CN113937737A - Ground fault processing method for generator stator and auxiliary power system - Google Patents
Ground fault processing method for generator stator and auxiliary power system Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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Abstract
The invention discloses a method for processing ground faults of a generator stator and an auxiliary power system, which comprises the steps of monitoring zero sequence voltage of the generator stator and zero sequence voltage of a bus of the auxiliary power system in real time, comparing the zero sequence voltage with corresponding setting values to determine a fault occurrence side, and then connecting a voltage source to the fault occurrence side through a voltage source switching device to reduce the voltage of a fault point to be lower than arcing voltage. The invention has the technical effects that the flexible regulation and control of the ground fault phase voltage of the stator and the station service system are realized, so that the fault phase voltage is actively reduced; the arc extinction device can be switched between neutral points of the stator and the service system, and can act on the ground fault treatment of the stator and the ground fault treatment of the service system; the method has the advantages that the fault can be eliminated without power failure, the defects of the existing arc extinction method of the stator and the service system are effectively overcome, the power supply reliability and safety are greatly improved, the power failure accident can be effectively prevented, the power supply reliability is high, and the method has profound significance and wide application prospect.
Description
Technical Field
The invention relates to the technical field of ground fault suppression of power systems, in particular to a method for processing ground faults of a generator stator and an auxiliary power system.
Background
The power generating sets and the service power systems at home and abroad generally adopt a neutral point non-effective grounding mode, and the grounding fault accounts for 70 percent of the system fault. Causing the national blackout loss to be billions yuan every year. The existing ground fault processing and operation modes of the stator and the auxiliary power system mainly comprise two categories of fault suppression and fault removal.
The ground fault suppression mainly comprises the steps of regulating and controlling neutral point grounding impedance and suppressing fault point voltage and current by modifying or regulating a power grid primary system neutral point grounding mode, so that the ground fault suppression of a stator or a station service system is realized, but the operation can be carried out only for 1-2 h in a short time, overvoltage is easily generated, and potential safety hazards exist.
The earth fault removal mainly comprises the steps of selecting a fault line and removing a fault point as soon as possible after the system is grounded so as to ensure the safe operation of the system. For example, the plant power system performs 'trial pull' from the traditional manual line by line, then performs line selection by using a fault line selection device and a fault indicator, and then quickly isolates the fault by using a feeder automation technology, but the fault removal technology causes overlong power failure time and high investment cost, and the power supply reliability index of the plant power system is seriously reduced.
The selection of the grounding mode of the neutral point of the generator is closely related to the single-phase grounding fault of the stator of the generator, because the neutral point and the stator form a loop to the ground capacitor when the stator has the grounding fault, the grounding mode is selected as an important means for protecting the stator, and the ignition degree of the stator by the fault current is directly determined, the existing neutral point of the stator of the generator processes the grounding fault by adopting three modes of grounding through an arc suppression coil, resistance grounding of a power inlet and distribution transformer or ungrounded mode, the single-phase grounding fault is generated in the operation mode that the neutral point of the stator of the generator is grounded through the arc suppression coil, the stator capacitor current and the arc suppression coil have similar directions, the weakening effect on the fault current can be realized, and the function of limiting the overlarge fault current and preventing an iron core from being damaged can be realized. However, the intermittent stator single-phase earth arc combustion easily causes the accumulation of charges on the stator winding, and the repeated change of fault current causes the fluctuation and impact of capacitance current and neutral compensation current, so that transient overvoltage is generated on the capacitor. The high-resistance grounding mode of the neutral point through the distribution transformer is to increase the system damping coefficient in a zero sequence loop, can well inhibit transient overvoltage caused by repeated charge and discharge, but has less ideal compensation effect on capacitance current than the grounding mode of an arc suppression coil. Therefore, different grounding modes have advantages and disadvantages for the protection effect of the stator single-phase grounding fault, which also facilitates the extensive study on the grounding mode of the neutral point of the large-scale generator.
The learners compare the grounding of the arc suppression coil with the high-resistance grounding of the distribution transformer, comprehensively consider the damage of the stator core caused by the grounding fault, the transient overvoltage caused by the capacitance current, the matching protection sensitivity and other aspects, obtain the arc suppression grounding mode which can better suppress the grounding fault current and has high zero sequence voltage protection sensitivity, and indicate that the frequency deviation of a large generator is large because the operation mode is unchanged after the fault and the connection with a power grid is kept without the operation of tripping, so that only the frequency deviation in a small range can occur, and the probability of the transient overvoltage of a stator system is low. In order to give consideration to the effect of suppressing the fault current by the arc suppression coil grounding mode and better avoid transient overvoltage, the literature proposes a mode of connecting the arc suppression coil and a small resistor in series, and the mode is applied to a hydraulic turbine unit with single-machine capacity increased and single-phase relative ground capacitance current reaching more than 4 muF, so that the problem of transient voltage caused by L-C resonance is avoided.
The essential mechanism for extinguishing the arc of the generator stator ground fault is as follows: after the fault current is extinguished in the zero crossing mode, the recovery speed of the fault point insulating medium is higher than that of the fault voltage, and the electric arc reignition is effectively prevented. Therefore, the paper starts from the source of a fault arc extinction mechanism, researches a stator winding ground fault point voltage regulation and control method, combines the recovery characteristics of an insulating medium, provides a stator ground fault voltage arc extinction and safe operation method, realizes flexible absorption of fault transient state energy, releases distributed capacitance charge, effectively inhibits the initial speed and the voltage peak value of fault recovery voltage, radically destroys the arc reignition condition, realizes rapid and reliable arc extinction, completely eliminates ground fault current, and ensures the continuous and safe operation of a generator.
Therefore, research on an active arc suppression method for suppressing current and voltage at a fault point is started at home and abroad, and an active current arc suppression method is disclosed: when the earth fault occurs, the earth residual current is taken as a control target, the residual current compensator injects current to the neutral point to compensate the earth fault total current (including reactive component and active component residual current), and the voltage of the fault point is reduced to zero, thereby achieving the aim of earth fault current total compensation. However, the system earth fault current is difficult to measure accurately and is difficult to be applied to engineering practice. However, no research has been made on applying the voltage source arc suppression method to the stator ground fault or the service system, and a method capable of processing the stator ground fault and the service system ground fault is provided.
In a word, the existing processing mode cannot take the effect of processing the ground fault of the auxiliary power system and the stator into consideration, and the power supply reliability is guaranteed.
Disclosure of Invention
In order to overcome the defects of the prior art and effectively solve the problem that the existing arc extinction technology of the stator and the auxiliary power system cannot simultaneously consider the reliability and the safety of power supply, the invention provides a method for processing the ground fault of the stator of the generator and the auxiliary power system, and the method reduces the phase voltage of the fault and achieves the aim of effectively eliminating the ground fault of the stator and the auxiliary power system and ensuring the safe and stable operation of the system for a long time. The purpose of the invention is realized by the following technical scheme:
a method for processing ground faults of a generator stator and an auxiliary power system is applied to ground fault processing of a generator or the auxiliary power system, when a single-phase ground fault occurs to the stator or the auxiliary power system, a voltage source is connected between a neutral point of the generator stator and the ground, or a voltage source is connected between a neutral point of the auxiliary power system and the ground, the voltage source is switched between the generator stator and the neutral point through a switching method, phase voltage regulation and control of the current source at the ground fault of the generator stator and the auxiliary power system are achieved, and ground fault processing of a power plant and the generator is achieved.
On the basis of the prior art, the following technical means can be adopted by the invention so as to better or more specifically solve the technical problems to be solved by the invention:
step 1: by stator zero sequenceVoltage transformer and station service system bus zero sequence voltage transformer for real-time monitoring generator stator zero sequence voltage, U1Indicating the zero sequence voltage, U, of the stator of the generator under test2Representing the zero sequence voltage of the bus of the detected station power system to obtain the zero sequence voltage U of the generator stator1And station service power system bus zero sequence voltage U2And step 2 is executed to judge whether the stator winding ground fault or the service system bus occurs;
step 2: according to the obtained zero sequence voltage U of the generator stator1And station service power system bus zero sequence voltage U2When is coming into contact with
And is
Then, it is determined that a ground fault occurs on the generator stator side, and step 3 is performed, in which U1A scalar quantity is represented by a quantity of a scalar,
is a vector; when in use
And is
Determining that the ground fault occurs at the auxiliary power system side, and executing the step 4; when in use
And is
When the grounding fault is not judged to occur on the generator stator side or the auxiliary power system side, the step 5 is executed, and when the grounding fault occurs on the generator stator side or the auxiliary power system side
And is
When the system is judged not to have the ground fault, the zero sequence voltage detection state is kept;
and step 3: switching the voltage source to the neutral point of the stator of the generator to ensure that
The voltage of the fault point is reduced to the arcing voltage,
the electromotive force of the stator fault coil is large, the negative sign indicates that the phase angle is 180 degrees, the voltage source exits after three to four cycles are delayed, and the step 2 is returned;
and 4, step 4: switching the voltage source to the neutral point of the service system to make
The voltage of the fault point is reduced to the arcing voltage,
the voltage is a fault phase voltage of the auxiliary power system, the voltage source is withdrawn after three to four cycles are delayed, and the step 2 is returned;
and 5: the voltage source is not switched to any position of a neutral point of a generator stator or a neutral point of the service system, and the locking state is kept in an inactive state. And (5) after manually confirming the fault point to reset the voltage source switching device, executing the step 2. The locking and resetting operation is executed when the zero sequence voltage on both sides exceeds a setting value, and the operation is required to be executed in order to ensure the safe and stable operation of the system.
Further, the zero sequence voltage setting value of the generator stator
And station service power system bus zero sequence voltage setting value
The method is characterized in that: zero sequence voltage setting value of generator stator
Rated phase voltage for stator, coefficient K1The value range is (0, 0.15)](ii) a Setting value of zero sequence voltage of bus of station power system
Phase voltage and coefficient K for normal operation of the service power system2＝0.15。
The invention has the beneficial effects that: (1) the flexible regulation and control of the phase voltage of the ground fault of the stator and the station service power system are realized, so that the phase voltage of the fault is actively reduced; (2) the method enables the arc extinction device to be switched between the neutral point of the stator and the service system, and can act on the ground fault processing of the stator and act on the ground fault processing of the service system; (3) the invention does not need to cut off the fault in power failure, effectively overcomes the defects of the existing arc extinction method of the stator and the service system, greatly improves the reliability and safety of power supply, can effectively prevent the occurrence of power failure accidents, has high reliability of power supply, and has profound significance and wide application prospect.
Drawings
Fig. 1 is a schematic diagram of a flexible regulation structure of a ground fault phase voltage of a generator stator and a station service power system.
Fig. 2 is an equivalent circuit of the high-low voltage side wiring of the service transformer.
Fig. 3 is a zero sequence equivalent circuit diagram of a generator stator when a ground fault occurs.
FIG. 4 is a zero sequence equivalent circuit diagram of a controllable voltage source for processing generator stator ground fault.
Fig. 5 is a zero sequence equivalent circuit diagram of the service power system when a ground fault occurs.
Fig. 6 is a zero sequence equivalent circuit diagram of a ground fault of a power system of a controllable voltage source processing plant.
Detailed Description
The invention will be further explained and explained with reference to the drawings.
The ground fault processing method of the generator stator and the service system is mainly based on the research that zero sequence voltage and current of the ground fault of the generator stator and the ground fault of the power plant system do not influence the other side through the service transformer, and meanwhile, the terminal voltage of each branch coil of a stator fault phase and the fault phase voltage of the service system can be regulated and controlled to effectively process the ground fault of the corresponding side without influencing the two sides. Therefore, the relationship that the voltage and the current of the generator stator ground fault and the voltage and the current of the ground fault of the auxiliary power system are not influenced mutually and the theoretical relationship of the stator ground fault phase voltage regulation and the auxiliary power system ground fault phase voltage independent regulation are introduced.
As shown in fig. 1, which is a system structure diagram, the controllable flexible voltage source can be switched between the neutral point of the stator and the neutral point of the grounding transformer of the service system,
a flexible controllable voltage source connected to the neutral point, wherein
For three-phase electromotive force of the stator winding of the generator, Ca1、Cb1、Cc1Respectively, three phase to ground capacitances of the stator, Ca2、Cb2、Cc2Respectively, the three-phase station service system is a ground capacitor, and when the three-phase parameters of the system are balanced to the ground, Ca1＝Cb1＝Cc1＝C1、Ca2＝Cb2＝Cc2＝C2，CtSetting that the single-phase earth fault of the sub-winding and the earth fault of the station power system occur in A phase (not simultaneously) for the capacitance value of the external equipment at the machine end to the earth, and setting the transition resistance to be Rf。T1For high-voltage power stationAnd the system transformer is connected with the generator end and the station power system bus. T is2The transformer is an auxiliary power bus grounding transformer, and a neutral point led out by the auxiliary power system grounding transformer is connected with a controllable voltage source and injected into the transformer because the high-voltage side of the auxiliary power system is triangular.
Transformer T according to high-voltage station service system1The high-low voltage side connection modes of the transformer are all triangular connection, and as can be seen from fig. 2, when a system has a ground fault, zero-sequence current flows into the high-voltage side of the station transformer; according to the sequence component, the magnitude and direction of each phase zero sequence current of the stator or the station service electric system are equal, zero sequence circulation current cannot form a zero sequence passage, and the zero sequence passage is obtained by kirchhoff current theorem
Similarly, when the ground fault occurs at the side of the station service system, the method can be obtained
Therefore, when the stator side has a ground fault or the service system has a ground fault, the zero-sequence current on the fault side cannot form a loop in the service transformer with triangular wiring, so that no zero-sequence current magnetic flux exists, and the zero-sequence current cannot be induced on the non-fault side.
When the zero-sequence voltage is regulated and controlled at the neutral point of the stator side or the auxiliary power system side, the neutral point is connected with a voltage source which is equivalent to the distribution of the zero-sequence current of the system changed from the zero-sequence voltage of the regulating and controlling system, further, a circuit of the zero-sequence current forms a passage through a ground zero-sequence voltage source and a ground fault point, and the zero-sequence current cannot form a passage through a grounding transformer, so that the electrical quantity of the secondary side system is influenced to keep the secondary side line voltage and the zero-sequence current unchanged, and the zero-sequence voltage current of the regulating and controlling fault side and the normal operation of the non-fault side can be realized.
When the generator stator side has ground fault, the stator zero sequence loop is as shown in fig. 3, and the stator pair ground fault zero sequence voltage is as follows, assuming that the ground fault occurs in phase a
Alpha is the grounding of the statorThe number of barrier turns accounts for the proportion of the total number of turns, and theta is an included angle between the electromotive force at the fault and the electromotive force of the phase A; therefore, when the zero sequence voltage of the stator ground fault is detected, the threshold value is set
Coefficient K1Will affect the stator ground fault detection dead zone range when K1The smaller the approach to zero, the more sensitive it is to detect the smaller the dead zone, but K1The smaller the size, the more easily the false start is generated, and the main reasons are several: 1. neutral point unbalanced voltage caused by three-phase unbalance during normal operation, and normally, the unbalanced zero-sequence voltage at the generator end during normal operation can exceed 10V (secondary side of a voltage transformer); 2. it is also possible that the unbalanced zero sequence voltage may sometimes exceed 20V due to the saturation of the voltage transformer; 3. when the neutral point of the high-voltage system is directly grounded or ungrounded, the zero-sequence voltage protection sensitivity can be influenced by the zero-sequence overvoltage transmitted by the fault at the high-voltage power grid side; 4. transmitting zero sequence voltage exceeding a stator zero sequence voltage setting value to malfunction due to the ground fault of the side of the service electric system; in consideration of improving the detection sensitivity of the fundamental zero-sequence voltage, because unbalanced zero-sequence voltage is mainly generated by third harmonic during normal operation, the third harmonic component is filtered out in a fundamental zero-sequence voltage secondary circuit, and unbalanced voltage during normal operation is reduced. For the influence of the transmitted zero-sequence voltage on the zero-sequence voltage of the stator, the zero-sequence voltage delay needs to be considered to be increased, or the braking quantity is added in a zero-sequence protection secondary circuit, so as to eliminate the influence of the zero-sequence voltage transmitted through the coupling capacitor. However, fundamental zero sequence voltage protection cannot meet 100% protection of a stator section, so that the addition of a third harmonic component realizes 100% coverage of stator grounding protection, and the third harmonic voltage of a neutral point of a generator is measured
Third harmonic voltage at generator terminal
Is set when
When beta is in the range,
In order to adjust the coefficient, the value of the adjustment coefficient is matched with the fundamental wave zero sequence voltage protection of the generator, so that the 100% protection of the generator stator can be realized.
Referring to fig. 4, when the controllable voltage source is switched to the stator side to handle the ground fault, the clamped voltage applied by the voltage source can be adjusted according to the position of the ground fault point, so that the clamped voltage can be adjusted
In order to adjust the neutral point voltage of the neutral point,
is the electromotive force from the end of the mth turn coil on the d-th branch to the neutral point on the failed phase; then the voltage of the fault point
The voltage of the fault point is clamped to be 0, so that the grounding fault current of the stator is reduced to zero, and the grounding fault of the stator of the generator is effectively eliminated.
When the ground fault occurs to the power system of the power plant, since the power system is mostly a non-grounded system with neutral points, the zero sequence voltage of the system can be known from the zero sequence equivalent circuit of the power system of fig. 5
When a ground fault is detected to be satisfied
When the voltage reduction and arc extinction device is started, the controllable voltage source is switched to the side of the station service system, and if the station service system is a 6kV system, the voltage reduction and arc extinction device is taken
Is the phase voltage.
Controllable voltage source according to kirchhoff current equation as shown in fig. 6
Injecting the neutral point current of the station service power system
Comprises the following steps:
zero sequence admittance to ground of auxiliary power system in formula
Three-phase ground conductance
Three phase to ground capacitance 3C2Fault to ground electrical conduction
Is a zero sequence voltage.
Considering the influence of the zero sequence voltage generated by the asymmetry of the ground parameters of the three phases under the normal operation condition of the plant power system, injecting the zero sequence voltage U of the current into the formulaNUsing zero sequence voltage variation delta UNReplacing; and after considering fault arc extinction, the transition admittance Y of the fault pointf0, simplifying:
in order to reduce the voltage after the fault phase voltage for the voltage reduction and arc extinction device,
the voltage of the system phase before voltage reduction. Therefore, during the voltage reduction process of the auxiliary power system, the changed injection current of the voltage source is measured and calculated
Regulating and controlling controllable voltage source
Magnitude and phase of
I.e. to achieve a fault point voltage clamping to eliminate the fault current, where0The zero sequence admittance to the ground when the auxiliary power system operates normally.
Therefore, after the ground fault occurs to the service power system, the voltage source is switched to the service power bus side, the fault phase voltage reduction and arc extinction are realized through the neutral point controllable voltage source, the voltage source output voltage is uniquely determined by the target value of the service power fault phase voltage reduction, and the purpose can be realized after the controllable voltage source is switched to the service power bus.
It should be emphasized that the examples described herein are illustrative and not restrictive, and thus the invention is not to be limited to the examples described herein, but rather to other embodiments that may be devised by those skilled in the art based on the teachings herein, and that various modifications, alterations, and substitutions are possible without departing from the spirit and scope of the present invention.
Claims (10)
1. A generator stator ground fault processing method is characterized in that when a generator stator is judged to have a single-phase ground fault, a voltage source is connected between a neutral point of the generator stator and the ground, the voltage of a fault point is reduced to be lower than an arcing voltage, and the connected voltage source is disconnected after a preset period.
2. The method according to claim 1, wherein the single-phase ground fault of the generator stator is determined when the zero-sequence voltage of the generator stator is not less than the setting value of the zero-sequence voltage of the generator stator and the zero-sequence voltage of the bus of the service system is less than the setting value of the zero-sequence voltage of the bus of the service system.
3. The method as claimed in claim 1, wherein the input voltage source is an output of the input voltage source that is a reverse value of an electromotive force of a stator fault coil.
4. A method for processing ground fault of an auxiliary power system is characterized in that when the single-phase ground fault of the auxiliary power system is judged, a voltage source is connected between a neutral point and the ground of the auxiliary power system, the voltage of a fault point is reduced to be below an arcing voltage, and the connected voltage source is disconnected after a preset period.
5. The method according to claim 4, wherein the determination of the occurrence of the single-phase ground fault in the utility power system is made when the zero-sequence voltage of the bus of the utility power system is not less than the setting value of the zero-sequence voltage of the bus of the utility power system and the zero-sequence voltage of the stator of the generator is less than the setting value of the zero-sequence voltage of the stator of the generator.
6. The method according to claim 1, wherein the access voltage source is an output of the access voltage source from a reverse value of a fault phase voltage of the auxiliary power system.
7. A ground fault processing method for a generator stator and an auxiliary power system is characterized by comprising the following steps:
step 1: according to the zero sequence voltage of the generator stator and the zero sequence voltage of the bus of the service system, which are obtained in real time, when the zero sequence voltage of the generator stator is not less than the setting value of the zero sequence voltage of the generator stator and the zero sequence voltage of the bus of the service system is less than the setting value of the zero sequence voltage of the bus of the service system, the occurrence of the ground fault on the side of the generator stator is determined, and the step 2 is skipped; when the zero sequence voltage of the bus of the service system is not less than the zero sequence voltage setting value of the bus of the service system and the zero sequence voltage of the stator of the generator is less than the zero sequence voltage setting value of the stator of the generator, determining that the ground fault occurs at the side of the service system, and skipping to the step 3; when the zero-sequence voltage of the stator of the generator is not less than the zero-sequence voltage setting value of the stator of the generator and the zero-sequence voltage of the bus of the service system is not less than the zero-sequence voltage setting value of the bus of the service system, the occurrence of the ground fault on the side of the stator of the generator or the side of the service system can not be judged, and the step 4 is skipped, when the zero-sequence voltage of the stator of the generator is less than the zero-sequence voltage setting value of the stator of the generator and the zero-sequence voltage of the bus of the service system is less than the zero-sequence voltage setting value of the bus of the service system, the system is judged not to have the ground fault, and the step 1 is executed again;
step 2: switching a voltage source to a neutral point of a stator of the generator to reduce the voltage of a fault point to be below an arcing voltage, disconnecting the switched-in voltage source after a preset period, and returning to the step 1;
and step 3: switching a voltage source to a neutral point of the service system to reduce the voltage of a fault point to be below an arcing voltage, disconnecting the switched-in voltage source after a preset period, and returning to the step 1;
and 4, step 4: and (3) the voltage source is not switched to any place of a neutral point of a generator stator or a neutral point of the service system, the locking is carried out to keep the non-action state, and after the fault point is manually confirmed and the switching state of the voltage source is reset, the step 1 is returned.
8. The method as claimed in claim 7, wherein in the step 2, the voltage source uses a magnitude of an electromotive force reversal value of the stator fault coil as an output magnitude of the connected voltage source.
9. The method as claimed in claim 7, wherein in the step 3, the voltage source takes a magnitude of a fault phase voltage of the utility power system and a reverse value as an output magnitude of the accessed voltage source.
10. The ground fault handling method according to claim 2, 5 or 7, characterized by: zero sequence voltage setting value of generator stator
Rated phase voltage for stator, coefficient K1The value range is (0, 0.15)](ii) a Setting value of zero sequence voltage of bus of station power system
Phase voltage and coefficient K for normal operation of the service power system2＝0.15。
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| CN101188354A (en) * | 2007-11-30 | 2008-05-28 | 昆明理工大学 | Test simulation method for failure line selection of small current ground system |
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