阅读说明：本技术 一种在线监测发电机失磁保护状态的方法 (Method for monitoring loss-of-excitation protection state of generator on line ) 是由 孙健 周祎力 戴小云 薛志伟 花新宏 于 2019-09-26 设计创作，主要内容包括：本发明公开了一种在线监测发电机失磁保护状态的方法,包括转子低电压判据、机端低阻抗判据Z＜和系统低电压判据Um＜；所述转子低电压判据能够反应转子侧的电气量,具体为通过测量励磁电压Ufd是否小于动作值；所述机端低阻抗判据Z＜能够反应定子侧的电气量,具体为反应发电机机端感受阻抗,当感受阻抗落入阻抗圆内时,保护动作；所述系统低电压判据Um＜能够反应系统侧的电气量,具体为当汽轮发电机失磁后发电机高压侧母线电压低于允许值时,带时限动作于解列或程序跳闸。本发明提供的一种在线监测发电机失磁保护状态的方法,监测准确、可靠,有效保证发电机运行的安全性。(The invention discloses a method for monitoring the loss-of-field protection state of a generator on line, which comprises a rotor low-voltage criterion, a machine-end low-impedance criterion Z and a system low-voltage criterion Um; the rotor low-voltage criterion can reflect the electric quantity at the rotor side, specifically, whether the excitation voltage Ufd is smaller than an action value is measured; the machine end low impedance criterion Z is less than the electrical quantity capable of reflecting the stator side, specifically reflects the machine end sensed impedance of the generator, and protects the action when the sensed impedance falls into an impedance circle; the system low-voltage criterion Um is less than and can reflect the electric quantity on the system side, and specifically, when the voltage of a bus on the high-voltage side of the generator is lower than an allowable value after the turbine generator is demagnetized, the system low-voltage criterion Um is subjected to disconnection or program tripping with time limit. The method for monitoring the loss-of-field protection state of the generator on line provided by the invention is accurate and reliable in monitoring and effectively ensures the safety of the generator operation.)

1. A method for monitoring the loss-of-excitation protection state of a generator on line is characterized by comprising the following steps: the method comprises a rotor low-voltage criterion, a machine-end low-impedance criterion Z and a system low-voltage criterion Um;

the rotor low-voltage criterion can reflect the electric quantity at the rotor side, specifically, whether the excitation voltage Ufd is smaller than an action value is measured;

the machine end low impedance criterion Z is less than the electrical quantity capable of reflecting the stator side, specifically reflects the machine end sensed impedance of the generator, and protects the action when the sensed impedance falls into an impedance circle;

the system low-voltage criterion Um is less than and can reflect the electric quantity on the system side, and specifically, when the voltage of a bus on the high-voltage side of the generator is lower than an allowable value after the turbine generator is demagnetized, the system low-voltage criterion Um is subjected to disconnection or program tripping with time limit.

2. The method for monitoring the loss-of-excitation protection state of the generator on line according to claim 1, characterized in that: in the rotor low-voltage criterion, when the excitation voltage Ur of the generator rotor suddenly drops to 0 or amplitude, the excitation voltage criterion acts rapidly and acts before the generator reaches a static stability limit, and the criterion is as follows:

U_r＜U_rlzd。

3. the method for monitoring the loss-of-excitation protection state of the generator on line according to claim 1, characterized in that: when the generator transmits active and inductive reactive power outwards, the measured impedance of the generator end is positioned in a first quadrant, when the generator only outputs active power, the measured impedance of the generator end is positioned on an abscissa axis, when the generator transmits the active power and absorbs a part of inductive reactive power from a power grid, the measured impedance of the generator end is positioned in a fourth quadrant, when the absorbed inductive reactive power is more and more, the measured impedance of the generator end falls into the protective asynchronous boundary impedance circle of the generator, the generator is tripped by protection action, and under the condition that the generator has low excitation and loss of excitation, the generator firstly runs through the static boundary impedance circle and then turns into the asynchronous boundary impedance circle to run;

the method comprises the following specific steps of monitoring the loss-of-field protection state of the generator on line according to the condition that the terminal low impedance criterion Z is less than the value:

the method comprises the following steps: the method comprises the following steps of realizing online monitoring of a generator protection asynchronous boundary impedance circular diagram in DCS:

drawing a generator protection asynchronous boundary impedance circular diagram according to the asynchronous boundary impedance fixed value, and calculating the asynchronous boundary impedance fixed value:

in the formula: x_dIs a direct-axis synchronous reactance, X'_dIs the direct-axis transient reactance (unsaturated value), U_GNRated voltage for the generator, S_GNFor rated capacity of the generator, n_aFor current transformer transformation ratio, n_vThe transformation ratio of the voltage transformer is obtained;

mixing X_A、X_BConverted to the rated voltage U of the relay_NRated current I_NPer unit value for benchmark:

in the formula:I_N＝R1*5＝3.85A；

the circle center of the generator protection asynchronous boundary impedance circle is on the Y axis, (0, X)_A) And (0, X)_B) Respectively is the intersection point of the asynchronous boundary impedance circle and the Y axis, thereby obtaining the asynchronous boundary impedance circle;

step two: realizing on-line monitoring of an impedance value trace diagram of a real-time working condition point in a DCS;

calculating and describing an impedance value track of a working condition point according to real-time working condition parameters of the generator, and when the track falls into a generator protection asynchronous boundary impedance circle, performing a loss-of-excitation protection action on the generator;

calculating the real-time load working condition point impedance value:

real-time impedance

Real-time resistor

Real-time reactance

In the formula: u is the real-time voltage of the generator, P is the real-time output power of the generator, Q is the real-time output reactive power of the generator, n_aFor current transformer transformation ratio, n_vThe transformation ratio of the voltage transformer is obtained;

calculating the resistance and reactance of the generator under corresponding load through real-time active power and reactive power of the generator to obtain the position of a real-time load working condition point; when the load working point is close to the protection asynchronous boundary impedance circle of the generator, the reactive power of the generator is manually increased, and the generator is prevented from tripping;

step three: realizing an active impedance chart such as online monitoring in DCS:

the equal active impedance circular diagram is formed by drawing the generator according to different reactive impedance values under the same active condition;

when the generator operates in a deep entry mode, the generator operates under the same active condition; changing the reactive power of the generator in the running process; changing the reactive power Q from-infinity to + ∞accordingto the real-time impedance Z, the real-time resistance R and the real-time reactance X, respectively calculating the resistance R and the reactance X of the generator, and drawing a curve to obtain an equal active impedance circle; when the intersection point of the active impedance circle and the generator protection asynchronous boundary impedance circle is the entry limit of the generator in the current active power, the loss of excitation protection of the generator cannot act as long as the reactive power of the generator is ensured to be greater than the limit value in the operation process, so that the safe operation of the generator is ensured; the phase advance limit calculation is according to the following equation:

and P is active, and the corresponding resistance R and reactance X on the asynchronous boundary circle under the current active condition can be obtained by planning and solving in the EXCEL, so that the corresponding minimum reactive power is obtained.

4. The method for monitoring the loss-of-excitation protection state of the generator on line according to claim 1, characterized in that: when the system low voltage criterion Um is less than, the influence on the voltage when the magnetic loss occurs is firstly shown in that the reactive power is reduced until the direction is reversed, and a large amount of reactive power is absorbed to the system, so that the voltage of a bus is reduced; after the generator is demagnetized, the three-phase voltage at the generator end is sharply reduced due to the reduction of rotor excitation; the system low voltage criterion Um is set for reflecting the terminal voltage drop;

the system low voltage criterion Um is less than the bus three-phase voltage or the terminal three-phase voltage; a low voltage criterion of a locking system is adopted when the TV is disconnected; three-phase simultaneous low-voltage criterion:

U_PP＜U_lezd。

Technical Field

The invention belongs to the technical field of generator protection monitoring, and particularly relates to a method for monitoring the loss-of-excitation protection state of a generator on line.

Background

During operation of the synchronous generator, the excitation may suddenly be lost, in whole or in part. The reasons for the loss of field are not only due to open circuit of the excitation circuit (such as mis-tripping of a field-extinguishing switch), short circuit, disappearance of an excitation power supply, or rotor winding failure. After the generator has a loss of field fault, a large amount of reactive power is absorbed from the system, so that the voltage of the system is reduced, and even the system is collapsed due to voltage collapse; causing the generator to run out of step and generating mechanical torque which endangers the safety of the generator; the occurrence of difference frequency current in the rotor circuit causes additional temperature rise and other hazards. Therefore, the safe operation of the large-scale unit is seriously influenced by the loss of field fault of the generator.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention provides the method for monitoring the loss-of-field protection state of the generator on line, which is accurate and reliable in monitoring and effectively ensures the running safety of the generator.

The technical scheme is as follows: in order to achieve the purpose, the method for monitoring the loss-of-field protection state of the generator on line comprises a rotor low-voltage criterion, a machine end low-impedance criterion Z and a system low-voltage criterion Um, wherein the rotor low-voltage criterion Z is smaller than the system end low-impedance criterion Um;

the rotor low-voltage criterion can reflect the electric quantity at the rotor side, specifically, whether the excitation voltage Ufd is smaller than an action value is measured;

the machine end low impedance criterion Z is less than the electrical quantity capable of reflecting the stator side, specifically reflects the machine end sensed impedance of the generator, and protects the action when the sensed impedance falls into an impedance circle;

the system low-voltage criterion Um is less than and can reflect the electric quantity on the system side, and specifically, when the voltage of a bus on the high-voltage side of the generator is lower than an allowable value after the turbine generator is demagnetized, the system low-voltage criterion Um is subjected to disconnection or program tripping with time limit.

Further, in the rotor low voltage criterion, when the excitation voltage Ur of the generator rotor suddenly drops to 0 or amplitude, the excitation voltage criterion acts rapidly and acts before the generator reaches a steady state limit, and the criterion is as follows:

U_r＜U_rlzd

furthermore, in the machine-end low-impedance criterion Z < the impedance circle of the magnetic loss protection comprises a static-stability boundary impedance circle, an apple impedance circle and an asynchronous boundary impedance circle, when the generator transmits active power and inductive reactive power outwards, the machine-end measured impedance is positioned in a first quadrant, when the generator only outputs active power, the machine-end measured impedance is positioned on an abscissa axis, when the generator transmits the active power and simultaneously absorbs a part of inductive reactive power from a power grid, and the machine-end measured impedance is positioned in a fourth quadrant, when the absorbed inductive reactive power is more and more, the machine-end measured impedance falls into the generator protection asynchronous boundary impedance circle, the generator is tripped by protection action, and under the condition that the generator has low excitation and magnetic loss faults, the generator firstly runs through the static-stability boundary impedance circle and then turns into the asynchronous boundary impedance circle to run;

the method comprises the following specific steps of monitoring the loss-of-field protection state of the generator on line according to the condition that the terminal low impedance criterion Z is less than the value:

the method comprises the following steps: the method comprises the following steps of realizing online monitoring of a generator protection asynchronous boundary impedance circular diagram in DCS:

drawing a generator protection asynchronous boundary impedance circular diagram according to the asynchronous boundary impedance fixed value, and calculating the asynchronous boundary impedance fixed value:

in the formula: x_dIs a direct-axis synchronous reactance, X'_dIs the direct-axis transient reactance (unsaturated value), U_GNRated voltage for the generator, S_GNFor rated capacity of the generator, n_aFor current transformer transformation ratio, n_vThe transformation ratio of the voltage transformer is obtained;

mixing X_A、X_BConverted to the rated voltage U of the relay_NRated current I_NPer unit value for benchmark:

in the formula:I_N＝R1*5＝3.85A；

the circle center of the generator protection asynchronous boundary impedance circle is on the Y axis, (0, X)_A) And (0, X)_B) Respectively is the intersection point of the asynchronous boundary impedance circle and the Y axis, thereby obtaining the asynchronous boundary impedance circle;

step two: realizing on-line monitoring of an impedance value trace diagram of a real-time working condition point in a DCS;

calculating and describing an impedance value track of a working condition point according to real-time working condition parameters of the generator, and when the track falls into a generator protection asynchronous boundary impedance circle, performing a loss-of-excitation protection action on the generator;

calculating the real-time load working condition point impedance value:

real-time impedance

Real-time resistor

Real-time reactance

In the formula: u is the real-time voltage of the generator, P is the real-time output power of the generator, Q is the real-time output reactive power of the generator, n_aFor current transformer transformation ratio, n_vThe transformation ratio of the voltage transformer is obtained;

calculating the resistance and reactance of the generator under corresponding load through real-time active power and reactive power of the generator to obtain the position of a real-time load working condition point; when the load working point is close to the protection asynchronous boundary impedance circle of the generator, the reactive power of the generator is manually increased, and the generator is prevented from tripping;

step three: realizing an active impedance chart such as online monitoring in DCS:

the equal active impedance circular diagram is formed by drawing the generator according to different reactive impedance values under the same active condition;

when the generator operates in a deep entry mode, the generator operates under the same active condition; changing the reactive power of the generator in the running process; changing the reactive power Q from-infinity to + ∞accordingto the real-time impedance Z, the real-time resistance R and the real-time reactance X, respectively calculating the resistance R and the reactance X of the generator, and drawing a curve to obtain an equal active impedance circle; when the intersection point of the active impedance circle and the generator protection asynchronous boundary impedance circle is the entry limit of the generator in the current active power, the loss of excitation protection of the generator cannot act as long as the reactive power of the generator is ensured to be greater than the limit value in the operation process, so that the safe operation of the generator is ensured; the phase advance limit calculation is according to the following equation:

and P is active, and the corresponding resistance R and reactance X on the asynchronous boundary circle under the current active condition can be obtained by planning and solving in the EXCEL, so that the corresponding minimum reactive power is obtained.

Further, in the system low voltage criterion Um <, the influence on the voltage when the magnetic loss occurs is firstly shown in that the reactive power is reduced until the direction is reversed, and a large amount of reactive power is absorbed to the system, so that the voltage of the bus is reduced; after the generator is demagnetized, the three-phase voltage at the generator end is sharply reduced due to the reduction of rotor excitation; the system low voltage criterion Um is set for reflecting the terminal voltage drop;

the system low voltage criterion Um is less than the bus three-phase voltage or the terminal three-phase voltage; a low voltage criterion of a locking system is adopted when the TV is disconnected; three-phase simultaneous low-voltage criterion:

U_PP＜U_lezd

has the advantages that: the method for monitoring the loss-of-excitation protection state of the generator on line has the following beneficial effects:

1) the invention realizes the on-line monitoring of the loss-of-excitation protection of the generator through the rotor low-voltage criterion, the terminal low-impedance criterion Z and the system low-voltage criterion Um, the monitoring is accurate and reliable, and the running safety of the generator is effectively ensured;

2) according to the principle that the terminal low impedance criterion Z is less, the invention realizes online monitoring of the generator protection asynchronous boundary impedance circle in the DCS, online monitoring of the real-time working condition point impedance value track in the DCS and online monitoring of the active impedance circle in the DCS, so as to judge and ensure the operation stability and safety of the generator, and has high accuracy and good safety.

Drawings

FIG. 1 is a diagram of an asynchronous boundary impedance circular trace;

FIG. 2 is a first diagram of asynchronous boundary impedance and phase advance test impedance traces for field loss protection of a generator;

FIG. 3 is a schematic diagram of the phase advance operation at a load condition point;

FIG. 4 is a second diagram of the asynchronous boundary impedance and phase advance test impedance trace of the loss-of-excitation protection of the generator.

Detailed Description

The present invention will be further described with reference to the accompanying drawings.

A method for monitoring the loss-of-field protection state of a generator on line comprises a rotor low-voltage criterion, a terminal low-impedance criterion Z and a system low-voltage criterion Um;

the rotor low-voltage criterion can reflect the electric quantity at the rotor side, specifically, whether the excitation voltage Ufd is smaller than an action value is measured;

the machine end low impedance criterion Z is less than the electrical quantity capable of reflecting the stator side, specifically reflects the machine end sensed impedance of the generator, and protects the action when the sensed impedance falls into an impedance circle;

the system low-voltage criterion Um is less than and can reflect the electric quantity on the system side, and specifically, when the voltage of a bus on the high-voltage side of the generator is lower than an allowable value after the turbine generator is demagnetized, the system low-voltage criterion Um is subjected to disconnection or program tripping with time limit.

In the rotor low-voltage criterion, when the excitation voltage Ur of the generator rotor suddenly drops to 0 or amplitude, the excitation voltage criterion acts rapidly and can act before the generator reaches a static stability limit, and the criterion is as follows:

U_r＜U_rlzd

when the generator transmits active and inductive reactive power outwards, the measured impedance of the generator end is positioned in a first quadrant, when the generator only outputs active power, the measured impedance of the generator end is positioned on an abscissa axis, when the generator transmits the active power and absorbs a part of inductive reactive power from a power grid, the measured impedance of the generator end is positioned in a fourth quadrant, when the absorbed inductive reactive power is more and more, the measured impedance of the generator end falls into the protective asynchronous boundary impedance circle of the generator, the generator is tripped by protection action, and under the condition that the generator has low excitation and loss of excitation, the generator firstly runs through the static boundary impedance circle and then turns into the asynchronous boundary impedance circle to run;

the method comprises the following specific steps of monitoring the loss-of-field protection state of the generator on line according to the condition that the terminal low impedance criterion Z is less than the value:

the method comprises the following steps: the method comprises the following steps of realizing online monitoring of a generator protection asynchronous boundary impedance circular diagram in DCS:

drawing a generator protection asynchronous boundary impedance circular diagram according to the asynchronous boundary impedance fixed value, and calculating the asynchronous boundary impedance fixed value:

in the formula: x_dIs a direct-axis synchronous reactance, X'_dIs the direct-axis transient reactance (unsaturated value), U_GNRated voltage for the generator, S_GNFor rated capacity of the generator, n_aFor current transformer transformation ratio, n_vThe transformation ratio of the voltage transformer is obtained;

mixing X_A、X_BConverted to the rated voltage U of the relay_NRated current I_NPer unit value for benchmark:

in the formula:I_N＝R1*5＝3.85A；

the circle center of the generator protection asynchronous boundary impedance circle is on the Y axis, (0, X)_A) And (0, X)_B) Respectively is the intersection point of the asynchronous boundary impedance circle and the Y axis, thereby obtaining the asynchronous boundary impedance circle;

step two: realizing on-line monitoring of an impedance value trace diagram of a real-time working condition point in a DCS;

calculating and describing an impedance value track of a working condition point according to real-time working condition parameters of the generator, and when the track falls into a generator protection asynchronous boundary impedance circle, performing a loss-of-excitation protection action on the generator;

calculating the real-time load working condition point impedance value:

real-time impedance

Real-time resistor

Real-time reactance

In the formula: u is the real-time voltage of the generator, P is the real-time output power of the generator, Q is the real-time output reactive power of the generator, n_aFor current transformer transformation ratio, n_vThe transformation ratio of the voltage transformer is obtained;

calculating the resistance and reactance of the generator under corresponding load through real-time active power and reactive power of the generator to obtain the position of a real-time load working condition point; when the load working point is close to the protection asynchronous boundary impedance circle of the generator, the reactive power of the generator is manually increased, and the generator is prevented from tripping;

step three: realizing an active impedance chart such as online monitoring in DCS:

the equal active impedance circular diagram is drawn by the generator according to different reactive impedance values under the same active condition, and is shown in figure 4;

when the generator operates in a deep entry mode, the generator operates under the same active condition; changing the reactive power of the generator in the running process; changing the reactive power Q from-infinity to + ∞accordingto the real-time impedance Z, the real-time resistance R and the real-time reactance X, respectively calculating the resistance R and the reactance X of the generator, and drawing a curve to obtain an equal active impedance circle; when the intersection point of the active impedance circle and the generator protection asynchronous boundary impedance circle is the entry limit of the generator in the current active power, the loss of excitation protection of the generator cannot act as long as the reactive power of the generator is ensured to be greater than the limit value in the operation process, so that the safe operation of the generator is ensured; the phase advance limit calculation is according to the following equation:

wherein P is active, and the corresponding resistance R and reactance X on the asynchronous boundary circle under the current active power can be obtained by using the planning and solving in EXCEL, so as to obtain the corresponding minimum reactive power, as shown in the following table:

as shown in fig. 2, in the trace diagrams of the asynchronous boundary impedance of the field loss protection and the phase advance test impedance of the generator, the traces of the test operating condition points are marked, and it can be seen that the impedance circle closest to the asynchronous boundary impedance of the generator protection is at the active 325MW and the reactive-240 Var, as shown in the following table:

in fig. 2, all load points falling within the generator protection asynchronous boundary impedance circle can trigger a protection action, i.e. the generator loss-of-excitation protection action trips;

as shown in fig. 3, the key point of the present invention is to check the safety desire of the unit by monitoring the real-time load operating point, after the phase advance operation, the reactive power is a negative value, so the reactance will also be a negative value, and then the point change will enter the fourth quadrant for operation. In fig. 3, the low excitation curve is the operating warning line of the load operating point.

When the system low voltage criterion Um is less than, the influence on the voltage when the magnetic loss occurs is firstly shown in that the reactive power is reduced until the direction is reversed, and a large amount of reactive power is absorbed to the system, so that the voltage of a bus is reduced; after the generator is demagnetized, the three-phase voltage at the generator end is sharply reduced due to the reduction of rotor excitation; the system low voltage criterion Um is set for reflecting the terminal voltage drop;

the system low voltage criterion Um is less than the bus three-phase voltage or the terminal three-phase voltage; a low voltage criterion of a locking system is adopted when the TV is disconnected; three-phase simultaneous low-voltage criterion:

U_PP＜U_lezd

the above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.