JP3517531B2 - Excitation control device for AC generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an excitation control device for a thyristor direct excitation type AC generator that utilizes a residual voltage of an AC generator for initial excitation. 2. Description of the Related Art A thyristor direct excitation method is one of the excitation methods for an AC (synchronous) generator, and the circuit configuration thereof is shown in FIG. In the figure, 1 is an AC generator (synchronous generator), 2 is an AC circuit breaker, 3 is an exciting transformer, 4 is an instrument transformer (PT) for detecting the output voltage of the generator 1 and 5 is power generation. A current transformer (CT) 6 detects the machine current on the load side (power system side) of the circuit breaker 2 and uses it for cross current compensation. The current transformer 6 receives the detected voltage and current from the PT 4 and CT 5 and outputs the current. An automatic voltage regulator (AVR) that automatically adjusts the voltage, a voltage relay that operates when the generator output voltage is equal to or higher than a predetermined value, and 8 that excites the field winding of the generator 1 from the exciting transformer 3. A field current adjusting thyristor for supplying a current, and receives a gate signal from the AVR 6. Reference numeral 9 denotes a field circuit breaker, 10 denotes a current measuring device for measuring a field current, 11 denotes a voltage measuring device for measuring a field voltage, 12 denotes a discharge resistor (DR), and 30 denotes an initial excitation circuit. The initial excitation circuit 30 includes a resistor 31, a diode 3
2 and a field changing contactor 33, and is connected to a battery of an initial excitation power supply (for example, DC100V). At the time of starting the generator, when the rotation speed of the generator 1 reaches a specified rotation speed, the field breaker 9 and the field change contactor 3
3 to start the initial excitation, and when the output voltage of the generator 1 reaches the specified voltage, the flow shifts to the field control by the AVR 6. That is, the initial excitation by the battery is stopped when the generator output voltage becomes 70 to 80% of the rated voltage, and thereafter, the field control is performed by the gate control of the thyristor 8 by the AVR 6. In this type of excitation system, a voltage control operation (control operation of the AVR 6) starts when the output voltage of the generator 1 reaches 70 to 80% of the rated voltage. Until then, initial excitation using a separate battery as a power source is required. Since the large-capacity generator has a large initial exciting current and a correspondingly large battery capacity, the installation space and the cost required for maintenance management also increase. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an excitation control device for an AC generator capable of greatly reducing equipment costs and maintenance costs. SUMMARY OF THE INVENTION The present invention provides an exciting transformer connected to an output terminal of an AC generator and serving as an exciting power supply, and an exciting transformer connected to a field winding of the AC generator. A thyristor for adjusting a field current for supplying a field current from a thyristor; and a gate change signal for supplying a gate signal from the automatic voltage regulator to the thyristor to adjust the field current. A self-excited initial excitation circuit formed by an auxiliary transformer and a rectifier is provided in parallel with the thyristor. FIG. 1 shows an embodiment of the present invention. In the figure, 1 is an AC generator (synchronous generator), 2 is an AC circuit breaker, 3 is an exciting transformer, 4 is an instrument transformer (PT) for detecting the output voltage of the generator 1 and 5 is power generation. A current transformer (CT) 6 detects the machine current on the load side (power system side) of the circuit breaker 2 and uses it for cross current compensation. The current transformer 6 receives the detected voltage and current from the PT 4 and CT 5 and outputs the current. An automatic voltage regulator (AVR) that automatically adjusts the voltage, a voltage relay that operates when the generator output voltage is equal to or higher than a predetermined value, and 8 that excites the field winding of the generator 1 from the exciting transformer 3. A field current adjusting thyristor for supplying a current, and receives a gate signal from the AVR 6. Reference numeral 9 denotes a field breaker provided on the output side of the exciting transformer 3, 10 denotes a current measuring device for measuring a field current, 11 denotes a voltage measuring device for measuring a field voltage, and 12 denotes a discharge resistor (DR). ) And 20 are self-excited initial excitation circuits provided in parallel with the thyristor 8. The self-excited initial excitation circuit 20
It is formed by a field change contactor 21, an auxiliary transformer 22, and a rectifier (diode) 23. Next, the operation will be described. The generator 1 is started, and when the number of revolutions of the generator 1 reaches the specified number of revolutions, the field breaker 9 and the field change contactor 21 are turned on to start the initial excitation. The generator 1 and the residual voltage of 2 to 3% at the specified rotational speed is generated, the voltage through the exciter transformer 3, field shielding <br/> cross 9 and the field changes the contactor 21 Auxiliary transformer 22
Is applied. The secondary output of the auxiliary transformer 22 is supplied to the field winding of the generator 1 via the diode 23. Due to this excitation, that is, self-excitation, the output voltage of the generator 1 increases. Then, when the voltage reaches the specified voltage, the voltage relay 7 operates, the control operation of the AVR 6 is started, and the field change contactor 21 is opened. Thereafter, the gate control of the thyristor 8 is performed by the AVR 6, the field current is adjusted, and the output voltage of the generator 1 becomes constant. As described above, according to the present invention, since the residual voltage of the AC generator is used as the initial excitation power supply, a battery as the initial excitation power supply is not required, and equipment and maintenance costs are reduced. It can be greatly reduced.

[Brief description of the drawings] FIG. 1 is a connection diagram showing one embodiment of the present invention. FIG. 2 is a connection diagram showing a conventional example. [Explanation of symbols] 1: AC generator 2. AC circuit breaker 3. Excitation transformer 6 ... AVR 7 ... Voltage relay 8. Field current adjustment thyristor 9 ... Field circuit breaker 20: Self-excited initial excitation circuit 21 ... Field change contactor 22 ... Auxiliary transformer 23 rectifier (diode)

Claims (1)

(57) [Claim 1] An excitation transformer connected to an output terminal of an AC generator and used as an excitation power supply, and a field winding from the excitation transformer to a field winding of the AC generator. A thyristor for adjusting a field current for supplying a magnetic current, and an excitation control device for an AC generator for adjusting a field current by supplying a gate signal from the automatic voltage regulator to the thyristor; An excitation control device for an AC generator, wherein a self-excited initial excitation circuit formed by a transformer and a rectifier is provided in parallel with the thyristor.