JPH036756B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides a method for
The present invention relates to an overexcitation limiting device that detects this and limits and controls the field current so that it is below the allowable field current value.

A conventional overexcitation limiting device of this type is shown in FIG. In the figure, 1 is an alternator, 2
is the field coil of the alternator, 3 is the potential transformer (hereinafter referred to as PT), and 4 is the automatic voltage regulator (hereinafter referred to as PT).
5 is an allowable field current setting device, 6 is a shunt, 7 is an isolation amplifier whose input and output are isolated,
8 is a deviation detector, and 9 is a deviation amplification device.

Next, the operation of the conventional device will be explained. The generator voltage is detected by PT3, and the field current is increased or decreased by AVR4 to control the generator voltage so that the generator voltage is constant. On the other hand, a maximum current (permissible field current) is determined for the field coil 2 of the generator 1 in relation to the temperature rise of the generator 1, and it is necessary to limit the current to below this maximum current. For this reason, in FIG. 1, an allowable field current setting device 5, a shunt 6 for detecting the field current, and an insulation amplifier 7 that insulates the output of the shunt 6 and supplies it to the AVR 4 are provided. A deviation detector 8 detects the difference between the output signal of the setting device 5 and the output of the isolation amplifier 7, and increases the difference to a value suitable for inputting to a signal mixer (not shown) provided in the AVR 4. The width is increased using a width device 9 and then given to the AVR 4. In other words, the AVR 4 normally controls the generator voltage to be constant, but when the field current exceeds the allowable field current value, it limits the generator 1 so that it does not exceed the allowable field current value. act to protect.

Therefore, in order to increase the allowable field current of the generator 1, it is necessary to prevent the temperature from rising due to the field current, and therefore the field coil 2 is cooled.

However, in general, the allowable field current for the internal cooling gas pressure of the generator 1 increases as the internal cooling gas pressure increases, as shown in FIG. Since only one point can be set, the allowable field current is actually set to a low value with a considerable margin, assuming the worst conditions. For this reason, the generator 1 could not be used to its fullest allowable field current value.
In addition, this allowable field current value is set on the condition that the current is continuously applied, so when an accident occurs in the grid and the voltage drops, the AVR4 must output a magnetizing output to restore the voltage of the grid. However, since the magnetization output is limited even though the system is not used, it has the disadvantage that it is not possible to quickly restore the system voltage. In other words, if overexcitation of generator 1 is for a short time, there will be no problem until the temperature rises, and if an accident occurs, the bus protection relay etc. will operate and after a certain period of time, the faulty bus will be disconnected and the system voltage will be reduced. will recover, so the disadvantage of always applying a conventional overexcitation limit with a considerable margin even during short periods of time, such as during a grid failure, is that it erases the voltage control characteristics of the grid. It was hot.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above. When the generator voltage becomes higher than the normal operating range, overexcitation is immediately limited, and when the generator is normal, the system voltage drops. In the event of a shock, in order to contribute to the voltage recovery of the grid, the overexcitation limit is not applied for a certain period of time, and full following is performed, and after a certain period of time, the step signal generation circuit gradually reduces the overexcitation limit in order to reduce the shock. The allowable field current can be changed in proportion to the generator's internal cooling gas pressure by applying over-excitation, which allows the generator to be used up to its maximum limit and also contributes to improving the stability of system voltage control. The purpose is to provide a restriction device.

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 3, 1 to 4 and 6 to 8 are the same as in Fig. 1, 10 is a converter that converts the internal cooling gas pressure of the generator into DC voltage, and 11 is the allowable field current value of the generator. A base amount setting device that sets a base amount unrelated to the internal cooling gas pressure; 12 is the generator 1;
A permissible field current setting circuit for setting a permissible field current as shown in Fig. 2 proportional to the internal cooling gas pressure of the
3 is a detector that detects when the actual field current exceeds the allowable field current value, 14 is a time-limited instant return timer T1, 15 is a relay T1X that opens and closes when timer T114 operates after a certain time limit, and 16 is a Time-limited instant return timer T2, 17 is timer T2
A relay that opens and closes when 16 operates after a certain period of time.
T2X, 23 is an AC voltage to DC voltage converter, 24
is a comparison detector; 25 is a relay that operates when the generator voltage is above the upper limit of the normal operating range; 26 is a setting device that sets the upper limit of the normal operating range of the generator voltage;
27 and 28 are input resistors, 29 is a feedback resistor, 30 is an operational amplifier, 40 is a gain adjustment amplifier, 41 is a negative voltage detector, 42 is a positive voltage detector,
43 is a mercury contact relay R, 44 is a mercury contact relay L, 45 is a DC voltage transmitter, 46 is a V/F converter that converts the DC voltage into a pulse with a frequency proportional to this, and 47 is a memory for incoming pulses. Reversible up-down BCD counter, 48
is a D/A converter, and 49 is a polarity conversion amplifier.
In addition, A is a comparison detection part, B is an allowable field current setting circuit, C is an instantaneous signal generation circuit, D is a timer, and E is a step signal generation circuit.

Next, the operation of this invention will be explained. As shown in FIG. 4, the base amount Vb, which is unrelated to the internal cooling gas pressure of the generator 1, is set using the base amount setting device 11 shown in FIG. Voltage proportional to internal cooling gas pressure
Vg is added to create a set voltage as shown in Fig. 4, and this is set to match the allowable field current value shown in Fig. 2.

Next, detection relay HL25 detects whether the generator voltage is within the normal operating range. The normal operating range is plus 5% to minus 5% of the generator rated voltage.
The operating point of the detection relay HL25 can be precisely set using the setter 26, and is set, for example, with the goal of operating at +5% or more.

If the generator voltage is +5% or more and the field current reaches the allowable field current value, the relay HL25 is energized by the output of the comparison detector 24, and its contact HLb2 is activated.
5b opens, disconnecting the output of the D/A converter 48, and at the same time, two contacts HLa 25a close, one of which inputs a reset signal to the BCD counter 47 to reset it to zero count, and outputs an instantaneous signal. It becomes a generation circuit. The other inputs the signal from the deviation detector 8 to the gain adjustment amplifier 40 and operates to give an immediate overexcitation limiting signal to the automatic voltage regulator 4 to limit the field current.

Next, when the generator voltage is within the normal operating range and the grid voltage drops, full focusing (continuing to output maximum output) causes the field current to exceed the allowable field current value, but at this time the generator voltage relay to detect
HL25 is inactive, and detector 13 detects that the field current has become excessive. This energizes the timer T114, but the timer T114 is set to a period of several seconds to several tens of seconds during which the field coil 2 of the generator 1 can withstand the excessive current, and during this set time, the relay T1X contact T1XA15
Since a is not closed, no rising pulse is input to the BCD counter 47, the output of the D/A converter 48 is zero V, and the overexcitation limit signal is not applied to the AVR 4.

After a certain period of time, relay T1X15 operates and contacts
When T1Xa 15a is switched to close, a rising pulse is input to BCD counter 47 through contact Ra 43a of relay 43, which is energized based on the deviation between allowable field current and actual field current. That is, normally the output of the D/A converter 48 is almost zero, and when a deviation appears in the output of the deviation detector 8, the positive input to the operational amplifier 30 increases and the output becomes negative. The negative voltage detector 41 detects this, energizes the mercury contact relay R43, operates the contact Ra43a, and the set voltage from the DC voltage transmitter 45 changes to V/V.
It is converted into a pulse by the F converter 46, and the contact
When the T1Xa 15a is closed, the signal is input to the BCD counter 47. For example, the BCD counter 47 uses a BCD of about 3 digits and can count 0 to 999 pulses. When a rising pulse is input, it counts from 0 to 999 and stores it in memory. The D/A converter 48 converts 0 to 999 pulses into 0 to 10 V, and the output of the D/A converter 48 changes stepwise and increases each time a rising pulse is input.
When the output of the D/A converter 48 becomes the same as the output of the deviation detector 8, the output of the operational amplifier 30 becomes zero,
Both relay R43 and relay L44 no longer work.
The BCD counter 47 no longer receives pulses.
The reason why the limit signal is set in the form of small steps is to prevent the AVR 4 from being shocked by suddenly applying a large limit.

The timer T216 operates later than the timer T114, and when the output of the operational amplifier 30 becomes zero and the output of the D/A converter 48 and the output of the polarity conversion amplifier 49 become almost the same. Set it so that it works. When relay T2X17 operates, contact T2Xb17b closes and D/A
The output of the converter 48 is disconnected, the contact T2Xa17a is closed, and the output of the deviation detector 8 is changed to the polarity conversion amplifier 4.
The signal is directly applied to the AVR 4 via the gain adjustment amplifier 40 of No. 9. The polarity conversion amplifier 49 has a gain of 1 and reverses the polarity. That is, when the timer T216 operates, the step signal generation circuit is excluded and a direct proportional limit signal is applied to the AVR 4 as an overexcitation limit signal. Timer T21 above
6 is a DC voltage transmitter 45, a V/F converter 46,
If the step signal generation circuit consisting of the BCD counter 47 and the D/A converter 48 is left on, a time delay will occur, so the D/A converter 48
This is to disconnect the step signal generating circuit when the output of the deviation detector 8 almost matches the output of the deviation detector 8, thereby eliminating the time delay of the overexcitation limit signal. Relay Y18 is also used for operation display, timer measurement, etc.

Note that in the above embodiment, the timer T216 is used, but even if this is omitted, approximately the same effect can be achieved with only a slight time delay.

Further, although FIG. 3 has been described for the case without an exciter, the same effect can be achieved even when a DC exciter or a brushless exciter is used.

As described above, according to the present invention, the allowable field current is made proportional to the internal cooling gas pressure of the generator, and when the generator voltage becomes higher than the normal operating range, overexcitation is immediately restricted. If the generator is normal and the grid voltage drops, the step signal generation circuit will gradually limit overexcitation after a certain period of time, so the generator can be used to its full capacity and the grid This also contributes to improving the stability of voltage control by reducing the shock given to the generator.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a conventional overexcitation limiting device.
Fig. 2 is an explanatory diagram showing the relationship between the internal cooling gas pressure of the generator and the allowable field current, Fig. 3 is a schematic configuration diagram of an overexcitation limiting device showing an embodiment of the present invention, and Fig. 4 is the present invention. FIG. 3 is a diagram for explaining a method of setting an allowable field current in the embodiment. 1... Generator, 2... Generator field coil, 3
... PT, 4 ... AVR, 6 ... shunt, 7 ... insulation amplifier, 8 ... deviation detector, 10 ... converter that converts the internal cooling gas pressure of the generator into an electrical signal,
11...Base amount setting device, 12...Circuit for obtaining a set value of allowable field current proportional to the generator's internal cooling gas pressure, 13...Allowable field current proportional to the generator's internal cooling gas pressure Detector that detects when the value exceeds the value, 14, 16... Timer that immediately returns to the time-limited operation, 15, 17... Relay, 19...
Input resistance, 24...Comparator, 46...V/F converter, 47...BCD counter, 48...D/
A converter. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. The field current is controlled by an automatic voltage regulator according to the output voltage of the generator, and the field current is compared with a preset allowable field current, and the deviation between the two is calculated as a deviation. In an overexcitation limiting device for a generator, which is detected by a detector and outputs an overexcitation limiting signal based on the deviation to limit the field current when the field current exceeds the allowable field current, A comparison detection unit that compares and detects when the output voltage of the generator is higher than the upper limit of the normal operating range; and a comparison detection unit that converts the internal cooling gas pressure of the generator into an electrical signal and allows an allowable field current proportional to the gas pressure. The allowable field current setting circuit to obtain the value and the output voltage of the above generator are within the normal operating range,
and when the field current exceeds the permissible field current value, the detector for detecting this and the comparison detector operate, and when the field current exceeds the permissible field current value,
an instantaneous signal generation circuit that applies an instantaneous overexcitation limit signal to the automatic voltage regulator; a timer that outputs an output after a certain period of time based on the operation of the detector; and an overexcitation limit signal that changes in steps when the timer operates. An overexcitation limiting device for a generator, comprising a step signal generating circuit that gradually applies voltage to the automatic voltage regulator. 2. The allowable field current setting circuit combines the converter output that converts the internal cooling gas pressure of the generator into an electrical signal and the base amount setting device output that sets the base amount unrelated to the internal cooling gas pressure. The overexcitation limiting device for a generator according to claim 1, characterized in that the device is configured to create an allowable field current proportional to internal cooling gas pressure.