JPH0526902Y2 - - Google Patents

Description

[Detailed explanation of the invention] [Purpose of the invention] (Field of industrial application) This invention is a gas insulated switchgear (hereinafter referred to as GIS).
This invention relates to grounded instrument transformers (hereinafter referred to as PT) installed in

(Prior art) In Figure 2, which shows an equivalent circuit of a conventional PT installed in a GIS, 1 is a power supply, 2 is a circuit breaker,
C ₁ is the interelectrode capacitance of circuit breaker 2 (hereinafter referred to as C ₁ ),
C ₂ is the ground capacitance of the GIS bus (hereinafter referred to as C ₂ ),
5 indicates the PT, 6 indicates the iron core of the PT5, 7 indicates the primary winding of the PT5, 8 indicates the secondary winding of the PT5, and 9 indicates the load on the PT5.

Now, when the circuit breaker 2 is opened in Fig. 2, in the circuit composed of C ₁ of the circuit breaker 2, C ₂ of the GIS bus bar, and the resistance and inductance of PT5, the voltage peak value at the time of interruption, the interruption phase If the following conditions are met, the frequency will be as the secondary terminal voltage of PT5.
A waveform may appear that is lower than the rated frequency, has a voltage peak value higher than the voltage division ratio of C ₁ and C ₂ , and continues without attenuation. This phenomenon is well known as the fero-resonance phenomenon of PT installed in GIS.

As a method for suppressing this iron resonance, it is known to connect a saturable reactor 10 to the secondary winding 8 of the PT in parallel with the load 9, as shown in FIG. Here, since the saturable reactor 10 is always connected to the secondary terminal of the PT, it is a condition that magnetic saturation is not reached in the normal use state of the PT, that is, at the rated frequency and the maximum working voltage.

As described above, the saturable reactor 10 shown in FIG. 3 does not reach magnetic saturation in normal use, and therefore has a high impedance, so that almost no current flows into it. On the other hand, when ferroresonance occurs, a low-frequency voltage is applied between the terminals of the saturable reactor 10, resulting in magnetic saturation, resulting in low impedance, and a sufficiently large current flows into the saturable reactor 10 compared to the normal operating state. Flow into. Therefore, the ferroresonance is suppressed by the damping effect due to the resistance loss of the saturable reactor 10.

However, with this method, the residual voltage E ₀ (V) when the circuit breaker 2 is opened is expressed by equation (1).

E ₀ = C ₁ / C ₁ + C ₂ E ₁ (V) ...(1) However, E ₁ is the power supply voltage value. If this residual voltage E ₀ is large, the energy energized by power supply 1 via C ₁ On the other hand, the energy consumed by the saturable reactor 10 may become small, and therefore, it may not be possible to suppress ferroresonance.

For this reason, as another method for suppressing the iron resonance more reliably, there has been proposed, for example, Japanese Utility Model Application No. 60-99837. This will be explained with reference to FIG. When iron resonance occurs, the PT iron core 6 periodically repeats magnetic saturation and non-saturation. When the iron core 6 of the PT is magnetically saturated, the excitation impedance becomes small, and therefore a large excitation current flows. This large excitation current is detected by a current relay 11 connected to the ground side of the primary winding 7. Then, current relay 1
The first contact 11a is closed and the resistor 12 is inserted between the terminals of the secondary winding 8. This resistor 12
If it is made sufficiently smaller than the impedance of the load 9, most of the secondary current will flow into the resistor 12, and fero-resonance will be suppressed by the damping effect due to resistance loss.

(Problems to be solved by the invention) The resistor input method described in the prior art has the following problems. In other words, when the inserted resistor 12 is tripped after the ferroresonance has been suppressed, a transient phenomenon occurs to cut off the large current flowing through the resistor 12, which may cause an overvoltage or return to the ferroresonant state again. Ta.

Further, the current relay 11 must operate reliably when fero-resonance occurs. However, the current at the time of iron resonance is a distorted wave, and therefore it is difficult to set the operating accuracy of the current relay 11. Furthermore, current relay 11
There was also a risk that the resistor 12 would malfunction due to rush current or surge current when the voltage was turned on, and that the resistor 12 would be turned on even though ferroresonance was not occurring.

The purpose of this invention is that after the CB of the system is opened,
An object of the present invention is to provide a voltage transformer that can reliably prevent the occurrence of iron resonance.

[Structure of the device] (Means and effects for solving the problem) The present invention is a connection system that is connected to a system having a circuit breaker and is composed of an iron core and a primary winding and a secondary winding wound around the iron core. In topographic instrument transformers,
Between the terminals of the secondary winding, there is a contact that closes almost simultaneously with the opening of the circuit breaker and opens after a certain period of time, so that magnetic saturation does not occur at the residual voltage at the rated frequency after the circuit breaker is opened, but when the circuit breaker is closed. This system is characterized by the connection of a saturable reactor that magnetically saturates at an operating voltage of .

According to the present invention, when the system breaker opens,
Almost at the same time, the contacts connected to the secondary side of the potential transformer close, ensuring that the suppressing impedance is injected between the terminals of this secondary winding, so that current flows into the saturable reactor of the suppressing impedance, causing resistance loss. As a result, a damping effect is produced, and the ferro-resonance is effectively suppressed. In addition, the saturable reactor is opened after the ferroresonance has been suppressed, but since the saturable reactor is not magnetically saturated and has high impedance when opened, only a small excitation current flows, and this Even if a very small current is cut off, there is no occurrence of overvoltage or recurrence of ferroresonance.

(Example) An example of the present invention will be described with reference to FIG. In Fig. 1, 6 is the iron core of PT5 according to the present invention, 7
is the primary winding of PT5, 8 is the secondary winding of PT5, 13
is the suppression impedance. 14 is the operation circuit 1
8, the contactor connected to the control lines P and N, 14a is the a contact of the contactor 14, 15 is the auxiliary relay, 15a is the a contact of the auxiliary relay, 16 is the timer, 16a is the contact of the timer, 17 is the contact of the circuit breaker It is a contact that is linked to opening and closing operations.

Next, the operation of the voltage transformer of the present invention will be explained. Now in Figure 1, when the circuit breaker opens, contact 1
7 is closed, and since the timer 16 is inactive and its contact 16a is closed, the auxiliary relay 15 is energized and its contact 15a is closed. Therefore, the contact 14a of the contactor is closed and the suppressing impedance 13 is applied between the terminals of the secondary winding 8 of the PT5. Next, when the time set by the timer 16 (sufficiently longer than the time required for suppressing ferro-resonance) has elapsed, the contact 16a of the timer 16 opens, the auxiliary relay 15 is deenergized, and the contact 15a opens. Therefore, the contact 14a of the contactor 14 opens and the suppressing impedance 13 becomes PT.
5 is removed from between the terminals of the secondary winding 8.

In the present invention, the suppressing impedance 13 can be reliably introduced between the terminals of the secondary winding 8 of the PT 5 in a simple manner without using a conventional current relay or the like for detecting the ferro-resonance phenomenon.

Furthermore, a saturable reactor is used as the suppressing impedance 13, and this saturable reactor has a terminal voltage that is not magnetically saturated at least at the voltage value E (V) shown in equation (2) at the rated frequency, and is magnetically saturated at the rated frequency and rated voltage. If this is done, the following advantages will arise.

E=C ₁ /C ₁ +C ₂ Emax (V) ...(2) However, Emax: Secondary conversion maximum working voltage In other words, the saturable reactor is applied between the terminals of the secondary winding 8 of PT5 almost at the same time as CB is opened. If ferro-resonance occurs at this time, a low-frequency voltage is applied between the terminals of the saturable reactor, leading to magnetic saturation.

Furthermore, in the present invention, the voltage value at which the saturable reactor reaches magnetic saturation is smaller than that of the constantly connected saturable reactor shown in FIG. Therefore, compared to the case where a constantly connected saturable reactor is connected, magnetic saturation occurs for a longer time, and a large excitation current flows.

Therefore, the resistance loss of the saturable reactor of the present invention is larger than that of the conventional always-connected saturable reactor, and therefore a large fero-resonance suppressing effect can be obtained. Further, the saturable reactor is opened after the fero-resonance is suppressed. When open, the saturable reactor is not magnetically saturated and has a high impedance, and only a small excitation current flows. Therefore, even if this current is cut off, an overvoltage as explained in Fig. 4 of the conventional example or iron There is no resonance recurrence. Therefore, it can be said that this is an extremely reliable ferroresonance suppression method.

[Effects of the invention] As explained above, according to the invention, when the system breaker opens, the suppression impedance is reliably injected into the secondary side of the potential transformer almost at the same time, so that the current flows through the suppression impedance. flows into the saturable reactor, and can effectively suppress ferroresonance. Furthermore, the saturable reactor is opened after ferroresonance has been suppressed, but since it has a high impedance, only a small excitation current flows, and there is no occurrence of overvoltage or recurrence of ferroresonance.

Therefore, it is possible to obtain a voltage transformer with a large effect of suppressing fero-resonance.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the instrument transformer of the present invention, Fig. 2 is an equivalent circuit diagram showing the principle of occurrence of ferroresonance phenomenon, and Figs. 3 and 4 are conventional ferroresonance suppressing devices. FIG. 5...Instrument transformer, 6...PT iron core, 7...
...PT primary winding, 8...PT secondary winding, 9...
Load, 10... Saturable reactor, 13... Suppression impedance, 14... Contactor, 14a... Contact of contactor, 15... Auxiliary relay, 15a... Contact of auxiliary relay, 16... Timer, 16a... …
Timer contact, 17...A contact that operates when the circuit breaker opens and closes.

Claims (1)

[Scope of utility model registration request] In a grounded instrument transformer connected to a system having a circuit breaker and consisting of an iron core and a primary winding and a secondary winding wound around the iron core, the circuit breaker is connected between the terminals of the secondary winding. A saturable reactor that is not magnetically saturated at the residual voltage of the rated frequency after the circuit breaker is opened, but is magnetically saturated at the operating voltage when the circuit breaker is closed, is created through a contact that closes almost simultaneously with the opening of the circuit breaker and opens after a certain period of time. An instrument transformer characterized in that it is connected.