KR20130131109A - Adaptive protection overcurrent control system and method for responding the change of power system - Google Patents

Abstract

An adaptive protection overcurrent control system and method is provided for a power system that responds to a power system change that can actively respond to a change in state, such as linking a distributed power supply and increasing or decreasing a load. The adaptive protection overcurrent control method corresponding to the power system change may include determining a correction value according to a load current for each time interval based on data on an accident current of the power system before the change; Detecting whether there is a change in the power system; Calculating a new correction value or correction lever value for the changed power system; Detecting whether an accident has occurred in the power system; And identifying a current occurrence position of the accident current when the accident occurs in the power system to perform main protection or post-protection operation.

Description

Adaptive protection overcurrent control system and method for responding the change of power system

The present invention relates to a system and method for protecting an adaptive controlled overcurrent relay, and more particularly, to an adaptive protection corresponding to a change in a power system that can actively respond to a change in a state such as a connection of a distributed power supply and a change in load. An overcurrent control system and method.

As society develops, the demand for stable supply of electricity and the improvement of quality are increasing rapidly as the dependence on electric energy throughout society and the information society are advanced. In addition, since many power generation, substation, and transmission and distribution facilities are intricately connected to each other in the power system, if the protection relay does not separate the fault section from the system quickly in case of a fault, the power facility is not only damaged significantly but also the fault spreads to the adjacent section. As a result, the scope of the accident expands. Therefore, it is absolutely necessary to secure the system and secure stability, and the importance of the protection relay is increasing.

Power systems can often be changed due to section switching and recovery due to faults, inspection of equipment or facilities, and especially in power distribution systems. In the case of such a system change, it is necessary to change the correction value of the protective relay according to the changed system for proper protection.

However, since the correction work is one of very difficult tasks, it is currently made by a correction expert by hand, which makes it practically impossible to respond to frequent system changes in real time.

The general operational task of overcurrent relays (OCRs) is to determine the load current and fault current, cooperate with the surrounding protective relay in the event of a fault and eliminate the fault as soon as possible. The protection method by the overcurrent relay is the most basic method among the protection relay methods of transmission and distribution lines, has a simple and economic advantage. At present, the main protection path is limited to protection of radioactive power distribution lines or internal circuits of substations and is generally used as back protection.

The basic principle of the overcurrent relay is to detect a fault current larger than the load current in case of an accident on the transmission line, and to operate a blocking signal at a time that is inversely proportional to the high current so as to operate quickly at a large fault current. That is, a value larger than the maximum load current and smaller than the minimum fault current is set as a pickup current, which is an operation threshold of the protection relay, and when more current flows in the system, it is determined to be an accident and operates in cooperation with the surrounding protection relay.

Meanwhile, the transition to smart grids and the linkage of distributed power supplies will be further accelerated, resulting in two-way power flow and fault current flow. Therefore, there is a need to establish a protection system different from the protection system used in the existing radial system.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and system for protecting a controlled overcurrent relay capable of responding to a power system change capable of actively responding to a change in a state such as connection of a distributed power source and increase or decrease of a load. .

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

One aspect of the adaptive protection overcurrent control method corresponding to the power system change of the present invention for solving the above problems comprises the steps of determining a correction value according to the load current for each time interval based on the data on the accident current of the power system before the change; Detecting whether there is a change in the power system; Calculating a new correction value or correction lever value for the changed power system; Detecting whether an accident has occurred in the power system; And identifying a current occurrence position of the accident current in the event of an accident in the power system, and performing main protection or post-protection operation.

One aspect of the adaptive protection overcurrent control system corresponding to the power system change of the present invention for solving the above problems is a power system change detection unit for detecting whether there is a change in the power system; A parameter calculator configured to determine a correction value or a correction lever value according to a load current for each time interval, based on data on an accident current of the power system before and after the change; An accident detection unit detecting whether an accident has occurred in the power system; And a protection operation controller configured to determine a location of an accident current when an accident occurs in the power system to control main protection or post-protection operation.

Other specific details of the invention are included in the detailed description and drawings.

According to the adaptive protection over-current control system and method corresponding to the power system change according to the embodiments of the present invention, it is possible to actively respond to the state change, such as the connection of the distributed power supply and the increase or decrease of the load for the power system.

Furthermore, the time required for calculating the operating parameters of the overcurrent relay, such as the correction value and the correction lever value, can be shortened.

1 is a flowchart of an adaptive protection overcurrent control method corresponding to a power system change according to an exemplary embodiment of the present invention.
2 is a schematic diagram showing the application of an overcurrent relay to a radial distributed system.
3 is a schematic diagram showing an increase in the fault current according to the distributed power supply and the resulting power flow.
4 is a graph illustrating a protection cooperation time interval between main protection and hobby protection when distributed power is connected.
5 is a flowchart illustrating an adaptive protection overcurrent control method corresponding to a power system change according to an embodiment of the present invention in more detail.
6 is a block diagram of an adaptive protection overcurrent control system corresponding to a power system change according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. It is noted that the terms "comprises" and / or "comprising" used in the specification are intended to be inclusive in a manner similar to the components, steps, operations, and / Or additions.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used in a sense that can be commonly understood by those skilled in the art. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

1 is a flowchart of an adaptive protection overcurrent control method corresponding to a power system change according to an exemplary embodiment of the present invention.

First, referring to FIG. 1, an adaptive protection overcurrent control method corresponding to a power system change according to embodiments of the present invention may include a correction value according to a load current for each time interval based on data on an accident current of a power system before change. Determining (S101), detecting whether there is a change in the power system (S103); Calculating a new correction value or a correction lever value for the changed power system (S105); Detecting whether an accident has occurred in the power system (S107); And identifying a current occurrence location of the accident current when the accident occurs in the power system to perform main protection or post-protection operation (S109).

In order to describe an adaptive protection overcurrent control method corresponding to a change in power system according to an embodiment of the present invention, a radial distributed system and an effect when a distributed power source is connected to the system will be described.

As mentioned earlier, the use of distributed generation (DG) is increasing due to the growing interest in renewable energy. If fixed parameters are used, changes in the radial distribution system occur. Can not guarantee proper operation. This is because the preset protection coordination between the overcurrent relays is affected by the increased fault current due to the distributed power supply.

In the embodiments of the present invention, an adaptive protection scheme based on a digital protection relay is used to solve this problem. The digital protection relay is equipped with a microcontroller and a memory to store data about an accident in real time, It is assumed that it can be programmed. Furthermore, it is possible to exchange data or operational signals between each digital protective relay and also with higher-level systems such as supervisory control and data acquisition (SCADA) systems, which eventually leads to changes in distributed systems. It is assumed that the operating parameters can be adjusted correspondingly.

In the present invention, there are representative parameters to be adjusted by the system, ipick-up (pick-up current) and correction lever value (TDS, time dial setting).

The overcurrent relay monitors the magnitude of the fault current, and if the fault current exceeds a preset setpoint, it will send a trip signal to begin performing the protective action. The inverse time current characteristic is expressed by the following [Formula 1] and [Formula 2].

[Formula 1]

[Formula 2]

Where T0 is the operating time, I is the fault current sensed by the overcurrent relay, and TDS is the correction lever value as already described, which will be described in more detail below. M is the ratio of the fault current to the correction value and is expressed as I / Ipick-up. A, B, and p are values representing various types of overcurrent relays, respectively, and are constant values already defined in the IEEE standard.

As can be seen in equations (1) and (2), the trip time t is a function of the fault current I, integrated from 0 to T0, at which time the overcurrent relay starts to operate.

2 is a schematic diagram showing the application of an overcurrent relay to a radial distributed system.

As can be seen in Figure 2, in most cases the overcurrent relay is installed in a radial distributed system. Since current flows in only one direction downward from the substation, the overcurrent relay is connected to the radial line directly behind the associated bus. One overcurrent relay is used in one protection zone, but two different overcurrent relays may be required if bidirectional flow of fault current is considered. On the other hand, the one-way incident current flowing downwards passes through a current transformer (CT) located between the distributed line and the overcurrent relay, which is then measured by the CT, which is then passed to the overcurrent relay to determine the operating time. do.

In Fig. 2, the main protection region and the posterior protection region for OCR-1 and OCR-2 are shown. In order to isolate the area where the accident occurred, the relays in the protection area will operate preferentially based on the location where the accident occurred, and the relevant back protection relays will operate only if the relays in charge of the main protection fail. For example, if an accident occurs at any point between bus 2 and bus 3 in FIG. 2, OCR-2 operates to assume the main protection function to minimize the leakage area. If the OCR-2 does not function properly, the OCR-1 acts as a back-off protection to cut off the fault current. Furthermore, it is essential to maintain an appropriate time interval between main and post protection, which is called a coordination time interval (CTI), typically about 0.2 to 0.5 seconds. These CTIs need to be applied to all protection devices such as reclosers and fuses as well as relays in distributed distribution systems. The related equation is as follows.

[Equation 3]

Here, tprimary means the main protection operation time, and tback-up means the operation time of the rear guard.

On the other hand, when the distributed power supply is connected to the power system, the amount of accident current may be increased, and the direction of power flow may be reversed, which will be described with reference to FIG. 3.

3 is a schematic diagram showing an increase in the fault current according to the distributed power supply and the resulting power flow.

In FIG. 3, the distributed current DG is connected to the bus 2, indicating that the fault current flow is changed. That is, the fault current flows in the reverse direction from the point where the distributed power source is located to the fault occurrence point F1, which is added to the fault current flowing from the substation. This results in increased fault currents compared to the absence of distributed power supplies. Furthermore, if an accident occurs at the F2 point, the distributed current will increase the amount of fault current, although there is no reverse flow of the fault current. If the fault current occurs at F3 on the proximity feeder, the current from the distributed supply flows in the reverse direction to F3, so the magnitude of the current sensed by the OCR-n is also greater. Thus, OCR-n will not function properly if the operating parameters are not changed properly.

As a result, an increase in the fault current adversely affects the operation of the relays in a distributed system. As in equations (1) and (2), the relays have inverse-time current characteristics, so that the operating time decreases with increasing degree of accident current. In other words, the greater the fault current, the faster the relay operates. However, if the relay runs too fast, it may unnecessarily shut down a wide range of systems.

4 is a graph illustrating a protection cooperation time interval between main protection and hobby protection when distributed power is connected.

In the case of protective coordination, if the incident current is increased, it may be difficult for the relay in charge of the main protection to cooperate with the relay in the rear protection, since the required coordination time is reduced. If the fault current increases above the value specified by the main protective relay, it may not cooperate with the back-hobo relay, which will lead to a malfunction. Therefore, the operating parameters of the relays must be properly adjusted for various accident situations with the ability to sense the direction in which the current will flow.

However, when multiple distributed power supplies are connected to a distributed system, it is difficult to optimize the order of operation of all protection devices while maintaining protection coordination. In particular, as the number of overcurrent relays increases, the computation time required to determine their operating parameters also increases. Accordingly, the present invention provides an adaptive protection method for efficiently reducing the time required for calculation.

First, the Ipick-up of the overcurrent relay is periodically calculated from the load current. The correction value will have a different value each time the configuration of the system changes. For each time interval, the load current calculated after a fixed time from the start time point is used to calculate the correction value. The time delay to stabilize the distributed system is necessary to select a stable load current in response to the connection of the distributed power supply. The correction value is set as 1.5 times the load current, as shown in [Equation 4], to give a safety margin.

[Formula 4]

In this case, IL│N means a load current calculated after a fixed period from the start of the Nth time interval. Thus, a correction can be obtained with the load current, which reflects the state of the system. On the other hand, the length of the time interval should be set appropriately so as not to calculate the correction value too often. After an additional time delay, the correction is used to determine the operating parameters of the overcurrent relay. This time delay is necessary to allow the overcurrent relay to operate with previously determined parameters in the event of an IL | N being obtained at a specific point. In other words, if such a fault current is used as a correction of the overcurrent relay, it is too large to properly separate the fault occurrence area from the distributed system. Furthermore, this waiting period provides a time margin to calculate a new correction lever value, which will be described below.

As already explained, the overcurrent relay has two important operating parameters: Ipick-up and Correction Lever Value (TDS). The correction value is calculated first through [Equation 4], and then a new correction lever value, TDSnew, is calculated via [Equation 5] to maintain the original operating time and CTI regardless of system state change. In other words, according to the overcurrent relay characteristic in [Equation 2], a new correction lever value is determined to operate the overcurrent relay similarly at a predetermined operating time.

[Formula 5]

Where A, B and p are the relevant constants of the overcurrent relay, M 'is the I / Ipick-up for the current time interval, and M' is the previous time if the correction and the fault current have changed according to the system state. It is different from M determined in the interval. The relationship between these two values is shown in [Equation 6].

[Formula 6]

In Equation 5, A, B, and p are values that remain constant even when the state of the system changes, and M can be known from the fault current stored in the memory of the overcurrent relay. Thus, M 'is easily calculated by sending it to the overcurrent relay via the communication link. After all, it is possible to get TDSnew quickly because we already know all the values in [Equation 5]. In addition, the TDS can be more easily obtained in the case of a change in load and a change in overcurrent relay characteristics. In summary, when the load is changed, it is unnecessary to update the fault current data because there is no actual change in the value. On the other hand, the correction value is replaced with a new value as the load current changes. Therefore, only M is changed to M ', and TDSnew is obtained using [Equation 5].

In addition, if only the characteristics of the overcurrent relay are changed, TDSnew is calculated by [Equation 7]. In this case, M for the previous time interval is equal to M 'for the current time interval because neither the correction nor the fault current changes.

[Equation 7]

Where (A ₁ , B ₁ , p ₁ ) and (A ₂ , B ₂ , p ₂ ) are constants for the previously and newly selected properties, respectively. After the correction value and the correction lever value are newly calculated, these operating parameters are immediately applied to the overcurrent relay.

FIG. 5 is a flowchart illustrating the adaptive protection overcurrent control method corresponding to the power system change according to an embodiment of the present invention in more detail.

In the step S110 determines the initial correction value according to the load current for each time interval based on the data on the accident current of the power system before the change. As can be seen from S111, the correction value, correction lever value and fault current data of the previous section are already stored in the memory of the digital protection relay. Based on this, the initial correction value is determined as already described in [Equation 4] and related parts (S113). Then, this is maintained as a correction value for a predetermined delay time (S115).

In step S130, it is determined whether there is a change in the power system (S131), and if there is a change, what kind of change is made (S133 to S137). Herein, the change of the power system may include a first change (S133) in which a load on the power system is changed, a second change including any one of adding a distributed power source to the power system or removing a distributed power source from the power system ( S135) and a third change S137 in which the characteristics of the overcurrent controller itself are changed.

In each case, a new correction value or a new correction lever value for the changed power system is determined through slightly different equations or processes (S150).

When the load is changed (S133), each new correction lever value TDSnew for main protection and rear protection is calculated through [Equation 5] (S161), and the correction value and TDSnew obtained based on this are calculated after the delay time. Applies to (S163).

When the distributed power supply is connected and removed (S135), the changed fault current is analyzed (S151), and the result is transmitted to the overcurrent controller (S153). Thereafter, similarly, each new correction lever value TDSnew and a correction value Ipick-up for the main protection and the rear protection are obtained, and these parameters are applied after the delay time (S163).

When the characteristics of the overcurrent relay are changed (S155), the constant values for the various characteristics are transferred and stored to the digital protection relay (S155), and each new value for the main protection and the rear protection by using [Equation 7] is used. The correction lever value TDSnew is calculated (S157), and the correction value and TDSnew obtained based on this are applied after the delay time (S163).

If it is detected that there is no change in the power system (No in S131), and if the time interval is first (Yes in S159), each new correction lever value (TDSnew) and correction value (Ipick) for main protection and pick protection. -up), these parameters are applied after the delay time (S163), otherwise (No in S159) the operation parameters are kept the same as the parameters of the previous time interval (S165).

Next, in steps S170 and S190, whether the accident occurred in the power system to perform a protection operation, if the accident occurs (Yes of S171) to check the accident point (S191) to the main operation mode A protection operation mode or a dobby protection operation mode is determined (S193, S195, S197). If no accident occurs (No in S171), the process proceeds to the next section (S199).

6 is a block diagram of an adaptive protection overcurrent control system corresponding to a power system change according to an embodiment of the present invention.

Referring to FIG. 6, an adaptive protection overcurrent control system corresponding to a power system change according to an embodiment of the present invention includes a power system change detector 610, a parameter calculator 620, an accident detector 630, and The protection operation control unit S640 is included.

The parameter calculator 620 determines a correction value or a correction lever value according to the load current for each time period, based on the data on the accident current of the power system before and after the change. The process described in FIG. 1 is involved in steps S110 and S150.

The parameter calculator 620 detects whether there is a change in the power system, and the accident detector 630 detects whether an accident has occurred in the power system.

The protection operation control unit S640 detects an accident current generation position when an accident occurs in the power system and applies the parameters determined by the parameter calculation unit 620 to control the main protection or post protection protection operation.

The functions of the respective components constituting the adaptive protection overcurrent control system corresponding to the power system change according to an embodiment of the present invention can be understood through FIGS. 1 to 5 and corresponding descriptions, in order to avoid repetition. Detailed description will be omitted.

Each component of FIG. 6 may refer to software or hardware such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). However, the components are not limited to software or hardware, and may be configured to be in an addressable storage medium and configured to execute one or more processors. The functions provided in the components may be implemented by a more detailed component or may be implemented by a single component that performs a specific function by combining a plurality of components.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

610: power system change detection unit
620: parameter calculator
630: accident detection unit
640: protection operation control unit

Claims (10)

Determining a correction value according to the load current for each time period based on data on an accident current of the power system before the change;
Detecting whether there is a change in the power system;
Calculating a new correction value or correction lever value for the changed power system;
Detecting whether an accident has occurred in the power system; And
Adaptive protection over-current control method corresponding to the power system change comprising the step of performing the main protection or after-protection operation by identifying the location of the accident current generation when the accident occurs in the power system. The method of claim 1,
The change of the power system,
A second change including any one of a first change in which the load on the power system is changed, an addition of distributed power supply to the power system, or removal of distributed power supply from the power system, and a characteristic of the overcurrent controller itself is changed Adaptive protection overcurrent control method corresponding to a power system change comprising at least one of the third modifications. 3. The method of claim 2,
Adaptive protection overcurrent control method corresponding to a power system change that changes the correction value only in the case of the first change and the second change. 3. The method of claim 2,
The adaptive protection over-current control method corresponding to the power system change to update the accident current data only in the case of the second change. The method of claim 1,
And the correction lever value corresponds to a power system change including a correction lever value for the main protection and a correction lever value for the rear protection. A power system change detection unit detecting whether there is a change in the power system;
A parameter calculator configured to determine a correction value or a correction lever value according to a load current for each time interval, based on data on an accident current of the power system before and after the change;
An accident detection unit detecting whether an accident has occurred in the power system; And
Adaptive protection over-current control system corresponding to the power system change including a protection operation control unit for controlling the main protection or after-protection operation by identifying the location of the accident current generation when the accident occurs in the power system. The method according to claim 6,
The change of the power system,
A second change including any one of a first change in which the load on the power system is changed, an addition of distributed power supply to the power system, or removal of distributed power supply from the power system, and a characteristic of the overcurrent controller itself is changed Adaptive protection overcurrent control system corresponding to a power system change including at least one of the third modifications. The method of claim 7, wherein
Adaptive protection overcurrent control system corresponding to a power system change that changes the correction value only in the case of the first change and the second change. The method of claim 7, wherein
Adaptive protection over-current control system corresponding to the power system change to update the accident current data only in the case of the second change. The method according to claim 6,
And the correction lever value corresponds to a power system change including a correction lever value for the main protection and a correction lever value for the rear protection.

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