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Патент USA US3021481

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Feb. 13, 1962
3,021,471
G. P. EN GSTRQM
DIRECT VOLTAGE SYSTEM COMPRISING STATIC CONVERTERS
INTERCONNECTED THROUGH INTER-PHASE TRANSFORMERS
Filed Aug. 26. 1958
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[1 3,021,471.
Pyatented'Feb. 13, 1962
1
?oating grids. Floating grid means that the potential of
'
"
3,021,471-
,
I
the unburning grids'in relation to the cathode is deter
mined by the voltage difference between these grids and
the grid which at the moment burns,’ which, due to the arc,
. assumes a potential which diverges very slightly from‘
the potential of the cathode. A high ohmic resistor is
.
DIRECT VOLTAGE SYSTEM COMPRISING STATIC
CONVERTERS INTERcoNNEcTED THROUGH
INTER-PHASE TRANSFORMERS
'
. ‘Gunnar P. ‘Engstrom, Ludvika, Sweden, assignor to All
manna Svenska Elektrislra ‘Aktiebolaget, Vasteras,
' usually connected between the neutral point'of the grid
Sweden, a corporation of Sweden’ " ' -
system and the cathode of the converter in order to de?ne
the potential of the grid during no load conditions.
Theinvention is, in the following, described further,
10
. .
. 10 Claims. (Cl. 321-19)
'
with reference to the enclosed drawing. In the drawing
The present invention relates to a directvoltage system i ‘ FIGURE 1 is a current-voltage diagram which shows the
fed from grid controlled recti?ers consisting of commutat
under-critical operation range. FIGURE 2 shows one
ing groups of discharge paths which are displaced in phase
embodiment of the invention with two recti?ers Working
Filed Aug.'26, 1958, Ser. No. 757,313
a
. ~Claims priority, application Sweden Aug. 31, 1957
in relation to one anotherv and have at least the‘pulse
in parallel upon a direct current network. FIGURE 3
shows in principle a ?oating grid system of a commutat
ing group of discharge paths with three anodes.
'
FIGURE 1 shows the relationship between the direct
voltage D and the direct current I in percent of their
vrated values. VWhen the direct current has decreased to
0.5 or 1% the above mentioned limit for the excitation
of the inter-phase transformers is reached and due to the
number 2 and are inter-connected through inter-phase
transformers.
‘
i
' A direct voltage system which in its most usual form"
, consists of twothree-phase groups of discharge paths,
inter-connected through an inter-phase transformer has, 20
during normal ‘service, a‘direct voltage which in un
‘smoothed'stateyis determined by the phase voltages of
each three~phase group. 'As’the inter-phase transformer
fact that at this stage, commutation will take place be
constitutes a large inductance between the three phase
' tween anodes which are normally separated by inter-phase
groups, any commutation between anodes belonging to 25 transformers, a voltage increase ‘will occur so that the
‘ di?erent groups is prevented.
Across‘ the inter-phase,
voltage, for instance as shown in the ?gure, rises to 115%
transformers an alternating voltage will appear which
of the rated voltage at no-load. The diagram also shows
I‘ ‘that the direct voltage system has an internal voltage drop
7values of the direct voltages of the two three-phase ‘groups.
which gives a slightly falling voltage characteristic so that
This alternating voltage causes an. excitating current‘ 30 rated current is reached at a voltage which is some percent
corresponds to the difference between the momentary
through the inter-phase transformer and this current must
lower than the no-load voltage.
be super-imposed upon the direct current ?oating through "
.
j
.
.
,
FIGURE 2 shows a direct voltage system consisting
veach separate three-phase group. Due to the‘ unidirec I of two recti?ers one of which hasits gas-?lled recti?er 1
tional properties of the recti?er this composed current can? 7 connected to two three phase groups 2 and 3 vwith star‘
not, however, become ‘negative, which'wouldoccur when 35 connected secondary windings 4_and 5 of a recti?er trans;
the direct current component through one three-phase
former 6. The neutral point of the secondary windings
‘group becomes so low thatit is smaller than the peak I ' are inter-connected through an inter-phasetransformer 7 .'
value of the excitating currentof the inter-phase trans
The primary windings of the transformer 6 are, through
former. The value of the direct current at which this
the terminals 8, connected to an alternaing current Source.
phenomenonoccurs is usually called the critical one. If 40 The cathode of the gas-?lled recti?er 1, is connected to
the excitating current of the inter-phase transformer is‘ pre
one bar‘ 10 in the direct voltage system, throughga con
' vented in this way ‘from ?owing, the inter~phase transform
er cannot take careof the voltage difference between
iductor 9. The other bar 11 is connected through a
smoothing reactor 12 to the central point of the inter
the two commutating groups of, discharge paths because
.phase transformer 7. The grids 13 and 14 of the gas
of which commutation will start between anodes belong 45 ?lled recti?er are'connected to a grid voltage device,15
ing to different groups. The recti?er then passes succes
‘ which may be of conventional type. ‘The Schematic
Jsively into six phase operation, whichfor an unloaded
symbol shows, by way of example,.that the device com;
recti?er means a voltage increase of about 15%. The
prises two separate groups of secondary windings. These
" load range within which such an increase in voltage ca
are connected mom of the grid groups 13 and ‘14 each,
arise is usually calledthe under-critical one.
~
j
The direct voltage system can however, also comprise
several. parallel working aggregates, eachof which Qmay
be, ‘of the above‘ ‘described. type. If ‘the aggregates are‘,
50 in‘such a way that a ?oating grid system is obtained.
' The grid voltage device‘15 is connected'to a blocking de
vice 16 which consists of a transductor ampli?er 17
which, in series with a metal recti?er 18, is connected to
therebyintergconnected, through ,inductances and‘ all sec
an alternating voltage source at the terminals 19. The
ondary voltages ,of, the separate recti?er transformers have 55', current through the metal recti?er 18 produces the nec
‘different
phase
angles,
a
voltage
rise
can
appear,
even.
in
.
.
.
;essar blockin voltave across aresistor 20 which is con
,_ this case, if the load current falls below a certam value, ~
y in parallel
g ‘ with
° ‘the smoothing capacitor 21'. The
nected
so that commutationjstarts between anodes belonging to‘ 1
‘5' separate aggregates.
transductor amplifier 17 is self-excited and has three con
trol windings. , A ?rst control winding 22 is connected
H
_, .Theobject of the present invention is to prevent a volt 60 to‘ the direct voltage of the system between the bars 10
and , 11. A second control winding 23 is ‘connected
; ‘agerise of (the; above mentioned type indirect current
“systems ofthetype described above.
,
‘
g
through arecti?er 24, consisting of a transformer 25 and
V In accordance with the, present invention'fthe direct” , a metal recti?er v.276, to the alternating voltage vof the V
‘current system comprises a means, sensitive to the direct ‘ ‘ recti?er transformer 6. ‘
-
voltage and the alternating voltage of the system for 65. In order to ‘explain the blocking operation reference
I, blocking ‘those of the commutating groups of’discharg'e ‘ ,‘is made to [FIGURE 3 which shows the grid supply of a
paths, the ‘current of which’ temporarily becomes zero,
three pulse group according to the ?oating system.‘ The
when the direct voltage ‘exceeds, the no-load value,jwhich
grids of the, three anodes‘ 35, 36, and 37 are connected to
during normal service corresponds to the alternating volt
one phase each of the Secondarywin'ding ‘38 of the grid
, age of the commutating group.
"
~
' o
r,
v
70, voltagearansformer, through grid! resistors R8. (The
The invention is applicable on different types of grid "“ neutral point of‘ the winding isconnected to .the' cathode
“control but it i'snespecially suitable for ,lre'cti?ershvwithy ,
3’ eff-the;gae?llad-waiter-tarsus“ retinal-<0; with
3,021,471
A
has to be considerably larger than Rg, and through the
blocking device 16.
The resulting grid voltage of an unburning grid can be
load voltage.
in?uenced by the voltage E, if the current which is pro
duced by E0 causes a voltage drop across Rg. It can be
recti?er 33 which is connected in parallel with the ?rst
mentioned one, to the bars 10 and 11. The recti?er 33
is assumed to be provided with a blocking device of the
shown mathematically that if R0 is considerably larger
than Rs, E0 must be considerably larger than the second
ary phase voltage Eg of the grid voltage transformer.
direct voltage is somewhat lower than the normal no
FIGURE 2 shows the described recti?er and another
described‘ type whereby it is possible that the recti?ers
are successively blocked when the load decreases and
deblocked when their co-operation becomes necessary.
If the recti?er emits a current which is larger than the
In order that at least one three phase group shall
critical one and a negative potential has to be supplied to 10
the 'grid of an unbu'rning anode and if the value of R0 is
assumed to be only IORg, it is necessary that E0 is about
remain in operation and not become blocked, the current
from the last unblocked remaining three phase group
30Eg.
cannot be allowed to pass through zero and it may con
‘voltage drop caused by the grid current, is caused, that a
‘considerably lower value of E0 is necessary in order to
resistor the direct voltage in?uenced control windings in
sequently be necessary to connect a basic load resistor
if, on the other hand, the resulting current from the
three anodes passes through zero, such a change in the 15 34 between the bars lit and 11. Instead of a basic load
the transductor-s in the blocking device 16 can be so
dimensioned that they can constitute the desired basic
load.
'\/2Eg.
Instead of providing the transductor with a current
If the load current in a direct voltage system, according 20 sensitive
control winding so that the recti?ers are de
block the anodes.
In such a case E0 only has to exceed
to the invention, decreases to its critical value, a block
ing voltage of the approximate size \/2Eg can be sup
blocked at a voltage which is somewhat lower than the
no-load voltage, the transductor may, in the event that
it is provided with two voltage sensitive control windings,
plied to_the grid circuit of the recti?er after which the
three pulse group, the current of which ?rst passes through 25 be labilly self-excited and so dimensioned that a block
Zero, will become blocked. As a result a voltage in
ing voltage is produced at a direct voltage which is
crease is prevented, as the remaining three pulse group
somewhat higher than the critical voltage and that the
of therecti?er continues to emit current and gives the
recti?ers are deblocked at a direct voltage which is
same direct voltage value as the total converter during
somewhat lower than said ?rst mentioned voltage.
normal service. What I claim is:
A grid system of the ?oating type has the advantage
l. A recti?er station fed from an A.C. network and
that the necessary blocking voltage can be supplied to
feeding a D.C. network; said recti?er station comprising
the neutral point of the grid voltage transformer after
groups of commutating discharge paths, each including
which blocking is performed when the current of one
grid controlled recti?er means, said groups being dis
commutating group passes through zero. In other types
placed in phase in relation to each other, an inter-phase
of grid systems it is necessary to have a device which
transformer interconnecting said groups, the pulse num
indicates when the current of the recti?er passes through
ber of each of said groups being at least two and means
zero and at this moment performs the blocking.
V
sensitive to the voltage of said D.C. network and of
The two control windings 22 and 23 in FIGURE 2
said A.C. network for in?uencing the grid voltage of
are in themselves su?icient to procure the desired result. 40 said recti?er means, when said D.C. voltage at under
critical load exceeds the ideal no-load D.C. voltage so
The control windings can be so arranged that their num
as to block those of said commutating groups the current
ber of ampere turns balance each other at a certain point
of which ?rst temporarily becomes zero.
'upon the characteristic curve of the transductor 17 above
which ‘the transductor produces the necessary blocking
2. A direct voltage system as claimed in claim 1, in
voltage. ‘5 the recti?er operates within its undercritical
which said means for blocking said commutating groups
range, the number of ampere turns‘of the winding 22 be 45 are so arranged that said blocked commutating groups
comes larger than the ampere turns of the windings 23
are deblocked when the direct voltage of the system at
and one commutating group will be blocked. _ As soon
over-critical load becomes lower than the ideal no-load
value.
as the load of the system increases again the direct volt
3. A direct voltage system as claimed in claim 1, in
age decreases and the blocked group is deblocked.
In order to prevent repeated blocking and deblocking
which is possible under certain load conditions the trans
ductor 17 is provided with a third control winding 27
which said recti?ers have ?oating grids and a blocking
voltage is supplied to the grid circuit of each commutat
ing group in such a way that those commutating groups
are blocked, the current of which temporarily becomes
which is connected to a device sensitive to the current
zero.
of the recti?er 1. The device 28 shown in FIGURE 2
4. A direct voltage system as claimed in claim 1, in
is an example of a suitable circuit which consists of a 55
measuring transductor 29, connected for indicating the
minimum current, whereby the output voltage of the de
which said means for blocking said commutating groups
comprises an ampli?er comprising a transductor having
vice is dependent cn the current, only within a very nar
row range close to zero. The device consists fundamen
a ?rst control winding, in?uenced by a current propor
tional to the direct voltage of the recti?er and a second
tally of a bridge circuit in which two branches consist 60 control winding in?uenced by a current proportional to
the mean value of the alternating voltage of a commutat
of one half each of a resistor 30 and the two other
ing group said transductor producing necessary blocking
branches consist of one each of the series connected
voltage when the number of ampere turns of said ?rst
windings of the measuring transductor 29. Alternating
control Winding is equal to or larger than the number
voltage is supplied from the terminals 31 to one diagonal
of the bridge and a metal recti?er 32 is connected to the 65 of ampere turns of said second control winding.
other diagonal. This metal recti?er 32 has an output
5. A direct voltage system as claimed in claim 4, in
voltage which is substantially constant until the direct
which said transductor ampli?er is labilly self-excited in
such a Way that a blocking voltage is produced when the
current through the measuring transductor sinks to a
direct voltage of the recti?er exceeds a certain value and
value close to zero when the output voltage from the
metal recti?er will decrease quickly.
70 that said blocking voltage vanishes when said direct volt
, The control winding 27 is so arranged that its number
of ampere turns co-operate with that of the winding 23
and the strength of the control winding 27 is so dimen
sioned that blocking is achieved at the critical load cur
age falls below a value lower than said ?rst value at
which it was produced.
6. A direct voltage system as claimed in claim 4, in
which said transductor‘has a third control winding in
rent, whereas the blocking is achieved ?rst when the 75 ?uenced by a current proportional to the direct current
3,021,471
a
6,
and each having at least the pulse number 2, an inter
of the recti?er, and said transductor produces necessary
blocking voltage when the number of ampere turns of
phase transformer, a source of alternating current, means
connecting said transformer to said source of alternating
said ?rst control winding is larger than the sum of the
number of ampere turns of said second and said third
control windings.
current, means interconnecting said discharge paths
through said transformer, and means sensitive to the
>
7. A direct voltage system as claimed in claim 6, com
direct voltage and to the alternating voltage of the sys
prising a current sensitive means feeding said third con—
tem for blocking those only of said commutating groups
the current of which at under-critical load ?rst becomes
current voltage exceeds its ideal
trol winding, the output voltage of said current sensitive
, zero when said direct
. means being dependent on the direct current of the recti- ,
?er only when said current is close to zero.
8. A direct voltage system as claimed in claim 1, com
10,
such a value that the direct current from one remaining
unblocked commutating group is larger than zero at every
.
,
»
References Cited in the ?le of this patent
prising a load connected to the system, said load having
moment.
no~load value. I
UNITED’ STATES PATENTS,
_ 2,186,244
‘
Hartel ____________ __‘__.._ Jan. 9, 1940
9. A direct voltage system as claimed in claim 8, in
which said load consists of transductor control windings.
10. A direct voltage system, fed’ from grid controlled ‘
2,291,349
Schmidt ________ __'.'_____ July 28, 1942
2,331,643
2,394,013
,Winograd' ____________ __ Oct. '12, 1943
Rose ________________ .__ Feb. 5, 1946
recti?ers, and comprising commutating groups of dis
charge paths displaced in phase in relation to each other
2,550,115 *
Geiselman ___________ __ Apr. 24, 1951
2,775,732
‘Winograd ___________ .__ Dec, 25, 1956
so
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