JPS5819128A - Dc system and generator cooperation control system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method when a large power source such as a nuclear power source is connected to multiple DC power transmission systems, and in particular maintains the stability of the nuclear power source side AC system in the event of a DC system ground fault. This invention relates to a control method suitable for.

While electric power systems are being expanded and strengthened in response to increasing demand for electric power, power sources are becoming more remote and larger in scale, and various problems are arising, such as more complex system operations and environmental constraints. One way to deal with these power system problems is to set up nuclear power plants at locations far away from power demand areas.
A method is being considered in which the power is transmitted via direct current to the load point. To explain using Figure 1, 11 to 14 are nuclear power generators, 21 to 28 are conversion transformers, and 31 to 38 are AC to DC (31 to 34) or DC to AC (35 to 38).
41-48 are DC reactors for smoothing the DC current, 51-54 are DC transmission lines, 6
1 indicates the AC system in the demand area. 1σ0 is a system command device that commands the operating status of the AC system to which the generator is connected, the AC system and the DC system in the demand area, and 101 to 104 are the system command devices that start and operate the generators 11 to 14 according to commands from the system command device.
Generator control circuit for stopping, setting output, etc., 300°30
Reference numeral 9 denotes a DC system command device that starts/stops the AC/DC converters 31 to 38, sets output, etc. according to commands from the system command device 100, and 301 to 308 activates the AC/DC converters 31 to 38 according to commands from the DC system command device. This is a converter control circuit that controls 38.

If a ground fault occurs in a DC transmission line in such a DC system, for example, if a fault occurs in one of the four systems, the power transmitted by the remaining healthy DC systems will be increased by 33%, and the generator will be turned off. The DC system is controlled so as to equalize the output and the power transmission output and maintain the transient stability of the generator side AC system. However, if an accident occurs in two or more of the four systems, an attempt is made to maintain a balance between the generator output and the transmitted power of the DC system. (Designed to be able to do so) If the power balance of the AC system is not maintained, the generator will lose synchronization and the AC system will collapse. Nuclear power generators are equipped with a power load unbalance relay (RLURA) to control and protect the generator in the event of an accident like this, but it may not function adequately in the event of a DC transmission line accident. .

This will be explained using Fig. 2.1. Fig. 2 shows the DC transmission line when a ground fault occurs in the DC transmission lines 51 and 52 of two of the four systems at A schematic diagram of current and power in the system is shown.When a ground fault occurs, there is a transient overcurrent and low voltage in the DC system, so a ground fault in the transmission line is detected, and the converter where the fault occurred is immediately The fault current at the time of a DC system ground fault as shown in 51.52 increases transiently. On the other hand, in a healthy DC system53,54, the excess power increases by 33% to compensate for the loss of power due to the accident (the transmitted power is zero due to voltage drop on the faulty line). Load operation is performed after time t2.

For this reason, due to the DC system total power Pdi'Tj accident, 5.
The transmitted power drops to 0%, but the transmitted power recovers to 66.7% due to healthy overload operation of the DC system.

By the way, the PLUR of a nuclear power generator generally operates with an imbalance between turbine output and load (current) of 40% or more and a current reduction rate of 40%/1 oms or more. In this case, it does not operate and nuclear power output control is not performed. As a result, the transient stability of the AC system to which the generator is connected deteriorates, leading to the shutdown of the entire nuclear power generator. Especially in DC systems, even if an accident occurs on a power transmission line, the constant current control function of the converter allows
There is an inconvenience that there is no change in the DC current even though the transmitted power has decreased, so the characteristics of the currently used PLUR are those that only look at the magnitude and rate of change of the current, so it is not possible to operate. Instead, an additional device is required to detect accidents.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control system for stably operating an AC system, which eliminates the drawbacks of the prior art described above.

In order to improve the transient stability of an AC system connected to a nuclear power generator, the present invention compares the power that can be transmitted by a healthy DC system with the output power of a nuclear power generator, and calculates the amount of power that can be transmitted by a DC system. The output of the generator is reduced by a certain amount only when the output of the nuclear power generator becomes larger than the output of the nuclear power generator.

An embodiment of the present invention is shown in FIG. The same numbers as in FIG. 1 indicate the same things, so only the different ones will be explained. 110 is a signal from the system control device 100, which indicates the total output value I of the nuclear power generator, and the system control device 300.
An output comparison circuit that inputs the signal ■2 indicating the DC system in operation and outputs a signal that becomes 1 when the total output value of the nuclear power generator becomes greater than the total power that can be transmitted by the DC system. The details of this circuit are shown in Fig. 4.
In the figure, Pa1. Pd2...P a 4 is a setting device, SWI, that sets the maximum allowable transmission power of each DC system.

SW2...SW4 are switches SU that are turned on when the DC system is in operation and turned off when the DC system is stopped due to an accident, etc., by the switch drive circuit SD according to the signal engineer 2 indicating the DC system in operation.
M is 11 and Pdl + Pd21 P'+31 Pa
Adder that calculates the difference between all or any of the sums of 4, CO
M is when this difference is positive, that is, when the total output value of the nuclear power generator ■1 becomes larger than the total transmitted power that can be transmitted during DC system operation. It is a comparator that The output 01 of this circuit is led to the system control device 100, and when OI is + or IT+, it is output to the generator control circuits 101 to 104 so that the output of the nuclear power generator is reduced by a certain amount. A reduction order is issued. Through this operation, the total output value of the nuclear power generator is again compared with the maximum transmission power that can be transmitted by the operating DC system, and if the former is still larger than the latter, the output of the nuclear power generator is again reduced by a certain amount. The system eventually reaches a point where the maximum power that can be transmitted by the operating DC system becomes greater than the output of the nuclear power generator. When the power transmitted by the DC system is larger than the output of the nuclear power generator, the difference in output can be solved by providing a constant power control function to the DC system to balance the power transmitted by the DC system and the output of the nuclear power generator. can. Therefore, the balance between the output of the nuclear power generator and the output of the DC system is always maintained, and it is possible to prevent deterioration of the transient stability of the AC system to which the generator is connected.

In the above example, the case where the DC system consists of four systems was explained, but it is clear that it is possible to easily infer from this example and obtain the same effect even when the number of systems is increased or decreased. .

Note that the signal 2 indicating the DC system in operation is an operation command signal from the DC system command device 300, and although it is not shown in the diagram, it is a DC transmission line ground fault signal from a fault detection device installed in each DC system. , can be easily created using accident detection signals such as inverter load cutoff.

FIG. 5 shows an output reduction command generation circuit for a nuclear power generator according to another embodiment in which the DC system consists of four systems. 3
11 to 314 are accident detection devices (outputs "1" when an accident is detected) that detect accidents when the power transmission in the DC system is stopped, such as ground faults in DC transmission lines and inverter load cutoffs in each DC system, and AN is an AND The circuit, EX is an exclusive logic circuit, OR is an OR circuit, and this circuit has two or more fault detection devices "1"
When the output becomes ``, the output 02 becomes ``■++''. Therefore, assuming that the overload capacity of the DC system is 133%, even if one of the four DC systems goes down, overload operation will be performed on the other healthy DC systems, which will increase the output of the generator and the transmitted power of the DC system. However, when two or more systems fail, the output of the circuit shown in Figure 5 becomes In, so the output of the generator can be adjusted as in the previous example (Figure 3). By decreasing the amount, it is possible to prevent the transient stability of the AC system connected to the generator from deteriorating, and it is possible to obtain the same effect as described above.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing the object of the present invention, Fig. 2 is a schematic diagram of current and voltage waveforms of the DC system at the time of a system fault in Fig. 1, and Fig. 3 is a control circuit block diagram showing an embodiment of the present invention. , FIG. 4 is a block diagram of the output comparison circuit in FIG. 3, and FIG. 5 is a generator output reduction command generation circuit according to another embodiment of the present invention. 11-14... Nuclear power generator, 21-28... Conversion transformer, 31-38... AC/DC converter, 41-48.
...DC reactor, 51-54...DC transmission line, 6
1... AC system (load), 101-104... Generator control circuit, 100... System command device, 300...
DC envy 10, 2, payment 30, 4 times D, 50

Claims (1)

[Claims] 1. In a DC transmission system where the output of the generator is transmitted to the power demand area through multiple DC transmission systems, the maximum allowable power that can be transmitted in the DC system is compared with the output power of the generator, and the latter is larger than the former. A cooperative control system between the DC system and the generator, which is characterized by reducing the output of the generator when