JPH0480613B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a relay device that detects a ground fault current in the event of a ground fault accident on a high voltage line, etc. and performs a protective operation. Concerning what is detected by a flow device.

Conventional technology A ground fault relay device detects ground fault current when a ground fault occurs on a line, and when this ground fault current flows over a certain value, it issues an alarm or disconnects the faulty line. This is a relay device that performs certain protective operations such as.

Penetrating zero-phase current transformers are widely used to detect this ground fault current. A through-type zero-phase current transformer winds the secondary windings distributed around an iron core that has through holes through which three-phase primary conductors pass, and one
When a ground fault occurs in the next circuit, an output proportional to the ground fault current is output to the secondary winding.

Problems to be Solved by the Invention When a zero-phase current transformer is installed in a high-voltage distribution board, the through-hole of the zero-phase current transformer has a relatively small diameter, so it is necessary to insert three-phase high-voltage primary conductors into this through-hole. When penetrating, it is necessary to strictly insulate between each conductor and between the conductor and the core or secondary winding, and before and after penetrating, it is necessary to separate the conductors of the three phases by a certain distance. It is not easy and requires space.

Therefore, a method has been attempted in which separate current transformers are installed in the high-voltage primary conductors of each phase, and the secondary sides are connected in parallel to obtain zero-sequence current output from both ends (hereinafter referred to as the 3CT method). However, when there is a sudden increase in load current, for example when a switch is turned on, residual current output (if a current exceeding the rated current flows, the iron core will become saturated,
Since the saturation point is not the same for each current transformer, the secondary output becomes unbalanced and an apparent zero-sequence current flows. )
Since this output cannot be distinguished from the zero-sequence current caused by a ground fault accident, it has the disadvantage that the ground fault relay malfunctions, and is not put to practical use.

The present invention has been made in view of the above points, and uses the 3CT method, which requires a small installation area of the switchboard and is easy to install. The purpose of the present invention is to provide a ground fault relay device that does not malfunction by determining whether the ground fault is caused by a ground fault.

Measures to solve the problem Detect the zero-sequence current by connecting current transformers installed in each of the three phases in parallel, and output a zero-sequence current output signal when the zero-sequence current reaches a set level. A ground fault relay device configured to operate a relay includes a detection means for detecting a zero-sequence voltage using the stray capacitance of each current transformer, and a detection means for detecting a zero-sequence voltage by using the stray capacitance of each current transformer, and a storage means for storing a residual voltage signal based on capacitance unbalance; a synthesis means for synthesizing the stored signal and a zero-sequence voltage signal generated at the time of a ground fault; and when the synthesized signal reaches a set level. The apparatus includes level detection means for outputting a zero-phase voltage output signal, and means for operating the relay when the zero-phase voltage output signal and the zero-phase current output signal are output simultaneously.

Operation Under normal conditions with no ground faults, zero-sequence current does not flow, and even if residual voltage occurs when the stray capacitance of the current transformer installed in each phase is unbalanced, the zero-sequence current does not flow. Since no voltage is generated, there is no combined output signal, so the relay does not operate.

When a ground fault occurs and the zero-sequence current exceeds the set level, the zero-sequence voltage also reaches the set level when the composite voltage of the stored normal residual voltage and the zero-sequence voltage that occurred due to the ground fault occurs. Then, output signals of zero-sequence current and zero-sequence voltage are output, an AND condition is established, and the relay operates. In addition, if the load current suddenly changes when the load switch is turned on and an apparent zero-sequence current flows and reaches the set level, a zero-sequence current signal is output, but no zero-sequence voltage is generated. Therefore, the AND condition does not hold and the relay does not operate.

As described above, it is possible to obtain this type of relay device that does not operate unless the zero-sequence current due to a ground fault flows at a set level or higher, and is free from malfunctions.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a block wiring diagram showing an embodiment of the present invention, where I ₀ is a zero-sequence current, 1 is an amplifier for amplifying the zero-sequence current, and 2 is a zero-sequence current amplified by a rectifier. rectify. 3 is a level detection circuit which outputs a zero-phase current output signal to an AND gate 9, which will be described later, when the output of the rectifier 2 exceeds a set level. V ₀ is the zero-sequence voltage, 4 and 5 are amplifiers arranged in parallel to amplify the zero-sequence voltage, and 6 is a memory circuit (for example, a delay circuit), which is the output of the amplifier 5 during normal operation. remember. 7 is a differential amplifier, which combines the outputs of the amplifier 4 and the memory circuit 6, extracts the amount of change at the time of a ground fault from the residual output voltage, amplifies it, and sends it to the level detection circuit 8.
Output to. When the output of the differential amplifier 7 exceeds a set value, the level detection circuit 8 outputs an AND gate 9.
output signal to. AND gate 9 outputs an output signal to timer 10 when output signals from level detection circuits 3 and 8 are input simultaneously. When the timer 10 receives the signal from the AND gate 9, it outputs an output to the relay 11 after a set time, activates the relay, and disconnects the breaker (not shown) or the like.

Figure 2 is a circuit diagram for detecting zero-sequence current I ₀ and zero-sequence voltage V ₀ , where R, S, and T are high voltage 1 of each of the three phases.
The secondary conductors, CT1, CT2, and CT3, are current transformers provided individually in each high-voltage primary conductor, and their secondary windings are connected in parallel with each other and connected to a resistor r. A zero-phase current signal I ₀ is detected from both ends of this resistor r. ZPC
is a zero-phase voltage detection device, and each current transformer CT1, CT2,
Provided between one of the common connection lines of CT3 and earth E. CP is a voltage dividing capacitor, T is a transformer, and the zero-phase voltage signal is output from the secondary winding side of this transformer T.
Detect V ₀ . LS indicates the load switch.
Figure 3 shows an equivalent circuit for detecting this zero-sequence voltage, C ₁ , C ₂ , and C ₃ represent the stray capacitance between each current transformer and the high-voltage primary conductor, and Figure 4 shows each current transformer. This is to explain the residual voltage output when the stray capacitance of the device is unbalanced. When there is unbalance, the original neutral point N becomes the neutral point N' due to the stray capacitance, and N-N ′ residual voltage always appears.

Next, the operation of the above configuration will be explained.

Current transformers CT1, CT2, CT3 installed in each phase
The stray capacitances C ₁ , C ₂ , C ₃ are the shape of each current transformer,
They are not the same due to differences in installation methods, etc. Therefore, even in normal conditions, simply combining these capacitances will always output a residual voltage V _x equivalent to N-N' as shown in Figure 4. ing. This residual voltage
V _x is input as the zero-phase voltage signal V ₀ in FIG. This residual voltage V _x is amplified by amplifiers 4 and 5, and one is inputted to a differential amplifier 7 via a storage circuit 6, and the other is inputted as is to a differential amplifier 7. Therefore, under normal conditions, the input signal of the amplifier 4 is also V _x , so the input signal of the differential amplifier 7 is compared with V _x , and since there is no output signal of the difference, the level detection circuit The zero-phase voltage output signal from 8 is not output. Further, since the zero-sequence current does not flow under normal conditions, no zero-sequence current output signal is output from the level detection circuit 3, so no output signal is output from the AND gate 9, and the relay 11 is in a non-operating state.

In such a normal state, for example, a load switch
If Ls is turned on and an inrush current larger than the rated current instantaneously flows through the primary conductors R, S, and T, an imbalance will occur in the output currents of current transformers CT1, CT2, and CT3, and the An apparent zero-sequence current I ₀ is generated, which may exceed the set level of the level detection circuit 3 and output a zero-sequence current output signal to the AND gate 9. However, in this case, the zero-phase voltage V ₀ is only the residual voltage V _x and is unchanged from the normal state, so no output signal is output from the level detection circuit 8, so the AND condition of the AND gate 9 is not satisfied, and the relay 11 side It does not output any output signal.

Next, if a ground fault occurs at point g of one line of conductors R, S, and T, and the zero-sequence current _I0 reaches the set level of level detection circuit 3, an output signal is sent to AND gate 9. At the same time, a zero-phase voltage is also generated, and the voltage N'→g in FIG. 4 appears and is input to the differential amplifier 7. A voltage corresponding to N′→g and N′−N is input to the differential amplifier 7, and the zero-phase voltage signal NN→g that should be originally obtained is obtained by the differential amplifier 7, and the level detection circuit 8 is input. When the output signal of this level detection circuit 8 exceeds a set level, an output signal is outputted from the level detection circuit 8 and inputted to the AND gate 9. At this time, the AND condition is satisfied and an output signal is sent to the timer 10, and after a set time, a signal is given to the relay 11, which causes the relay 11 to cut off the breaker or issue an alarm to perform a protective operation.

Effects of the Invention As described above, it was conventionally believed that zero-sequence current detection using the 3CT method involved a large residual current, which would lead to error differences and be difficult to put into practical use when used for ground fault relaying. In the invention, the zero-sequence voltage is detected using the stray capacitance between each current transformer of the 3CT and the high-voltage primary conductor, and the relay is operated according to the AND condition of this zero-sequence voltage signal and the above-mentioned zero-sequence current signal. In this way, it is possible to obtain a ground fault relay that does not malfunction due to residual current, and since the high-voltage primary conductor of each current transformer can be installed separately for each phase, the installation area within the switchboard is greatly reduced, making the switchboard more compact. It also makes installation and wiring work extremely easy. Furthermore, in order to obtain a zero-sequence voltage signal, conventionally it was necessary to separately install a high-voltage capacitor for zero-sequence voltage detection in the electrical circuit in the switchboard, but with the present invention, the stray static Since it utilizes capacitance, it has excellent effects such as no need for new installation and the total cost of this type of relay device can be reduced.

[Brief explanation of drawings]

Fig. 1 is a block wiring diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram for detecting zero-sequence current and zero-sequence voltage, Fig. 3 is an equivalent circuit diagram of Fig. 2, and Fig. 4 is an explanatory diagram of residual voltage. 1, 4, 5...amplifier, 2...rectifier, 3,8
... Level detection circuit, 6 ... Memory circuit, 7 ......
Differential amplifier, ZPC...Zero phase voltage detection device, CT1,
CT2, CT3...Current transformer, _C1 , _C2 , _C3 ...Stray capacitance.

Claims (1)

[Claims] 1 A ground fault system in which current transformers installed in each of the three phases are connected in parallel to detect the zero-sequence current, and when the zero-sequence current reaches a set level, an output signal is output to operate the relay. In the relay device, the zero-sequence voltage is detected using the stray capacitance of each current transformer, and the zero-sequence voltage is stored in advance as a residual voltage signal based on the unbalance of the stray capacitance of each phase. This stored signal and the zero-sequence voltage signal that occurs during a ground fault are synthesized, and when the combined signal reaches a set level, a zero-sequence voltage output signal is output, and the zero-sequence voltage output signal and the zero-sequence current are output. A ground fault relay device characterized in that the relay is operated when an output signal is output at the same time.