JP2533186B2 - Excitation current judgment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exciting inrush current determination method for recognizing an exciting inrush current when an exciting inrush current is generated and preventing malfunction of a distance relay due to impedance calculation of a system. .

[Conventional technology]

Today, as the scale of a power system expands, the frequencies of harmonic components contained in the current amount I and the voltage amount V at the time of a system fault are becoming lower and increasing. This so-called low-order harmonic is generated according to the differential equation of the following equation (1), and by solving the following equation (1), the impedance of the system is calculated and the distance is calculated. Has been put to practical use.

V = R · I + L · J (1) where R = resistance to the fault point of the system L = inductance to the fault point of the system J = differential term of the current For example, in the core of the main transformer When a voltage is applied with the residual magnetic flux remaining above a certain amount, an exciting inrush current is generated in the system. When such an exciting inrush current of the transformer appears in the system, this current does not satisfy the equation (1), and thus this type of distance relay cannot perform appropriate impedance calculation. Not only that, it may lead to malfunction of the relay. As described above, when there is a fear that the relay malfunctions due to the occurrence of the exciting inrush current, it is required to detect the exciting inrush current and forcibly lock the relay operation.

Therefore, an example of the impedance that the relay can detect when the exciting inrush current is generated is as shown in FIG. In this case, as is clear from FIG. 5, the locus of impedance over time shows the characteristic of looping with the fundamental frequency of the system as the cycle.

However, in the conventional detection of the exciting inrush current, the periodicity of such impedance change is utilized, and one cycle time of the fundamental frequency component is monitored for the inductance change amount by the following equation (2), and the following equation ( When the condition 2) is met even once, a system that locks the relay that may malfunction due to the exciting inrush current is used.

| Lm−Ln | δ? (2) (δ: constant) FIG. 6 shows an example of a flow having the functions of detecting the exciting inrush current and locking the relay described above. That is, in FIG. 6, reference numeral 10 is an impedance calculation output unit, 12 is a distance relay operation region determination unit, 14 is an inductance change amount calculation unit, 16 is a NAND gate, and 18 is an ON delay timer for setting the one cycle time. , 20 and 22 are OFF delay timers, and 24 is an AND gate.

In the equation (2), m, n accompanying the inductance amount L means that the inductance amount L is at the time t = m, n, and n is 1/2 of the fundamental frequency component from m.
It means the data of the time before the cycle. Therefore, the time-dependent characteristics of the amount of change in inductance (| Lm-Ln |) when the above equation (2) is applied to the impedance shown in FIG. 5 are compared with the amount of voltage and the amount of current (inrush current) in the system. The relationship is as shown in FIG.

[Problems to be Solved by the Invention]

However, according to the excitation inrush current determination method as shown in the equation (2) and FIG. 6 described above, when an ordinary accident occurs in the system, it is possible to detect the transient change of the inductance immediately after the occurrence of the accident. Is determined to be an exciting inrush current, and the operation of the relay is temporarily locked, which causes a delay in the operation of the relay.

That is, FIG. 8 shows the locus of impedance that can be detected by the relay when an accident occurs in the system. Therefore, when the equation (2) is applied to the impedance shown in FIG. 8, the amount of change in inductance (| Lm
The change characteristics of −Ln |) with time in relation to the voltage amount and the current amount of the system are shown in FIG. Therefore, as is apparent from FIG. 9, the value on the left side of the equation (2) changes twice in one cycle time, which causes a malfunction of the relay or a delay in the operation of the relay.

Therefore, an object of the present invention is to provide an exciting inrush current determination method capable of improving a delay in relay operation by clearly distinguishing a transient change in inductance due to occurrence of a system fault and a change in inductance due to exciting inrush current. To provide.

[Means for solving the problem]

The exciting inrush current determination method according to the present invention, when the exciting inrush current occurs in the system, continuously calculates the impedance based on the voltage amount and the current amount of each phase of the system, and thereby the cycle time equal to the fundamental frequency of the system. In the excitation inrush current determination method for determining the generation of the excitation inrush current by obtaining the impedance locus that changes with the impedance and detecting the continuous change of the inductance from the impedance, the continuous change of the inductance is calculated at two different times t = m. , It is detected as the change amount of n (| Lm | − | Ln |), and when this detected value exceeds a certain level, there is a risk of malfunction when the inrush current of the excitation occurs.An output that locks the relay operation is generated. It is characterized in that it is configured.

[Action]

According to the exciting inrush current determination method according to the present invention, when the exciting inrush current occurs in the system, based on the voltage amount and current amount of each phase of the system, for example, the impedance calculation method by the distance measurement method based on the differential equation, etc. Impedance calculation is performed using this, and by continuously performing this, an impedance locus that changes with a cycle time equal to the fundamental frequency of the system can be obtained. Therefore, by detecting the continuous change of the inductance from this impedance as the change amount (| Lm | − | Ln |) at two different times t = m, n, when this detected value exceeds a certain level, the excitation is performed. There is a risk of malfunction when an inrush current occurs. Judgment is performed to generate an output that locks the relay operation.

〔Example〕

Next, an embodiment of an exciting inrush current determination method according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a flow having a function of detecting an exciting inrush current and locking a relay for implementing an exciting inrush current determination method according to the present invention, and FIG. 2 shows a function of the flow shown in FIG. An example of the hardware configuration of a digital protective relay in which is incorporated is shown. In addition, in FIG.
The same components as those in the flow having the function of detecting the excitation current applied and locking the relay shown in FIG. 6 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, in the present invention, the impedance calculation output section 10 is based on the impedance calculation formula shown by the above formula (1) and the resistance component R up to the fault point of the system and the inductance component L up to the fault point of the system. To calculate. Next, the calculated resistance R and inductance L are calculated.
Therefore, the distance relay operation area determination unit 12 and the inductance change amount calculation unit 14 perform predetermined determination and calculation. In this case, the amount of change in inductance is calculated by the following equation (3).

| Lm | − | Ln |> δ? … (3) (δ: constant) Regarding the inductance change amount calculated by the equation (3), one cycle time of the fundamental frequency component is monitored in the same manner as in the case shown in FIG. When the above formula (3) is satisfied even once, the relay which may malfunction due to the exciting inrush current is configured to be locked.

In FIG. 2, the digital protective relay 30 to which the flow having the function of detecting the exciting inrush current and locking the relay shown in FIG. 1 is applied is an input transformer 32, an analog filter 34, an A / D converter. 36, relay arithmetic processing unit 3
8. Detecting the current amount I and the voltage amount V in each phase of the system (transmission line) for the input transformer 32, which are configured by the operation output processing unit 40, and input these, and the operation output processing unit 40 obtains them. It is configured to output a trip command, etc.

Therefore, in the present invention, the temporal change characteristics of the amount of change in inductance (| Lm | − | Ln |) when the equation (3) is applied to the impedance shown in FIG. The relationship with the inrush current) is shown in FIG.

However, when an accident occurs in the system without any accident, the inductance changes from a large value to a small value. At this time, the left side of the equation (3) has a negative value, and the equation (3) does not hold. That is, when an accident occurs,
The relay does not judge that an exciting inrush current has occurred and does not lock the relay operation. Also, when a small inductance L value is already taken in a fault-free state, such as in a system with a large load near the installation point of the relay, a filter added to the current input and voltage input of the relay will cause the failure immediately after the occurrence of the accident. The inductance L value may transiently increase, but in this case as well, the inductance L value shifts to decrease at an early time, so the determination of the occurrence of the inrush current is canceled at an early time. That is, the above formula (3)
If the variation of inductance (| Lm | − | Ln |) with time is applied to the impedance shown in FIG. 8 in relation to the voltage and current of the system,
As shown, it will be appreciated that this has a shorter cycle time than the conventional scheme shown in FIG.

On the other hand, when the exciting inrush current is generated, the value on the left side of the equation (3) with respect to the impedance locus as shown in FIG. 5 is as shown in FIG. 3, and there is a time when the equation (3) is satisfied. Therefore, this time point is detected and it is determined that the exciting inrush current is generated, and the relay operation is locked according to the flow shown in FIG.

〔The invention's effect〕

As is clear from the above-described embodiments, according to the present invention, in the main transformer, when a voltage is applied in a state where the residual magnetic flux remains in the iron core in a certain amount or more, etc. Phase voltage V and current I
Then, the voltage amount V and the current amount I thus obtained are used to perform impedance calculation using, for example, an impedance calculation method based on a distance measurement method based on a differential equation. An impedance locus that changes with a cycle time equal to the fundamental frequency is obtained, and with this impedance, a continuous change of the inductance is detected as the change amount (| Lm | − | Ln |) between two different times t = m, n. When this value exceeds a certain value, it is possible to lock the operation output of a relay, such as a digital protection type electric appliance, which has a risk of malfunction when an inrush current for excitation is generated.

As described above, according to the present invention, it is possible to prevent malfunction of the relay due to the occurrence of the exciting inrush current, and to appropriately and surely improve the delay of the operating time of the relay due to the determination of the exciting inrush current when an accident occurs. it can.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various design changes can be made without departing from the spirit of the present invention. is there.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a flow having a function of detecting an exciting inrush current and locking a relay for implementing the exciting inrush current judging method according to the present invention, and FIG. 2 shows an exciting inrush current judging method according to the present invention. FIG. 3 is a block circuit diagram showing an example of the hardware configuration of the applicable digital protective relay, and FIG. 3 shows the current amount and the voltage amount based on the change amount of the impedance with time that can be detected by the distance relay when the system inrush current is generated. FIG. 4 is a waveform diagram showing the characteristic of the inductance change amount according to the invention method, and FIG. 4 is a current amount and voltage amount based on the change amount of the impedance with time that can be detected by the distance relay when a system fault occurs, and the inductance change amount according to the present invention method. Fig. 5 is a waveform diagram showing the characteristics. Fig. 5 shows the time-dependent variation of the impedance that can be detected by the distance relay when the system's exciting inrush current occurs 6 is a graph showing a locus of the amount, FIG. 6 is an explanatory diagram showing a flow having a function of detecting the exciting inrush current and locking the relay, which implements the conventional exciting inrush current determination method, and FIG. 7 is an exciting inrush current of the system Fig. 8 is a waveform diagram showing the characteristics of the amount of current and voltage based on the amount of change in impedance that can be detected by the distance relay at the time of occurrence, and the amount of change in inductance according to the conventional method in Fig. 6. Fig. 8 is the distance in the event of a system fault. Fig. 6 is a graph showing the locus of the change in impedance with time that can be detected by the relay, Fig. 9 is the amount of current and voltage based on the amount of change in impedance with time that can be detected by the distance relay, and Fig. 6 FIG. 6 is a waveform diagram showing the characteristic of the amount of change in inductance according to the conventional method of FIG. 10 …… Impedance calculation output section 12 …… Distance relay operation area judgment section 14 …… Inductance change amount calculation section 16 …… NAND gate 18 …… ON delay timer 20,22 …… OFF delay timer 24 …… AND gate 30… … Digital protective relay 32 …… Input transformer 34 …… Analog filter 36 …… A / D converter 38 …… Relay calculation processor 40 …… Operation output processor

Claims (1)

(57) [Claims] 1. When an exciting inrush current is generated in a system, impedance is continuously calculated based on the voltage amount and current amount of each phase of the system, and an impedance locus that changes with a cycle time equal to the fundamental frequency of the system is thereby obtained. In the exciting inrush current determination method for determining the occurrence of the exciting inrush current by finding the continuous change of the inductance from this impedance, the continuous change of the inductance is detected at two different times t.
Detected as the amount of change in m = n (| Lm | − | Ln |), and when this detected value exceeds a certain level, there is a risk of malfunction when an inrush current is generated. An output that locks the relay operation is generated. An inrush current determination method characterized by being configured as described above.