JPS6347046B2 - - Google Patents

Description

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

Conventionally, this type of device was not installed, but as semiconductor technology progressed 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 done.

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 alternator 1 is
The field coil 2 is excited by the DC output of a thyristor exciting device 7. The alternator 1 is an automatic voltage regulator (not shown, hereinafter abbreviated as AVR)
The DC output of the thyristor excitation device 7 is controlled by the signal given by the thyristor excitation device 7 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.

Now, if some abnormality occurs or if you want to stop the generator 1, the field or disconnector is tripped to open the main contact 5 and the energy stored in the alternator's field is transferred to the field. It is discharged by flowing through the field discharge resistance circuit created by the auxiliary contact 6 of the breaker.

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. flows. The fundamental wave alternating current component of the armature is passed through the field coil 2 as a direct current component, and the armature current i
The DC component of the field coil 2 is supplied with 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 according to 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 element, which is energized at that time. It had the disadvantage of damaging the element. 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
The purpose of the present invention is to provide a device that fully fires the thyristors in the output section of a thyristor excitation device, makes all the thyristors conductive, and shunts the reaction current to all the thyristors to prevent damage to the thyristor elements. There is.

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 and 22 are instrument transformers (hereinafter abbreviated as PT), 23 and 24 are auxiliary transformers (with iron core shield to prevent high voltage surges), 25 to 3
0 is a diode assembled in a 3-phase full-wave rectifier circuit, 3
1 is a resistor, 32 is a capacitor, 33 and 34 are input resistors, 35 is a variable resistor (for bias setting), 3
6 is an operational amplifier, 37 and 38 are resistors, 39 is a hysteresis adjustment resistor, 40, 41, and 42 are instrument current transformers (hereinafter abbreviated as CT), and 43, 44, and 45 are AC/DC voltage converters. , 46, 49 are resistances, 50
is a variable resistor, 51 is an operational amplifier, 52 and 53 are resistors, 54 is a hysteresis setter (for bias setting), 55 and 56 are input resistors, 57 is a resistor, and 58
is a diode, 59 is a resistor, 60 is a transistor, 61 to 67 are resistors, 68 is a diode, 6
9, 70 are transistors, 71 is a capacitor, 7
2 is a unidirectional transistor, 73 is a pulse transformer, 74, 75 are resistors, 76, 77 are diodes, 78, 79 are capacitors, 80, 8
1 is a resistor, 82 is a transistor, 83 is a relay,
84 is a diode, 85 is a contact of relay 83,
86 is a diode.

Next, the operation will be explained. First, when a three-phase short circuit occurs, the terminal voltage of the generator decreases extremely and a sudden short circuit current flows through each phase of the generator 1.

Reference numerals 21 to 39 in FIG. 3 are circuits for detecting that the terminal voltage of the generator 1 has decreased. Auxiliary transformers 23 and 2 are installed so that the generator voltage can be increased to 110V by PT21 and PT22 and then input to the semiconductor circuit.
Lower the voltage at step 4. This auxiliary transformer is equipped with a shield to absorb lightning surges, etc., and the shield is grounded to prevent surges from entering the semiconductor circuit. The signal is rectified by a three-phase bridge type rectifier circuit, converted to direct current, filtered by a resistor 31 and a capacitor 32, and then fed to a comparison circuit using an operational amplifier 36. That is, 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 operational amplifier 36 Since the input of is larger when it is negative, 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 No. 5 becomes larger and the "positive" input voltage becomes larger, the output becomes "negative".

In FIG. 3, circuits 40 to 46 and 49 to 54 detect when the output current of the generator becomes larger than the normal value. CT40~42 for each phase current of the generator
The AC current is detected and converted into a DC voltage by insulation converters 43 to 45 that convert the AC current into a DC voltage. The "negative" terminal of this converter 45 is connected to zero V, the output voltages of the three converters are connected to be the sum, and this is compared with the bias setting device 50. During normal operation, if the "negative" voltage of the bias setter 50 is set to be larger, the output of the operational amplifier 51 becomes "positive".

Next, when a three-phase short circuit occurs, each phase current increases, so the "positive" voltage of the sum of the output voltages of the above converters becomes larger than the "negative" voltage of the bias setting device, so the operational amplifier The output of is "negative".

55 to 60 in Figure 3 are NOR circuits; when both inputs are positive, the output is zero V; when either one is positive and the other is negative, the output is also zero V; The output is positive only when both are negative.

3 are circuits 61 to 79 that continuously generate ignition pulses. When the output of the above NOR circuit is zero V (when the transistor 60 is conductive),
Transistor 69 is cut off, transistor 7
0 is conductive and the voltage across the capacitor 71 is 0V
Therefore, the unijunction transistor 72 is not conductive and no current flows through the pulse transformer 73, so that no ignition pulse is generated.
When the output of the NOR circuit becomes positive, transistor 6
A base current flows through transistor 9, causing a short circuit between the collector and emitter of transistor 69, and transistor 7
Since the base current of 0 does not flow, the transistor 7
0 is the cutoff, and the capacitor 71 is charged through the resistor 66. When the terminal voltage of the capacitor 71 exceeds a certain value, the unidirectional transistor 72 becomes conductive, and a pulse current flows to the primary side of the pulse transistor 73, and a pulse current flows to the secondary side. The corresponding pulse voltage is generated. If the output of the NOR circuit remains positive, the capacitor 71 repeats charging and discharging and outputs a pulse each time. capacitor 71
If the value of is kept small, high frequency pulses will be continuously output while the output of the NOR circuit is positive.

That is, the terminal voltage of the generator becomes abnormally low [the output of the operational amplifier 36 becomes negative], and the output current of the generator increases abnormally [the operational amplifier 51
If the output of the pulse transformer 73 becomes negative], then the pulse transformer 73
Continuous pulses are generated from the thyristor element 8 of the thyristor exciter 7, which connects the secondary side of six similar pulse transformers (only two are shown, four are omitted).
If applied to the gates of 8 to 13, all thyristor elements will fire, and even if a back electromotive force is generated due to the reaction of the sudden short circuit current due to a three-phase short circuit, thyristor element 8
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.

Transistor 82 operates exactly the same as transistor 69, and if the terminal voltage of the generator becomes abnormally low and the output current of the generator increases abnormally, relay 83 will operate and a three-phase short circuit will occur. A contact 85 is provided to issue an alarm.

In the above embodiments, a three-phase alternating current generator is used, but a single-phase alternating current generator has the same effect.

Moreover, the transistors 60, 69, 70, 82 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 the output voltage of the generator abnormally decreases and the output current of the generator abnormally increases, When detected, all the thyristor elements of the thyristor excitation device are fired, and the current of the back electromotive force of the field coil due to the reaction of the short-circuit current is shunted to all the thyristor elements, thereby preventing damage to the thyristor of the thyristor excitation device. This has the effect of protecting the thyristor excitation device without causing meltdown of the fast-acting fuse.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional excitation circuit, and FIG. 2 is a circuit diagram illustrating that a back electromotive force is generated due to the reaction of the short circuit current when a three-phase short circuit occurs, and the field current increases. FIG. 3 is a configuration 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, 21 to 39 is a detector for detecting an abnormal decrease in the terminal voltage of the generator, 40
~46, 49-54 are detectors that detect an abnormal increase in the output current of the generator, and 55-60 are detectors that detect that both of the above two detectors have detected.
NOR circuits 61 to 79 are circuits that continuously generate ignition pulses, and 80 to 85 are relay circuits that operate when both of the above two detectors detect them. Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (1)

[Claims] 1. Detection for detecting an abnormal drop in the output voltage of the generator in a thyristor excitation device that supplies output current to the field coil of the generator to control the terminal voltage of the generator. When both the detector and the above two detectors detect an abnormal increase in the output current of the generator, a circuit is provided to detect this, and when this circuit detects, an ignition pulse is generated. All the thyristor elements of the thyristor excitation device are ignited by a circuit that continuously generates , and the current of the back electromotive force of the field coil due to the reaction of the sudden short-circuit current of the generator is shunted to all the thyristor elements. Features a short circuit protection device. 2 Equipped with a detector that detects an abnormal drop in the terminal voltage of the generator and a detector that detects an abnormal increase in the output current of the generator, and operates when both of the above two detectors detect 2. The short-circuit protection device according to claim 1, wherein a relay is used to give a warning to an operator and prompt emergency processing.