CN104899677B - The radial supply network load maximum reactive requirements of 500kV estimate method soon during disturbance restores - Google Patents
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Abstract
The radial supply network load maximum reactive requirements of 500kV estimate method soon during a kind of disturbance restores, and include the following steps：1) operation data calculates under limit：1.1 main transformer synthetic load equivalent impedances calculate；1.2 induction conductivity equivalent impedance perunit values calculate；1.3 constant-impedance load equivalent impedance calculates；2) 500kV substations supply network equivalent circuit relevant parameter calculates；3) failure removal moment relevant parameter calculates；4) failure removal moment, the 10kV side bus voltages estimation of 220kV and 110kV substations；5) 500kV main transformer synthetic load maximum dynamic reactive estimated demands in restoring after major network failure.Basic data is few, speed is fast, time saving and energy saving needed for present invention calculating.
Description
Technical Field
The invention relates to a method for quickly estimating the maximum reactive power demand of a load of a 500kV radial power supply network in disturbance recovery, in particular to a method for quickly estimating the maximum reactive power demand of a comprehensive load (approximately considered to occur at the moment of fault removal) of a 500kV substation radial power supply network after a main network fault.
Background
In the analysis and calculation of the power system, power users which are difficult to win in a wide area covered by a power grid are often combined into a small number of comprehensive loads, and the comprehensive loads are tapped on buses of different voltage levels of a transformer substation. In power system voltage stability studies, the combined load is often expressed as a combination of constant impedance and induction motor of different proportions.
When the high-voltage side of the main transformer has a short-circuit fault, the relay protection device of the power system can rapidly remove the fault. In the process of recovery after a fault, the comprehensive load can generate obvious dynamic reactive power demand, and the size of the dynamic reactive power demand depends on the type of the fault, the duration time of the fault, the load characteristic and the voltage recovery of a system; the system voltage recovery is affected by the alternating current system strength and the load dynamic reactive power requirement, and the alternating current system strength and the load dynamic reactive power requirement are coupled with each other. For the dynamic reactive power demand of the comprehensive load, the calculation can be realized more accurately only by means of calculation and analysis software of the power system, and the method is time-consuming and labor-consuming.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for quickly estimating the maximum reactive power demand of the load of a 500kV radial power supply network in disturbance recovery, aiming at the fault type of the most serious three-phase metallic grounding short circuit of a power system, and having the advantages of less basic data, high speed, time saving and labor saving.
The technical scheme adopted by the invention is as follows:
a method for quickly estimating the maximum reactive power demand of a 500kV radial power supply network load in disturbance recovery comprises the following basic data:
1) the method comprises the following steps that (1) the number n of main transformers of a 500kV transformer substation and the short-circuit current level Id of a high-voltage bus are in a unit kA;
2) active power proportion K of induction motor in transformer substation main transformer high-voltage side active power P, unit MW and comprehensive load during normal operationP；
3) Inertia time constant T of induction motorjLoad factor KLAnd equivalent electric road single parameter: stator resistance RsStator reactance XsExcitation reactance XMRotor reactance XRRotor resistance RR；
4) The fault duration Δ t;
the method requires the use of the following basic formula:
1) basic formula of induction motor
Referring to fig. 1, the induction motor has the equivalent: stator resistors R connected in series in sequences、Stator reactance Xs、Rotor reactance XRAnd a variable resistance R ═ RRS, in rotor reactance XRAnd a variable resistance R ═ RRThe two ends of/s are provided with excitation reactance XM；
The equivalent impedance Z of the induction motor is calculated as formula (1):
the defining variables are as in formula (2):
the equivalent admittance Y of the induction motor is calculated as formula (3):
wherein,
when the operating voltage of the induction motor is V, the consumed power P + jQ is calculated as the formula (5):
2) equivalent impedance calculation formula of electrical element
If the operating voltage of the electrical element is V and the consumed power is P + jQ, the equivalent impedance Z of the electrical element is r + jx, and the equation (6) is calculated:
the method comprises the following steps:
1) running data calculation under steady state conditions
1.1 calculation of the equivalent impedance of the integrated load of the main transformer
According to the active power P on the high-voltage side of the main transformer of the transformer substation in normal operation in basic data, the unit MW is considered, P is the active power consumed by the comprehensive load on the 10kV side of the main transformer, the power factor is 0.95, and the reactive power Q (cos) consumed by the comprehensive load on the 10kV side of the main transformer with the parallel capacitance is obtained-1(0.95)). And (3) obtaining the comprehensive load equivalent impedance Z on the 10kV side of the main transformer according to the formula (6) by taking the comprehensive load operating voltage V as 1p.uΣ0；
1.2 Induction Motor equivalent impedance per Unit value calculation
Taking the terminal voltage V of an induction motor as 1p.u., and taking the active power P as KLp.u., according to formulae (2) and (4), and let:
obtaining equivalent resistance of the rotor of the induction motor in normal operation:
initial slip of induction motor:
calculating the equivalent impedance per unit value Z of the induction motor by the formula (1)M*；
1.3 constant impedance load equivalent impedance ZZ
According to the active power P of the high-voltage side of the transformer substation main transformer in normal operation, unit MW and the active power ratio K of the induction motor in the comprehensive load given in the basic dataPKnown as KPP is the active power consumed by the motor, according to ZM*Corresponding power factor angle, to obtain the reactive power consumed by the motor
Subtracting the power consumed by the induction motor from the total load power of the main transformer to obtain the power consumed by the constant impedance load, and then obtaining the equivalent impedance Z of the constant impedance load by using the step (6)Z；
2) Calculation of equivalent circuit related parameters of 500kV transformer substation power supply network
A common form of a 500kV substation supply network is shown in figure 2 a: the 500kV transformer substation supplies power to the 220kV transformer substation, and a comprehensive load is connected to the 10kV side of the 220kV transformer substation; the 220kV transformer substation supplies power to the 110kV transformer substation, and a comprehensive load is connected to the 10kV side of the 110kV transformer substation; FIG. 2a is equivalent to FIG. 2 b: the main network power supply is connected with the power supply through a transformation ratio of 1: e equivalent reactance Xs of an ideal transformer series system, and equivalent impedance X of a power transmission loop to a comprehensive load ZΣ0The form of the power supply;
the system equivalent reactance Xs is estimated according to equation (10):
estimating the electrical distance between the comprehensive load and the high-voltage side of the 500kV main transformer according to the X-140 omega;
estimating the power supply return road sign unitary transformation ratio E according to the condition that the comprehensive load terminal voltage is 1p.u. during normal operation as shown in the formula (11):
3) calculation of relevant parameters at fault removal time
Induction motor terminal voltage during fault is considered to be zero, induction motor electromagnetic torque TeInduction motor load torque T of 0load＝KLAnd delta t is the fault duration, and the induction motor rotating speed change delta omega at the fault removal moment is obtained according to the step (12):
the induction motor slip at the end of the fault is obtained according to equation (13):
s＝s0-Δω (13)；
induction motor rotor resistance at the time of failure completion:
reference value of power of induction motor:
calculating equivalent impedances of various induction motor loads in the comprehensive loads at the moment of fault removal according to the formula (1); integrated load equivalent impedance ZΣCalculating the parallel value of the induction motor and the constant impedance load according to the formula (16):
Z∑＝∏(Z) (16)；
II represents parallel connection;
4) estimation of bus voltage on 10kV side of 220kV and 110kV transformer substations at fault removal time
5) Estimation of maximum dynamic reactive power demand of 500kV main transformer comprehensive load during main network fault
Will U(10)And (5) substituting the reactive calculation formula in the formula to obtain the maximum dynamic reactive value of various induction motors in the 500kV main transformer comprehensive load, and summing to obtain the maximum dynamic reactive requirement of the 500kV main transformer comprehensive load when the main network fails.
Remarking: 1) about 20% of the comprehensive loads are supplied by the low-voltage side of a 220kV transformer substation, the part of the loads are closer to the high-voltage side of a 500kV main transformer, and all the loads in the algorithm are supplied according to the low-voltage side of a 110kV transformer substation, so that the estimated maximum dynamic reactive power demand of the comprehensive loads is lower; 2) at the moment of fault removal, the voltage of a load bus is low, reactive power taken by equivalent impedance of a load and a parallel capacitor except an induction motor is correspondingly reduced, and the influence of the reactive power taken by the equivalent impedance of the load and the parallel capacitor is ignored in an algorithm, so that the maximum dynamic reactive power demand of the estimated comprehensive load is high; the two effects substantially cancel.
Has the advantages that: the maximum reactive power demand of the load of the 500kV radial power supply network in disturbance recovery is generally solved by adopting a simulation means, time and labor are wasted, and no relevant analytical calculation method is reported at present. The invention has the advantages of less basic data required by calculation, high speed, time saving and labor saving.
Drawings
FIG. 1 is an equivalent circuit diagram of an induction motor;
figure 2a is a diagram of a typical 500kV substation supply network;
FIG. 2b is an equivalent circuit of a typical 500kV substation power supply network diagram;
FIG. 3 is a system wiring and tidal flow diagram of an embodiment;
FIG. 4a is a single 220kV reactive power waveform of the embodiment under PSCAD/EMTDC;
FIG. 4b is a low-voltage side reactive power waveform diagram of a single 110kV main transformer according to the embodiment under PSCAD/EMTDC.
Detailed Description
FIG. 3 shows system wiring and a tidal flow diagram of an embodiment of the present invention: the Guangdong power grid 1 has the typical operation condition of 4 500kV transformer substations with 1000MVA main transformers.
The short-circuit current of the 500kV power supply bus is 40kA, and the requirement of short-circuit current control of the Guangdong power grid is met. The main transformer load factor is about 75%. The 500kV main transformer supplies power to 6 220kV main transformers through 3 identical 220kV lines. The length of each circuit of 220kV line is 50km, the power transmission flow is about 250MW, 2 220kV transformers are supplied with power, and the operation condition of 1 circuit of 220kV line is shown in detail in the figure. The system load flow calculation result is shown in fig. 3, the node voltages are all in a reasonable range, the load flow transmitted by each loop is reasonable, and the power factor meets the relevant operation and management requirements.
The power of the high-voltage side of the 500kV main transformer is 735.5 MW. In the comprehensive load of a 220kV main transformer at 10kV side, the large industrial load is 4.763MW, and the air-conditioning load is 4.818 MW. The 110kV main transformer 10kV side comprehensive load medium and large industrial load is 18.62MW, and the air conditioner load is 16.91 MW. The rest is constant impedance load.
In all the loads of 10kV voltage class of 1 500kV main transformer, the load of an induction motor is (4.763+4.818+18.62+16.91) × 6 is 270.666MW, and the load proportion K of the induction motorP270.666/735.5 × 100% ═ 36.8%, where the large industrial load is 140.298MW, accounting for 52%; the air conditioning load is 130.368MW, accounting for 48%. The motor parameters are shown in table 1.
TABLE 1 Large Industrial Motor and air conditioner Integrated Motor parameters
| Type (B) | Rs | Xs | XM | RR | XR | Tj | Load factor kL |
| Large-scale industrial motor | 0.013 | 0.067 | 3.8 | 0.009 | 0.17 | 3 | 0.8 |
| Air conditioner integrated motor | 0.064 | 0.091 | 2.23 | 0.059 | 0.071 | 0.68 | 0.8 |
And then, estimating the maximum dynamic reactive power requirement of the total station comprehensive load when the three-phase metallic short circuit is generated on the high-voltage side of the 500kV main transformer by adopting the algorithm.
The basic data and the specific numerical values required in the method are as follows:
1) the number n of main transformer stations of the transformer substation is 4 (stations) and the short-circuit current level I of the high-voltage busd＝40kA(kA)；
2) Active power ratio K of induction motor in transformer substation main transformer high-voltage side with active power P being 735.5(MW) and comprehensive load in normal operationP＝36.8％；
3) Inertia time constant T of induction motorjLoad factor KLAnd equivalent electric road single parameter: stator resistance RsStator reactance XsExcitation reactance XMRotor reactance XRRotor resistance RRSee table 1.
4) Failure duration Δ t is 0.1s
The method comprises the following steps:
as the running conditions of 4 main transformers are completely consistent, the following calculation data of 1 main transformer are given, and the result multiplied by 4 is the maximum dynamic reactive power requirement of the total station comprehensive load.
1) Running data calculation under steady state conditions
1.1 calculation of the equivalent impedance of the integrated load of the main transformer
When the system normally operates, the main transformer input power P is 735.5MW, the comprehensive load power factor is 0.95, and the total power of the comprehensive load is as follows: p + jQ ═ (735.5+ j241.75) MVA. By formula (6), the equivalent impedance of the integrated load of 1 500kV main transformer is as follows:
1.2 Induction Motor equivalent impedance per Unit value calculation
For large industrial motors:
obtained by the formula (2), XRM＝XR+XM＝3.97
XSM＝XS+XM＝3.867
XP＝XSXR+XSXM+XMXR＝0.912
Is obtained by the formula (4),
take V ═ 1.0p.u., P ═ KL0.8, obtained from formula (7),
is obtained by the formula (8),
the initial slip of the large industrial motor obtained by the formula (9) is as follows:
substituted into formula (1):
the initial slip of the air conditioner comprehensive motor can be obtained in the same way: rk0＝1.096，sk0＝0.0538；
1.3 constant impedance load equivalent impedance ZZ
Total load power of induction motor is P1＝KPX P36.8% x 735.5 270.7 MW. Among them, large scale industryThe load was 52%, 270.7 × 52% ═ 140.8 MW. The air conditioning load is 48%, and is 270.7 × 48% ═ 129.9 MW. Calculating in step 1.2 to obtain the equivalent impedance angle of the industrial load induction motor of 27.42 degrees and the equivalent impedance angle of the air-conditioning load induction motor of 31.78 degrees
Then: power consumption by industrial load: sg＝(140.8+j73.05)MVA
Air conditioning load power consumption: sk＝(129.9+j80.5)MVA
Constant impedance load dissipation power:
SZ＝(735.5+j241.75)-(140.8+j73.05)-(129.9+j80.5)
＝(464.8+j88.2)MVA
the constant impedance load equivalent impedance is obtained by equation (6):
2) calculating related parameters of the equivalent circuit of the power supply network of the 500kV transformer substation:
equivalent reactance behind 500kV generating line:
and (3) returning the power supply behind the 500kV bus to the post per unit transformation ratio E:
3) calculation of relevant parameters at fault removal time
Large industrial motor speed variation:fault cutterRemoving the time induction motor slip: s ═ s0- Δ ω ═ 0.00783+0.0267 ═ 0.03453, equivalent resistance of the induction motor rotor at the moment of fault removal:
the change of the rotating speed of the air conditioner comprehensive motor: induction motor slip at the end of the fault: s is 0.0538+0.1176 is 0.1714, and the equivalent resistance of the induction motor rotor at the end of the fault:
power reference value of large industrial load induction motor:
air conditioner integrated load induction motor power reference value:
equivalent impedance of large industrial motor:
equivalent impedance of the air conditioner integrated motor:
comprehensive load impedance:
ZΣ＝Z'g//Z'k//ZZ＝549.68∠44.35°//736.7∠28.583°//582.6∠10.74°
＝211∠28.23°Ω
4) 10kV side bus voltage at fault removal time:
5) estimating the maximum dynamic reactive power demand of the 500kV main transformer comprehensive load during the main network fault:
the dynamic reactive power requirement of the large-scale industrial motor is obtained by the following formula (5):
the dynamic reactive power requirement of the air conditioner comprehensive motor is as follows: qk＝0.7952×1.105×162＝113Mvar
Total dynamic reactive power demand maximum: qΣ＝Qg+Qk＝334.5Mvar
Fig. 4 is a reactive power waveform diagram of a single 220kV and 110kV main transformer low-voltage side of a specific embodiment system under PSCAD/EMTDC, which is a reactive power waveform diagram of a 220kV and 110kV main transformer low-voltage side obtained by simulation, and 1 500kV main transformer with 6 220kV and 18 110kV main transformers operates, and the total dynamic reactive power demand maximum value: q∑＝6×4+18×16.5＝321MVar。
The estimation result is well matched with the simulation result.
Claims (1)
1. A method for quickly estimating the maximum reactive power demand of a 500kV radial power supply network load in disturbance recovery comprises the following basic data:
the number n of main transformers of a 1,500 kV transformer substation and the short-circuit current level Id of a high-voltage bus in a unit kA;
2, the active power of the induction motor in the high-voltage side P, unit MW and the comprehensive load of the transformer substation during normal operationP；
3, inertia time constant T of induction motorjLoad factor KLAnd equivalent electric road single parameter: statorResistance RsStator reactance XsExcitation reactance XMRotor reactance XRRotor resistance RR；
4, fault duration Δ t;
the method requires the use of the following basic formula:
1) basic formula of induction motor
The induction motor has the equivalent of: stator resistors R connected in series in sequencesStator reactance XsRotor reactance XRAnd a variable resistance R ═ RRS, in rotor reactance XRAnd a variable resistance R ═ RRThe two ends of/s are provided with excitation reactance XM；
The equivalent impedance Z of the induction motor is calculated as formula (1):
the defining variables are as in formula (2):
the equivalent admittance Y of the induction motor is calculated as formula (3):
wherein,
when the operating voltage of the induction motor is V, the consumed power P + jQ is calculated as the formula (5):
2) equivalent impedance calculation formula of electrical element
If the operating voltage of the electrical element is V and the consumed power is P + jQ, the equivalent impedance Z of the electrical element is r + jx, and the equation (6) is calculated:
the method is characterized by comprising the following steps:
s1, calculating running data under steady state conditions
S1.1 main transformer comprehensive load equivalent impedance calculation
According to the active power P on the high-voltage side of the main transformer of the transformer substation in normal operation in basic data, the unit MW is considered, P is the active power consumed by the comprehensive load on the 10kV side of the main transformer, the power factor is 0.95, and the reactive power Q (cos) consumed by the comprehensive load on the 10kV side of the main transformer with the parallel capacitance is obtained-1(0.95)); and (3) obtaining the comprehensive load equivalent impedance Z on the 10kV side of the main transformer according to the formula (6) by taking the comprehensive load operating voltage V as 1p.uΣ0；
S1.2 Induction Motor equivalent impedance per unit value calculation
Taking the terminal voltage V of an induction motor as 1p.u., and taking the active power P as KLp.u., according to formulae (2) and (4), and let:
obtaining equivalent resistance of the rotor of the induction motor in normal operation:
initial slip of induction motor:
calculating the equivalent impedance per unit value Z of the induction motor by the formula (1)M*；
S1.3 constant impedance load equivalent impedance ZZ
According to the active power P of the high-voltage side of the transformer substation main transformer in normal operation, unit MW and the active power ratio K of the induction motor in the comprehensive load given in the basic dataPKnown as KPP is the active power consumed by the motor, according to ZM*Corresponding power factor angle, to obtain the reactive power consumed by the motor
Subtracting the power consumed by the induction motor from the total load power of the main transformer to obtain the power consumed by the constant impedance load, and then obtaining the equivalent impedance Z of the constant impedance load by using the step (6)Z；
S2, calculating related parameters of the equivalent circuit of the power supply network of the 500kV transformer substation;
s3, calculating related parameters at the fault removal time;
s4, estimating the maximum dynamic reactive power demand of the 500kV main transformer comprehensive load when the main network fails
Will U(10)Substituting the reactive calculation formula in the formula (5) to obtain the maximum dynamic reactive value of various induction motors in the 500kV main transformer comprehensive load, and summing to obtain the maximum dynamic reactive requirement of the 500kV main transformer comprehensive load when the main network fails;
the step S2 specifically includes: let the general form of a 500kV substation power supply network be: the 500kV transformer substation supplies power to the 220kV transformer substation, and a comprehensive load is connected to the 10kV side of the 220kV transformer substation; the 220kV transformer substation supplies power to the 110kV transformer substation, and a comprehensive load is connected to the 10kV side of the 110kV transformer substation;
the general form is equivalent to: the main network power supply is connected with the power supply through a transformation ratio of 1: e equivalent reactance Xs of an ideal transformer series system, and equivalent impedance X of a power transmission loop to a comprehensive load Z∑0The form of the power supply;
the system equivalent reactance Xs is estimated according to equation (10):
estimating the electrical distance between the comprehensive load and the high-voltage side of the 500kV main transformer according to the X-140 omega;
estimating the power supply return road sign unitary transformation ratio E according to the condition that the comprehensive load terminal voltage is 1p.u. during normal operation as shown in the formula (11):
the step S3 specifically includes: induction motor terminal voltage during fault is considered to be zero, induction motor electromagnetic torque TeInduction motor load torque T of 0load＝KLAnd delta t is the fault duration, and the induction motor rotating speed change delta omega at the fault removal moment is obtained according to the step (12):
the induction motor slip at the end of the fault is obtained according to equation (13):
s＝s0-Δω (13)；
induction motor rotor resistance at the time of failure completion:
reference value of power of induction motor:
calculating equivalent impedances of various induction motor loads in the comprehensive loads at the moment of fault removal according to the formula (1); integrated load equivalent impedance ZΣCalculating the parallel value of the induction motor and the constant impedance load according to the formula (16):
Z∑＝Π(Z) (16)；
II represents parallel connection;
s4, estimating the voltage of the bus at the 10kV side of the 220kV and 110kV transformer substations at the fault removal time
TjRefers to the inertia time constant of the motor.
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