U.S. patent number RE30,678 [Application Number 05/670,851] was granted by the patent office on 1981-07-14 for dormant oscillator ground to neutral protection for ground fault interrupters.
This patent grant is currently assigned to Eaton Corp.. Invention is credited to Russell P. Schuchmann, Donald L. Van Zeeland.
United States Patent |
RE30,678 |
Van Zeeland , et
al. |
July 14, 1981 |
Dormant oscillator ground to neutral protection for ground fault
interrupters
Abstract
Ground to neutral fault protection employing dormant oscillators
which are only energized and function on the .[.occurance.].
.Iadd.occurrence .Iaddend.of such type of a ground fault. Combined
with known types of two and three wire single phase AC ground fault
interrupters to provide circuit interruption regardless of which
wire is faulted to ground.
Inventors: |
Van Zeeland; Donald L.
(Franklin, WI), Schuchmann; Russell P. (Racine, WI) |
Assignee: |
Eaton Corp. (Cleveland,
OH)
|
Family
ID: |
24692151 |
Appl.
No.: |
05/670,851 |
Filed: |
March 26, 1976 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
434988 |
Jan 21, 1974 |
03878435 |
Apr 15, 1975 |
|
|
Current U.S.
Class: |
361/44 |
Current CPC
Class: |
H02H
3/331 (20130101) |
Current International
Class: |
H02H
3/32 (20060101); H02H 3/33 (20060101); H02H
003/28 () |
Field of
Search: |
;361/44,45,46 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moose, Jr.; Harry E.
Attorney, Agent or Firm: Rather; Hugh R. Autio; William
A.
Claims
We claim:
1. In a ground fault interrupter for an alternating current
distribution circuit which has a neutral electrically grounded
conductor and at least one electrified conductor, of an
electro-responsive circuit breaker having contacts for connection
between each electrified conductor of an alternating circuit supply
source and corresponding conductors of said distribution circuit,
normally dormant means responsive to a low resistive fault between
said neutral conductor and ground to initiate generation of a high
frequency oscillatory potential and means responsive to the
resulting oscillatory, current to effect energization of said
electro-responsive circuit breaker.
2. The combination according to claim 1 wherein said normally
dormant means comprises amplifying means and two differential
transformers each having cores through which the conductors of said
distribution circuit pass and a secondary winding in circuit with
said amplifying means.
3. The combination according to claim 2 wherein said amplifying
means includes an operational amplifier, wherein secondary winding
of one of said transformers has a capacitor connected thereacross
and is connected to the input terminals of said amplifier, and
wherein the secondary winding of the other of said transformers has
a capacitor connected thereacross and is in circuit with the output
of said operational amplifier.
4. The combination according to claim 3 wherein the inductance of
said secondaries and the capacitance of the capacitors connected
thereacross provide a pair of high frequency resonant tank circuits
that are insensitive to normal distribution circuit
frequencies.
5. The combination according to claim 3 together with a third
differential transformer having a core through which the conductors
of said distribution circuit pass and a secondary winding in
circuit with the input terminals of said operational amplifier and
a capacitor connected across the last mentioned secondary winding,
said last mentioned secondary winding and capacitor having
inductance and capacitance values such that an alternating
potential will be generated in their parallel combination when a
fault occurs between any electrified line and ground at the
distribution circuit frequency.
6. The combination according to claim 3 wherein the cores and
secondary windings of said transformers upon .[.occurance.].
.Iadd.occurrence .Iaddend.of a neutral conductor to ground fault
are thereby effectively coupled by said neutral conductor and the
fault established ground return path to initiate and sustain the
generation of said high frequency oscillatory current, and wherein
the gain of the circuit inclusive of said coupled secondary
windings of said transformers and said amplifier is equal to or
greater than unity. .Iadd. 7. A protective system for use in an
electrical system having at least a first conductor and a second
conductor extending from a source of alternating current to a load,
said protective system comprising:
a transformer having a core, a primary on said core and a secondary
formed by said at least first and second conductors;
an amplifier;
means to couple the output of said amplifier to said primary of
said transformer; and
means including said transformer for causing said amplifier to
break into self-sustained oscillations upon the occurrence of a
given event relating to said at least first and second conductors.
.Iaddend..Iadd. 8. A protective system as defined in claim 7
wherein said given event is the establishing of a parallel
conductive shorting path across at least one of said at least first
and second conductors. .Iaddend..Iadd. 9. A protective system as
defined in claim 7 wherein one of said at least first and second
conductors is a neutral conductor grounded at the source side of
said electrical system and said given event is the establishment of
a low impedance to ground in said neutral conductor on the load
side of said electrical system. .Iaddend..Iadd. 10. A protective
system as defined in claim 8 wherein said means for causing said
amplifier to break into self-sustained oscillations also includes a
differential transformer having a core, a primary formed by said at
least first and second conductors and a secondary on said core,
said secondary being coupled to the input of said amplifier.
.Iaddend. .Iadd. 11. A protective system as defined in claim 9
wherein said means for causing said amplifier to break into
self-sustained oscillations also includes a differential
transformer having a core, a primary formed by said at least first
and second conductors and a secondary on said core, said secondary
being coupled to the input of said amplifier. .Iaddend..Iadd. 12. A
protective system as defined in claim 8 wherein responsive means is
coupled to the output of said amplifier, said responsive means
responding to the voltage developed at the output of said amplifier
when said amplifier breaks into self-sustained oscillations.
.Iaddend..Iadd.13. A protective system as defined in claim 12
wherein said responsive means is a circuit breaker coil coupled to
the output of said amplifier. .Iaddend..Iadd. 14. A protective
system as defined in claim 9 wherein responsive means is coupled to
the output of said amplifier, said responsive means responding to
the voltage developed at the output of said amplifier when said
amplifier breaks into self-sustained oscillations. .Iaddend..Iadd.
15. A protective system as defined in claim 14 wherein said
responsive means is a circuit breaker coil coupled to the output of
said amplifier..Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to ground fault interrupters which
are sensitive to low resistance faults occurring between neutral
conductors in an A.C. distribution circuit and ground.
National and local code standards require that ground fault
interrupters used to protect grounded neutral, two and three wire
A.C. distribution circuits function to interrupt the supply of
power to such distribution circuit on .[.occurence.].
.Iadd.occurrence .Iaddend.of a low resistive ground fault between
any electrified or neutral line and ground. All prior systems used
for detecting the presence of a fault between ground and a neutral
line have employed circuits which are continuously energized. These
have taken the form of circuits energized by transformer or
inductive windings connected between the distribution lines, or by
circuits that require active high frequency superimposed voltages
that are interrupted or otherwise attenuated when such ground
faults occur. Such circuits are subject to influence by transient
currents, and in the case of high frequency superimposed voltages
the entire distribution system is subjected to these signals which
may be highly objectionable in some instances.
OBJECTS OF THE INVENTION
It is a primary object of the present invention to provide an
improved form of neutral-to-ground fault protection system which
under normal conditions is dormant and thus superimposes no
unwanted signal on a protected distribution circuit yet immediately
detects and responds to neutral-to-ground faults.
Another object of the invention is to provide a ground fault
protection system of the aforementioned type that employs a dormant
oscillator which is triggered into oscillation to initiate
disconnection of the protected distribution circuit upon
.[.occurance.]. .Iadd.occurrence .Iaddend.of a neutral-to-ground
type of fault.
A further object of the invention is to provide ground fault
protection of the aforementioned type which can be readily combined
with known types of ground fault interrupters which normally
function-upon .[.occurance.]. .Iadd.occurrence .Iaddend.of a fault
between electrified lines and ground.
Other objects and advantages of the invention will hereinafter
appear.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of one embodiment of the present
invention.
FIG. 2 is a more complete diagram of the embodiment of the
invention, and
FIG. 3 is a diagram of a modified form on the invention, and
FIG. 4 is a diagram of still another modified form of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the basic form of the invention as applied to a single
phase alternating power circuit comprising to a conductors or lines
designated L1 and N. Line N, the "neutral" wire, has connection to
earth ground and line L1 carries an alternating voltage with
respect to line N and is termed the "electrified" wire. Lines L1
and N may be assumed to be connected at their left hand ends to a
source of single phase, alternating current and at their right hand
ends to a load or to several loads connected thereacross in
parallel.
Lines L1 and N pass through the cores of 12, 20 and 27 of three
differential transformers 10, 19 and 25, respectively, and each
line provides a primary winding for each of these transformers. The
core 12 of transformer 10 has a secondary winding 14 wound thereon
and the ends thereof are connected to the input side of a ground
fault interrupting circuit 17 which has an output connected to the
coil CBT1 of a circuit breaker CBT which has contacts CBS2 in
circuit with line L1. In one preferred form GFI 17 is like that
disclosed in the Van Zeeland et al., application Ser. No. 345,731,
filed Mar. 28, 1973 and assigned to the assignee of this
application. As therein disclosed, upon .[.occurance.].
.Iadd.occurrence .Iaddend.of a ground fault between line L1 and
ground, GFI 17 will immediately respond to energize CBT1 to cause
opening of contacts CBS2 and effect disconnection of the loads from
the alternating current source.
The core 20 of transformer 19 has a secondary winding 23 which has
its ends connected to the input terminals of an amplifier A, and
the core 27 of transformer 25 has a secondary winding 28 connected
to other input terminal of amplifier A. The output of amplifier A
is connected to a third input terminal of GFI 17. Let it be assumed
that a fault from neutral wire N to earth occurs, as indicated by
the broken lines, and that such fault has a resistance on the order
of 4 ohms or less. It will be observed that line N together with
the ground return provides a means for coupling the windings of
transformers 19 and 25. Thus it can be seen that the circuit can
now oscillate provided the loop gain is equal to or exceeds unity.
With the output voltage of windings set in proper phase relation,
amplifier A will provide a suitable output voltage which causes the
GFI 17 to respond to energize winding CBT1 and trip open contact
CBS2. Transformer 19 and 25 and amplifier A thus act as a "dormant
oscillator" and only oscillate to provide a GFI tripping output
voltage when a neutral-to-ground fault occurs.
FIG. 2 is a more complete detailed study showing of a preferred
embodiment of the circuit briefly disclosed in FIG. 1. The portion
of the actual circuitry in GFI 17 actually involved is described,
and for sake of clarity the elements thereof bear the same
reference numerals as corresponding elements in the preferred form
disclosed in the aforementioned Van Zeeland application. The right
hand end of secondary winding 23 of transformer 19 is connected in
series with a capacitor C1 and a resistor R1 to the inverting input
terminal 16 of an operational amplifier OA, and the left hand end
of winding 23 is connected in series with a resistor R2 to the
non-inverting input terminal 18 of amplifier OA. A capacitor C2 is
connected across winding 23. The output terminal 26 of amplifier OA
is connected in series with a coupling capacitor C3 to the point Z
which is common to the left hand end of secondary winding 28 of
transformer 25, the anode of a diode D1 and the left hand plate of
a capacitor C6 that is connected across winding 28.
The output terminal 26 of amplifier OA is also connected in series
with a feed-back resistor R3 to the inverting input terminal of the
amplifier. A source of D.C. potential is provided by a series
connection of a diode D2, resistor R4, and diode D3 and D4
connected across the lines L1 and N as shown. A filter capacitor C7
is connected between the point Y common between resistor R4 and D3
and line N. The positive D.C. bias terminal 22 of amplifier OA is
connected to the point Y and may be assumed to be subject to a D.C.
bias to +20 volts. A resistor R5 is connected from the point common
between diodes D3 and D4 and the non-inverting input terminal
.[.24.]. .Iadd.18 .Iaddend.of amplifier OA. The ground terminal is
connected to line N. The point X is connected through diode D1 to
the point common between resistors R10 and R11, and the gate of
SCRQ1 of GFI 17.
Let it be assumed that alternating load current is flowing normally
through lines L1 and N and no ground fault is .[.occuring.].
.Iadd.occurring .Iaddend.between either of these lines and ground.
Thus differential transformer 10, 19 and 25 will not develop any
ampere turns in the respective secondary winding 14, 23 and 28.
Amplifier OA will under these conditions develop a quiescent D.C.
output potential of 10 volts. Capacitor C3 blocks the flow of D.C.
current. No voltage exists across winding 28 and consequently no
current will flow through diode D1.
Now let it be assumed that a ground fault represented by the
phantom resistor occurs between line N and ground. It will be
appreciated that a ground current circuit will then be completed
which includes ground and conductor N, and such ground current
causes ampere turns to be developed in each of the windings 23 and
28 of the transformer 19 and 25. The input of the inverting and
non-inverting input terminals 16 and 18 of amplifier OA are then
subjected to an A.C. potential and amplifier OA then develops an
alternating potential of increasing magnitude. The increased
current flow thru capacitor C3 re-inforces the A.C. current
generated in the tank circuit comprising winding 28 and capacitor
C6. Consequently an oscillatory potential having a frequency
determined by the tank circuit components is developed which
increases abruptly in magnitude. Such A.C. potential across the
tank is detected by diode D1, and when it increases to a sufficient
magnitude, firing of silicon controlled rectifier SCRQ1 in the GFI
17 unit occurs. Firing of SCRQ1 in turn causes energization of
winding CBT1 of the circuit breaker which responds to open the
contacts CBS2 in line L1. This oscillatory action occurs within a
millisecond when the neutral-to-ground fault resistance is
sufficiently low to cause oscillation in the circuit.
The combination of the transformers 19 and 25, amplifier OA and the
components directly associated therewith, in effect, provide a
dormant oscillator. With no neutral-to-ground fault occurring no
oscillatory current is developed, but upon .[.occurance.].
.Iadd.occurrence .Iaddend.of such a ground fault, an oscillator
current of a magnitude sufficient to cause energization of the
circuit breaker CBT occurs. It is thus quiescent under normal
conditions and obviates need for continuous high frequency currents
to function. It is immune to transient currents on lines L1 and N,
and will only function when a completed ground circuit inclusive of
line N is developed. Moreover, if a ground fault develops between
line L1 and ground, this circuit remains dormant, and the other
ground fault interrupting circuit in GFI 17 functions to cause
interruption of circuit breaker CBT as described in the
aforementioned application Ser. No. 345,731.
FIG. 3 depicts a modified form of the invention as combined with a
preferred form of circuitry for the ground fault interrupter 17 of
FIG. 2 as disclosed in the aforementioned Van Zeeland et al.,
application Ser. No. 345,731. Corresponding elements in FIG. 3 are
given the same reference numerals found in FIG. 1 of the Van
Zeeland application which should be referred to for a complete
understanding of how such ground fault interrupter functions when a
line L1 to ground fault occurs.
In addition, as shown in FIG. 2 the circuitry includes differential
transformers 29 and 31 which correspond respectively to
.[.transformer.]. .Iadd.transformers .Iaddend.19 and 25 of FIGS. 1
and 2 of this application. The lower end of secondary winding 14 of
transformer 10 is connected to the upper end of that secondary
winding 30 of transformer 29. A capacitor C6 is connected across
winding 30 and the lower of the latter is connected in series with
resistor R2 to the non-inverting input terminal 18 of operational
amplifier OA.
The secondary winding 32 of transformer 31 has a capacitor C7
connected thereacross and its upper end is connected directly to
the base electrode of a P-N-P transistor Q4, and is also connected
in series with a resistor R13 to the output terminal 26 of
amplifier OA. The lower end of winding 32 is connected to the point
common between resistor R7, diode D2 and zener diode ZD2, and to
line N in series with a resistor R14. The emitter of transistor Q4
is connected in series with a resistor R15 to the point common
between resistor R7, diode D2, zener diode ZD2 and the collector of
Q4 is connected in series with resistors R16 and R17 to the point
common between resistor R10, resistor R11, and the control
electrode of silicon controlled rectifier SCRQ1. A capacitor C8 is
connected from the point common between resistors R16 and R17 to
line N.
In the preferred embodiment of FIG. 3 the number of turns in
secondary windings 30 and 32 is preferably 130, and the cores 34
and 36 are preferably formed from a ferrite material of medium
permeability. The values of each of the capacitors C6 and C7 is 0.1
and the parallel combination of each of such secondary windings and
its associated capacitor has a resonant frequency approximately of
4 KHz. The transformer 10 preferably has its core 12 formed from a
Supermalloy type material providing high permeability and its
secondary winding is preferably 1,000 turns. This provides that the
parallel combination of winding 14 and capacitor C2 will have
resonant frequency of approximately 60 Hz.
It will be appreciated that when fault from line L1 to ground
occurs that transformer 10 will function in conjunction with
amplifier OA, and transistor Q2, to successively energize SCRQ1 and
winding CBT1 of the circuit breaker as described in the Van Zeeland
et al. application. As current induced in secondary winding 14 will
be 60 Hz in frequency, winding 30 will afford low impedance to the
flow of current to the non-inverting input terminal 18 of amplifier
OA. The tank circuits 30-C6 and 32-C7 of transformers 29 and 31
will be insensitive to 60 Hz frequency current and will thus be
passive whenever line L1 to ground faults occur.
When a neutral line N to ground fault occurs with a resistance in
the range of 0 to 4 ohms, the line N as aforedescribed provides a
link between the cores 34 and 36 of transformers 29 and 31 to
sustain oscillatory current generated in the tank circuits 30-C6
and 32-C7. Accordingly, the inverting and non-inverting input
terminals, 16 and 18 of amplifier OA are subjected to a 4 K Hz A.C.
potential of increasing amplitude. The output potential of
amplifier OA will be alternating and correspondingly increase. Such
output potential will through resistor R13 be imposed on the tank
circuit 32-C7 of transformer 31 which through the link of line N
with transformer 29 will sustain the .[.oscillator.].
.Iadd.oscillatory .Iaddend.current.
The base of Q4 will also be subjected to the increasing alternating
potential output from amplifier OA. As a result Q4 conducts
alternating current of increasing amplitude through its
emitter-collector circuit which flows through resistor R16 into
capacitor C8 to line N. Capacitor C8 acts as an integrating
capacitor, and when its charge potential reaches a predetermined
value it will cause SCRQ1 to conduct by virtue of the connection of
capacitor C8 through resistor R17 to the gate of SCRQ1. Conduction
of SCRQ1 as aforedescribed results in energization of winding CBT1
and opening of contacts CBS2 of the circuit breaker CBT.
As will be observed that when 4 K Hz A.C. current is generated in
the tank circuit 30-C6 and flows into the non-inverting input
terminal 18 of amplifier OA, its circuit path is then through
capacitor C2 of the tank circuit 14-C2 of transformer 10, as the
latter will afford a low impedance path at this high frequency.
FIG. 4 discloses another preferred embodiment of the invention in
combination with a line to ground fault interrupter as applied to a
single phase, three wire, grounded neutral A.C. distribution
system. As shown the neutral wire designated N is grounded to earth
and circuit breaker contacts CBS1 and CBS2 in each of the
electrified A.C. lines L1 and L2 are opened whenever winding CBT is
energized. Many of the circuit elements of the ground fault
interrupter of FIG. 4 are the same as those of FIG. 2 and have been
given corresponding reference numbers.
It will be noted that in the embodiment of FIG. 4 that the field
effect transistor Q3 and resistor R3 of FIG. 3, have been omitted.
Instead a resistor R18 is connected across the non-inverting and
inverting input terminal 16 and 18 of amplifier OA. D.C. potential
is supplied from lines L1 and L2 being through diodes D1 and D3
that have their cathodes connected in circuit with the upper end of
resistor R4, and in series with a resistor R19 and a smoothing
capacitor C9 to ground through line N. In place of transistor Q2 of
FIG. 3, a P-N-P transistor Q5 is used, and is provided with a
filter network comprising resistors R20 and R21 connected between
the output terminal 26 of amplifier OA and its base resistor R9,
and capacitors C10 and C12 connected in parallel between the
emitter of Q5 and the points common between resistors R20-R21 and
R21-R9 as shown. The point common between resistors R19 and
capacitor C9 is connected in series with a resistor R22 and
resistor R5 to the point common between resistors R9 and R21 and
capacitor C12. Varistors VR2 and VR3 are connected across each of
the lines L1 and L2 to line N.
With no ground faults existing between either of the lines L1 or L2
and ground, amplifier OA will have a quiescent D.C. output
potential of approximately 10 volts. The base of Q5 will be at
approximately 11.7 volts and accordingly Q5 will be biased off. The
aforementioned filter network comprising resistors R20, R21 and
capacitors C10 and C12 act as a low pass filter and thus render the
base of transistor Q5 insensitive to high frequency alternating
type noise that might otherwise tend to render it conducting.
Whenever a ground fault from either lines L1 or L2 to ground
occurs, amplifier OA will provide an alternating output of an
amplitude sufficient to render Q5 conducting which in turn triggers
SCRQ1 into conduction to energize winding CBT which in turn opens
the circuit breaker contacts CBS1 and CBS2. When a ground fault
occurs between neutral line N and ground, transformers 29 and 31,
and amplifier OA functions as aforedescribed in conjunction with
FIG. 3 to render Q4 and SCRQ1 successively conducting.
It will be apparent to those skilled in the art that other forms of
amplification and detector circuitry may be employed without
departing from the basic concepts and scope of the present
invention.
* * * * *