JPH0343876B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a field overvoltage protection device for a synchronous machine, and particularly a field overvoltage protection device suitable for an excitation control device that uses a thyristor rectifier to adjust the field of a synchronous machine. Regarding.

In a synchronous machine, a negative induced current is generated in the field during an asymmetric short circuit, ground fault, or asynchronous operation on the output side, and semiconductor rectifiers such as thyristors block this current, so the field circuit Overvoltage occurs. Therefore, conventional excitation control devices are provided with overvoltage protection means to prevent the overvoltage from destroying semiconductor rectifying devices such as thyristors.

Conventionally, nonlinear resistance elements such as selenium have been used as this type of overvoltage protection device, but as the capacity of the excitation device increases, overvoltage coordination with semiconductor rectifying elements such as thyristors becomes difficult, and asynchronous operation becomes difficult. As the value of field-induced current that occurs at certain times increases, it has become difficult to provide protection using nonlinear resistance elements in terms of current capacity.

From this point of view, a method has recently been proposed in which a thyristor switch is provided between the positive and negative poles of the field, and when an overvoltage occurs in the field circuit, the thyristor switch is rendered conductive to suppress the overvoltage. In this case, an overvoltage suppression resistor is generally connected in series with the thyristor switch, but if the cause of the field overvoltage is a voltage source such as a surge, the lower the resistance value of the overvoltage suppression resistor, the lower the field voltage will be limited. However, it was considered necessary to increase the current capacity of the thyristor switch. However, if the cause of field overvoltage is a current source based on field induced current such as during an asymmetric short circuit or asynchronous operation, it is necessary to determine the current capacity of the thyristor switch regardless of the resistance value of the overvoltage suppression resistor. . Moreover,
In this case, it is desirable that the resistance value of the overvoltage suppression resistor is low.

However, considering the case where a field overvoltage occurs due to the generation of a negative induced current in the field, after the thyristor switch operates, the semiconductor rectifier consisting of the thyristor of the excitation device also causes current to flow through the overvoltage suppression resistor. However, there were some difficulties, such as the need to consider the current capacity of the semiconductor rectifier.

Therefore, as a result of various studies to overcome all the problems of the conventional field overvoltage protection device described above, the inventor of the present invention discovered that, in the field circuit of the excitation device, a pair of thyristor switches are connected in series together with an overvoltage suppression resistor. This is connected in parallel to the field winding, and the intermediate connection point of these thyristor switches and one phase of the input AC voltage of the semiconductor rectifier are connected via a current suppression resistor to prevent overvoltage that can self-extinguish. By configuring the protection device, even if the resistance value of the overvoltage suppression resistor is set low, it is possible to secure the reverse voltage for restoring the thyristor switch, and there is no need to increase the current capacity of each element of the semiconductor rectifier. It has been found that the above problems can be solved.

Therefore, an object of the present invention is to provide a circuit configuration that does not increase the current capacity of a semiconductor rectifier even if the resistance value of the overvoltage suppression resistor is set low in order to limit field overvoltage, and can self-extinguish the current. The present invention provides a field overvoltage protection device using a thyristor switch.

In order to achieve the above object, in the present invention, a series circuit of a thyristor switch and an overvoltage suppression resistor is connected in parallel with the field winding of a synchronous machine, and when an overvoltage occurs in the field, the thyristor switch is turned on. In a field overvoltage protection device configured to protect a field winding and a semiconductor rectifier from overvoltage, a series circuit of a pair of thyristor switches and an overvoltage suppression resistor is connected in parallel with the field winding, The intermediate connection point of the thyristor switch and one phase that forms the input alternating voltage of the semiconductor rectifier are connected via a current suppression resistor having a resistance value similar to that of the overvoltage suppression resistor, so that the thyristor switch can self-extinguish. Additionally, the present invention is characterized in that the current value flowing from the semiconductor rectifier after the thyristor switch becomes conductive is reduced.

In addition, a series circuit of a thyristor switch and an overvoltage suppression resistor is connected in parallel with the field winding of the synchronous machine.
In a field overvoltage protection device configured to make the thyristor switch conductive when an overvoltage occurs in the field to protect the field winding and the semiconductor rectifier from overvoltage, a pair of thyristor switches are arranged in parallel with the field winding. and an overvoltage suppression resistor are connected in series, and the intermediate connection point of these thyristor switches and one phase forming the input AC voltage of the semiconductor rectifier are connected through a current suppression resistor having a resistance value similar to that of the overvoltage suppression resistor. The thyristor switch is connected to the thyristor switch so that it can self-extinguish, and is configured to reduce the value of current flowing from the semiconductor rectifier after the thyristor switch becomes conductive, and the overvoltage of either of the pair of overvoltage suppression resistors is The suppression resistor is also used as a rapid demagnetization resistor, and by connecting a reverse thyristor switch in series with this resistor, the reverse thyristor switch is made conductive when the field circuit breaker is opened, thereby enabling rapid demagnetization. can be achieved.

Next, embodiments of the field overvoltage protection device for a synchronous machine according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of the device of the present invention. That is, in FIG.
0 indicates a synchronous machine, and 12 indicates a field winding. The field circuit for energizing the field winding 12 connects a semiconductor rectifier 18 to the output bus 14 of the synchronous machine 10 via an excitation transformer 16, and connects the semiconductor rectifier 18 to the output end of the semiconductor rectifier 18. It is constructed by connecting field windings 12. Further, the semiconductor rectifier 18 is subjected to phase control by an automatic voltage regulator 22 connected to the output bus 14 of the synchronous machine 10 via a voltage detection transformer 20 to control the output voltage. .

However, in the present invention, in the field circuit having the above configuration, a pair of thyristor switches 24, 24 connected in series with overvoltage suppressing resistors 26, 26, respectively, are connected in parallel with the field winding 12. Thyristor switch 24, 24
The intermediate connection point of the semiconductor rectifier 18 and one phase of the input AC voltage of the semiconductor rectifier 18 are connected via a current suppressing resistor 28 to constitute a self-extinguishable overvoltage protection device. In this case, each thyristor switch 24, 24
Ignition circuits 30 and 30 are connected to the ignition circuits 30 and 30, respectively. That is, in this embodiment, the thyristor switches 24, 24 are connected in the forward direction between the positive and negative poles of the field along with the overvoltage suppressing resistors 26, 26, respectively. In FIG. 1, the field circuit breaker, reverse thyristor switch, etc. are omitted.

Next, the operation of the field overvoltage protection device of this embodiment configured as described above will be explained.

Now, if an accident such as an asymmetric short circuit, a ground fault, or an asynchronous operation (step-out) occurs in the output circuit of the synchronous machine 10, a field induced current determined by the operating conditions of the synchronous machine 10 is generated. Since the semiconductor rectifier 18 in which this induced current becomes "negative" cannot flow a reverse current, the output of the current source becomes open and an overvoltage occurs in the field circuit. This overvoltage causes thyristor switch 2
When the value exceeds the value set by the ignition circuits 30, 30 of 4, 24, the thyristor switches 24, 24
A firing command is given to thyristor switch 2.
4 and 24 become conductive in sequence. In this way, when the thyristor switches 24, 24 are turned on, the semiconductor rectifier 18 also causes current to flow through the overvoltage suppression resistors 26, 26, but in this case, the current due to the reverse voltage of the S phase and the Y phase flows into the overvoltage suppression resistance. Rather than flowing directly through 26, 26, these currents flow through a current limiting resistor 28. Therefore, the current in each phase of the semiconductor rectifier 18 is controlled by the overvoltage suppressing resistors 26, 26.
and the sharing ratio of the current suppressing resistor 28.

Here, using FIG. 1, the method of setting the resistance values of the resistors 26 and 28 will be explained in more detail.

As shown in Figure 1, the value of the field reverse induced current due to step-out etc. is Ifr, the peak repetitive reverse voltage of the semiconductor rectifier 18 is Vrrm, and the average on-current is Itav.
Then, the resistance value R26 of the overvoltage suppression resistor 26 is set so as to satisfy the following condition: Ifr×2R26<Vrrm (1). Resistance value R2 of resistor 26
If 6 is too large and the condition of equation (1) above is not satisfied,
The peak repetitive reverse voltage is applied to the semiconductor rectifier 18.
A voltage higher than Vrrm will be applied, and there is a risk that the semiconductor rectifier 18 will be destroyed.

Furthermore, after the thyristor switch 24 is turned on, current is also caused to flow from the semiconductor rectifier 18 to the resistor 26, so that the AC input voltage is changed as shown in FIG.
Ve, and if the resistance value of the current suppression resistor 28 is R28, ignoring the influence of the thyristor firing angle, it is necessary to set it so as to satisfy the following condition: Itav>Ve/(R26+R28) (2).
If the condition of the above equation (2) is not satisfied, a current higher than the average on-state current will flow through the semiconductor rectifier 18, which may lead to destruction of the semiconductor rectifier 18.

Now, assuming that R28=0, that is, the resistor 28 is not connected, the above equation (2) becomes Itav>Ve/R26 (3). Therefore, only thyristor switch 2
4 and 24 and one phase that forms the input AC voltage of the semiconductor rectifier 18, the resistance value R26 of the overvoltage suppression resistor 26 must be set small; In addition, in order to reduce the current capacity of the overvoltage suppression resistor 26, R26 must be set large, which is a contradictory problem.

Therefore, in the present invention, a current suppression resistor 28 is provided in order to solve both the problems of suppressing overvoltage and limiting the inflow current value when the thyristor switch 24 is turned on. However, current suppression resistor 28
If the resistance value R28 is set to a too large value, it will not be possible to secure the reverse voltage to return the thyristor switch 24 (self-extinguishing) after the field reverse induced current disappears, so care must be taken.
Actually, since the reverse voltage changes depending on the firing angle of the semiconductor rectifier 18 at that time, the preferable relationship between R26 and R28 has a certain range.

Usually, 2R28=R26, but in calculation,
There is no problem even if R28=R26. However, assuming a margin, R28 = R26 seems to be the preferable limit for the resistance value R28.

FIG. 2 is a circuit diagram in which a field circuit breaker 32 and a reverse thyristor switch 34 are additionally connected to the circuit shown in FIG. That is, in this case, the overvoltage suppression resistor 26 is connected and arranged so that it is commonly used as a rapid demagnetization resistor for the reverse thyristor switch 34. Note that reference numeral 36 is an ignition circuit for the reverse direction thyristor switch 34. The other configuration is completely the same as the circuit configuration shown in FIG.

In FIG. 2, when opening the field circuit breaker 32, the field is first short-circuited with a resistance via a contactor in order to prevent reverse induced voltage in the field winding 12 and shorten the field time constant. do. However, if the field current immediately before opening the field circuit breaker 32 is small, the reverse induced voltage will not increase significantly. Therefore, in the circuit shown in FIG. 2, by providing the reverse direction thyristor switch 34, there is no need to provide a contactor for rapidly demagnetizing resistance, and when the field voltage suddenly increases when the field circuit breaker 32 is opened. Then, the reverse thyristor switch 34 becomes conductive and rapid demagnetization can be performed via the resistor 28.

As is clear from the embodiments described above, according to the present invention, in the field circuit, a pair of thyristor switches are connected in series together with an overvoltage suppressing resistor, and the intermediate connection point of these thyristor switches and the input AC voltage of the semiconductor rectifier are connected in series. By connecting one phase through a current suppression resistor, it is possible to secure a reverse voltage to restore the thyristor switch even if the resistance value of the overvoltage suppression resistor is lowered to lower the field overvoltage limit value. Moreover, there are advantages such as no need to increase the current capacity of each element of the semiconductor rectifier.

Furthermore, when opening the field circuit breaker, the overvoltage suppressing resistor is also used as a rapid demagnetizing resistor, and by connecting a reverse thyristor switch in series with this resistor, the rapid demagnetizing resistor closing contactor can be omitted and the above-mentioned Rapid demagnetization can be effectively achieved with a reverse thyristor switch.

Although the preferred embodiments of the present invention have been described above, the present invention can be widely applied not only as a field overvoltage protection device for synchronous machines but also as an overvoltage protection device for semiconductor rectifiers. Of course, various design changes can be made without departing from the spirit of the invention.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a field overvoltage protection device for a synchronous machine according to the present invention, and FIG. 2 is a main circuit diagram showing an example of application of the circuit shown in FIG. 10...Synchronous machine, 12...Field winding, 14...
Output bus bar, 16...Excitation transformer, 18...Semiconductor rectifier, 20...Voltage detection transformer, 22...
... automatic voltage regulator, 24 ... thyristor switch, 26 ... overvoltage suppression resistance, 28 ... current suppression resistance, 30 ... ignition circuit, 32 ... field breaker,
34...Reverse direction thyristor switch, 36...Ignition circuit.

Claims (1)

[Claims] 1. A series circuit of a thyristor switch 24 and an overvoltage suppression resistor 26 is connected in parallel with the field winding 12 of the synchronous machine 10, and the thyristor switch 24 is made conductive when an overvoltage occurs in the field. In the field overvoltage protection device configured to protect the field winding 12 and the semiconductor rectifier 18 from overvoltage, a series circuit including a pair of thyristor switches 24 and an overvoltage suppression resistor 26 is connected in parallel with the field winding 12. The intermediate connection point of these thyristor switches 24 and one phase forming the input AC voltage of the semiconductor rectifier 18 are connected via a current suppression resistor 28 having a resistance value similar to that of the overvoltage suppression resistor 26, and the thyristor A field overvoltage protection device for a synchronous machine, characterized in that the switch 24 is capable of self-extinguishing, and is configured to reduce the value of current flowing from the semiconductor rectifier 18 after the thyristor switch 24 is turned on. 2. A series circuit of a thyristor switch 24 and an overvoltage suppression resistor 26 is connected in parallel with the field winding 12 of the synchronous machine 10, and when an overvoltage occurs in the field, the thyristor switch 24 is made conductive and the field winding 12 is turned on. And in a field overvoltage protection device configured to protect a semiconductor rectifier 18 from overvoltage, a series circuit of a pair of thyristor switches 24 and an overvoltage suppression resistor 26 is connected in parallel with the field winding 12, and these thyristor switches 24 and one phase that forms the input AC voltage of the semiconductor rectifier 18 are connected via a current suppression resistor 28 having a resistance value similar to that of the overvoltage suppression resistor 26, and the thyristor switch 24 is self-extinguished. The present invention is configured to reduce the value of current flowing from the semiconductor rectifier 18 after the thyristor switch 24 becomes conductive, and rapidly demagnetizes one of the pair of overvoltage suppression resistors 26. A field overvoltage protection device for a synchronous machine, characterized in that the resistor is used commonly as a resistor, and a reverse thyristor switch 34 is connected in series with this resistor.