JPH036136Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a ground fault directional relay used for ground fault protection of ungrounded distribution lines.

Figure 1 shows an example of a bank configuration of a normal non-grounded power distribution substation. In Figure 1, T is a transformer connected to the power supply, and a feeder is connected to the secondary side of the transformer.
F ₁ to F ₃ are connected, and a ground voltage instrument transformer GPT is also connected. Each feeder F ₁ ~ _{F 3}
Zero-phase current transformers ZCT ₁ to _{ZCT 3} are inserted, and ground fault direction relays DG ₁ to DG ₃ are connected thereto. In addition, a limiting resistor CLR is connected to the open delta circuit constituted by the tertiary winding of the ground potential transformer GPT, and the zero-sequence voltage V ₀ generated between the ends of the circuit in the event of a ground fault is reduced. The earth fault direction relay
It is designed to be input to DG ₁₁ to DG ₃ .

In such a bank configuration, if a ground fault occurs in feeder F ₁ , for example, a zero-sequence voltage V ₀ will be generated across the limiting resistor CLR connected to the open delta circuit on the tertiary side of the ground potential transformer GPT.
occurs, and the zero-phase current transformer of each feeder F ₁ to F ₃
Zero-sequence current I ₀ flows through ZCT ₁ to ZCT ₃ . This zero-sequence voltage V ₀ and zero-sequence current I ₀ are the ground fault direction relays of each feeder.
It is introduced into DG ₁ to DG ₃ , and the ground fault feeder is selected based on the phase relationship.

In this case, the phase characteristics of the earth-fault directional relay are such that the phase of the zero-sequence current I ₀ with respect to the zero-sequence voltage V ₀ advances from 0° and changes to about 90° depending on the bank configuration and the ground capacitance C ₁ to C ₃ of the line. Therefore, it is normal to set the characteristics such that the maximum sensitivity is achieved at a 45° advance.

By the way, recently there has been a tendency for cables to be used frequently as power distribution lines, and intermittent ground faults are becoming more common in the distribution line. The ground fault current is as shown in Figure 2a, and the zero-sequence currents I ₀₁ and I ₀₂ of the faulty feeder and healthy feeder detected by the zero-sequence current transformer are pulse-like as shown in Figures 2b and c. , the waveform of the zero-sequence voltage V ₀ is shown in Figure 2 d.
It often becomes a square wave like this.

For this reason, ground fault direction relays are configured so that they are sensitive to such waveforms and can accurately select the fault feeder.
As shown in the figure. In Figure 3, TA is an input transformer connected to the secondary side of the zero-sequence current transformer, and a current I _0a proportional to the zero-sequence current I ₀ flows through the secondary side, and a corresponding voltage V ₁₀ occurs. BPF ₁ is an active bandpass filter for the fundamental wave that inputs this voltage V ₁₀ , TV is an input transformer connected to the tertiary side of the ground voltage instrument transformer, and is used to take in the zero-sequence voltage. It is something. BPF ₂ is a band pass filter provided at the zero-phase voltage input section, and like the filter BPF ₁ , a filter with a high Q is used in order to extract only the fundamental wave component. PS is a phase shift circuit, and PC is a phase comparison circuit, which is used to compare the phases of each fundamental wave. ID is the zero-sequence current detection circuit, AND is the output of this zero-sequence current detection circuit ID and the phase comparison circuit PC
An AND circuit whose input is the output of the AND circuit, and X is an output relay driven by the output of the AND circuit.

In this way, high Q active bandpass filters BPF ₁ and BPF ₂ are provided at the I ₀ input section and V ₀ input section, extracting only the fundamental wave component of each waveform, comparing the phases of the outputs, and performing I ₀ detection. If you go to the AND output and drive relay X, feeder F ₁
If a cable ground fault occurs in the feeder
Zero-sequence current I ₀₁ ′ of F ₁ and zero-sequence current of healthy feeder F ₂
The fundamental wave component of I ₀₂ ' has a phase relationship as shown in FIG. 4 with respect to the fundamental wave component of the zero-sequence voltage V ₀ , and the device operates normally. In other words, the zero-sequence current I ₀₁ ' is the operating range (shaded area side)
to go into.

Let us now consider the influence of zero-phase current transformers. The equivalent circuit of a zero-phase current transformer is as shown in FIG. 5, if the resistance of the winding is ignored. In the diagram, X ₀
is the excitation impedance of the zero-phase current transformer, and R _L is the load resistance of the zero-phase current transformer. The load of a zero-phase current transformer is a combination of the impedance of the lead wire, auxiliary current transformer, and relay, but the inductance component is small compared to the resistance component, so it is ignored and treated as pure resistance.

Now, when a pulsed ground fault current as shown in FIG. 6a flows as an input to the zero-phase current transformer, what kind of current flows in the secondary side of the zero-phase current transformer will be explained below.

In Fig. 6, when time t is in the range t ₀ ≦ t < t ₁ , the pulsed input current I ₀ consists of a component I _pL flowing through the load resistance R _L and a component flowing through the excitation impedance X ₀ .
Divided as I _pX . Since the excitation impedance X ₀ is several tens of times as large as the load resistance R _L , t ₀ ≦t
In the range <t ₁ , the following relationship holds between the currents I ₀ , I _pL , I _pX and the voltage V.

I ₀ = I _pL + I _pX ≒ I _pL (1) V = R _L・I _pL (2) Next, at time t = t ₁ , the current I _pX (t ₁ ) flowing through the excitation impedance X ₀ is (1 ), using equation (2), I _pX (t ₁ )=1/L ₀ ∫ ^t1 ₀ Vdt=R _L /L ₀ ∫ ^t1 ₀ I _pL dt≒R _L
/L ₀ ∫ ^t1 ₀ I ₀ dt(3) However, L ₀ is the reactance of the impedance X ₀ , and I _pX (t ₁ ) is the integral value of the input current I ₀ , that is,
It is proportional to the area of the pulsed waveform. this current
Since the input current I ₀ has already reached o, I _pX (t ₁ ) will be discharged through the load resistor _RL .

That is, when the time t is in the range of t ₁ ≦t<t ₂ , the circuit becomes a closed circuit between X ₀ and R _L , and the currents I _pL and I _pX are expressed by equations (4) and (5).

I _pX = I _pX (t ₁ )ε ^-t/ 〓 (4) I _pL = −I _pX = −I _pX (t ₁ )ε ^-t/ 〓 =RL/L ₀ ∫ ^t1 ₀ I ₀ dt・ε ^{- t/} 〓 (5) However, time constant τ=L ₀ /R _L Thus, at t ₁ ≦ t < t ₂ , the current flowing through the load resistor R _L is opposite to that when the input current I ₀ is applied. direction, and its magnitude attenuates with the time constant τ=L ₀ /R _L . In a zero-phase current transformer, this time constant τ is
Since it is about 0.1 seconds, it is about half a cycle of the commercial frequency.
There is almost no attenuation in a time of about 10 msec, Figure 6b.
The current waveform becomes a rectangular wave like I _pC , and its magnitude is proportional to the integral value of the input current, that is, the area of the pulsed current, according to equation (5).

This current I _pC is due to the small ground capacity of the distribution line.
This is hardly a problem when the pulse current is small, but as the number of cable distribution lines increases and the ground capacity increases, it becomes a big problem.

This is because the bandpass filter shown in Figure 3
Since BPF ₁ is an active bandpass filter, its output cannot exceed the control voltage, and the dynamic range cannot exceed this control voltage. If an input higher than the control voltage is input, the active filter function will be lost, so in order to limit the input within this range, varistor V ₁ is connected between the zero-phase terminal of bandpass filter BPF ₁ as shown in Figure 3. Connect and clip the upper limit of the input,
It is common to obtain phase characteristics as shown in FIG.

However, since ground fault directional relays require high sensitivity such as 0.2A at the primary of the zero-phase current transformer,
The upper limit of the dynamic range cannot be set extremely high. However, in recent cable ground faults, large pulse currents with peak values of several hundred amperes have started to flow, although the pulse width remains the same. This tendency is particularly noticeable at the beginning of a ground fault when the ground capacity of the cable ground fault is large.

For example, the peak value of the pulse current can be calculated using an equivalent circuit as shown in FIG. 1st
In Figure 0, E is the voltage value when a ground fault occurs, L is the reactance of the power supply impedance, C is the sum of the ground capacity of healthy feeders, and R is the limiting resistance of the ground voltage instrument transformer GPT.

FIG. 11 shows the calculated values using the equivalent circuit of FIG. 10. As can be seen from FIG. 12, the peak value of the pulse current increases as the ground capacity of the cable increases. For example, if the ground capacity of the cable is 5 μF, the peak value of the pulse current will be approximately 400 A, and the secondary current I _pC of the zero-phase current transformer will be several A according to equation (5).

In this case, as discussed earlier, the pulse area of current I ₀ increases, so the secondary current of the zero-phase current transformer
Since I _pC (I _pL in Figure 6b) increases while the clip voltage of varistor V ₁ remains constant, the input of bandpass filter BPF ₁ has a waveform like V ₁₀ in Figure 6d. I'm getting old. When the fundamental wave is extracted with a bandpass filter, this waveform becomes the waveform shown in Figure 6e (the dotted line indicates when there is no varistor), and on the phase characteristics, the zero-sequence current I ₀₁ of the failed feeder and the zero-sequence current of the healthy feeder. The apparent phase of I ₀₂ is as shown in Figure 4, and the faulty feeder's ground-fault direction relay malfunctions, and the healthy feeder's ground-fault direction relay malfunctions, completely opposite to the originally expected operation. This becomes a big problem.

In addition, on the healthy side I _0C2 (I ₀₂ in Figure 2), the current I _gpt discharged through the neutral point of the ground voltage voltage transformer GPT is superimposed on the current equivalent to the previous I _pC . Become.

The present invention was made to solve the above problems, and by inserting a low-pass or band-pass passive filter on the input side of the fundamental wave active band-pass filter of the _I0 input section,
It is an object of the present invention to provide a ground fault directional relay that can provide accurate ground fault protection even when the ground capacity is large.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

Figure 7 shows an embodiment of the present invention.
and TV is the input transformer, BPF ₁ is the active bandpass filter for I ₀ fundamental wave, BPF ₂ is the active bandpass filter for V ₀ fundamental wave, PS is the phase shift circuit, PC is the phase comparison circuit, ID is zero phase current detection circuit,
_{AND is an} AND circuit _, path) and this passive filter
The difference from the conventional model (Figure 3) is that it has a PF. The circuit constants of this passive filter PF are selected so that even when the maximum predictable pulse is applied to its input _I01 , the peak value of its output remains below the clipping voltage _V1C of the clipper _V1 .

FIG. 8 shows a specific circuit configuration of the passive filter PF, in which resistors R ₁ and R ₂ and a capacitor C constitute a T-shaped circuit, forming a low-pass filter. In this case, R ₁ C is set so that the peak value of the output V ₁₀ is less than the clipping voltage of the clipper V ₁ even for the maximum value of the input pulse that can be predicted.
Select the time constant of

Note that the resistor _R2 allows charging of the capacitor C even if the peak value of the input pulse is abnormally large and _the terminal voltage of the capacitor C exceeds the clipping voltage of the clipper _V1 . This is to effectively incorporate energy into the band pass filter BPF ₁ .

Next, the operation will be described. If the input transformer TA's input _I0 is below the clipping voltage of the clipper _V1 , the zero-sequence current
The fundamental waves of I ₀ and zero-phase voltage V ₀ are extracted by the active bandpass filter without being restricted, and their phases are compared. As a result, if there is a predetermined phase relationship and the detection circuit ID detects that the zero-sequence current _I0 is above a predetermined level, the relay X is driven by the output of the AND circuit AND, and the ground fault protection will be held.

In addition, if the input _I0 is large enough to exceed the clip voltage, the input of the passive filter PF
I ₀₁ also has a high peak value that is higher than the clip voltage as shown in Fig. 9, but after passing through the filter PF it is suppressed to below the clip voltage V _1C as shown in V ₁₀ in Fig. 9, and this is the active band pass. Input to filter BPF ₁ . As a result, even a pulse input with a high peak value can be effectively input to the active bandpass filter BPF ₁ without being cut off by the clipper V ₁ , and the ground fault direction can be accurately determined.

Note that the passive filter PF may be a two-stage or three-stage RC low-pass filter, or an LC low-pass filter or band-pass filter.

As described above, according to the present invention, a passive filter whose circuit constants are selected so that the output is below the upper limit of the dynamic range of this filter is inserted on the input side of the active bandpass filter for _I0 . Even if the ground capacity of the distribution line cable increases and the peak value of pulse current at the time of a cable ground fault increases, the passive filter allows that energy to be effectively incorporated into the active bandpass filter, preventing malfunctions and damage to the system. Judgments can be made accurately. Therefore, even with a bank configuration having a large ground capacity, there is no risk of malfunction or malfunction, and reliability can be improved.

[Brief explanation of drawings]

Figure 1 is a bank configuration diagram of a distribution substation, Figures 2 a to d are current and voltage waveform diagrams at the time of a ground fault, and Figure 3
The figure is a block diagram showing an example of a conventional ground fault directional relay, Figure 4 is a phase characteristic diagram of the same ground fault directional relay, Figure 5 is an equivalent circuit diagram of a zero-phase current transformer, and Figures 6 a to e are
Waveform diagram of bandpass filter for I ₀ fundamental wave, 7th
The figure is a block diagram showing one embodiment of the ground fault directional relay according to the present invention, Figure 8 is a circuit diagram of a passive filter in the same embodiment, Figure 9 is a waveform diagram for explaining operation, and Figure 10 is a ground fault diagram. FIG. 11, which is an equivalent circuit diagram of the system at the time of occurrence, is a graph showing the relationship between the ground capacity of the cable and the peak value of the pulse current. ZCT...Zero-phase current transformer, GPT...Grounding voltage transformer, TA and TV...Input transformer, BPF ₁ and
BPF ₂ ...Band pass filter for fundamental wave, PC...
...Phase comparison circuit, ID...Zero-sequence current detection circuit,
AND...AND circuit, X...output relay, V ₁ ...
...Input limiting clipper (varistor), PF...passive filter, _R1 and _R2 ...resistor, C...capacitor.

Claims (1)

[Scope of utility model registration request] The fundamental waves of zero-sequence current and zero-sequence voltage are extracted using an active bandpass filter, and their phases are compared.
In a ground fault direction relay that operates an output relay when the zero-sequence current is at a predetermined level or higher with a predetermined phase relationship, the output is connected to the input side of the active bandpass filter of the zero-sequence current input section. A ground fault directional relay characterized in that a passive filter is inserted, the circuit constant of which is selected to be below the upper limit of the dynamic range of the bandpass filter.