JPH0320976B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a power transmitting and receiving device that can transport alternating current power (hereinafter referred to as AC power) and direct current power (hereinafter referred to as DC power) in a single power transmission network. In particular, we aim to integrate AC and DC transmission lines, and furthermore,
By improving the DC shedding system,
Enables unified operation of AC and DC power
This relates to power transmission and reception equipment for AC/DC multiplex power transmission lines.

Since the present invention belongs to a somewhat special field, there is no established conventional example.
As a device to superimpose AC power on the same transmission line,
For example, there is a document such as Figure 2.6 on page 30 of "DC Power Transmission" by Takehiko Machida, published by Tokyo Denki University Press, March 1978. In this specification, this will be explained as FIG. 1a with some arrangement to make it easier to understand.

First, the advantages of superimposed AC and DC power transmission are:
The following are listed.

(a) There is no need for direct current or disconnectors, which are difficult to develop, and Figure 1b
The branch load can be set freely as shown in the figure.

(b) DC power can be superimposed beyond the power transmission capacity limit due to the stability of the AC system, making it suitable for long-distance power transmission.

(c) Since AC lines are used as shown in Figure 1c,
No new DC line is required.

In FIG. 1a, the AC system circuit is a three-layer AC circuit. 1 is the AC power supply, 2 is the power transmission side transformer, 3 is the primary coil of the power transmission side transformer 2, 4
is the secondary coil of transformer 2, 5 is the multiplex transmission line, and 6 is the secondary coil of transformer 2.
is the transformer on the receiving side, 7 is the primary coil of the transformer 6 on the receiving side, 8 is the secondary coil of the transformer 6, and 9 is the secondary coil of the transformer 6 on the receiving side.
AC load, 12 is ground.

40 is a block capacitor for blocking the DC power supply.

On the other hand, 10 is a DC power source, 41 is a DC connection transformer on the power transmission side, and 43 is its col.

43 is a DC reactor for DC voltage smoothing.
11 is a DC load, and this DC load is symmetrically connected to the DC power supply 10 between the neutral point of the DC coupling transformer 44 on the receiving side and the ground 12.

Next, the effect will be explained.

The three-phase AC power is sent from the transformer 2 on the power transmission side to the transformer 6 on the power reception side via the block capacitor 40, and is consumed by the AC load 9.

DC power is supplied from the DC connection transformer 41 on the power transmission side.
It is sent to the DC coupling transformer 44 on the power receiving side via the DC reactor 43, and is consumed by the load 11 connected to its neutral point. DC power supply AC transformer 2,
6 is blocked by blocking capacitor 40.

In addition, when the three-phase AC is balanced, the interference of the AC voltage to the DC power supply 10 is caused by the DC coupling transformer 4.
This is prevented by the neutral point potential of 1,44 becoming zero.

Furthermore, the DC coupling transformer has the function of suppressing the inflow of AC current through the inductance of its windings.

In the multiplex transmission line 5, the current is the AC load current
The transmission current is a superimposition of the DC load current, and the potential is
It is a superimposition of AC voltage and DC voltage.

However, the circuit of FIG. 1a has the following drawbacks.

(a) Since AC power is sent through the block capacitor 40, the voltage at the receiving end changes greatly due to fluctuations in the load 9.

(b) When the three-phase load 9 is not balanced, a zero-phase voltage is generated at the neutral point of the DC coupling transformers 41 and 44, and the voltage of the DC load fluctuates.

(c) In the case of a ground fault in multiple power transmission lines, the potential at the neutral point of the DC coupling transformers 41 and 44 increases, and there is a possibility of an accident due to the ground fault current flowing from the AC system to the DC system.

(d) DC coupling transformer 41,
In order to prevent the magnetic circuit of 44 from becoming saturated,
A huge iron core is required. If the magnetic circuit becomes saturated, excessive alternating current will flow in, potentially causing an accident. Therefore, the DC coupling transformer becomes extremely expensive.

The present invention was made to eliminate the drawbacks of the AC/DC multiplex power transmission/reception device as described above.
By using the series resonant circuit as an AC filter and the LC parallel resonant circuit as a DC filter, AC
Electrically separate the system and DC system, and connect them to the AC system.
AC/DC with transient mutual interference removed from DC system
The purpose is to provide a power transmission/reception device for multiple power transmission lines.

FIG. 2 is a basic circuit diagram of the present invention, in which three-phase alternating current is expressed as a single phase. In Figure 2, 1 is
AC power supply, 2 is the power transmission transformer, 3 is this transformer 2
4 is the secondary coil of transformer 2,
13 is a capacitor, and 14 is a reactor. The capacitor 13 and the reactor 14 have a series resonance relationship at the AC frequency. The power receiving side of the AC is configured symmetrically to the power transmitting side of the AC. That is, 9
is the AC load, 6 is the power receiving transformer, 8 is the secondary coil of this transformer 6, 7 is the primary coil of the transformer 6, 13 is the capacitor, 14 is the reactor,
There is a series resonance relationship at the AC frequency.

On the other hand, 10 is a DC power supply, 15 is a capacitor, 1
6 is a reactor. The capacitor 15 and reactor 16 have a parallel resonance relationship at the AC frequency. Similarly, on the power receiving side, 11 is a DC load, and a capacitor 15 and a reactor 16 are the aforementioned parallel resonant circuit. Reference numeral 5 denotes a multiplex power transmission line, which interconnects the AC/DC power transmitting device A and the AC/DC power receiving device B. 17
is a cutout inserted into the multiplex power transmission line 5.

The operation of the present invention will be explained below. Multiplex transmission line 5
Consider that AC voltage and DC voltage are superimposed.
Since the capacitor 13 and the reactor 14 have a series resonance relationship at the AC frequency, from the perspective of the AC power supply 1,
Impedance is zero. On the other hand, when viewed from the DC power source, the impedance of the capacitor 13 is infinite. Therefore, the current flowing through the series resonant circuit of the capacitor 13 and the reactor 14 is only an AC current.

Similarly, the capacitor 15 and reactor 16 are
Since there is a parallel resonance relationship at AC frequency, AC power supply 1
When viewed from above, the impedance is infinite. On the other hand, when viewed from the DC power supply 10, the impedance of the reactor 16 is zero. Therefore, the current flowing through the parallel resonant circuit of the capacitor 15 and the reactor 16 is only a DC current. As a result, the voltage of the AC power supply 1 is applied to the AC load 9, and the voltage of the DC power supply 10 is applied to the DC load 11.

The transmission line voltage and line current of the multiplex transmission line 5 are:
The waveforms are shown in FIGS. 3 and 4. In other words, the line voltage and line current of the multiplex transmission line 5 are equal to the AC power supply voltage.
It can be seen that the DC power supply voltage, AC load current, and DC load current are superimposed. What should be noted here is that when the peak value of AC current is larger than that of DC current, a current zero point exists. this is,
This is extremely important for DC system breakdown.

The embodiment of FIG. 2 overcomes the disadvantages a to d of FIG. 1a because the AC system circuit and the DC system circuit are electrically separated. It is DC in Figure 1 a.
While the power supply 10 is connected to the multiplex transmission line 5 via the DC coupling transformer 41, in the embodiment circuit of FIG. 2, the DC power supply 10 is connected only via the reactor. , is the decisive reason.

Next, in FIG. 5, starting from the basic circuit of the present invention shown in FIG.
This is a power transmission/reception device for an AC/DC multiple power transmission line that has been improved by repeatedly simulating transient phenomena such as when an AC system or a DC system starts up, or when a ground fault occurs in the multiple power transmission line 5.

In FIG. 5, the same components as those in FIG. 2 are given the same reference numerals, and their explanations will be omitted. In FIG. 5, the configuration of an AC power transmission device (hereinafter referred to as ACS) 25 will be explained first. 15 ₂₅ is a capacitor, 16 ₂₅ is a reactor, and the capacitor 15 ₂₅ and the reactor 16 ₂₅ constitute a parallel resonant circuit that resonates at the AC frequency. 22 ₂₅ is the resistance,
It is connected in series with the parallel resonant circuit. 25
₂₅ is a parallel resonant circuit input switch, 13 ₂₅ is a capacitor, and a zinc oxide element 24 ₂₅ for suppressing AC short circuit current is connected in parallel to this capacitor 13 ₂₅ . 14 ₂₅ is a reactor. 31 ₂₅ is
This is a disconnector connected to reactor ₁₄₂₅ of ACS25.

Next, the configuration of the AC power receiving device (hereinafter sometimes referred to as ACR) 16 will be explained. 17 and ₂₆ are load disconnectors, 23 and ₂₆ are closing switches, 15 _{and 26} are capacitors, and _{16 and} 26 are reactors. These capacitors 15 _{and 26} and reactors 16 _{and 26} form a parallel resonant circuit that resonates at the AC frequency. . 25 _{and 26} are resistors, which are connected in series with the parallel resonant circuit.
13 ₂₆ is a capacitor, and in parallel with this capacitor 13 ₂₆ is a zinc oxide element 24 ₂₆ for suppressing AC short circuit current.
is connected. 14 ₂₆ is reactor, 31 ₂₆
is a disconnector.

Next, the configuration of the DC power transmission device (hereinafter sometimes referred to as DCS) 27 will be explained. 18 ₂₇ is a reactor that suppresses the rush current of the capacitor 15 ₂₅ flowing into the DC power supply 10 ₂₇ when the AC power transmission device 15 is activated. Reference numeral 19 ₂₇ denotes a zinc oxide element that suppresses the back electromotive force of the reactor 18 ₂₇ when the sheath disconnector 17 ₂₉ of the multiple power transmission line 5 is disconnected. 15 ₂₇ is a capacitor, 16 ₂₇ is a reactor, and these capacitors 15 ₂₇ and reactor 16 ₂₇ constitute a parallel resonant circuit that resonates at the AC frequency. 31 ₂₇ is a disconnector connected to the reactor 14 ₂₅ of the AC power transmission device 25.

Next, the configuration of the DC power receiving device (hereinafter sometimes referred to as DCR) 28 will be explained. 31a is a DC load disconnector. 20 ₂₈ is a capacitor, 21 ₂₈
are reactors, which form a series resonant circuit that resonates at AC frequencies. 22 ₂₈ is resistance,
It serves as a charging resistor for the capacitor ₂₀₂₈ . Further, 23 ₂₈ is a bypass switch for resistor 22 ₂₈ . 15 and ₂₈ are capacitors, and 16 _{and 28} are reactors, which constitute a parallel resonant circuit that resonates at the AC frequency. 31b is a disconnector connected to the reactor ₁₄₂₆ of the AC power receiving device 26.

Next, the AC/DC multiplex power transmission line 29 will be explained. 5
is a multiple transmission line. Reference numeral 17 ₂₉ denotes a breaker that interrupts the current of the multiplex power transmission line 5.

Next, the current zero point adjustment load (hereinafter sometimes referred to as ACZ) 30 will be explained. 23 ₃₀ is a power-on switch, which is a power-on switch 23 ₂₆ of the AC power receiving device 26.
It is connected to the. 18 ₃₀ is a reactor load with a tap. Reference numerals 19 _{and 30} are zinc oxide elements for suppressing back electromotive force when the cable breakers 17 to ₂₉ of the multiple power transmission line 5 are cut off.

In addition, in the figure, V1 to V7 are the voltages of each part I1 and I
4, I5, I7 are the currents of each part, V _B is AC/DC
The voltage between the poles of the multiplex transmission line 29 and the disconnector 17 ₂₉ is
I _L is a symbol indicating the current of the multiple power transmission line 5.

Now, before explaining the detailed function and operation of this embodiment, in order to clarify the overall picture of the present invention,
The simulation results using the power transmitting/receiving device shown in FIG. 5 are shown in FIGS. 6 to 17. The constants used in this simulation were determined to be as realistic and economical as possible, with reference to the manufacturing experience of each device.

The basic assumptions of this simulation are as follows.

AC system AC power supply voltage 550kV/√3 AC rated current 2000A Frequency 60Hz DC system DC power supply voltage +250kV DC rated current 1200A AC/DC multiple transmission line Line length 100Km Surge impedance 300Ω Surge propagation speed 300m/μs First, AC power transmission The power receiving device will be explained.
In the AC power transmission device 25, the capacitor 13
Let the capacitance of ₂₅ be Cs, and the inductance of reactor 14 ₂₅ be Ls. Similarly, in the AC power receiving device 26, the capacitance of the capacitor 13 ₂₆ is Cr, and the inductance of the reactor 14 ₂₆ is Lr. Further, when the inductance of the multiplex power transmission line 5 is L1, and the frequency of the AC power source is f, the following relationship holds true.

(2πf) ² (Ls+Ll+Lr)CsCr/Cs+Cr=1 In other words, the inductance L and capacitor C between the AC power source 1 and the AC load 9 are in a series resonance relationship,
Impedance is zero. Therefore, if the resistance of the line is ignored, the AC power supply voltage V1 in Fig. 6 is
It becomes equal to the AC load voltage V4 in the figure.

On the other hand, the DC current is
6, each capacitor 13 ₂₅ , 13 ₂₆ cuts the voltage in the steady state.

As shown in Figure 7, the power transmission side capacitor voltage V2
is biased by DC power supply voltage +250kV. Further, as shown in FIG. 8, the power receiving side capacitor voltage V3 is different from the power transmitting side capacitor voltage V2 in FIG.
₂₅ , 14 and ₂₆ , indicating that the drop was due to the inductance component of the multiple power transmission line 5. but,
It is raised again to the same level as the power supply voltage V1 by the capacitor ₁₃₂₆ on the receiving side, resulting in a load voltage V4 as shown in FIG. Incidentally, at this time, the AC power supply current I1 in FIG. 10 and the AC load current I4 in FIG. 12 are naturally equal. The multiplex transmission line current I _L in FIG. 11 is the AC load current I4 shown in FIG. 12 and the DC load current I7 shown in FIG. 17.
are superimposed. Here, AC load current I
It can be seen that a current zero point exists when the peak value of 4 is larger than the DC load current I7. Therefore, this current zero point can be used to quickly disconnect the DC system.

Next, FIGS. 18 to ₂₁ show simulations in which the multiple transmission line current I _L of FIG. Show the results.

In FIG. 18, at the AC load voltage V4, a damping oscillating voltage is generated due to the discharge of the charge in the capacitor ₁₃₂₆ several cycles after the damping. The frequency of this oscillating voltage is approximately equal to the frequency of the AC power supply, 60 Hz.

Figure 19 shows DC load voltage V7, 150
Discharge of the capacitor's charge is observed for about [ms].

Figure 20 shows the current I _L of the multiplex transmission line 5, which is 250 [m
It can be seen that the current zero point of s] is interrupted.

FIG. 21 shows the voltage between poles of the AC/DC multiplex power transmission line 29 after the current sheath of the sheath breaker ₁₇₂₉ is disconnected. Here, the maximum value of the inter-electrode voltage in a steady state when the shield breaker ₁₇₂₉ is open is as follows.

The restart voltage, which plays an important role in the success or failure of the circuit breaker, increases linearly, and the steepness of the increase is
dv/dt=0.35kV/μs, which is not a problem considering the ability of the 500kV AC switch and disconnector.

Additionally, the fact that the peak value of the line voltage immediately after a shear break is only 65% of the steady voltage of +754.5kV is another condition that favors a shear break. What is important regarding this shrunken phenomenon is the position of the reactor 14 ₂₅ in the AC power transmission device 15 on the circuit.

That is, in the reactor 14 on the AC power transmission side of the basic circuit of the present invention shown in FIG. 2, when the current flowing through the multiplex power transmission line 5 reaches zero, a current -Id that cancels the DC load current Id flows. become. Therefore,
When the multiplex transmission line 5 is disconnected, 1/2 LID ² of electromagnetic energy remains in the reactor 14, and this becomes a sudden re-electromotive voltage that appears at the power supply side pole of the disconnector 17, causing the disconnection to occur. This includes the problem of extremely poor conditions.

On the other hand, in the multiplex power transmission/reception device according to the embodiment shown in FIG. 5, the currents flowing through the reactors 14 ₂₅ on the power supply side and the multiplex power transmission line 5 are the same, so as shown in the shunt results shown in FIG. 21, That problem has been resolved.

Reactors 14 ₂₅ on the power transmission side and power reception side in Figure 5,
14 ₂₆ has the function of AC power transmission/reception device 2
5 and 26, but judging from the installation location, it is rather included as a part of the multiplex power transmission line 5. Therefore, reactors 14 ₂₅ , 14 ₂₆
may be placed in a concentrated manner in the middle of the line, or may be distributed at any number of locations without causing any problems. In short, it is sufficient to maintain a series resonance relationship with the capacitors 13 ₂₅ , 13 ₂₆ of the AC power transmitting/receiving devices 25 , 26 .

Next, the effects of the zinc oxide elements 24 25 , 24 ₂₆ used in parallel with the capacitors 13 ₂₅ , 13 ₂₆ of the AC power transmission/reception devices 25 , ₂₆ will be explained. When the multiple power transmission line 5 has a ground fault, LC series resonance may occur depending on the ground fault point, and a huge AC ground fault current may flow. At this time, the ground fault current _{of the} DC system is
Because it flows through many reactors such as 14 _{and 25} , it increases very slowly compared to AC systems. Therefore, in the event of a ground fault, a large amount of AC current is not required to generate the current zero point of the ground fault current. Rather, the important issue is how to limit the huge ground fault current at the LC resonance point. The zinc oxide elements 24 ₂₅ and 24 ₂₆ have a current limiting effect for this purpose.

That is, if the ground fault current increases, the terminal voltage of the capacitor 13 ₂₅ on the power transmission side increases, and when it exceeds a preset voltage value, the resistance of the zinc oxide element 24 ₂₅ decreases rapidly, causing LC series resonance. The reactor ₁₄₂₅ acts as a current limiting reactor. It will be easier to understand if instead of the zinc oxide elements _24-25 , we consider a gap or a switch that discharges when the terminal voltage of the capacitors _13-25 exceeds a certain voltage value.

In short, if the zinc oxide elements 24 _{to 25} are variable impedances that change rapidly at the terminal voltage of the capacitor 13 _{to 25} , similar effects can be obtained in principle, but in this embodiment, the zinc oxide elements 24
₂₅ was selected with emphasis on the responsiveness and continuity of the discharge. Furthermore, the zinc oxide element 24 ₂₆ of the capacitor 13 ₂₆ on the power receiving side is inserted in consideration of the degree of ground fault on the power receiving transformer 6 side, and provides the same effect as described above.

Next, the capacitors 15 25 , 15 ₂₆ and the reactor 1 are connected to the transformers 2 _and 6 by the input switches 23 ₂₅ and 23 26 in the AC power transmission and reception devices _{25 and 26} .
6 ₂₅ , 16 ₂₆ LC parallel resonant circuit and resistor 22 ₂₅ , 2
2 _{The 26} circuits will be explained. This circuit is
This circuit is required during transient conditions such as AC/DC startup. Here, we will explain the case where the DC system is activated while the AC system is running.

In order for the DC system to enter a steady operating state, capacitors 13 ₂₅ and 13 ₂₆ need to be charged to +250 kV. However, the AC power transmission/reception device 25,
The 26 capacitors 13 ₂₅ and 13 ₂₆ are installed through the coils 4 and 7 of the transformers 2 and 6, both of which have large inductances.

When a charging current is applied to this from the DC power supply ₁₀₂₇ ,
Since the charging current has an extremely small resistance component, it becomes an oscillating current with a long period and extremely slow attenuation. For this reason, capacitors 13 ₂₅ , 13
The charging voltage of _{the 26} does not stabilize at +250kV.
In order to solve this problem without interrupting AC power transmission, it is sufficient to insert a resistor in parallel with the coils 4 and 7 of the transformers 2 and 6, but the capacitors 13 ₂₅ and 1
If the resistor is made smaller in order to increase the charging speed of 3 ₂₆ , a huge amount of power will be injected into the resistor from the AC system, and its heat capacity will also become huge. This circuit solves these problems.

First, since the capacitors 15 ₂₅ , 15 ₂₆ and the reactors 16 ₂₅ , 16 ₂₆ are parallel resonant circuits that resonate at the AC frequency, only a small amount of AC current flows through them.
Therefore, the capacitor 1 is connected to the resistors 22 ₂₅ and 22 ₂₆ .
Since only the charging currents 3 ₂₅ and 13 ₂₆ flow through the reactor 16, its resistance value can be made sufficiently small and its heat capacity can be made small. That is, in AC operation state, capacitor 13 ₂₅ ,1
₃₂₆ high-speed charging is possible. In addition, in this example,
This is extremely effective in reducing the transient vibration components of the LC circuit even when the multiplex power transmission line 5 is interrupted.

Furthermore, since almost no DC system transient current flows through the transformers 2, 6 and coils 4, 7, transient effects on the AC system can be eliminated. 22nd
Figures 24 to 24 show simulation results when the sheath disconnector ₁₇₂₉ of the AC/DC multiplex power transmission line 29 shown in Figure 5 is turned on at 250 [ms]. Here each power supply is
AC/DC full voltage startup, load connected simultaneously to AC/DC. It is clearly seen that the fast charging circuit of this embodiment reaches a steady state in only about 100 [ms] after charging.

At the initial stage of AC load voltage V4 in Fig. 22,
The voltage drops because a voltage drop occurs due to the transient resonance shift of the LC series resonant circuit.

Furthermore, as shown in FIG. 23, at the beginning of the DC load voltage V7, current inflow from the AC system is observed due to transient resonance shift of the parallel resonant circuit of the capacitor 15 ₂₈ and reactor 16 ₂₈ of the DC power receiving device 28. It will be done.

As shown in FIG. 24, at the beginning of the multiplex transmission line current I _L , the current zero point is reached due to the superposition of the charging currents of the capacitors 13 ₂₆ of the AC power receiving device 26 and the capacitors 20 ₂₈ of the DC power receiving device 28 from the DC system. I can see that it's floating. The magnitude of the charging current is
The current zero point can be controlled by controlling the stepwise charging of the capacitors 13 _{to 26} , the size of the charging resistance, etc.

Next, the current zero point adjustment load 30 will be explained. When the peak value of the AC load current I ₄ is smaller than the DC load current I 7 , the current I _L of the multiple power transmission line 5 does not have a current zero point, and the multiple power transmission line 5 is difficult to break. For example, this occurs when the AC power receiving side is in a no-load state.

The current zero point adjustment load 30 is an auxiliary protection device designed for this purpose.In short, by forcing the AC load current _I4 to flow, a current zero point is created in the current of the multiplex power transmission line 5, making it possible to cut the current. It is something that makes you Although any impedance load may be used as the load, we used a reactor load of _{1830 mm} due to heat capacity. This reactor load 18 ₃₀
By providing a tap or the like in the AC current having a peak value slightly exceeding the DC load current _I7 , the multiple power transmission line 5 can be cut very smoothly.

When the current zero adjustment load 30 is applied, the capacitors 15 ₂₅ , 15 ₂₆ and the reactors 16 25 , 1 that constitute the high-speed charging circuit of the AC power transmission and reception devices 25 _{and 26}
When 6 ₂₆ and resistors 22 ₂₅ and 22 ₂₆ are input at the same time,
Improves transient stability after shedding. In addition, the zinc oxide element ₁₉₃₀ has a reactor load of 18
This is to suppress the back electromotive force of _30% . Since this zinc oxide element ₁₉₃₀ is always disconnected from the circuit, it is characterized in that the limiting voltage can be set low.

Next, the DC power transmission device 27 will be explained.
The capacitor 15 ₂₇ and the reactor 16 ₂₇ are a parallel resonant circuit that resonates at the AC frequency. Therefore,
During steady state, only a small amount of AC current flows. However _, in _the case of DC current, since the impedance of the reactor is considered to be zero, the DC current _is
25 and flows into the multiplex transmission line 5.

When the AC power transmission device 25 is activated at full voltage while the DC power transmission device 27 is in operation, a maximum voltage of 550/√ is applied between V2 and V5 in FIG.
A potential difference of 3×√2=449kV _crest may be generated instantaneously. At this time, a rush current (flash current) of the capacitor 15 ₂₇ flows through the forward arm of the DC power supply 10 ₂₇ composed of a thyristor valve. Here, if there is no reactor ₁₈₂₇ , due to the sudden current change di/dt of the rush current,
The thyristor may be damaged.

Therefore, the reactor ₁₈₂₇ is provided to reduce the magnitude of this rush current and the current change. The zinc oxide element 19 ₂₇ connected in parallel with the reactor 18 ₂₇ is for suppressing back electromotive force when the multiple power transmission line 5 is cut. This zinc oxide element 19 is characterized in that the limiting voltage can be lowered because almost no voltage is normally applied to it. Further, the back electromotive force of the reactor 16 ₂₇ does not pose a problem because it is relaxed and absorbed by the capacitor 15 ₂₇ . So to speak, capacitor 15 ₂₇ and reactor 16
₂₇ parallel resonant circuits are back emf reduction filters.

Next, the DC power receiving device 28 will be explained.
Capacitor 15 ₂₈ and reactor 16 ₂₈ are a parallel resonant circuit that resonates at the AC frequency. On the other hand, the capacitor 20 ₂₈ and the reactor 21 ₂₈ are a series resonant circuit that resonates at the AC frequency.

Now, if we close the bypass switches 23 _{and 28} of the resistors 22 _{and 28} , the parallel resonant circuit has the property of blocking AC current and passing DC current, and the series resonant circuit has the property of blocking DC current and passing AC current. If you combine these in several stages as shown in the diagram, you can cut out the AC component due to resonance shift,
A highly purified DC load voltage will be obtained. Therefore, this figure is shown in Figures 13 to 17.
A waveform diagram obtained from simulation results of a DC system is shown.

In Figure 13, the DC power supply voltage V5 is +250 [kV]. FIG. 14 shows the first filter voltage V6.
It can be seen that the AC voltage is superimposed as a ripple due to the resonance shift caused by the resistance components of the capacitor 15 ₂₈ and the reactor 16 ₂₈ .

However, one more step is the LC parallel resonant circuit.
When a second filter consisting of an LC series resonant circuit is connected, the second filter voltage, that is, the load voltage V7, becomes completely smooth as shown in Figure 15.
It becomes a DC voltage. In this way, by connecting filters in multiple stages, the DC voltage can be purified as necessary. The DC power supply current I ₅ in Figure 16 is AC
An inflow of current due to resonance deviation from the grid can be seen. If smoothing of this current is desired, the filter used in the DC power receiving device 28 may be added.

Figure 17 shows the DC load current I ₇ , which is of course the same as in Figure 15.
It can be seen that it corresponds to the DC load voltage.
Resistor 22 ₂₈ is a charging resistance for capacitor 20 ₂₈ ,
Typically, the resistance value is selected to provide a non-oscillatory charging current. Bypass switches 23 and ₂₈ can be closed after charging is completed, thereby minimizing the impedance of the AC system and reducing ripples.
It is for removing AC current. In addition, when the circuit of this embodiment is in a transient state such as turning on or off, the bypass switch 23 ₂₈ is opened and the resistor 22 ₂₈ is opened.
If inserted, it is also extremely effective in damping the transient vibration components of the LC circuit.

Up until now, the explanation has been limited to the circuit shown in FIG. 5, but the various parts and devices of the present invention are essentially independent from each other. For example, in Figure 5,
It can be seen that even if the positions of the DC power transmitting device 27 and the DC power receiving device 28 are switched, the above explanation holds true. That is, in the above case, only the DC component of the current in the multiple power transmission line 5 flows in the opposite direction.

Therefore, we will consider disassembling the respective units 25 to 30 shown in FIG. 5 to construct a multiple power transmission line network. First, in the multiple power transmission line network that we are going to consider, there is always a current zero point of the ground fault current because the peak value of the AC current is always larger than the DC current at any ground fault point. Let us clarify that this is a multiplex power transmission network. As explained above, this is nothing but a multiplex power transmission network in which ground fault currents can always be interrupted or interrupted.

Here, in the steady state of the multiplex power transmission line, the individual multiplex power transmission lines of the multiplexed power line are classified as follows according to the line current flowing through the multiplex power line.

(a) AC system multiplex transmission line A multiplex transmission line where a current zero point exists in a steady state (b) DC system multiplex transmission line A multiplex transmission line where a current zero point exists in a steady state Of course, a certain multiplex transmission line , D.C.
Depending on the state of the load current in the system, it is possible for the system to change from an AC system to a DC system, or vice versa.

Here, when considering the steady-state shearing of multiple power transmission lines, based on the results so far, there is no problem in the case of AC multiple transmission lines. The problem is DC multiplex transmission lines. As already explained, one method for this disconnection is to use the current zero point adjustment load 30 shown in Figure 5 to temporarily change the DC multiplex transmission line to the AC multiplex transmission line. It is.

However, since the placement of AC power receiving devices within the multiplex transmission line network is restricted from an economical perspective, it may not necessarily be sufficient to make any multiplex transmission line an AC system with only the current zero point adjustment load. is possible.

Furthermore, the embodiment of FIG. 5 has the disadvantage that, even with high-speed reclosing, a momentary interruption of the AC load current is inevitable due to the interruption of the DC load current. Here, it is possible to forcefully cause a ground fault with a short-circuit switch and then break it, but as a method of breaking the steady current, there is a method that ensures smooth and transient stability of the system. , it is not appropriate to prevent equipment damage and deterioration. What we created in response to this problem was a current zero point adjustment device.
Functionally, this device is a combination device of the AC power receiving device 16 and the current zero point adjustment load 30 shown in Fig. 5, with the AC power receiving function removed. It has a function as a dedicated device, and FIG. 25 shows its configuration.

In FIG. 25, the same components as in FIG. 5 are given the same reference numerals. DCR of DC power using multiple transmission lines 5
Power is being transmitted to 28. Therefore, the multiplex transmission line 5 is
It is a DC multiplex transmission line. 34 is a current zero point adjustment device. 31 is a disconnector, and 32 is a capacitor. 23 _{and 34} are input switches. 15 ₃₄ is a capacitor, and 16 ₃₄ is a reactor, which is a parallel resonant circuit that resonates at AC frequency. 22 ₃₄ is a charging resistor. 33 is a high resistance for compensating for leakage current of the capacitor 32. 23 _{and 34} are bypass switches for the resistor 33. 18 ₃₄ is a reactor, which is a zinc oxide element for suppressing the back electromotive force of the reactor 18 ₃₄ when the 19 ₃₄ or disconnector 17 ₂₅ is disconnected.

Regarding the operation of the current zero point adjustment device 34,
Since this is the same as the description of the AC power receiving device 26 and the current zero point adjustment load 30, the description will be omitted and only some differences will be explained. In order to reduce power loss,
Preferably, capacitor 32 is disconnected from the circuit after charging.

However, the charge on capacitor 32 gradually decreases due to its own leakage resistance. When this device is connected and AC current is applied to the reactor 18 ₃₄ when the charge on the capacitor 32 has decreased too much,
Since a charging current flows superimposedly into the capacitor 32 from the DC power supply, the current zero point may float, for example, as shown in FIG. 24, although this is an extreme case. The resistor 33 is a resistor for preventing this.
This is an extremely high-resistance charging resistor for supplying a current corresponding to the leakage current of the capacitor from the multiple power transmission line 5. Therefore, the power loss of the current zero point adjustment device 34 during steady state can be ignored. The switches 23 to ₃₄ are used to bypass the high resistance 33 when charging the capacitor 32 at high speed.

The basic role of this current zero point adjustment device 34 is as follows:
By passing an AC current that cancels out the DC current, the multiplex power transmission line 5 is temporarily changed from a DC system to an AC system, thereby achieving smooth operation or disconnection of the multiplex power transmission line 5. The weeping phenomenon is basically the same as the shearing phenomenon of AC multiplex transmission lines.

Thus, by installing this current zero point adjustment device 34, a multiple power transmission line network is constructed. In the multiple power transmission line network, the multiple power transmission line 5 through which only pure AC current or DC current can flow during steady state is defined as a feeder line. Specifically, ACS25, DCS27,
This is a power transmission line originating from DCR28 etc. here,
Note that the feeder line is determined by the nature of the current flowing through it, and is therefore independent of the current and length of the transmission line. Considering the breakage in this feeder wire, there is no problem with AC power transmission/reception equipment, but DC power transmission equipment can be interrupted by the block of the DC power supply (thyristor valve), so the problem is limited to DCR28. becomes. However, as described above, this can also be cut off by the current zero point adjustment device 34.

Furthermore, breaks in the multiplex power transmission line 5 other than the feeder line can be made by distributing the current zero point adjustment device 34 or by using the current zero point adjustment load 30 added to the AC power receiving device. Become. From the above, it becomes possible to cut the power over the entire multiplex power transmission network.

FIG. 26 conceptually expresses this idea. In Figure 26, 17 bridges and disconnectors,
25 is an AC power transmission device (ACS), 26 is an AC power reception device (ACR), 27 is a DC power transmission device (DCS), and 28 is a DC power reception device (DCR).

In addition, 30 is a current zero point adjustment load (ACZ), 34
is a current zero point regulator (DCS), 35 is an AC/DC multiple transmission line network, 36 is a feeder line, and 37 is an AC/DC multiple transmission line network.
This is an AC power transmission network that is connected to a DC power transmission/reception device, and of course the connection with DC power is performed through an AC/DC conversion device.

Next, the concept of LC series resonance of ACS25 and ACR26 will be explained. Between the two terminals of the AC system in Figure 5
Although the idea of LC series resonance was quite obvious,
The question is how to think about it when it comes to multiplex power transmission networks.

As an extremely simple concept, for example, multiple power transmission lines excluding feeder line 36 in Figure 26 can be combined into one
If it is considered as an AC power source, it is sufficient to obtain resonance between the reactor and capacitor including the inductance of the feeder line 36.

Furthermore, the reactance of the line is actively compensated for using a capacitor. In order to effectively provide the function of a so-called series capacitor, there is a method of calculating the power flow of a multiple power transmission line network and selecting the optimum values of reactance and capacitor.

In the explanation of this embodiment, we have assumed the existence of an AC load, but the DCZ34
Of course, it is possible to achieve a signal break even if the load current is not in a multiplex wire network.

Therefore, it is clear that the sheathing method of this embodiment can be used in a shearing system for a DC-only power transmission line network. The AC power supply voltage at this time can be extremely low compared to the DC transmission voltage, and in short, even a current source that can flow an AC current with a peak value larger than the DC current value in the event of a ground fault is sufficient. All you have to do is do it.

Finally, the lowering of the power transmitting and receiving device of the AC/DC multiplex transmission line network of the present invention will be explained below.

(a) Electric power mail can be operated economically. in general,
DC power transmission is said to be superior to AC power transmission in terms of long-distance power transmission, large-power power transmission, and cable power transmission. On the other hand, when considering the conversion efficiency of AC power transmission,
It can be said that it is superior to DC power transmission in short distance power transmission and small power transmission. In the present invention, AC power and
Since DC power distribution can be changed freely, economical and efficient power transportation can be achieved by taking advantage of the advantages of AC power transmission and DC power transmission.

(b) It is economical because AC and DC transmission lines can be integrated. Construction of power transmission lines requires a huge amount of funds, but it is not only economically difficult to construct transmission lines for DC power transmission, which will continue to develop in the future, but also because of the large demand for DC power. In urban areas, land issues also arise. According to the power transmission/reception device of the present invention, DC power can be superimposed on an existing AC power transmission line. Further, if the present invention is applied to a power distribution line, AC/DC power can be selectively received depending on the suitability of the load.

(c) Because the DC system can be cut easily, the DC
A diverse network of transmission lines becomes possible. Due to the difficulty of interrupting DC current, DC power grids
In particular, a multi-terminal branch type line configuration has not yet been realized, but according to the shingle disconnection system considered in this invention, these problems can be solved at once, and the DC power transmission network can be expanded. It can be brought up to the same level as the AC power grid.

(d) Earth fault currents can be easily broken or broken, making it possible to create a power transmission network that is resistant to accidents. DC power grid is complex
When the system becomes more flexible, fault current interruptions such as ground faults in DC transmission lines and flash faults in thyristor valves and filters become important issues.However, in the AC/DC multiplex transmission line network of the present invention, Because it inherently has the ability to break or cut short circuit current by securing a current zero point, other
It has overwhelmingly advantageous conditions compared to DC transmission lines.

(e) Reverse current transmission is possible. Reverse current power transmission is a form of power transmission that receives AC power, converts it directly to DC power, and sends it back to the same power transmission line that received the AC power. It is also a form of power transmission that converts that DC power into AC power and sends it back. This is a characteristic advantage of the present invention, and is extremely effective in avoiding duplication of AC and DC transmission lines when the DC converter station is far away from the DC power receiving area.

In addition, AC power and
It is also effective to simply adjust the distribution of power energy with DC power.

(f) The reliability of the transmission/conversion device can be increased.
For operation of power inverter, valve commutation is required.
Requires AC reactive power. Therefore, if this reactive power cannot be obtained on the DC power receiving side, as in the case of the Hokkaido-Honshu DC power transmission converter station being shut down, for example, reverse conversion becomes impossible. However, in the present invention, this inverse transformation requires
Since AC reactive power can also be transmitted as DC power, the reliability of inverse conversion can be further improved. This means that it is particularly effective for cross-strait cables, etc.

(g) It can be used in a shedding system for DC-only power transmission lines. According to the present invention, except for the AC power receiving device and the current zero point adjustment load, it is possible to create a DC-only electric wire network while still utilizing the DC and disconnection systems based on AC/DC multiplex power transmission. Of course, multi-terminal branch type line configurations, which have been considered difficult until now, can also be created freely.

(h) AC has the same effect as a series capacitor installation in a transmission line. Since the present invention includes an LC series resonant circuit including the inductance of the power transmission line in the AC system, it has the same effect as a series capacitor installation that compensates for the inductance of the power transmission line.

(i) It has a current limiting effect on ground fault current in AC systems. By the action of the zinc oxide element connected to both ends of the capacitor of the LC series resonant circuit of the AC power transmission system of the present invention, the resonance is shifted in the event of a short circuit, and the reactor acts as a current limiting reactor, thereby suppressing the ground fault current. can do. This is extremely effective in facilitating the interruption of fault currents, ensuring transient stability of the system, and preventing damage and deterioration of equipment.

[Brief explanation of the drawing]

Fig. 1 is a basic circuit diagram of a power transmission/reception device for an AC/DC multiplex power transmission line that has been considered in the past; 3 and 4 are line voltage and current waveform diagrams based on the simulation results of FIG. 2, respectively, and FIG. 5 is an AC/DC multiplex transmission diagram that is an embodiment of the present invention that is a further improvement of the invention shown in FIG. The overall configuration diagram of the electric wire power transmission/reception device, Figures 6 to 24,
Figure 25 is a diagram of the voltage and current waveforms of various parts based on the simulation results shown in Figure 25. Figure 25 is a configuration diagram of a current zero point adjustment device applied to the power transmission/reception device of the AC/DC multiplex power transmission line of the present invention. According to the example of
Consists of power transmitting and receiving equipment for AC/DC multiplex power transmission lines.
FIG. 2 is a conceptual diagram of an AC/DC multiplex transmission line network. 1... AC power supply, 2... Power transmission transformer, 5...
Multiplex transmission line, 6...Power receiving transformer, 9...AC load, 10...DC power supply, 11...DC load, 12...
...Grounding, 13...Capacitor, 14...Reactor, 15...Capacitor, 16...Reactor,
17...Shiya disconnector, 18...Reactor, 19...
...Zinc oxide element, 20...Capacitor, 21...
Reactor, 22...Resistor, 23...Switch,
24...Reactor, 25...AC power transmission device,
26... AC power receiving device, 27... DC power transmitting device, 28... DC power receiving device, 29... AC/
DC multiplex transmission line, 30...Current zero point adjustment load, 3
2... Capacitor, 33... Resistor, 34... Current zero point adjustment device, 35... AC/DC multiple transmission line network.
Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1 A first series resonant circuit that has an overvoltage suppressor in the secondary coil of the power transmission side transformer of the power transmission line and resonates with the above AC frequency is connected in series, and a switch that resonates with the AC frequency is connected to both ends of the above secondary coil. an AC power transmission device including a first parallel resonant circuit connected in series with a resistor; and a second series resonance device having an overvoltage suppressor in a primary coil of a power receiving transformer of the power transmission line and resonating at the AC frequency. An AC power receiving device having circuits connected in series, and a second parallel resonant circuit and a resistor connected in series to both ends of the primary coil to resonate at the AC frequency, and a DC power source and a resistor to resonate at the AC frequency. A DC power transmission device in which a series connection circuit of a third parallel resonant circuit and a suppression reactor having an overvoltage suppressor connected in parallel is connected in parallel to the AC power transmission device, a DC load with one end grounded, and the AC power transmission device. A series connection circuit with a fourth parallel resonant circuit that resonates with the frequency is connected in parallel to the AC power receiving device, and is arranged between the fourth parallel resonant circuit and the ground, and in parallel with the DC load. A third series resonant circuit that resonates at the above AC frequency and a series circuit of resistors each having a bypass switch are connected in multiple stages to a DC power receiving device, and an overvoltage suppressor, a reactor, and a parallel circuit are connected to each other via the switch.
a current zero point adjustment device connected in parallel to a series circuit of a second parallel resonant circuit and a resistor of the AC power receiving device to ensure a voltage zero point of the AC power receiving device;
Power transmission and reception equipment for AC/DC multiplex power transmission network.