U.S. patent number 3,643,405 [Application Number 05/017,176] was granted by the patent office on 1972-02-22 for circuit arrangement for automatic control of the voltage of an electrical filter.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Rudolf Hofmann, Lovro Vukasovic.
United States Patent |
3,643,405 |
Vukasovic , et al. |
February 22, 1972 |
CIRCUIT ARRANGEMENT FOR AUTOMATIC CONTROL OF THE VOLTAGE OF AN
ELECTRICAL FILTER
Abstract
A control unit comprises a charging circuit which connects a
guide capacitor to a source of DC voltage whereby a control voltage
supplied to a control system is produced by the control unit in
accordance with the voltage of a guide capacitor. A discharging
circuit is connected in parallel with the guide capacitor and
includes a controllable resistor having a resistance value
dependent upon the voltage of the filter. A photoelement is in
operative proximity with a glow lamp in a manner whereby light
produced by the glow lamp impinges on the photoelement. The
photoelement is coupled by a circuit to the discharging circuit for
supplying a control signal dependent upon the irradiation of the
photoelement whereby the control signal controls the controllable
resistor of the discharging circuit to a low resistance value when
the glow lamp does not glow and controls the controllable resistor
to a high resistance value when the glow lamp glows. A cutoff
circuit supplies a cutoff signal to the control system and the
control system controls a control circuit to interrupt the filter
current without delay when a sparkover occurs in the filter.
Inventors: |
Vukasovic; Lovro (Munich,
DT), Hofmann; Rudolf (Munich, DT) |
Assignee: |
Siemens Aktiengesellschaft
(Berlin and Munich, DT)
|
Family
ID: |
25757102 |
Appl.
No.: |
05/017,176 |
Filed: |
March 6, 1970 |
Foreign Application Priority Data
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|
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Mar 8, 1969 [DT] |
|
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P 19 11 924.5 |
Mar 8, 1969 [DT] |
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P 19 11 925.6 |
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Current U.S.
Class: |
96/21; 96/82;
323/271; 323/903 |
Current CPC
Class: |
B03C
3/66 (20130101); Y10S 323/903 (20130101) |
Current International
Class: |
B03C
3/66 (20060101); B03c 003/66 () |
Field of
Search: |
;55/105,2,159,104,106,107 ;323/23SC |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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248,429 |
|
Oct 1963 |
|
AU |
|
701,855 |
|
Jan 1954 |
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GB |
|
705,604 |
|
Mar 1954 |
|
GB |
|
Primary Examiner: Talbert, Jr.; Dennis E.
Claims
We claim:
1. A circuit arrangement for automatic control of the voltage of an
electrical filter, said circuit arrangement comprising
a control circuit coupled to an electrical filter for changing the
voltage of said filter;
a source of voltage coupled to said control circuit;
a control system having an input coupled to said source of voltage,
input means and an output connected to said control circuit for
supplying to said control circuit a control magnitude, said control
magnitude depending upon a control voltage supplied to the input
means of said control system;
a glow lamp;
a voltage divider connecting said glow lamp in parallel with said
filter; and
a control unit having an input coupled to said source of voltage
and output means coupled t the input means of said control system,
said control unit comprising a source of DC voltage, a guide
capacitor, a charging circuit connecting said guide capacitor to
said source of DC voltage whereby the control voltage supplied to
said control system is produced by said control unit in accordance
with voltage of said guide capacitor, a discharging circuit
connected in parallel with said guide capacitor and including a
controllable resistor having a resistance value dependent upon the
voltage of said filter, a photoelement having a photosensitive area
provided in operative proximity with said glow lamp in a manner
whereby light produced by said glow lamp impinges upon the
photosensitive area of said photoelement, and circuit means
coupling said photoelement to said discharging circuit for
supplying a control signal dependent upon the irradiation of the
photosensitive area of said photoelement whereby said control
signal controls the controllable resistor of said discharging
circuit to a low resistance value when said glow lamp fails to glow
and controls said controllable resistor to a high resistance value
when said glow lamp glows.
2. A circuit arrangement as claimed in claim 1, wherein said
control unit further comprises a reversing switch, a switching
component having a switching condition which depends upon the
switching position of said reversing switch and the magnitude of
current flowing through said filter, said switching component being
in its conductive condition only during the time between the
energization of said circuit arrangement, with the assistance of
said reversing switch, and the time during which the current
flowing through said filter reaches a critical value for the first
time after the energization of said circuit arrangement by said
reversing switch, said switching component being connected in a
manner whereby said control signal is ineffective when said
switching component is in its nonconductive condition.
3. A circuit arrangement as claimed in claim 2, wherein said
control unit further comprises auxiliary circuit means connecting
said switching component in parallel to the charging circuit of
said guide capacitor.
4. A circuit arrangement as claimed in claim 2, wherein said
control unit further comprises a capacitor, a resistor, a
monostable multivibrator having a pair of input and output
transistors of the same conductivity type and the controllable
resistor of said control unit comprises a first transistor having a
base-emitter path coupled via said capacitor and said resistor to
the output of said monostable multivibrator whereby when said glow
lamp glows, the input transistor of said monostable multivibrator
is in its fully conductive condition, a resistor, a decoupling
diode, a second transistor, the output of said monostable
multivibrator being connected to the negative polarity terminal of
said source of DC voltage via said resistor, decoupling diode and
the emitter-collector path of said second transistor, said
switching component comprising said second transistor whereby when
said second transistor is in its fully conductive condition
approximately the same potential is applied at the output of said
monostable multivibrator as at the extinguished glow lamp, a third
transistor having a control path connected in parallel with said
first transistor and a base electrode of the third transistor, a
reversible voltage divider, a diode connects the base electrode to
said reversible voltage divider and conducting the control current
of said third transistor, the control current of said third
transistor flowing through said reversible voltage divider as long
as the current flowing through said filter is below the critical
value and said first transistor is in a condition other than its
fully conductive condition.
5. A circuit arrangement as claimed in claim 4, wherein said
control unit further comprises a fourth transistor of the same
conductivity type as the pair of transistors of the monostable
multivibrator, said fourth transistor having a collector electrode,
a relay having an energizing winding connected to the collector
electrode of said fourth transistor, a control circuit for said
relay winding including the base-emitter path of said fourth
transistor, said base-emitter path being connected to said relay
winding, a decoupling diode connecting the control circuit of said
relay in parallel with the output of said monostable multivibrator
in a manner whereby when the glow lamp glows and said second
transistor is in its nonconductive condition a control current
flows, a resistor and a decoupling diode, said fourth transistor
having an emitter electrode connected to the collector electrode of
said second transistor, the emitter electrode of said fourth
transistor having a potential of a magnitude which is such that
when said second transistor is in its conductive condition said
fourth transistor remains in its fully conductive condition.
6. A circuit arrangement for automatic control of the voltage of an
electrical filter, said circuit arrangement comprising
a control circuit coupled to an electrical filter for changing the
voltage of said filter;
a source of voltage coupled to said control circuit;
a control system having an input coupled to said source of voltage,
input means and an output connected to said control circuit for
supplying to said control circuit a control magnitude depending
upon a control voltage supplied to the input means of said control
system; and
a control unit having an input coupled to said source of voltage
and output means coupled to the input means of said control system,
said control unit comprising a source of DC voltage, a guide
capacitor, a charging circuit connecting said guide capacitor to
said source of DC voltage whereby the control voltage supplied to
said control system is produced by said control unit in accordance
with the voltage of said guide capacitor, a discharging circuit
connnected in parallel with said guide capacitor and including a
controllable resistor having a resistance value dependent upon the
voltage of said filter, and cutoff circuit means for supplying a
cutoff signal to the input means of said control system, said
control system controlling said control circuit for interrupting
the filter current without delay when a sparkover occurs in said
filter.
7. A circuit arrangement as claimed in claim 6, wherein said
control circuit comprises thyristor means and the control magnitude
supplied by said control system controls said thyristor means, and
wherein the cutoff circuit means of said control unit switches the
thyristor means of said control circuit via said control system
when a sparkover occurs in said filter.
8. A circuit arrangement as claimed in claim 7, wherein the cutoff
circuit means of said control unit comprises a first transistor
having an emitter-collector path and a control path, said cutoff
signal being derived from a point in the emitter-collector path of
said first transistor, a second transistor of complementary type to
said first transistor having a control path connected in parallel
with the control path of said first transistor, the controllable
resistor of said discharging circuit comprising the control path of
said second transistor, a first voltage divider having a tap point,
each of said first and second transistors having a base electrode
connected to said first voltage divider, said first transistor
being in its fully conductive condition during normal operation of
said filter, a third transistor of the same conductivity type as
said first transistor, said third transistor being in its
nonconductive condition during normal operation of said filter and
switching to its conductive condition upon the occurrence of a
sparkover in said filter, said third transistor having an emitter
electrode coupled to the emitter electrode of said second
transistor, a capacitor, a resistor, said third transistor having a
collector electrode coupled to the base electrode of said second
transistor via said capacitor and said resistor, the collector
electrode of said third transistor being connected to the tap point
of said first voltage divider, said capacitor discharging via the
control path of said second transistor when said third transistor
is in its conductive condition whereby the discharging of said
capacitor switches said second capacitor to its conductive
condition, a reversing switch, a diode and a second voltage divider
connected to the base electrode of said second transistor via said
diode, said diode being connected with a polarity which is such
that said second voltage divider is supplied a fully advanced
control current via said reversing switch in an operating position
of said reversing switch and said second transistor is in its
nonconductive condition.
9. A circuit arrangement as claimed in claim 8, wherein said
control unit further comprises a fourth transistor functioning with
said third transistor as a monostable multivibrator, said capacitor
and said discharging circuit having time constants which prevent
the termination of the fully conductive condition of said second
transistor prior to the termination of the reset condition of said
monostable multivibrator.
10. A circuit arrangement as claimed in claim 8, wherein said
control unit further comprises a diode connecting said second
voltage divider to said reversing switch, a fifth transistor having
an emitter-collector path connected to said second voltage divider
via said diode, said reversing switch having an operable switching
position wherein it connects said second voltage divider to said
source of DC voltage, and wherein said circuit arrangement further
comprises a current transformer connected between said source of
voltage and said control circuit and having an output connected to
the input of said control unit for supplying a signal to said
control unit when the current flowing through said filter exceeds a
predetermined critical value, the fifth transistor of said control
unit being fully controlled by the signal supplied by said current
transformer to said control unit.
11. A circuit arrangement as claimed in claim 10, wherein said
control unit further comprises a resistor, a second guide capacitor
connected to said first-mentioned guide capacitor via said
resistor, said control voltage being derived from said second guide
capacitor, another resistor, the controllable resistor of said
discharging circuit being connected in parallel with said second
guide capacitor via said other resistor, the period of interruption
of the filter current and the time constant of said second guide
capacitor and said discharging circuit being adjusted to each other
in a manner whereby upon the termination of the interruption said
second guide capacitor is substantially completely discharged, said
second guide capacitor and said resistor having a time constant
which is such that the voltage of said filter increases as rapidly
as possible without overshooting.
Description
DESCRIPTION OF THE INVENTION
The invention relates to the control of the voltage of an
electrical filter, such as an electrical precipitator. More
particularly, the invention relates to a circuit arrangement for
the automatic control of the voltage of an electrical filter.
A control circuit controls the filter voltage. A control system
supplies a control magnitude to the control circuit, which
magnitude varies in accordance with a control voltage supplied to a
control unit, which control unit is in turn connected to the
control system. The control unit includes a guide capacitor
connected to a source of DC voltage via a charging circuit. The
control voltage depends upon the voltage of the guide capacitor. A
discharge circuit is connected in parallel with the guide capacitor
and contains a controllable resistor having a resistance value
which depends upon the filter voltage.
The control circuit may comprise a control transformer, a
transducer, a positioner including thyristors, or a controlled
rectifier. The source of energizing voltage may be single or
multiphase.
Known circuit arrangements of the aforedescribed type have
essentially not been utilized, since the galvanic connection
between the filter, conducting high voltage, and the control
circuit, resulted in difficulties. These difficulties may be
avoided by our invention.
Tests have shown that after a sparkover in the filter, a
considerably higher current flows temporarily through the filter.
This results in higher maintenance costs and causes the filter to
have a shorter lifespan. The temporarily increased filter current
is due to the control circuit and control system having time
constants, which time constants prevent the filter voltage from
being decreased without delay after the occurrence of a sparkover
in the filter.
The principal object of the invention is to provide a new and
improved circuit arrangement for the automatic control of the
voltage of an electrical filter.
An object of the invention is to provide a circuit arrangement for
the automatic control of the voltage of an electrical filter which
overcomes the difficulties ensuing in similar circuit arrangements
previously known.
An object of the invention is to provide a circuit arrangement for
the automatic control of the voltage of an electrical filter, which
circuit arrangement has lower maintenance costs and results in a
longer lifespan for the filter.
An object of the invention is to provide a circuit arrangement for
the automatic control of the voltage of an electrical filter, which
circuit arrangement prevents the temporary occurrence of an
increased current magnitude after sparkover in the filter.
An object of the invention is to provide a circuit arrangement for
the automatic control of the voltage of an electrical filter, which
circuit arrangement interrupts the filter current by a control
circuit whenever a sparkover occurs in the filter.
An object of the invention is to provide a circuit arrangement for
the automatic control of the voltage of an electrical filter, which
circuit arrangement includes a control system for controlling a
control circuit having thyristors by cutting off the supply of
control pulses to the thyristors when a sparkover occurs in the
filter.
The termination of the cutoff of control pulses, or the
reinstallment of said control pulses would result in an abrupt
increase in the filter voltage and thereby cause an overshooting of
said filter voltage. Another object of the invention is therefore
to provide a circuit arrangement for the automatic control of the
voltage of an electrical filter, which circuit arrangement prevents
overshooting of the filter voltage.
An object of the invention is to provide a circuit arrangement for
the automatic control of the voltage of an electrical filter with
efficiency, effectiveness and reliability.
In accordance with the present invention, a circuit arrangement for
automatic control of the voltage of an electrical filter comprises
a control circuit coupled to an electrical filter for changing the
voltage of the filter. A source of voltage is coupled to the
control circuit. A control system has an input coupled to the
source of voltage, input means and an output connected to the
control circuit for supplying to the control circuit a control
magnitude. The control magnitude depends upon a control voltage
supplied to the input means of the control system. A voltage
divider connects a glow lamp in parallel with the filter. A control
unit has an input coupled to the source of voltage and output means
coupled to the input means of the control system. The control unit
comprises a source of DC voltage. A charging circuit connects a
guide capacitor to the source of DC voltage whereby the control
voltage supplied to the control system is produced by the control
unit in accordance with the voltage of the guide capacitor. A
discharging circuit is connected in parallel with the guide
capacitor and includes a controllable resistor having a resistance
value dependent upon the voltage of the filter. A photoelement has
a photosensitive area provided in operative proximity with the glow
lamp in a manner whereby light produced by the glow lamp impinges
upon the photosensitive area of the photoelement. Circuit means
couples the photoelement to the discharging circuit for supplying a
control signal dependent upon the irradiation of the photosensitive
area of the photoelement whereby the control signal controls the
controllable resistor of the discharging circuit to a low
resistance value when the glow lamp fails to glow and controls the
controllable resistor to a high resistance value when the glow lamp
glows.
The control unit further comprises a reversing switch. A switching
component has a switching condition which depends upon the
switching position of the reversing switch and the magnitude of
current flowing through the filter. The switching component is in
its conductive condition only during the time between the
energization of the circuit arrangement, with the assistance of the
reversing switch, and the time during which the current flowing
through the filter reaches a critical value for the first time
after the energization of the circuit arrangement by the reversing
switch. The switching component is connected in a manner whereby
the control signal is ineffective when the switching component is
in its nonconductive condition.
The control unit further comprises auxiliary circuit means
connecting the switching component in parallel to the charging
circuit of the guide capacitor.
The control unit further comprises a capacitor. A monostable
multivibrator has a pair of input and output transistors of the
same conductivity type and the controllable resistor of the control
unit comprises a first transistor having a base-emitter path
coupled via the capacitor and a resistor to the output of the
monostable multivibrator whereby when the glow lamp glows, the
input transistor of the monostable multivibrator is in its fully
conductive condition. The output of the monostable multivibrator is
connected to the negative polarity terminal of the source of DC
voltage via a resistor, a decoupling diode and the
emitter-collector path of a second transistor. The switching
component comprises the second transistor whereby when the second
transistor is in its fully conductive condition approximately the
same potential is applied at the output of the monostable
multivibrator as at the extinguished glow lamp, a third transistor
having a control path connected in parallel with the first
transistor and a base electrode. A diode connects the base
electrode of the third transistor to a reversible voltage divider
and conducts the control current of the third transistor. The
control current of the third transistor flows through the
reversible voltage divider as long as the current flowing through
the filter is below the critical value and the first transistor is
in a condition other than its fully conductive condition.
The control unit further comprises a fourth transistor of the same
conductivity type as the pair of transistors of the monostable
multivibrator. A relay has an energizing winding connected to the
collector electrode of the fourth transistor. A control circuit for
the relay winding includes the base-emitter path of the fourth
transistor. The base-emitter path is connected to the relay
winding. A decoupling diode connects the control circuit of the
relay in parallel with the output of the monostable multivibrator
in a manner whereby when the glow lamp glows and the second
transistor is in its nonconductive condition a control current
flows. The fourth transistor has an emitter electrode connected to
the collector electrode of the second transistor. The emitter
electrode of the fourth transistor has a potential of a magnitude
which is such that when the second transistor is in its conductive
condition the fourth transistor remains in its fully conductive
condition.
In accordance with the invention, a circuit arrangement for
automatic control of the voltage of an electrical filter comprises
a control circuit coupled to an electrical filter for changing the
voltage of the filter. A source of voltage is coupled to the
control circuit. A control system has an input coupled to the
source of voltage, input means and an output connected to the
control circuit for supplying to the control circuit a control
magnitude depending upon a control voltage supplied to the input
means of the control system. A control unit has an input coupled to
the source of voltage and output means coupled to the input means
of the control system. The control unit comprises a source of DC
voltage. A charging circuit connects a guide capacitor to the
source of DC voltage whereby the control voltage supplied to the
control system is produced by the control unit in accordance with
the voltage of the guide capacitor. A discharging circuit is
connected in parallel with the guide capacitor and includes a
controllable resistor having a resistance value dependent upon the
voltage of the filter. Cutoff circuit means supplies a cutoff
signal to the input means of the control system. The control system
controls the control circuit for interrupting the filter current
without delay when a sparkover occurs in the filter.
The control circuit comprises thyristor means and the control
magnitude supplied by the control system controls the thyristor
means. The cutoff circuit means of the control unit switches the
thyristor means of the control circuit via the control system when
a sparkover occurs in the filter.
The cutoff circuit means of the control unit comprises a first
transistor having an emitter-collector path and a control path. The
cutoff signal is derived from a point in the emitter-collector path
of the first transistor. A second transistor of complementary type
to the first transistor has a control path connected in parallel
with the control path of the first transistor. The controllable
resistor of the discharging circuit comprises the control path of
the second transistor. Each of the first and second transistors has
a base electrode connected to a first voltage divider. The first
transistor is in its fully conductive condition during normal
operation of the filter. A third transistor of the same
conductivity type as the first transistor is in its nonconductive
condition during normal operation of the filter and switches to its
conductive condition upon the occurrence of a sparkover in the
filter. The third transistor has an emitter electrode coupled to
the emitter electrode of the second transistor. The third
transistor has a collector electrode coupled to the base electrode
of the second transistor via a capacitor and a resistor. The
collector electrode of the third transistor is connected to the tap
point of the first voltage divider. The capacitor discharges via
the control path of the second transistor when the third transistor
is in its conductive condition whereby the discharging of the
capacitor switches the second capacitor to its conductive
condition. A second voltage divider is connected to the base
electrode of the second transistor via a diode. The diode is
connected with a polarity which is such that the second voltage
divider is supplied a fully advanced control current via a
reversing switch in an operating position of the reversing switch
and said second transistor is in its nonconductive condition.
The control unit further comprises a fourth transistor functioning
with the third transistor as a monostable multivibrator. The
capacitor and the discharging circuit have time constants which
prevent the termination of the fully conductive condition of the
second transistor prior to the termination of the reset condition
of the monostable multivibrator.
The control unit further comprises a diode connecting the second
voltage divider to the reversing switch. A fifth transistor has an
emitter-collector path connected to the second voltage divider via
the diode. The reversing switch has an operable switching position
wherein it connects the second voltage divider to the source of DC
voltage and wherein the circuit arrangement further comprises a
current transformer connected between the source of voltage and the
control circuit and has an output connected to the input of the
control unit for supplying a signal to the control unit when the
current flowing through the filter exceeds a predetermined critical
value. The fifth transistor of the control unit is fully controlled
by the signal supplied by the current transformer to the control
unit.
The control unit further comprises a resistor. A second guide
capacitor is connected to the first-mentioned guide capacitor via
the resistor. The control voltage is derived from the second guide
capacitor. The controllable resistor of the discharging circuit is
connected in parallel with the second guide capacitor via another
resistor. The period of interruption of the filter current and the
time constant of the second guide capacitor and the discharging
circuit are adjusted to each other in a manner whereby upon the
termination of the interruption the second guide capacitor is
substantially completely discharged. The second guide capacitor and
the resistor have a time constant which is such that the voltage of
the filter increases a s rapidly as possible without
overshooting.
It is frequently preferred that a signal be produced when the glow
lamp remains extinguished for longer than a specific period of
time, since this usually indicates a metallic short circuit in the
filter. The relay is utilized for this purpose. The relay is
coupled to the source of DC voltage via the emitter-collector path
of a transistor, the control path of which receives the control
signal. The relay is thus unable to produce a faulty alarm signal
when the switching component is in its fully conductive condition,
that is, during the acceleration period. The emitter electrode of
the transistor may also be coupled to the switching component via a
resistor and a diode, so that when the resistor has a suitable
resistance value, the transistor will remain in its fully
conductive condition even when the switching component is in its
nonconductive condition.
In order that the invention may be readily carried into effect, it
will now be described with reference to the accompanying drawing,
wherein:
FIG. 1 is a block diagram of an embodiment of the circuit
arrangement of the invention; and
FIG. 2 is a circuit diagram of the control unit St of FIG. 1.
In FIG. 1, an electrical filter F is coupled to the secondary
winding of a high voltage transformer T via a rectifier G. The
electrical filter, also called electrical precipitator, is shown
diagrammatically as a high voltage wire d and a grounded metallic
tube t. The primary winding of the transformer T is coupled to an
input terminal U of a single or multiphase AC voltage power system
via a smoothing choke D, a control circuit S and a current
transformer W. The current transformer W, the control circuit S and
the smoothing choke D are connected in series circuit arrangement
between the input terminal U and the transformer T. The smoothing
choke D functions to improve the shape of the signals supplied to
the transformer T. The control circuit S comprises thyristors
connected in antiparallel arrangement, that is, with the anode of
one connected to the cathode of the other and the cathode of the
first connected to the anode of the second.
Control pulses for the thyristors of the control circuit S are
supplied by a control system I. In order to synchronize the control
system I, the alternating voltage of the AC voltage power supply,
applied via the input terminal U, is applied to said control
system. A control voltage U.sub.MA is applied to the control system
I via an input terminal A. The control voltage U.sub.MA determines
the phase position of the control pulses relative to the
alternating voltage of the AC voltage power supply. Control system
I can consist of a known standard unit, for instance control unit
teb- p4 se 401, manufactured by Siemens AG, Germany.
The provision of control pulses by the control system I may be
blocked without delay, and without regard to the magnitude of the
control voltage U.sub.MA, by a cutoff signal supplied to said
control system via an input terminal L thereof. The control voltage
U.sub.MA and the cutoff signal are supplied by a control unit St.
The cutoff signal is supplied to the control system I by the
control unit St when a short circuit or similar fault occurs in the
filter F.
At the onset of operations, a specific instance may occur. The
control voltage U.sub.MA is applied to the control system I by the
control unit St and depends upon a signal supplied to said control
unit by the current transformer W. The signal supplied by the
current transformer W to the control unit St is proportional to the
filter current and indicates a short circuit, breakdown, light arc,
or the like, in the filter F. The signal is obtained via a
photosensitive semiconductor device included in the control unit St
and exposed to light produced by a glow lamp LA. The glow lamp LA
is connected in parallel with the filter F via a pair of resistors
r28 and r29, so that said glow lamp glows only when said filter is
in operation. When a sparkover occurs in the filter F, the glow
lamp LA is extinguished.
FIG. 2 illustrates the circuit arrangement of the control unit St.
The control unit St includes a rectifier g, which is preferably a
full-wave rectifier, and has applied to it via an input terminal B
a voltage proportional to the filter current. The rectifier g is
connected via a resistor r27 to an RC member c6, r26. The resistor
r26 of the RC member has a variable resistance. The variable
resistance of the resistor r26 is coupled in parallel with voltage
divider r24, r25 via a Zener diode n14. The resistor r24 of the
voltage divider r24, r25 is connected in parallel with a series
circuit arrangement of the control path of a transistor p10 and a
thyristor p9. The collector electrode of the transistor p10 is
coupled to a positive polarity terminal P of a DC voltage source
via a resistor r6 and a resistor r8. The emitter electrode of the
transistor p10 is connected to the control electrode of the
thyristor p9. The base electrode of the transistor p10 is connected
to a common point in the connection between the resistors r24 and
r25 of the voltage divider r24, 425.
The direct voltage source has, in addition to the positive polarity
terminal P, a negative polarity terminal N and an intermediate
terminal or tap M, and delivers a voltage of 24 volts between said
positive polarity terminal and said intermediate terminal and
between said intermediate terminal and said negative polarity
terminal. A series circuit arrangement of a first guide capacitor
c4, a resistor r20, a diode n10, the emitter-collector path of a a
transistor p8 and a diode n13 is connected between the intermediate
terminal M and the negative polarity terminal N. The base electrode
of the transistor p8 is connected to the anode of the thyristor p9.
The cathode of the thyristor p9 is connected to the negative
polarity terminal N.
The emitter-collector path of a transistor p7 is connected in
parallel with a resistor r20, a diode n10, the transistor p8 and
the diode n13, all of which components are connected in series
circuit arrangement. The emitter-collector path of the transistor
p7 is connected in series circuit arrangement with a resistor r18.
The base electrode of the transistor p7 is connected to a voltage
divider r16, r17 which is connected between the intermediate
terminal M and the emitter electrode of the transistor p8. The
transistor p7 maintains constant a charging current flowing
therethrough. The transistor p7 maintains the charging current
constant at a value which may be readily adjusted, within a large
range, by the variable resistor r17 of the voltage divider r16,
r17, or by the resistor r18.
The first guide capacitor c4 is connected in parallel with a second
guide capacitor c5 via a resistor r15. The control voltage U.sub.MA
is derived from the second guide capacitor c5 for the control
system I. The capacitance of the second guide capacitor c5,
however, is only a fraction of the capacitance of the first guide
capacitor c4.
In order to discharge the first guide capacitor c4, in accordance
with the filter current, said capacitor is connected in parallel
with the emitter-collector path of a transistor p4 via a resistor
11. The base electrode of the transistor p4 is connected to the
positive polarity terminal P via a resistor r8.
To discharge the guide capacitors during a sparkover in the filter
F, the emitter-collector path of a transistor p5 is connected in
parallel with the first guide capacitor c4 via a variable resistor
r13 and is connected in parallel with the second guide capacitor c5
via a resistor r14 and a diode n9. The time constant provided by
the second guide capacitor c5 and the resistor r14 is selected so
small that said capacitor is discharged when the transistor p5 is
in fully conductive condition whereby the discharge is
substantially complete due to a sparkover in the filter F. On the
other hand, the charging time constant determined by the second
guide capacitor c5 and the resistor r15 is also so small that the
voltage at said capacitor increases extremely rapidly to the
voltage of the first guide capacitor c4 after the elimination of a
sparkover in the filter F and the switching of the transistor p5 to
its nonconductive condition.
The discharge of the first guide capacitor c4 during a sparkover of
the filter F and during fully conductive condition of the
transistor p5, is much slower and is determined by the resistance
value of the variable resistor r13. Thus, after a sparkover in the
filter F, the voltage at the first guide capacitor c4 is lower than
that prior to the sparkover by only a small percentage adjustable
by the variable resistor r13.
A sparkover of the filter F is measured by the glow lamp LA. The
glow lamp LA is positioned above a photoelement f in a manner
whereby the photosensitive region of said photoelement is exposed
to light produced by said glow lamp. The photoelement f is
connected in parallel with the base-emitter path of a transistor p1
via a diode n1. The transistor p1 and the diode n1 are so connected
that during the irradiation of the photoelement f, the voltage at
said photoelement controls said transistor to its fully conductive
condition.
The transistor p1 and a transistor p2 function as a monostable
flip-flop with resistors r2, r3 and r4 and a capacitor c1. When the
glow lamp LA glows or produces light, that is, during normal
operation of the filter, the transistor p1 is in its fully
conductive condition and the transistor p2 is in its nonconductive
condition. When there is a sparkover in the filter F, and during
the occurrence of such sparkover, the glow lamp LA is extinguished
or quenched and the transistor p1 is switched to its conductive
condition. The transistor p2 is then switched to its fully
conductive condition. The capacitor c1, which was charged via the
resistors r4 and r2 and the transistor p1, discharges via the
transistor p2, a diode n3, the diode n2 and the resistor r2 thereby
maintaining, regardless of the operational condition of the filter
F, the transistor p1 in its nonconductive condition. The full
control of the transistor p2 is thereby maintained, regardless of
the operational condition of the filter F, for a specific period
determined by the time constant of the discharge circuit.
The base electrode of the transistor p5 is connected to the
collector electrode of the transistor p2 via a resistor r9 and a
capacitor c3 connected in series circuit arrangement with each
other. The base electrode of the transistor p5 is connected to the
negative polarity terminal N via a resistor r19. A resistor r10 is
connected in parallel with the series circuit arrangement of the
resistor r9 and the capacitor c3. When the transistor p2 is in its
nonconductive condition, during normal operation of the filter F,
the capacitor c3 is charged to a voltage having the indicated
polarity. When the transistor p2 is in its fully conductive
condition, the capacitor c3 may discharge via the transistor p2, a
diode n3, the emitter-base path of the transistor p5 and the
resistor r9. The transistor p5 is thus always in its fully
conductive condition simultaneously with the transistor p2. The
discharge circuit of the capacitor c3 is preferably so rated that
the fully conductive condition of the transistor p5 is not
terminated prior to the termination of the flip-flop reset time of
the monostable flip-flop circuit.
Each of the transistors p1, p2, p3, p7, p8 and p10 is an NPN-type
transistor. Each of the transistors p4 and p5 is a PNP-type
transistor. A transistor p6 is an NPN-type transistor. The control
path of the transistor p5 is connected in parallel with the control
path of the transistor p6. The emitter-collector path of the
transistor p6 is connected between the positive polarity terminal P
and the intermediate terminal M via a resistor r12. The output
terminal L of the control unit St, connected to the control system
I, is connected to the collector electrode of the transistor
p6.
A voltage divider r4, r10, r19 is so rated that the voltage applied
to the control path of the transistor p6 when the transistor p2 is
in its nonconductive condition, is sufficient to switch the
transistor p6 to its fully conductive condition. The transistor p5
is then in its nonconductive condition. The base electrode of the
transistor p6 is coupled to the positive polarity terminal P via a
diode n8 and the resistor r8. The resistance values of the
resistors r8 and r6 are so rated that the potential at the junction
point of said resistors is such that the diode n8 is in its
nonconductive condition. This occurs during the illustrated
position of a reversing switch s shown in FIG. 2, or when the
transistor p10 is in its fully conductive condition. The diode n8
is in its conductive condition when the reversing switch s is in
its position not shown in FIG. 2 and the transistor p10 is in its
nonconductive condition.
In order to determine a metallic short circuit in the filter F, the
control unit St includes a relay R having a working contact. The
relay R is coupled between the positive and negative polarity
terminals P and N via the emitter-collector path of a transistor
p3, a diode n5 and the reversing switch s. The base electrode of
the transistor p3 is connected to the collector electrode of the
transistor p2 via resistors r5 and r7 and a diode n7. The
transistor p3 is thus switched to its fully conductive condition
when the transistor p2 is switched to its conductive condition,
during normal operation of the filter F.
A capacitor c2 is connected between a common point in the
connection between the resistors r5 and r7 and the emitter
electrode of the transistor p3. The capacitor c2 has a relatively
high capacitance of a magnitude which determines, together with the
resistance value of the resistor r5, the time which elapses between
a short circuit in the filter F, the transistor p2 being in its
fully conductive condition, and the deenergization of the relay
R.
The collector electrode of the transistor p8 is connected to the
collector electrode of the transistor p2 via a diode n11 and a
resistor r21 connected in series circuit arrangement. The collector
electrode of the transistor p8 is also connected to the emitter
electrode of the transistor p3 via a diode n12 and a resistor r22.
The emitter electrode of the transistor p3 is connected to the base
electrode of the transistor p8 via a resistor r23. The resistor r21
is rated at approximately the same resistance value as the resistor
r4, so that when the transistor p2 is in its nonconductive
condition, and the transistor p8 is in its fully conductive
condition, the approximate potential of the intermediate terminal
is applied to the collector electrode of the transistor p2. This
prevents the capacitor c3 from being charged while the transistor
p8 is in its fully conductive condition, during the increasing of
the voltage at the filter F, following the switching of said
transistor to its conductive condition. The periodic extinguishing
of the glow lamp LA, when the transistor p2 is in its fully
conductive condition, due to the ripple or pulsation factor of the
filter voltage during the increase thereof, may therefore not
result in a voltage drop during such period. A control current is
therefore supplied to the transistor p6 via the resistor r8 and the
diode n8, if the reversing switch s is in its condition opposite
that shown in FIG. 2 and the transistor p10 is in its nonconductive
condition.
The resistance values of the relay R and of the resistor r22 are so
rated that the emitter electrode of the transistor p3 is
sufficiently negative during such condition of operation that the
diode n5 is switched to its nonconductive condition and the
transistor p3 remains in its fully conductive condition.
The reversing switch s functions to maintain a predetermined
initial condition during the commencement of the installation. In
the position of the reversing switch s shown in FIG. 2, the base
electrode of the transistor p8 is connected to the negative
polarity terminal N via the resistor r23 and the diode n5, so that
said transistor is switched to its nonconductive condition. On the
other hand, the transistor p4, which is connected in parallel with
the first guide capacitor c4, is in its fully conductive condition,
since the base electrode of said transistor is connected to the
negative polarity terminal N via the resistor r6 and the diode n6.
Since no voltage is applied to the filter F, the transistors p2 and
p5 are in their fully conductive condition. The transistor p6 is in
its nonconductive condition and a cutoff signal is supplied to the
terminal L of the control unit St. The first and second guide
capacitors c4 and c5 are discharged.
When the reversing switch s is in its position shown in FIG. 2, the
thyristor p9 is quenched, extinguished or switched to its
nonconductive condition, after the installation is switched
off.
To initiate the installation the reversing switch s is moved into
its second switching position, opposite to that shown in FIG. 2, in
which the cathodes of the diodes n5 and n6 are connected to the
intermediate terminal M. The junction point of the resistors r6 and
r8 thus becomes so positive that the transistor p4 is switched to
its nonconductive condition and the transistor p6 is switched to
its conductive condition. This eliminates the cutoff signal
supplied to the terminal L of the control unit St, so that the
control system I (FIG. 1) supplies control pulses to the control
circuit S (FIG. 1). The phase position of the control pulses
supplied to the control circuit S by the control system I depends
upon the control voltage U.sub.MA at the second guide capacitor
c5.
The transistor p8 is supplied with a control current which switches
it to its fully conductive condition, via the transistor p3 and the
resistor r23. The first and second guide capacitors c4 and c5 are
therefore charged to a voltage of the polarity indicated in FIG. 2,
via the resistor r20, the diode n10, the transistor p8 and the
diode n13. The charging time constant has a very low value, since
the filter voltage, which depends upon the voltage at the second
guide capacitor c5, is to obtain the breakthrough value as soon as
possible, following the switching on of the installation.
As soon as the transistor p8 is in its conductive condition, after
the reversal of the reversing switch s, a current also flows via
the resistors r4 and r21 and the diodes n11 and n13. At the
aforedescribed rating of the resistors, this means that the
potential at the collector electrode of the transistor p2
corresponds approximately to the potential of the intermediate
terminal M, regardless of the operating condition of the filter F
and the condition of the monostable flip-flop or multivibrator
circuit. Despite this, the transistor p3 is supplied with a control
current via the diode n7, the resistor r7, the resistor r5, the
resistor r22, the diode n12, the emitter-collector path of the
transistor p8 and the diode n13, since the emitter potential of the
transistor p3 is more negative at the aforedescribed rating of the
relay R and the resistor r22 than the potential of the intermediate
terminal M. The relay therefore remains in its energized
condition.
During the rapid charging of the first and second guide capacitors
c4 and c5 via the transistor p8 in its conductive condition, the
transistor p6 is supplied a full control current, via the resistor
r8 and the diode n8. Thus, no cutoff signal is supplied to the
terminal L of the control unit St. The control system I (FIG. 1)
therefore delivers control pulses to the control circuit S. The
phase position of the control circuit therefore depends upon the
control voltage U.sub.MA at the second guide capacitor c5.
The increase of the voltage at the second guide capacitor c5 and
the corresponding increase of the filter voltage causes the filter
current to increase also. The voltage derived at the resistor r26
thus also increases. At a specific value of the voltage at the
resistor r26, which is the reference value of the filter current,
the Zener diode n14 is switched to its conductive condition and
conducts current and the transistor p10 and the thyristor p9 are
switched to their fully conductive condition. Thence the current
through the relay R flows through the thyristor p9, via the
transistor p3 and the resistor r23. The transistor p8 is switched
to its nonconductive condition, since the control path of said
transistor is short-circuited by the transistor p9. This terminates
the exponential rapid charging of the first and second guide
capacitors via the transistor p8 and the output signal provided by
the monostable multivibrator via the resistor r21 and the diode
n11.
The thyristor p9 remains in its conductive condition until the
reversing switch s is reversed in position or the installation is
switched off. Regardless of the conductive condition of the
transistor p10, the thyristor p9 remains in its fully conductive
condition. The first and second guide capacitors c4 and c5 may
therefore be charged with a constant current during operation, only
via the transistor p7 and the resistor r18. The charge of the guide
capacitors c4 and c5 is substantially independent of the ambient
temperature, due to the diode n13 coupled to the base electrode or
control circuit of the transistor p7. This is of considerable
importance when the time constant is very large. The control
circuit of the transistor p7 is of relatively low resistance, so
that it is easily possible to position the variable resistor r17
far away from the remainder of the installation, on a control
board.
If the filter current exceeds the reference value during operation,
the transistor p10 and the transistor p4 are temporarily in their
fully conductive condition, so that the first and second guide
capacitors c4 and c5 are slightly discharged. The filter voltage
therefore decreases. The filter current again decreases to a value
less than the reference value and the transistors p10 and p4 are
switched to their nonconductive condition. The voltage of the first
and second guide capacitors c4 and c5 and of the filter F
thereafter slowly commences to increase linearly. The filter
current is limited in this manner to the reference value, without a
voltage-dependent decrease, during the time that no sparkover
occurs in the filter F.
During a sparkover in the filter F, the transistor p5 is switched
to its fully conductive condition by the discharge of the capacitor
c3, regardless of the magnitude of the filter current. The first
guide capacitor c4 is thereby discharged, via the resistor r13, by
a specific, relatively small, amount. The second guide capacitor c5
discharges almost completely, via the resistor r14 and the diode
n9. Furthermore, when the transistor p5 is in its fully conductive
condition, the transistor p6 is switched to its nonconductive
condition, so that a control pulse is not supplied to the control
circuit S (FIG. 1) due to the supply of a cutoff signal to the
terminal L of the control unit St.
Upon the termination of the reset time of the monostable flip-flop
circuit, the transistor p5 is switched to its nonconductive
condition and the second guide capacitor c5 is charged relatively
rapidly to the voltage of the first guide capacitor c4. The filter
voltage increases correspondingly rapidly, since the transistor p5
is in its conductive condition. Therefore, there is no longer a
cutoff signal at the terminal L. The rate of charging of the second
guide capacitor c5 is adjusted to the installation in a manner
whereby the filter voltage increases as rapidly as possible without
varying abruptly the value determined by the first guide capacitor
c4.
During the exponential charging of the first and second guide
capacitors c4 and c5, with the transistor p8 in its fully
conductive condition, the transistor p5 may not be supplied with a
control current via the resistor r18. This is due to the fact that
the transistor p6 is supplied with a control current for switching
it to its fully conductive condition, via the resistor r8 and the
diode n8, so that the voltage applied to the base-emitter path of
the transistor p6 is applied as a blocking bias voltage to the
control path of the transistor p5. The control current for the
transistor p6, via the resistor r8 and the diode n8, is omitted,
however, if the filter current reaches the value of the reference
current at the end of the voltage increasing period and the
transistor p10 is thereby fully controlled or switched to its fully
conductive condition. If there is no sparkover in the filter F at
such time, and the transistor p2 of the monostable flip-flop
circuit is therefore in its nonconductive condition, the transistor
p6 is supplied with a full control current via the resistors r4 and
r10 and is switched thereby to its fully conductive condition.
If, however, during the initial response of the transistor p10
after the initiation of the installation a sparkover or a light arc
occurs in the filter F, as a result of which the transistor p2 is
switched to its fully conductive condition, the transistor p6 is
not supplied with control current, either via the resistors r4 and
r10 or the resistor r8 and the diode n8, so that the transistor p6
is switched to its nonconductive condition and a cutoff signal is
provided at the output terminal L for obstructing the control pulse
provided for the control circuit F.
Simultaneously, the transistor p5 is supplied with a full control
current via the resistor r19 to switch said transistor to its fully
conductive condition. This assures the discharge of the second
guide capacitor c5. A full control of the transistor p5 by the
capacitor c3, via the transistor p2, would not be possible,
however, at the termination of the exponential charging of the
guide capacitors, since the capacitor c3 could not yet be charged
due to the transistor p8 being in its full conductive condition.
Thus, although in the period following the exponential charging of
the guide capacitors, a cutoff signal is provided at the output
terminal L and the discharge of both said guide capacitors is
effected by the transistor p5 during each sparkover of the filter
F, regardless of the filter current, a voltage drop in said
transistor and the provision of a cutoff signal are initiated after
the exponential charging, if a sparkover or a light arc is present
in the filter and if the filter current has reached or exceeded the
reference value.
The invention may also be utilized in installations for the control
of an electron beam or an ion beam, for material processing.
While the invention has been described by means of a specific
example and in a specific embodiment, we do not wish to be limited
thereto, for obvious modification will occur to those skilled in
the art without departing from the spirit and scope of the
invention.
* * * * *