CN111999562B - Method for measuring system impedance by using generator phase-in operation - Google Patents
Method for measuring system impedance by using generator phase-in operation Download PDFInfo
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- CN111999562B CN111999562B CN202010826614.0A CN202010826614A CN111999562B CN 111999562 B CN111999562 B CN 111999562B CN 202010826614 A CN202010826614 A CN 202010826614A CN 111999562 B CN111999562 B CN 111999562B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0092—Details of emergency protective circuit arrangements concerning the data processing means, e.g. expert systems, neural networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/006—Calibration or setting of parameters
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Abstract
The invention discloses a method for measuring system impedance through the phase-in operation of a generator. According to the method, three parameters of generator terminal voltage, stator current and power factor angle of the generator are recorded by utilizing the generator phase-entering operation process, the generator terminal impedance parameter is obtained through simple calculation, and then the generator terminal impedance parameter is fitted on an R-X coordinate plane through a least square method, so that the accurate system impedance parameter can be finally obtained. The system impedance of the system is calculated through the operation parameters of the generator during normal grid-connected phase-entering operation, the duration of the phase-entering operation of the generator is short, expensive special instruments are not needed for measurement, normal power production is not influenced, and the operation and the implementation are convenient. Compared with the traditional method for updating the system impedance according to the superior sending file, the method can update the system impedance parameters of the current power grid in time. The system impedance is calculated and obtained by adopting actual operation data, and more real and accurate system impedance parameters can be obtained.
Description
Technical Field
The invention belongs to the technical field of power system relay protection, and particularly relates to a method for measuring system impedance by utilizing the phase-in operation of a generator.
Background
In the relay protection setting calculation and the modeling simulation of the power system, the system impedance of the power grid is an indispensable important parameter, and the system impedance of the power grid directly influences the magnitude of short-circuit current provided by the system, so that the sensitivity of a relay protection setting value is influenced. In the grid-related protection of the generator, such as the loss-of-field protection and the loss-of-step protection, the system impedance is directly used to form a protection constant value.
At present, the method for acquiring system parameters is mainly a theoretical calculation method, and a calculation method for calculating a system impedance value in a short circuit loop through short circuit impedance parameters of each electrical device is provided on the premise that parameters of a topological structure of a power grid system and equipment parameters such as lines and transformers can be acquired. At present, the work is mainly performed by a power grid dispatching mechanism, and according to a patent of 'method and device for updating impedance of a power system', the existing system impedance management work is classified management and gradual updating, and the system impedance is updated by sending files by superior units every year. For example, the network regulator is responsible for managing and updating the system impedance of 330kV and above, then the city regulator is responsible for managing and updating the system impedance of 220kV and above, and finally the network regulator is responsible for managing and updating the system impedance of 110kV and below, and often the network regulator is adjusted once a year or more.
For a power plant, as a subordinate unit of a power grid, the power plant can only passively receive system impedance parameters issued by a power grid dispatching mechanism, and can only receive a relay protection fixed value of the power plant once in a year or more. In the power system, a new grid-connected power supply and a new line are continuously provided, and the operation mode is also changed, so that the system impedance is continuously changed. For example, in a certain power plant in Weinan of Shanxi, the reference capacity is 100MVA, the system impedance in 2019 is 0.001669+ j0.011548, and the system impedance in 2020 is 0.000713+ j0.007105, so that the system impedance is reduced by nearly 40% after one year. When the system impedance changes and the relay protection setting value is not adjusted in time, the effectiveness of the protection setting value is inevitably influenced.
The system impedance parameter related to the relay protection of the power plant is not the impedance parameter of the whole system, but only the system impedance of the power plant grid-connected point is reduced. Under the condition that the topological structure of a power grid system and equipment parameters such as lines, transformers and the like cannot be obtained, the power plant cannot calculate the system impedance by itself; for the calculated impedance issued by the power grid, it cannot be verified whether the calculated impedance is equal to the real system impedance of the power grid. Although a short-circuit test method can also be adopted to measure the short-circuit impedance of the system directly through a short-circuit test, the short-circuit impedance can only be obtained when the system has a short-circuit fault, and when the system has the short-circuit fault, large current flows through equipment such as a line and a transformer, so that the impact on the power equipment is large, and the damage to the power equipment can be possibly caused.
Disclosure of Invention
The invention aims to provide a method for measuring system impedance through the in-phase operation of a generator, which can obtain the system impedance of a current system reduced to a power plant grid-connected bus.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a method of measuring system impedance using generator in-phase operation, comprising the steps of:
1) Under the low-load working condition, the generator is driven to operate in a phase by gradually reducing the exciting current; in the process of the phase-in operation of the generator, the active load of the generator is kept unchanged;
2) Recording generator stator current I, active power P and reactive power Q in the phase-entering operation process, and recording N groups of data after the phase-entering test is finished;
3) Using experimental data, calculations can yield:
the resistance parameters of the termination impedance are:
reactance parameters of the termination impedance are:
wherein i =1,2,3.. N-1, N;
4) Fitting the N groups of data on an R-X coordinate plane by a least square method, wherein the fitting curve equation is (R-A) 2 +(X-B) 2 ＝R 2 The coordinates of the center of the circle are (A, B), the radius of the circle is R, wherein R = A;
5) If the generator is directly connected with the system, the longitudinal coordinate B of the center of the fitting circle is a secondary value of the system impedance, and the CT transformation ratio at the generator end is set to be n TA PT ratio of n TV The first order value of the system impedance is
If the generator is connected with the system through the transformer, the vertical coordinate B of the circle center of the fitting circle is the sum of the short-circuit impedance of the transformer and the system impedance, and the short-circuit impedance of the transformer is setIs X T The generator terminal CT transformation ratio is n TA PT ratio of n TV The first order value of the system impedance is
The invention is further improved in that the generator is under 30% -50% load condition.
Compared with the prior art, the invention has at least the following beneficial technical effects:
1. according to the method, three parameters of generator terminal voltage, stator current and power factor angle of the generator are obtained by utilizing the normal phase-in operation process of the generator, generator terminal impedance parameters are obtained through simple calculation, and then the generator terminal impedance parameters are fitted through a least square method, so that accurate system impedance parameters can be obtained finally. The generator has short duration of the phase-in operation, does not need expensive special instruments, does not need to stop the generator, and does not influence the normal power production.
2. Compared with the traditional method for updating the system impedance according to the superior file, the method can update the system impedance parameters of the current power grid in time. The method adopts actual operation data to calculate and obtain the system impedance, and can obtain more real and accurate system impedance parameters compared with the traditional method for calculating the system impedance according to the power grid equipment parameters.
Compared with the prior art, the invention has the following remarkable advantages:
1. the system impedance of the system is calculated through the operation parameters of the generator during normal grid-connected phase-in operation, the generator is normally operated in a grid-connected mode in the whole process, the phase-in operation duration is short, expensive special instruments are not needed for measurement, normal power production is not influenced, and the operation and implementation are convenient.
2. Compared with the traditional method for updating the system according to the superior sending file, the power plant can update the current system impedance parameter in time by measuring the system impedance through the generator phase-entering operation, and further adjust the relay protection setting value, thereby ensuring the effectiveness of the relay protection setting value. Although the patent "method and apparatus for updating impedance of power system" also proposes a method for updating impedance of power system, it still adopts traditional calculation method, and it cannot guarantee accuracy of calculation result.
In summary, the present invention provides a method for measuring system impedance by using a generator. When the generator runs in a grid-connected mode, exciting current is gradually reduced, so that the generator is changed from providing reactive power for a system to absorbing the reactive power from the system, stator current is changed from lagging to leading generator terminal voltage in an angle, and the process is phase-in running. According to the classical theory of the generator, when the running generator runs in a phase, the electromotive force of the generator is attenuated along with the reduction of the exciting current, in the process, the output active power of the generator is kept unchanged, and on an impedance complex plane, the generator terminal impedance track of the generator is that
A circle, U, as the center of the circle s Is the system voltage, X con The terminal is connected with the reactance of the system, and P is the active power generated by the generator. Because the P values of all points on the locus circle are equal, the locus circle is also called an equal active impedance circle. The invention obtains the equivalent active circle by a method of curve fitting through a least square method, and then calculates to obtain a real system impedance parameter.
Drawings
FIG. 1 is a schematic diagram of calculating system impedance using the method of the present invention.
Detailed Description
The invention is further described below with reference to the figures and examples.
FIG. 1 is a schematic diagram of calculating system impedance using the method of the present invention. In fig. 1, the solid line is a generator terminal impedance trajectory graph drawn according to the measured data in the phase advance test, the dotted line is a circle obtained by fitting the generator terminal impedance trajectory by the least square method, and the coordinates (19.55, 3.15) are the coordinates of the center of the fitted circle.
The invention provides a method for measuring system impedance during the phase-in operation of an over-generator, which comprises the following specific steps:
1) The 660MW generator operates under the working condition of 36.2% load, and the generator is operated in an incoming phase by gradually reducing exciting current;
2) In the process of the phase-entering operation of the generator, the active load 239MW of the generator is kept unchanged;
3) Recording generator stator current I, active power P and reactive power Q in the phase-entering operation process, and recording N groups of data after the phase-entering test is finished;
4) Using experimental data, calculations can yield:
the resistance parameters of the terminal impedance are as follows:
reactance parameters of the termination impedance are:
wherein i =1,2,3.. N-1, N;
5) Fitting the N groups of data on an R-X coordinate plane by a least square method, wherein the fitting curve equation is (R-A) 2 +(X-B) 2 ＝R 2 The coordinates of the center of the circle are (A, B), the radius of the circle is R, wherein R = A, the fitting result is (R-19.55) 2 +(X-3.15) 2 ＝19.55 2 Wherein B =3.15.
In this example, the generator is connected with the system through the transformer, the vertical coordinate B of the center of the fitting circle is the sum of the short-circuit impedance of the transformer and the system impedance, the short-circuit impedance of the transformer is XT =0.114 Ω, and the CT transformation ratio at the generator end is n TA =25000/5A, PT transformation ratio is n TV If the voltage is not less than 20/0.1kV, the first value of the system impedance after the system impedance is reduced to the generator terminal voltage is
Claims (1)
1. A method for measuring system impedance using generator in-phase operation, comprising the steps of:
1) Under the low-load working condition, the generator is enabled to run in a phase by gradually reducing the exciting current; in the process of the phase advance operation of the generator, the active load of the generator is kept unchanged; the generator is under the working condition of 30-50% load;
2) Recording generator stator current I, active power P and reactive power Q in the phase advancing operation process, and recording N groups of data after the phase advancing test is finished;
3) Calculating to obtain the resistance of the terminal impedance and the reactance of the terminal impedance by using the test data; the resistance parameters of the termination impedance are:
reactance parameters of the terminal impedance are:
wherein i =1,2,3.. N-1, N;
4) Fitting the N groups of data on an R-X coordinate plane by adopting a least square method; the fitting curve equation is (R-A) 2 +(X-B) 2 ＝R 2 The coordinates of the center of the circle are (A, B), the radius of the circle is R, wherein R = A;
5) If the generator is directly connected with the system, the vertical coordinate B of the center of the fitting circle is a secondary value of the system impedance;
if the generator is connected with the system through the transformer, the vertical coordinate B of the circle center of the fitting circle is the sum of the short-circuit impedance of the transformer and the impedance of the system;
setting the CT transformation ratio at the generator terminal as n TA PT ratio of n TV The first order value of the system impedance is
Let the short-circuit impedance of the transformer be X T The generator terminal CT transformation ratio is n TA PT ratio of n TV The first order value of the system impedance is
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