CN109633350B

CN109633350B - Method and system for detecting virtual grounding reason of generator stator of load direct supply system

Info

Publication number: CN109633350B
Application number: CN201811519106.7A
Authority: CN
Inventors: 潘向华; 高广玲; 牟旭涛; 井雨刚; 孙健; 赵阳德; 张国辉; 孙运涛; 张用; 苏文博
Original assignee: State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd
Current assignee: State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd
Priority date: 2018-12-12
Filing date: 2018-12-12
Publication date: 2020-12-15
Anticipated expiration: 2038-12-12
Also published as: CN109633350A

Abstract

The embodiment of the invention provides a method and a system for detecting the reason of the virtual grounding of a generator stator of a load direct supply system. The embodiment of the invention provides a method and a system for detecting the virtual grounding reason of a generator stator of a load direct supply system, which can effectively identify the virtual grounding reason of the generator stator.

Description

Method and system for detecting virtual grounding reason of generator stator of load direct supply system

Technical Field

The invention relates to the technical field of substation protection of an electric power system, in particular to a method and a system for detecting the reason of unreal grounding of a generator stator of a load direct supply system.

Background

In recent years, the generator end associated with a plurality of load direct supply systems has the problems that the stator virtual ground protection false tripping is caused because the fixed value of the stator ground protection is not proper and the three-phase unbalanced voltage of the generator access system exceeds the standard. On the one hand, the method causes loss of power plants in different degrees, and simultaneously causes disorder on safe and stable operation of a power supply system. For example, a kaiser thermal power plant, a Shandong Xinhua thermal power plant, a Hui chemical thermal power plant and the like all belong to power generator plants related to a load direct supply system, and accidents of protection misoperation and switch tripping caused by virtual grounding of a stator of a power generator occur successively. For a load direct supply system, the operation index of the system voltage is mainly the balance degree of the three-phase line voltage, the balance requirement on the three-phase voltage is relatively low, only an alarm is given, and the rule specifies that a single-phase grounding system can operate for 3 hours; the requirements of the generator connected into the load direct supply system are different, and the generator stator grounding protection is the grounding protection of the generator and the grounding protection of the load direct supply system. Because of the 3U of the generator₀The numerical value of (1) directly reflects the grounding position of the stator, and is not the problem of simple unbalance of three-phase voltage. Therefore, the key point of distinguishing the zero sequence voltage generated by unbalanced three-phase voltage from the zero sequence voltage generated by grounding of the stator of the generator is the problem. In addition, the problem to be considered is that other factors of the generator access system can cause unbalance of three-phase voltage, so that the ground protection of the stator malfunctions. For example, a system ground fault, a difference in insulation resistance between the three phases, a compensation offset of a capacitance current, an influence of a system load size, and the like. Due to the fact thatThe problem of unbalance between the stator grounding and the three-phase voltage of the access system must be considered as the generator stator grounding protection, and the requirements on sensitivity, rapidity, selectivity and reliability must be met by taking the generator stator grounding as the main protection. In a system of generator-transformer assembly wiring, a generator outlet does not have a direct distribution line, the stator grounding protection range is 90-95%, and the output voltage of the generator is 3U₀The voltage is generally set to 5-10V and the operation time is set to 0.2 s. The generator end of the load direct supply system is not portable, and the difference of the wiring mode and the difference of the system parameters need to be considered.

The generator end associated with the load direct supply system is almost a forgotten technical field, and although related reports exist in previous data, the analysis problem is far from the problem solution idea. Similar to the load direct-fed power plant described in the above example, the problem of the false operation of the virtual ground protection of the generator stator has not been found in the field for a long time.

Disclosure of Invention

In view of the above disadvantages, the embodiments of the present invention provide a method and a system for detecting the reason of the phantom grounding of the generator stator of the load direct supply system, which can accurately detect the reason of the phantom grounding of the generator stator of the load direct supply system.

The embodiment of the invention provides a method and a system for detecting the virtual grounding reason of a generator stator of a load direct supply system, wherein the method is realized based on the load direct supply system, and the load direct supply system comprises a generator end and a load end; the generator end is an output voltage end consisting of three-phase stator windings of the generator; the load end is used for receiving the voltage output by the generator end; the generator end and the load end are connected through a connecting line; a high-voltage circuit breaker is arranged between the generator end and the load end; the high-voltage circuit breaker is used for cutting off or closing no-load current and load current in a high-voltage circuit, and comprises the following steps:

acquiring parameters of a load direct supply system; the parameters of the load direct supply system comprise that zero sequence voltage is 3U when the end of the generator is in no-load₀₁After the high-voltage circuit breaker is switched on, the zero sequence voltage at the generator end is 3U₀And the general fixed value of the generator stator grounding protection is 3U_0dzAfter the high-voltage circuit breaker is disconnected, the zero sequence voltage at the generator end is 3U₀₁The independent fixed value of the generator stator grounding protection is 3U_0dz1Zero sequence voltage of load end is 3U₀₂The independent fixed value of the load end grounding protection is 3U_0dz2；

According to the obtained parameters of the load direct supply system, the generator voltage in the generator end is continuously increased from 0V to the rated voltage and is increased to 3U_0dz1Judging whether a generator stator in the generator end is in the unreal grounding state or not in a comparison mode; the 3U is connected to the power generator end through the main transformer under the condition of grid-connected operation by adopting a cut-off high-voltage circuit breaker₀₁And 3U_0dz1Judging whether the generator stator is unreal grounded due to the asymmetric voltage between the generator end and the main transformer in a comparison mode; detecting 3U by using a cut-off high-voltage circuit breaker under the condition that a load end is supplied with power by a separate power grid₀₂The value of the voltage value is obtained, and the mode of the insulation resistance to the ground of each phase is checked after the power failure of the load end, and whether the generator stator is in virtual grounding caused by the damage of the load end to the insulation to the ground is judged; judging whether the generator stator is in unreal grounding caused by load unbalance at the load end by adopting a mode of detecting the voltage and current phasor value of a connecting line after the generator end is associated when the high-voltage circuit breaker is closed and the generator end is in grid-connected operation; when the high-voltage circuit breaker is closed and the generator end is in grid-connected operation, the zero-sequence voltage 3U of the system is judged₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L) And judging whether the generator stator is connected to the ground in an imaginary manner or not due to the resonance of the generator end and the load end.

Further, the adoption continuously raises the generator voltage in the generator terminal from 0V to the rated voltage and is equal to 3U_0dz1The comparison method is to make the generator end idle, raise the generator voltage in the generator end from 0V to the rated voltage value UeV, and detect 3U on the secondary opening triangle side of generator outlet PT by using voltmeter₀₁' if the voltage rises from 0V toRated voltage value UeV process, 3U₀₁'＞3U_0dz1Then it is not the generator stator phantom ground.

Furthermore, the 3U is connected to the power generator end through the main transformer under the condition that the high-voltage circuit breaker is disconnected and the power generator end runs in a grid-connected mode₀₁And 3U_0dz1The comparison method is to judge whether the generator stator is unreal grounded caused by the asymmetric voltage between the generator end and the main transformer, and the method is to disconnect the high-voltage circuit breaker and detect 3U on the triangular side of the secondary opening PT secondary opening of the generator end outlet by a voltmeter under the condition that the generator end is connected with the grid through the main transformer₀₁If 3U is present_01＞3U_0dz1The voltage asymmetry between the generator end and the main transformer results in the virtual grounding of the generator stator.

Furthermore, the method adopts a cut-off high-voltage circuit breaker to detect the 3U under the condition that the load end is supplied with power by a separate power grid₀₂And the mode of checking the insulation resistance to ground of each phase after the power failure of the load end, and judging whether the generator stator is in unreal grounding caused by the damage of the insulation to ground of the load end comprises the steps of disconnecting the high-voltage circuit breaker, and detecting 3U on the secondary opening triangle side of the standby PT (potential transformer) of the load end by using a voltmeter under the condition that the load end is supplied with power by a single power grid₀₂While checking the insulation resistance to ground R of each phase after the power failure at the load end, if the unit is operated by a single machine in 3U₀₁The voltage is normal, and the three-phase unbalanced voltage of the load end is 3U₀₂Exceeding standard, wherein the insulation resistance R of one phase to the ground is more than 0.5 megaohm after the power failure of the load end; after the high-voltage circuit breaker is closed, the 3U appears repeatedly₀>3U_0dz1Is the phantom grounding of the generator stator caused by the damage of the load end to the ground insulation.

Further, the method for detecting the voltage and current phasor value of the connecting line after the generator end is associated during the grid-connected operation of the generator end and judging whether the generator stator is in the unreal grounding caused by the unbalanced load of the load end comprises the steps of closing the high-voltage circuit breaker, carrying out the grid-connected operation of the generator end, and testing the voltage and current phasor value of the connecting line after the generator end is associated at the high-voltage circuit breaker by using the voltage meter, the current meter and the phase meter.

Ua, Ia, Ub, Ib, Uc and Ic, if the unit runs 3U₀₁Normal voltage, generator side and load side

......

After correlation, unbalance of three-phase load phasor Ua, Ia, Ub, Ib, Uc and Ic results in 3U₀>U_0dz1The imaginary grounding of the generator stator caused by the load imbalance at the load end.

Further, when the generator is operated in a grid-connected mode, the zero sequence voltage 3U of the system is judged₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L) The method for judging whether the generator stator is in the unreal grounding state caused by the resonance of the generator end and the load end comprises the steps of closing the high-voltage circuit breaker, carrying out grid-connected operation on the generator end, and detecting the whole load direct supply system 3U on the secondary opening triangular side of the PT secondary opening of the generator end outlet by using a voltmeter₀The value of (d); method for compensating reactance current I after testing generator end association by ammeter at generator end tail part_LThe value of (d); the tapping positions of the compensation reactance at the generator end are changed to respectively detect 3U₀Obtaining the zero sequence voltage 3U of the system₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L)，3U₀＝f(I_L) The relation characteristic changes with the tapping position of the compensating reactance, and the zero sequence voltage 3U of the load direct supply system appears₀>U_0dz1The imaginary grounding of the generator stator is caused by the resonance of the generator end and the load end.

The system for detecting the unreal grounding reason of the generator stator of the load direct supply system comprises a parameter acquisition module and a fault judgment module;

the parameter acquisition module is used for acquiring the zero sequence voltage of 3U when the end of the generator is in no-load₀₁After the high-voltage circuit breaker is switched on, the zero sequence voltage at the generator end is 3U₀And the general fixed value of the generator stator grounding protection is 3U_0dzAfter the high-voltage circuit breaker is disconnected, the zero sequence voltage at the generator end is 3U₀₁The independent fixed value of the generator stator grounding protection is 3U_0dz1Zero sequence voltage of load end is 3U₀₂The independent fixed value of the load end grounding protection is 3U_0dz2；

The fault judgment module is used for continuously increasing the voltage of the generator in the generator end from 0V to the rated voltage and is matched with 3U_0dz1The comparison mode is used for judging whether the generator stator in the generator end is in the unreal grounding state or not, adopting a cut-off high-voltage circuit breaker, and under the condition that the generator end runs in a grid-connected mode through a main transformer, connecting 3U₀₁And 3U_0dz1The comparison method is used for judging whether the generator stator is in unreal grounding caused by the voltage asymmetry between the generator end and the main transformer or not, adopting a cut-off high-voltage circuit breaker, and detecting 3U under the condition that the load end is supplied with power by a single power grid₀₂The method comprises the steps of detecting the mode of earth insulation resistance of each phase after power failure of a load end, judging whether the generator stator is in virtual earth caused by the damage of the load end to the earth insulation, closing a high-voltage circuit breaker, detecting the voltage and current phasor value of a connecting line after the generator end is connected in parallel operation, judging whether the generator stator is in virtual earth caused by the unbalanced load of the load end, closing the high-voltage circuit breaker, and judging the zero sequence voltage 3U of a system when the generator end is connected in parallel operation₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L) And judging whether the generator stator is connected to the ground in an imaginary manner or not due to the resonance of the generator end and the load end.

Further, the parameter acquisition module comprises a first parameter acquisition module, a second parameter acquisition module and a third parameter acquisition module;

the first parameter acquisition module is used for acquiring the zero sequence voltage of 3U when the end of the generator is in no-load₀₁'；

The second parameter acquisition module is used for acquiring the zero sequence voltage at the end of the generator to be 3U after the high-voltage circuit breaker is switched on₀And the general fixed value of the generator stator grounding protection is 3U_0dz；

The third parameter acquisition module is used for acquiring the zero sequence voltage at the generator end to be 3U after the high-voltage circuit breaker is disconnected₀₁Stator of generatorThe independent fixed value of the grounding protection is 3U_0dz1Zero sequence voltage of load end is 3U₀₂The independent fixed value of the load end grounding protection is 3U_0dz2。

Further, the fault judgment module comprises a first fault judgment module, a second fault judgment module, a third fault judgment module, a fourth fault judgment module and a fifth fault judgment module;

the first fault judgment module is used for continuously increasing the voltage of the generator in the generator end from 0V to the rated voltage and is matched with 3U_0dz1Judging whether a generator stator in the generator end is in the unreal grounding state or not in a comparison mode;

the second fault judgment module is used for adopting a disconnected high-voltage circuit breaker to carry out 3U on the condition that the generator end is connected to the grid through the main transformer for operation₀₁And 3U_0dz1Judging whether the generator stator is unreal grounded due to the asymmetric voltage between the generator end and the main transformer in a comparison mode;

the third fault judgment module is used for detecting 3U by adopting a disconnected high-voltage circuit breaker under the condition that a load end is supplied with power by an independent power grid₀₂The value of the voltage value is obtained, and the mode of the insulation resistance to the ground of each phase is checked after the power failure of the load end, and whether the generator stator is in virtual grounding caused by the damage of the load end to the insulation to the ground is judged;

the fourth fault judgment module is used for judging whether the generator stator is in virtual grounding caused by load unbalance at the load end in a mode of detecting the voltage and current phasor value of a connecting line after the generator end is associated when the high-voltage circuit breaker is closed and the generator end is in grid-connected operation;

the fifth fault judgment module is used for judging the zero sequence voltage 3U of the system when the high-voltage circuit breaker is closed and the generator end is connected to the grid for operation₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L) And judging whether the generator stator is connected to the ground in an imaginary manner or not due to the resonance of the generator end and the load end.

The effect provided in the summary of the invention is only the effect of the embodiment, not all the effects of the invention, and one of the above technical solutions has the following advantages or beneficial effects:

the embodiment of the invention provides a method and a system for detecting the virtual grounding reason of a generator stator of a load direct supply system, wherein the method comprises the steps of firstly enabling the generator end to be idle, increasing the generator voltage in the generator end from 0V to a rated voltage value Ue, and detecting 3U on the secondary opening triangle side of a generator outlet PT by using a voltmeter₀₁' if during the generator voltage rises from 0V to the rated voltage value Ue, 3U₀₁'＞3U_0dz1Then there is a node fault with the generator stator, but not phantom ground. Secondly, the high-voltage circuit breaker is disconnected, and under the condition that the generator end runs in a grid-connected mode through a main transformer, a voltage meter is used for detecting 3U on the triangular side of a PT secondary opening at an outlet of the generator end₀₁If 3U is present_01＞3U_0dz1The voltage asymmetry between the generator end and the main transformer results in the virtual grounding of the generator stator. Thirdly, the high-voltage circuit breaker is disconnected, and under the condition that the load end is supplied with power by a single power grid, a voltage meter is used for detecting 3U on the secondary opening triangle side of the standby PT of the load end₀₂While checking the insulation resistance to ground R of each phase after the power failure at the load end, if the unit is operated by a single machine in 3U₀₁The voltage is normal, and the three-phase unbalanced voltage of the load end is 3U₀₂Exceeding standard, and after the power failure of the load end, the insulation resistance R of one phase to the ground is more than or equal to 0.5 megaohm; after the high-voltage circuit breaker is closed, the 3U appears repeatedly₀>3U_0dz1The condition (2) is that the motor stator is virtually grounded due to the load end. Fourthly, the high-voltage circuit breaker is closed, the generator end is in grid-connected operation, and the voltage meter, the current meter and the phase meter are used for high-voltage circuit breaking

......

Testing voltage and current phasor values Ua, Ia, Ub, Ib, Uc and Ic of a connecting line after generator end association at a circuit breaker, and if the unit runs 3U₀₁The voltage is normal, and three-phase load phasor is obtained after the generator end is associated with the load end.

An imbalance of Ua, Ia, Ub, Ib, Uc, Ic results in 3U₀>U_0dz1Generator determination caused by load end load imbalanceThe sub-phantom is grounded. Fifthly, the high-voltage circuit breaker is closed, the generator end is in grid-connected operation, and a voltmeter is used for detecting the whole load direct supply system 3U on the side of the PT secondary opening triangle at the generator end outlet₀The value of (d); method for compensating reactance current I after testing generator end association by ammeter at generator end tail part_LThe value of (d); the tapping positions of the compensation reactance at the generator end are changed to respectively detect 3U₀Obtaining the zero sequence voltage 3U of the system₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L)，3U₀＝f(I_L) The relation characteristic changes with the tapping position of the compensating reactance, and the zero sequence voltage 3U of the load direct supply system appears₀>U_0dz1The imaginary grounding of the generator stator is caused by the resonance of the generator end and the load end. The method and the system for detecting the virtual grounding reason of the generator stator of the load direct supply system can effectively identify the virtual grounding reason of the generator stator.

Drawings

Fig. 1 is a power supply system diagram of a load direct supply system according to embodiment 1 of the present invention;

fig. 2 is an operation interface diagram of zero sequence voltage protection at the stator ground and load ends of the generator in embodiment 1 of the present invention;

fig. 3 is a zero sequence current distribution circuit diagram when the arc suppression coil grounding network is grounded in a single phase according to embodiment 1 of the present invention;

fig. 4 is a zero sequence equivalent network at the time of series resonance according to embodiment 1 of the present invention;

fig. 5 is a zero sequence equivalent network diagram of a generator stator grounded according to real-time example 1 of the present invention.

Detailed Description

In order to clearly explain the technical features of the present invention, the following detailed description of the present invention is provided with reference to the accompanying drawings. The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. It should be noted that the components illustrated in the figures are not necessarily drawn to scale. Descriptions of well-known components and processing techniques and procedures are omitted so as to not unnecessarily limit the invention.

Example 1

The embodiment of the invention provides a method and a system for detecting the virtual grounding reason of a generator stator of a load direct supply system, and fig. 1 shows a power supply system diagram of the load direct supply system in the embodiment 1 of the invention. The system comprises a generator end and a load end, wherein the generator end and the load end are connected through a connecting line, and a high-voltage circuit breaker 1111 is arranged between the generator end and the load end; the high voltage circuit breaker 1111 is used to break or close the no load current and the load current in the high voltage circuit.

Fig. 3 shows a zero sequence current distribution circuit diagram when the arc suppression coil grounding network of embodiment 1 of the present invention is grounded in a single phase. The generator is grounded through the group of arc suppression coils, and zero-sequence current is distributed when a single-phase grounding fault occurs in a direct supply system of the 10kV generator. Wherein, G: a generator; l: a neutral arc suppression coil inductance; c_0G: the generator is capacitance to ground; c_0I: i, a line capacitor; c_0II: II, a line capacitor; u shape_k0: a zero sequence supply voltage; i is_L: arc suppression coil current; i is_0G: generator capacitive current; i is_0I: i line capacitance current; i is_0II: II, line capacitance current; sigma I₀: the sum of the zero sequence currents of the injection system.

The generator neutral point has no arc suppression coil, the neutral point in the figure 2 is disconnected, and when one point of the system is grounded, the voltage of the neutral point is as follows:

U₀＝(E_a×jωC_a+E_b×jωC_b+E_c×jωC_c)/(jωC_a+jωC_b+jωC_c)

＝(E_a C_a+E_b C_b+E_c C_c)/(C_a+C_b+C_c)

in the formula E_a，E_b，E_cThree-phase electromotive force;

C_a，C_b，C_cis a three-phase capacitor.

If, the generator end is 3U₀>3U_0dz1Then the action is protected. Obviously, the protection action condition is easy to meet when any part of the 10kV system except the generator end is grounded, and the protection misoperation phenomenon is easy to occur.

When the neutral point at the generator end is provided with the arc suppression coil, the zero sequence voltage generated by the neutral point without the arc suppression coil at the generator end is connected in series with 3L and C_ΣIn between, as shown in fig. 4, a zero sequence equivalent network diagram at the time of series resonance is given. Wherein U is₀: zero sequence supply voltage of equivalent network, C_Σ: equivalent system capacitance.

When the system parameters satisfy the series resonance, the voltage U₀A high resonance voltage will be generated in the series resonant circuit, which will cause a severe increase in the generator-side neutral voltage, which is not allowed.

When the system is in overcompensation operation, the current of the arc suppression coil is I_LTotal system capacitance current is I ═ Ea/j ω L_0ΣThe total current flowing back from the ground point, i.e. the residual current after compensation, is I_K＝I_L+I_0ΣIf I is_L>I_0ΣWhen the compensated residual current is inductive, the system has no problem of generating series resonance overvoltage, and at the moment, the residual current is 3U₀<<3U_0dz1The protection will not malfunction. It can be seen that the application of overcompensation eliminates the problem of generator stator phantom ground glitches caused by resonance.

Similarly, when the system is in under-compensation operation, the zero sequence voltage reaches a setting value, namely 3U, because the change of the operation mode easily meets the resonance condition₀＝3U_0dz1And protecting the misoperation.

Fig. 5 is a zero sequence equivalent network diagram of the generator stator grounded according to real-time example 1 of the present invention. Wherein a: coefficient of position of generator stator to ground, C_0W: the outside of the generator is respectively relative to the ground capacitance.

When the alpha point is grounded, the zero sequence voltage of a fault point is as follows:

U_k0＝(Uad+Ubd+Ucd)/3＝—αEa

in the formula, Uad, Ubd, Ucd are voltages to ground at the generator terminal, α is a fault point percentage, and when α is 1, the zero sequence voltage is equal to the phase voltage.

Zero sequence voltage 3U when generator stator is grounded₀＝αEa>3U0dz1, the protection is performed.

Therefore, the protective action behavior when the generator stator is grounded is closely related to the position of the grounding point as long as alpha is>10％，3U₀>3U0dz1, the protection can be reliably operated.

When the neutral point of the generator has no arc suppression coil, for the phase A zero sequence current:

I_ka＝—j 3ω(C_0G—C_0W)]αEa，

when the neutral point of the generator has an arc suppression coil, for the phase A zero sequence current:

I_ka＝j[1/ωL—3ω(C_0G—C_0W)]αEa，

according to the operation experience, no matter whether the neutral point at the generator end is provided with the arc suppression coil or not, as long as the zero sequence current exceeds an allowable value (10kV system 20A), the grounding protection must act on tripping.

The problem that the zero sequence voltage alarm occurs for a plurality of times in 9, month and 14 days in the load direct supply system provided by the embodiment 1 of the invention, and the generator stator grounding protection is 3U in 9, month and 24 days₀Starting the jump machine.

The generator end stator grounding protection zero sequence voltage 3U appears in 9-month and 14-day days₀When alarming, the electric operation record shows that the voltage of the three-phase line of the 10kV system is normal, the voltage of the three-phase line is unbalanced, and the current of the direct supply load line of the generator is normal.

10kV II section 3U at generator end in fault₀And alarming, and meanwhile, turning on an action indicator lamp of the biological I-line harmonic elimination device.

Therefore, the method for detecting the virtual grounding reason of the generator stator of the load direct supply system is adopted in the embodiment 1.

First, the hair is obtainedZero sequence voltage at no load of motor end is 3U₀₁After the high-voltage circuit breaker is switched on, the zero sequence voltage at the generator end is 3U₀And the general fixed value of the generator stator grounding protection is 3U_0dzAfter the high-voltage circuit breaker is disconnected, the zero sequence voltage at the generator end is 3U₀₁The independent fixed value of the generator stator grounding protection is 3U_0dz1And the general stator grounding protection constant value is an action interface of the generator stator grounding and the load end zero sequence voltage protection. The zero sequence voltage of the load end is 3U₀₂The independent fixed value of the load end grounding protection is 3U_0dz2. Fig. 2 is an operation interface diagram of zero sequence voltage protection at the stator ground and load ends of the generator in embodiment 1 of the present invention; and then detecting whether the generator stator has the unreal grounding or not and the reason of the unreal grounding according to the acquired related parameters.

Firstly, zero sequence voltage 3U in zero-rise voltage test of generator₀₁' of the above.

Idling the generator end raises the generator voltage in the generator end from 0V to the rated voltage value UeV. 9 months and 14 days, the generator end is connected with the grid and the power is turned on and off 1, and in the off position, the generator stator is withdrawn from the grounding 3U under the controllable precondition₀Protected trip pressure plate to raise generator voltage to rated value UeV, and voltage meter to detect 3U on generator outlet PT secondary opening triangle side₀₁' is used. Detecting 3U₀The data and the variation trend of (A) are shown in the following Table 1:

the generator no-load test secondary data P is equal to 0, Q is equal to 0, cos phi is equal to 1

	3U0	U0	UAN	UBN	UCN	UAB	UBC	UCA
									Generator	1.6	1.3	58.1	59.0	59.3	102.2	103.2	102.0
Segment A	2.06	1.6	63.0	63.7	64.0	110.6	111.4	110.6
									Segment A	2.06	1.6

Wherein U in Table 1₀Is the generator neutral voltage.

3U₀₁The' third harmonic content is 18%, and the phase voltage waveform is normal.

Secondly, zero sequence voltage 3U when the generator is connected to the power grid through the main transformer₀₁Detection of (3).

The high-voltage circuit breaker 1111 is disconnected, and a generator end detects 3U on the triangular side of a PT secondary opening of a generator outlet by using a voltmeter under the grid-connected operation mode of a main transformer₀₁The value of (d);

and after 9 months and 14 days, the high-voltage circuit breaker 1111 is disconnected, the zero-sequence voltage stator grounding alarm is eliminated, namely after the generator end and the load direct supply system are disconnected, the generator is in 3U₀The stator ground fault alarm disappears. At that time, the load is 4.0MW, the three-phase voltage Ua is 6.17kV, Ub is 6.15kV, Uc is 6.12kV, and the #1 unit 1PT secondary opening triangle voltage is 2.4V. The results of the examination are summarized in table 2 below:

time of day	Delivery load	Unit Ua	Unit Ub	Unit Uc	Unit 3U0
						After being off-net	4.0MW	6.17kV	6.15kV	6.12kV	2.4V

Third, system balance condition checks when the direct supply load is supplied by a separate generator side.

And in 9 months and 14 days, when the zero sequence voltage at the generator end gives an alarm, the load end is checked as follows:

the biological I line 1101 switch is disconnected, the high-voltage circuit breaker 1111 is in the on-off position, and the system voltage is normal when the direct supply load is supplied with power only from the generator end. The load balance condition is good, the phase current is about 400A, and the three-phase current difference is not more than 5A and 3U₀₁＝2.00V。

The high-voltage circuit breaker 1111 is in the off position, the load is supplied by the power grid, and a voltmeter is used for detecting 3U on the secondary opening triangle side of the standby section PT of the load end₀₂The value of (d); the power supply switch of the power grid is disconnected, and the insulation resistance R to the ground of each phase is checked after the power failure of the load end; and after the load end is powered off, the insulation resistance R of each phase to the ground is checked to be less than 0.5 megaohm, so that the requirement is met.

9 months and 14 days, when the generator-end high-voltage circuit breaker 1111 is in the off position and the load is only powered by the biological I-line 1101 switch, a voltmeter is used for detecting 3U on the secondary opening triangle side of the standby section PT of the load end₀₂The values of the voltage values are all less than 2.4V, the system voltage is normal, 9 months and 14 days, after the power failure of the load end, all equipment of the load end is subjected to insulation test, the result is correct, and the insulation level of the equipment is normal.

4. And detecting the vector of the power supply load of the tie line.

Firstly, the zero sequence voltage 3U of the load direct supply system₀Testing balance condition with power supply load

The generator is operated in a grid-connected mode, the high-voltage circuit breaker is in a switch-on position, the biological I line 1101 switch is in a switch-on position, and the voltage, current and phase table is used for testing the system voltage and the connecting line current phase value after the generator is related at the connecting line 1111 high-voltage circuit breaker

9 months and 14 days, and zero sequence voltage of 3U₀When alarming, recording and displaying three-phase unbalanced voltage and zero sequence 3U voltage of 10kV system₀The system voltage and tie line current detection results during alarm are shown in table 3 below:

visible, zero sequence voltage 3U₀And alarming is carried out regardless of the symmetrical condition of the direct supply load.

Secondly, the zero sequence voltage 3U of the load direct supply system₀Testing of direct load conditions

In 14 days after 9 months, when the zero sequence voltage of the generator-end #1 unit alarms, the pressing plate of the stator grounding protection is in the disconnection position, the unit parameters are adjusted, and the relationship between the zero sequence voltage and the direct supply load of the whole direct supply system is monitored as shown in the following table 4:

time of day

Delivery load

Unit Ua

Unit Ub

Unit Uc

Unit 3U₀

Unit 3I₀

7：00

8.10MW

6.70kV

6.60kV

5.20kV

19V

7：20

7.93MW

6.67kV

6.20kV,

5.26kV

15V

7：30

7.6MW

6.66kV

6.09kV,

5.45kV

11V

7：40

5.0MW

6.53kV

6.03kV

5.69kV

8V

7：50

4.0MW

6.3kV

6.0kV

5.90kV

5V

0.75A

The test result shows that the larger the direct supply load is, the higher the zero sequence voltage is.

5. Zero sequence voltage 3U when generator end main transformer with direct supply load₀Detection of (2)

The generator is in grid-connected operation, the high-voltage circuit breaker 1111 is in the switch-on position, and a voltmeter is used for detecting the 3U of the whole system at the secondary opening triangular side of the PT outlet of the generator₀The value of (d); the ammeter is arranged at the tail part of the generator end, and compensates the reactance current I after testing the generator end correlation close to the load end_LThe value of (d); changing the tapping position of the compensation reactance at the generator end to detect the relevant 3U₀The numerical value of (3) is used as the zero sequence voltage of the system₀Characteristic 3U of relationship with generator-end neutral point reactance current compensation share₀＝f(I_L) And (4) testing.

When I line operation of biology, closing high voltage circuit breaker 1111 switch, when generator end and load end correlation power supply, the unbalanced phenomenon of three-phase voltage all appears in whole 10kV system, and a set of data of gathering are: ua 6.43kV, Ub 5.71kV, Uc 5.20kV, 3U₀＝9.49V

Changing the tapping position of the compensation reactance at the generator end to detect the relevant 3U₀The numerical value of (3) is used as the zero sequence voltage of the system₀Reactance with generator-side neutral point I_LDependence of the compensation fraction 3U₀＝f(I_L) And (4) testing.

And in 9 months and 14 days, the automatic neutral point compensation system of the #1 unit is checked when the system fails, and a group of acquired data is that the tap position of the reactor is in the 1-gear, the current of the compensation reactor is 5.0A, and the voltage is 5.5V.

When the neutral point reactor at the generator end is in a 9-gear position, zero sequence voltage alarm disappears, the three-phase voltage of the system tends to be balanced, and test data are shown in the following table 5:

tapping position	1	2	3	4	5	6	7	8	9
										Current (A)	4.25	4.90	5.60	6.40	7.20	8.25	9.40	10.80	12.45
3U₀(V)	20.0	16.0	12.0	9.0	6.0	3.5	2.6	2.3	2.0
										U₀(V)

In addition, the equipment condition of a load end is checked, the static action behavior of the stator grounding protection device of the #1 unit is checked, and the number of the units is 3U₀The action voltage is 10V, the time delay is 10s, and the action result is that the generator is disconnected and demagnetized. The shielding condition of the 1PT secondary cable at the outlet of the #1 unit is checked, and the shielding layer is grounded at a single end.

According to the above results of the field test, 3U is satisfied when the direct supply load side of the generator has a ground fault₀>3U_0dz1Or satisfaction of 3U caused by external system load imbalance₀>3U_0dz1I.e. the so-called generator stator ghost problem occurs.

For the faults of 9 months, 14 days and 9 months, 24 days, the 3U at the generator end can be known according to the secondary data of the no-load test at the generator end₀₁The' is 2.06V, so the generator stator has no problem of direct grounding, and the direct supply load end at the generator end has no 3U caused by grounding fault and the like₀>3U_0dz1The condition (2) is satisfied. From this it can be concluded that 3U₀The reasons for protection fault alarms are due to other factors, namely the existence of so-called other problems causing the stator phantom grounding problem.

As can be seen from the compensation current of different gears of the reactor in the table 5, the tap position of the reactor is in the 1-gear, the current of the compensation reactor is 5.0A, the voltage is 5.5V, and the compensation share is insufficient. The over-compensated condition is not reached at the generator end. Therefore, the problem of false grounding protection of the generator stator is inevitable.

For the load end, when the biological I line is disconnected, the three-phase voltage balance condition is good, which shows that the imbalance phenomenon of the three-phase voltage is caused by system problems.

Firstly, according to the inspection result, whether the equipment of a 10kV system at the generator end or the load end is normal, secondly, the fixed value of the grounding protection of the stator of the generator is 10V, the numerical value is lower, and thirdly, according to the data result of the no-load zero-lifting-voltage test of the generator, the insulation of the stator winding is normal. When the fourth biological I line runs, the voltage unbalance phenomenon occurs in the 10kV system at the generator end and the load end, and the numerical values are basically consistent. Therefore, the alarm of the zero sequence voltage is correct when the biological I line runs. The fixed value of the three-phase voltage unbalance protection of the 10kV load end is only 10V, and the numerical value is low. Fifthly, the zero sequence voltage alarm phenomenon occurs when the generator end is provided with a biological I line, and the zero sequence voltage alarm problem does not occur when the generator end is only operated in a grid-connected mode and is not provided with the biological I line; the unbalanced degree of the three-phase voltage of the 10kV system is related to the load of the biological I line, and the larger the load is, the larger the unbalanced degree of the three-phase voltage is; and the load current of the biological I line is basically balanced. It follows that the degree of three-phase voltage imbalance is related to the system parameters. Sixthly, the biological I line has more cables in the whole 10kV system, so that the cumulative length is longer, and the capacitance current is larger. When the electric reactor at the generator end can not realize overcompensation operation, under certain modes, the phenomena of three-phase voltage unbalance and zero-sequence voltage alarm are easy to occur when voltage fluctuates or a system is operated. Therefore, when the neutral point reactor at the generator end is in the 9-gear position, the zero sequence voltage alarm disappears, the three-phase voltage of the system tends to be balanced, and the compensating current is larger than 12A at the moment. It can be seen that the zero sequence voltage alarm is related to the condition of capacitance current compensation, but correct compensation only covers other problems, and is not related to the problems.

According to the method for detecting the virtual grounding reason of the generator stator of the load direct supply system, provided by the embodiment of the invention, the zero sequence voltage 3U associated with the generator end can be known₀The determination of the under-compensation, full compensation and over-compensation conditions is completed according to the test result. In the case of full compensation, resonance is liable to occur to make 3U₀Rising, resulting in phantom grounding of the stator; when under-compensation is carried out, the resonance process can occur due to the change of the operation mode, and the result is the same as that of full compensation; in the case of overcompensation, there is no resonance problem. Factors that cause system resonance are switching operation, system failure, and the like.

The embodiment 1 of the invention also provides a system for detecting the virtual grounding reason of the generator stator of the load direct supply system, which comprises a parameter acquisition module and a fault judgment module;

The parameter acquisition module comprises a first parameter acquisition module, a second parameter acquisition module and a third parameter acquisition module;

The third parameter acquisition module is used for acquiring the zero sequence voltage at the generator end to be 3U after the high-voltage circuit breaker is disconnected₀₁The independent fixed value of the generator stator grounding protection is 3U_0dz1Zero sequence voltage of load end is 3U₀₂The independent fixed value of the load end grounding protection is 3U_0dz2。

The fault judgment module is used for continuously increasing the generator voltage in the generator end from 0V to the rated voltage and is matched with 3U_0dz1The comparison mode is used for judging whether the generator stator in the generator end is in the unreal grounding state or not, adopting a cut-off high-voltage circuit breaker, and under the condition that the generator end runs in a grid-connected mode through a main transformer, connecting 3U₀₁And 3U_0dz1The comparison method is used for judging whether the generator stator is in unreal grounding caused by the voltage asymmetry between the generator end and the main transformer or not, adopting a cut-off high-voltage circuit breaker, and detecting 3U under the condition that the load end is supplied with power by a single power grid₀₂And the mode of checking the insulation resistance to ground of each phase after the power failure of the load end is adopted to judge whether the generator stator is in virtual grounding caused by the damage of the insulation to ground of the load end, and the high-voltage circuit breaker is closedWhen the generator end is in grid-connected operation, a mode of detecting a voltage and current phasor value of a connecting line after the generator end is associated is adopted to judge whether the generator stator is in virtual grounding caused by unbalanced load of the load end or not and adopt to close a high-voltage circuit breaker, and when the generator end is in grid-connected operation, a judgment system zero sequence voltage 3U is adopted to judge whether the system is in zero sequence voltage 3U₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L) And judging whether the generator stator is connected to the ground in an imaginary manner or not due to the resonance of the generator end and the load end.

The fault judgment module comprises a first fault judgment module, a second fault judgment module, a third fault judgment module, a fourth fault judgment module and a fifth fault judgment module;

the first failure judgment module is used for continuously increasing the generator voltage in the generator end from 0V to the rated voltage and is used for comparing the increased voltage with the rated voltage by 3U_0dz1Judging whether a generator stator in the generator end is in the unreal grounding state or not in a comparison mode;

the second fault judgment module is used for adopting a disconnected high-voltage circuit breaker to carry out 3U on the condition that the generator end is connected to the grid through the main transformer₀₁And 3U_0dz1Judging whether the generator stator is unreal grounded due to the asymmetric voltage between the generator end and the main transformer in a comparison mode;

While the invention has been described in detail in the specification and drawings and with reference to specific embodiments thereof, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted; all technical solutions and modifications thereof which do not depart from the spirit and scope of the present invention are intended to be covered by the scope of the present invention.

Claims

1. The method for detecting the virtual grounding reason of the generator stator of the load direct supply system is realized based on the load direct supply system, and the load direct supply system comprises a generator end and a load end; the generator end is an output voltage end consisting of three-phase stator windings of the generator; the load end is used for receiving the voltage output by the generator end; the generator end and the load end are connected through a connecting line; a high-voltage circuit breaker is arranged between the generator end and the load end; the high-voltage circuit breaker is used for cutting off or closing no-load current and load current in a high-voltage circuit; characterized in that the method comprises the following steps:

According to the obtained parameters of the load direct supply system, the generator voltage in the generator end is continuously increased from 0V to the rated voltage and is increased to 3U_0dz1Judging whether a generator stator in the generator end is in the unreal grounding state or not in a comparison mode; by breaking the high-voltage circuit breaker, the generator end is connected to the grid through the main transformerIn the case of operation, 3U is used₀₁And 3U_0dz1Judging whether the generator stator is unreal grounded due to the asymmetric voltage between the generator end and the main transformer in a comparison mode; detecting 3U by using a cut-off high-voltage circuit breaker under the condition that a load end is supplied with power by a separate power grid₀₂The value of the voltage value is obtained, and the mode of the insulation resistance to the ground of each phase is checked after the power failure of the load end, and whether the generator stator is in virtual grounding caused by the damage of the load end to the insulation to the ground is judged; judging whether the generator stator is in unreal grounding caused by load unbalance at the load end by adopting a mode of detecting the voltage and current phasor value of a connecting line after the generator end is associated when the high-voltage circuit breaker is closed and the generator end is in grid-connected operation; when the high-voltage circuit breaker is closed and the generator end is in grid-connected operation, the zero-sequence voltage 3U of the system is judged₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L) Judging whether the generator stator is in virtual grounding caused by the resonance of the generator end and the load end or not according to the change condition of the generator;

the method for judging whether the generator stator in the generator end is the virtual ground or not by continuously increasing the generator voltage in the generator end from 0V to the rated voltage and comparing the generator voltage with 3U0dz1 is characterized in that the generator end is in no-load, the generator voltage in the generator end is increased from 0V to the rated voltage value UeV, the value of 3U01 'is detected on the secondary opening triangle side of the generator outlet PT by a voltmeter, and if the generator voltage is increased from 0V to the rated voltage value UeV, 3U01' > 3U0dz1 is not the virtual ground of the generator stator.

2. The method for detecting the virtual grounding reason of the generator stator of the load direct supply system as claimed in claim 1, wherein the generator side is connected to the grid through the main transformer by disconnecting the high-voltage circuit breaker and then connecting 3U to the grid₀₁And 3U_0dz1The comparison method is to judge whether the generator stator is connected to the ground in phantom due to the asymmetrical voltage between the generator end and the main transformer, and includes disconnecting the high voltage breaker, and using the voltage meter to connect the generator end to the main transformer for operationPT Secondary opening triangular side detection 3U₀₁If 3U is present_01＞3U_0dz1The voltage asymmetry between the generator end and the main transformer results in the virtual grounding of the generator stator.

3. The method for detecting the virtual grounding reason of the generator stator of the load direct supply system as claimed in claim 1, wherein the method for detecting the 3U of the load end supplied with power from the separate power grid by opening the high-voltage circuit breaker is adopted₀₂And the mode of checking the insulation resistance to ground of each phase after the power failure of the load end, and judging whether the generator stator is in unreal grounding caused by the damage of the insulation to ground of the load end comprises the steps of disconnecting the high-voltage circuit breaker, and detecting 3U on the secondary opening triangle side of the standby PT (potential transformer) of the load end by using a voltmeter under the condition that the load end is supplied with power by a single power grid₀₂While checking the insulation resistance to ground R of each phase after the power failure at the load end, if the unit is operated by a single machine in 3U₀₁The voltage is normal, and the three-phase unbalanced voltage of the load end is 3U₀₂Exceeding standard, wherein the insulation resistance R of one phase to the ground is more than 0.5 megaohm after the power failure of the load end; after the high-voltage circuit breaker is closed, the 3U appears repeatedly₀>3U_0dz1Is the phantom grounding of the generator stator caused by the damage of the load end to the ground insulation.

4. The method for detecting the virtual grounding reason of the generator stator of the load direct supply system as claimed in claim 1, wherein the method for determining whether the virtual grounding of the generator stator caused by the unbalanced load at the load end is caused by the way of detecting the voltage and current phasor value of the connecting line after the generator end is associated during the grid-connected operation at the generator end comprises the steps of closing the high-voltage circuit breaker, performing the grid-connected operation at the generator end, and testing the voltage and current phasor value of the connecting line after the generator end is associated at the high-voltage circuit breaker by using a voltage meter, a current meter and a phase meter

If the unit operates 3U independently₀₁Normal voltage, generator side and loadThree-phase load phasor after end correlation

Imbalance results in 3U₀>U_0dz1The imaginary grounding of the generator stator caused by the load imbalance at the load end.

5. The method for detecting the virtual grounding reason of the generator stator of the load direct supply system as claimed in claim 1, wherein the judgment of the zero sequence voltage 3U of the system is adopted when the generator side is adopted for grid-connected operation₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L) The method for judging whether the generator stator is in the unreal grounding state caused by the resonance of the generator end and the load end comprises the steps of closing the high-voltage circuit breaker, carrying out grid-connected operation on the generator end, and detecting the whole load direct supply system 3U on the secondary opening triangular side of the PT secondary opening of the generator end outlet by using a voltmeter₀The value of (d); method for compensating reactance current I after testing generator end association by ammeter at generator end tail part_LThe value of (d); the tapping positions of the compensation reactance at the generator end are changed to respectively detect 3U₀Obtaining the zero sequence voltage 3U of the system₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L)，3U₀＝f(I_L) The relation characteristic changes with the tapping position of the compensating reactance, and the zero sequence voltage 3U of the load direct supply system appears₀>U_0dz1The imaginary grounding of the generator stator is caused by the resonance of the generator end and the load end.

6. The system for detecting the unreal grounding reason of the generator stator of the load direct supply system is characterized by comprising a parameter acquisition module and a fault judgment module;

the parameter acquisition module is used for acquiring the zero sequence voltage of 3U when the end of the generator is in no-load₀₁', high-voltage circuit breaker closingThen, the zero sequence voltage at the generator end is 3U₀And the general fixed value of the generator stator grounding protection is 3U_0dzAfter the high-voltage circuit breaker is disconnected, the zero sequence voltage at the generator end is 3U₀₁The independent fixed value of the generator stator grounding protection is 3U_0dz1Zero sequence voltage of load end is 3U₀₂The independent fixed value of the load end grounding protection is 3U_0dz2；

The fault judgment module is used for continuously increasing the voltage of the generator in the generator end from 0V to the rated voltage and is matched with 3U_0dz1The comparison mode is used for judging whether the generator stator in the generator end is in the unreal grounding state or not, adopting a cut-off high-voltage circuit breaker, and under the condition that the generator end runs in a grid-connected mode through a main transformer, connecting 3U₀₁And 3U_0dz1The comparison method is used for judging whether the generator stator is in unreal grounding caused by the voltage asymmetry between the generator end and the main transformer or not, adopting a cut-off high-voltage circuit breaker, and detecting 3U under the condition that the load end is supplied with power by a single power grid₀₂The method comprises the steps of detecting the mode of earth insulation resistance of each phase after power failure of a load end, judging whether the generator stator is in virtual earth caused by the damage of the load end to the earth insulation, closing a high-voltage circuit breaker, detecting the voltage and current phasor value of a connecting line after the generator end is connected in parallel operation, judging whether the generator stator is in virtual earth caused by the unbalanced load of the load end, closing the high-voltage circuit breaker, and judging the zero sequence voltage 3U of a system when the generator end is connected in parallel operation₀With neutral point reactance I of the generator_LDependence of the compensation fraction 3U₀＝f(I_L) Judging whether the generator stator is in virtual grounding caused by the resonance of the generator end and the load end or not according to the change condition of the generator; the method for judging whether the generator stator in the generator end is in the unreal grounding by adopting the mode of continuously increasing the generator voltage in the generator end from 0V to the rated voltage and comparing the generator voltage with 3U0dz1 is characterized in that the generator end is in no-load, the generator voltage in the generator end is increased from 0V to the rated voltage value UeV, the value of 3U01 'is detected on the secondary opening triangle side of the generator outlet PT by using a voltmeter, and if the generator voltage is increased from 0V to the rated voltage value UeV, 3U01' > 3U0dz1, it is not the generator stator phantom ground.

7. The system for detecting the virtual grounding reason of the generator stator of the load direct supply system as claimed in claim 6, wherein the parameter acquisition module comprises a first parameter acquisition module, a second parameter acquisition module and a third parameter acquisition module;

8. The system for detecting the virtual grounding reason of the generator stator of the load direct supply system according to claim 6, wherein the fault judgment module comprises a first fault judgment module, a second fault judgment module, a third fault judgment module, a fourth fault judgment module and a fifth fault judgment module;

the third fault judgment module is used for adopting a high-voltage circuit breaker to be disconnected and adopting a loadDetecting 3U with terminals supplied by separate grids₀₂The value of the voltage value is obtained, and the mode of the insulation resistance to the ground of each phase is checked after the power failure of the load end, and whether the generator stator is in virtual grounding caused by the damage of the load end to the insulation to the ground is judged;