JPS6242466B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improved excitation device for a brushless synchronous machine.

[Conventional technology]

Conventional excitation devices mainly include three-phase Graetz-connected diodes, and require each diode to be installed insulated on a cooling fin, or at least two fins on the positive and negative sides, and rectification. In order to prevent the diode from being destroyed by surge voltage during commutation, a method was adopted in which a distribution (surge absorption) resistor was connected in parallel with the diode.

Here, the operating characteristics during Graetz connection commutation in the conventional example will be explained.

FIG. 6 is a conceptual connection diagram of the conventional example.

The induced voltage generated in each phase U, V, and W of the star-shaped winding 30 of the exciter is converted to direct current through the phase-graetz connected diodes 7 to 12, and the field ring F of the synchronous machine is excited. Then, the armature SG generates power and supplies it to the load.

By the way, when the diode commutates due to rectification, even if the forward current in the conductive state becomes zero due to the carrier accumulation effect, as shown by the dotted line in Figure 6,
It has a property that it does not recover to the blocked state and remains conductive for a certain period of time, and current continues to flow in the opposite direction. The diode 7 in the extinguishing arm appears to be a capacitor with a capacitance of _C0 .

As shown in FIG. 7, when the carrier disappears, this reverse current rapidly tries to become zero, and the diode becomes in a blocking state. Since the current change di/dt when this reverse current shifts to zero is steep, a large voltage is induced in the inductance of the carrier passing circuit, and the power supply voltage is added to this voltage and applied to the diode.

This is the so-called commutation surge voltage (jump reverse voltage)
It is.

Since the operating voltage and allowable voltage (reverse withstand voltage) of diodes are relatively close to each other compared to general electrical equipment, it is necessary to avoid applying this commutation surge (repetitive) voltage to diodes as much as possible.

Therefore, in order to suppress this commutation surge voltage to a low level, conventionally, as shown in Fig. 8, a discharge shunt circuit consisting of a combination of RC (resistor and capacitor) in parallel with a diode was installed for each diode 7 to 12. The common method was to connect them individually. By installing this RC shunt discharge circuit, most of the carriers are discharged through this circuit, and only a small amount flows into the carrier passage path before installation.

Therefore, the commutation surge voltage is suppressed to a value slightly higher than the operating voltage. For example, the voltage values shown in Figure 7b are one example.
The peak value of the jump reverse voltage is suppressed from 550V with the characteristic without the discharge shunt circuit (solid line) to 250V with the characteristic with the discharge shunt circuit (dotted line).

Therefore, the load circuit of the exciter including the diode bridges 7 to 12 must be protected against overvoltages and overcurrents that may enter the load circuit due to external factors.

In the case of a synchronous (generator) machine, when an accident occurs and the machine is operating abnormally, that is, when the power factor is in a negative range, the field wire ring F receives a reverse voltage induced from the armature SG side.
This attempt to cause a current to flow is called a reverse current.

Normally, in a brushless synchronous (generator) machine, the field excitation circuit is comprised of a diode as shown in FIG. 6, so this reverse current is blocked by this diode.

As mentioned above, this reverse current is due to the electromagnetic effect of the generator, is quite large in proportion to the capacity of the generator, and is persistent in the event of an accident.

If this reverse current is blocked and left as is, the current will be high (several 1000s) depending on the number of turns in the field winding.
volts) voltage may be induced that can damage the diode.

On the other hand, the above-mentioned commutation surge absorption RC circuit section is generally smaller in terms of current carrying capacity than the (AC) exciter of a synchronous (generator) generator, so it cannot sufficiently absorb this reverse current. Thermal damage may occur due to the electric current.

Therefore, in order to discharge and absorb this reverse current, it is common to insert a discharge resistor into the field, as shown by the dotted line DR in FIG.

[Problem that the invention seeks to solve]

In order to prevent the diode from being destroyed by commutation surges and asynchronous operation, it was necessary to connect a distribution resistor in parallel with the diode, which sometimes required as much space as the exciter itself.

The present invention has been made to improve the above-mentioned drawbacks, and an object of the present invention is to provide an excitation device for a brushless exciter that has a significantly simplified configuration.

[Means for solving problems]

In the present invention, a double star-shaped winding is wound around the rotor of an exciter, and an excitation wire ring of a synchronous machine is connected between the neutral points of these windings. Two diodes are connected in cascade between each phase, and the connecting points of these cascades are electrically shared by a ring fin, and the ring fin is connected to the middle point of the excitation wire.

[Effect]

In this way, the present invention has two rotor windings of an exciter.
As a double star winding, the cascade connection point of each two diodes is shared through a ring fin, so that one side of the winding is connected so that the induced voltages of the two star windings are mutually weighted and distributed. It flows from the neutral point to the field wire ring of the synchronous machine, flows into the other neutral point of the winding via the field wire ring, and this resistance also flows from the connection between the ring fin and the field wire ring. The carrier is smoothly discharged during diode commutation via a field wire ring with low inductance, eliminating the need for a distribution resistor connected in parallel with each diode as seen in conventional examples.

〔Example〕

An embodiment of the present invention shown in the drawings will now be described.

In FIG. 1, 1 is an exciter, and a rotor 2 is equipped with a double star-shaped winding 3. 4 is a ring fin, which is insulated and fixed to the shaft 6 with a bolt 5. The ring fin 4 has diodes 7, 8, 9 and 10, 11, 12 as shown in FIG.
is attached directly. As shown in FIG. 3, the coil ends U ₁ , V ₁ , W ₁ of one side 3a of the double star-shaped winding 3
The cathodes of the diodes 7, 8, 9 connected to the ring fin 4 are respectively attached to the ring fin 4, and the anodes of the diodes 10, 11, 12 connected to the ring ends U ₂ , V ₂ , W ₂ of the other 3b are attached to the ring fin 4. . The diodes 7, 8, and 9 are of the studded cathode type, and the diodes 10, 11, and 12 are of the studded anode type. The windings 3a and 3b have neutral points J and K drawn out,
It is connected to both ends of the field wire ring F of the synchronous machine. R
is a discharge resistor, which is connected in parallel with the field wire ring F. The field wire ring F and the discharge resistor R are provided with center taps C and D, which are connected to the ring fin 4, respectively.

Next, the operation of the present invention will be explained in more detail.

FIG. 4 shows a voltage waveform diagram generated in the winding 3 due to the rotation of the rotor 2 in the exciter 1, and FIG. 5 shows its current path diagram.

Let E _u , E _v , and E _w be the induced voltages of each star connection in the double star winding 3. For example, the current path at a certain moment t ₁ when E _u = −E ₁ E _v = E ₁ flows in the direction indicated by the dotted arrow in the loop indicated by the thick solid line, forming a flat ring exposed at one end of the rotor 2, and the ring fin 4 made of a conductive member also serves as a current-carrying part. Note that at time t ₂ , diode 1 is connected from winding W ₂
2 and reaches the ring fin 4, where it is divided into two, and the current from one diode 7 through winding U ₁ and the current from the other diode 8 through winding V ₁ join at point J and go to field winding F. Inflow.

Also, in the case of, for example, four poles among the field windings F of the synchronous generator SG, when one of the two poles of the winding is _F1 and the other two poles of the winding is _F2 , then C The point is the function between J and K and the midpoint of the resistance value divided into two.

Therefore, in steady state, the voltage is halved at point C.

Also, point C′ of ring fin 4 also reduces the induced voltage by 1/2.
This is the point.

Therefore, points C and C' should have the same potential, and no current will flow there even if points C and C' are connected.

However, due to an abnormal load applied to the synchronous generator SG or other transient conditions, the field winding is electromagnetically disconnected.
A reverse induced voltage may be generated in F ₁ and F ₂ .

In such a case, if points C to C' are not connected, the voltage will mainly be applied to the diodes 7, 8, and 9, and not so much to the diodes 10, 11, and 12.

However, if C to C' are connected, they will share approximately the same voltage.

Furthermore, the reason why C to C' are connected is that the commutation surge that occurs during commutation of diodes 7 to 12 discharges the field wire F, which has low resistance and inductance, as a discharge resistance, which is different from the conventional example. It is not necessary to provide a shunt resistor to such a diode.

However, since the discharge current that discharges the electrical energy generated in the field winding F by the rotation of the armature of the synchronous generator SG is as small as the leakage current of diodes 7 to 12, it is not very large. The reverse induced voltage does not decrease.

Here, if necessary, insert and connect the discharge resistor R in parallel with the neutral points J and K, and make the resistance value 1/2 at the point D.
When C to C' are connected, the reverse induced voltage is mainly discharged through the discharge resistor R, and the voltage decreases greatly.
9 and diodes 10 to 12, and operates as a very simple surge absorbing and voltage dividing device.

By the way, the reason why the present invention uses a double star type winding 3 of the rotor 2 and employs a disk-shaped ring fin is as follows.

Diodes (silicon rectifiers) 7 to 12 are each half cathode studs 7 to 9 and cathode studs 10 to 12, and the three-phase terminals are connected to each of the diodes 7 to 12 as a double star winding.
If the diodes 7 to 12 are fixed to the ring fin 4, which is a conductor, the conductor 4 can be used as a current-carrying body that also serves as a cooling fin.

Moreover, by forming the mounting conductors of the diodes 7 to 12 into an integrated disk, it is possible to provide a cooling and conductive means (ring fin 4) that is easy to attach to the rotor 2, is mechanically strong, and has a reduced number of parts. can.

〔Effect of the invention〕

As described above, according to the present invention, the diodes 7,
Since 8, 9, 10, 11, and 12 are all directly attached to the ring fin 4, heat radiation is good and space is not taken up, so that the entire structure can be made small and lightweight. If the center taps C and D of the field wire ring F and the discharge resistor R are connected to the ring fin 4, commutation surges and surges during asynchronous operation can be efficiently dealt with in one or both of the field wire ring and the discharge resistor. Since it is absorbed by the diode, there is no need to provide a distribution resistor in parallel with the diode, making the structure extremely simple.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing the main parts of an embodiment of the present invention, Fig. 2 is a plan view of the ring fin, Fig. 3 is a connection diagram, Fig. 4 is a diagram of induced voltage waveform of the exciter rotor,
FIG. 5 is an operating principle diagram showing the current path of the present invention.
FIGS. 6 to 8 are explanatory diagrams of conventional examples. 1 is an exciter, 2 is its rotor, 3 is a double star winding, 3a is one winding, 3b is the other winding, 4 is a ring fin, 5 is a mounting bolt, 6
is the shaft, 7, 8, 9, 10, 11, 12 are diodes, U ₁ , V ₁ , W ₁ are the coil ends of the winding 3a, J is the neutral point, U ₂ , V ₂ , W ₂ are the K is the wire end of the winding 3b, K is its neutral point, F is the field wire ring of the synchronous machine, C is its center tap, R is the discharge resistance, and D is its center tap.

Claims (1)

[Claims] 1. An exciter 1 equipped with a double star-shaped winding 3, and a ring fin 4 fixed to the shaft 6 of the exciter 1.
and a coil end U ₁ of one side 3a of the double star-shaped winding 3,
Diodes 7, 8, 9 whose cathodes connected to V ₁ and W ₁ are attached to the ring fin 4, respectively.
and the coil ends U ₂ , V ₂ , of the other 3b of the double star-shaped winding 3,
Diodes 10, 11, 12 each having an anode connected to W ₂ and attached to the ring fin 4;
means for connecting the two neutral points J and K of the double star-shaped winding 3 to both ends of the field wire ring F of the synchronous machine, respectively; and the ring fin 4 and the field wire ring F. An excitation device for a brushless synchronous machine, comprising means for connecting a center tap C of the brushless synchronous machine. 2. The excitation device for a brushless synchronous machine according to claim 1, wherein a discharge resistor R is provided in parallel with the field wire F of the synchronous machine. 3. The excitation device for a brushless synchronous machine according to claim 2, wherein the field wire ring F and center taps C and D of the discharge resistor R of the synchronous machine are connected to the ring fin 4.