CN104104293B - A kind of minimum exciting current method for limiting based on electromotor steady state stability limit - Google Patents

Abstract

The invention discloses a kind of minimum exciting current method for limiting of electromotor.At present, the restriction of electromotor minimum exciting current adopts the method for fixing threshold values, static stability analysis during according to generator operation, and electromotor allows the minima of exciting current and electromotor and electrical network parameter and operating condition relevant.The minimum exciting current method for limiting of fixing threshold values cannot adapt to the change of electromotor operating mode, it is impossible to gamut ensures that engine health runs.The present invention adopts the specificity analysis based on electromotor steady state stability limit, the minimum exciting current permissible value under the different operating mode of electromotor is obtained according to electromotor pattern, electric parameter and electrical network parameter, based on this, the minimum exciting current adjusted under the design various operating mode of electromotor limits threshold values, exciter current of generator is not less than minimum exciting current restriction threshold values to adopt the method that closed loop regulates to ensure, reach to prevent the target of electromotor step-out comprehensively, improve the safe and reliable operation level of the equipment such as electromotor, excitation system.

Description

A kind of minimum exciting current method for limiting based on electromotor steady state stability limit

Technical field

The present invention relates to the design of adjusting of the restriction of minimum exciting current in generator excited system, regulable control field, specifically a kind of based on electromotor steady state stability limit, be used for preventing electromotor owing to exciting current is too small the minimum exciting current method for limiting of step-out.

Background technology

The precondition of generator connecting in parallel with system generating is to have sufficiently large exciting current in the winding of magnetic field, could be that electric energy is delivered to electrical network by changes mechanical energy, and namely excitation system is supplied with the equipment of exciter current of generator.The size of excitation system output electric current is determined by field regulator, and field regulator measures operation state of generator and system mode in real time, runs required exciting current through calculating output generator.Once the running status of field regulator measurement is wrong or some abnormal operating condition occurs in electromotor, it is possible to exciting current can be occurred too small and cause electromotor step-out and tripping operation, limit, accordingly, it would be desirable to a kind of, the method that exciter current of generator is too small.

At present, domestic and international common practice is: preset a single minimum exciting current threshold values, time normal, field regulator, according to electromotor and operation of power networks state and demand, regulates excitation system output electric current in real time, simultaneously, also detecting exciter current of generator in real time, when detecting that exciter current of generator is less than threshold values set in advance, namely field regulator interrupts normal regulative mode, change into exciter current of generator for regulating target, exciting current is maintained threshold values set in advance.

But according to field engineering real running results show, although adopting the method exciter current of generator can be limited in threshold values set in advance, but sometimes still can there is the accident of electromotor out-of-step tripping, show only to determine the method for limiting of a single minimum exciting current threshold values, electromotor safe operation under any operating mode cannot be ensured, it is necessary to invent the minimum exciting current method for limiting of a kind of electromotor suitable in electromotor different conditions and operating condition.

Summary of the invention

The technical problem to be solved is the technological deficiency overcoming above-mentioned existing method to exist, there is provided a kind of can according to operation state of generator change, the minimum exciting current method for limiting of electromotor that step-out all will not occur under any operating mode that ensure that electromotor, the problem that the minimum exciting current method for limiting that the excitation system to solve current Generator Set configures does not adapt to electromotor working conditions change.

For this, the present invention adopts the following technical scheme that: a kind of minimum exciting current method for limiting based on electromotor steady state stability limit, and its step is as follows:

1) the minimum exciting current theoretical characteristic curve of electromotor obtaining under electromotor steady state stability limit is calculated according to electromotor pattern, electric parameter and electrical network parameter；

2) minimum for electromotor exciting current theoretical characteristic curve is converted to multiple data pair being made up of active power and minimum exciting current；

3) computational methods of threshold values margin of safety are limited according to minimum exciting current, by step 2) in data to adjusting as being limited, by active power and the minimum exciting current corresponding with active power, the data pair that threshold values form, and limited broken line by these data to forming one permission corresponding with active power minimum exciting current of operation；

4) field regulator detects generator active power and exciting current in real time, according to step 3) permission corresponding with active power determined run minimum exciting current restriction broken line, calculates the minimum exciting current restriction threshold values that currently practical active power is corresponding；

5) compare the currently practical exciting current of electromotor and step 4) described in currently practical active power corresponding minimum exciting current restriction threshold values, when the minimum exciting current restriction threshold values that actual exciting current is corresponding less than currently practical active power, field regulator regulates excitation system output, it is ensured that the minimum exciting current restriction threshold values that the actual exciting current of electromotor will not be corresponding less than currently practical active power.

Further, step 1) in, the corresponding relation of minimum exciting current and active power is as follows: have for non-salient pole generator: I_fmin=P_ex_d, salient pole generator is had:Wherein: P_eFor generator active power, I_fminFor the minimum exciting current of electromotor, δ₀For the generator power angle corresponding to minimum exciting current；x_d,x_qFor electromotor longitudinal axis impedance and transverse axis impedance, for non-salient pole generator, both are equal.

Further, step 3) in, the computational methods of minimum exciting current restriction threshold values margin of safety are as follows:

$I_{f\min .\mathrm{set}}=\left\{\begin{array}{cc}{k}_1{I}_{f\min }+k_2& I_{f\min }\&GreaterEqual;0\\ k_2& I_{f\min }<0\end{array}\right.$

Wherein: I_fmin.setThreshold values, I is limited for minimum exciting current_fminFor step 2) in minimum exciting current；k₁,k₂For nargin coefficient.

The present invention adopts the specificity analysis based on electromotor steady state stability limit, according to electromotor pattern, electric parameter obtains the minimum exciting current permissible value under the different operating mode of electromotor with electrical network parameter, based on this, the minimum exciting current designed in electromotor actual motion under various operating modes of adjusting limits threshold values, the method that closed loop regulates is adopted to regulate excitation system output, ensure that exciter current of generator is not less than minimum exciting current restriction threshold values, reach to prevent the target of electromotor step-out comprehensively, improve electromotor, the safety of the equipment such as excitation system, reliability service level.

Accompanying drawing explanation

Fig. 1 is that synchronous generator runs phasor diagram.

Fig. 2 is the minimum exciting current theoretical characteristic curve figure of the present invention (Fig. 2 a is hidden pole type, and Fig. 2 b is salient pole type).

Fig. 3 is permission operation minimum exciting current restriction broken line graph (Fig. 3 a is hidden pole type, and Fig. 3 b is salient pole type) that the present invention is corresponding with active power.

Fig. 4 is the minimum exciting current restriction schematic diagram of electromotor of the present invention.

Detailed description of the invention

Below in conjunction with specification drawings and specific embodiments, the invention will be further described.

Synchronous generator is divided into hidden pole type and salient pole type, and synchronous generator runs shown in phasor diagram 1, under assuming that set end voltage is specified, it is possible to calculate synchronous operation active power and exciting current is:

$\begin{array}{c}{P}_e=\frac{E_q}{x_d}\sin \mathrm{\&delta;}+(\frac{1}{x_q}-\frac{1}{x_d})\sin \mathrm{\&delta;}\cos \mathrm{\&delta;}\\ I_f=E_q=\frac{P_e{x}_d}{\sin \mathrm{\&delta;}}-(\frac{x_d}{x_q}-1)\cos \mathrm{\&delta;}\end{array}---\left(1\right)$

In formula: P_eFor generator active power；

E_qFor electromotor built-in potential；

I_fFor exciter current of generator；

δ is generator power angle；

x_d,x_qFor electromotor longitudinal axis impedance and transverse axis impedance, for non-salient pole generator, both are equal.

When electromotor is hidden pole type, formula (1) can be converted into:

$I_f=\frac{P_e{x}_d}{\sin \mathrm{\&delta;}}\&DoubleRightArrow;I_{f\min }=P_e{x}_d---\left(2\right)$

Then the minimum exciting current theoretical characteristic curve of non-salient pole generator is as shown in Figure 2 a.

When electromotor is salient pole type, condition when exciting current arrives minimum in formula (1) is:

$\frac{{\mathrm{dI}}_f}{\mathrm{d\&delta;}}=0\&DoubleRightArrow;-\frac{P_e{x}_d\cos \mathrm{\&delta;}}{{\sin }^2\mathrm{\&delta;}}+(\frac{x_d}{x_q}-1)\sin \mathrm{\&delta;}=0$

$(\frac{x_d}{x_q}-1){\sin }^3\mathrm{\&delta;}=P_e{x}_d\cos \mathrm{\&delta;}\&DoubleRightArrow;{\sin }^3\mathrm{\&delta;}=\frac{P_e{x}_d{x}_q}{x_d-x_q}\cos \mathrm{\&delta;}$

${\left({\sin }^2\mathrm{\&delta;}\right)}^3+{\left(\frac{P_e{x}_d{x}_q}{x_d-x_q}\right)}^2{\sin }^2\mathrm{\&delta;}-{\left(\frac{P_e{x}_d{x}_q}{x_d-x_q}\right)}^2=0$

Note: $k={\left(\frac{x_d{x}_q}{x_d-x_q}\right)}^2$ Then above formula is:

${\left({\sin }^2\mathrm{\&delta;}\right)}^3+k{P}_e^2\&times;{\sin }^2\mathrm{\&delta;}-k{P}_e^2=0---\left(3\right)$

The efficient solution of formula (3) unitary 3 equation of n th order n is:

$\begin{array}{c}{\sin }^2{\mathrm{\&delta;}}_0=\\ \sqrt[3]{1/18}\&times;(\sqrt[3]{\sqrt{81k^2\&times;P_e^4+12k^3\&times;P_e^6})+9k\&times;P_e^2+}-\sqrt[3]{\sqrt{81k^2\&times;P_e^4+12k^3\&times;P_e^6}-9k\&times;P_e^2})\end{array}$

${\mathrm{\&delta;}}_0=\arcsin {(\sqrt[3]{1/18}\&times;(\sqrt[3]{\sqrt{81k^2\&times;P_e^4+12k^3\&times;P_e^6})+9k\&times;P_e^2+}-\sqrt[3]{\sqrt{81k^2\&times;P_e^4+12k^3\&times;P_e^6}-9k\&times;P_e^2}))}^{0.5}$

Then to should the exciting current minima under active power be:

$I_{f\min }=\frac{P_e{x}_d}{\sin {\mathrm{\&delta;}}_0}-(\frac{x_d}{x_q}-1)\cos {\mathrm{\&delta;}}_0---\left(4\right)$

Then the minimum exciting current theoretical characteristic curve of salient pole generator is as shown in Figure 2 b.It can be seen that after active power is less than certain value, the minimum exciting current of salient pole generator is less than 0, this illustrates, after active power is less than certain value, even if excitation system does not export electric current, salient pole generator can also stable operation, namely now do not call for minimum exciting current restriction.

According to electromotor pattern, electric parameter, electrical network parameter and steady state stability limit condition, after drawing minimum exciting current theoretical characteristic curve, may determine that the minimum exciting current restriction broken line allowed in operation, retaining certain margin of safety between restriction broken line and theoretical curve, on theoretical curve, the exciting current curve less than 0 calculates with 0 simultaneously.Margin of safety computational methods are as follows:

$I_{f\min .\mathrm{set}}=\left\{\begin{array}{cc}{k}_1{I}_{f\min }+k_2& I_{f\min }\&GreaterEqual;0\\ k_2& I_{f\min }<0\end{array}\right.---\left(5\right)$

I in formula (5)_fmin.setThreshold values is limited for minimum exciting current；

I_fminFor the calculated minimum exciting current of formula (2) or (4)；

k₁,k₂For nargin coefficient.

The minimum exciting current calculated by formula (5) limits broken line as shown in Figure 3.

The minimum exciting current restriction broken line of electromotor is saved in field regulator after determining, when generator excited system runs, field regulator detects generator active power and exciting current in real time, the minimum exciting current restriction threshold values under current active power is calculated according to active power and restriction broken line, with minimum exciting current, actual for electromotor exciting current is limited threshold values compare, if the actual exciting current of electromotor limits threshold values less than minimum exciting current, field regulator regulates excitation system output, output increases the order of exciting current, ensure that exciter current of generator is not less than minimum exciting current restriction threshold values, the minimum exciting current restriction principle of electromotor is as shown in Figure 4.

Claims (2)

1., based on a minimum exciting current method for limiting for electromotor steady state stability limit, its step is as follows:

1) the minimum exciting current theoretical characteristic curve of electromotor obtaining under electromotor steady state stability limit is calculated according to electromotor pattern, electric parameter and electrical network parameter；

2) minimum for electromotor exciting current theoretical characteristic curve is converted to multiple data pair being made up of active power and minimum exciting current；

3) computational methods of threshold values margin of safety are limited according to minimum exciting current, by step 2) in data to adjusting as being limited, by active power and the minimum exciting current corresponding with active power, the data pair that threshold values form, and limited broken line by these data to forming one permission corresponding with active power minimum exciting current of operation；

4) field regulator detects generator active power and exciting current in real time, according to step 3) permission corresponding with active power determined run minimum exciting current restriction broken line, calculates the minimum exciting current restriction threshold values that currently practical active power is corresponding；

5) compare the currently practical exciting current of electromotor and step 4) described in currently practical active power corresponding minimum exciting current restriction threshold values, when the minimum exciting current restriction threshold values that actual exciting current is corresponding less than currently practical active power, field regulator regulates excitation system output, it is ensured that the minimum exciting current restriction threshold values that the actual exciting current of electromotor will not be corresponding less than currently practical active power；

Step 3) in, the computational methods of minimum exciting current restriction threshold values margin of safety are as follows:

$I_{fmin.set}=\left\{\begin{array}{cc}{k}_1{I}_{fmin}+k_2& I_{fmin}\&GreaterEqual;0\\ k_2& I_{fmin}<0\end{array}\right.$

Wherein: I_fmin.setThreshold values, I is limited for minimum exciting current_fminFor step 2) in minimum exciting current；k₁,k₂For nargin coefficient.

2. the minimum exciting current method for limiting based on electromotor steady state stability limit according to claim 1, it is characterised in that step 1) in, the corresponding relation of minimum exciting current and active power is as follows: have for non-salient pole generator: I_fmin=P_ex_d, salient pole generator is had:Wherein: P_eFor generator active power, I_fminFor the minimum exciting current of electromotor, δ₀For the generator power angle corresponding to minimum exciting current；x_d,x_qFor electromotor longitudinal axis impedance and transverse axis impedance, for non-salient pole generator, both are equal.