current-limiting capacitor 8 and newly introduced resistors 9 11, a zener diode 12 and an anti-noise capacitor 13.

 The proposed device operates as follows.

где U_~ и U_ст.5 напряжение соответственно сети и стабилитрона 5;
R₉ и R₄ сопротивление резистора 9 и катушки реле 4;
X₈ емкостное сопротивление конденсатора 8.When applying 220 V voltage to the input terminals of the device, an alternating current is established in the alternating current circuit of the rectifier bridge 7, the effective value of which is determined from the expression:

where U _~ and U _st.5 voltage respectively of the network and the zener diode 5;
R ₉ and R _{4 the} resistance of the resistor 9 and the relay coil 4;
X ₈ capacitance of the capacitor 8.

A rectified alternating current, a constant component (average value) of which is I _- = I _~ / K _f , where K _f the form factor, which depends on the degree of filtration by the capacitor 6, flows through two parallel circuits. One circuit, let's call it "power", consists of a resistor 9, a relay coil 4, a zener diode 5, voltage U, _{article 5 of} which powers a threshold element 2. Another circuit, let's call it "control", consists of a resistor 10, resistor 11 and zener diode 12.

 Let us consider in turn the processes in each circuit, starting with the "power" circuit, taking into account that the current in the power circuit is 20-30 times greater than the current in the control circuit. On this basis, when considering processes in the power circuit, the current in the control circuit is not taken into account.

From the expression (1) it can be seen that in those cases where X ₈ > R _Σ R ₉ + R ₄ , the value of I _~ and I ₌ depend little on the change in R _Σ . Therefore, if the relay coil 4 is switched by shunting it using a transistor switch 3, then the current changes I _~ and I ₌ will be insignificant. We illustrate the above with a numerical example, in which the numerical values of the nominal values of the components of the circuit correspond to the ratings in a real product: R ₉ 820 Ohm, R ₄ 1400 Ohm, C ₈ 0.47 mF, X ₈ 6770 Ohm, U _~ = 220 V ,, U _{Art. 5} 30 V. For these values we have: in mode A, when the relay coil is shunted by an open transistor, R _Σ R ₉ and I _~ = 27.8 mA; in mode B, when the transistor is closed, R _Σ R ₉ + R ₄ and I _~ = 26.6 mA.
This example shows that in the proposed device, the current increment in the zener diode 5 during the transition from mode A to mode B is insignificant (only 1.2 mA), and in the prototype this increment, depending on the relay used, is 25.30 mA.

We turn to the consideration of the transistor control circuit. As can be seen from the diagram in figure 2, the direct connection of the output of the threshold element 2 with the base of the transistor 3 will not provide switching of the transistor and the state is "open" due to the fact that the potential at the output of the element 2 in any mode is lower than the potential of the emitter. Therefore claimed transistor control circuit, which allows to displace the base potential relative to the emitter in the range of -5 V with U _2.A ≈0 V to +1.0 V at 1.5 U _2.B ≥20 W.

Consider, as in the case of the prototype, two modes: mode A, when the voltage at the output of the threshold element does not exceed 2 V (U _2.A ≅ 2 V); Mode when U ≈U _{2. In Article 5,} ie when the threshold element has entered the state of a logical unit, (the element "worked").

где U₆, U_ст.12, U₂ напряжение соответственно на элементах 6, 12 и 2;
R₁₀, R₁₁ сопротивление резисторов 10 и 11.In any mode, the current is set in the circuit with elements 10-11-12-2:

where U ₆ , U _{Art. 12} , U ₂ voltage respectively on the elements 6, 12 and 2;
R ₁₀ , R ₁₁ resistance of resistors 10 and 11.

Напряжение между базой и эмиттером равно

При выборе определенных значений входящих в выражение (4) составляющих, например, для режима А, U_2.А 2 В, U_ст.12 8,2 В, U _ст.5 30 B, U₆ 60 В, R₁₀ 47 кОм, R₁₁ 20 кОм, получаем напряжение U_бэ.А -4,934 В. При этом напряжении в режиме А транзистор закрыт, а реле включено, так как через катушку проходит полностью ток I₌= I_~/K_ф.
В режиме В выходное напряжение порогового элемента U_2.В≥28 В. Подставив U_2.В 28 В в выражение (4) при прочих неизмененных значениях, получим U_бэ.В +13,3 В. Таким образом, в режиме В произошло изменение полярности напряжения на базе транзистора и он перешел в насыщенное состояние (открылся), зашунтировав катушку реле. Контакты реле при этом размыкаются.Express the potentials of the base and emitter of transistor 3 relative to the negative pole of the rectifier:

The voltage between the base and the emitter is

When choosing certain values of the constituents included in expression (4), for example, for mode A, U _2.A 2 V, U _{st. 12} 8.2 V, U _{st. 5} 30 V, U ₆ 60 V, R ₁₀ 47 kOhm , R ₁₁ 20 kOhm, we obtain a voltage of U _be.A -4.934 V. At this voltage in mode A, the transistor is closed and the relay is turned on, since the current passes completely through the coil I ₌ = I _~ / K _f .
In mode B, the output voltage of threshold element U _2.B ≥28 W. Substituting U _2.B 28 in the expression (4) with other values unaltered obtain 13.3 U _be.V B. Thus, B-mode occurred a change in the polarity of the voltage at the base of the transistor and it went into a saturated state (opened) by shunting the relay coil. The relay contacts open.

Actually, the voltage is U _{BeV. It} does not reach 13.3 V, but the base-emitter junction of the transistor is installed at the voltage level pn, but this is not essential for considering the operation of the proposed device.

 The proposed circuit provides a virtually unchanged current consumption from the mains in modes A and B, as a result of which the value of the capacitor B is reduced, overload of the zener diode 5 is excluded, overall reliability of the device is increased, and overall dimensions are reduced.

 It is not possible to analyze the sensitivity of the device to electromagnetic interference by calculation, therefore, the increase in noise immunity is carried out empirically on the basis of laboratory tests of prototypes and prototypes. It has been experimentally established that the connection through the capacitor 13 of the output of the threshold element 2 to the ground or to any network wire increases the noise immunity of the device in the "ready" mode (mode A) and reduces the noise immunity in the "off" mode (mode B). Therefore, the anti-interference capacitor 13 is connected to the network in mode B, due to which the noise immunity is maintained in this mode.

 Technical and economic efficiency is expressed in the minimum current consumption from the network, reducing the power dissipated by the zener diode, and thereby increasing the reliability of the device, as well as increasing the reliability of power supply of the protected electrical installation by increasing the noise immunity of the device.

Claims (2)

 1. A device for protective shutdown in an alternating current electric network, comprising a sensor connected to an input of a threshold element by its output, a transistor, an output relay, a first zener diode connected to a filter capacitor connected in parallel with the output of the rectifier bridge, whose alternating current circuit is connected in series with a current limiting a capacitor, characterized in that the first, second and third resistors and the second zener diode are included so that the output of the rectifier bridge is connected through the first resistor with the output relay coil and through the second resistor with the base of the transistor, the other end of the relay coil is connected to the other output of the first zener diode, parallel to the output relay coil, taking into account the polarity, the collector-emitter junction of the transistor is connected, the base of which is connected through a third resistor and a second Zener diode to the output of the threshold element.  2. The device according to claim 1, characterized in that a capacitor is introduced into it, which is connected by one output to the output of the threshold element, and the other with one of the output contacts of the relay.