RU97873U1 - DEVICE FOR PROTECTING THE GENERATOR FROM CIRCUIT TO THE EARTH IN THE STATOR WINDING - Google Patents

Abstract

 1. Device for protecting the generator from earth faults in the stator winding, comprising a first current organ selectively responding to a single-phase earth fault, and a second current organ selectively reacting to a double earth fault, the inputs of which are connected to the output of the zero sequence current sensor, the first a trigger that responds to any earth fault in the generator voltage network, and a second trigger that responds to an earth fault near the neutral of the stator winding, the inputs of which are connected to the output a zero sequence voltage sensor, an interphase short circuit sensor and a logic unit connected to the output of the protection by the output, and the first, second, third, fourth and fifth inputs to the outputs of the first current organ, second current organ, first trigger, second trigger and interphase short circuit sensor, respectively, while the logic unit is configured to! prohibition of operation of protection against the first current organ after a set exposure time after the operation of the first or second starting organs,! lifting the prohibition when the first or second current organs are triggered,! prohibition of operation of protection against the first current organ when the interphase short-circuit sensor is triggered,! prohibition of operation of protection from the first current organ for a specified time after the return of the interphase short-circuit sensor,! prohibition of operation of protection against current organs in the absence of operation of at least one of the starting organs,! lifting the prohibition of operation of protection against the first�

Description

Technical field

The proposal relates to electrical engineering and can be applied in devices protecting the generator from earth faults in the stator winding.

State of the art

A device for protecting the generator from earth faults in the stator winding [US Pat. RU 2096885, IPC H02H 7/06, 1997], selected as a prototype.

The prototype contains a current converter, the output of which is connected to the inputs of the first and second reacting organs. The first reacting body is made in the form of a series-connected blocking filter, amplifier, rectifier, smoothing element and a comparison body with a set point. The device also contains a trigger, the first and second locking bodies. The input of the starting block is connected to the input of the first blocking organ, the output of which is connected to the first input of the first element And, the second input of which is connected to the output of the first reacting organ, and the third input is connected to the output of the second blocking organ. The output of the second reacting organ is connected to the first input of the second AND element, the second input of which is connected to the output of the starting organ, and the third to the output of the second locking organ. The output of the first AND element through the first element of the delay time for operation is connected to the first input of the OR element, the second input of which through the second element of the delay time for operation is connected to the output of the second element AND, and the output is connected to the input of the executive body.

The disadvantages of the prototype are as follows.

Protection is sensitive only to stable single-phase faults in the stator winding, in which the duration of the zero sequence current exceeds the trip time delay necessary to detune from single short-circuit faults. Meanwhile, studies show that damage to the stator winding of a generator operating on busbars in a compensated neutral network is characterized in the initial stage by repeated repeated short-circuit faults, each of which has a duration of 2-5 ms, repeated at intervals of 40-200 ms.

At certain time ratios, an unreasonable blocking of protection is possible with the following sequence of faults:

- an external single-phase earth fault in the network, turning into a double circuit with one point in the external network, and the second in the protection zone;

- disconnection of an external circuit by network protections while maintaining a single-phase circuit at a second point in the protection zone.

In addition, the prototype unreasonably blocks the protection against double faults in the protection zone, if the latter are accompanied by high current.

Utility model creature disclosure

The objective of the utility model is to eliminate the indicated disadvantages of the prototype.

The technical result of the utility model is to ensure the sensitivity of protection not only to stable earth faults in the generator, but also to intermittent short-circuits and to prevent unreasonable interlocks during the transition of a double circuit to a single-phase circuit and when double circuits are accompanied by high currents.

The subject of a utility model is a device for protecting the generator from earth faults in the stator winding, containing a first current organ selectively responding to a single-phase earth fault, and a second current organ selectively reacting to a double earth fault, the inputs of which are connected to the output of the zero-sequence current sensor , the first starting organ that responds to any earth fault in the generator voltage network, and the second starting organ that responds to an earth fault near the neutral of the stator winding, the moves of which are connected to the output of the zero-sequence voltage sensor, an interphase short circuit sensor and a logic unit connected by an output to the protective actuation element, and the first, second, third, fourth and fifth inputs to the outputs of the first current organ, second current organ, first starting organ, the second starting body and the interphase short circuit sensor, respectively, while the logic unit is configured to:

prohibiting the operation of protection from the first current organ after a specified exposure time after the operation of the first or second starting organs;

lifting this prohibition when the first or second current organs are triggered;

prohibiting the operation of protection from the first current organ when the interphase short circuit sensor is triggered;

prohibiting the operation of protection from the first current organ for a specified time after the return of the interphase short circuit sensor;

prohibition of operation of protection against current organs in the absence of operation of at least one of the starting organs;

removing the ban on the operation of protection from the first current organ when triggered by at least one of the starting organs;

removing the ban on the operation of protection against the second current organ when the first trigger is triggered;

prohibition of tripping of protection during short-term tripping of current and starting organs;

ensuring the protection is triggered by the continuous operation of at least one starting element and the simultaneous N-fold repeated and short-time operation of the first current organ with an interval not exceeding the specified one.

This allows you to get the specified technical result.

The development of the utility model consists in the fact that the first current organ is equipped with a compensation unit for the capacitive component of the zero sequence current, the input of which is connected to the output of the zero sequence voltage sensor.

This eliminates the need for roughening the protection when the cables connecting the generator with the switchgear are included in the protection zone, and thereby increase its sensitivity and selectivity.

Utility Model Implementation

Figure 1 presents an example diagram of a device connected to the electrical equipment of the protected generator. The diagram shows:

- the first current organ 1, selectively reacting to a single-phase earth fault, and the second current organ 2, selectively reacting to a double earth fault, the inputs of which are connected to the output of the zero-sequence current sensor 3;

- the first starting element 4, responding to any earth fault in the generator voltage network, and the second starting organ 5, responding to an earth fault near the neutral of the stator winding, the inputs of which are connected to the output of the zero-sequence voltage sensor 6;

- an interphase short circuit sensor 7, which compares the phase currents of the generator with the settings, and the triggered (issuing signal) when at least one of them is exceeded;

- a logical unit 8, which is connected by an output to the actuator 9 of the protection, and the first, second, third, fourth and fifth inputs 10, 11, 12, 13 and 14 to the outputs of the first current organ, second current organ, first trigger, second trigger body and sensor 7 interphase short circuit, respectively.

In addition, figure 1 shows the stator winding 15 of the protected generator and installed on its terminals three-phase group of measuring current transformers 16.

Currents 1 _a and 1 _with two phase windings of the transformer 16 passes through the sensor input circuit 7 and summed with the current of the third phase windings of the transformer 16 to the sensor input 3 of the current I ₀ the zero sequence. The sensor 3 is a current to voltage converter (for example, a low-resistance resistor) introduced into the total current circuit of the three phases of the transformer 16.

Sensor 6 voltage U ₀ zero sequence is made on the basis of a voltage transformer with series-connected secondary windings.

Figure 1 also shows the internal structure of the first current organ 1 and block 8.

Body 1 is equipped with a block 17 for compensating the capacitive component of the zero sequence current, which is connected to the output of the zero sequence voltage sensor 6 by an input. The composition of the first current organ 1 includes sequentially connected blocking filter 18, amplifier 19, rectifier 20, adder 21 and organ 22 for comparison with the set point. The compensation unit 17 form a series-connected blocking filter 23, a differentiating element 24 and a rectifier 25, the output of which is connected to the first input of the adder 21.

The logical block 8 includes: the first 26 and second 27 elements of the delay time for the response, the first 28, second 29 and third 30 elements of the delay time for the return, the first 31, second 32, the third 33 and fourth 34 elements OR, the first 35 and second 36 And elements, as well as a counter 37. The time delay element 28, in addition to the triggering input connected to the output of the element 31, is equipped with a blocking input connected to the output of the element 33.

This embodiment of block 8 is not the only possible one. Block 8 can also be performed on the basis of a programmable microprocessor and realize its functions under the control of the corresponding program.

The device operates as follows.

A current Io flows through a current sensor 3 from a three-phase group of current transformers 16, containing both a component of the industrial frequency and higher harmonics. In the mode without earth fault, the current Io is the unbalance current, and in the case of an external single-phase earth fault, it is the sum of the unbalance current and the zero sequence current through the capacitance of the stator winding 15 of the generator to earth.

To the inputs of the starting organs 4 and 5 and the input of the first current organ 1, a voltage of zero sequence 3Uo is supplied from the sensor 6, which is close to zero in the non-short circuit mode. When a single-phase earth fault occurs, the voltage 3Uo increases, and its magnitude and harmonic composition depends on the type of single-phase earth fault. The first starting element 4 is triggered and generates a logical unit signal at its output if the total voltage 3Uo exceeds a predetermined value. The second starting element 5 is triggered and generates a logical unit signal at its output if the third harmonic component of the zero sequence voltage (150 Hz) exceeds a predetermined value. In the absence of an earth fault in the generator voltage network, the starting elements 4 and 5 are in an unworked state, and at their outputs the signal corresponds to a logical zero. These signals are fed to the inputs 12 and 13 of the logic block 8, respectively.

The blocking filter 23 extracts from the total voltage 3Uo the components of all frequencies except the component of the industrial frequency. The received signal is differentiated by element 24, the output of which is a signal proportional to the zero sequence current flowing to the ground through the capacitance of the generator stator winding. The signal from the output of the element 24 is rectified by the rectifier 25 and with a minus sign is fed to the first input of the adder 21.

The signal from the output of the current sensor 3 enters the first current organ 1 to the blocking filter 18, which selects the components of higher harmonics. Further, after passing through the amplifier 19, the rectifier 20, the plus signal is supplied to the second input of the adder 21. Element 21 summarizes the plus signal received from the output of the rectifier 20 and the minus brake signal from the output of the rectifier 25. Received at the output of the adder 21, the signal is supplied to the input of the comparison element 22 with the setpoint. The setting of element 22 provides a detuning from unbalance currents. Therefore, in the absence of a single-phase earth fault, a logical zero signal is generated at the output of element 22, which corresponds to the unworked state of organ 1. This signal is fed to input 10 of block 8.

The signal from the output of the current sensor 3 also arrives at the second current organ 2, designed to detect double earth faults with one point in the protection zone, and the second in the external network. In the absence of such a circuit at the output 2 of the body, a logical zero signal is generated, which is fed to input 11 of block 8.

Through the input circuit of the sensor 7 flows the currents of two phases (A and C) of the stator windings 15 of the protected generator. The sensor 7 is designed to block the protection action in the event of external external short circuits accompanied by saturation of the current transformers 16, a sharp increase in their errors and, as a result, an increase in the unbalance current at the input of the sensor 3. At phase currents Ia and Ic not exceeding the specified level, at the output of the sensor 7, a signal of a logical unit is generated, and when any of the currents Ia, Ic exceeds a predetermined level, the sensor 7 is triggered and its output signal takes a logical zero value, which is fed to input 14 of block 8.

Thus, in the normal mode, without single-phase earth faults, inputs of logic 10, 11, 12 and 13 of unit 8 have logic zero signals, and input 14 contains a logic one signal.

When an external single-phase earth fault occurs under the action of a zero-sequence voltage of 50 Hz frequency, the starting element 4 is triggered and a logical unit signal appears at the input 12 of block 8. Through the OR element 31, this signal triggers the time delay element 28, which for a predetermined time passes the trigger signal to the first input of the 35 element I. However, due to the fact that the organ 1 does not work during the delay of the element 28 to the second input of the element 35 And the logical zero signal is received and at the output of the element 35 And the logical zero signal is also stored. The signal of a logical unit from input 12 also goes to the first input of element 36 I. However, due to the fact that the organ 2 does not work, a logical zero signal is supplied to the second input of element 36 AND, and a logical zero signal is also stored at the output of element 36 AND. The signal of the logical unit from the output of the first element 31 OR through the second element 32 OR on the zero-setting circuit releases the counter 37. However, due to the failure of the first current organ 1, there are no pulses at the counting input of the counter 37 and a logic zero signal is stored at its output. Thus, at all three inputs of the fourth element 34 OR there are logical zero signals, and the Executive protection 9 does not work.

When a stable single-phase earth fault occurs in the stator winding 15 of the protected generator under the action of the zero-voltage voltage, either the trigger 5 (when closing near the generator neutral) or the trigger 4 (when the rest of the winding closes) are triggered. At the input 12 or 13 of block 8, a signal of a logical unit appears. Through the OR element 31, this signal triggers the time delay element 28, which for a predetermined time passes the trigger signal to the first input of the 35 I element. Since a single-phase circuit occurs in the stator winding 15 of the protected generator, the zero-sequence current through the sensor 3 goes to the input of the blocking filter 18 , which highlights the components of higher harmonics. These components through the amplifier 19 and the rectifier 20 are fed to the second input of the adder 21 as a working signal. The input of the blocking filter 23 receives the zero sequence voltage from the sensor 6. The blocking filter 23 separates the components of higher harmonics, which from the output of the filter through the differentiating element 24 and rectifier 25 are fed to the first input of the adder 21 as a brake signal, the sign of which is opposite to the sign of the working signal second entrance. The brake signal is proportional to the own capacitive current of the generator stator winding. Since in the single-phase earth fault mode in the stator winding 15 the working signal significantly exceeds the brake signal, a positive sign signal appears at the output of the adder 21, exceeding the setting of element 22 and causing it to operate. Thus, at the input 10 of block 8, a signal of a logical unit is formed. This signal is supplied to the second input of element 35 I. If there is no blocking at the third input of element 35 AND from the sensor 7 side, a logic unit signal is generated at the output of element 35 AND, which triggers the time delay element 26. Through element 33, OR a signal of a logical unit from input 10 blocks the time delay element 28 by setting a logic unit signal independent of the time delay at the first input of the element 35. After the set time has passed, the launched element 26 generates a logic unit signal at its output, which, through element 34 OR causes the actuation of the actuator 9, the output signal of which causes the protected generator to be turned off.

In the event of an intermittent, intermittent single-phase earth fault in the stator winding 15 of the protected generator, the operation of the device is fundamentally similar, except that the element 22 is also activated intermittently and the signal at the input of the logic unit 10 is intermittent. The zero sequence voltage in the pause between individual faults decreases relatively slowly, with a time constant determined by the network capacity and active losses in the network insulation, therefore, with small (less than 0.4 seconds) pauses, the trigger elements 4 and 5 are continuously activated and form at its outputs a continuous signal of a logical unit. Due to the discontinuity of the signal of the logical unit at the second input of the And element 35, the signal at the input of the element 26 is less than the value of the time delay of this element and a logic zero signal is stored at the output of the element 26. The action of the device to turn off the generator when this is done on the counter circuit 37 of intermittent short circuits. The trigger elements in a chain of elements 31 OR and 32 OR remove a logical zero signal from the zero setting input of the counter 37, thereby allowing the counting of pulses from the input 10 of block 8, which is connected to the counting input of the counter 37. When the number of pulses counted by the counter 37 from the moment of resolution of the count will reach the set value, a logic unit signal is generated at its output, which through the first input of the 34 element OR causes the actuator 9 to work. The pause between intermittent short circuits is controlled by the element in Derzhko time 29, which at its output through OR element 32 resets to zero the counter 37 when a pause exceeds a predetermined value element 29.

In the event of a double earth fault with one point in the stator winding 15 of the protected generator, and the second point in the external network, under the influence of the appeared voltage of zero sequence with a frequency of 50 Hz, the trigger 4 is triggered and a logic unit signal appears at the input 12 of block 8. Under the action of a zero sequence current appearing at the input of the sensor 3, a frequency of 50 Hz triggers the current element 2 and generates a logic unit signal at its output and at the input 11 of block 8. Under the action of the signals of a logical unit at the first and second inputs of the element 36 And at its output a signal appears that starts the element 27 time delay. After a specified delay, the output of the element 27 appears a signal of a logical unit, through the element 34 OR received at the input of the executive body 9 and causing it to operate with the effect of turning off the protected generator.

In the event of an external single-phase earth fault with a transition to a double fault with a second point in the stator winding 15 of the protected generator and disconnection of the external fault by the network protections before the expiration of the element 27, the single-phase earth fault remains in the stator winding 15 of the protected generator. Since the time delay of the element 28 has expired by the time the external single-phase fault switches to double, the blocking signal at the first input of the element 35 And the start of the time delay element 26 is prohibited and there is a danger of failure of the protection device if the remaining single-phase fault in the stator winding 15 after the external fault has been disconnected . To prevent a failure, when a short-term logic unit signal appears at the input 10 of block 8 caused by a double circuit, the time delay element 28 is released via the second input of the OR element 33, and it is restarted after the signal at the input 10 of the block 8 passes to the logical zero state. From this moment on, the further operation of the device is similar to the work described above when a single-phase earth fault occurs in the stator winding.

In the event of external short circuits with a large current, there is a danger of non-selective operation of the device due to the appearance of unbalance currents of a three-phase group of measuring current transformers 16 containing a high level of higher harmonics. Non-selective operation is prevented by a sensor 7, which monitors the currents of phases A and C and when they exceed a predetermined level (i.e., when external short circuits occur), it triggers a logic zero signal at its output. This signal is fed to input 14 of block 8 and through the delay time element 30 to return and the third input of element 35 AND prohibits the start of element 26 for a predetermined time after the return of sensor 7 (until the external circuit is closed and the time delay after the trip expires, necessary to reduce the unbalance current )

Claims (2)

1. Device for protecting the generator from earth faults in the stator winding, comprising a first current organ selectively responding to a single-phase earth fault, and a second current organ selectively reacting to a double earth fault, the inputs of which are connected to the output of the zero sequence current sensor, the first a trigger that responds to any earth fault in the generator voltage network, and a second trigger that responds to an earth fault near the neutral of the stator winding, the inputs of which are connected to the output a zero sequence voltage sensor, an interphase short circuit sensor and a logic unit connected to the output of the protection by the output, and the first, second, third, fourth and fifth inputs to the outputs of the first current organ, second current organ, first trigger, second trigger and interphase short circuit sensor, respectively, while the logic unit is configured to prohibition of operation of protection from the first current organ after a predetermined exposure time after the operation of the first or second starting organs, lifting the prohibition when the first or second current organs are triggered, prohibition of operation of the protection against the first current organ when the sensor interphase short circuit, prohibiting the operation of protection from the first current organ for a specified time after the return of the interphase short-circuit sensor, prohibition of operation of protection against current organs in the absence of operation of at least one of the starting organs, lifting the prohibition of operation of the protection against the first current organ when triggering at least one of the starting organs, lifting the prohibition of the operation of protection against the second current organ when the first trigger is activated, prohibition of tripping of protection during short-term tripping of current and starting organs, ensuring the protection is triggered by the continuous operation of at least one starting element and the simultaneous N-fold repeated and short-time operation of the first current organ with an interval not exceeding the specified one. 2. The device according to claim 1, in which the first current body is equipped with a compensation unit for the capacitive component of the zero sequence current, the input of which is connected to the output of the zero sequence voltage sensor.