JPS6248299A - Starting system of induction generator - Google Patents

Abstract

PURPOSE:To prevent rush currents on forced parallel by connecting a capacitor having capacitance, which can be self-excited, to a stator winding for an induction generator. CONSTITUTION:When a connector 3 is closed during a time when an induction generator 2 is driven by a prime mover 1, a self-excitation phenomenon is generated in an output winding from the induction generator 2 by the remanence of the induction generator 2 and a capacitor 4 for excitation. A thyristor 6 is firing-angle controlled by a controller 7, and currents flowing through a reactor 5 in currents fed from the capacitor 4 are adjusted, thus regulating reactive currents flowing through a stator winding for the induction generator 2, then conforming output voltage from the induction generator 2 to system voltage. When the coincidence of an output from the induction generator 2 and the phase of a system is detected by a detector 8, a switch 10 is closed, and the induction generator 2 is made to run parallel forcibly with the system 9.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention applies to induction generators, especially excitation windings. Regarding the starting method of an induction generator, which is operated by using the active part of the current flowing through the stator windings for output and the reactive part for full excitation, we will introduce the This invention relates to a starting method that aims to forcibly connect induction generators in parallel without generating inrush current.

[Conventional technology]

Induction generators are simpler in structure and control than synchronous generators, and have recently begun to be reconsidered for use in, for example, small water turbine power generation. Looking at this induction generator from the perspective of excitation, in addition to the output winding, there is a separate excitation winding, and not only the excitation winding, but also the 7 current supplied from the power system, and the stator winding. There are two types: the effective part (cosine part) of the flowing current is used for output, and the reactive part (sine part) is used for full excitation.

In general, induction generators and induction motors are based on the same principle and have many parts in common. In particular, the latter type of induction generator, which does not have an excitation coil, is just like an electric motor.
From the perspective of a manufacturer of induction equipment, this is a great advantage in reducing manufacturing costs.

[Problem that the invention seeks to solve]

However, since the latter induction generator does not have an excitation winding, it has 1. When starting up, an excitation current must be taken in from the power system and used to create the entire magnetic field. In other words, in order to generate electricity, the generator must first be connected in parallel to the entire generator system. Moreover, this generator has the problem that an inrush current of about 6 to 10 times the rated current flows through the stator windings when the generators are paralleled, which disturbs the entire voltage range when the power capacity of the system is small.

Moreover, the current taken in as the excitation current is a reactive current as described above, so the phase is 90° with respect to the grid voltage.
'There is also the problem of worsening the power factor of the system due to misalignment.

For this reason, induction generators, especially those without excitation windings, are disliked by those who supply them and are virtually unusable.

However, this generator itself has many advantages, such as the structure is the same as that of the same type of electric motor as mentioned above, it is easy to manufacture, and the structure and control are simple. 9. Therefore, it goes without saying that if the inrush current can be prevented when the devices are paralleled, the range of use will be significantly expanded, and the effect will be great.

[Means to resolve all issues]

The invention utilizes power generation through self-excitation to completely prevent inrush current during forced paralleling, and its features are:
An induction generator M is operated by using the full output of the effective part of the current flowing through the stator winding and the reactive part for excitation. In order to forcibly connect all induction generator systems in parallel, in order to prevent all inrush current during forced paralleling, the capacitor generates self-excitation in the induction generator, and the voltage between the system and the induction generator output is The point is to match the voltage, phase, and frequency as much as possible, and then force them in parallel.

[Effect]

Needless to say, induced departure '+1! The self-excitation phenomenon itself in machines is well known. That is, when an induction generator is not connected to a capacitor, it generates a small voltage due to residual magnetism. If a capacitor of appropriate capacity is connected to this, a weak lead current will flow through the capacitor.
This becomes the exciting current of the induction I electric machine and increases the magnetic flux,
By amplifying this, the magnetic field necessary for power generation is obtained. Conventionally, this self-excitation was thought to be used to supply excitation current when no excitation current was supplied to the system, but there are other examples of using this self-excitation locally in forced paralleling. I don't see it.

According to the starting method of the present invention, electromagnetic energy is stored in the stator windings by self-excitation power generation.

In the first place, the inrush 1 (current) during forced paralleling is thought to occur as a function of fully filling the large-capacity output winding because p4Q energy is not stored in the large output winding before forced paralleling. IK is generated in advance by excitation power generation.
E? By storing '4 energy, most of the inrush current will disappear.

Also, if electromagnetic energy is stored in the output winding, what happens between the power system and power generation? It is also easy to match the IV pressure, phase, and frequency, and this makes it easy to match the IV pressure, phase, and frequency.
'nl It becomes possible to make it as small as possible using reasonable means.

To explain in more detail from another perspective, when power generation is performed by self-excitation with no load, a relatively small excitation current corresponding to no load is supplied to the output winding, but this is not supplied by the capacitor. At this time, the power factor of the generator's output as seen from outside the system is essentially 1. Although the capacity of this capacitor is insufficient to cover the required excitation current at full load, it is possible to supply 9+ excitation RM current after 95% mj. Therefore, if a trigger generator self-magnetized by a capacitor with 1 qlJ is connected in parallel to the system, the 59 resultant power factor of the system will hardly change, and in fact, the power capacity can be completely increased.

〔Example〕

(a) Capacitor connected to the output winding This capacitor is required to have a capacity sufficient to supply the entire excitation current of the induction generator. The required capacity is determined in relation to the magnetic saturation characteristics of the induction generator. This relationship is illustrated in Figure @1.

When self-excited power generation occurs with no load, the terminal voltage of the output winding of the induction generator rises to the intersection of the magnetic saturation curve and the straight line representing the capacitor capacity.

In the example of FIG. 1, if a capacitor with a display capacity of 601 LF is connected and self-excitation power generation is achieved at 1200 rpm/60 Hz, the power will rise to 242 cm and 8.18 A (no load). Conversely, with a 40μF capacitor,
It has no intersection with the saturation curve, so 1200 rl
) m does not lead to self-excitation power generation.

That is, in the case of the example shown in FIG. 1, a capacitor with a capacity exceeding 50 PF'i is required to achieve self-excitation power generation at 1200 rpm'60 Hz.

Note that the slope k of the capacitance straight line of the capacitor is given by the following equation.

I, AV k-3X2πf-z Engineering: Line current (-8 x phase current) ■: Phase voltage f: Frequency C: Capacitor display capacity , (2) is an induction generator, (3) is a connector, (4) is an induction generator <21
excitation capacitor connected in parallel to the output winding of (5)
is the source connected in parallel to the excitation capacitor (4)! Voltage control reactor /l/, (61 is reactor) /I/(53 current, current control thyristor, (7) is firing angle controller of thyristor (6), (8) is frequency and phase detector , (9
) is the power system in which the induction generator <21 is to be forcibly connected in parallel, and 0α is the switch with the power system (9). Note that the capacitance of the excitation capacitor (4) is set to enable self-excitation with no load as described above.

Due to the residual magnetism in (2) and the excitation capacitor r41,
Although self-excitation occurs in the output winding of the induction generator <21 and magnetic energy is stored, there are differences in voltage, phase, and frequency between it and the system (9), so it is forced into the system (9) as it is. If they are connected in parallel, even if a large inrush current does not flow, it is inevitable that the system (9) will be disturbed.

Therefore, first, the controller (7) controls the firing angle of the switch (6) to adjust the current flowing to the reactor (5) out of the current supplied from the capacitor (4), and this causes the generator ( 2) Adjust the reactive current (excitation current) flowing through the stator winding to match the output voltage of the induction generator <21 with the grid voltage.

At this time, it is generally assumed that the output frequency and phase of the generator (2) do not match. It is mathematically clear that the generator output and the system phase match every cycle corresponding to the least common multiple of these frequencies, and this match is detected by the detector (8), and the moment the phases match, the system opens and closes. 00 is closed and the induction generator (2) is forcibly connected in parallel to the entire system (9).

If there is no large difference in frequency between the induction generator (2) and the grid (9), forced paralleling will hardly disturb the grid (9). If the frequencies are significantly different, the rotation speed of the rotor of the induction generator (21) may be adjusted.

It goes without saying that these adjustments can be made on your own.

The allowable voltage difference, allowable phase difference, and allowable frequency difference between the induction generator (2) and the grid (9) are usually specified by the side that supplies the grid power.

〔Effect of the invention〕

As is clear from the above explanation, the activation method of the present invention is
Taking advantage of induction generation, which is characterized by generating electricity by being supplied with an external excitation current, we have eliminated the inrush current during forced paralleling, which was its fatal flaw, and suppressed the impact on the power system as much as possible. This will have a great effect on expanding the scope of use of this type of generator.

[Brief explanation of the drawing]

FIG. 1 is a graph showing all the relationships between the induction generator magnetic saturation curve, the capacitance of the excitation capacitor, and self-excitation, and FIG. 2 is a system diagram showing all the embodiments of the starting method of the present invention. In the mouth, 1: prime mover, 2: induction generator, 4: excitation capacitor, 5: reactor, 6: thyristor, 8: frequency and phase detector, 9: power system.

Claims (1)

[Claims] (1) A capacitor with a self-excitable capacity is connected to the stator winding of an induction generator that is operated by outputting the active part of the current flowing through the stator winding and using the reactive part for excitation, and the induction generator When the machine is forcibly paralleled to the grid, in order to prevent inrush current during forced paralleling, the induction generator is self-excited by the capacitor, and the voltage, phase, and frequency are changed between the grid and the induction generator output. An induction generator starting method characterized by forcing parallelization after matching as much as possible.