JPH0152969B2 - - 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 a power distribution line, and particularly to a method for detecting a disconnection accident in a distribution line when a motor is included in the load on the load side of the disconnection point (hereinafter referred to as The present invention relates to a method for detecting a single wire disconnection (hereinafter referred to as a single wire disconnection when the motor is loaded).

Prior Art The following method has been proposed as a method for detecting a break in a distribution line at a power source end such as a substation. That is, the line current is monitored at the power supply end to determine the change vector of the line current of each phase, and attention is paid to the difference between the vector change due to a single wire disconnection accident and the vector change due to load release. Then, a discriminant that clearly represents this difference is set, and this discriminant is used to detect wire breakage. However, with this method, it was not possible to express in a discriminant the difference between the vector change in the line current when one wire is disconnected when the motor is loaded and the vector change in the line current when the three-phase load is opened. It was not possible to distinguish between a change in the current vector and a change in the current vector when the three-phase load was opened, and it was not possible to accurately detect a disconnection fault.

Purpose of the Invention The purpose of the present invention is to propose a method for detecting a single wire breakage when a motor is loaded on a power distribution line, which can accurately detect a breakage accident when a motor is included in the load beyond the breakage point. There is a particular thing.

Structure of the Invention As a result of various studies, the inventor of the present invention found that the direction of phase sequence is different between the current change vector when a three-phase load is opened and the current change vector when a single wire is disconnected when the motor load is located beyond the disconnection point. I found the opposite to be true. The present invention was made by focusing on the difference in the phase order of the change vectors, and when the three-phase line current is detected at the power supply end and a current change vector with the opposite phase order to the current change vector is obtained. It is determined that one wire disconnection has occurred under load.

Figure 1 shows the state of the current vector when one wire is disconnected (A-phase disconnection) when the motor is loaded on the distribution line where the motor is loaded. The line current vectors of the a-phase, b-phase, and c-phase before disconnection are shown, respectively. If the a-phase line is disconnected, the a-phase line current I〓a' after the accident becomes zero, so the current change vectors of the a-phase to c-phase ΔI〓a', ΔI〓b' and ΔI 〓c′ becomes as shown,
a phase 1
Current vectors I〓b′ and b-phase and c-phase after wire breakage
I〓c′ becomes as shown. From Figure 1, the current change vector ΔI〓a′~ when one wire disconnection occurs when the motor is loaded
If only ΔI〓c' is extracted and illustrated, the result will be as shown in Fig. 2. On the other hand, the current change vector ΔI〓a~ΔI〓c when the three-phase load is opened is as shown in Figure 3, and the current change vector ΔI〓a′~ due to one wire breakage when the motor is loaded.
The direction of the phase order is opposite to ΔI〓c′. From this,
It can be seen that by determining the direction of the phase sequence of the current change vector, it is possible to detect a single wire disconnection when the motor is under load.

Embodiment FIG. 4 shows an example of the configuration of a detection device that implements the above detection method, and in the same figure, 1a to 1
c indicates the distribution line of the a phase to the c phase. Current transformers 2a to 2c are installed at the power supply ends of the distribution lines 1a to 1c, respectively.
are installed, and detection signals corresponding to the line currents Ia to Ic of the a-phase to c-phase are obtained on the output sides of these current transformers, respectively. These detection signals are converted into voltage signals by current/voltage converters (I/V converters) 3a to 3c and then input to storage devices 4a to 4c. The storage devices 4a to 4c read out the stored information on the a-phase to c-phase line currents Ia to Ic after a short 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, changes ΔIa to ΔIc of the line currents Ia to Ic of the a-phase to c-phase per minute time Δt are obtained on the output side of the subtractors 5a to 5c, respectively. Signals indicating the current changes ΔIa and ΔIb of the a-phase and b-phase are input to the phase comparator 6, and when ΔIb is ahead of ΔIa, the logical value from this phase comparator 6 is "1".
signals are now available. In addition, signals indicating current changes ΔIa and ΔIc of the a-phase and c-phase are input to the phase comparator 7, and when ΔIc lags behind ΔIa, a signal with a logic value of "1" is sent from the phase comparator 7. It is becoming possible to obtain The outputs of the phase comparators 6 and 7 are input to an AND circuit 8, and when ΔIb leads ΔIa and ΔIc lags ΔIa, that is, the current change vector is in the reverse order as shown in FIG. Sometimes the output of the AND circuit becomes "1". The signals indicating the current changes ΔIa, ΔIb, and ΔIc are also compared by level detectors with a level k at which the absolute values of the current changes ΔIa to ΔIc are constant. The level detectors 9a to 9c each output a signal whose logical value is "1" when the absolute value of the current change amount ΔIa to ΔIc is larger than a certain level k. The outputs of these level detectors 9a to 9c are input to an AND circuit 10, and this AND circuit has 3
When phase current changes ΔIa to ΔIc are all greater than a certain value, an input with a logic value of "1" is generated.
The output of the AND circuit 10 is input to the AND circuit 11 together with the output of the AND circuit 8. In the AND circuit 11, an AND is established when the current change vectors are in the reverse order as shown in Fig. 2 and the current changes of all three phases are above a certain magnitude, and a one-wire disconnection accident occurs on the output side when the motor is loaded. Generates a disconnection detection output es indicating that a disconnection has occurred.

Next, FIG. 5 shows a flowchart when the detection method of the present invention is implemented using a computer. In the procedure shown in FIG. 5, first, time t _1
The current value Ia of line current I〓a to I〓c of phase a to c at
~Ic ₁ and the respective phases φa ₁ ~φc ₁ are read into the storage device. Next, the current values Ia _{2 to} Ic ₂ of the line currents and the respective phases φa ₂ to φc ₂ at time t ₂ delayed by a minute time Δt from time t 1 are read. Next, the above Ia ₁ ~ Ic ₁
Δt from Ia ₂ ~ _{Ic 2} , φa ₁ ~ φc ₁ , and φa ₂ ~ φc ₂
The magnitudes ΔIa to ΔIc and the phases θa to θc of the current change vectors ΔI〓a to ΔI〓c over time are calculated 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) θa＝tan ^-1 {(Ia ₂ sinφa ₂ −Ia ₁ sinφa ₁ )／(Ia ₂ cos
φa ₂ −Ia ₁ cosφa ₁ )}……(4) θb＝tan ⁻¹ {(Ib ₂ sinφb ₂ −Ib ₁ sinφb ₁ )／(Ib ₂ cos
φb ₂ −Ib ₁ cosφb ₁ )}……(5) θc＝tan ⁻¹ {(Ic ₂ sinφc ₂ −Ic ₁ sinφc ₁ )／(Ic ₂ cos
φc ₂ −Ic ₁ cosφc ₁ )}...(6) Next, compare θa and θb and θa and θa obtained as above, and find that θb leads with respect to θa and θc lags with respect to θa. Determine whether or not the
As a result of this determination, if θb is ahead of θa and θc is behind θa, it is further determined whether ΔIa, ΔIb, and ΔIc are all larger than a constant value k, and ΔIa to ΔIc are all A disconnection detection output is generated when the value is greater than or equal to k. If θb lags behind θa or θc leads θa,
Or at least one of ΔIa, ΔIb, and ΔIc is k
If it is smaller, change the time t ₂ to a new time t ₁
and the magnitude and phase of the current at time t ₂
Ia ₂ ~ Ic ₂ and φa ₂ ~ φc ₂ are respectively the magnitude and phase of the current at the new time t ₁ Ia ₁ ~ Ic ₁ and φa ₁ ~
Store it as φc ₁ and repeat the above process.

Effects of the Invention As described above, according to the present invention, when the motor is loaded 1
Since the wire breakage accident is detected by focusing on the phenomenon peculiar to the occurrence of wire breakage, it is possible to detect wire breakage by focusing on the phenomenon peculiar to the occurrence of wire breakage.
This has the advantage that disconnection faults can be accurately detected without being confused with phase load opening.

[Brief explanation of drawings]

Figure 1 is a current vector diagram when a single wire disconnection occurs when the motor is loaded, Figure 2 is a current change vector diagram when the same disconnection occurs, Figure 3 is a current vector diagram when a 3-phase load is released, FIG. 4 is a block diagram showing an example of the configuration of a detection apparatus for implementing the detection method of the present invention, and FIG. 5 is a flowchart showing an algorithm when implementing the detection method of the present invention using a computer. 1a-1c...3-phase distribution line, 2a-2c...current transformer, 3a-3c...current-voltage converter, 4a-4
c...Storage device, 5a-5c...Subtractor, 6...
Phase comparator, 8 to 11...AND circuit.

Claims (1)

[Claims] 1. In a method for detecting a single-wire disconnection at the time of a motor load on a distribution line, which detects a single-wire disconnection accident occurring between the motor load and the power source end of a distribution line where the load includes a motor load, at the power source end. detecting the line current of each phase of the distribution line to obtain a current change vector;
1. A method for detecting a single wire breakage when a motor is loaded on a distribution line, characterized in that it is determined that the breakage accident has occurred when a current change vector in the reverse order of the current change vector when the three-phase load is opened is determined.