JPH0135600B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides a method for
This 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 a field coil of the alternator, 3 is a potential transformer (hereinafter referred to as PT), 4 is an automatic voltage regulator (hereinafter referred to as AVR), 5 is an allowable field current setting device, 6
7 is an isolation amplifier whose input and output are isolated, 8 is a deviation detector, and 9 is a deviation amplifier.

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 ATR4 to control the generator voltage so that the generator voltage is constant. On the other hand, a maximum current (allowable 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 that detects 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 by a width device 9 and then given to the AVR 4. In other words, normally AVR4 controls the field current so that the generator voltage is constant, but if the field current exceeds the allowable field current value, it limits the field current so that it does not exceed the allowable field current value. operates to protect the machine.

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 up to its original allowable field current limit. 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 to eliminate the above-mentioned drawbacks, and when the generator voltage becomes higher than the normal operating range, overexcitation is immediately limited, so that the generator is normal and the system voltage drops. In such cases, 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 focusing is carried out, and after a certain period of time, the overexcitation limit is gradually applied via an integral circuit to reduce the shock. We provide an overexcitation limiting device that allows the allowable field current to be changed in proportion to the generator's internal cooling gas pressure, allowing the generator to be used to its maximum capacity and contributing to improving the stability of system voltage control. It is intended to.

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 a generator within the allowable field current value. 12 is an allowable field current setting circuit that sets an allowable field current as shown in FIG. 2, which is proportional to the internal cooling gas pressure of the generator; 1
3 is a detector that detects when the actual field current exceeds the allowable field current value, 14 is a time-limited instantaneous return timer T ₁ , and 15 is a timer T ₁ A relay T that opens and closes when 14 operates after a certain time limit _{1 _ _}
A relay that opens and closes when 16 operates after a certain period of time.
T ₂ Relay operating above 2
6 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, 31 is a voltage dividing resistor, and 35 is an integrator; It is composed of a resistor 32, an integrating capacitor 33, and an operational amplifier 36. 37 is an input resistor, 38 is a feedback resistor, 39 is an operational amplifier, and 40 is a gain adjustment amplifier.

Next, the operation of this invention will be explained. As shown in FIG. 4, a base amount Vb unrelated to the internal cooling gas pressure of the generator 1 is set using the base amount setting device 11 shown in FIG. Voltage Vg proportional to internal cooling gas pressure
A set voltage as shown in FIG. 4 is created by adding , 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.
Normally means between detection relay HL2
5, its operating point can be precisely set using the setting device 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 exceeds the allowable value, the output of the comparator 24 will trigger the relay.
HL25 is energized, its contact HLb25b is opened, disconnecting the output of the integrator 36, and at the same time two contacts HLa25a are closed, one of which is connected to the integrator 35.
The integrating capacitor 33 is short-circuited and discharged, and the other is applied to the signal from the deviation detector 8 as an immediate overexcitation limiting signal to the automatic voltage regulator 4 via the operational amplifier 39 to limit the field current. Operate.

Next, when the generator voltage is within the normal operating range and the grid voltage drops, full focusing occurs and the field current exceeds the allowable field current value, but at this time relay HL25, which also detects the generator voltage, is inactive. Yes, the detector 13 detects that the field current has become excessive. This activates timer T ₁ 14, but
The timer T ₁ 14 is set to a time that the generator can withstand, from several seconds to several tens of seconds, and since the contact T ₁ Xb 15b of the relay T ₁ is zero V, and no overexcitation limit signal is applied to AVR4.

After a certain period of time, relay T ₁ X15 operates and contacts
When the T ₁ Xb 15b is switched to open, a ramp signal is generated that increases at an integral rate determined by the resistor 32 and capacitor 33 from this time, and a gradually increasing signal is applied to the AVR 4. Arithmetic amplifier 3
Since the output of 9 is fed back to the input resistor 27, when it becomes the same as the deviation signal, the operational amplifier 3
The output of 0 becomes zero and the integration stops. The reason for using the slope signal is to avoid giving a shock to the AVR4.

The timer T ₂ 16 operates later than the timer T ₁ 14, and is set so that it operates after the output of the operational amplifier 30 becomes zero and integration is stopped. Contact when relay T ₂ X17 operates
T ₂ Xb 17b opens to disconnect the output of the integrator 35, and contact T ₂ Xa 17a closes to bypass the output of the deviation detector 8 to the operational amplifier 39. The operational amplifier 39 is a polarity converter with a gain of 1,
If the integration is stopped, there will be almost no fluctuation in the output of the operational amplifier 39 by switching by the contact of the relay T ₂ X17. Further, the gain of the operational amplifier 30 is normally set to a very high gain of 100 times or more in order to improve the linearity of the slope signal. That is, when the timer T ₂ 16 operates, the integrator 35 is excluded and a direct proportional signal is given to the AVR 4 as an overexcitation limit signal.

The above-mentioned timer T ₂ 16 uses the integrator 35 because a time delay will occur if the integrator circuit is left on even if the field current decreases to around the allowable field current value.
This is to disconnect the integrator 35 when the output of the deviation detector 8 approaches the output of the deviation detector 8, thereby eliminating the time delay of the overexcitation limit signal. Further, the relay Y18 is used for operation display, time measurement of a timer, and the like.

In the above embodiment, the timer T ₂ 16 is used, but even if this is omitted, approximately the same effect can be achieved with only a slight time delay.

Furthermore, 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 short-term overexcitation is allowed, so the generator can be used to its full capacity. This contributes to the recovery of the grid voltage, and also reduces the shock given to the generator when overexcitation limitation is applied.Also, by using an integrator, the overexcitation state is controlled by the automatic voltage regulator to a predetermined level. It has the excellent effect of accurately obtaining voltage as a command signal.

[Brief explanation of drawings]

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...Isolation 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... Set value of allowable field current proportional to the internal cooling gas pressure of the generator 13. A detector for detecting that the field current exceeds a permissible threshold proportional to the internal cooling gas pressure of the generator, 1
4, 16...Timer that instantly returns from time-limited operation, 1
5, 17... Relay, 19... Input resistance, 24... Comparator, 35... Integrator. In addition, in the figures, the same reference numerals indicate the same or equivalent 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. a permissible field current setting circuit that obtains the value; a detector that detects when the field current is equal to or higher than the permissible field current value; If you exceed
an instantaneous signal generation circuit that applies an instantaneous overexcitation limiting signal to the automatic voltage regulator; and an instantaneous overexcitation limit signal that is constant when the output voltage of the generator is within the normal operating range and the field current exceeds the allowable field current value. 1. An overexcitation limiting device for a generator, comprising: a timer that operates after a time limit has elapsed; and an integrator that gradually applies an overexcitation limiting signal to the automatic voltage regulator when the timer operates. 2. The allowable field current setting circuit includes the output of a converter that converts the internal cooling gas pressure of the generator into an electrical signal, and the output of a base amount setting device that sets a base amount that is unrelated to the internal cooling gas pressure of the generator. 2. The overexcitation limiting device for a generator according to claim 1, wherein the overexcitation limiting device for a generator according to claim 1 is configured to synthesize an allowable field current proportional to the internal cooling gas pressure. 3. The overexcitation limiting device for a generator according to claim 1, wherein the integrator is disconnected from the automatic voltage regulator after a certain period of time.