JPS6347045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for a thyristor exciter which prevents the exciter from being damaged in the event of a short circuit in a generator.

Previously, this type of device had not been installed, but as semiconductor technology developed and rotary exciters began to change to thyristor excitation devices, it became necessary to prevent damage to thyristors due to overcurrent, so this invention was developed. It has been announced.

FIG. 1 shows a basic configuration diagram of a conventional thyristor excitation circuit. 1 is an alternating current generator, 2 is an exciting coil of the generator 1, 3 is a shunt that measures the exciting current, 4 is a field discharge resistor, 5 is the main contact (A contact) of the field switch and disconnector, 6 is a Auxiliary contact (b contact) for field magnetization and disconnection, 7 is a thyristor excitation device, 8 to 13 are thyristor elements assembled in the three-phase bridge of the output part of the thyristor excitation device 7, 14 is a field ammeter, 1
5 is a field voltmeter.

Next, the operation will be explained. The alternating current generator 1 has its field coil 2 excited by the DC output of a thyristor exciting device 7 .

In the AC generator 1, the DC output of the thyristor excitation device 7 is controlled by a signal given from an automatic voltage regulator (not shown, hereinafter abbreviated as AVR) so that the output voltage of the generator 1 is constant. The controlled DC output is checked by the operator using the excitation voltmeter 15 and the excitation ammeter 14 during operation.

If an abnormality occurs now or if you want to stop the generator 1, trip the field magnet or disconnector to open the main contact 5, and the energy stored in the field of the alternator will be released. It is discharged by flowing through the field discharge resistance circuit created by the auxiliary contact 6 of the device.

Figure 2 shows a conventional generator 1 in which three phases are short-circuited. When a sudden short-circuit current flows through the three-phase alternating current generator, a reaction current (ifr) also flows to the field coil side. . The fundamental alternating current component of the armature flows through the field coil 2 as a direct current component, and the direct current component of the armature current i flows through the field coil 2 as an alternating current component of the rotational frequency.

The current due to this reaction rises relatively rapidly when a short circuit occurs, and gradually attenuates in accordance with the short circuit transient time constant T'd.

Conventional thyristor excitation circuits are configured as described above, so if a three-phase short circuit occurs in the output of the alternator, an excessive current due to this reaction will flow to the thyristor elements that are energized at that time. There was a defect that caused damage. Further, when a fast-acting fuse for protecting the thyristor element is connected in series with the thyristor (not shown), there is a drawback that the fast-acting fuse is blown out.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and even if a three-phase short circuit occurs in the output of an alternator, it can be automatically detected and
Full firing the thyristor at the output part of the thyristor excitation device to make all the thyristors conductive,
It is an object of the present invention to provide a device that prevents damage to thyristor elements by dividing a reaction current to all thyristors.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, numerals 1 to 14 are the same as those described in FIG. 21 is a potential transformer (hereinafter abbreviated as PT), 22 is also a PT, 23 and 24 are auxiliary transformers, 25 to 30 are diodes assembled in a three-phase full-wave rectifier circuit, 31 is a resistor, 32 is a capacitor, 33, 34 are input resistors, 35 is a variable resistor (bias setting device), 36 is an operational amplifier, 37, 3
8 is a resistor, 39 is a hysteresis adjustment resistor, 41 is an isolation amplifier, 42 and 43 are resistors, 44 is a variable resistor (bias setting device), 45 is an operational amplifier, 46,
47 is a resistor, 48 is a hysteresis adjustment resistor, 4
9, 50, 51, 52 are resistors, 53 is a transistor, 54 is a diode, 55 to 61 are resistors, 62
is a diode, 63 and 64 are transistors, 65
is a capacitor, 66 is a unidirectional transistor, 67 is a pulse transformer, 68, 69 are resistors, 70, 71 are diodes, 72, 73 are capacitors, 74, 75 are resistors, 76 is a transistor, 77 is a diode, 78 is a relay , 79 is a diode, and 80 is an a contact of the relay 78.

Next, the operation of this invention will be explained. First 3
What happens when a phase short circuit occurs is that the terminal voltage of the generator decreases extremely, and when this sudden short circuit current flows, the field current rapidly increases due to the reaction.

Reference numerals 21 to 39 in FIG. 3 are circuits for detecting a decrease in the terminal voltage of this generator. Auxiliary transformers 23 and 2 are installed to input the generator voltage to 110v to the semiconductor circuit using PT21 and PT22.
Step 4 lowers the voltage, rectifies it with a three-phase bridge rectifier circuit, converts it to DC, and connects it to the resistor 31 and capacitor 3.
After filtering with step 2, the signal is applied to a comparator circuit using an operational amplifier 36. In other words, when the absolute value of the positive voltage set by the bias setting resistor 35 is smaller than the negative voltage detected by the generator voltage (during normal operation), the input to the operational amplifier 36 is Since the negative value is larger, the output is positive. If a three-phase short circuit occurs, the generator voltage will drop extremely, so the input of the operational amplifier 36 is connected to the bias setting device 3.
Since the input of 5 is larger and the positive one is larger, the output is negative.

Reference numerals 41 to 48 in FIG. 3 are circuits for detecting an increase in the field current of the generator. The field current of the generator is converted to mV by a shunt 3, and converted to DC voltage by an isolation amplifier (isolator) 41.

The negative terminal of this voltage is connected to zero v, and the positive output terminal is used to generate a positive voltage proportional to the field current. The bias setter 44 is transmitting a negative voltage, and normally the bias setting 44 is higher than the positive field current.
Since the negative voltage of 4 is increased, the operational amplifier 4
The output of 5 is positive.

When the field current increases due to the reaction of the sudden current caused by a three-phase short circuit in the generator, the positive input becomes larger than the negative value of the bias setting device 44.
The output of is negative.

49 to 54 are NOR circuits, when both inputs are positive, the output is 0 V, when either one is positive and the other is negative, the output is 0 V, and both inputs are negative. The output is positive only when

55 to 73 are circuits that continuously generate firing pulses when the output of the NOR circuit is positive; when the input is 0 V, the transistor 63 is cut off, the transistor 64 is conductive, and the voltage across the capacitor 65 is 0 V. Therefore, the unijunction transistor 66 is not conductive and no ignition pulse is generated.

When the input becomes positive, the collector and emitter of transistor 63 are short-circuited, and transistor 64
is cut off, the capacitor 65 is charged through the resistor 60, and when the terminal voltage of the capacitor 65 exceeds a certain value, the unijunction transistor 6 is turned off.
6 becomes conductive, a pulse current flows through the primary side of the pulse transformer 67, and a corresponding pulse voltage is generated on the secondary side. If transistor 64 remains cut off, capacitor 65 will charge and discharge repeatedly, producing a pulse each time. capacitor 65
If the value of is kept small, high frequency pulses will be continuously output while the transistor 64 is cut off.

That is, if the generator voltage becomes low [the output of the operational amplifier 36 becomes negative] and the field current becomes larger than a predetermined value [the output of the operational amplifier 45 becomes negative], the pulse Continuous pulses are generated from the transformer 67, and if six secondary pulse transformers (only two are shown and four are omitted) of similar pulse transformers are applied to the gates of thyristor elements 8 to 13 of the thyristor excitation device 7. , all of the thyristor elements 8 to 13 are fired, and even if a back electromotive force is generated in the field coil 2 due to the reaction of the short-circuit current of the three-phase short circuit, the thyristor elements 8 to 13 are fired.
Since the current is divided into three parts such as 11, 9 and 12, and 10 and 13, the thyristor element will not be damaged.

Of course, the thyristor excitation device 7 is a three-phase full-wave rectifier, so the peak voltage is reached, but when a three-phase short circuit occurs, the field current is several times as large as the field current at the peak voltage, so this is discharged. It is something.

Transistor 76 operates in exactly the same way as transistor 63, and relay 78 and its a-contact 80 are for warning that a three-phase short circuit has occurred.

In the above embodiment, a three-phase alternating current generator has been described as an example, but a single-phase alternating current generator can also have the same effect.

Furthermore, the transistors 53, 63, 64, and 76 are
A similar effect can be achieved by using an IC NAND circuit.

As described above, according to the present invention, when a short circuit occurs in the output of the generator, that is, when it is detected that both the generator voltage has decreased and the generator field current has exceeded a predetermined value, All the thyristor elements of the thyristor excitation device are ignited, and the field current increased by the reaction is shunted to the thyristor elements, so that the thyristor of the thyristor excitation device is not damaged or the fast-acting fuse is melted. This has the effect of protecting the thyristor excitation device.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional excitation circuit, Fig. 2 is a circuit diagram to explain that a back electromotive force is generated due to a reaction when three phases are shorted, and the field current increases. Fig. 3 1 is a block diagram showing an embodiment of the present invention, 1 is a generator, 2 is a field coil of the generator, 7 is a thyristor excitation device, 8 to 13 are thyristor elements, and 21 to 39 are generator voltage drops. Detectors 41-48 detect that the field current of the generator exceeds a predetermined value; 49-48;
53 is a NOR circuit that detects that both of the above two detectors have detected, 55 to 73 are circuits that continuously generate firing pulses, and 74 to 80 are relays that operate when both of the above two detectors have detected. . Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Supplying an output current to a field coil of a generator,
In a thyristor excitation device that controls the terminal voltage of a generator, there is a detector that detects that the generator voltage has decreased, and a detector that detects that the field current of the generator has exceeded a predetermined value. A circuit is provided to detect when both detectors detect this.
When this circuit detects this, a circuit that continuously generates firing pulses fires all the thyristor elements of the thyristor excitation device, and the field current increased by the reaction of the short circuit current of the generator is shunted to the thyristor elements. A short circuit protection device characterized by: 2 Equipped with a detector that detects that the generator voltage has decreased and a detector that detects that the field current of the generator exceeds a predetermined value, and a relay that operates when both of the above detectors simultaneously detect 2. The short-circuit protection device according to claim 1, wherein the short-circuit protection device is configured to give a warning to an operator to prompt emergency treatment.