WO2006123962A1

WO2006123962A1 - Method for protecting a user of a three-phase alternating-current network against operating emergency conditions and device for carrying out said mehtod

Info

Publication number: WO2006123962A1
Application number: PCT/RU2005/000271
Authority: WO
Inventors: Sergei Vladimirovich Kozhelsky; Vladimir Leonidovich Krushev; Vladimir Timofeevich Krushev; Alexandr Leonidovich Krushev
Original assignee: Sergei Vladimirovich Kozhelsky; Vladimir Leonidovich Krushev; Vladimir Timofeevich Krushev; Alexandr Leonidovich Krushev
Priority date: 2005-05-18
Filing date: 2005-05-18
Publication date: 2006-11-23

Abstract

The inventive method for protecting a user of a three-phase alternating-current network against operating emergency conditions consists in determining actual values of a phase-shift between a feeding voltage and a consumption current(s) in at least two phase conductors, in comparing said actual values with permitted phase-shift values within a range which is determined taking into account the maximum and minimum values of a user's power factor (cos?) and in disconnecting the user from the network when a current value exceeds a specified permitted value range. The inventive device for protecting the user of a three-phase alternating-current network against operating emergency conditions comprises current sensors (4, 5, 6), voltage sensors (7, 8, 9) and a unit (2) for disconnecting in the phase conductors. Said device also comprises a phase shift control unit (16), which is embodied in such a way that it makes it possible to produce a signal that the user id disconnected from the alternating-current network when said phase shift exceeds a specified permitted value range and a synchronising unit (19) whose inputs are connected to the network phase conductors, whereas the output thereof is connected to the phase shift control unit (16).

Description

METHOD FOR PROTECTING ENERGY CONSUMERS OF THREE-PHASE AC NETWORK FROM EMERGENCY OPERATION MODES AND DEVICE

FOR ITS IMPLEMENTATION

Technical field

The invention relates to the field of electrical engineering and more specifically relates to a method for protecting consumers of AC power from emergency operating modes and devices for its implementation.

State of the art

There is a method of protecting consumers of energy of a three-phase alternating current network from emergency conditions, based on measuring currents and their differences in various phases of the supply voltage, followed by comparing the differences of the currents of two phases with the current in the remaining phase and generating a shutdown output signal when any of the obtained threshold difference values is exceeded [SU, A, 1314411, H 02 H Z / 26, 1987].

However, this method of protection is characterized by relatively low accuracy associated with the error of the measuring transducers of phase currents and the error in the implementation of computational operations. In addition, in this case, it is necessary to set operation thresholds individually for each type of motor, depending on its power and, accordingly, the magnitudes of the currents in the supply conductors.

There is a method of protecting the motor against overload, based on measuring currents and voltages in the electric motor at the time of start-up, calculating the rated value of the load current Iн from the results of measurements and the nameplate of the electric motor and comparing it with the measured real load current Ip in steady state; in the case when the ratio I _p / Iн becomes more than one, the electric motor is disconnected from the network [RU, A, 2027272, H 02 H 7/08, 1995].

This method is also characterized by low accuracy associated with the error of the measuring transducers of current and voltage, as well as the error of computational operations.

Close in its technical solution is the method of protection induction motors from damage and abnormal modes of operation, based on measuring currents and voltages at the motor inputs and determining the active power at the input and output of the protected motor, the latter being determined by the torque on the shaft and the angular speed of the rotor. According to the measurement results and taking into account the operating characteristics of the electric motor, the active power losses in the electric motor are calculated and a protection signal is generated if the specified losses exceed the permissible active power losses in the nominal operating mode [SU ₃ A, 1594642 H 02 H 7/08, 1990].

This method is difficult to implement and, in addition, is characterized by relatively low accuracy, which is due to the error of the measuring transducers of current and voltage, the error of computational operations, as well as the error in determining active losses by operating characteristics.

The closest in its technical solution is a method of protection against earth faults of an alternating current contact network (SU, A, 637890 H 02 H 3/16, 3/38), in which the phase angle between the current and voltage is continuously measured, compared with the reference angle and form a trip signal, in case the measured angle is less than the reference, moreover, the current value in the contact network is continuously measured and the reference angle is continuously determined from the measured current value depending on the measured current value.

However, this method has a limited scope and provides protection only against short circuit or network overload), and the need to measure the absolute value of the current in the network narrows the range of controlled power consumption from the network.

SUMMARY OF THE INVENTION

The basis of the invention is the task of creating a method of protecting consumers of energy of a three-phase AC network from emergency operating modes, which would protect the consumer from the maximum possible number of emergency operating modes, reduce the influence of errors of current and voltage transducers, and increase the accuracy of measurements of power parameters, consumed from the mains and eliminated false positives, as well as create a device for the implementation of such a method, which would be simple to implement and reliable in operation.

The problem is solved in that the method of protecting the energy consumer of a three-phase AC network from emergency operation, according to the invention, consists in determining the current values of the phase shifts between the supply voltage and the current consumption or current consumption in at least two phase conductors, compare these current values with acceptable values of the phase shift in the range specified taking into account the maximum and minimum values of the consumer power factor and disconnect the consumer from the network if kuschee phase shift value is beyond a predetermined range.

It is possible to determine the phase shift between the voltage and the consumed current in each of the three conductors of a three-phase network.

It is also possible to determine the phase shift between the voltage of one of the phases of the three-phase network and the total current consumption in the conductors of the other two phases.

In another embodiment, it is possible to determine the phase shift between the interphase voltage of the two phases of the three-phase network and the total current consumption in the conductors of these phases.

It is preferable for determining the current value of the phase shift to choose an arbitrary reference point on the time axis during the network period, to set time intervals relative to this point, in which the reference curves of changes in currents and voltages reach the same specified value, to measure the actual time intervals through which currents and voltages reach the specified set value and compare the measured value of the intervals with the set value, in this case, if the difference exceeds the permissible limits, turn off the Fucker from the mains.

In order to protect the consumer from an asymmetric operating mode, it is advisable to additionally determine the current value of the phase shift between currents in at least two different phases, compare the measured value with the acceptable values of the phase shift in the range specified taking into account the permissible asymmetry of the consumed currents in time and disconnect the consumer from the network if the specified shift is outside the specified range. The problem is also solved by the fact that the device for protecting consumers of AC power from emergency operation, containing current sensors, voltage sensors and a shutdown unit in the phase conductors connected to the consumer, according to the invention, contains a phase shift control unit connected by inputs to outputs sensors of current and voltage and configured to issue a signal to disconnect the consumer from the AC network to the control input of the shutdown node in the event that the phase shift is outside the range range of permissible phase shift values.

It is desirable that the device further comprises an input / output device connected to the phase shift control unit, adapted to input and output the values of the set allowable phase shift range, as well as consumer parameters, before and after the trip.

In a preferred embodiment, the device further comprises a synchronization unit, the inputs of which are connected to the phase conductors of the network, and the output is connected to the phase shift control unit.

The phase shift between the voltages and the consumed currents in the three-phase network, as well as between the consumed currents in the various phase conductors, is essentially the only and sufficient indicator of the consumer's work with the reactive nature of the load, controlling which according to the proposed method it is possible to protect the consumer from any emergency operating conditions. The mentioned phase shift can be measured both in the time domain and in the frequency domain. Conversion from one unit of measure to another can be done through operations that are obvious to those skilled in the art. Due to the fact that the time measurement corresponding to the phase shift can be performed with much higher accuracy than the measurement of currents or voltages, taking into account the need to ensure the linearity of their conversion, the present invention can significantly improve the accuracy of measurements.

Brief Description of the Drawings

The invention is further illustrated by the description of specific variants of its implementation and the accompanying drawings, in which: Fig. L depicts a diagram of an AC power consumer protection device that implements the method according to the invention for the case a three-phase network with phase shift control between phase voltage and current consumption in each supply conductor; figure 2 - diagram of another variant of the same device for the case of a three-phase network with phase shift control between the phase voltage of one conductor and the total current of two other conductors for two different combinations of conductors; FIG. 3 is a diagram of a variant of the same device for a three-phase network with phase shift control between the phase-to-phase voltage of two conductors and the total currents of these conductors for two different combinations of conductors; 4 is a timing diagram of the control of the phase shift between all phase voltages and currents in a three-phase consumer network, where the values of voltages "U" and currents "1" in the network conductors are plotted along the ordinate axis, and the time "t" is the abscissa axis; 5 is a timing diagram of the control of the phase shift between the phase voltage of one conductor and the total current of two other conductors, as well as the phase shift between the two total currents; figb is a timing diagram of the control of the phase shift between the interphase voltage of two conductors and the total current of the same conductors relative to the selected reference point t0, synchronized with the frequency of the network, as well as the phase shift between the two total currents;

DETAILED DESCRIPTION OF THE INVENTION

The proposed protection device is designed to protect energy consumers from emergency operating modes - overload, underload; breaks and short circuits in the power circuits, both on the source side and on the consumer side; voltage imbalances and other violations of the operating mode in three-phase AC networks.

In the smallest possible configuration, the proposed device contains: current and voltage sensors connected to phase conductors in the consumer circuit; converters of alternating voltage of sensor signals to pulse voltages; a phase shift control unit, to the inputs of which the outputs of said converters are connected; the body that responds to the control signal from the output of the phase shift control unit, as well as the disconnection unit, which directly disconnects the consumer from the network. Optionally, an input / output device can be connected to the phase shift control unit for inputting the necessary consumer data into the microprocessor memory and outputting data on its operating mode, as well as fixing time instants, reasons for disconnection, and other parameters.

An important advantage of the invention is that phase shift measurements can be made between the current and voltage of any phase conductors in various combinations, for example, between the current of one phase and the current of another, the current and voltage of one phase, the current of one phase and voltage in the other, different voltages phases, currents of several phases relative to the current in another, etc.

In a specific embodiment of the protection device shown in FIG. L, current sensors 4, 5, 6 are connected in series to each of the conductors of the three-phase AC network 1 through the shutdown unit 2 from the consumer 3. In addition, voltage sensors 7, 8 and 9 are connected to each of the conductors. Sensors 4 to 9 of current and voltage can operate using any principle of operation. A general requirement is the possibility of their response to currents and voltages in the phase conductors both from the consumer 3 and from the network 1. For example, induction-type current transformers or Hall effect sensors can be used as current sensors 4-6. As sensors 7 - 9 voltage can be used voltage transformers, resistive, capacitive or resistive-capacitive voltage dividers, etc.

The information outputs of the sensors 4 to 9 are connected to the corresponding inputs of the converters 10 to 15 of an alternating voltage to pulsed, the outputs of which are connected to the information inputs of the phase shift monitoring unit 16. Various threshold devices (limiters, comparators, etc.) can be used as converters. The phase shift control unit 16 in the most preferred embodiment can be implemented on the basis of a microprocessor. It is assumed that in the case of the implementation of a phase shift control unit based on a microprocessor, it also includes a memory device in which a program for controlling the microprocessor and the necessary data for its operation are stored. To the output of the control unit 16 is connected by its input an element 17 for generating a trip signal (intermediate relay), made on the basis of a semiconductor device, in this case, optosimistor, the output of which is connected to the shutdown unit 2. To the control unit 16 is connected, in addition, the device 18 input / output of controlled values, made in the form of a standalone remote control, however, this device is not required.

The embodiment of the device shown in FIG. 2, differs from the above in that current sensors 4 and 5 are each connected to a pair of conductors (B, C and A, B, respectively), one of which (B) is common to both sensors, and voltage sensors 7 and 8 are connected each to the third conductor (A and C, respectively) of the three-phase network. The outputs of the sensors 4,5,7 and 8 through the converters 10 - 13 AC to pulsed connected to the inputs of the block 16 control the phase shift, the output of which through the element 17 of the formation of the shutdown signal is connected to the node 2 shutdown. An I / O device 18 is connected to the control unit 16.

The embodiment of the device shown in FIG. 3, differs from the above in that the voltage sensors 7 and 8 are connected between the same conductors to which the total current sensors 4 and 5 are connected. The outputs of the sensors 4,5,7 and 8 through the converters 10 - 13 AC to pulsed connected to the inputs of the block 16 control the phase shift, the output of which through the element 17 of the formation of the shutdown signal is connected to the node 2 shutdown. In addition, in this embodiment of the device, a synchronization unit 19 is additionally introduced, the inputs of which are connected to the network conductors, and the output is connected to the synchronizing input of the control unit 16. Block 19 synchronization is used to set the moment to reference time intervals in block 16 control. In the same way as in the previous embodiment, the input / output device 18 is connected to the control unit 16.

The essence of the method of protecting consumers of AC energy from emergency conditions according to one embodiment is as follows.

The time shifts between the voltages on the conductors and the currents in the conductors in various combinations are determined by the time points of the change in the direction of the currents in the conductors supplying the consumer (according to the signals of the sensors 4 to 6) and by the moments of the change in the polarity of the voltage (according to the signals from the sensors 7 to 9) The corresponding time shifts are compared with each other, determining the current values of the phase shift, which are then compared with the boundary (limit) values of the range of permissible changes, given taking into account the maximum and minimum values of the power factor of the protected consumer. When at least one of the controlled relative time shifts exceeds the pre-set limit values, an adequate signal for disconnecting the consumer from the network is formed.

The operation of the device according to the embodiment shown in Fig. 1 is illustrated by the diagrams shown in Fig. 4.

After connecting to the three-phase network 1 of consumer 3, the time shifts Δti, At ₂ and Δtз between the currents I _A , IB _? IC And phase voltage U _A? U _B and U _C, respectively. The range of acceptable values of the time shift between voltage and currents is determined by the values Δtmiп and Δt _ma χ, which are established by the maximum and minimum values of the power factor (cos φ) of a particular consumer, which, in turn, can be set by the manufacturer and the nature of the consumer's work.

In the event that the phase shift between the current and voltage in any of the monitored conductors does not change and is outside the predetermined range of permissible values, or it does not change in the range of permissible values for a time that exceeds the set minimum time, the consumer switches off ( load) from the network, followed by blocking the re-inclusion for adaptive time, with fixing the time and reason for the disconnection. The mentioned parameters are the minimum time, boundary values of the interval of admissible values, adaptive time are pre-recorded in the memory of the phase shift control unit 16 or input from the input / output device 18.

When any of the monitored parameters goes beyond the set limits of the range of permissible values, the consumer switches off 3 by the shutdown node 2, followed by a lock for the adaptive time of the consumer's repeated switching on, with a possible fixation of the time and reason for the disconnection.

For example, in the absence of an overload, the phase shift φ, between phase currents and voltages, is greater than the value φ _max , while at the outputs of the control unit 16 there are control signals corresponding to the normal operation of the electric motor. If the rated load value is exceeded on the motor shaft, the condition φ <φ _{max is met} , and at the output of the control unit 16, the control signal corresponds to the trip signal.

If the lower limit of the engine load is additionally set, then when the load is greater than the minimum φ <cpm _{m, the} control signals corresponding to the normal operation of the electric motor are present at the output of the phase shift control unit 16.

When the load is dropped (idle), the condition φ> cf _m b is satisfied, and at the output of the control unit 16, the control signal corresponds to the trip signal.

Since in the phase monitoring unit 16 only phase shift between the signals is controlled, neither the value of the phase current and voltage conversion coefficients nor their stability are of principle importance.

This circumstance greatly simplifies the implementation of sensors 4 - 9 current and voltage, since they do not have strict requirements for accuracy and linearity of conversion.

Typical values of the nominal load factor of induction motors are within cos φ _n = 0.6 ... 0.95, which corresponds to a phase shift of 53 ° ... 18 °. With a mains frequency of 50 Hz, this corresponds to a time interval Δt ~ 1 ... 3.3 ms. In one embodiment, the implementation of this range can be taken as a range of valid values. As already mentioned, time intervals can be measured with a very high degree of accuracy, therefore, the comparison error can be quite small, and the reliability of the protection device can be high.

For a multiphase network, electrical processes occurring in one phase are unambiguous functions of others. For example, electrical processes occurring in the third phase of a three-phase network are unambiguous functions of the first two, therefore, for reliable consumer protection, it is sufficient to control two of the three phases. For this purpose, the device can be connected as shown in FIG. 2, while the current sensor 4 controls the total current of the two phases B and C, and the current sensor 5 monitors the total current of the two phases A and B, respectively. The total current of phases B and C is equal to the current of phase A with the opposite sign. When connecting the device according to figure 2, phase shifts are measured between: l) the voltage in phase A and the total current of phases B and C, 2) voltage in phase C and the total current of phases A and B.

Timing diagrams corresponding to such a phase shift control method are shown in FIG.

Additionally, to control the balance of currents in phases, the parameter Δtз can be measured, which should be equal to 1/3 of the period T of the network when the consumer is operating in normal mode.

In some cases, there is no “neutral” N in the consumer’s supply circuits. In this case, the protection device is made according to the way it is shown in FIG. 3. In this case, phase shifts between:

1) the total current of phases A and B, and the interfacial voltage in the same phases A and B.

2) the total current of phases B and C and interfacial voltage in the same phases B and C.

Timing diagrams corresponding to this method of phase shift control are shown in Fig.6.

To determine the time shifts of currents and voltages in the device, an arbitrary moment t0 of the start of measurements is set, which is set using the synchronization unit 19.

The device for protecting consumers of AC power energy from emergency operating conditions according to the present invention can also be used in other devices, for example, “direct fuse” devices, as a unit that directly protects the consumer's power circuits.

Thus, the main integral criterion for consumer protection, for example, an asynchronous electric motor (transformer), is the comparison of phase shifts between currents and voltages in the supply conductors with the limit deviations established on the basis of the passport values of cs φ _n .

Additional criteria may include:

• Phase voltage alternation;

• The shift between the phases of the voltage of the supply conductors;

• The shift between the phases of the flowing currents in the conductors. The proposed technical solutions allow: fast recognition of an emergency during the period of the current frequency; ensuring independence from the frequency of the supply network (50 Hz or another frequency) and shape (sinusoidal, triangular, rectangular) and high accuracy of measuring the power factor, because essentially time intervals are measured, which guarantees protection against false alarms. The device can be used in a wide range of consumer capacities.

Due to the fact that the range of permissible deviations of the phase shift is limited by the maximum and minimum values of the power factor of the consumer and the control of the current value of the phase shift is carried out for the case of a three-phase network in at least two conductors, the method according to the invention protects the energy consumer essentially from all possible emergency situations in the consumer's electrical circuit.

Industrial applicability

The invention can be successfully used to protect induction motors and transformers from overload, underload (idle); when the voltage is distorted; a break in the supply conductors, both on the source side and on the consumer side; short circuits in power circuits and other emergency operation modes.

Claims

CLAIM

1. A method of protecting an energy consumer of a three-phase AC network from emergency operation, which consists in determining the current values of the phase shift between the supply voltage and the consumed current or consumed currents in at least two phase conductors, compare these current values with allowable phase shift values in the range specified taking into account the maximum and minimum values of the power factor (cosφ) of the consumer and disconnect the consumer from the network if any of the defined current phase shifts output It extends beyond the predetermined permissible range of phase shift values.

2. The method according to claim 1, wherein the phase shift is determined between the voltage and the consumed current in each of the three conductors of the three-phase network.

3. The method according to p. L, in which the phase shift is determined between the voltage of one of the phases of the three-phase network and the total current consumption in the conductors of the other two phases.

4. The method according to claim 1, wherein the phase shift is determined between the interphase voltage of the two phases of the three-phase network and the total current consumption in the conductors of these phases.

5. The method according to any one of p. 1-4, in which to determine the current value of the phase shift, an arbitrary reference point is selected on the time axis, time intervals are set relative to this point, in which the reference curves of current and voltage changes reach the same set value, measure the actual time intervals at which currents and voltages reach the specified set value and compare the measured value of the intervals with the set, in this case, if the difference exceeds the permissible limits, disconnect the consumer from power network.

6. The method according to any one of claims 1 to 4, in which the current value of the phase shift between the currents, at least in two different phases, is further determined, the measured value is compared with the acceptable values of the phase shift in the range specified taking into account the allowable asymmetry consumed currents in time and disconnect the consumer from the network if the specified shift goes beyond this given range.

7. A device for protecting an energy consumer of a three-phase AC network from emergency operating conditions, comprising current sensors (4, 5, 6), voltage sensors (7, 8, 9) and a disconnection unit (2) in the phase conductors (A, B, C) ) connected to the consumer (3), characterized in that it contains a phase shift control unit (16) connected by the inputs to the outputs of the current and voltage sensors (4 - 9) and configured to provide a signal for disconnecting the consumer from the AC mains to the control input of the shutdown unit (2) in case the said phase shift is beyond a given range of acceptable phase shift values.

8. The device according to claim 7, which further comprises an input / output device (18) connected to the phase shift control unit (16), adapted to input and output the values of the set allowable phase shift range, as well as the consumer parameters (3) before shutting down and at the time of shutdown.

9. The device according to any one of claims 7 or 8, which further comprises a synchronization unit (19) connected by inputs to the phase conductors of the network, and an output to the phase shift control unit (16).