Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2051~26
Constant voltage asynchronous generator with stator
slot bridges
Inventors: CSETVEI, Gyula
KINCSES, Istvan
residents in Budapest
Filing date: 09. 02. 1990.
The subject matter of the invention is a constant voltage
asynchronous generator with stator slot bridges providing
electric power as one- and multiphase alternating current for
independent mains.
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In general, synchronous and asynchronous generators are applied
to produce alternating current power.
Synchronous generators are usually made with brushes but recently
their brushless construction has been used more and more. In
both constructions wound-up parts of rotors represent the field
poles. Stability of output voltage is ensured by an elect~ic
circuit.
Asynchronous generators are actually asynchronous motors having
squirrel-cage rotor which supply electric power to an existing
network when they work beyond the synchronous speed. In this
case they take the reactive energy from the mains.
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Power generation of asynchronous generators for independent mains
requires capacitors which ensure autoexcitation and reactive
energy for maintaining the rotating magnetic field.
In the course of technological development the size of capacitors
were reduced remarkably which resulted in the economic efficiency
of further developments and manufacture of self-exciting
squirrel-cage asynchronous generators.
So far the well-known solutions have been directed mainly to the
utilization of completely closed asynchronous motors of standard
type. These generators are able to provide a nominal output
voltage ~ith fluctuation of +/- 5 % in both cold and warm running
conditions at steady speed and nominal power with cos ~ in the
0,8-1,0 range. Regarding the fact that in the driven working
machine the load-depending variation of speed is generally in the
+/- 3,5 % range, the fluctuation of output voltage at the
generator's side can reach the +/- lO % value. (~his can be read
from curves 12 and 13 in Figure 6 as shown later.)
In order to keep the output voltage in a narrow range the
following solutions were developed:
- Application of "Vario" capacitors having adjustable
capacity.
- Application of a saturable reactor coil whose inductance
varies as a function of output voltage. It is working
~- against the effect of capacitors connected with the
generator and its magnitude depends on the capacity.
- Application of a speed regulator to the driving engine
which is able to increase the speed in function of load's
growth to such an extent that the decxease in generator's
output voltage will be compensated.
- Application of crown-coil generators.
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The above mentioned solutions are not so frequently used in
practice because they do not represent an up-to-date level, their
operation is not economic and they do not make asynchronous
generators competitive as compared with synchronous ones.
"Vario" capacitors are not fabricated for their high
manufacturing cost while the saturable reactor coil has such
dimensions and weight that make the weight/power relation of
asynchronous generators very unfavourable. As regards speed
regulation as a function of load the problem is that it does not
make possible the complete control of voltage level variation
caused by quick, dynamic fluctuations in the load.
Crown-coil generators can be made in form of open constructions
by difficult technology, since the regulating coil is arranged
around the stator's crown in toroidal shape.
.
The basic aim of this invention is to implement an asynchronous
generator with brushless, robust and completely closed
construction that supplies power to independent mains and
similarly to synchronous generator it is able to produce
sinusoidal, steady state output voltage which is independent from
power fluctuation.
Dynamic power fluctuations have to be regulated within some
periods by means of electronic voltage control of squirrel-cage
generators.
Both control power and control current must be kept at low level
in order to ensure as small size of voltage regulator as
possible.
The essence of the invention is that plates are placed into the
slots of the stator and they make "bridge" for magnetic lines of
force between two teeth.
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According to the invention the squirrel-cage generator with slot
bridges is made of a standard asynchronous motor using its plate
bundles. The electronic voltage regulator connected with the
outlets and the capacitor battery take place in the terminal box
of the generator. The regulator winding is arranged in the slots
of the stator next to the the traditional, one- or three-phase
main winding.
The invented solution is shown by means of the figures enclosed.
Terminal couplings of the squirrel-cage generator with one-phase
or three-phase arrangement can be seen in Figure 1 and 2,
respectively.
The scheme of the electronic voltage regulator is set out in
Figure 3.
.
The arrangement of windings in the well-known crown-coil
generator can be seen in Figure 4.
Figure 5 shows the section of main winding and the regulator
winding which surrounds the crown in the constant voltage
asynchronous generator with slot bridges described by the
invention.
The external characteristic of a self-excited asynchronous
generator can be seen in Figure 6, in comparison with that of the
constant voltage asynchronous generator with slot bridges
described by the invention.
The usual layout of the squirrel-cage, one- and three-phase
generators is shown by Figure 1 and 2, where FT and ST are for
the main winding and the regulator winding, respectively. The
voltage regulator (FS) is connected by the terminals 14 and 15 in
order to ensure the inner tapping of the main winding(s) of the
generator. The regulator winding is connected with the terminals
16 and 17 of the voltage regulator (FS).
The main windings (FT) have star terminals as shown by Figure 2.
.
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Figure 3 shows a possible solution for the voltage regulator
(FS). This regulator (FS) consist of an output stage (6) with
thyristor bridge, a transverter (7) connected with the terminals
14 and 15 of the main winding (FT), a zener-type diode (5), a
potentiometer (P) for setting the required value, an amplifier
(8), a signal inverter (9) and an impulse signal shaping unit
(10) .
The operation of the electronic voltage regulator shown by Figure
3 is as follows: the transverter (7) "observes" the output
voltage of the generator and its output signal goes to the
amplifier's (8) input through the Zener diode (5). The amplifier
(8) makes comparison between the standard signal coming from the
Zener diode and the reference signal set by the potentiometer
(8). The output signal of the amplifier (8) goes to the impulse
signal shaping unit (10) through the signal inverter (9) and this
unit sets the output stage (6) consisting of the semi-controlled
thyristor bridge in accordance with the required extent and, at
the same time, it adjustes the voltage coming to the regulator
winding (ST) through the terminals 16 and 17.
Figure 4 shows the arrangement of windings in the well-known
; crown-coil, squirrel-cage generator. The regulator winding (ST)
and the main winding(s) (FT) take place in the slots of the
stator (AL). The regulator winding (ST) is supplied through the
terminals 16 and 17.
The invented asynchronous generator with stator slot bridges
(HAG) is shown by Figure 5. The essence of the invention can be
found in the arrangement of the regulator winding (ST) and in the
slot bridges (HH) as arranged slot by slot for conducting
magnetic flux.
The number of coil legs forming the regulator winding (ST) is
equivalent to that of teeth (FG) in the stator (AL) since they
are wound up between them.
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The slot bridges (HH) made of plates are arranged slot by slot
with a minimum air gap.
During installation of windings of the asynchronous generator
with slot bridges (HAG) the regulator winding (STJ is arranged at
first, it is followed by the setting of slot bridges (HH) made of
plates and the laying of the double-layer main winding(s) (FT).
The operation of the asynchronous generator with slot bridges
(HAG) as shown by Figure 5 is the following:
The regulator winding (ST) is supplied with direct current
through the terminals 16 and 17, therefore a regulating flux (~s)
comes into being in the teeth (FG) next to the main flux (~F) and
it increases the magnetic resistance of the rotating magnetic
field on account of which the induced electromotive force and the
output voltage will decrease.
Changing the direct current intensity the teeth (FG) are
premagnetizing accordingly and it creates varying saturation in
consequence of which the magnetic resistance of the main flux (~F)
in the asynchronous generator with slot bridges ~HAG) will change
as well. After all it appears in the change of the output
voltage.
The required control power is less than 5 % of the generator's
nominal power. It derives from that the magnetic circuit of the
regulator winding (ST) has a minimum air gap and therefore a few
ampere-turns are enough to produce regulating flux (~s) and
magnetic saturation of the teeth (FG).
Accordingly, the terminal coupling of the coil legs (TL) is
carried out by such way that the regulating flux (~s) induced
makes the teeth of the stator (AL) saturate. The slot bridges
(HH) which are made of plates and arranged slot by slot with
minimum air gap ensures the closure of ~s
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For this reason the output voltage can be varied in wide range by
changing the intensity of the exciting direct current. With
increasing current the voltage is decreasing and in turn it is
increasing when the current decreases. Wave form of direct
voltage and current in the regulator winding (ST) has no effect
on wave form of output voltage.
,
The external characteristic of a self-exciting asynchronous
generator in comparison with that of the constant voltage
asynchronous generator with slot bridges as described by the
invention can be seen in Figure 6.
The characteristic curves show the variation of output voltage
U /V/ in terms of load P /KVA/.
The curve 12 refers to inductive load with cos ~ = 0,8 while the
curve 13 is relating to ohmic load with cos ~ = 1,0.
It can be seen from the curves 12 and 13 that the output voltage
of the self-exciting generator without voltage control and slot
bridges reaches its maximum (U0) in idle running state and it is
decreasing steadly with increasing load (P) up to the maximum
output power when the voltage drops abruptly to zero and
short-circuit state sets in.
The invented solution, that is the application of the regulator
winding (ST), the slot bridge (HH) and the voltage regulator (FS)
results in the curve ll.
In case of increasing load (P) the exciting current must be
reduced to such an extent that keeps the output voltage always at
the required value (UN).
The effective external characteristic of the invented
asynchronous generator with slot bridges (HAG) is shown by the
curve ll in Figure 6. It holds its straight character up to the
maximum output power.
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Our invention, the asynchronous generator with slot bridges
(HAG), is a machine with short-circuited rotor thus it has no
sliding and wearing parts therefore its mechanical lifetime is
determined exclusively by its ball-bearings. Windings are not
subjected to critical overheating because in both overloaded and
short-circuited states the generator is de-energizing and its
voltage and current drop to zero.
The asynchronous generator with slot bridges (HAG) produces
neither conductive nor convective radio-frequency disturbances.
It is suitable to supply electric power to consumers having
special demands as in cases of shipping, mining, transport of
hydrocarbons, etc. even under extreme climatic conditions and in
explosive environment.
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