CN104899677B - The radial supply network load maximum reactive requirements of 500kV estimate method soon during disturbance restores - Google Patents

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

Quick Estimation of Maximum Reactive Power Demand of 500kV Radial Power Supply Network in Disturbance Restoration method

technical field

The present invention relates to a method for quickly estimating the maximum reactive power demand of a 500kV radial power supply network load during disturbance recovery, specifically referring to a method for estimating the maximum reactive power demand of a comprehensive load of a 500kV substation radial power supply network after a main network failure (approximately considered to occur at the time of fault removal) ) for a quick estimate.

Background technique

In the analysis and calculation of the power system, the innumerable power users in the vast area covered by the power grid are often combined into a small number of comprehensive loads, which are tapped on the buses of different voltage levels in the substation. In the study of power system voltage stability, the integrated load is often represented as a combination of constant impedance and induction motors with different proportions.

When a short-circuit fault occurs on the high-voltage side of the main transformer, the power system relay protection device will quickly remove the fault. In the recovery process after a fault, the integrated load will generate a significant dynamic reactive power demand, and its size depends on the fault type, fault duration, load characteristics and system voltage recovery; and the system voltage recovery is affected by the AC system strength and load dynamic reactive power The impact of demand, the two are coupled with each other. For the dynamic reactive power demand of the comprehensive load, it is necessary to use power system calculation and analysis software to achieve a more accurate calculation, which is time-consuming and laborious.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for quickly estimating the maximum reactive power demand of a 500kV radial power supply network in disturbance recovery. Less basic data, fast speed, save time and effort.

To solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A fast estimation method for the maximum reactive power demand of a 500kV radial power supply network in disturbance recovery. The basic data required in the method are:

1) The number n of main transformers in the 500kV substation and the short-circuit current level Id of the high-voltage bus, in kA;

2) During normal operation, the active power P of the high-voltage side of the main transformer of the substation, unit MW, and the active power ratio K _P of the induction motor in the comprehensive load;

3) Inertia time constant T _j of induction motor, load rate K _L , equivalent circuit unit parameters: stator resistance R _s , stator reactance X _s , excitation reactance X _M , rotor reactance X _R , rotor resistance R _R ;

4) Fault duration Δt;

The method described requires the use of the following basic formula:

1) Basic formula of induction motor

Referring to Figure 1, the equivalent value of the induction motor is: the stator resistance R _{s, the} stator reactance X _{s, the} rotor reactance X _R and the variable resistance R=R _R /s in series, and the rotor reactance X _R and the variable resistance R=R There is an exciting reactance X _M at both ends of _R /s;

The equivalent impedance Z of the induction motor is calculated as formula (1):

Define variables as formula (2):

Then the equivalent admittance Y of the induction motor is calculated as formula (3):

in,

When the operating voltage of the induction motor is V, the power consumption P+jQ is calculated as formula (5):

2) Calculation formula of equivalent impedance of electrical components

If the operating voltage of the electrical component is V and the power consumed is P+jQ, then the equivalent impedance Z=r+jx of the electrical component is calculated as formula (6):

The method comprises the steps of:

1) Calculation of operating data under steady state conditions

1.1 Calculation of the equivalent impedance of the main transformer comprehensive load

According to the basic data in the normal operation of the substation main transformer high-voltage side active power P, the unit is MW, and it is considered that P is the active power consumed by the comprehensive load on the 10kV side of the main transformer, and the power factor is 0.95, which has taken into account the parallel capacitance of the main transformer 10kV side Reactive power Q=P·tg(cos ^-1 (0.95)) consumed by integrated load. Take the comprehensive load operating voltage V=1p.u., and obtain the comprehensive load equivalent impedance Z _Σ0 of the 10kV side of the main transformer according to formula (6);

1.2 Calculation of equivalent impedance per unit value of induction motor

Take induction motor terminal voltage V=1p.u., active power P=K _L pu, according to formula (2) and formula (4), and make:

Obtain the equivalent resistance of the induction motor rotor during normal operation:

Induction motor initial slip:

Calculate the per unit value Z _M* of the equivalent impedance of the induction motor by formula (1);

1.3 Constant impedance load equivalent impedance Z _Z

According to the active power P of the high-voltage side of the main transformer substation given in the basic data during normal operation, the unit is MW, and the active power ratio of the induction motor in the comprehensive load K _P , it is known that K _P P is the active power consumed by the motor, according to Z _M* Corresponding power factor angle, get the reactive power consumed by the motor

Subtract 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 use (6) to obtain the equivalent impedance Z _Z of the constant impedance load;

2) Calculation of relevant parameters of equivalent circuit of 500kV substation power supply network

The general form of the 500kV substation power supply network is shown in Figure 2a: the 500kV substation supplies power to the 220kV substation, and the 10kV side of the 220kV substation is connected to the integrated load; the 220kV substation supplies power to the 110kV substation, and the 10kV side of the 110kV substation is connected to the integrated load; Figure 2b: The power supply of the main network passes through the equivalent reactance Xs of the ideal transformer series system with a transformation ratio of 1:E, and supplies power to the comprehensive load Z _Σ0 through the equivalent impedance X of the transmission circuit;

Estimate system equivalent reactance Xs according to formula (10):

The electrical distance between the integrated load and the high voltage side of the 500kV main transformer is estimated by X=140Ω;

According to the comprehensive load terminal voltage during normal operation is 1p.u. Estimate the per-unit transformation ratio E of the power supply circuit as formula (11):

3) Calculation of relevant parameters at the time of fault removal

During the fault period, the terminal voltage of the induction motor is considered to be zero, the electromagnetic torque of the induction motor T _e = 0, the load torque of the induction motor T _load = K _L , Δt is the duration of the fault, and the speed change of the induction motor at the moment of fault removal is obtained according to (12) Δω:

Calculate the slip of the induction motor at the end of the fault according to formula (13):

s=s ₀ -Δω (13);

The rotor resistance of the induction motor at the end of the fault:

Induction motor power reference:

Calculate the equivalent impedance of various induction motor loads in the comprehensive load at the time of fault removal by formula (1); the comprehensive load equivalent impedance Z _Σ is the parallel connection value of the induction motor and the constant impedance load, calculated as formula (16):

Z _∑ = ∏(Z) (16);

Π means parallel connection;

4) At the time of fault removal, the bus voltage estimation on the 10kV side of 220kV and 110kV substations

5) Estimation of the maximum dynamic reactive power demand of the 500kV main transformer comprehensive load when the main grid fails

Substituting U ⁽¹⁰⁾ into the reactive power calculation formula in (5), the maximum value of dynamic reactive power of various induction motors in the comprehensive load of the 500kV main transformer can be obtained. work needs.

Remarks: 1) About 20% of the comprehensive load is powered by the low-voltage side of the 220kV substation. This part of the load is relatively close to the high-voltage side of the 500kV main transformer. In the algorithm, all loads are considered as the power supply of the low-voltage side of the 110kV substation, which will result in a comprehensive estimate. The maximum dynamic reactive power demand of the load is low; 2) When the fault is removed, the load bus voltage is low, and the reactive power taken by the load other than the induction motor and the equivalent impedance of the parallel capacitor will also decrease accordingly. The algorithm ignores its influence, which will cause The estimated maximum dynamic reactive power demand of integrated load is on the high side; the effects of the two aspects are basically offset.

Beneficial effects: Generally, the simulation method is used to obtain the maximum reactive power demand of the 500kV radial power supply network load in the disturbance recovery, which is time-consuming and labor-intensive, and there is no report on the relevant analytical calculation method at present. The invention requires less basic data for calculation, is fast, and saves time and effort.

Description of drawings

Figure 1 is an equivalent circuit diagram of an induction motor;

Figure 2a is a typical 500kV substation power supply network diagram;

Figure 2b is the equivalent circuit of a typical 500kV substation power supply network diagram;

Figure 3 is the system wiring and power flow diagram of the specific implementation example;

Fig. 4 a is the single 220kV reactive waveform diagram of the specific embodiment under PSCAD/EMTDC;

Fig. 4b is a reactive power waveform diagram of a single 110kV main transformer low-voltage side of a specific embodiment under PSCAD/EMTDC.

Detailed ways

Fig. 3 shows the system wiring and power flow diagram of a specific embodiment of the present invention: a typical operation situation of a 500kV substation with four 1000MVA main transformers in Guangdong Power Grid.

The short-circuit current of the 500kV power supply busbar is 40kA, which meets the short-circuit current control requirements of Guangdong power grid. The main transformer load rate is about 75%. The 500kV main transformer supplies power to six 220kV main transformers via three identical 220kV lines. Each 220kV line is 50km long, and the transmission flow is about 250MW, which supplies power to two 220kV transformers. The figure shows the operation of one of the 220kV lines in detail. The power flow calculation results of the system are shown in Figure 3. The node voltages are all within a reasonable range, the transmission power flow of each circuit 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 735.5MW. Among the comprehensive loads on the 10kV side of the 220kV main transformer, the large industrial load is 4.763MW, and the air conditioning load is 4.818MW. The comprehensive load on the 10kV side of the 110kV main transformer is 18.62MW for medium and large industrial loads, and the load for air conditioning is 16.91MW. The rest are constant impedance loads.

Among all the loads of a 500kV main transformer with 10kV voltage level, the induction motor load is (4.763+4.818+18.62+16.91)×6=270.666MW, and the induction motor load ratio K _P is 270.666/735.5×100%=36.8%. The 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 Parameters of large industrial motors and comprehensive motors for air conditioners

type R _s X _s X _M R _R X _R Tj Load rate k _L large 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

The above-mentioned algorithm is used to estimate the maximum dynamic reactive power demand of the comprehensive load of the whole station when the three-phase metallic short circuit on the high voltage side of the 500kV main transformer is used.

The basic data and their specific values required in the method are as follows:

1) The number of main transformers in the substation n=4 (sets) and the short-circuit current level of the high-voltage busbar I _d =40kA (kA);

2) During normal operation, the active power of the high-voltage side of the substation main transformer P = 735.5 (MW) and the active power ratio of the induction motor in the comprehensive load K _P = 36.8%;

3) Induction motor inertia time constant T _j , load rate K _L , equivalent circuit unit parameters: stator resistance R _s , stator reactance X _s , excitation reactance X _M , rotor reactance X _R , rotor resistance R _R , see Table 1 .

4) Fault duration Δt=0.1s

The method comprises the steps of:

Since the operation conditions of the four main transformers are exactly the same, the calculation data of one main transformer is given below, and the result multiplied by 4 is the maximum dynamic reactive power demand of the comprehensive load of the whole station.

1) Calculation of operating data under steady state conditions

1.1 Calculation of the equivalent impedance of the main transformer comprehensive load

During normal operation, the input power of the main transformer is P=735.5MW, and the comprehensive load power factor is 0.95, then the total power of the comprehensive load is: P+jQ=(735.5+j241.75)MVA. From formula (6), the comprehensive load equivalent impedance of a 500kV main transformer is:

1.2 Calculation of equivalent impedance per unit value of induction motor

For large industrial motors:

From formula (2), X _RM ＝X _R +X _M ＝3.97

X _SM ＝X _S +X _M ＝3.867

X _P ＝X _S X _R +X _S X _M +X _M X _R ＝0.912

From formula (4), we get,

Take V=1.0pu, P=K _L ＝0.8, get from formula (7),

From formula (8), we get,

From formula (9), the initial slip of the large industrial motor is:

Substitution (1):

In the same way, the initial slip of the integrated motor of the air conditioner can be obtained: R _k0 = 1.096, s _k0 = 0.0538;

1.3 Constant impedance load equivalent impedance Z _Z

The total load power of the induction motor is P ₁ =K _P ×P=36.8%×735.5=270.7MW. Among them, the large-scale industrial load accounts for 52%, which is 270.7×52%=140.8MW. Air-conditioning load accounts for 48%, which is 270.7×48%=129.9MW. Taking into account the calculation in step 1.2, the equivalent impedance angle of the industrial load induction motor is 27.42°, and the equivalent impedance angle of the air-conditioning load induction motor is 31.78°

Then: industrial load power consumption: S _g = (140.8+j73.05) MVA

Air conditioning load power consumption: S _k = (129.9+j80.5)MVA

Constant impedance load power consumption:

S _Z ＝(735.5+j241.75)-(140.8+j73.05)-(129.9+j80.5)

=(464.8+j88.2)MVA

From formula (6), the equivalent impedance of constant impedance load is:

2) Calculation of relevant parameters of equivalent circuit of 500kV substation power supply network:

Equivalent reactance behind the 500kV busbar:

The power supply circuit behind the 500kV bus bar has a per-unit transformation ratio E:

3) Calculation of relevant parameters at the time of fault removal

Large industrial motor speed change: Slip of the induction motor at the time of fault removal: s=s ₀ -Δω=0.00783+0.0267=0.03453, the equivalent resistance of the induction motor rotor at the time of fault removal:

Air conditioner integrated motor speed change: Slip of induction motor at the end of the fault: s=0.0538+0.1176=0.1714, equivalent resistance of the induction motor rotor at the end of the fault:

Large Industrial Duty Induction Motor Power References:

Air conditioner integrated load induction motor power reference value:

Equivalent impedance of large industrial motors:

Equivalent impedance of integrated air conditioner motor:

Integrated Load Impedance:

Z _Σ ＝Z' _g //Z' _k //Z _Z ＝549.68∠44.35°//736.7∠28.583°//582.6∠10.74°

＝211∠28.23°Ω

4) The bus voltage on the 10kV side at the time of fault removal:

5) Estimation of the maximum dynamic reactive power demand of the 500kV main transformer comprehensive load when the main grid fails:

The dynamic reactive power demand of large industrial motors can be obtained from formula (5):

Dynamic reactive power demand of integrated motor of air conditioner: Q _k ＝0.795 ² ×1.105×162＝113Mvar

Maximum value of total dynamic reactive power demand: Q _Σ ＝Q _g +Q _k ＝334.5Mvar

Figure 4 is the reactive power waveform diagram of the low-voltage side of a single 220kV and 110kV main transformer under PSCAD/EMTDC. 220kV and 18 sets of 110kV main transformers are running, the maximum value of total dynamic reactive power demand: Q _∑ ＝6×4+18×16.5＝321MVar.

The estimated results are in good agreement with the simulation results.

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 operation_P；

3, inertia time constant T of induction motor_jLoad factor K_LAnd equivalent electric road single parameter: statorResistance R_sStator reactance X_sExcitation reactance X_MRotor reactance X_RRotor resistance R_R；

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 sequence_sStator reactance X_sRotor reactance X_RAnd a variable resistance R ═ R_RS, in rotor reactance X_RAnd a variable resistance R ═ R_RThe two ends of/s are provided with excitation reactance X_M；

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.u_Σ0；

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 K_Lp.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 Z_Z

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 data_PKnown as K_PP is the active power consumed by the motor, according to Z_M*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 T_eInduction motor load torque T of 0_load＝K_LAnd 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 Z_ΣCalculating 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

T_jRefers to the inertia time constant of the motor.