JPH05344653A - Automatic voltage controller for power plant - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to obtain an automatic voltage control device capable of improving the efficiency of a power plant connected to a step-up transformer. An automatic voltage control device according to the present invention calculates a loss in the operating state and means for specifying the operating state of a generator and a step-up transformer according to a voltage control command or a reactive power command to a power plant. And means for performing control by selecting an operating point that minimizes the total loss of the generator and the step-up transformer when a plurality of operating states can be selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic voltage control device for a power plant in which a generator is connected to a power transmission system via a step-up transformer having a load tap switching means.

[0002]

2. Description of the Related Art For normal operation of electric equipment supplied with electric power from the electric power system, the electric power system is required to maintain a stable voltage with a small voltage fluctuation. The power station, which is a component of the power system, controls the voltage and contributes to the voltage stability of the power system.

However, this type of power plant voltage control device includes a generator voltage control by an automatic voltage control device for a generator, and a tap change at load of a step-up transformer interposed between the generator and the transmission system. There is also one that uses voltage control on the transmission system side of a step-up transformer by a device.

FIG. 3 is a single line connection diagram showing an example of such a control device. In FIG. 3, the electric power generated by the generator 1 is stepped up by the step-up transformer 2 to the required voltage of the electric power system and supplied to the electric power system 3. On the other hand, the terminal voltage, the terminal current, and the field current of the generator 1 are the transformer for the meter 4, the current transformer 5 for the meter installed on the output end side of the generator 1, and the current for the meter installed in the field circuit. It is detected by the device 10 and is input to the automatic voltage controller (AVR) 6, respectively. Further, the voltage setting value from the voltage setting device 7 that sets the voltage setting value corresponding to the above-mentioned predetermined value is also input to the automatic voltage controller 6. Further, in the automatic voltage controller 6, the generator 1 terminal voltage from the instrument transformer 4 is compared with the voltage setting value from the voltage setting device 7, and the generator exciting power supply device 8 is adjusted based on the deviation between the two. By supplying an exciting current to the generator field winding 9, the terminal voltage of the generator 1 is automatically controlled to a predetermined value. The setting of the voltage set value by the voltage setter 7 is performed manually or by a command from a separately provided control device such as a reactive power control device.

The voltage on the secondary side of the step-up transformer is also controlled by switching the load tap changer (LTC) 12 by using the LTC operating mechanism 13. The command to the LTC operating mechanism 13 is issued manually or from a setting device such as a program setting device provided separately.

In any case, control is performed so that the reactive power generated at the power plant or the secondary voltage of the step-up transformer is set to a required value. However, the generator terminal voltage has a permissible range, and the generator terminal voltage may exceed the permissible range in order to obtain the required reactive power or secondary voltage of the step-up transformer.

[0007] Conventionally, when the generator terminal voltage exceeds the allowable range, it is manually operated, or a command having a preset setting value which is predicted and programmed beforehand, or an LTC operating mechanism.
By inputting to 13 and switching the tap of the step-up transformer 2 by the LTC 12, the generator terminal voltage is kept within an allowable range and required reactive power or step-up transformer secondary side voltage is obtained.

[0008]

As described above, conventionally, only when the generator terminal voltage exceeds the allowable range, the step-up transformer tap is moved so that it falls within the allowable range. However, the allowable fluctuation range of the generator voltage is usually ± 5%, while the tap voltage of the step-up transformer is usually 1.
Since it is about 5%, a plurality of generator voltages are generated for the generated reactive power command or the step-up transformer secondary voltage command.
You may be able to choose a combination of step-up transformer taps. In each combination, the total loss of the generator and the main transformer has different values, but in the past it was not always the combination that minimizes the total loss of the generator and the main transformer. It was

According to the present invention, a combination of a generator voltage and a step-up transformer tap corresponding to a generated reactive power command or a step-up transformer high-voltage side command is set so that the total loss of the generator and the step-up transformer is minimized. It is an object of the present invention to provide an automatic voltage control device that contributes to improving the efficiency of the above.

[0010]

To achieve the above object, the present invention is directed to a power plant for supplying electric power generated by a generator to a power system through a step-up transformer having a load tap changer LTC. The automatic voltage control device that automatically controls the terminal voltage of the generator to a predetermined value and automatically switches the taps of the boost transformer, and sets the generator voltage to the voltage setting value corresponding to the predetermined value. Setting means, LTC operation command generating means for setting the tap of the step-up transformer to a predetermined position, and electric quantity detection for detecting the terminal voltage, terminal current, field current of the generator and secondary side voltage of the step-up transformer, respectively. Means, a circuit for calculating the operating state of the power plant from the amount of electricity detected by the electricity amount detecting means, a circuit for calculating the deviation between the operating state of the power station and the command of the power station, and the deviation can be generated. Generator voltage and A circuit that calculates the combination of voltage transformer tap positions, a circuit that calculates the loss for each combination and selects the combination that minimizes the loss, the generator voltage target that minimizes the loss from the loss calculation result, and the step-up transformer tap position. And a circuit for setting.

[0011]

Therefore, in the automatic voltage control system for a power plant of the present invention, by providing the above means, the operating point with the minimum loss of the generator and the step-up transformer can be achieved with respect to the required operating condition. Since it can be selected, it can contribute to the improvement of the operating efficiency of the power plant.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a single-line connection diagram showing a structural example of a power plant to which the automatic voltage control device according to the present invention is applied.
The same parts as those of the above are denoted by the same reference numerals and the description thereof will be omitted, and only different parts will be described here.

That is, the automatic voltage control apparatus in this embodiment includes a voltage transformer 11, and a signal input circuit 14, an operating state calculating circuit 15, a deviation calculating circuit 17, and a possible operating state, as shown by a broken line in the drawing. A state calculation circuit 18, a loss calculation circuit 19, a setting circuit 20, and an LTC tap position setter 21 are provided in addition to FIG.

Here, the instrument transformer 11 is for detecting the secondary side voltage of the step-up transformer 2. Further, the signal input circuit 14 includes a voltage signal from the instrument transformers 4 and 11, a current signal from the instrument current transformers 5 and 10 via the automatic voltage controller 6, and a step-up transformer from the LTC operating mechanism 13. The tap position of the container 2 is input.

On the other hand, the operating state calculation circuit 15 is a signal input circuit.
The generator reactive power and the generator active power are calculated based on the voltage signal and the current signal input at 14.
The deviation calculation circuit 17 calculates the deviation between the power station reactive power output and voltage signal from the operating state calculation circuit 15 and the command 16 to the power station.

Also, the possible operating state calculation circuit 18 is a generator voltage that can make the power station reactive power deviation or the step-up transformer secondary side voltage deviation calculated by the deviation calculation circuit 17 zero. Based on the combination of the step-up transformer tap position and the generator field current at that time, the preset generator constant, step-up transformer constant, system constant and generator operation allowable range, and the input value of the signal input circuit 14. It is something that is calculated.

Further, the loss calculating circuit 19 calculates the loss based on the generator constant and the step-up transformer constant stored in advance for the combination of the generator voltage and the step-up transformer tap position selected by the possible operating state calculating circuit 18. Then, the combination with the minimum loss is selected. The setting circuit 20 outputs to the voltage setting device 7 and the LTC tap position setting device 21 the generator voltage and the step-up transformer tap position, which are selected by the loss calculation circuit 19 and have the minimum loss. Next, the operation of the automatic voltage control device configured as described above will be described.

The generator transformer 4 installed on the output end side of the generator 1, the instrument current transformer 5, and the generator current 1 detected by the instrument current transformer 10 installed in the field circuit of the generator 1. Terminal voltage,
The terminal current, the field current, and the secondary side voltage of the step-up transformer 2 detected by the instrument transformer 11 installed on the secondary side of the step-up transformer 2 are input to the signal input circuit 14. Then, the operating state calculation circuit 15 calculates the generator reactive power and the generator active power based on the voltage signal and the current signal input from the signal input circuit 14.

Next, in the deviation calculation circuit 17, the command 16 of the generator reactive power or the step-up transformer secondary side voltage to the power plant is given.
Then, the deviation from the generator reactive power or the step-up transformer secondary side voltage obtained by the operating state calculation circuit 15 is calculated.

Next, the possible operating state calculation circuit 18 calculates a combination of the generator voltage and the step-up transformer tap position that can make the deviation calculated by the deviation calculation circuit 17 zero. This point will be described in detail below. FIG. 2 is a diagram showing an equivalent circuit of the generator 1, the step-up transformer 2, and the power system 3 in FIG.

In FIG. 2, V _G is the generator terminal voltage, P
_G is generator active power, Q _G is generator reactive power, X _t is step-up transformer impedance, n is step-up transformer transformation ratio, V _T
Is the secondary voltage of the step-up transformer, X _e is the impedance of the transmission line, and V _B is the virtual infinite bus voltage.

In this case, V _B is constant and V _G , n is
Change ΔV in V _T and Q _G when ΔV _G and Δn are changed
_T and ΔQ _G can be expressed as follows.

[0024]

ΔV _T = A _n Δn + A _VG ΔV _G (1) ΔQ _G = B _n Δn + B _VG ΔV _G (2) where A _n , A _VG , B _n , and B _VG are generally voltage-reactive power coefficients It can be expressed as follows using the unit method.

[0025]

[Equation 2]

Since x _t and x _e are known as step-up transformer constants and system constants, the required ΔV _T or ΔQ
The combination of Δn and [Delta] V _G to achieve a _G can be obtained by calculation. Next, the loss calculation circuit 19 calculates the loss of the generator and the loss of the step-up transformer in the combination of Δn and ΔV _G calculated by the possible operation state calculation circuit 18. This point will be described in detail below. The generator loss L _G and the step-up transformer loss L _T are determined by their operating conditions and can be expressed by the following functions.

[0027]

L _G = A ₁ (V _G ) + A ₂ (I _G ) + A ₃ (I _f ) + A ₄ (3) L _T = B ₁ (n, V _G ) + B ₂ (n, I _G ) … (4)

Here, I _G is a generator current, I _f is a generator field current, A ₁ (V _G ), B ₁ (n, V _G ) are iron losses, and A ₂ (I _G ). , B ₂ (n, I _G ) is the load loss, A
₃ (I _f ) corresponds to field circuit resistance loss, and A ₄ corresponds to mechanical loss. Various quantities of V _G , I _G , _If , and n are input to the signal input circuit 14, and based on this, from Δn and ΔV _G calculated by the possible operating state calculation circuit.

[0029]

## EQU4 ## V _G (new) = V _G (old) + ΔV _G (5) n (new) = n (old) + Δn (6) is calculated. On the other hand, Q _G and P _G are obtained by the operating state calculation circuit 15, and ΔQ _G obtained by the equation (2)
Using,

[0030]

[Equation 5] Is required. I _f (new) is obtained from P _G and Q _G (new) using the generator V-curve. As above
New V _G , I _G , _If , and n corresponding to Δn and ΔV _G are obtained by calculation, and each function of equations (3) and (4) is known from the design value and test value of the generator and the step-up transformer. Therefore, the generator loss L _G and the step-up transformer loss L _T are obtained.

When there are a plurality of possible combinations of Δn and ΔV _G , the combination that minimizes (L _G + L _T ) is selected.

Next, the setting circuit 20 outputs the generator voltage and the step-up transformer tap position, which are selected by the loss calculation circuit 19 and which minimizes the loss, to the voltage setting device 7 and the LTC tap position setting device 21. The present invention is not limited to the above embodiments, but can be implemented in the same manner as described below.

In the above embodiment, the transmission line impedance is treated as a system constant, but the transmission line impedance usually changes slightly every moment, and is regularly or at an arbitrary time point. If the transmission line impedance can be estimated, the possible operating state of the power plant may be calculated based on the numerical value.

[0034]

As described above, according to the present invention,
Select the generator terminal voltage change amount and the step-up transformer switching tap so as to minimize the sum of the generator loss and step-up transformer loss for the required generator reactive power or step-up transformer secondary voltage. Therefore, it is possible to provide an automatic voltage control device that can contribute to improving the efficiency of a power plant.

[Brief description of drawings]

FIG. 1 is a single wire connection diagram showing an embodiment in which an automatic voltage control device of the present invention is connected to a power system.

FIG. 2 is an equivalent circuit of a power system when the automatic voltage control device of the present invention is connected to the power system.

FIG. 3 is a single line connection diagram showing a conventional example.

[Explanation of symbols]

 1 generator 2 step-up transformer 3 power system 4 instrument transformer 5 instrument current transformer 6 automatic voltage controller 7 voltage setting device 8 exciting power supply device 9 field winding 10 instrument current transformer 11 instrument transformer 12 Tap switch during load 13 LTC operating mechanism 14 Signal input circuit 15 Operating state calculation circuit 16 Command to power plant 17 Deviation calculation circuit 18 Possible operating state calculation circuit 19 Loss calculation circuit 20 Voltage target value tap position setting circuit 21 LTC tap Position setter

Claims (1)

[Claims] 1. A power plant in which a generator is connected to a power transmission system via a step-up transformer having a load tap switching means, the generator and the step-up transformer responding to a voltage control command or a reactive power command to the power plant. Means for identifying the operating state of the generator, means for calculating the loss in that operating state, and an operating point at which the total loss of the generator and the step-up transformer is minimum when a plurality of operating states can be selected An automatic voltage control device for a power plant, comprising: