JP2695958B2 - Secondary overvoltage protection device for wound induction machines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a secondary overvoltage protection device for a wound-type induction machine in which the secondary side of a winding-type induction machine is subjected to secondary excitation control by an AC excitation device. About.

(Prior Art) The primary side of a wound induction machine is connected to an electric power system, and the secondary side is excited at a slip frequency. Then, a negative-phase current flows, and a current having a frequency of 2f ₁ ± sf ₁ (f ₁ is a system frequency, s is a slip) on the secondary side flows.
When a DC component is applied to the primary side, a current of f _r (rotation frequency of the rotor) flows to the secondary side.

However, the frequency converter for excitation control of the secondary side of the wound induction machine, 2f ₁ ± sf ₁ or it is difficult to flow a current at a frequency of f _r,, elements within the frequency converter (for example thyristors, GTO) Cannot be fired, the secondary side of the wire wound induction machine is opened, and an abnormally high voltage is generated. Therefore, when a high voltage is generated on the secondary side of the wound-type induction machine, insulation breakdown of the secondary winding and the frequency converter occurs, which may lead to a serious accident as a power plant.

Therefore, if an overvoltage occurs on the secondary side of a wound-type induction machine, the secondary winding can be short-circuited directly, or short-circuited through a resistor to suppress the voltage to almost zero. Methods have been considered to protect the frequency converter from overvoltage.

FIG. 5 shows an example of a circuit configuration of a secondary overvoltage protection device for a conventional wound-type induction machine. In FIG. 5, reference numeral 1 denotes a winding type induction machine, and a primary winding terminal of the winding type induction machine 1 is connected to a system bus 3 via a transmission line 2. A frequency converter 4, for example, a cycloconverter connected to the transmission line 2 is connected to a secondary winding terminal of the wound induction machine 1. Further, the secondary winding terminal of the wound induction machine 1 is connected to a short circuit device 6 via a resistor 5.
A current detector 7 is provided in an output circuit of the frequency converter 4, and the detection signal is input to a frequency converter control device 8. The frequency converter control device 8 controls the frequency converter 4 based on the deviation between the current command value and the detection signal of the current detector 7, and the short-circuit device 6 short-circuits the secondary side of the wound induction machine 1. Then, the output side of the frequency converter 4 is also short-circuited.

In the secondary overvoltage protection device of the winding type induction machine having such a configuration, an accident occurs in the system bus 3 or the transmission line 2 now,
When the primary side of the wound wire induction machine 1 becomes unbalanced, an alternating current of 2f ₁ ± sf ₁ is generated on the secondary side due to the negative phase component. In this case, since the frequency converter 4 cannot completely follow this, the secondary winding of the wound induction machine 1 is momentarily opened, and an overvoltage occurs. When an overvoltage occurs in the secondary winding of this wound-type induction machine 1, the short-circuit device 6 operates, and the secondary winding of the winding-type induction machine 1 and the output side of the frequency converter 4 are resistance-short-circuited in all three phases. Therefore, a short-circuit current flows on the secondary side of the wound-type induction machine 1 via the short-circuit device 6, and the short-circuit current is attenuated according to the time constant of the secondary winding of the wound-type induction machine 1. The frequency converter 4 releases the short circuit when the current flowing through the short circuit device 6 becomes almost zero, and shifts to the normal control. FIG. 6 shows a time chart from the time when the overvoltage is generated in the secondary winding of the wound-type induction machine 1 and the short-circuiting machine 6 is operated until the operation is restarted.

(Problems to be Solved by the Invention) As described above, when an overvoltage occurs in the secondary winding of the wound-type induction machine 1, the short circuit 6 causes the secondary side of the wound-type induction machine 1 and the frequency converter 4 to operate. Normally, the output side is short-circuited, the short-circuiting device 6 is released and the frequency converter 4 is started in anticipation of the time when the current flowing between the secondary winding of the wound induction machine 1 and the short-circuiting device 6 becomes zero. Has resumed operation.

However, in such a conventional method, it is necessary to wait until the current flowing through the short-circuit device 6 becomes zero. Therefore, as the reactance of the wound-type induction machine 1 increases, the waiting time increases on the order of several seconds, and the restart is performed. Slows down. Also,
In some cases, the current flowing through the short circuit device 6 does not become zero. In this case, the short circuit of the short circuit device 6 is forcibly released.
Overvoltage will be generated again. In addition, resistor 5
Even if the value is increased to increase the attenuation, the rating of the resistor 5 is increased, which is disadvantageous in terms of cost and occupied area.

The present invention relates to a secondary of a wound-type induction machine that can recover from a system fault in a short time without being influenced by a time constant of a secondary winding of a wound-type induction machine, a resistance value of a resistor, and operating conditions (slip). It is an object to provide an overvoltage protection device.

[Means for Solving the Problems] In order to achieve the above object, the present invention connects the primary side to a power system, and connects the secondary side to a frequency converter that excites with a slip frequency AC. In the secondary overvoltage protection device for a wound-type induction machine, when a fault occurs in the power system, a short-circuit device that short-circuits between the phases of the wound-type induction machine and the frequency converter, and a current flowing through the short-circuit device is detected. A short-circuit current detector, and a current detector that detects the output current of the frequency converter, and always controls the frequency converter based on a deviation from a current command value by taking in the output of the current detector, In the event of a power system accident, the output of the short-circuit current detector and the output of the current detector is taken in, and the current flowing through the short-circuit device through the frequency converter, which has been stopped by the short-circuit operation of the short-circuit device, becomes substantially zero. Again And dynamic control, the current flowing through the short-circuit device is that a frequency converter control device for releasing the shorting of the shorting device to become substantially zero.

(Operation) In the secondary overvoltage protection device for a wound-type induction machine having such a configuration, when an overvoltage is generated in the secondary winding of the wound-type induction machine and the secondary side is short-circuited by a short circuit device, When the short circuit current flowing in the short circuit is detected, the frequency converter is controlled by the detection signal so that the current flowing in the short circuit becomes zero, and when the current becomes almost zero, the short circuit by the short circuit is released and the normal operation is performed. Since the operation returns to the operation, it is possible to recover from the accident in a short time without being affected by the time constant of the secondary winding of the wound induction machine, the resistance value of the resistor, and the operating conditions.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a circuit configuration of a secondary overvoltage protection device for a wound-type induction machine according to the present invention, and the same parts as those in FIG. As shown in FIG. 1, a primary winding terminal of the wound induction machine 1 is connected to a system bus 3 via a transmission line 2.
It is connected to the. Further, a frequency converter 4 composed of, for example, a cycloconverter connected to the transmission line 2 is connected to a secondary winding terminal of the wound induction machine 1, and a current detector 7 is connected to an output circuit of the frequency converter 4. Is provided. Further, a short-circuit device 6 is connected to the secondary winding terminal of the wound induction machine 1, and a short-circuit current detector 9 for detecting a short-circuit current is connected to a connection circuit between the secondary winding terminal and the short circuit device 6. Provided.
The detection signal of the short-circuit current detector 9 and the detection signal of the current detector 7 are input to the frequency converter control device 8, and the frequency converter control device 8 normally uses the detection signal of the current detector 7 to output the frequency converter 4 When an operation signal is input from the short circuiter 6 when an overvoltage occurs, the frequency converter 4 is controlled based on the detection signal of the short circuit current detector 9 so that the short circuit current becomes zero. When it becomes almost zero, a short-circuit release command is given to the short-circuit device 6.

FIG. 2 shows an example of the internal configuration of the frequency converter control device 8. The frequency converter control device 8 includes a controller 8-1 for controlling the frequency converter 4 as shown in FIG.
Switching contacts 8-2a and 8-2b that are switched when an operation command is input from the short-circuit device 6, and contacts 8-2b when the short-circuit device 6 is inoperative.
A subtractor 8-3 which obtains a deviation between a current command from a higher order and a detection signal of the current detector 7 through a controller 8-1 and supplies the deviation to a controller 8-1
When the short-circuit device 6 operates, the detection signal of the short-circuit current detector 8 and the detection signal of the current detector 7 are added, and the added value is sent as a current command value to the subtractor 8-3 via the switching contact 8-2a. And an adder 8-4.

Next, the operation of the secondary overvoltage protection device for a wound-type induction machine configured as described above will be described with reference to a timing chart shown in FIG.

Now, when an accident occurs in the system bus 3 or the transmission line 2 and an unbalanced voltage is generated in the primary winding of the wound induction machine 1, the secondary side has a frequency of 2f ₁ ± sf ₁ due to a negative phase component. AC voltage is generated. For this reason, the frequency converter 4 cannot fully follow the control according to the voltage at that time, and the secondary winding of the winding induction machine 1 is momentarily opened, and an overvoltage occurs. Then, the short-circuit device 6 operates by detecting this overvoltage, short-circuits the secondary winding of the wound-type induction machine 1 and the output side of the frequency converter 4 in three phases, and operates the frequency converter control device 8 to operate the short-circuit device. Input the signal. At this time, since the frequency converter 4 is stopped, a fault current flows between the secondary winding of the wound-type induction machine 1 and the short-circuit device 6 while a fault occurs. Also,
After the recovery from the accident, a current flows between the wound induction machine 1 and the short-circuit device 6 due to the voltage induced in the secondary winding.

Here, in the frequency converter control device 8, as shown in FIG. 3, the following relationships exist between the respective currents. That is, the output i _2g of the adder 8-4 just before the short circuit operation signal is input from the short circuit 6 is i _2g = ic + i _OVP (1) ic = 0.

However, when the switching contacts 8-2b are opened and the switching contacts 8-2a are closed by the short-circuit operation signal from the short-circuit device 6, the current command value i ₂ ^* input to the subtractor 8-3 is i ₂ ^* = i _2g = Ic + i _OVP (2) Here, assuming that the deviation between the current command value i ₂ ^* and the actual current ic is Δic, Δic = i ₂ ^* −ic (3), and from the expressions (2) and (3), i ₂ ^* = ic + i _OVP i ₂ ^* −ic = i _OVP ∴Δic = i _OVP (4) This indicates that when the current command is used during the short circuit and the frequency converter 4 is used as in the equation (2), the current deviation Δic flows through the short circuit device 6.

Therefore, assuming that the current deviation Δic becomes zero by the control of the frequency converter 4 by the controller 8-1, (4)
By formula Thus, the current flowing through the short-circuit device 6 is taken by the frequency converter 4, and the response speed of the current flowing through the short-circuit device 6 can be reduced to zero.

As described above, even if an overvoltage occurs in the secondary winding of the wound-type induction machine 1 due to a system failure and the short-circuit 6 is operated to cause a short-circuit current to flow on the secondary side of the wound-type induction machine 1, the frequency converter 4 Of the frequency converter 4 and the current command value ic ^* of the
By calculating and controlling using the sum of the current i _OVP flowing through the frequency converter 4, the current flowing through the short-circuit device 6 can be taken by the frequency converter 4, the short-circuit can be quickly released, and the wound induction machine 1 operates normally. Can be restored.

[Effects of the Invention] As described above, according to the present invention, when an overvoltage occurs in the secondary winding of a wound-type induction machine, the frequency converter is restarted when short-circuited by a short-circuit device to restart the frequency converter. Accordingly, a secondary overvoltage protection device for a wound-type induction machine can be provided in which a short-circuit can be quickly released by taking up a current flowing through the short-circuit device, and the wound-type induction machine can be quickly restored.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing one embodiment of a secondary overvoltage protection device for a wound-type induction machine according to the present invention. FIG. 2 is a circuit diagram showing an internal configuration example of a frequency converter control device in the embodiment.
FIG. 3 is a diagram for explaining the relationship between the current flowing between the induction motor, the frequency converter, and the short-circuit device during the short-circuit operation of the short-circuit device in the embodiment, and FIG. 4 is a diagram for explaining the operation of the embodiment. FIG. 5 is a circuit diagram showing a secondary overvoltage protection device for a conventional wound induction machine, and FIG. 6 is a timing chart for explaining the operation of the conventional device. DESCRIPTION OF SYMBOLS 1 ... Induction winding type induction machine, 2 ... Transmission line, 3 ... System bus, 4 ... Frequency converter, 6 ... Short circuiter, 7 ... Current detector, 8 ... Frequency converter control device, 8-1 Controller, 8-2a, 8-2b Switching contact, 8-3 Subtractor, 8
-4: adder, 9: short-circuit current detector.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hirokazu Kaneko 1-3-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Inside Tokyo Electric Power Company (72) Inventor Takahisa Kageyama 1-Toshiba-cho, Fuchu-shi, Tokyo Inside the factory (56) References JP-A-63-140697 (JP, A)

Claims (1)

(57) [Claims] 1. A secondary overvoltage protection device for a wire wound induction machine having a primary side connected to a power system and a secondary side connected to a frequency converter that excites with alternating current of a slip frequency, wherein an accident occurs in the power system. A short-circuit device that short-circuits between the phases of the wound-type induction machine and the frequency converter when it occurs, a short-circuit current detector that detects a current flowing through the short-circuit device, and a current detector that detects an output current of the frequency converter And always take in the output of the current detector and control the frequency converter according to the deviation from the current command value, and in the event of an accident in the power system, take in the outputs of the short-circuit current detector and the current detector. Restart control of the frequency converter that is stopped by the short-circuit operation of the short-circuit device so that the current flowing through the short-circuit device becomes substantially zero, and that the current flowing through the short-circuit device becomes substantially zero. Short circuit A secondary overvoltage protection device for a wound-type inductor, comprising: a frequency converter control device for canceling a short circuit.