SU1695439A1 - Overcurrent protective gear - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to devices for relay protection and automation of power systems, and is intended to protect an electrical consumer operating in a long-term and repeated short-time mode from overloads and short circuits. The purpose of the invention is to expand the field of application of the device by ensuring the protection of electrical installations operating in an intermittent mode both from overload and short circuits. The goal is achieved by additionally introducing a constant voltage source, an exponentially decreasing voltage generating unit, two keys, a second triggering organ, a second element NOT, and the first pulse counter is reversible with a preset. 4 il.

Description

The invention relates to electrical engineering, in particular, to devices for relay protection and automation of power systems, and is intended to protect an electrical consumer operating in a long-term and repeated short-time mode against overloads and short circuits.

The aim of the invention is to expand the field of application by providing protection for electrical installations operating in an intermittent manner.

FIG. 1 shows a block diagram of a device for overcurrent protection of a power consumer; in fig. 2, 3, 4 - examples of the specific implementation of electronic keys and the executive body

The device contains an AC-DC to DC converter 1, a first starting unit 2, a voltage-to-pulse converter 3, a digital-to-analog converter 4, a second counter 5 pulses, the first

element NOT 6, element OR 7, the first pulse counter 8, the comparison element 9, the executive body 10, the constant voltage source 11, the exponential-decreasing voltage generating unit 12, the first key 13, the second key 14, the second trigger body 15, the second element NOT 16.

The device works as follows.

Converter AC input voltage to a constant voltage generates a voltage that through the node forming an exponentially decreasing voltage enters the inputs of the voltage converter 3 to the pulse frequency and the first triggering organ 2. At an input current not exceeding the nominal for the protected electric power, this voltage is less than the reference voltage U0n 1, so the output of the first starting body 2 is the same (L

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The value is 0, which gives the presence at the outputs of the first element NOT 6 and the logic element OR 7 a high voltage level that sets the counters 5 and 8 pulses to the zero state. Executive authority 10 issues a signal permitting operation. When an overload occurs, the voltage at the input of the first triggering organ 2 exceeds the reference one, so the logical unit level appears at its output, and the output of the first HER 6 element produces a low level that permits the operation of the first pulse counter 8. Since the second counter 5 was previously in the zero state, the voltage at the output of the digital-analog converter A is zero, the output voltage of the comparison element 9 is low, so the output of the OR element 7 is a logical zero the second counter 5 pulses, which starts counting the pulses coming from the voltage converter 3 to the frequency. Since the control input of the first switch 13 is supplied with a voltage from the output of the alternating current converter 1 to a constant voltage, it is set in such a state that the input voltage of the digital-to-analog converter 4 is powered from the output of the exponentially decreasing voltage forming unit 12 wives Since the counting rate of the second counter 5 is proportional to the overload current, the magnitude of the reference voltage at the input of the D / A converter 4 is also directly proportional to this current, the rate of voltage change at the output of the D / A converter is directly proportional to the square of the input current of the device. At the moment when the voltage at the input of the comparison element 9 exceeds the reference voltage UCp.2, the output level of the logical unit is formed, which is fed to the input of the second key 14. As the first control input of this key is more intense than the output of the AC converter 1 in a constant voltage, this key is set to a state in which the level of the logical unit from the input of the key 14 is fed to the input of the addition of the first counter 8, which counts the first pulse. At the same time, the voltage of the logical unit from the output of the reference element 9 is fed to the input of the element OR 7, forming at its output a high level of voltage that the second counter of 5 pulses is zeroed at. At the same time, the output of the digital-to-analog converter 4 reduces the voltage to zero, the output of the comparison element 9 and the output of the logic element OR 7 produce a low voltage level that enables the second pulse counter 5 to work, after which the whole process repeats until

5 filling the first counter 8 pulses. Then he issues a command to actuate the executive body 10.

In the intermittent mode, the output of the converter 1 of an alternating current to a constant voltage periodically appears and disappears, the output of the node 12 of the formation of an exponentially decreasing voltage is determined by the voltage

5, the discharge rate of the capacitor 17 through the resistor 18, and the parameters of the circuit resistor 18 - capacitor 17 are chosen so that the graph of the voltage reduction at the output of the node 12 of the form of the exponentially decreasing voltage and the graph of the decrease in the temperature of the protected consumer after switching off coincide in time. Since the second counter 5 is now filled with an extremely potential decreasing speed, and the first key 13, when the voltage at the output of the AC converter 1 to the DC voltage disappears, is set to the position at which

0 the input voltage of the reference digital-to-analog converter 4 is supplied from the output of the DC voltage source 11, the reference element 9 forms a series of pulses with exponentially

5 decreasing frequency. The switch 14, when the voltage at the output of the converter 1 of the alternating current to the constant voltage disappears, is set to the state in which the pulses from the output of the element 9

0 comparisons are fed to the input. Subtracting the second counter, causing a decrease in the number written to it. The magnitude of the output voltage of the constant voltage source 11 is chosen in such a way

5 so that the moments of zeroing of the first counter 8 when the voltage at the input of the starting organ 2 is lower than the reference voltage Uon.1 and with the sequential decrease in the information recorded in it as a result

0 subtractions matched in time.

If the re-activation of the protected electrical equipment occurred before the moment of zeroing of the first counter 8, then the addition of the next pulse occurs to the number already recorded in the counter.

In the event of a short circuit in the power supply circuit, the voltage at the input of the second starting body 15 exceeds the reference voltage Uon.3, at its output it forms, with a high level that goes to

The inputs for pre-recording the first counter are 8 pulses. From the output of the second element NOT 16 to the input of the first counter 8, a low voltage level is applied, and the presence of voltage at both control inputs of the second key 14 leads to the formation of high levels at the inputs of the Addition and Subtraction of the first counter of 8 pulses, resulting in an instantaneous parallel recording into this counter the numbers filling all its bits, which leads to the immediate triggering of the executive body 10.

For normal operation of the device, the inputs of the keys 13 and 14. connected to the output of the inverter 1 of an alternating current to a constant voltage, must be protected against overvoltage. Due to the presence of an integrating circuit, the resistor 18-capacitor 17 will not exceed the voltage at the output of the node 12 of the formation of an exponentially decreasing voltage when the reference voltage Uon.i short-circuits. To increase the protection performance, the resistor 18 must have a low resistance.

The first switch 13 is an electronic relay (Fig. 1).

The second key 14 is an IC1515 integrated circuit.

When using the K155IE7 chip as the first counter 8, the connection circuit of the K155IDZ chip is shown in FIG. 2

For normal operation of the K155WE7 counter in Addition or Subtraction mode, short negative pulses must be applied to the corresponding input, and a high voltage will be maintained at the second input. At the moment of parallel recording of information in the K155IE7 counter at both inputs, Addition and Subtraction will be maintained at a high level. All these conditions are satisfied by the K155IDZ chip. In the period during which the protected electrical consumer is disconnected from the mains or its current consumption is within acceptable limits, at the A1 input of the K155IDZ decoder, the voltage varies between 0-0.4 V, which corresponds to the logic zero level. The inputs of AO and A2 are also low logic levels. In this case, the inputs Addition and Subtraction of the counter 8 - high levels. The counter is reset, there is no account. When a current overload occurs, the voltage at the input A1 will reach a high logic level. Counter 5 starts counting pulses at the moment when

at the output of the comparison element 9, a short positive pulse is formed. The input of the addition of counter 8 is a negative pulse, which is recorded

in the counter, etc. before filling counters. If the current consumption of the protected device has decreased to the permissible level before, at the A1 input of the K155IDZ decoder a logical zero is generated.

0 In this case, the pulses arriving at the AO input in inverse form are fed to the input of the Subtraction of the counter 8. When a short circuit occurs in the circuit to be protected, a high voltage level is formed

5 at the input A2 of the decoder. In this case, at both involved outputs of the decoder, there are high levels, which is one of the conditions of the parallel recording mode of the K155IE8 counters. As counter 8

0, another chip may be used, with the requirements for the second key 14 changing accordingly.

One example of the implementation of the executive organ 10 is shown in FIG. 4. The work is carried out as follows. After briefly pressing the Start button, the supply voltage is supplied to the protected electrical receiver,

0 drive it into action, as well as on the protection device. Since the counter is not filled at this moment, the output level R15 of the decoder of the executive body 10 is high. In this case, the relay turns on and, with its closing contact, provides power to the protected consumer. After filling the counter 8 as a result of an overload or short circuit at the output 15 of the decoder, a logic zero level is formed, disabling the relay CT and providing the protected electrical receiver together with the protection device. To disconnect the load in the normal mode, a short voltage supply is required. When protecting a high power consumer, the relay K is used as an intermediate, controlling its normally open contact operation.

0 powerful contactor.

An exponentially decreasing stress node is a well-known integrator. An example of the implementation of the node 12 for forming an exponentially decreasing voltage, consisting of diode 19, capacitor 17, resistors 18 and 20, is presented in detail in the block diagram (Fig. 1) and ensures the normal operation of the device, consisting in that the resistor

18 of the node 12 for the formation of an exponentially decaying voltage must have low resistance, and the start body 2 of the voltage-to-frequency converter 3 and the first switch 13 must have a high input resistance. The method of implementing the first key 13, shown in FIG. 1, eliminates the possibility of the effect of this key on the discharge rate of the capacitor 17 of the node 12, since as the current consumption of the protected consumer to decrease to a permissible value and below the relay (FIG. 2), opens its contact.

An exponentially decreasing voltage node can be built on a different principle, for example, on the basis of a digital-to-analog converter, which provides higher accuracy of operation and stability to the device. In addition, in this case, there is no need to provide a high input resistance of the triggering organ 2, the voltage-to-frequency converter 3, and the first key 13. The first key 13 is easier to implement using an electromagnetic relay, the second key 14 is performed on logic elements.

The use of this device allows to expand the area of use of the device by providing an instantaneous cut-off in the event of a short circuit and protection against overloading of electrical consumers operating in intermittent operation. In addition, the device improves reliability by providing a lightweight operation of the circuit blocks during a short circuit.

The device can be used in a wide power range of protected electrical consumers. The adjustment is made by changing the reference voltages and adjusting the output voltage of the constant voltage source 11.

Claims (1)

Formula of gain A device for overcurrent protection of an electrical installation, containing an AC / DC converter, a first starting element, the first input of which is connected to the input of a voltage converter to a pulse frequency, the second input is connected to the first reference source voltage, the output of the first triggering organ is connected to the input of the element NOT, the output of which is connected to the first input of the OR element and to the installation input of the first pulse counter, the second input of the OR element is connected to the output of the reference element, one of the inputs of which is connected to the second reference voltage source The other input is connected to the output of a digital-analogue converter, whose digital inputs are bitwise connected to the bit outputs of the second pulse counter, the counting input of which is connected to the output of the voltage converter to the pulse frequency, and the installation input is connected to the output of the OR element, the output of the first pulse counter is connected to the executive authority, characterized in that, in order to expand the field of application by providing protection for electrical installations operating in a short-term mode, a source is added to it constant voltage, unit for the formation of an exponentially decreasing voltage, two keys, a second starting body with a third source of reference voltage, a second element NOT, the first impulse counter The bridges are reversible with presetting, with the input of the exponentially decreasing voltage generating unit, the key control inputs and the first input of the second triggering organ connected to the output of the AC-DC converter, the output of the exponentially-decreasing voltage shaping unit is connected to the voltage converter pulse frequency and the first input of the first key, the second input of which is connected to the output of a DC voltage source, the output of the reference element is connected to n The first input of the second key, the second input of which, the pre-recording inputs of the first pulse counter and the input of the second element are NOT connected to the output of the second trigger, the first and second outputs of the second key are connected; respectively to the inputs of the addition and subtraction of the first pulse counter, and the S input of the first counter is connected to the output of the second element NOT, the input voltage of the digital analog converter is connected to the output of the first key. G4 Vont I6x. eleven 3t- V0Xj /five fPuz.l i / sxy corner To source i of constant - “- | - torn //. By pr905rassn and - HtMtrnepe - body is not. 6pcs / day warp i 1 WЈ No L ± P Vcpt Output  TVM L  To digital-oЈf a & o0a / r e lk t Fig. / tf & (0 & y m in / / gyu # & e cvemtsv / ra f.  K & o l Sosteml Cvemwra &. Fig.Z