RU2472168C2 - Method of early detection of turn-to-turn short circuits and diagnostics of technical state of turbine generator rotor winding with determination of rotor current as per stator parameters - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention is meant for monitoring of technical state of turbine generators (TG) and equipage of TG systems and can be used for diagnostics of turbine generators of any capacity with any excitation system. Essence of the invention consists in the fact that calculation of reference rotor current corresponding to the operating mode is carried out as per simultaneously measured actual electric parameters of stator. Adjusting coefficient is determined as per initial basic characteristic obtained at heating tests and considering the change of synchronous induction resistance of stator winding. Calculation of the number of short-circuited turns in the rotor is performed considering the adjusting coefficient, and the conclusion on the presence of defect in the rotor is made as per detection of short-circuited turns.

EFFECT: improving the evaluation accuracy of the winding state in real-time mode; providing the possibility of detecting the winding defects at early stage.

3 cl, 1 dwg, 10 tbl

Description

The invention relates to techniques for operating turbogenerators, is intended for technical monitoring of the condition of turbogenerators (TG) and equipment of TG systems, and can be used to diagnose turbogenerators of any power.

Operating experience of TG shows that underestimation of the danger of latent defects during their rapid development leads to damage to the TG and lengthy restoration work.

The occurrence and development of such defects of the TG rotor is mainly facilitated by:

- dynamic loads on the rotating parts of the TG, temperature effects inside the TG case, pollution: dust, oil;

- the impossibility during operation of the TG of direct visual or instrumental control and detection at an early stage of a developing defect of the rotor element;

- the inability to directly measure the current of the TG rotor in the case of installing a brushless excitation system on the TG;

- lack of automated continuous monitoring and diagnosis of comparison and analysis of the current readings of various sensors of direct and indirect measurement of rotor current, with calculated values of the rotor current.

In this case, the rotor current means the main rotor current — the TG excitation current, which corresponds to the working state of the generator. A known method for the diagnosis and control of winding circuits in the rotor of a synchronous machine, which consists in using a fixed induction sensor installed near the surface of a rotating rotor of a synchronous machine at the input of a measuring voltmeter when a DC rotor is fed into the winding, characterized in that they perform a spectral analysis of the electromotive force induced in the induction sensor (RF patent No. 2192649, OJSC Electrosila, publication date 10.11.2002). The disadvantage of this method is the lack of conclusions and displays on the number of short-circuited turns when a defect occurs and the need for the TG to go into idle mode, according to a signal of a possible short circuit for analysis and comparison of EMF curves, amplitudes and phases of spectral components with passport data and determining the severity of the accident.

A known method of finding inter-turn faults in the windings of rotors when powered by alternating current (see Gemke R.G. Faults in electrical machines. Energoatomizdat, L., 1989, pp. 182-185). For turbine generators, this method gives reliable results if the bandages are removed and the interpolar and intercoil connections are removed, which means that the rotor is disassembled and leads to large losses of time and money, since removing the bandages can overheat the bandage insulation and often require replacement. During rotation of the rotor, this method is used when installing an auxiliary contact ring and brush.

There is a method of monitoring turn-in circuits in a rotor using an IVZ type device (turn-off indicator), similar to a generator manufactured by Parsons sending pulses with a steepness of the front of 75 ns (Wood JW, Hindmarch RT Rotor winding short detection. // IEEE Proceedings. 1986 Vol.133, pt B, N 3. P.181-189). Comparing the shape of the reflected signals with the calibration curves, they conclude that there are coil faults in the rotor. When interpreting the results obtained, difficulties arise due to the ambiguity of the qualitative comparison. This disadvantage is also characteristic of other methods of controlling coil circuits.

There is a method of controlling coil short circuits in the rotor by using a test coil extended into the air gap from the stator, the electromotive force of which is induced by the rotor field is supplied to the oscilloscope, and, based on the shape of the curve, make a conclusion about the absence of coil short circuits in the rotor (see A.E. Alekseev , Kostenko M.P. Turbogenerators, SEI, M. - L., 1939, p. 201, 341). This method has found wide application. For example, half of the 500 and 660 MW turbo generators in the UK are equipped with magnetic field sensors for detecting windings in the rotor (Jackson RJ, Roberts IA, Thurston RC, Worsfold JH Generator rotor monitoring in the United Kingdom. // CIGRE. 1986. Report 11- 04, 8 p.). The disadvantage of this method is the subjectivity of the qualitative conclusion of the shape of the curve. The lack of quantitative criteria leads to the ambiguity of the conclusions about the presence of coil closures in the rotor.

The technical result of the invention is to increase the reliability of the assessment of the state of the TG by using a mathematical model of the electrical parameters of the TG in real time, which allows you to carry out early detection of developing defects of the winding of the TG rotor

The method is disclosed by the example of detecting a winding in the rotor winding, according to the structural calculation scheme (Fig. 2), using a block diagram of the device (Fig. 1).

The essence of the invention lies in the fact that the measured current current parameters of the stator calculates the reference current of the rotor corresponding to this mode of operation, calculates the number of short-circuited turns in the rotor and at the beginning of the number of short-circuited turns, the rotor defect is detected at an early stage in normal operation TG. This allows you to take measures to prevent damage to the rotor.

A technical result is achieved due to the fact that previously in the device data processing system:

- the factory nominal initial data and data of the latest heating tests, calibration data of the induction rotor current sensors, calculated data of the rotor current according to the load characteristic of the pathogen (for brushless excitation system) are entered into table 1 of figure 4 for each TG:

P - active power, MW,

Q - reactive power, MVAr,

U is the voltage, kV,

f is the current frequency, Hz,

I _rn - rated rotor current,

n is the number of turns of the rotor winding,

x _{d *} ^! - longitudinal transient inductive resistance of the generator,

r ₁₅ - resistance of the rotor winding to direct current at a temperature of 15 ° C,

I _fa is the calculated value of the reaction current of the stator TG,

I _fk - value of the excitation current according to HKZ, corresponding to the rated current of the stator,

h.kh.kh. - idle characteristic

h.k.z. - short circuit characteristic,

- calculate additional parameters, calculate the rated current of the rotor, the calculation results are entered in the source data base of the device in table 1 of figure 4;

- measure the electrical parameters of the current mode of operation of the TG:

P - active power, MW, Q = reactive power, MVAr, U - stator voltage, kV, f - current frequency, Hz, I _{p meas} - rotor current A,

- calculates the current reference current of the rotor I _PE according to the mathematical model of figure 3.

The number of short-circuited turns is determined by the formula:

Where

n _KZ - the number of turns that are closed,

n is the total number of turns of the rotor winding,

I _RE - reference current of the rotor (i.e. calculated according to the stator parameters),

I _{P ISM} - rotor current measured in the current mode.

In the presence of short-circuited turns n _kz ≥1 (more than one turn), an alarm is triggered, which indicates the onset of damage in the rotor winding.

Brief Description of the Drawings

Figure 1 is a block diagram of a device that allows you to implement a method for detecting a winding circuit in the rotor winding by comparing the calculated reference and measured values of the rotor current and calculating the short-circuited turns in the rotor at the current electric load, and their changes.

Figure 2 is a structural diagram of the calculation of the reference current of the rotor.

Figure 3 is a mathematical model for calculating I _RE and n _KZ .

Figure 4 - table 1, which contains the factory source data and data of the latest heating tests, additional calculated data.

5 is an explanatory diagram of Potier.

6-9 - XXX and HKZ with data tables, polynomials of equations XXX.

Figure 10 is a polynomial of the equation of the dependence of the correction coefficient k _p = f (E _p ) from the EMF E _r according to the results of thermal tests.

The device contains:

Block 1 processing the parameters of the thermal state of the generator for the j-th mode of the current load.

Temperature sensors 2.

Current and voltage sensors 3.

Unit 4 for processing electrical parameters and calculating S, I _c , cosφ, sinφ, for the j-th mode of the current load.

Block 5 for processing the initial, additionally calculated data and processed data of the current TG mode, coming from blocks 1 and 4 to calculate the reference rotor current and the number of short-circuited turns.

Block 6 displays the parameters of the technical condition of the generator on the monitor screen.

Block 7 indication.

As an example, the calculated reference current of the rotor TG type TVV-500-2UZ according to the structural diagram of the calculation of figure 2:

The reference design current of the rotor and the coefficients of bringing the stator parameters to the rotor field winding at nominal stator parameters are preliminarily determined.

Rating data:

P = 500 MW, Q = 310 MBAp, U _c = 20 kV, Cosφ = 0.85, f = 50 Hz, n = 126 turns, I _fa = 2310 A, I _fk = 2550 A, x _{d *} ^! = 0,355, I _pH = 3530A - the nominal design value of the rotor current.

The total power S is calculated by the formula:

,

,

where S is the total power,

- the correction factor k _f is calculated taking into account the change in voltage drop at the calculated inductive resistance of the Potje dispersion x _p when the current frequency f _T deviates from the nominal frequency equal to 50 Hz, according to the formula:

,

,

k _f = 50/50 = 1,

- the stator current is calculated by the formula I _c .

- determined by the sinφ of the phase angle between the voltage U _c and current I _c according to the formula:

,

,

sinφ = (1-0.85 ² )) ^ 0.5 = 0.5268

- determined by x _{p *} is the calculated inductive resistance of the scattering of the armature winding, according to the formula:

,

,

x _{p *} = 0.81972 * 0.355 = 0.291

- determined by x _p in named units by the formula:

x _p = 0.355 * 0.81972 * 20 / √3 * 1 7 = 0.19766 Ohms;

- determined by ΔU _Xp voltage drop at x _p according to the formula:

,

,

ΔU _Xp = √3 * 17 * 0.19766 * 1 = 5.82 kV;

- is determined from the source data, the component of the excitation current I _fsн , inducing the electromotive force of the dispersion EMF, proportional to and equal to the voltage drop ΔU _Xp on the inductive resistance Potier,

I _fsn = 2550-2310 = 240 A

- is determined by the initial rectilinear part XXX (explanatory Potier diagram of Fig. 5, XXX for TVB-500-2UZ of Fig. 7) coefficient k _s - reduction of the magnetizing dissipation force or stator dissipation current to the field winding and corresponding to the rotor current I _fsн to create a drop voltage ΔU _Xp , in the short circuit mode with a stator current equal to the rated current I _sn according to the formula:

,

,

k _s = √3 * 17 * 0.19766 / 0.240 = 24.25 kV / kA

- is determined by HKZ (Fig. 5, Fig. 7) the coefficient k _β is the reduction of the total magnetizing force or the rated stator current to the field winding in the short-circuit mode according to the formula:

k _β = 17 / 2.55 = 6.6666

- determine by XXX and HKZ (Fig.5, Fig.7) the coefficient k _a - bringing the magnetizing force or the stator reaction current to the field winding in the short circuit mode according to the formula:

k _a = (24.25-√3 * 0.19766 * 6.6666) / 24.25 * 6.6666 = 0.1359;

- determines the resulting electromotive force EMF E _P according to the vector diagram of the voltage of the generator (figure 5) and the formula:

- determined by sin (γ + φ) - the angle between the vectors E _P and I _C according to the formula:

sin (γ + φ) = (5.8 + 20 * 0.5268) / 23.59 = 0.693

- determined by cos (γ + φ + 90 °) - the angle between the components of the rotor current according to the combined voltage diagram and the diagram of the magnetizing forces of the generator (according to the Potier diagram of figure 5) according to the formula:

- after this, XXX TG is extrapolated according to the dependence I _f = f (U) to obtain a polynomial:

Where

and ₀ - a _n are the coefficients of the polynomial.

In idle mode E = U and the rotor current I _frj for the j-th mode is determined by the corresponding current, the resulting EMF E _pj . Substituting in (16) the coefficients of the polynomial obtained by extrapolating XXX, the polynomial equation for a particular generator takes the form:

I _frj = -623567.89 + 183460 * Е _рj -22434.1 * Е _рj ^ 2 + 1460.4 * Е _pj ^ 3-53.346 * Е _рj ^ 4 + 1.0363 * E _pj ^ 5-0.0083576 * E _pj ^ 6,

- the excitation current I _frn is determined, according to the resulting current EMF E _p = 23.59 for the nominal mode:

I _frn = -623567.89 + 183460 * 23.59-22434.1 * 23.59 ^ 2 + 1460.4 * 23.59 ^ 3-53.346 * 23.59 ^ 4 + 1.0363 * 23.59 ^ 5-0.0083576 * 23.59 ^ 6 = 1.511 kA

- determined by the rated rated current of the rotor I _fn according to the diagram of the magnetizing forces of the generator of figure 5 according to the formula:

The obtained additional calculated data k _s , k _a , polynomials with calculated coefficients have well-defined values for each specific generator and are entered into the database of unit 5 of the device, table 1 - “Factory input data, additionally, calculated data and data of recent heating tests” (figure 4). Similarly, the parameters are calculated for the other types of TG.

Next, using the device of figure 1, the reference rotor current is calculated in modes different from the nominal mode, using the mathematical model of figure 3 and the data of table 1 (figure 4). For example, the calculation for the TG type TVV-500-2UZ:

TG mode type TVV-500-2UZ:

P = 304 MW, Q = 12 MVAr, U _c = 19.90 kV, f = 50 Hz, I _p = 1784 A is the measured rotor current.

Current and voltage sensors 3 of the device respectively measure the current flowing through the stator winding, and the stator voltage, active and reactive power, frequency in the power system, the rotor current sensor measures, respectively, the current flowing through the rotor winding. The signals carrying information about the magnitude of the current and voltage of the stator, active and reactive power, is fed to the input of block 4, which calculates:

- current value of apparent power;

;

;

- stator current;

- coefficient determined by the formula (3)

k _f = 50/50 = 1;

- cosφ - phase angle between current and voltage according to the formula:

- sinφ - phase angle between current and voltage according to the formula (5)

sinφ = (1-cosφ ² ) ^ 0.5

sinφ = (1-0.9967 ² ) ^ 0.5 = 0.041.

Further, signals carrying information about the magnitude of the measured rotor current and the calculation results obtained in block 4 are sent to block 5 — calculating the reference rotor current I _fE at current load and determining the number of short-circuited turns n _ks in the rotor.

In block 5, according to the data received from block 4, according to the additional parameters calculated and calculated for the nominal mode, in the presence of a signal from block 1 to block 5, about the steady-state thermal mode of the generator, the base current of the rotor is determined, the number of short-circuited turns is calculated by the formula ( one). To do this, in block 5 is pre-calculated:

- voltage drop across the inductive resistance Potier ΔU _Xp at the calculated current value of the stator current I _c according to the formula:

,

,

Where

I _fsn - the excitation current to create EMF scattering in the short circuit mode with a stator current equal to the nominal - I _n determined by the formula (9),

k _s is the coefficient of reduction of the magnetizing force or stator dissipation current to the field winding in the short-circuit mode at a stator current of I _n , determined by the formula (10),

k _f - coefficient taking into account the frequency deviation, determined in the current mode by the formula (3)

ΔU _Xp = 0.240 * 24.25 * 1 * 8.849 / 17 = 3.029 kV

- stator reaction current I _fa at current I _s according to the formula:

,

,

Where

k _a is the coefficient of reduction of the magnetizing force or the stator reaction current to the field winding in the short circuit mode at a stator current equal to the nominal one, determined by the formula (12),

I _fa = 8.849 * 0.1359 = 1.202 kA;

- the resulting electromotive force of the EMF of the generator according to the formula (13),

-sin (γ + φ) - the angle between the vectors Е _Р and I _С according to the formula (14),

sin (γ + φ) = (3.029 + 19.9 * 0.5268) / 20.256 = 0.190;

-cos (γ + φ + 90 °) - the angle between the components of the rotor current according to the formula (15):

cos (γ + φ + 90 °) = - sin (γ + φ) = - 0.190;

- the component of the calculated rotor current is determined to create the resulting EMF E _p = 20,256 kV according to the formula (16):

I _fp = -623567.89 + 183460 * 20.256-22434.1 * 20.256 ^ 2 + 1460.4 * 20.256 ^ 3-53.346 * 20.256 ^ 4 + 1.0363 * 20.256 ^ 5-0.0083576 * 20.256 ^ 6 = 1.127 kA.

According to the calculated I _fa , I _fp , the calculated current I _f is determined by the formula (17);

- is determined by the correction coefficient k _p, taking into account statistical variation synchronous inductive resistance of the stator windings x _d when the value of the resultant emf E _rn = 23.59 kW for rated operation to the value of the resultant emf E _pj = 20,256 kW j-th current mode, which corresponds to the actual state of saturation of the magnetic circuit in this mode of operation by plotting _{k pj = f (E pj)} , the source base characteristic polynomial (4 table1) obtained in tests on heat when the generator is deemed known to be working, according to the formula:

and ₀ - a _n are the polynomial coefficients for a particular generator,

k _p = 1.678 * 10 ^ -8 + 1.224 * 10 ^ -4 * 20256-4.749 * 10 ^ -9 * 20256 ^ 2 + 5.742 * 10 ^ -14 * 20256 ^ 3 = 1.008

- the reference rotor current is determined taking into account k _p according to the formula:

I _RE = 1,798 / 1,008 = 1,784 kA

- the number of short-circuited turns is determined by the formula (1)

n _short = n (1-I _RE / I _{P rev} ) = 126 (1-1.784 / 1.784) = 0 turns

The signals that carry information from the outputs of blocks 1, 2, 3, 4 and 5 are fed to the corresponding inputs of block 6 displaying the parameters of the technical state of the generator on the monitor screen.

The signal from the output of block 5, carrying information on the value of n _kz , is fed to the input of the signal indication display unit 7, which monitors the parameter n _kz in the interval 0 <n _kz <1.

In the case when the number of short-circuited turns n _kz exceeds more than 1 turn, block 7 displays a signal about the appearance of a defect in the rotor of the generator.

The proposed method is simple, gives unambiguous conclusions about the presence of turns in the rotor, does not require additional changes in the design of the TG, the installation of additional measuring instruments.

Claims (3)

1. A method for early detection of coil faults and diagnosing the technical condition of the turbogenerator rotor winding with determining the rotor current by the stator parameters, which consists in the fact that preliminary initial data for a specific generator are previously determined from the initial nominal factory data, the stator electrical parameters are measured in the steady-state thermal mode of the generator measure the rotor current if it is possible to directly measure the rotor current, and if not, with a brushless system excitation - by other indirect methods, at a given moment of time corresponding to a given TG operating mode, the rotor reference current is calculated and the number of short-circuited turns is determined from the measured and calculated reference values of the rotor current by the formula
n _KZ = n (1-I _RE / I _{P ISM} ),
where n _KZ - the number of turns that are closed;
n is the total number of turns of the rotor winding;
I _RE - reference current of the rotor (i.e., calculated according to the stator parameters);
I _{P ISM} - rotor current measured,
judge the onset of damage in the rotor winding in the presence of short-circuited turns n _kz ≥1. 2. The method according to claim 1, characterized in that the coefficients of bringing the stator parameters to the field winding are determined from the initial nominal factory data, the idling characteristic and the short circuit characteristic, which have specific values for each particular generator, for calculating the reference current in all modes according to the formulas
k _s = √3 · I _sn · x _p / I _fsн ;
k _β = I _cn / I _fc ;
k _a = (k _s -√3 · x _p · k _β ) / k _s · k _β ,
where k _s is the coefficient of reduction of the stator scattering current to the field winding in the short circuit mode;
k _β is the coefficient of reduction of the rated current of the stator to the field winding in the short circuit mode;
k _a is the coefficient of reduction of the stator reaction current to the field winding in the short circuit mode;
I _sn - rated current of the stator;
I _fsn is the excitation current for creating EMF scattering in the short circuit mode at a stator current equal to the nominal;
I _fк - field current during short circuit, corresponding to the rated current of the stator;
x _p is the inductive dissipation of Potier. 3. The method according to claim 1, characterized in that the reference rotor current I _{REj is calculated} for the j-th current mode with the correction of the rated current according to the stator parameters I _fj by the coefficient k _pj according to the formula
I _REj = I _fj / k _pj ,
where k _pj is the correction coefficient for the j-th heating test mode, determined by the polynomial of the initial basic characteristic obtained during the heating test, when the generator is considered to be known to be working, according to the formula
k _pj = a ₀ + a ₁ · E _pj + a ₂ · E _pj ² + ... + a _n · E _pj ⁿ ,
where k _pj is a correction coefficient that takes into account the change in the synchronous inductive resistance of the stator winding x _d , which corresponds to the actual saturation state of the magnetic circuit in the j-th current mode of operation;
E _pj - resulting EMF for the j-th current operating mode;
a ₀ -a _n - polynomial coefficients for a particular generator.

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