JPH0636647B2 - Ground fault protection relay system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault protection relay system for preventing malfunction of a ground fault direction relay used for ground fault protection of an ungrounded power distribution system.

(Prior Art) Normally, this type of ground fault direction relay outputs the relay output when the phase difference between the zero-phase current and the zero-phase voltage generated at the time of ground fault is within approximately 90 ° in electrical angle based on the phase comparison principle. Is configured to obtain.

The principle block diagram is shown in Fig. 3, where 11 is a limiter to which the zero-phase current from the secondary side of the zero-phase current transformer is input, 12 is a filter, and 13 is a square wave conversion. Circuit, 14 is a phase shift circuit to which the zero phase voltage from the secondary side of the grounding type transformer is input, 15 is a filter, 16 is a square wave conversion circuit, 17 is an AND circuit, 18 is a zero phase current and zero Reference numeral 19 denotes a phase overlap angle measuring circuit for generating a phase comparison output when the phase overlap angle with the phase voltage exceeds a predetermined value, and 19 denotes an integrating circuit for the purpose of continuous operation output and operation delay.

Here, since the power factor angle of the ground charging current is 60 ° to 80 °, the phase of the input zero phase voltage V ₀ is changed to the maximum sensitivity angle φ (at the minimum input in the phase shift circuit 14 as shown in FIG. Phase difference angle between the zero-phase current I ₀ and the zero-phase voltage V ₀ : 60 °, for example
Only kV ₀ (k is a constant) and the phase overlap angle of kV ₀ and I ₀ is 90 ° or more (overlap time is 5 ms / 50H).
z input), that is, the phase difference between kV ₀ and I ₀ is
When the angle is within 90 °, a phase comparison output is generated from the phase overlap angle measuring circuit 18, and then an operation output of the ground fault direction relay is obtained via an integrating circuit 19.

The filters 12 and 15 are for removing distortion of current or voltage, and are constituted by low-pass filters or the like.

FIG. 5 is a single-line diagram showing a simulation circuit for a one-line ground fault in an ungrounded power distribution system. In FIG. 5, F ₀ is a bus bar, F _{1 to} Fn are distribution lines, GPT is a grounding type instrument transformer, CLR is a current limiting resistance on its tertiary side, DG
_{1 to} DGn are ground fault direction relays installed on the respective distribution lines F _{1 to} Fn, ZCT is a zero-phase current transformer, CB _{1 to} CBn are circuit breakers,
C ₀ and C _{1 to} Cn are respectively a bus F ₀ and distribution lines F _{1 to} Fn.
To ground, R ₀ is an equivalent ground resistance on the primary side of the grounding type instrument transformer GPT, and Rg is a fault point resistance.

In this simulated circuit, when a _one- line ground fault occurs on the distribution line F ₁ as shown in the figure, at the fault point, the total sum of the primary zero-phase currents 3In of the grounding-type instrument transformer GPT and the discharge due to the ground capacitance. The zero-phase current 3I _{0, which} is the sum of the current sum 3Ic, flows. Therefore, in the ground fault relay DG ₁ , based on the zero-phase voltage V ₀ detected from the tertiary side of the grounding type instrument transformer GPT and the zero-phase current I ₀ from the zero-phase current transformer ZCT, the above-mentioned phase comparison is performed. The direction of the zero-phase current I ₀ is determined according to the principle, and the trip command for the circuit breaker CB ₁ is output.

Then, when the ground fault is recovered and the circuit breaker CB ₁ is closed again, in the zero-phase equivalent circuit of the grounding instrument transformer GPT shown in FIG. The electric charge of the ground capacitance C ₁ is a grounding type instrument transformer GPT
Is discharged and disappears in a circuit including the exciting inductance L _m and the current limiting resistance CLR. At this time, the exciting circuit of the grounding type instrument transformer GPT is subjected to DC excitation, and due to DC saturation, the exciting inductance L _m ( (Primary conversion) is almost zero, capacitance to ground C ₁ and transformer for grounding type instrument GPT
The rapid charging / discharging is repeated with the third winding inductance Lt. In FIG. 6, R _p is the primary winding resistance of the grounded instrument transformer GPT, L _p is the same leakage inductance, In (t) is the same primary zero-phase current, and I (t) is the same 3 The next zero-phase current, V _0, represents the zero-phase voltage.

(Problems to be Solved by the Invention) The vibration phenomenon due to charging and discharging between the ground capacitance C ₁ and the tertiary winding inductance Lt is repeated until the electric energy is completely consumed by the current limiting resistance CLR. And
A low frequency damping vibration (V ₀ vibration) indicated by e ₀ (t) in FIGS. 6 and 7 is generated as a subharmonic of 1/2 to 1/5 or less of the fundamental frequency (for example, 50 Hz).

During this oscillation, if a discharge current of a sound line, for example, the capacitance Cn of the ground Fn in FIG. 5 flows into the ground fault direction relay DGn via the current transformer ZCT, the phase of the zero-phase voltage V ₀ and the current When the relationship enters the operation phase region of the ground fault direction relay DGn, the ground fault direction relay DGn may malfunction, and there are cases in which a mistrip actually occurs.

Therefore, in the related art, in order to prevent the malfunction of the ground line direction relay DGn of the above-mentioned sound line, the local line direction relays DG _{1 to} GDn should be waited for the time for V ₀ vibration to disappear.
The operation time limit of is set to about 200 ms, and measures are taken by time coordination. However, in this way, the ground fault direction relay DG
Sending the operation time limit of _{1 to} DGn is not preferable in terms of protection cooperation.

The present invention has been proposed to solve the above problems, and an object of the present invention is to detect the fundamental wave frequency of the zero-phase voltage at the time of low-frequency damped vibration by a frequency detection relay composed of a digital relay to ensure soundness. A ground fault protection relay system that prevents malfunction of the ground fault direction relay by obtaining the lock command of the line ground fault direction relay, improves the relay performance without delaying the operation time period, and facilitates protection cooperation. To provide.

(Means for Solving Problems) In order to achieve the above object, the present invention provides a ground fault protection relay system using a ground fault direction relay of an ungrounded distribution system,
The fundamental wave frequency of the zero-phase voltage of the system shall be monitored by a frequency detection relay consisting of a digital relay, and the low-frequency damping oscillation of the zero-phase voltage that occurs after restoration of the ground fault should be positive and negative waves at regular sampling intervals. Is detected by counting the number of times, and the operation output of the ground fault direction relay of the sound line is locked for a certain period by the output signal of the frequency detection relay, and unlocked when the frequency is restored.

(Operation) In the present invention, the final operation output of the ground fault direction relay is obtained by the logical product of the phase comparison output of the ground fault direction relay, the inverted output of the frequency detection relay, and the output of the ground fault overvoltage relay. Here, the frequency detection relay outputs a relay lock command when the fundamental wave frequency falls below a certain value and low-frequency damping vibration is detected by monitoring the positive and negative waves of the zero-phase voltage. Lock the ground fault direction relay of the sound line to prevent its malfunction.

In addition, when the low frequency damping vibration disappears and the fundamental frequency is restored, an off delay time of about 1 second is provided to prevent unnecessary operation of the ground fault direction relay, and the relay lock command is continued during that time. While outputting, the lock is released after the off-delay time has elapsed.

(Example) An example of the present invention will be described below with reference to the drawings. First,
FIG. 1 shows a block diagram of a ground fault protection relay system according to the present invention.

In the figure, 1 is a ground fault overvoltage relay to which the zero-phase voltage V ₀ is input, 2 is a ground fault direction relay for preventing malfunction, 3
Is a frequency detection relay that detects the fundamental wave frequency of the zero-phase voltage. The output of the ground fault overvoltage relay 1, the phase comparison output of the ground fault direction relay 2, and the inverting output of the frequency detection relay 3 are connected to the AND circuit 4. The final operation output of the ground fault direction relay 2 is input from the output terminal of the AND circuit 4.

The ground fault overvoltage relay 1 is used as an AND condition in order to prevent malfunction due to mechanical shock or reaction when an external accident is recovered when the ground fault direction relay 2 is, for example, an electromagnetic type. Further, since the frequency detection relay 3 is composed of a digital relay, and the zero-phase voltage V ₀ as its input is common to the power distribution system, there are a plurality of ground fault direction relays 2 but the installation thereof. A single number would be fine.

In this embodiment, the fundamental wave of the zero-phase voltage V ₀ is sampled by the frequency detection relay 3 every 30 ° (every 1.667 ms),
Whether the sampling data is a positive wave or a negative wave is determined. Then, for example, if the sampling data is a positive wave, the fundamental wave frequency of the _zero- phase voltage V ₀ becomes 1 / (1.667 ms × 9 × 2) = 33.3 Hz when the number of times of continuity reaches 9 times, which is below this frequency. Ground fault direction relay 2 for low frequency vibration of
The lock command (“H” level) is output. It should be noted that this frequency detection is similarly performed for negative waves, and a relay lock command is obtained under the AND condition of both positive and negative waves.

Next, the function of the frequency detection relay 3 will be described in more detail with reference to the flowchart of FIG.

The program for executing this flowchart is started every 1.667 ms corresponding to the sampling interval of 30 °. In FIG. 2, first, in step S1, it is determined whether or not a relay lock release flag is present. here,
If there is a release flag, the off-delay operation is performed for about 1 second after the frequency is restored, and therefore the process proceeds to step S17 described later. If there is no release flag, whether the zero-phase voltage V ₀ is positive or negative is determined in step S2.

If this is positive, the process proceeds to step S3, 1 is added to the count value P on the positive wave side, and the count value M on the negative wave side is cleared. On the contrary, if the negative wave is determined in step S2, 1 is added to the negative wave side count value M and the positive wave side count value P is cleared in step S10.

Now, when a normal wave is detected, the presence or absence of the lock flag is determined in step S4. If this lock flag does not exist, it is determined in the next step S5 whether or not the count value P exceeds 9 (the fundamental wave frequency corresponds to 33.3 Hz). Here, if the frequency does not exceed 9, the frequency is 33.3 Hz or higher, so that the lock command is not output and step S9 is performed.
At, the plus ON flag is reset and the process ends. If the count value P exceeds 9, there is a possibility of V ₀ vibration, so in the next step S6 a plus O
The N flag is set, and the determination result in step S7 as to whether or not the count value M exceeds 9 is set on the negative wave side (that is, whether or not the minus ON flag is set).

On the other hand, if the count value M exceeds 9 even on the negative wave side through steps S10 to S11, the minus ON flag is set in step S12 and the process proceeds to step S13. If it does not exceed, the minus ON flag is reset in step S14, and the process ends.

In step S13, if there is a plus ON flag, the process proceeds to step S8, the lock flag of the ground fault direction relay 2 is set, and at the same time, the count value p for off-delay is cleared and the process ends. At this time, the frequency detection relay 3 outputs a lock command for the ground fault direction relay 2, and the ground fault direction relay 2 is forcibly locked. Also,
If there is no plus ON flag in step S13, the process proceeds to step S9, the plus ON flag is reset, and the process ends.

On the other hand, in the previous step S7, it is determined whether or not the minus ON flag is set. If it is present, the process of step S8 is similarly performed, and if it is not present, the process of step S9 is performed.

That is, in this embodiment, the frequency is monitored for both the positive wave and the negative wave of the zero-phase voltage.

In the subsequent cycle, it is determined in step S4 that there is a lock flag, and the process proceeds to step S15. In this step S12, it is judged whether or not the fundamental wave frequency of the zero-phase voltage V ₀ is gradually recovered and becomes equal to or higher than a predetermined return value (for example, 37.5 Hz).

That is, the fundamental frequency when the count value P is 8 is 1 /
(1.667ms x 8 x 2) = 37.5Hz, so count value P
If becomes smaller than 8, the V ₀ vibration disappears and the frequency becomes 50H.
Since it is recovering toward z, the release flag is set in the next step S16, and 1 is added to the off-delay count value p in step S17. If the count value P is greater than 8 in step S12, the count value p is cleared in step S20.

Next, in step S18, it is determined whether or not 1 second has elapsed after the fundamental wave frequency returned to 37.5 Hz or higher. That is, one second elapses when the count value p reaches 600 by counting every 1.667 ms which is the program start cycle, and therefore the process proceeds to the next step S19 after waiting for the off delay time. In step S19, the lock flag and the release flag are reset and the off-delay count value p is cleared. As a result, the relay lock command of the ground fault direction relay 2 is released.

Therefore, the output signal of the frequency detection relay 3 becomes “L” level, that is, the input of the AND circuit 4 in FIG. 1 becomes “H” level, and thereafter, the ground fault overvoltage relay 1 and the ground fault direction relay 2
The relay operation output will be obtained under the AND condition with.

When the release flag is set in step S16, the determination result of step S1 is affirmed in the subsequent cycles, and the process immediately proceeds to step S17.

In this embodiment, since the ground fault direction relay 2 is continuously locked for 1 second after the frequency is restored, it is possible to prevent the malfunction of the ground fault direction relay 2 in an unstable state after the restoration of the accident.

Here, the operating time of the ground fault direction relay 2 is the basic frequency 50Hz.
For 50ms to 60ms, for low frequency of 25Hz 55ms to 65ms
On the other hand, if the V ₀ vibration frequency is 33.3 Hz, the cycle is about 30 ms, and if it is 30 Hz, the cycle is about 33.3 m.
In the case of s, 25 Hz, the cycle is 40 ms, which is sufficiently shorter than the operating time. Therefore, according to the present invention, the ground fault direction relay 2 can be reliably locked.

(Effects of the Invention) As described in detail above, according to the present invention, a frequency detection relay is combined to detect a low-frequency damping vibration at the time of recovery from a ground fault and detect both positive and negative waves of a zero-phase voltage to detect a ground fault in a sound line. Since it locks the directional relay, it is possible to reliably prevent malfunction of the ground fault direction relay in a healthy line without delaying the operation time as in the past, and to improve the performance of the ground fault direction relay. It is possible to increase the margin of ground fault protection cooperation with other protection relays.

In addition, since the frequency detection relay can be realized by software, there is no need to add special hardware to the conventional ground fault protection relay system, which is extremely economical.

This method detects the low-frequency damping vibration frequency of the zero-phase voltage, so it can be used even when the damping time of the damping vibration differs depending on the charging capacity of the system, etc.A method that locks by setting a fixed time limit with a timer It is possible to prevent the malfunction of the ground fault direction relay with higher accuracy than in the above. In addition, when the accident reoccurs after locking the output of the ground fault direction relay, there is no omission in the detection of the accident and there is no blind spot period.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of the present invention, and FIG.
Fig. 3 is a flow chart showing the function of the frequency detection relay, Fig. 3 is a block diagram of the ground fault direction relay, Fig. 4 is a phase characteristic diagram showing the operating range of the ground fault direction relay, and Fig. 5 is an ungrounded distribution system. FIG. 6 is a simulation circuit diagram, FIG. 6 is a zero-phase equivalent circuit diagram of the transformer for grounding type instrument, and FIG. 7 is a waveform diagram showing low-frequency damping vibration when the ground fault is recovered. 1 …… Ground fault overvoltage relay, 2 …… Ground fault direction relay 3 …… Frequency detection relay, 4 …… AND circuit

Claims (1)

[Claims] 1. A ground fault protection relay system in which a phase difference between a zero phase voltage and a zero phase current of a non-grounded distribution system is detected to determine the direction of the zero phase current to obtain an operation output of a ground fault direction relay. , The frequency of the low-frequency vibration of the zero-phase voltage after the ground fault is recovered is detected by the frequency detection relay over the positive and negative waves,
A ground fault protection relay system characterized by locking the operation output of a ground fault direction relay installed in a sound line when the frequency of the low frequency vibration is below a certain value for both positive and negative waves.