JPS6134879Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a control device for an alternator when the load advances and becomes a power factor load, and in particular compares the short circuit ratio of the generator itself even when the leading power factor load advances. The object of the present invention is to provide a control device that can be made smaller in size and can operate stably.

In general, when multiple load groups are connected to the output bus of a generator, and some of the loads fluctuate significantly in these load groups, or when heating objects by induction with a high-frequency generator, tank circuit If the coil is disconnected for some reason, the load will lead to a power factor, and as is well known, the generator will exhibit a self-excitation phenomenon due to the addition of the magnetomotive force generated by the armature current and the field magnetic flux, and the generator will not be able to generate electricity. Not only does the machine output voltage rise abnormally, causing serious accidents such as dielectric breakdown and burnout of the generator windings, but the abnormal voltage itself poses a serious threat to the load group. This type of self-excitation phenomenon will be specifically explained using an example of a conventional circuit shown in FIG.

The conventional device shown in Figure 1 has two field windings of an AC exciter.
This is a commonly used circuit example, because by using a field, the generator itself has very good voltage recovery characteristics even when the load, a large-capacity induction motor, starts. Figure AG shows the armature of the generator, F ₁ shows its field winding, and EX shows the armature of the AC exciter, F ₂ and F ₃ show its first and second field windings. . The field winding F ₁ of the generator and the armature EX of the AC exciter are arranged on the same axis,
A rotary rectifier Rf ₂ in which diodes are connected in Graetz connection is mounted on this rotating part, and this rotary rectifier Rf ₂ is used to rectify the exciter armature output as is well known.

CT is a power current transformer for extracting a current proportional to the load current. A rectifier circuit Rf ₁ is provided on the secondary side of this current transformer CT, and this rectifier circuit Rf ₁ rectifies the extracted current. The rectified output of the lever is used to constantly excite the first field winding _F2 of the exciter.
As is well known in the automatic voltage regulator, the AVR compares the reference value and the voltage detection amount, and uses the deviation amount based on the comparison result to appropriately control the firing of the thyristor group of the rectifier circuit Rf ₃ described below to control the excitation. the second field winding of
It adjusts the excitation current supplied to F ₃ and indirectly controls the generator output voltage automatically according to the command. The second rectifier circuit Rf ₃ generally has a configuration in which thyristors are connected in a Graetz connection, or a thyristor and a diode are connected in a mixed bridge.

Now, since the operation of the conventional device configured as described above during steady state is well known, the description thereof will be omitted, and first, the operation when the load advances and becomes a power factor load will be briefly explained. As is well known, when a leading power factor load occurs, the generator exhibits a self-excitation phenomenon and the generator output voltage increases abnormally. Therefore, in order to maintain and control the generator output voltage according to the voltage setting command amount, an automatic voltage regulator is used.
The AVR gradually advances the firing angle of the thyristor of the second rectifier circuit Rf _{3 and} , as far as possible,
An operation is performed to reduce the excitation current supplied to the field winding _F3 . However, even if we tried to widen the firing angle of the thyristor group of the second rectifier circuit Rf ₃ to the maximum limit in order to narrow down the excitation current as much as possible, the generator output voltage did not decrease at all as expected, and finally the thyristor The group becomes uncontrollable.

As described above, in the conventional device shown in FIG. 1, even if the load becomes a leading power factor load, it is possible to control the load to a certain extent, and the leading load can be taken to some extent. To express the rate at which a leading power factor load can be taken in terms of the short-circuit ratio of the generator itself, Figure 2 shows the short-circuit current I _S on the vertical axis and the excitation current I _F on the horizontal axis. From the phase short circuit characteristic a and the first rectifier circuit Rf ₁ , the first
The short circuit ratio SR is the ratio of the exciting current (field current) _{I 2 to} any short circuit current value I ₀ as is well known. Therefore, it can be expressed as SR=I ₀ /I ₂ .

The reason why the excitation current characteristic b curves upward in Fig. 2 is due to saturation, and if some of the loads in the load group cause a short-circuit accident, as is well known, the generator It must be capable of carrying a sustained short-circuit current for a duration of 2 seconds. Therefore, the condition for allowing a sustained short circuit current to flow is that curve b must be below straight line a in the relationship diagram of FIG.

Now, ignoring the saturation of the power current transformer CT, in order to flow a sustained short-circuit current, it is only necessary to match the a line and the b line in Fig. 2. In this state, if the leading power factor load is α ^PU , the current supplied from the power current transformer CT to the first field winding F ₂ of the exciter is αI ₂ . On the other hand, since the required field current is approximately I ₀ −αI ₂ , unless the relationship αI ₂ ≦I ₀ −αI _{2 .} . . is not present, overexcitation will occur and the generator output voltage will rise. Therefore, when α is calculated from the above formula by substituting the short circuit ratio SR=I ₀ /I ₂ into the formula, α=SR/2... is obtained. What this formula means is that it indicates the ratio of the leading power factor load to the short circuit ratio, and if the above relational expression does not hold, the generator will become overexcited.

Based on this understanding, let us specifically describe the ratio of leading power factor load that a generator can take.As it is well known, in recent years, as generators have become smaller, the short-circuit ratio SR has been decreasing. Currently, the short circuit ratio is generally 0.3 to 0.4
Therefore, the leading power factor load α that the generator can take is only 20% at most, which is α=0.15 to 0.2 from the above formula. Actually a power current transformer
It is obvious that the value becomes smaller due to the saturation of CT. In this way, with conventional equipment, if the saturation of the power current transformer is ignored, the short circuit ratio of the generator itself is 1/2
However, even if the leading power factor load can be taken to the maximum limit, the thyristor group in the second rectifier circuit Rf ₃ of the excitation control system will become uncontrollable. Needless to say, the possible leading power factor load is approximately 10 to 15%.

In order to solve these drawbacks of conventional devices, for example, in the circuit example shown in FIG. 1, the second rectifier circuit Rf ₃ has only the function of forward excitation, whereas this second rectifier circuit _Rf In the case of a leading power factor load, the second rectifier circuit is
With the reverse excitation function that Rf ₃ has, it supplies a reverse excitation current to the second field winding F ₃ of the exciter EX, suppressing abnormalities in the generator output voltage and increasing the leading power factor load. A method has been proposed that provides stability in terms of control even when However, this conventional method is second
As for the configuration of the rectifier circuit, for example, the part that performs forward excitation and the part that performs reverse excitation must have the same configuration, which requires twice as many expensive thyristor elements and diode elements, making the device itself very expensive. It's about the economy.

The present invention has been devised in view of this point, and in particular, the present invention is designed to connect a thyristor and an integrating circuit between the terminals of a rectifier circuit that provides a predetermined current component to the first field winding of the exciter. By installing parallel circuits in parallel,
The purpose of this invention is to obtain a control device that can take a larger lead load and prevent overvoltage even when the short-circuit ratio is the same as that of the conventional device, and will be described in detail below based on the embodiment shown in FIG.

In the embodiment shown in FIG. 3, the same parts as in _{FIG .}
One feature of the circuit is that a series circuit consisting of R ₁ and capacitor C ₁ and a parallel circuit consisting of thyristor S are connected in parallel, and the series circuit of resistor R ₁ and capacitor C ₁ also has an integral function. For example, the thyristor S is inserted to limit the peak value of the field voltage of the first field winding _F2 of the exciter EX, while the thyristor S is inserted to limit the peak value of the field voltage of the first field winding F2 of the exciter EX. Magnetic winding _F2
By keeping the field voltage F _V at a certain required value, securing the base portion of the excitation current supplied to the generator field, and firing the thyristor S only when the load progresses and becomes a power factor load. The first rectifier circuit Rf ₁ is short-circuited, and the first field winding is connected to the power current transformer CT.
It performs a predetermined operation to suppress all the excitation current flowing into _F2 , and the ignition circuit of this thyristor S is connected to the generator output bus U, as shown in Figure 4.
A voltage detection transformer T is provided to take out a signal related to the terminal voltage from V and W, and a relaxation oscillation circuit consisting of a rectifier circuit Rf ₄ that rectifies the voltage component taken out from this transformer T, a double base diode UJT, etc. The circuit of capacitor C ₂ and variable resistor VR ₁ is a time constant circuit that determines the oscillation period of the relaxation oscillation circuit. PT is a pulse transformer and thyristor S
This is to obtain the gate signal. Note that the synchronization of this oscillation circuit is performed by connecting the first field winding _F2 to the synchronization circuit SC.
is inserted and taken through this circuit.

Now, the operation of this embodiment configured as described above will be explained in detail with reference to the time chart shown in FIG. This voltage component is once rectified by the third rectifier circuit Rf ₄ , and the rectified output charges the capacitor C ₂ of the time constant circuit to approximately the input power supply voltage value. This charge voltage V
When _C2 reaches the voltage at the top point of the double base diode UJT, the double base diode UJT becomes conductive, and the electric charge charged in the capacitor _C2 is transferred from the double base diode UJT to the pulse transformer.
A pulse signal with a steep rising waveform is obtained on the secondary side of the pulse transformer PT by being descharged through the path of the PT. Thyristor S
When the thyristor S fires, the first rectifier circuit Rf ₁ is short-circuited by the thyristor S, so it is supplied to the first field winding F ₂ of the exciter EX. The excitation current is cut off, so that the field voltage F _V of the first field winding F ₂ becomes zero when the thyristor S fires.

Therefore, if it is desired to maintain the field voltage F _V of the first field winding F ₂ of the exciter EX at a certain required value, the time constant that regulates the firing point of the thyristor S, that is, the oscillation period of the relaxation oscillation circuit may be adjusted accordingly.

The time chart in Fig. 5 shows such steady state operation, and in this time chart, Fig. 5B shows the capacitor voltage V _C2 of the time constant circuit,
Similarly, FIG. 5C shows the waveforms of the gate signal V _G supplied to the thyristor S, and as is clear from FIG. 5, when the thyristor S is fired, the first field winding F ₂ The field voltage F _V becomes zero as shown in Figure 5A, and it is clear that if you want to change the base portion of the excitation current supplied to the field, you can arbitrarily change the firing point of the thyristor S. be.

In this way, in steady state, by arbitrarily selecting the firing point of the thyristor S, only the base portion of the excitation current required by the field is secured, and the generator output voltage is adjusted to the voltage setting command amount. Adjustment of the excitation current supplied to the field in order to keep the field constant is performed via the excitation system of the automatic voltage regulator AVR→the second rectifier circuit _Rf3 .

Now, to describe the operation when the load advances and becomes a load for some reason, the detection of the advance load is as follows:
For example, the conventional well-known power factor detector PF may be used, or the excitation control system may be modified as already proposed by the present inventor in Utility Model Application No. 53-146916 (Utility Application No. 52848). For example, in the embodiment of FIG. 3, the control lead angle or control delay angle of the thyristor group of the second rectifier circuit Rf ₃ is detected, and if these control angles are less than the reference value, the leading power factor load is detected. It is also possible to use a power factor detection device that determines that the vehicle has entered the area.

In this manner, when the load progresses and the detection device detects that it is a power factor load, the thyristor S shown in FIG. 3 is immediately fully fired (conducted and released) in response to this detection signal. In this case, it goes without saying that the detection signal should be used to short-circuit the ignition circuit of the thyristor S shown in FIG. 4 by some means in order to make it inoperable.

With the excitation of one field winding of the exciter EX cut off in this way, next the automatic voltage regulator AVR
→ Second rectifier circuit Rf ₃ → The control angle of the thyristor group of the second rectifier circuit Rf ₃ is gradually narrowed down through the excitation system of the second field winding F ₃ of the exciter EX. This is an operation to reduce the excitation current supplied to the second field winding _F3 as much as possible.

In this way, if the excitation of one field winding of the exciter EX is cut off and the excitation current supplied to the other field winding is reduced, the generator In combination with the decrease in output voltage, the excitation current supplied to the other field winding is tried to be reduced as much as possible, so that abnormal voltage due to self-excitation phenomenon can be effectively suppressed. That is, first of all, the field voltage of the first field winding _F2 of the exciter EX is set to zero, so the generator output voltage decreases, and in this decreased state, the second field voltage is applied via the excitation control system. Since an attempt is made to throttle the excitation current supplied to the field winding _F3 , even if a leading power factor load progresses, according to the present invention, the thyristor group of the second rectifier circuit _Rf3 becomes uncontrollable. It is possible to expand the range of up to 100 kW, and it is possible to take a higher leading power factor load than conventional devices.

As described above, according to the present invention, the desired purpose can be achieved even if a circuit having only a forward excitation function is applied as the second rectifier circuit, but the above explanation is based on bridge-connecting diodes as a rotary rectifier. For example, we have described the case where a pure bridge connection of only thyristors or a mixed bridge connection of thyristors and diodes is applied as a rotary rectifier, and the excitation has a configuration in which the second rectifier circuit is bridge connected with diodes. It goes without saying that this method can also be applied to a system, and furthermore, a series circuit of resistor R ₁ and capacitor C ₁ can be used as a circuit to limit the peak value of the field voltage F _V of the first field winding F ₂ . Although the application case has been described, since this series circuit only needs to have an integrating function, there is no problem in operation even if it is a circuit consisting only of capacitors.

Furthermore, in this embodiment, a case has been described in which the first rectifier circuit Rf ₁ is configured with a single-phase bridge-connected diode, but the reason for this is that the thyristor S inserted on the output side of the rectifier circuit cannot be turned off naturally. Although the rectifier circuit is a single-phase one, for example, if a new forced extinguishing circuit is provided to forcibly extinguish the thyristor S, the rectifier circuit Rf ₁ may be configured as a three-phase one. If a gate turn-off thyristor that can be turned on and off by a gate is used instead of the thyristor S, the rectifier circuit may have a three-phase configuration.

As described above, in the present invention, the field of the exciter is configured as two fields, and the system supplies the current component taken in from the power current transformer to the first field winding as an exciting current. thyristor S short-circuiting the rectifier circuit
This thyristor is simply turned on during normal operation.
A fixed base amount is ensured in the excitation current supplied to the field by off-control, and only when the load advances and becomes a power factor load, the thyristor S is simply fully fired and the first field winding is turned off. The excitation current supplied to the line is cut off, and in parallel with this operation, control is performed to minimize the excitation current supplied to the second field winding via the excitation control system of the automatic voltage regulator. This is what I did. Therefore, the present invention provides various effects as shown below.

Even when the short-circuit ratio is small, the leading power factor load can be taken more than in the conventional device, so the generator itself can be further downsized and a very economical device can be realized.

It is very stable in operation even when a leading power factor load progresses, and this feature can be fully utilized if this device is applied especially when the load frequently advances and becomes a power factor load.

Since the rectifier circuit of the excitation control system operated by the output of the automatic voltage regulator only has to have a forward excitation function, the apparatus itself can be provided with a further cost advantage.

In some cases, the field voltage may rise abnormally during normal operation, but since a circuit with an integral function is connected in parallel with the thyristor S, this circuit limits the peak value of the field voltage. If the field winding burns out or the field becomes high voltage, the influence on other parts (especially the rectifier circuit) can be alleviated.

[Brief explanation of the drawing]

Figure 1 is a specific circuit configuration diagram showing a conventional device when the field of the AC exciter is set to two fields, and Figure 2 is a short circuit diagram showing the relationship between the three-phase short circuit characteristics and exciting current characteristics of the generator. Current _IS - excitation current characteristic diagram, FIG. 3 is a specific circuit configuration diagram showing an embodiment of the present invention,
FIG. 4 is a specific circuit diagram showing a thyristor ignition circuit according to the present invention, and FIG. 5 is a time chart showing the operation of the present invention. AG is the generator armature, F ₁ is its field winding, EX
is the armature of the AC exciter, F ₂ and F ₃ are its field windings, Rf ₁ , Rf ₃ and Rf ₄ are the rectifier circuits, Rf ₂ is the rotary rectifier, AVR is the automatic voltage regulator, SC is the synchronous circuit,
CT is a power current transformer, T is a power transformer, UJT is a double base diode, S is a thyristor, PF
is a power factor detector.

Claims (1)

[Claims for Utility Model Registration] (1) A first rectifier circuit that rectifies a current component proportional to the load current of an AC generator and supplies it to a first field winding of an AC exciter; an integrating circuit that is connected in parallel and limits the peak value of the field voltage of the alternator; a thyristor that is connected in parallel to the rectifier circuit; and an ignition circuit that controls the thyristor on and off at a predetermined period during steady state. A power factor detector detects the load power factor of the generator and fully fires the thyristor at a set leading power factor load; a unidirectional second rectifier circuit that supplies the field winding of the AC exciter to the field winding of the generator; an automatic voltage adjustment circuit that is connected to a terminal of the alternator and adjusts the current supplied to the field winding of the alternator so as to zero the deviation between a voltage detection signal proportional to the voltage and a reference value. An alternator control device characterized by the following. (2) Claim 1 of the utility model registration application applies a gate turn-off thyristor that can be turned on and off with a gate as a thyristor, and the first rectifier circuit is configured with a circuit in which diodes are connected in a three-phase bridge. A control device for the alternator described.