JPH053207B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for detecting a disconnection accident in an electric line, and in particular, the present invention relates to a method for detecting a disconnection accident in an electric line, and in particular, the present invention relates to a method for detecting a disconnection accident in an electric line, and in particular, the present invention relates to a method for detecting a disconnection accident in an electric line. The present invention relates to a method for detecting wire breaks that can be detected well.

[Prior art]

JP-A-59-222032 discloses a method for detecting a wire breakage in a three-phase electric line on the power supply side of a substation. In other words, the current change vector when the three-phase load is opened, and the current change vector when the motor load is beyond the disconnection point.
This was done by focusing on the fact that the direction of the phase order is opposite to the current change vector when the wire is disconnected.The line current of three phases is detected at the power supply end, and the current change vector and the phase order are reversed. When the change vector is determined, it is determined that a one-line disconnection has occurred.

Figure 3 shows the state of the current vector when one wire is disconnected (A phase disconnection) in the electric line where the motor is loaded. In the figure, I〓a, I〓b, and I〓c are respectively The line current vectors of the A phase, B phase, and C phase are shown. If the A-phase line is disconnected, the A-phase line current I〓a′ after the accident becomes zero, so
The current change vectors ΔI〓a′, ΔI〓b′, and ΔI〓c′ of the A phase to C phase are as shown in the figure, and the current vectors I〓b′ and I〓c′ becomes as shown. If only the current change vectors ΔI〓a' to ΔI〓c' when one wire breakage occurs from FIG. 3 are extracted and illustrated, the result will be as shown in FIG. 4. On the other hand, the current change vector ΔI〓a ~ ΔI〓c when the three-phase load is opened is as shown in Figure 5, and the current change vector ΔI〓a′ ~
The direction of the phase order is opposite to ΔI〓c′. From this,
It can be seen that one wire breakage can be detected by determining the direction of the phase sequence of the current change vector.

[Problem that the invention seeks to solve]

For example, when a load change occurs such as AB phase single-phase load application and BC phase single-phase load release at the same time, the current vector detected at the substation will look the same as when one wire is disconnected. Therefore, a current change vector in the reverse order may be obtained, and a disconnection may be erroneously detected during the above-mentioned load fluctuation.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention adds means for detecting changes in zero-sequence voltage _.
When the zero-sequence voltage changes to V〓o ₂ , the magnitude of the zero-sequence voltage change vector ΔV〓o exceeds a certain value, and
It is determined that a single wire breakage accident has occurred when a current change vector in the reverse order is determined based on the conventional wire breakage detection method.

[Effect]

In addition to finding the current change vector in the reverse order based on the conventional disconnection detection method, the zero-sequence voltage that occurs when the wire is disconnected is larger than the zero-sequence voltage that occurs when the wire is healthy, so the change at that time By adding the minute as one of the disconnection detection elements,
It is possible to distinguish between 1-wire disconnection and 3-phase load opening on the power supply side, and for example, it is possible to distinguish between AB phase single-phase load application and BC phase load opening.
When a load change occurs in which a single-phase load release occurs at the same time, it is no longer erroneously determined that a single wire is disconnected, so the accuracy of detecting a single wire disconnection can be improved.

〔Example〕

FIG. 1 is a block diagram showing an example of the configuration of a detection device for carrying out the disconnection detection method of the present invention. In the figure, 1a to 1c indicate A-phase to C-phase electric lines. Current transformers 2a to 2c are attached to the power supply ends of the electric lines 1a to 1c, respectively, and signals indicating the A-phase to C-phase line electric lines I〓a to I〓c are obtained at the output sides of these current transformers, respectively. It will be done. These signals are converted into voltage signals by current-voltage converters (I/V converters) 3a-3c, and then input into storage devices 4a-4c. The storage devices 4a to 4c read out signals indicating the stored A-phase to C-phase line currents I〓a to I〓c after a minute time Δt. The information read from the storage devices 4a to 4c is input to the subtracters 5a to 5c together with the current values of current information obtained from the I/V converters 3a to 3c. Therefore, on the output side of the subtractors 5a to 5c, the minute time of the signal indicating the line current I〓a to I〓c of the A phase to C phase, respectively, is the current change vector ΔI〓a~ per Δt.
A signal indicating ΔI〓c is obtained. For example, when signals indicating current change vectors ΔI〓a and ΔI〓b of A phase and B phase are input to the phase comparator 6, and ΔI〓b is leading with respect to ΔI〓a, that is, the current change vector is As shown in FIG. 4, when the order is reversed, a signal with a logical value of "1" is obtained from the phase comparator 6. The current change vectors ΔI〓a, ΔI〓b and ΔI〓c
The signals indicating
c, the absolute values of the current change vectors ΔI〓a to ΔI〓c are compared with a constant level K, and when the absolute values of the current change vectors ΔI〓a to ΔI〓c are larger than the constant level K, the logical value becomes " 1” signal is output. The outputs of these level detectors 9a to 9c are input to an AND circuit 10, which outputs a logical value of "1" when the three-phase current change vectors ΔI〓a to ΔI〓c are all greater than a certain level. ” output.

A grounding transformer 11 is also connected to the electric lines 1a to 1c, and the zero-sequence voltage V〓o obtained from this transformer 11 is input to the storage device 12, and the storage device 12 stores the stored zero-sequence voltage V 〓Read out the information of o after a minute time. The information read from the storage device 12 is input to the subtracter 13 together with the current value of zero-sequence voltage information obtained by the grounding transformer 11. Therefore, on the output side of the subtracter 13, a zero-phase voltage change vector ΔV〓o per minute time Δt of the zero-phase voltage is obtained. The signal indicating this zero-phase voltage change vector ΔV〓o is compared with a level L at which the absolute value of the zero-phase voltage change vector ΔV〓o is constant by the level detector 14, and the absolute value of the zero-phase voltage change vector ΔV〓o When is greater than a certain level L, a signal with a logical value of "1" is output.

The output of the phase comparator 6, the output of the AND circuit 10, and the output of the level detector 14 are input to the AND circuit 15, and the current change vectors are in the reverse order as shown in FIG. A disconnection detection signal indicating that a one-wire disconnection accident has occurred from the AND circuit 15 when all the changes are above a certain size and the zero-phase voltage change is above a certain size.
e _s is output. Note that the constant level L can be varied depending on the distance from the substation to the disconnection location so that disconnection at any location can be detected.

Furthermore, the above detection method can also be implemented using a computer. FIG. 2 is a flowchart showing the procedure for implementing the disconnection detection method of the present invention using a computer. When implementing the detection method of the present invention according to this flowchart, first, the magnitudes of the A-phase to C-phase line currents Ia ₁ to Ic ₁ at time t ₁ and the respective phases φa ₁ to φc ₁ and The magnitude of the zero-sequence voltage Vo ₁ and its phase φo ₁ are read into the storage device. Next, the magnitude of the line current at time t ₂ delayed by a minute time Δt from time t ₁
Read Ia ₂ to Ic ₂ , their respective phases φa ₂ to φc ₂ , the magnitude of the zero-sequence voltage Vo ₂ , and their phase φo ₂ . Next, the above Ia ₁ ~ Ic ₁ , φa ₁ ~ φc ₁ , Vo ₁ , φo ₁ , Ia ₂ ~ Ic ₂ ,
ΔIa, ΔIb, ΔIc, ΔVo, θa, and θb are calculated from Vo ₂ and φo ₂ using the following equations (1) to (6).

ΔIa={Ia ₁ ² +Ia ₂ ² −2Ia ₁・Ia ₂ cos(φa ₁ −φa ₂ )} ^1/2 …(1) ΔIb={Ib ₁ ² +Ib ₂ ² −2Ib ₁・Ib ₂ cos(φb ₁ −φb ₂ )} ^1/2 …(2) ΔIc={Ic ₁ ² +Ic ₂ ² −2Ic ₁・Ic ₂ cos(φc ₁ −φc ₂ )} ^1/2 …(3) ΔVo={Vo ₁ ² +Vo ₂ ² −2Vo ₁・Vo ₂ cos(φo ₁ −φo ₂ )} ^1/2 …(4) θa＝tan ⁻¹ {(Ia ₂ sinφa ₂ −Ia ₁ sinφa ₁ )/(Ia ₂ cosφa ₂ −Ia ₁ cosφa ₁ )} ^1/2 …(5) θb＝tan ^-1 {(Ib ₂ sinφb ₂ −Ib ₁ sinφb ₁ )／(Ib ₂ cosφb ₂ −Ib ₁ cosφb ₁ )} ^1/2 …(6) Like this It is determined whether or not θb is ahead of θa by comparing θa obtained in the above manner with θa. As a result of this determination, if θb is ahead of θa, it is further determined whether ΔIa, ΔIb, and ΔIc are all greater than a constant value K, and if they are, it is further determined whether ΔVo is greater than a constant value L. A disconnection detection signal is output when ΔIa to ΔIc are all greater than or equal to K and when ΔVo is greater than or equal to L. If θb lags behind θa, ΔIa,
If at least one of ΔIb and ΔIc is smaller than K or ΔVo is smaller than L, the time t ₂ is set as a new time t ₁ , and the magnitude of the current Ia ₂ to Ic ₂ at the time _{t 2} and each The phase φa ₂ ~ φc ₂ and the magnitude Vo ₂ of the zero-sequence voltage and its phase φo ₂ are respectively Ia ₁ ~ Ic ₁ , φa ₁ ~ φc ₁ at the new time t ₁ ,
Store them as Vo ₁ and φo ₁ and repeat the above process.

〔Effect of the invention〕

By adding the change in zero-phase voltage that occurs when a wire breaks as one of the wire break detection elements, the power supply can be detected without being confused with a single wire break, especially when a motor is included in the load on the load side from the break point. For example, AB phase single phase load input and
When load fluctuations occur at the same time as single-phase load opening in the BC phase, it is no longer mistakenly determined as a single-wire disconnection, which improves the accuracy of detecting single-wire disconnections, which is of great practical benefit. It is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus for implementing the wire breakage detection method of the present invention, FIG. 2 is a flowchart showing an algorithm when implementing the wire breakage detection method of the present invention using a computer, and FIG. Current vector diagram at the time of wire breakage (A phase wire breakage), Figure 4 is 1
A current change vector diagram when a wire is disconnected (A phase disconnection), and FIG. 5 is a current vector diagram when a three-phase load is opened. 1a-1c...3-phase electric line, 2a-2c...current transformer, 3a-3c...current-voltage converter, 4a-4c,
12...Storage device, 5a to 5c, 13...Subtractor,
6, 7... Phase comparator, 9a to 9c, 14... Level detector, 8, 10, 15... AND circuit, 11... Grounding transformer.

Claims (1)

[Claims] 1 The zero-sequence voltage V〓o ₁ detected at the power supply end of the three-phase electric line and the line currents I〓a ₁ , I〓b ₁ and I〓c ₁ of each phase are V〓o ₂ and I〓, respectively. Zero-sequence voltage change vector ΔV〓o=V〓o ₁ −V〓o ₂ and current change vector ΔI〓a=I〓a ₁ −I〓 when changing to _{a 2 ,} I〓b 2 and I〓c ₂ a ₂ , ΔI〓b＝I〓b ₁ −I〓b ₂
and ΔI〓c
＝I〓c ₁ −I〓c ₂ is calculated, and a current change vector whose phase order is opposite to the current change vector when the three-phase load is opened is calculated, and the current change vectors ΔI〓a, ΔI〓b, and ΔI A wire breakage detection method for determining that a wire breakage accident has occurred when all of the magnitudes of 〓c exceed a certain value and the magnitude of the zero-phase voltage change vector ΔV〓o exceeds a certain value.