RU2214612C2 - Facility monitoring leakage current - Google Patents

Abstract

FIELD: electric measurement technology. SUBSTANCE: invention can be employed to monitor leakage current from objects connected to electric voltage source, for instance, to measure leakage current through body of trolley bus to ground. Signals from generator 17 switch in step keys 8, 12, 13, key 8 connects and disconnects resistor 7 with resistance R_Д placed between body and ground. At same time voltage across body 4 is measured by means of meter 2 incorporating divider-limiter 6, rectifier 9 from which signals go to filters-converters 11, 14, 15 through keys 12, 13 and separating element 10. As result signals are fed to inputs of multiplier-divider 16 proportional to U_b - voltage on body 4 while key 8 is open; U_b-ΔU - voltage on body while key 8 is closed ( ΔU is drop of voltage U_b when resistor 7 with resistance R_Д is connected to body ); ΔU•R_Д - difference voltage between U_b and ( (U_b-ΔU) ) with due account of proportionality factor changing in line with R_Д. Voltage

is formed across output of multiplier- divider 16 where B is constant coefficient which value is chosen for reasons of convenient level of signals in elements of amplifier 2. Voltage U₁₆ shows in certain scale total leakage current from body to ground through indicator 5. EFFECT: reduced error in measurement of leakage current achieved thanks to indirect measurement of resistance between body of trolley bus and ground inaccessible for direct measurement, measurement of voltage between body and ground and computation of current according to Ohm's law. 4 dwg

Description

 The inventive device relates to the field of electrical engineering and can be used to control the leakage current from objects connected to electric voltage sources, for example, to measure the leakage current through the body of a trolley to the ground. It can be used in depots, control and dispatching points for timely detection of dangerous values of leakage current in order to prevent damage to humans and animals touching the elements of the trolleybus body.

 Known on-board signaling device for leakage current of a trolley bus (see the journal "Bulletin of urban electric transport of Russia" 6 (15), 1996, p. 7. ... 10), containing a source of compensating voltage with a measuring device, a control unit and an alarm. However, it can only be used in power supply systems of vehicles with a grounded negative pole. This relates to the disadvantage of the known signaling device, because in recent years, the newly introduced trolleybus facilities have been using a power system with poles isolated from the ground (see the book by D.K. Tomlyanovich, V.P. Chubukov. Protection of power supply devices M .: Transport, 1980, p. 11 ... 13, and also pages 88 ... 96).

 The closest adopted for the prototype is a device for measuring leakage current with an earthing switch (see the Standard Instructions for ensuring the safety of passengers of trolley buses from leakage currents. M. 1996, Ministry of Transport of the Russian Federation, Department of Road Transport, page 16, Fig. 1) . The closest known device belongs to the same class as the claimed one, namely with the grounding of the body at the time of measurement. It contains a test probe, a resistor shunted by a key, and a current meter - milliammeter. The disadvantages of this device include a large error in the measurement of leakage current, due to the fact that the leakage current component passing through the buses is not taken into account.

 In real power supply systems, both with a grounded negative bus and with isolated buses (see the journal "Bulletin of urban electric transport of Russia" 6 (33), 1999, p. 4, fig. 1; p. 5, fig. 3 ) there is always a leakage of current through the busbar resistance, which does not leak through the meter of a known device, i.e. the measuring device underestimates the leakage current, and this can lead to the case when a trolley with an increased leakage current may be on the line.

 The proposed device allows to reduce the error of measurement of leakage current. This is achieved due to the fact that in the device containing the meter, which is connected to the object by the input through the probe and the indicator by the output, the meter is made in the form of a divider-limiter with a resistor circuit connected in parallel to the input and connected in series with him first key. At the output, the divider is connected to the input of the rectifier, the output of which through the separation element is connected to the input of the first filter converter and directly to the information inputs of the second and third keys, the outputs of which, respectively, through the second and third filter converters are connected to the second and third inputs of the multiplier divider whose first input is connected to the output of the first filter converter, and the output to the output of the meter. In addition, a generator was introduced, the direct output of which is connected to the control inputs of the first and second keys, and the inverse output is connected to the control input of the third key. A power supply has also been introduced, the output of which is connected to a meter and an indicator.

 Figure 1 shows the structural diagram of the inventive device.

 Figure 2 presents a diagram of the flow of leakage current in an isolated trolley bus power system.

 In FIG. 3 shows a diagram of the leakage current flowing through the resistance of tires and a person in case of electrical contact with the trolleybus body.

 Figure 4 presents diagrams of electrical signals to explain the operation of the device.

The device contains a power supply 1 for supplying the functional elements of the device, a meter 2, which is connected electrically to the body 4 by a probe 3, indicator 5. The meter 2 includes: a divider 6, in parallel with the input of which a resistor 7 with resistance R _{d is} connected through a key 8 to ground, a rectifier 9 connected at the input to the output of the divider 6. The output of the rectifier through a dividing element 10, such as a capacitor, is connected to the input of the filter converter 11. Directly, the output of the rectifier is connected to the information input the keys 12 and 13, while the outputs of the keys are connected respectively to the inputs of the filter converters 14 and 15, the outputs of which are connected to the second and third inputs of the multiplier dividing device (MDU) 16. The output of the MDU 16 is the output of the meter, which is connected to the indicator input 5. The first input of the MDU 16 is connected to the output of the filter Converter 11.

 In meter 2 there is a generator 17 of periodic signals, for example, pulse, rectangular in shape and with a duty cycle of 2.

 From the direct output of the generator, the signals are supplied to the control inputs of the keys 8, 12, and from the inverse output of the generator to the control input of the key 13. The supply voltage from unit 1 is supplied to the measuring unit 2 and supplied to the generator 17, keys 12, 13, filter converters 11, 14, 15, MDU 16, as well as indicator 5.

 Divider-limiter 6 contains resistors 18, 19 and limiter 20, for example, in the form of a bi-directional zener diode.

To explain the operation of the proposed device, we consider the circuit of the leakage currents, shown in figure 2, 3, where indicated:
U is the power source of the trolleybus network;
U _P - voltage of the positive bus relative to the ground;
U _O - negative bus voltage relative to the ground;
U _K - voltage on the body relative to the ground;
R ₁ , R ₂ - insulation resistance, respectively, positive and negative tires relative to the ground;
R _P , R _O - insulation resistance of the trolley body relative to the positive and negative tires, respectively;
R _W - the resistance of the body relative to the ground;
R _H - the resistance of the body of a person standing on the ground and touching the body.

The leakage current I _P of the tire _P U flows along the chain U +, R _II, R _III R _CH parallel Land, R _2, -U. A similar circuit flows the leakage current I _O from the bus U _O.

As a result, a voltage U _K appears on the body.

The total leakage current I _{at the} leakage is equal to the algebraic sum of I _P and I _O : I _y = I _P + I _O.

In the absence of man, the leakage current I _y1 flows only through the resistance R _Ш. On the body relative to the ground there will be voltage U _K1 .

If a person touches the body, the leakage current I _у2 flows along two parallel chains: through R _Ш and R _Ч (Fig. 3)
By connecting the meter instead of R _W, as is done in the known device, it is impossible to measure the component of the current I _W R through _W, even though this component is the objective characteristic of the state of insulation trolley.

 Consider the operation of the device.

When applying power, the generator 17 generates pulses 21, 22 (figure 4). By pulses 21, switch 8 and key 12 are closed at positive levels and open at negative levels. As a result, the resistor 7 is connected or disconnected from the input of the meter 2. When you disconnect R _D at the input of the divider 6 there is a voltage U _K , and when connected U _K -ΔU, this is illustrated by the diagram U ₆ (figure 4), where ΔU is the voltage reduction at load connection R _D.

 Divider-limiter 6 is designed to reduce high voltage, which in an emergency may be on the trolley bus body, to a value that is safe for the device.

Для схемы (фиг.2) справедливо также

где

- эквивалентное сопротивление параллельно соединенных сопротивлений R_Ш и R_Д.Regardless of the power supply system, that is, regardless of whether the negative bus is grounded or isolated from the ground, the voltage on the body relative to the ground will be U _K with the switch open and U _K -ΔU with the switch closed. Accordingly, the leakage current I _r with an open key and I _C with a closed one can be determined according to Ohm's law by the formulas
I _p = U _K / R _W ; (1)

For the circuit (figure 2) is also true

Where

- equivalent resistance in parallel connected resistances R _W and R _D.

Подставляем значение R_Ш в (1)

Формула (7) позволяет найти полный ток утечки с кузова на землю через шины, который имеет место в реальном случае.But since R _P >> R _W ; R _O >> R _W and R _D >> R _W , with great accuracy, we can assume that
I _p ≈I _s (5)
Solving (1) and (2) taking into account (5), we find

Substitute the value of R _W in (1)

Formula (7) allows you to find the total leakage current from the body to the ground through the tires, which takes place in the real case.

At the output of rectifier 9, the signals U _{9 are} always positive. From the output of the rectifier 9 through the isolation capacitor 10, the variable component of the signal ΔU is fed to the input of the filter converter 11, which converts the pulse signal ΔU into a constant proportional to it, taking into account the value of R _D.

As the filter Converter 11, you can use a rectifier similar to the rectifier 9, with a smoothing RC filter at the output. And the multiplication of ΔU by a constant value of R _{D is} equivalent to the selection of the transfer coefficient of the rectifier.

At the first input of the divider MDU 16 receives a constant voltage proportional to ΔU • R _D. The information inputs of the keys 12, 13 receives a signal U ₉ . At the control inputs, the keys alternately close and open in antiphase with signals 21, 22. Synchronous detection occurs. As a result, pulses appear at the output of key 12, the amplitude of which is proportional to U _K -ΔU, and at the output of key 13, U _K.

где В - постоянный коэффициент, значение которого выбирают из соображений удобного уровня сигналов в элементах усилителя 2.The filter converters 14, 15, these signals are converted into constant voltage of positive polarity, which are proportional to the voltage U _K -ΔU and U _K observed at the input of the meter 2. These signals are fed to the second and third inputs of the MDU 16, the output of which produces a voltage

where B is a constant coefficient, the value of which is chosen for reasons of a convenient signal level in the elements of amplifier 2.

 This voltage is supplied to indicator 5, which displays it in units (milliamperes) of leakage current in accordance with formula (7).

 To test the operability of the proposed device and experimental confirmation of the above calculations, a prototype was made in which opto-thyristors type TO-125 were used as key 8 in the maximum operating current mode of 0.5 mA, which is several times less than the rectification current of the thyristor. In this mode, the opto-thyristors operate as bipolar transistors, they have a high reverse voltage (1600 V) and isolation from the control circuits.

 As a rectifier 9 and a filter converter 11, circuits similar to those described in the book by Falkenberry L. The use of operational amplifiers were used. Per. from English M.: Mir, 1985, pp. 241 ... 242, Fig. 9.6.

 As a generator, a circuit similar to the generator from the above book, p. 253, Fig. 9.12.

 A microchip of type 525PS2B was used as an MRL, as an indicator 5, an ADC of type 572PV2 with indicators of the type KIPTsZ 22-2 / 8k at the output was used.

 The prototype was tested for 1 year in the trolleybus park of the Izhevsk Tram-Trolleybus Office (address: 426057, Izhevsk, Mayakovsky St., 7, chief engineer A. Bagirov, tel. (3412) 75-14 -77). The test result is positive.

 Thus, the proposed device allows you to control the total leakage current from the body of the trolley to the ground, to identify with greater reliability the faulty trolley before releasing them to the line.

Claims (1)

A device for monitoring the leakage current from elements of an object connected to a source of electrical voltage, containing a meter connected at the input through the probe to the object, and at the output with an indicator, characterized in that the meter is made in the form of a divider connected to the input, and in parallel to a circuit from a series-connected load resistor and a first switch is connected to the input of the divider; at the output, the divider is connected to the input of the rectifier; the first, second, and third filter converters that convert pulse e signals arriving at their inputs in constant voltage, the output of the rectifier through a separation element is connected to the input of the first filter converter and directly to the information inputs of the second and third keys, the outputs of which, respectively, through the second and third filter converters are connected to the second and third the inputs of the factors of the multiplier divider, the first input of the divider of which is connected to the output of the first filter converter, and the output to the output of the meter, in addition, enter n generator, a direct output connected to the control inputs of the first and second keys, and the inverse output - to the control input of the third switch, introduced power supply unit connected on the output from the meter and an indicator, wherein the output reprographic-divider formed by voltage U _O that displays the leakage current on a certain scale, while U _o is determined in accordance with the mathematical expression

where U _K is the voltage at the object relative to the earth with the open first key;
ΔU - voltage reduction at the object when the first key is closed;
R _D is the resistance of the load resistor;
B is a constant coefficient, the value of which is chosen to obtain the desired level of electrical signals in the device.

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