JPH019276Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thyristor starting device, and more particularly to a thyristor starting device having a converter in its output circuit.

The basic circuit of a conventional thyristor starting device is shown in FIG. The operation of this type of thyristor starting device is described, for example, in Document 1.

(1: K.E. Hogberg, “Frequency
converter for starting the motor/generators
for Foyers Pumped Storage Power Station,”
ASEA Journal, Vc1.49, No.3, 1946, pp51~
56) In this method, first, switches 6 and 7 are opened, switch 8 is closed, and the output of converter 2 is directly connected to electric motor 9 to perform forced commutation and start. When the rotational speed of the electric motor 9 reaches a predetermined value, the switch 8 is opened, the switches 6 and 7 are closed, and the converter 2 is connected via the transformer 5.
accelerates the electric motor 9 as a natural commutation.

This type of thyristor starting device requires three switches 6, 7, and 8. However, as the output of the thyristor starter increases, the rated current of the switch 6 also increases, which not only increases cost but also makes implementation difficult.

For example, if the output of a thyristor starting device is 10000KW,
When the transformation ratio of transformer 5 is 1200V/13.2KV,
The DC voltage is 1200V, the DC current is about 8300A, the rated current of the switch 6 is 6800A, and the rated current of the switch 7 is about 620A. The rated current of the switch 8 may be the same as that of the switch 7 by lowering the current during forced commutation operation. If the capacity of the thyristor starting device becomes larger, the rated current of the switch 6 will also become larger.
It can be seen that it reaches 10,000A and becomes impossible to realize. In order to eliminate this difficulty, it is conceivable to increase the primary voltage of the transformer 5. However, if the voltage is increased, the number of thyristors in converters 1 and 2 must be connected in series to 2 or more, and the design of converters 1 and 2 must consider both series and parallel connections. It becomes difficult.

Another method for solving the above problem is to use a thyristor starter as shown in Figure 1 only for natural commutation operation, and use other methods for the initial stage of startup. There is a method using a cycloconverter.

(2: M.H. Fisher, et al. “Design
features of Mt・Elbert Pumped Storage
Powerplant,” IEEE Trans on PAS, Vol.
(PAS-94, No. 6, 1975, PP2170~) However, this method uses a completely different starting method, which complicates the entire system including the control system.

An object of the present invention is to provide a thyristor starting device whose converter is easy to design.

The feature of the present invention is that by providing a separate reverse converter exclusively for forced commutation operation, there is no need to switch the converter 2 to perform forced commutation operation, and a switch can be omitted.

An embodiment of the present invention is shown in FIG. In this embodiment, the converter 2 and the transformer 5 are directly connected as described above, and the switch 6 in FIG. 1 is omitted. on the other hand,
A converter 2a is newly added exclusively for forced commutation, and is connected to a motor 9 via a switch 8.

In this embodiment, first, the switch 8 is closed, and the switch 7 is closed.
Leave it open. Then, with the converter 2 gate-blocked, the converter 2a is forcibly commutated to start the motor 9.

When the electric motor 9 reaches a predetermined rotational speed,
The converter 2a is de-energized, the gate is blocked, the switch 8 is opened, and the switch 7 is closed. After that, the converter 2 undergoes natural commutation as in the conventional system, and the motor 9
accelerate.

The capacity of the additional converter 2a may be a fraction of that of the converter 2 or less, and there is no problem in terms of cost and size.
For example, in the case of the above-mentioned capacity, the capacity of the converter 2a is
Due to the transformation ratio of transformer 5, 1.2/13.2 of converter 2
The same torque as in operation can be obtained through the converter 2 and transformer 5 with a capacity of 1/11, and even considering that the capacity increases due to low frequency operation, it is only a few times smaller. Since the load torque is small during forced commutation operation, there is no problem even if the torque is reduced, so the capacity can be further reduced. Note that since the ripple of the DC current increases relatively due to the small current, a DC reactor may be added only to the converter 2a if necessary.
Note that by setting the switching speed between forced commutation and natural commutation to 1/11 or less, the rated voltage of the converter 2a does not increase. If the electric motor 9 is made to have a weaker field, it may be switched at a speed of 1/11 or more.

This control method only requires switching between the operating converters 2a and 2 (during forced commutation operation, the current is normally reduced, so no additional change in current setting is required).

Another embodiment of the invention is shown in FIG. In this embodiment, the number of rectification phases is 12 to reduce harmonics. During forced commutation operation using the converter 2a, the converter 2a performs six-phase rectification. Although the converter 2a requires an increase in the number of thyristors connected in series, the design is easy because the number of thyristors in parallel is small.

Another embodiment with 12-phase rectification is shown in FIG. In this embodiment, there are two sets of six-phase rectifiers, and only one of them is used during forced commutation operation. Since the capacitance of the converter 2a can be reduced to a fraction of that, there is no problem with the capacitance in this method. Note that two sets of converters may be connected in parallel, but the DCL increases.

According to the present invention, it is possible to omit the switch between the inverter and the output transformer, which makes it impossible to increase the capacity of a low-voltage thyristor starting device. (1) It is easy to increase the capacity.

(2) Thyristor converter design becomes easier.

(3) Even if the capacity is small, maintenance and inspection are easy due to the omission of a large current switch.

There is an effect.

[Brief explanation of the drawing]

Figure 1 shows the sequence of the conventional thyristor starting device, Figure 2 shows the sequence of the embodiment of the present invention, and Figure 3 shows the sequence of the conventional thyristor starting device.
4 is a sequence diagram of another embodiment of the present invention. 1, 2, 2a, 1', 2'... Thyristor converter, 3, 3'... DC reactor, 4, 5, 4',
5'...Transformer, 6,7,8...Switch switch, 9...
Electric motor.

Claims (1)

[Scope of utility model registration request] A first thyristor converter that converts alternating current to direct current, a second thyristor converter that converts the direct current output of the first thyristor converter to variable frequency alternating current, and boosts the alternating current output of the second thyristor converter. A first switch interposed between the transformer and the motor, and a second thyristor converter are connected in parallel, and the DC output of the first thyristor converter is connected in parallel to It includes a third thyristor converter for converting into alternating current, and a second switch interposed between the third thyristor converter and the motor,
A thyristor starting device characterized in that the first switch opens when the motor starts and closes when the motor accelerates, and the second switch closes when the motor starts and opens when the motor accelerates.