JPH0226448B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an open phase detection circuit applied to power distribution relays and the like.

Ground faults in distribution lines and the like are generally detected by utilizing the fact that zero-sequence voltage is generated during a ground fault, but zero-sequence voltage is also generated in the same way when an open-phase fault occurs due to a disconnection or the like. For this reason, even when an open phase occurs, there is a risk of erroneous detection, such as determining that it is a ground fault.

This invention has been made in view of this point, and aims to prevent relay malfunctions due to occurrence of phase loss by applying the phase loss detection circuit of the present invention to power distribution relays, etc. .

An embodiment of the present invention will be described below with reference to the accompanying drawings.

In Figure 1, 1a, 1b, 1c are star-connected three-phase balanced power supplies, and 2a, 2b, 2c are these three-phase balanced power supplies.
A three-phase distribution line connected to a phase-balanced power supply, 3 is a grounding resistance at the neutral point of the power supply. 4 is a three-phase phase shift transformer, which is connected to the three-phase distribution lines 2a, 2b, 2c and energized by the phase voltages v _a , v _b , v _c, for example, a triangularly connected one.
It has a secondary winding 4a and a star-connected secondary winding 4b which generates phase voltages e _a , e _b , e _c . 5
a, 5b, 5c are absolute value circuits that take the absolute values of the phase voltages e _a , e _b , e _c, respectively; 6 are absolute value circuits 5 a, 5
An adder that calculates the sum of the outputs of b and 5c, and 7 is a threshold value set in advance for the output of adder 6.
This is a voltage comparator that compares with Vth.

Next, the operation will be explained. The phase voltages of the three-phase balanced power supplies 1a, 1b, and 1c of the system under consideration can be expressed as follows.

v _a = E・sinωt v _b = E・sin (ωt−2/3π) v _c = E・sin (ωt−4/3π) However, in the 6.6KV distribution system, E=6600×√2/√
It can be expressed as 3.

In order to obtain a three-phase balanced voltage, the three-phase phase shift transformer 4 shown in Fig. 1 can be used, and since the primary winding 4a is a triangular connection, each winding of the primary winding 4a has the following configuration. line voltage is applied.

v _ac = v _a −v _c =√3E・sin(ωt−π/6) v _ba =v _b −v _a =√3E・sin(ωt−π/6−2/3π) =√3E・sin( ωt−5/6π) v _cb =v _c −v _b =√3E・sin(ωt−5/6π−2/3π) =√3E・sin(ωt−3/2π) When the winding ratio is a, if no phase loss occurs, this three-phase phase shift transformer 4
Accordingly, the following three-phase phase voltages e _a , e _b , e _c corresponding to the line voltages v _ac , v _ba , v _cb on the primary side are obtained at the secondary winding of the three-phase phase shift transformer 4. are generated on line 4b, respectively.

e _a =E1·sin(ωt−π/6) e _b =E1·sin(ωt−5/6π) e _c =E1·sin(ωt−3/2π) However, E1=√3E/a.

Each of these phase voltages is connected to an absolute value circuit 5a,
The state of the output when inputted to the adder 6 after passing through 5b and 5c is shown by waveform 8 in FIG. The sum of the absolute voltage values of each phase changes depending on the phase, but the minimum value is √3E1.

On the other hand, consider the case where an open phase occurs. First, when one phase (for example, A phase) is open, a line voltage of the following system is applied to the primary winding 4a of the three-phase phase shift transformer 4.

v _ac = v _a −v _c = −E・sin (ωt−4/3π) = E・sin (ωt−π/3) v _ba = v _b −v _a = E・sin (ωt−2/3π) v _cb = v _c − v _b = √3E・sin(ωt−3/2π) Each phase output from the secondary winding 4b of the three-phase phase shift transformer 4 corresponds to these primary side line voltages. The voltage will be as follows.

The above phase voltages are absolute value circuits 5a, 5b, 5c.
The output after passing through adder 6 is shown by waveform 9 in FIG.

Next, in the case of a two-phase (for example, A phase and B phase) open phase, the following system line voltage is applied to the primary winding 4a of the three-phase phase shift transformer 4.

v _ac = v _a −v _c = −E・sin(ωt−4/3π) =E・sin(ωt−π/3) v _ba =v _b −v _a =0 v _cb =v _c −v _b = E·sin(ωt−4/3π) Each phase voltage output from the secondary winding 4b of the three-phase phase shift transformer 4 corresponding to these primary side line voltages is as follows.

The above phase voltages are absolute value circuits 5a, 5b, 5c.
The output after passing through the adder 6 is shown in FIG. 2 as a waveform 10.

Also, if all three phases are open, naturally e _a = e _b = e _c
= 0, the output of the adder 6 is naturally also 0.

As you can see from this Figure 2, E1/√3Vth<
If the threshold value Vth of √3E1 is set appropriately, the sum of the absolute values of the three phases will be smaller than Vth at least in a certain phase in the event of a phase loss failure, so the comparator 7 will detect whether or not a phase loss has occurred. can do.
Further, since a one-line ground fault corresponds to waveform 8, the open phase detection circuit of the present invention will not erroneously determine a ground fault or an open phase fault.

In the embodiment described above, the phase voltages e _a , e _b , e _c are used as the three-phase balanced voltages, but instead of these, the secondary winding of the three-phase phase shift transformer shown in FIG. 1 is also used as the primary winding. The line voltages of the triangular connection are e _ab , e _bc ,
Even if e _ca is used as a three-phase balanced voltage, a circuit having the same function as the above embodiment can be obtained.

In addition, as shown in Figure 2, the output of the adder 6 has some overlap between the normal state and the one phase loss state, so the adder 6 should be provided with a function to hold the minimum value for a certain period of time τ. This allows for even more stable judgment. FIG. 3 shows this in a waveform diagram. FIG. 3 shows the output waveforms of the adder 6 under each phase loss condition when τ=10ms, where 11 is normal, 12 is 1 phase (A phase) loss, and 13 is when two phases (A phase and B phase) are open. Moreover, it is naturally 0 when all phases are open. In addition, the broken line in the figure shows the output of the adder 6 when it does not have the minimum value holding function.

In the embodiments described above, a three-phase phase shift transformer was used to calculate the phase voltages e _a , e _b , e _c or line voltages e _ab , e _bc , e _ca , but a voltage divider such as a capacitive voltage divider may also be used. It is also possible to use a resistor voltage divider. FIG. 4 shows an embodiment using a plurality of capacitance voltage dividers, for example three. In this case, the phase voltages e _a , e _b , e _c are calculated, and the phase outputs of the capacitive voltage divider 14 are inputted into adders 15 a, 15 b, 15 c, and the phase voltages e a , e _c are calculated.
Calculating e _b and e _c .

As described above, according to the present invention, since the sum of the absolute values of the detected three-phase outputs is compared with a threshold value, it has become possible to clearly distinguish between a ground fault and an open-phase fault. Furthermore, in this case, since the open phase phenomenon is detected from the relationship between the steady voltage value and the phase, stable determination can be made without being affected by transient phenomena or the like.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an open-phase detection circuit according to the present invention, FIG. 2 is a waveform diagram showing the output of the adder 6 for each open-phase condition, and FIG.
A waveform diagram showing the output when a minimum value holding function is provided for each open phase condition, and Fig. 4 is a circuit diagram showing part of another example of calculating phase voltage using a capacitive voltage divider. It is. 2a to 2c are three-phase distribution lines, 4 is a three-phase phase shift transformer, 4a is a primary winding, 4b is a secondary winding, 5a to 5
c is an absolute value circuit, 6 and 15a to 15c are adders,
7 is a voltage comparator, and 14 is a capacitive voltage divider.

Claims (1)

[Claims] 1. Consisting of a three-phase phase-shifting transformer connected to a three-phase distribution line and having a triangularly connected primary winding and a secondary winding associated with this primary winding, the transformer is a three-phase balanced transformer. means for generating a voltage; means for summing the absolute values of the three-phase balanced voltages and holding the minimum value for a certain period of time; and comparing the instantaneous value of the sum with a predetermined threshold value Vth. and the instantaneous value is the threshold value Vth
An open phase detection circuit characterized by comprising means for determining an open phase accident and outputting an output when the error is smaller. 2 Consists of multiple voltage dividers connected to the 3-phase distribution line and an adder connected to the output side of these voltage dividers, and generates phase voltages ea, eb, ec or line-to-line corresponding to the line-to-line voltage of the 3-phase distribution line. Voltage eab, ebc, eca 3
means for generating a phase balanced voltage; means for summing the three phase balanced voltages and holding the minimum value for a certain period of time; and comparing the instantaneous value of the sum with a predetermined threshold Vth; An open phase detection circuit comprising means for determining an open phase accident and outputting an output when the instantaneous value is smaller than the threshold value Vth.