CN105826908A - Quick distance protection method and apparatus for power transmission line containing UPFC - Google Patents

Abstract

The invention relates to a method and device for fast distance protection of transmission lines containing UPFC. By calculating the maximum equivalent impedance of UPFC during normal operation, when the system fails, the fault compensation voltage is calculated and the maximum equivalent impedance calculated during normal operation is calculated. , which can effectively prevent the risk of misoperation of the fast distance protection when the protection device is used on the side near the UPFC when the reverse direction exit fault occurs; In the event of a permanent fault, there is a risk of overriding action in the fast distance protection.

Description

Method and device for fast distance protection of transmission lines with UPFC

technical field

The invention belongs to the technical field of electric power system relay protection, and in particular relates to a fast-distance protection method for transmission lines containing UPFC.

Background technique

The unified power flow controller (UPFC) can quickly and flexibly control the power flow of the line, improve the power flow distribution characteristics of the power grid, and maximize the transmission capacity of the power grid; it also has the ability to damp system oscillation and improve the stability of the power grid; Scale load shedding; optimize power flow distribution, reduce circulation, and reduce network loss. By injecting a voltage phasor with controllable phase angle and amplitude into the line, UPFC directly changes the potential characteristics of the head and end of the line, thereby further changing the potential phase and amplitude distribution in the system, and regulating the power flow distribution in the entire area effect. While UPFC controls the power flow distribution of the line, it also changes the parameters of the transmission line. The equivalent impedance of the UPFC may present a large capacitive value, which in turn leads to the misoperation of the traditional distance protection.

The fast distance protection is based on the fault quantity, and adopts the operating voltage mutation value greater than the fixed threshold as the action equation. As a fault component protection, it is not affected by the load state and has a strong ability to withstand transition resistance. As a fast single-ended quantity protection, the fast distance protection can remove serious near-end faults at an extremely fast speed to ensure the safe operation of the power grid. For transmission lines containing UPFC, when installed near the UPFC side, the fast distance protection has the risk of misoperation when an outlet fault occurs in the reverse direction; when installed on the far UPFC side, when a metal fault occurs outside the forward direction There is a risk of overriding action in distance protection. Due to the fast distance protection action speed, it may act before the UPFC system body protection action. At present, there is no fast distance protection method suitable for transmission lines containing UPFC in the industry.

Contents of the invention

The purpose of the present invention is to provide a fast distance protection method for UPFC transmission lines, which is used to solve the problems of malfunction and overrunning when the distance protection in the prior art is used for UPFC lines. At the same time, the invention also provides a fast-distance protection device for transmission lines containing UPFC.

A method for fast distance protection of transmission lines containing UPFC, comprising the steps of:

(1) The line protection devices on both sides independently collect the voltage and current of each side;

(2) Real-time calculation of the maximum equivalent impedance Z _P of the UPFC when the line protection starting element is not in action;

(3) Real-time calculation of voltage variation and compensation current variation after the activation of the element;

(4) Calculate the fault compensation voltage according to the voltage variation and the compensation current variation; the UPFC maximum equivalent impedance Z _P before the line protection starting element in the step (2) is used in the calculation;

(5) When the fault voltage satisfies the action criterion, the exit will be activated after a delay.

Further, in the step (1), the method for collecting voltage and current on both sides is as follows: measure the line side PT for the voltage near the UPFC side, and measure the line CT for the current; measure the line side PT or the busbar side for the far UPFC side voltage PT, current measuring line CT.

Further, the formula of the starting element in the step (2) is: |iqd _[k] |>1.25|iqd _[k-2N] |+0.1In; wherein: iqd _k is any phase current on each side; N is each The number of cycle sampling points; In is the rated current value of CT; the formula for calculating the maximum equivalent impedance Z _P of UPFC is: Among them: U _Pmax is the maximum output voltage value of the series transformer of the UPFC system; is the current current.

Further, in the step (3), the formula for calculating the voltage variation is: in: is the current voltage phasor; is the voltage phasor two weeks ago; It is any phase or between phases; the calculation formula of current variation is: in: is the current current phasor; is the current zero-sequence current phasor; is the current current phasor; is the zero-sequence current phasor two weeks ago; Be any phase or between phases; the formula for calculating the voltage variation in the step (4) is: in: Impedance setting value for fast distance protection; For any phase or phase.

Further, the action criterion formula in the step (5) is: Among them: U _N is the voltage rating; α is the reliability coefficient, and its value ranges from 0 to 5, generally 0.5; It is any phase or between phases; the delay is dynamically adjusted in step (5), and the delay calculation formula is: T _P =(5-α)×20ms; where: α is the reliability coefficient in the action criterion.

The present invention also provides a transmission line fast distance protection device containing UPFC, including the following modules:

Module (1), the line protection devices on both sides independently collect the voltage and current on each side;

Module (2), used for real-time calculation of the maximum equivalent impedance Z _P of the UPFC when the line protection starting element is not in action;

Module (3), used for real-time calculation of voltage variation and compensation current variation after the activation of the element;

The module (4) is used to calculate the fault compensation voltage according to the voltage variation and the compensation current variation; the maximum equivalent impedance Z _P of the UPFC before the line protection starting element in the module (2) is used for calculation;

The module (5) is used for exiting after a delayed action when the fault voltage satisfies the action criterion.

Further, the method for collecting the voltage and current on both sides of the module (1) is as follows: measure the line side PT for the voltage near the UPFC side, and measure the line CT for the current; measure the line side PT or bus side for the far UPFC side voltage PT, current measuring line CT.

Further, the formula of the starting element in the module (2) is: |iqd _[k] |>1.25|iqd _[k-2N] |+0.1In; wherein: iqd _k is any phase current on each side; N is each The number of cycle sampling points; In is the rated current value of CT; the formula for calculating the maximum equivalent impedance Z _P of UPFC is: Among them: U _Pmax is the maximum output voltage value of the series transformer of the UPFC system; is the current current.

Further, in the module (3), the voltage variation calculation formula is: in: is the current voltage phasor; is the voltage phasor two weeks ago; It is any phase or between phases; the calculation formula of current variation is: in: is the current current phasor; is the current zero-sequence current phasor; is the current current phasor; is the zero-sequence current phasor two weeks ago; Be any phase or between phases; the formula for calculating the voltage variation in the module (4) is: in: Impedance setting value for fast distance protection; For any phase or phase.

Further, the action criterion formula in the module (5) is: Among them: U _N is the voltage rating; α is the reliability coefficient, and its value ranges from 0 to 5, generally 0.5; It is any phase or between phases; the delay is dynamically adjusted in module (5), and the delay calculation formula is: T _P =(5-α)×20ms; where: α is the reliability coefficient in the action criterion.

The difference between the present invention and the prior art mainly lies in: the maximum equivalent impedance of UPFC is calculated and saved during normal operation, and when the system fails and the fault compensation voltage is calculated, the maximum equivalent impedance of UPFC is no longer calculated in real time, but the fault The previous calculations occur and save the UPFC maximum equivalent impedance. This method can effectively prevent the risk of misoperation of the fast distance protection when the protection device is used on the side near the UPFC when the reverse direction exit fault occurs; When the outer metal property is faulty, the fast distance protection has the risk of overriding action.

The dynamically adjusted delayed action exit after the fault voltage meets the action criterion can not only effectively ensure the quick action of the protection action when a serious fault occurs, but also ensure the reliability of the protection under weak fault conditions.

Description of drawings

Figure 1 is a schematic diagram of a transmission line including a UPFC system;

Fig. 2 is a working flow chart of the embodiment of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings.

method embodiment

The fast-distance protection method for a transmission line containing UPFC in the method embodiment of the present invention is used in the protection of an AC transmission line containing UPFC system access. The transmission line with UPFC system is shown in Figure 1, and the fast distance protection workflow is shown in Figure 2. The method includes the following steps:

(1) The line protection devices on both sides independently collect the voltage and current of each side;

The method of collecting voltage and current on both sides is as follows: for the near UPFC side, the voltage is measured by the line side PT, and the current is measured by the line CT; for the far UPFC side, the voltage can be measured by the line side PT or the bus side PT, and the current is measured by the line CT.

(2) Calculate the maximum equivalent impedance Z _P of UPFC in real time when the starting element of the line protection does not operate, and the starting protection is no longer calculated, and Z _P calculated before starting is used for fault calculation;

The formula of the starting element is: |iqd _[k] |＞1.25|iqd _[k-2N] |+0.1In; where: iqd _k is any phase current on each side; N is the number of sampling points per cycle; In is the CT rated current value .

The formula for calculating the maximum equivalent impedance Z _P of UPFC is: Among them: U _Pmax is the maximum output voltage value of the series transformer of the UPFC system; is the current current.

(3) Real-time calculation of voltage variation and compensation current variation after the activation of the element;

The formula for calculating the voltage change is: in: is the current voltage phasor; is the voltage phasor two weeks ago; For any phase or phase.

The formula for calculating the amount of current change is: in: is the current current phasor; is the current zero-sequence current phasor; is the current current phasor; is the zero-sequence current phasor two weeks ago; For any phase or phase.

(4) Calculate the fault compensation voltage according to the voltage variation and the compensation current variation;

The formula for calculating the voltage change is: in: Impedance setting value for fast distance protection; For any phase or phase.

(5) When the fault voltage meets the action criterion, the delay action outlet is dynamically adjusted.

The action criterion formula is: Among them: U _N is the voltage rating; α is the reliability coefficient, and its value ranges from 0 to 5, generally 0.5; For any phase or phase.

The delay calculation formula for dynamic adjustment is: T _P =(5-α)×20ms; where: α is the reliability coefficient in the action criterion.

In this embodiment, by calculating the maximum equivalent impedance of the UPFC during normal operation, when a fault occurs in the system, the calculation of the fault compensation voltage and the maximum equivalent impedance calculated during normal operation can effectively prevent the protection device from being used near On the UPFC side, when the reverse direction exit fault occurs, the fast distance protection has the risk of malfunction; at the same time, it can also prevent the fast distance protection from overtaking action when the protection device is used on the far UPFC side when a metal fault occurs outside the forward direction. risks of. Furthermore, the dynamically adjusted delayed action exit after the fault voltage meets the action criterion can not only effectively ensure the quickness of the protection action in the event of a serious fault, but also ensure the reliability of the protection in the case of a weak fault.

The main idea of the present invention is to calculate and save the maximum equivalent impedance of UPFC during normal operation. When the system fails and calculates the fault compensation voltage, the maximum equivalent impedance of UPFC is no longer calculated in real time, but the calculation before the fault occurs and Save the maximum equivalent impedance of the UPFC. Therefore, the starting criterion, action criterion, delay calculation formula, voltage and current variation technical formula, compensation voltage formula, etc. involved in the above embodiments, as other implementation modes, other specific formulas in the prior art can be used to replace.

Device embodiment

A transmission line fast distance protection device containing UPFC, including the following modules:

Module (1), the line protection devices on both sides independently collect the voltage and current on each side;

Module (2), used for real-time calculation of the maximum equivalent impedance Z _P of the UPFC when the line protection starting element is not in action;

Module (3), used for real-time calculation of voltage variation and compensation current variation after the activation of the element;

The module (4) is used to calculate the fault compensation voltage according to the voltage variation and the compensation current variation; the maximum equivalent impedance Z _P of the UPFC before the line protection starting element in the module (2) is used for calculation;

The module (5) is used for exiting after a delayed action when the fault voltage satisfies the action criterion.

Each of the above modules is a software function module corresponding to each step in the method embodiment one by one, and the device formed by it is a software function framework, which is stored in the memory of the relay protection device in the form of software code. Since there is a one-to-one correspondence with the steps in the above method embodiments, details are not repeated here.

Under the idea given by the present invention, the technical means in the above-mentioned embodiments are transformed, replaced, and modified in ways that are easy for those skilled in the art, and the functions played are basically the same as those of the corresponding technical means in the present invention. 1. The purpose of the invention realized is also basically the same, and the technical solution formed in this way is formed by fine-tuning the above-mentioned embodiments, and this technical solution still falls within the protection scope of the present invention.

Claims (10)

1. a transmission line fast distance protection method containing UPFC, is characterized in that, comprises the steps: (1) The line protection devices on both sides independently collect the voltage and current of each side; (2) Real-time calculation of the maximum equivalent impedance Z _P of the UPFC when the line protection starting element is not in action; (3) Real-time calculation of voltage variation and compensation current variation after the activation of the element; (4) Calculate the fault compensation voltage according to the voltage variation and the compensation current variation; the UPFC maximum equivalent impedance Z _P before the line protection starting element in the step (2) is used in the calculation; (5) When the fault voltage satisfies the action criterion, the exit will be activated after a delay. 2. the transmission line fast distance protection method that contains UPFC according to claim 1, it is characterized in that: in the described step (1), both sides voltage and electric current quantity acquisition method are: measure line side PT for near UPFC side voltage , the current measurement takes the line CT; for the far UPFC side voltage measurement takes the line side PT or the bus side PT, the current measurement takes the line CT. 3. The transmission line fast distance protection method containing UPFC according to claim 1 or 2, characterized in that: the formula of the starting element in the step (2) is: |iqd _[k] |＞1.25|iqd _{[k -2N} ]|+0.1In; where: iqd _k is any phase current on each side; N is the number of sampling points per cycle; In is the rated current value of CT; the formula for calculating the maximum equivalent impedance Z _P of UPFC is: Among them: U _Pmax is the maximum output voltage value of the series transformer of the UPFC system; is the current current. 4. the transmission line fast distance protection method containing UPFC according to claim 3, is characterized in that: in the described step (3), the voltage variation calculation formula is: in: is the current voltage phasor; is the voltage phasor two weeks ago; It is any phase or between phases; the calculation formula of current variation is: in: is the current current phasor; is the current zero-sequence current phasor; is the current current phasor; is the zero-sequence current phasor two weeks ago; Be any phase or between phases; the formula for calculating the voltage variation in the step (4) is: in: Impedance setting value for fast distance protection; For any phase or phase. 5. the transmission line fast distance protection method containing UPFC according to claim 4, is characterized in that: in the described step (5), the action criterion formula is: Among them: U _N is the voltage rating; α is the reliability coefficient, and its value ranges from 0 to 5, generally 0.5; It is any phase or between phases; the delay is dynamically adjusted in step (5), and the delay calculation formula is: T _P =(5-α)×20ms; where: α is the reliability coefficient in the action criterion. 6. A transmission line fast distance protection device containing UPFC, characterized in that it comprises the following modules: Module (1), the line protection devices on both sides independently collect the voltage and current on each side; Module (2), used for real-time calculation of the maximum equivalent impedance Z _P of the UPFC when the line protection starting element is not in action; Module (3), used for real-time calculation of voltage variation and compensation current variation after the activation of the element; The module (4) is used to calculate the fault compensation voltage according to the voltage variation and the compensation current variation; the maximum equivalent impedance Z _P of the UPFC before the line protection starting element in the module (2) is used for calculation; The module (5) is used for exiting after a delayed action when the fault voltage satisfies the action criterion. 7. The transmission line fast distance protection device containing UPFC according to claim 6, characterized in that: in the module (1), both voltage and current acquisition methods are: measure the line side PT for the near UPFC side voltage , the current measurement takes the line CT; for the far UPFC side voltage measurement takes the line side PT or the bus side PT, the current measurement takes the line CT. 8. The transmission line fast distance protection device containing UPFC according to claim 6 or 7, characterized in that: the formula of the starting element in the module (2) is: |iqd _[k] |>1.25|iqd _{[k -2N} ]|+0.1In; where: iqd _k is any phase current on each side; N is the number of sampling points per cycle; In is the rated current value of CT; the formula for calculating the maximum equivalent impedance Z _P of UPFC is: Among them: U _Pmax is the maximum output voltage value of the series transformer of the UPFC system; is the current current. 9. The transmission line fast distance protection device containing UPFC according to claim 8, characterized in that: in the module (3), the voltage variation calculation formula is: in: is the current voltage phasor; is the voltage phasor two weeks ago; It is any phase or between phases; the calculation formula of current variation is: in: is the current current phasor; is the current zero-sequence current phasor; is the current current phasor; is the zero-sequence current phasor two weeks ago; Be any phase or between phases; the formula for calculating the voltage variation in the module (4) is: in: Impedance setting value for fast distance protection; For any phase or phase. 10. contain UPFC transmission line fast distance protector according to claim 9, it is characterized in that: in the described module (5), the action criterion formula is: Among them: U _N is the voltage rating; α is the reliability coefficient, and its value ranges from 0 to 5, generally 0.5; It is any phase or between phases; the delay is dynamically adjusted in module (5), and the delay calculation formula is: T _P =(5-α)×20ms; where: α is the reliability coefficient in the action criterion.