CN104104293A - Electric generator static stability limit based on minimum exciting current limiting method - Google Patents

Abstract

The invention discloses an electric generator minimum exciting current limiting method. Currently, electric generator minimum exciting current is limited by means of a fixed threshold value method; according to static stability analysis of an electric generator during operation, the electric generator allows the minimum value of exciting current to be relevant to the electric generator, power grid parameters and operation conditions. A minimum exciting current limiting method with a fixed threshold value cannot be adaptive to changes of the operation conditions of the electric generator, or cannot guarantee safe operation of the electric generator in full ranges. According to the electric generator minimum exciting current limiting method, by means of characteristic analysis of electric generator static stability limit, minimum exciting current allowable values under different work conditions of the electric generator are obtained according to the type of the electric generator, electric parameters and power grid parameters; on the basis of the minimum exciting current allowable values, minimum exciting current limiting threshold values under different work conditions of the electric generator are set and designed, the condition that exciting current of the electric generator is not less than the minimum exciting current limiting threshold values is guaranteed by means of a closed-loop regulation method, the purpose of comprehensively preventing step-out of the electric generator is achieved, and safe and reliable operation levels of devices such as the electric generator and the excitation system are increased.

Description

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

Technical field

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

Background technology

The precondition of generator connecting in parallel with system generating is in the winding of magnetic field, to have enough large exciting current, mechanical energy could be converted into power delivery to electrical network, and excitation system is the equipment of supply generator exciting current.The size of excitation system output current determines by field regulator, and field regulator is measured operation state of generator and system mode in real time, through calculating output generator, moves needed exciting current.Once the running status that field regulator is measured is wrong or some misoperation situations appear in generator, just may there is exciting current too small and cause generator step-out and tripping operation, therefore, need a kind of too small method of exciter current of generator that limits.

At present, domestic and international common way is: preset a single minimum exciting current threshold values, when normal, field regulator, according to generator and operation of power networks state and demand, regulates excitation system output current in real time, simultaneously, also detect in real time exciter current of generator, when exciter current of generator being detected, be less than predefined threshold values, field regulator interrupts normal regulative mode, change into and take exciter current of generator as regulating target, exciting current is maintained to predefined threshold values.

But according to field engineering real running results show, although adopt the method exciter current of generator can be limited in predefined threshold values, but sometimes still can there is the accident of generator out-of-step tripping, show only to determine the method for limiting of a single minimum exciting current threshold values, the safe operation of generator under any operating mode cannot be guaranteed, a kind of minimum exciting current method for limiting of generator that is applicable to generator different conditions and operating condition need to be invented.

Summary of the invention

Technical problem to be solved by this invention is to overcome the technological deficiency that above-mentioned existing method exists, provide a kind of and can, according to the minimum exciting current method for limiting of generator operation state of generator variation, that can guarantee all can not occur under any operating mode of generator step-out, to solve the minimum exciting current method for limiting of the excitation system configuration of current Generator Set, can not adapt to the problem of generator working conditions change.

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

1) according to generator pattern, electric parameter and electrical network parameter, calculate the minimum exciting current theoretical characteristics of the generator curve under generator steady state stability limit;

2) by the minimum exciting current theoretical characteristics of generator Curve transform, be a plurality of data pair that formed by active power and minimum exciting current;

3) according to the computational methods of minimum exciting current restriction threshold values margin of safety, by step 2) in data to adjusting as the data pair that formed by active power and corresponding with active power minimum exciting current restriction threshold values, and move minimum exciting current and limit broken line forming a permission corresponding with active power by these data;

4) field regulator detects generator active power and exciting current in real time, according to step 3) permission corresponding with active power determined move minimum exciting current restriction broken line, calculates minimum exciting current restriction threshold values corresponding to current actual active power;

5) the relatively current actual exciting current of generator and step 4) described in minimum exciting current restriction threshold values corresponding to current actual active power, when actual exciting current is less than minimum exciting current restriction threshold values corresponding to current actual active power, field regulator regulates excitation system output, guarantees that the actual exciting current of generator can not be less than minimum exciting current restriction threshold values corresponding to current actual active power.

Further, step 1) in, the corresponding relation of minimum exciting current and active power is as follows: for non-salient pole generator, have: I _fmin=P _ex _d, for salient pole generator, have: wherein: P _efor generator active power, I _fminfor the minimum exciting current of generator, δ ₀for the generator power angle corresponding to minimum exciting current; x _d, x _qfor the impedance of the generator longitudinal axis and transverse axis impedance, for non-salient pole generator, both equate.

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.setfor minimum exciting current restriction threshold values, I _fminfor step 2) in minimum exciting current; k ₁, k ₂for nargin coefficient.

The present invention adopts the specificity analysis based on generator steady state stability limit, according to generator pattern, electric parameter obtains the minimum exciting current permissible value under the different operating modes of generator with electrical network parameter, based on this, adjust and design the minimum exciting current restriction threshold values under various operating modes in generator actual motion, adopt the method for closed-loop adjustment to regulate excitation system output, guarantee that exciter current of generator is not less than minimum exciting current restriction threshold values, reach the target that comprehensively prevents generator step-out, improved generator, the safety of the equipment such as excitation system, reliability service level.

Accompanying drawing explanation

Fig. 1 is synchronous generator operation phasor diagram.

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

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

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

Embodiment

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, shown in synchronous generator operation phasor diagram 1, under postulated mechanism terminal voltage is specified, can calculates synchronous operation active power and exciting current and 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 generator built-in potential;

I _ffor exciter current of generator;

δ is generator power angle;

X _d, x _qfor the impedance of the generator longitudinal axis and transverse axis impedance, for non-salient pole generator, both equate.

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

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

The minimum exciting current theoretical characteristics of non-salient pole generator curve as shown in Figure 2 a.

When generator is salient pole type, the condition that exciting current arrives hour 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: $k={\left(\frac{x_d{x}_q}{x_d-x_q}\right)}^2$ 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) monobasic 3 equation of n th order n is:

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

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

To the exciting current minimum value under should active power, be:

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

The minimum exciting current theoretical characteristics of salient pole generator curve as shown in Figure 2 b.As we know from the figure, when active power is less than after certain value, the minimum exciting current of salient pole generator is less than 0, this explanation, when active power is less than after certain value, even excitation system output current not, salient pole generator also can stable operation, does not now need to do minimum exciting current restriction.

According to generator pattern, electric parameter, electrical network parameter and steady state stability limit condition, draw after minimum exciting current theoretical characteristics curve, can determine the minimum exciting current restriction broken line of permission in service, between restriction broken line and theoretical curve, retain certain margin of safety, on theoretical curve, exciting current is less than 0 curve with 0 calculating 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.setfor minimum exciting current restriction threshold values;

I _fminthe minimum exciting current calculating for formula (2) or (4);

K ₁, k ₂for nargin coefficient.

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

The minimum exciting current restriction of generator broken line is kept in field regulator after determining, during generator excited system operation, field regulator detects generator active power and exciting current in real time, according to active power and restriction broken line, calculate the minimum exciting current restriction threshold values under current active power, by the actual exciting current of generator and the comparison of minimum exciting current restriction threshold values, if the actual exciting current of generator is less than minimum exciting current restriction threshold values, field regulator regulates excitation system output, output increases the order of exciting current, guarantee that exciter current of generator is not less than minimum exciting current restriction threshold values, the minimum exciting current restriction of generator principle as shown in Figure 4.

Claims (3)

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

1) according to generator pattern, electric parameter and electrical network parameter, calculate the minimum exciting current theoretical characteristics of the generator curve under generator steady state stability limit;

2) by the minimum exciting current theoretical characteristics of generator Curve transform, be a plurality of data pair that formed by active power and minimum exciting current;

3) according to the computational methods of minimum exciting current restriction threshold values margin of safety, by step 2) in data to adjusting as the data pair that formed by active power and corresponding with active power minimum exciting current restriction threshold values, and move minimum exciting current and limit broken line forming a permission corresponding with active power by these data;

4) field regulator detects generator active power and exciting current in real time, according to step 3) permission corresponding with active power determined move minimum exciting current restriction broken line, calculates minimum exciting current restriction threshold values corresponding to current actual active power;

5) the relatively current actual exciting current of generator and step 4) described in minimum exciting current restriction threshold values corresponding to current actual active power, when actual exciting current is less than minimum exciting current restriction threshold values corresponding to current actual active power, field regulator regulates excitation system output, guarantees that the actual exciting current of generator can not be less than minimum exciting current restriction threshold values corresponding to current actual active power.

2. the minimum exciting current method for limiting based on generator steady state stability limit according to claim 1, is characterized in that step 1) in, the corresponding relation of minimum exciting current and active power is as follows: for non-salient pole generator, have: I _fmin=P _ex _d, for salient pole generator, have: wherein: P _efor generator active power, I _fminfor the minimum exciting current of generator, δ ₀for the generator power angle corresponding to minimum exciting current; x _d, x _qfor the impedance of the generator longitudinal axis and transverse axis impedance, for non-salient pole generator, both equate.

3. the minimum exciting current method for limiting based on generator steady state stability limit according to claim 1 and 2, is characterized in that 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.setfor minimum exciting current restriction threshold values, I _fminfor step 2) in minimum exciting current; k ₁, k ₂for nargin coefficient.