SU1746458A1 - Method of protection against turn-to-turn short-circuits in windings of three-phase electric machines - Google Patents

Abstract

Use: protection of electrical machines against winding short circuits and determination of deterioration of insulation with increased sensitivity. Summary of the Invention: when measuring the sum of magnetic fluxes generated by currents flowing in the frontal parts of the stator winding, the number, sequence numbers, and slip of the included machines L are fixed, depending on these numbers, the reference value (setpoint) for each machine and power source superimposed currents. 2 Il. Che

Description

The invention relates to electrical engineering and can be used to protect electrical machines against interturning short circuits in the stator winding and to determine the deterioration of the insulation.

A known method of protecting electrical. machines from winding short circuits in the windings, in which an operational overvoltage and an operating frequency voltage are supplied to the controlled windings, the operational signal currents are measured and the electric machine is switched off if it exceeds the allowable values.

The disadvantage of this method is the impossibility of its use simultaneously for a group of machines in operation, since the selectivity of the selection of the defective machine is not ensured, as well as the difficulty of securing the connection between the sources of the operational signal and the operating voltage.

There is also known a method of protecting electrical machines against winding short circuits, in which each machine measures the sum of magnetic fluxes created by superimposed currents flowing in the frontal parts of the stator winding and turns off this machine if the specified amount is greater than the reference value. In this method, the reference value (setpoint), which characterizes the sensitivity of protection, is determined by the sum of the fluxes Φ generated by the superposed currents flowing in the frontal parts of the stator winding in trouble-free modes. With the same power of the superimposed signal, it is Fiscal in magnitude depending on the number of machines running and on which of them work1.

The disadvantage of the method is low sensitivity, since for the protection to work properly according to this method, it is necessary to adjust to the highest fmax value, which can be significant at start-up.

The closest to the present invention is a method of protection against interturn short circuits in the windings of electric machines, based on the position of the voltage of increased frequency for all phases of the electrical network, fixing the number of

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machines, changing the protection settings and power of the high-frequency voltage source depending on this, the number, comparison with the symmetry setting of the higher-frequency currents of each of the protected machines and generating a protection signal in case of exceeding the set-up in violation of the symmetry of the currents of the increased frequency of the damaged machine.

The disadvantage of this method is the insufficient sensitivity of the protection, due to the need to rebuild from the starting and self-starting modes of electric motors when the resistance of the windings of electric machines decreases due to an increase in slip. The magnitude of the superimposed current and the total magnetic flux F created by it becomes significant, and so that the protection does not work falsely, one has to choose as the threshold the response F

K0-gc, where Kota 1,, 5.

The purpose of the invention is to increase the sensitivity.

This goal is achieved by the fact that, according to the method of protection against winding short circuits in the windings of three-phase electric machines, based on imposing a high frequency voltage on all phases of the electrical network, fixing the number of machines turned on, changing the protection settings and power of the high frequency voltage source depending on it numbers, comparison of the setpoint of current symmetry of the increased frequency of each of the protected machines and the formation of a protection signal in case of exceeding the setpoint in case of violation of the symmetry of currents of increased h simplicity harmed machine further measured rotor frequency of rotation for each of the electric machine, comparing the slip with a number of valid values in the case of exceeding the permissible level of the corresponding signal is formed for changing the protection settings and said power source.

The increase in sensitivity is based on the fact that when the slip of the electric machine changes, the protection settings change.

FIG. 1 shows a functional diagram of the device that implements the proposed method; in fig. 2 is a block diagram of the settings.

The device contains an alternating current voltage generator 1, a filter 2 for preventing the generator 1 from the operating frequency of the electric machine, the voltage converter 3,

For example, a voltage transformer, the secondary windings of which are connected to an open triangle, a block 4 for setting the settings for each machine 5 with a switch 6

(the diagram is shown in a single-line version for one machine, the other machines are connected in the same way), sensor 7, measuring the sum of magnetic fluxes created by currents in the frontal parts of all phases of the windings of the stator, inside the machine (for example, sensor), measuring body 8 The value of slip S (for example, a tachogenerator), a comparison organ with a filter 9, an actuator 10, block 4 has inputs 11–14 and outputs 15–18.

The outputs of the generator 1 are connected to the inputs of the filter 2, the outputs of which are connected to the converter 4, and the last to the three phases of the electrical network.

0 The inputs of the sensor 7 are electromagnetically connected to the currents flowing in each phase of the electric machine 5, and the output of the sensor 7 is connected to a filter tuned to the generator frequency, the output of the filter 5 to one of the inputs of the reference organ 9.

The output of the measuring unit 8 is connected to the input 11 of block 4, and the inputs 12-14 of block 4 are connected to the outputs (for example, via auxiliary contacts) of the switches 6 of machines 1, i, n (where i takes the values

2, 3 (p-1); exits 15-17-to the entrance of the body

9 comparisons for the corresponding machine, output 18 to the input of the generator 1.

The unit 4 for setting the settings can be higher on the basis of a computer, using a decoder, in the form of a diode grid.

Block 4 on the diode grid for 3 machines (Fig. 2) contains intermediate relays 19-26, contacts 27-29 of the relay off (open when the switches of the first, second and third machines are turned on), contacts 30-32 of the position switches, contacts 33 - relay position Enabled

5 first car; contacts 34-37 - relays 19,20, 22,23; voltage source 38; contacts 54-56 measuring bodies 8 of the first, second and third machines (closed when S 5kr); resistors 39-53. Resistors

0 39-42 and 51-53 have different resistance. Relay 19 gives a signal that all machines are on, relay 20 means that one third of the machine is off, relay 21 is first, relay 22 is second, relay 23 is first and second, relay 24 is 5 second and third, relay 25 is first and third , relay 26 - all cars,

The device works as follows.

If all three machines are in operation, then generator 1 produces the impressed current of a given frequency, for example 100 Hz, with a power Pi. At the same time, at the output of the sensors of 7 machines, there are respectively EMF Ei K Fy E2 K fg. Ез - К Фз, where ФгФз are the total magnetic fluxes created by the superimposed current in the respective machines, and at the outputs of the corresponding authorities 9 comparisons are the reference voltage values LH-Ua, issued by the unit 4 to the settings. Ui-Ua are calculated (U1 Cote Ei; U2 K0TcX xE2) or measured empirically (for example, for BP -41-4, when using a known sensor, EI 0.1 V, Ui 0.15B ),

In the absence of start-up and self-starting, short-circuiting of good insulation in the windings of machines Ui Ei, (Jz Еа, Кз Ез and comparison agencies 9 do not give signals. The values of F1-Фз are caused in these modes by their own asymmetry of the machine and the greater the greater the generator power one.

When insulation deteriorates or short circuits, for example, in the stator winding of the first machine, its resistance decreases, the current in it increases, which causes significant asymmetry and an increase in flow F1 without changing the reference standard Ui. Therefore, Ei Ui and the executive body 9 turns off the switch b of the first machine. At the input of block 4, a signal appears about its disconnection (for example, from the auxiliary contacts of the switch). The setpoint setting unit 4 outputs the corresponding signals to the inputs of the comparison organs 9 and generator 1 as new voltages Da, ub and power P2, with U 2 Е12 U13 Е1з, where Е12 and Е1з are the new EMF values at the input of sensors 7 second and third machines remaining in operation.

When starting and self-starting, for example, the first machine, the resistance of its winding decreases, the current in it increases, increasing the magnitude of the magnetic flux Φ |.

When slid Si exceeds a predetermined value, for example, Scr, the measuring body 8 feeds the input of block 4 (calculated according to the known formula) and for the engine 41 41 SKp 0.1, and S 0.12), according to which the block 4 rebuilds the setpoints and outputs the new voltage values, U ™ 2, to the inputs of the comparison and generator organs 1. U .3 and the power of Pe, with 1r4 1 Ei; u 4 2 2; 1R s Ez. Further, the device works in a similar way.

Switching the settings in block 4 is performed in accordance with the following

algorithms. If there are signals Ai-Az that the switches of the first, second and third machines are turned on, generator 1 produces the power Pi, and the reference voltages Ui-Lto are supplied to the inputs of the respective comparison organs.

If there are signals A2 and AZ that the switches of the second and third machines are on, and the signal At that the first machine

0 is turned off, then the generator 1 provides power P2. and the inputs of the comparison bodies for the second and third machines, respectively, are supplied with voltages 1 2 and 2.

In the presence of signals Ai-A4 that

5, the switches of the 1-3th machines are turned on and the first machine starts (self-starting), and the slip exceeds a predetermined amount, generator 1 produces power Pe. and at the inputs of the organs are 9

0, respectively, the voltage values of UW1 L and A.

Similarly, the remaining verbal control algorithms, which can be written in the form

5 functions of the algebra of logic.

Then, under Ai-Ab (when the switches are on), logical variables are accepted, taking in the presence of a signal 1, and in the absence of a signal.

0 Ai Az is characterized by the deflected position of the switches, the first, second and third machines, and Ad As Ae - that the slip of these machines is less than the specified value, and A / I As Ae - more than the specified value.

5 Thus, the number and sequence numbers of the included machines are recorded, as well as their slip.

The table shows the values of the powers produced by the generator 1 and the voltage applied to the inputs of the comparison organs 9 for three machines. The subscripts at voltages U indicate the numbers of the machines for which this value is established,

5 The change in the voltage settings at the input of the reference element 9, for example, the first machine, is carried out as follows.

When all three cars are turned on, the relay

0 20-28 are not flowed by current, as they are shunded by closed contacts 30- 32, resistors 40-42 are shorted, contacts of measuring bodies 8 are closed and to the comparison unit 9 of the first machine is fed

5, the voltage Ui through the resistor 39 (the contacts 34 are open, since the relay 19 has operated). When the second machine is disconnected, contact 31 is opened and the relay 22 is activated, opening contact 36 and changing the voltage Ui to U®1 (see table).

During start-up (self-starting) of the first machine, when its S SKp, and the second and third machines are also in operation, contacts 30, 31, 32, 56 and 55 are closed, and 54 are open, resistors 41, 42, 52 and 53 are short-circuited and The first machine comparing organ 9 is supplied with voltage and 4 hours through resistors 51, 40, 39. Similarly, the settings for voltage and power for other machines change.

Thus, the proposed method provides high sensitivity and selectivity of protection.

Claims (1)

Invention Formula The method of protection against winding short circuits in the windings of three-phase electric machines, based on imposing a higher frequency voltage on all phases of the electrical network, fixing the number of machines on, changing the current symmetry settings of their protection and the power of the high frequency voltage source depending set point the symmetry of the increased frequency currents of each of the protected machines and the formation of a protection signal in case of exceeding the setpoint in violation of the symmetry of the currents of the increased frequency of the damaged machine, characterized in that, in order to increase the sensitivity, the rotor speed for each electric machine is measured, the slip is compared with p the house of permissible values, and in case of exceeding the corresponding permissible level, form a signal for changing the protection settings and the power of said source, Yu t 12 flf & 15 four f8 jtf j / 7 u fe / 43 five # J5 # 36 56 37 FIG. g nineteen ft J ABOUT