JPH03135006A - Breaker for transformer excitation rush-current suppresion - Google Patents

Abstract

PURPOSE:To control a rush current satisfactorily without making a constitution large by a method wherein a series circuit, of a series resistance and a switch, which is connected in series to a main switch of a breaker is installed inside a breaker container and an opening operation and a closing operation of the switch is controlled as required in synchronization with a closing operation of the main switch. CONSTITUTION:A series circuit, of a series resistance 5 and a resistance switch 3, which is connected in series to a main switch 4 of a breaker for a transformer is installed inside a container 20 together with the main switch 4. When the switch 4 is closed via a link mechanism 10, a driving arm 43 of a closing means is moved to the left in synchronization with the switch 4, and moves a switch 3 in conjunction with it via a hook 33 which can be moved downward freely; the switch 3 is closed before the switch 4 is closed; an excitation rush current is suppressed by means of the resistance 5. In addition, when the switch 4 is moved to the left, the hook is moved downward via the arm 43; the switch 3 is opened by means of a coil spring 34 at a point of time not less than one cycle before the switch 4 is closed; also an exciation rush current at a closing operation of the switch 4 is suppressed. Thereby, it is possible to suppress the rush current satisfactorily without making a constitution large.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transformer excitation rush current suppression circuit breaker for suppressing an excitation rush current generated when a transformer is connected to a power system using a series resistor.

[Conventional technology]

It is well known that when a transformer is directly connected to a power source, a transient current called an excitation rush current flows through the primary side. The maximum value depends on the capacity of the transformer, but it can be several times or even several times the rated current. The generation of excitation rush current causes problems such as the malfunction of the differential current relay used to detect abnormalities inside the transformer and the generation of instantaneous voltage drops in the grid. This can be dealt with by measures such as keeping constant time difference current relays from operating, and voltage drops have not been a major problem to date.

However, with the spread of office automation equipment in recent years, and especially the spread of computers, higher quality power has come to be required. The stored data disappears in an instant, and voltage fluctuations can also cause malfunctions. In the case of large computers, measures are taken to prevent the above problems by installing a dedicated stabilized power supply, but in the case of small computers such as personal computers, sufficient measures cannot be taken. A stable supply of electricity will be particularly important. In this respect, as a result of the demand for the supply of higher quality power, it is necessary to suppress the excitation rush current to a level below the rated current of the transformer to the extent that it can be considered that the excitation rush current does not actually occur. Measures to suppress excitation rush current have become increasingly important.

The generation of excitation rush current is caused by the nonlinear saturation characteristics of the transformer core, and due to a hysteresis phenomenon called residual magnetic flux, the value of the excitation rush current may further increase due to the magnetic flux remaining in the transformer core after the power is cut off. just,
The value of the excitation rush current changes depending on the phase when voltage is applied to the transformer, and the value of the residual magnetic flux changes depending on the phase when the voltage is cut off, so the magnitude of the excitation rush current is uncertain.
The conditions under which the excitation rush current is maximum and its value will be studied and countermeasures will be taken. The excitation rush current generation phenomenon under these conditions will be explained based on Figures 4 and 5. Figure 4 is a wiring diagram including the transformer, and Figure 5 is the temporal change in voltage etc. when power is turned on to this transformer. FIG. In FIG. 4, when the voltage Vg of the single-phase power supply 65 becomes exactly zero, the switch 62
Suppose that the voltage is closed and applied to the primary side of the transformer 61. In order to generate a back electromotive voltage corresponding to the voltage Vg of the power source 65, the magnetic flux density B in the iron core must have the waveform Bo shown in FIG. That is, if the maximum rated magnetic density in the iron core in a steady state for this voltage is 81, the maximum value Bs of magnetic flux density in Fig. 5 is twice this B1 and the residual magnetic flux density B.
It is the sum of A and A, and is expressed by the following formula.

Bs = 2B, +B.

On the other hand, the rated magnetic flux density Bm is generally designed to be 80% or more of the saturation magnetic flux density B1 of the silicon steel plate used for the transformer core, and the maximum value of the residual magnetic flux density B, , is the rated magnetic flux Since the densities B and I are approximately 70%, the maximum value of the maximum magnetic flux density Bs is approximately 220% of the saturation magnetic flux density.

In Fig. 5, when the magnetic flux density B is smaller than the saturation magnetic flux density Bh, the relative magnetic permeability of the iron core is very large, so the inductance of the primary winding is very large, so the exciting current 1e is small and is ignored in Fig. 5 and becomes zero. It is displayed as 5. When the magnetic flux density B becomes larger than the saturation flux density B1, the magnetic flux density in the iron core becomes saturated and the inductance of the primary winding becomes the inductance of the air core.This value is approximately the ratio of the rated voltage to the rated current as the rated impedance. Since the impedance corresponding to this air-core inductance is a fraction of the rated impedance, the current at this time is several times the rated current, and this is an excitation rush current, which is 1p in FIG. 5.

Since the magnitude of the excitation current m of a transformer of approximately several tens of MVA is less than 1% of the rated current, this excitation current +e is approximately three orders of magnitude smaller than the magnitude of the excitation peak 1JtIρ.

Magnetic flux density B° indicated by points and lines in Figure 5, excitation rush 1,
1 is a waveform when the resistance of the winding etc. is ignored, but in reality, due to this resistance, the excitation rush current rρ becomes smaller by the resistance, and the waveform of the magnetic flux density B also decreases accordingly, resulting in a direct current component. is attenuated, and in the next cycle, the portion exceeding the saturation magnetic flux density B1 becomes smaller, and therefore the exciting rush current 1p in this cycle also becomes smaller. In this way, the excitation rush attenuates over time due to the resistance component of the circuit, and eventually reaches a steady state.

Since power systems are generally balanced three-phase AC systems, there is a high probability that at least one of the three phases will generate an excitation rush current, so excitation is performed more frequently than in the case of a single phase as described above. It is known that rush currents occur. Furthermore, as mentioned above, excitation rush currents are a problem in electric power systems, so measures to suppress excitation rush currents are usually aimed at balanced three-phase AC systems.

As mentioned above, the value of the exciting rush current is determined by the relationship between the amount of residual magnetic flux in the transformer core at the time of shutoff and the closing phase at the time of turning on, so a different value of the exciting rush current is generated each time the transformer is turned on. When conducting some kind of study or countermeasure against the excitation rush, it is common to use the maximum value of the excitation rush that can be theoretically obtained as the value of the excitation rush. In order to obtain a large value of the excitation rush amount from the excitation rush current that actually occurs, it can be obtained by repeatedly turning off and turning on the power to the transformer, but such measurements may be carried out on a trial basis. However, it is not common.

The value of the exciting rush current as a large value of the exciting rush amount changes depending on the capacity of the transformer, and generally, the larger the transformer capacity, the lower the ratio of the exciting rush current to the rated current.

A large capacity vessel of around 10,000 KVA is 5 or 6 times larger, 1,000 KVA.
For small capacity transformers before and after, it is about 10 times as much.

A practical method for suppressing excitation rush current is to select the tap with the largest number of turns on the primary side when the transformer has an on-load tap changer on the downstream side and then connect it to the system. However, a method is adopted in which the above-mentioned magnetic flux density B is made as small as possible. This method is a method of reducing the magnetic flux density B with respect to the voltage of the system, and although it depends on the value of the magnetic flux density B at the maximum number of turns, it cannot be expected to significantly suppress the excitation rush current.

Although not in practical use, the following methods have been proposed as methods for suppressing excitation rush currents.

B) Two-step resistor connection There are two steps to connect a transformer to the power system, such as connecting a series resistor between the switch and the transformer, and then removing the series resistance after a certain period of time. The excitation rush current is reduced by dividing the charge into two parts. This method has been considered for a long time, but the drawbacks of this method are as follows.

The conventional way of thinking about this method is that in the first stage, the voltage borne by the transformer is reduced by nearly half using a series resistor. It is necessary to have a resistor with a capacity that is large enough not to be damaged even when short-circuit current is applied. Another drawback is that the rated voltage of the resistor must be approximately twice the voltage applied to the transformer in the first stage, since the voltage drop across the resistor and the transformer are in different phases.

Furthermore, the phases of the voltages applied to the transformer are not in phase in the first stage and the second stage, and therefore a large excitation rush current is generated again after the resistance is removed in the second stage.

This method has not been put into practical use because it has been considered to have such drawbacks.

(1) A tap changeover transformer is installed on the primary side of the transformer to be turned on, and the primary side voltage of the transformer to be turned on is sequentially increased to make the turning on without causing an excitation rush.This system was proposed by the applicant of the present invention, and has This method is disclosed in Japanese Patent Application No. 62-255980, but there is a problem in that it takes a long time to turn on the system, which poses a problem in the operation of the system.

c) Memorize the phase when shutting off and match the closing phase to this phase. This method is shown in Japanese Patent Application Laid-Open No. 55-100034, but the residual magnetic flux of the three phases is not uniquely determined by the voltage phase at the time of interruption, but is determined by the transient voltage after interruption, Furthermore, even if the l phase is blocked, if the other phases are not blocked again, the magnetic flux of the blocked phase will still change due to the electrical and magnetic coupling of the three phases, so it will not necessarily match the residual magnetic flux of each of the three phases. Since it is not always possible to input three phases at the same time, there is a problem that the expected effect of suppressing the excitation rush current cannot be obtained.

2) One of the three phases is turned on at the phase where the voltage waveform has the maximum value, and the other two phases are turned on with a delay. This method was developed in the Japanese Unexamined Patent Application Publication No. 5
5-93619 and JP-A-55-94540, it is expected that the effect of reducing the excitation rush current will be about one third compared to the case without countermeasures, but the excitation rush current can be reduced substantially. There is a problem that it is impossible to do something.

In addition to this, a method of demagnetizing the residual magnetic flux by damping vibration of an LC circuit has been considered, but it has been found that the effect is not as good as expected.

By the way, in the above-mentioned two-stage resistance method, a series resistor with a resistance value similar to the excitation impedance of the transformer is used in order to share the voltage appropriately with the transformer. When a series resistor is connected, the current value is approximately the same as the excitation current of the transformer. Generally, the excitation current has a small value of 1% or less of the rated current. There is a practical excitation rush current suppression method that focuses on the fact that various problems caused by excitation rush current can be solved by suppressing the excitation rush current to the rated current level rather than to the excitation current level. , The outline of this method is as follows.

The value of the series resistance is set to an appropriate value that is one order of magnitude smaller than the excitation impedance and one order of magnitude larger than the rated impedance defined by the rated voltage divided by the rated current of the transformer. Since the excitation impedance is more than three orders of magnitude larger than the rated impedance, a suitable value for such a series resistance exists.

When a transformer is connected to the power system, it is first connected as a first step, with a series resistor inserted in series with the transformer, and after more than one cycle has passed, the transformer is directly connected as a second step. into the power grid, but it actually shorts out the series resistor.

FIG. 6 is a circuit diagram of a transformer excitation rush current suppressing device according to the above-described method. In this figure, a three-phase transformer 1 is connected to a three-phase power supply 100, and each phase U, V,
For each W, a main switch 4 and a series circuit of a series resistor 5 and a resistor switch 3 are connected in parallel to the main switch 4 to form a transformer excitation rush current suppression device.

When turning on the three-phase transformer 1 to the power supply 100, the following sequence is performed.

■The initial state is that both main switch 4 and resistance switch 3 are open.
, and the three-phase transformer 1 is disconnected from the power supply 100.

■As the first step, the resistor switch 3 is turned on.

Since the resistance value of the series resistor 5 is an order of magnitude smaller than the excitation impedance of the three-phase transformer 1, most of the voltage of the power supply 100 is applied to the three-phase transformer 1, and as mentioned above, the iron core becomes saturated. An excitation rush current flows. However, the value of this excitation rush current is suppressed by the series resistor 5, and the current does not exceed the rated current. If the resistance value of the series resistor is R8 and the value of the rated impedance is Zll, the excitation rush current I7 is the rated current z +
+/Rs times. As mentioned above, R8 is set to a value much larger than Zll, so the excitation rush current It becomes a value much smaller than the rated current. However, the value is much larger than the excitation current in a steady state at the rated voltage.

(2) As the second stage closing, the main switch 4 is closed after one or more cycles have elapsed since the first stage closing. As a result, the series resistor is short-circuited and the three-phase transformer 1 is directly connected to the type 1ioo. However, since the voltage applied to the three-phase transformer 1 changes at this time, an exciting rush current also occurs here. By setting the value of the series resistor optimally, the excitation rush current when the first stage is turned on and the excitation rush current when the second stage is turned on can be made to approximately the same value, and this condition is the optimum condition that has the greatest excitation rush current suppression effect. It is also a condition.

■Open the resistor switch 3 at an appropriate time after the second stage is turned on.

This is to prevent short-circuit current and the like from being interrupted by the main switch 4, and at this time, the resistance switch 3 does not interrupt the current.

[Problems to be Solved by the Invention] The structure of the transformer excitation rush current suppressing device that actually turns on and off the power supply 100 of the three-phase transformer 1 is as follows. Reuse the circuit breaker that is always provided regardless of the suppression device.

A series resistor 5 and a resistor switch 3 are connected in series in parallel to this circuit breaker as the main switch 4, but since the series resistor 5 has the same high voltage to ground as the power supply 100, this high voltage It is necessary to have dielectric strength sufficient to withstand
Since the resistance switch 3 only turns on the power and the current flows only for a short time, the rated current may be small, but in terms of insulation, it requires the same dielectric strength as the main switch 4. There is also the problem that they are expensive and require a large installation area because they are each installed independently. In addition, in order to set the closing time of the resistance switch 3 at least one cycle before that of the main switch 4, the switches 3 and 4 must be high-performance switches with small variations in the closing time. In addition, a control device is required to accurately control the closing point and to control the resistor switch 3 to return to the open state after the main switch 4 is closed. This makes the device expensive.

It is an object of the present invention to solve such problems and provide a transformer excitation rush current suppressing device that is inexpensive and hardly increases the installation area.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, in a circuit breaker for connecting or disconnecting a transformer from the power system, a series resistor connected in parallel to the circuit breaker and a resistor switch are connected in series. A circuit is provided in the case of the circuit breaker, and in synchronization with the movement of the movable contact of the circuit breaker as a main movable contact, a movable contact of the resistor switch as a movable contact for resistance is driven so that the main switch closing driving means for causing the resistor switch to close a predetermined time before the resistor switch becomes closed; and opening the resistor switch after a predetermined time elapses after the main switch becomes closed. It shall be provided with a return means for returning to the state.

[Effect]

In the configuration of this invention, a series circuit of a series resistor and a resistor switch is provided in the same container as the main switch and connected in parallel to the main switch, thereby making it possible to install only the circuit breaker which is the main switch. It is possible to create a transformer excitation rush current suppressing device with almost the same installation area as in the case of the present invention.

By driving the resistor movable contact in synchronization with the movement of the main movable contact by the closing drive means and closing the resistor switch before the main switch is closed, the series resistor is first connected to the transformer. Since the power is turned on while connected in series with the resistor, the series resistor suppresses the excitation rush current.

By setting the time for the main switch to close after the resistance switch is closed to a value not less than one cycle, the excitation rush generated when the main switch becomes closed can be reduced from the initial It can be suppressed to a value comparable to the excitation rush current.

By subsequently returning the movable resistance contact to its original position by means of a return means, it is possible to avoid trouble occurring when the resistance switch is opened and the transformer is cut off from the power system during subsequent operation. can.

(Embodiment) Fig. 1 is a sectional view of a transformer excitation rush current suppression circuit breaker showing an embodiment of the present invention.In this figure, a main switch 4 and a resistor switch 3 for a series resistor 5 are shown. The main switch 4 consists of a main fixed contact 41 and a main movable contact 42, and the main movable contact 42 is moved in the left-right direction in the figure by a link mechanism driven by a hydraulic jack (not shown). The main fixed contact 41 is connected to a pull-out lead 61, and the main movable contact 42 is connected to a pull-out lead 62, and these pull-out leads 61 and 62 are pulled out through the bushing 63 and 64. Main switch 4, drawer leads 61, 62, bushings 63.6
4 and the container 20 basically have the same configuration as a circuit breaker provided for turning on and cutting off a transformer, regardless of excitation rush current suppression.

The resistor switch 5 consists of a fixed resistor contact 31 and a movable resistor contact 32. A series resistor 5 is connected between the fixed contact 31 and the main fixed contact 41, and the movable resistor contact 32 is connected to the main movable contact. It is electrically connected to the contact 42, and is moved to the left side in the drawing in synchronization with the main movable contact 42 by a drive arm 43 when the main movable contact 42 is turned on. The drive arm 43 is fixed to the main movable contact and moves together with the main movable contact 42 which is driven by the link mechanism 10 and moves.

The separation distance between the main fixed contact 41 and the main movable contact 42 from the contact position is larger than the separation distance between the resistance fixed contact 31 and the resistance movable contact 32. Therefore, the main movable contact 32 When the movable resistor contact 42 moves together toward the left side of the figure, the movable resistor contact 42 contacts the fixed resistor contact 41 first.

FIG. 2 is an enlarged cross-sectional view of the main part of FIG. 1, and shows a portion including the resistor switch 3 on an enlarged scale. In this diagram,
The drive arm 43 moves together with the main movable contact 42 of FIG.
When pressed, the movable resistance contact 32 will also move with this force. The latch 33 is fixed in position in the horizontal direction in the figure with respect to the movable resistance contact 32, and is movable between the lower parts of the figure, and moves to the left to connect to the stopper 37. When it hits the upper slope, it is pushed downward, and as a result, it comes off the drive arm 43. When the latch 33 is removed from the drive arm 43, the restoring force of the coil spring 34 causes the movable resistance contact 32 to return to its original position. The drive arm 43 returns to the illustrated position when the main switch 4 is in the open state.

FIG. 3 is a diagram showing temporal changes in the stroke, which is the moving distance of the main movable contact 42, and the open/close states of the main switch 4 and the resistance switch 3 in FIGS. 1 and 2. FIG. In this figure, the horizontal axis represents time, and the vertical axis represents stroke distance, and also shows the distinction between the open state and closed state of the main switch 4 and the resistance switch 3.

The stroke, which is the moving distance of the main movable contact 42 in the left direction in the diagram, is initially at the lowest position, and the main switch 4 at this time is at the lowest position.
and resistance switch 3 are both in an open state. Driven by the link mechanism 10, it accelerates for a short period of time, increases at a substantially constant speed, and finally moves to the rightmost position and then stops. As the stroke increases, as mentioned above, the resistor switch 3 is configured so that the contacts come into contact with each other sooner, so the movable resistor contact 32 first changes to the fixed resistor contact 31 at time T. The resistance switch 3 is brought into a closed state by contact with
becomes closed. Further, as the latch 33 in FIG. 2 hits the stopper 37, the movable resistance contact 32 returns to its original position, so the resistance switch 3 returns to the open state at time T.

By setting the value of time ΔT, which is the difference between the times when the resistance switch 3 and the main switch 4 reach the closed state, to one cycle or more, the excitation that occurs when the main switch 4 becomes the closed state can be reduced. Rush current can be suppressed. One cycle is 20m5ec when the frequency is 507, and 18.3m5 when the frequency is 607.
ec, so it is set to a value that is common to 507, 60) IZ and has a margin, such as 22m5ec, taking into account machining errors and variations in the operating speed of the link mechanism. do.

In Figs. 1 and 2, a method is shown in which the separation distances between the fixed contacts and movable contacts of the main switch 4 and the resistance switch 3 are made different in order to secure the time ΔT. Alternatively, the resistance movable contact 32 may be moved earlier than the main movable contact 42 using the phosphor mechanism, thereby making a difference in the point at which the closed state is reached. Also, Figure 1 and 2
Contrary to the diagram, the drive arm is attached to the movable resistance contact 32, a latch is provided to the main movable contact 42, and the link mechanism 10 directly drives the movable resistance contact, and the movable resistance contact is placed at a certain distance. It is also possible to adopt a configuration in which the drive arm hits the latch when the main movable contact is moved and drives the main movable contact.

At this time, the return means for returning the movable resistance contact to its original open position will have an appropriate configuration depending on the drive means. In any case, the time points at which the two movable contacts reach the closed state can be reliably shifted by creating a time difference depending on the mechanical configuration.

Since the resistor switch 3 and the series resistor 5 are housed in the same container 20 as the main switch 4, they are made of the same insulating medium as the main switch 4, for example, sulfur hexafluoride, which is generally abbreviated as SF6. Since it is insulated with an insulating gas, a dielectric strength comparable to that of the main switch 3 can be easily and compactly achieved. The value of the series resistor 5 is set to such a value that the initial excitation rush current becomes a fraction of the rated current, and the energization time is only the aforementioned time ΔT, so the resistance between the series resistor 5 and the resistor switch 3 is The current capacity may be much smaller than that of the main switch 4, and by storing it in the same container 20, the container 2
The increase in the size of 0 will not be very large.

〔Effect of the invention〕

As mentioned above, in this invention, by installing the series resistor and its switch in the same container as the main switch, the transformer excitation rush current suppression circuit breaker is almost different from the case where only a conventional circuit breaker is installed. This makes it possible to install it in a small footprint. The main movable contact and the movable resistor contact are driven synchronously by a closing drive means so that the point in time when the resistor switch becomes closed is earlier than the time when the main switch becomes closed by a predetermined time. As a result, the series resistor is first connected to the transformer in series before the power is turned on, so that the series resistor suppresses the excitation rush current. By setting the difference in time to the closed state to a value not less than one cycle, the excitation rush that occurs when the main switch becomes the closed state can be suppressed to a value comparable to the initial excitation rush. Subsequently, the resistor movable contact is returned to its original position by the return means, and the resistor switch is opened, thereby avoiding trouble when the transformer is cut off from the power system during subsequent operation.

In this way, the installation area does not increase much compared to conventional circuit breakers, and the cost is reduced by storing the series resistor and its switch in one container compared to when each is provided separately. You can also get the effect of Since the installation area is not much different from conventional ones and the price is low, this transformer-excited rush current suppression circuit breaker can be easily installed on existing transformers, so it can be used in a wider range of power systems. This also has the effect of contributing to quality improvement.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a transformer exciting rush current suppression circuit breaker showing an embodiment of the present invention, Fig. 2 is an enlarged sectional view of the main part of Fig. 1, and Fig. 3 is a stroke of a movable contact and opening/closing of a switch. A line diagram showing changes over time with the state of , Figure 4 is a wiring diagram including a transformer,
FIG. 5 is a waveform diagram showing temporal changes in voltage, etc. when the power is turned on, and FIG. 6 is a circuit diagram of the transformer excitation rush current suppressing device. 2...Transformer excitation rush current suppression circuit breaker, 2o...Container,
3... Resistance switch, 31... Resistance fixed contact, 3
2... Movable contact for resistance, 33... Latch 33.34.
・・Fixed contact spring (returning means), 37 ・Weight, 4・
...Main switch, 41...Main fixed contact, 42...Main movable contact, 43...Drive arm (closing drive means), 5...Series resistance, 1...Three-phase transformer ( transformer), 100...power supply. 3 circles diagram 4

Claims (1)

[Scope of Claims] 1) In a circuit breaker for connecting or disconnecting a transformer from the power system, a series circuit consisting of a series resistor and a resistor switch connected in parallel to the circuit breaker is connected to the circuit breaker. A point in time when the movable contact of the resistance switch, which is a movable resistance contact, is driven in synchronization with the movement of the movable contact of the circuit breaker, which is a main movable contact, and the main switch is in a closed state. closing driving means for bringing the resistor switch into a closed state before a predetermined time; and return means for returning the resistor switch to an open state after a predetermined time has elapsed after the main switch has been in a closed state. A circuit breaker for suppressing a transformer excitation rush current, characterized by comprising: