U.S. patent number 3,693,122 [Application Number 05/142,942] was granted by the patent office on 1972-09-19 for flux transfer trip device for electric circuit breakers.
This patent grant is currently assigned to General Electric Company. Invention is credited to Henry G. Willard.
United States Patent |
3,693,122 |
Willard |
September 19, 1972 |
FLUX TRANSFER TRIP DEVICE FOR ELECTRIC CIRCUIT BREAKERS
Abstract
A sensitive magnetic trip device, adapted especially for use
with an electric circuit breaker for operation by a relatively low
power trip signal pulse, such as that developed by a zero-sequence
or differential transformer indicating presence of a ground fault
condition. The device is also highly suitable for use with "static"
or solid-state trip circuits operating in response to signals
generated by current transformers associated with phase conductors
of a multi-phase system. The trip device includes a magnetic
armature normally held in a retracted position against the bias of
a tripping spring by flux generated by a permanent magnet. The trip
device includes a magnetic frame member and a "flux-diverter"
interposed between the armature and the permanent magnet, providing
an alternate path for flux from the permanent magnet. The permanent
magnet flux is diverted from the armature path through the diverter
path by magnetomotive force (MMF) generated by a signal coil. The
diverter path includes an air gap normally causing the diverter
path to be of higher reluctance than the path through the armature.
Upon the occurrence of a trip signal of predetermined magnitude
through the trip coil, magnetomotive force (MMF) generated by the
trip coil opposes the flow of permanent magnet flux through the
armature and diverts it through the diverter path, including the
air gap, causing release of the armature. The armature is
dimensioned with respect to the diverter so that the armature is
driven to saturation by extra high current through the trip coil.
This limits the flow of flux from the trip coil, thereby preventing
demagnetization of the permanent magnet upon occurrence of such
high trip signal currents. The "flux-diverter" is formed and
dimensioned so that in combination with the permanent magnet, the
frame, and the trip coil, it minimizes stray flux and maximizes
sensitivity and effectiveness of the device.
Inventors: |
Willard; Henry G.
(Wethersfield, CT) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
22501896 |
Appl.
No.: |
05/142,942 |
Filed: |
May 13, 1971 |
Current U.S.
Class: |
335/174;
335/236 |
Current CPC
Class: |
H01H
71/322 (20130101); H01F 7/1615 (20130101); H01F
7/122 (20130101) |
Current International
Class: |
H01H
71/12 (20060101); H01F 7/16 (20060101); H01F
7/08 (20060101); H01H 71/32 (20060101); H01f
003/12 () |
Field of
Search: |
;335/174,179,170,229,230,234,235,236,253,254 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Broome; Harold
Claims
I claim:
1. A sensitive magnetic trip device comprising;
a. a generally rectangular closed-loop frame of highly magnetically
permeable material having opposed side walls, a back wall, and a
front wall;
b. a generally cylindrical armature of highly magnetically
permeable material supported for straight-line reciprocal movement
through a close-fitting generally circular hole in said front wall
of said frame;
c. spring means normally urging said armature for movement through
said hole outwardly of said frame;
d. a permanent magnet member having one end in flux-conductive
relation to said back wall of said frame one having its other end
in flux-conductive relation with said end of said armature so as to
normally hold said armature in a retracted position with respect to
said frame against the bias of said spring means;
e. an elongated flux-diverter member of highly magnetically
permeable material supported within said frame member and extending
between said opposed side walls of said frame at a point
intermediate said front and back walls thereof, said flux-diverter
providing an alternate flux path for flux from said other end of
said permanent magnet to return to said one end of said permanent
magnet member without passing through said armature, said alternate
flux path including at least one non-magnetic gap which is
substantially shorter in length than the spacing of said permanent
magnet from said side walls of said frame;
f. a tripping coil supported in said frame intermediate said back
and front walls thereof and surrounding at least a portion of said
armature, whereby current passing through said tripping coil in a
predetermined direction creates magnetomotive force in said
armature in a direction to oppose flux passing therethrough from
said permanent magnet causing flux from said permanent magnet to be
diverted to said path through said flux-diverter and through said
non-magnetic gap, thereby reducing the net flux through said
armature and causing release of said armature and movement of said
armature outwardly of said frame under the bias of said spring
means.
2. A sensitive magnetic trip device as set forth in claim 1 wherein
said flux-diverter comprises a generally flat plate having its
opposite ends in contact with said opposed side walls of said frame
and wherein said armature contacts said permanent magnet at a
juncture in a plane substantially co-planar with said
flux-diverter, said flux-diverter having a generally central
circular hole therein forming a circular air gap between said
flux-diverter and said juncture of said armature and said permanent
magnet.
3. A sensitive magnetic trip device as set forth in claim 1 wherein
said flux-diverter comprises a continuous solid member having its
opposite end portions in closely spaced magnetic gap relation to
said opposed side walls of said frame, and wherein said permanent
magnet member has one end thereof in contacting relation to a first
generally planar intermediate surface of said flux-diverter and
said armature has an end portion in contacting relation to an
intermediate generally planar surface of said flux-diverter
opposite from said first surface, whereby said air gaps between
said flux-diverter and said frame member are removed a substantial
distance from the contacting surface of said armature and said
flux-diverter member.
4. A sensitive magnetic trip device as set forth in claim 3 wherein
said flux-diverter member includes a generally centrally located
cylindrical extension at the surface thereof opposite said first
surface, said armature having one end thereof normally in contact
with the end of said cylindrical extension of said flux-diverter
member, and said trip coil includes a portion encircling at least a
portion of at least one of said armature and said cylindrical
extension portion of said flux-diverter.
5. A sensitive magnetic trip device as set forth in claim 4 wherein
said trip coil includes a portion encircling the meeting faces of
said armature and said cylindrical extension of said
flux-diverter.
6. A sensitive magnetic trip device as set forth in claim 4 wherein
the cross-sectional dimension of said armature and the dimensions
of said diverter are selected so that upon the occurrence of
tripping signals of excessively high magnitude, at least one of
said armature and cylindrical portion of said flux-diverter is
driven to magnetic saturation before the remaining portion of said
flux-diverter is driven to magnetic saturation, whereby
magnetomotive force generated by said tripping coil on the
occurrence of excessively high tripping currents does not
demagnetize said permanent magnet.
7. A sensitive magnetic trip device as set forth in claim 5 wherein
said device also includes a bobbin member of low magnetically
permeable material, wherein said bobbin member has a generally
centrally positioned hole therein receiving said cylindrical
extension of said flex-diverter and slidably receiving and guiding
at least a portion of said armature member.
8. A sensitive magnetic trip device as set forth in claim 1 wherein
said generally rectangular frame of said device comprises a pair of
generally L-shaped members interconnected to form a closed loop of
highly magnetically permeable material, said L-shaped members
having substantially identical in form and dimension whereby to
facilitate manufacture and assembly of said magnetic trip
device.
9. A sensitive magnetic trip device as set forth in claim 1 wherein
said armature and said flux-diverter are formed and dimensioned so
that excessively high tripping current in said trip coil causes
saturation of said armature before causing saturation of said
flux-diverter, whereby demagnetization of said permanent magnet by
said excessively high tripping coil current is substantially
prevented.
10. A sensitive magnetic trip device as set forth in claim 1
wherein said nonmagnetic gap in said alternate flux path through
said diverter is large enough to normally cause flux from said
permanent magnet to pass through said armature in its closed
position in preference to said alternate path, but is dimensioned
small enough to provide a flux path for flux generated by said
tripping coil when energized by an excessively large tripping coil
current to drive one of said elements comprising said armature and
said cylindrical portion of said flux-diverter to saturation
without causing demagnetization of said permanent magnet, such
excessive flux following a path through said flux-diverter and
across said nonmagnetic gap in preference to a path through said
permanent magnet in a direction opposing flux generated by said
permanent magnet.
11. A sensitive magnetic trip device comprising;
a. a generally rectangular closed-loop frame of highly magnetically
permeable material having opposed side walls, a back wall, and a
front wall;
b. a generally cylindrical armature of highly magnetically
permeable material supported for straight-line reciprocal movement
through a close-fitting generally circular hole in said front wall
of said frame;
c. spring means normally urging said armature for movement through
said hole outwardly of said frame;
d. a permanent magnet member having one end in flux-conductive
relation to said back wall of said frame and having its other end
in flux-conductive relation with one end of said armature so as to
normally hold said armature in a retracted position with respect to
said frame against the bias of said springs means;
e. an elongated flux-diverter member of highly magnetically
permeable material supported within said frame member and extending
between said opposed side walls of said frame at a point
intermediate said front and back walls thereof, said flux-diverter
being positioned between said permanent magnet and said armature
and having its ends in closely spaced proximity to said side walls
of said frame, the spacing between said ends of said flux diverter
and said side walls being substantially less than the thickness of
said frame walls;
f. a tripping coil supported on said frame, said tripping coil when
energized creating flux in said armature opposing flux from said
permanent magnet whereby said flux from said permanent magnet is
diverted through said flux-diverter member and across said spacing
between said ends of said ends of said flux-diverter and said side
walls thereby reducing the net flux through said armature and
causing release of said armature and movement of said armature
outwardly of said frame under the bias of said spring means, said
flux-diverter also providing a closed path for flux from said
tripping coil without such flux passing through said permanent
magnet, whereby said tripping coil flux does not tend to
demagnetize said permanent magnet.
Description
DESCRIPTION OF THE PRIOR ART
Flux cancelling and flux transferring or shifting trip devices of
various types have been developed in accordance with the prior art
for use with electrical circuit breakers. All of such devices known
to the present applicant, however, have suffered from one or both
of two disadvantages. First, some or all of such devices have
lacked the degree of sensitivity required for operation by
relatively low power signals such as those developed by a
zero-sequence or differential transformer indicating unbalance of
current in two or more current paths thereby indicating presence of
a ground fault condition. A similar disadvantage exists with
respect to static trip devices responsive to abnormal phase current
conditions. Secondly, some or all of such devices have suffered
from the disadvantage that if sensitive enough for operation by
relatively small amounts of energy, such, for instance, as by
0.0005 joules, they are subject to possible demagnetization of the
permanent magnet used if and when the trip signal becomes
exceptionally large. In addition, some or all of such devices have
suffered from the disadvantages of being relatively large in size,
relatively complicated and consequently costly.
Examples of such prior art magnetic trip devices are shown in the
following U.S. Pat. Nos.:
1,427,368 Fortescue - Circuit Interrupter - Aug. 29, 1922
2,130,871 Boehne - High Speed Tripping System - Sept. 20, 1938
2,915,681 Troy - Magnet Assemblies - Dec. 1, 1959
2,919,323 Drescher - Electric Relay - Dec. 29, 1959
3,253,098 Perry - Mechanical Actuator With Permanent Magnet - May
24, 1966
3,450,955 Johnson - Circuit Breaker With Magnetic Device Releasable
To Effect Opening Of The Breaker - June 17, 1969
It is an object of the present invention to provide a sensitive
magnetic trip device for electric circuit breakers which shall be
capable of operation by relatively small amounts of electrical
energy, such, for instance, as 0.0005 joules, while producing a
tripping force of substantial amount, such, for instance, as 5
pounds.
It is a further object of the invention to provide a sensitive
magnetic trip device of the type described which is not subject to
demagnetization of its permanent magnet by unusually high tripping
signals.
It is a further object of the invention to provide a sensitive
magnetic trip device of the type described which is relatively
small in size, simple and inexpensive to manufacture.
In accordance with the invention in one form, a sensitive magnetic
trip device is provided including a generally rectangular
magnetically permeable frame member having a permanent magnet
affixed to the inner surface of one end wall and an armature member
slidably supported for movement through an opening in the opposite
end wall and biased by a compression spring for movement outwardly
through the frame. A flux-diverter member is interposed between the
permanent magnet member and the armature, and has a base portion
extending between opposed side wall portions of the frame with a
small air gap provided between the ends of the flux-diverter member
and each of the corresponding side walls. The flux-diverter member
also includes a centrally located generally cylindrical portion
extending toward the armature. In normal closed or inactive
condition, the armature is in contact with the permanent magnet
member, forming a generally central leg portion extending between
central portions of the opposite end walls of the generally
rectangular frame member. Flux generated by the permanent magnet
member normally flows through the diverter member, through the
armature member and back through the opposed side wall portions of
the frame member to the opposite end of the permanent magnet
member. A trip coil is positioned so as to surround the meeting
faces of the armature and the flux diverter, and current is passed
therethrough in a direction to produce magnetomotive force (MMF)
opposing the flux of the permanent magnet member flowing across the
interface between the flux-diverter member and the armature member.
The occurrence of a trip signal of predetermined magnitude in the
trip coil creates such opposing MMF which causes the flux from the
permanent magnet member to take an alternate path through the
flux-diverter base portion and through the relatively small air
gaps between the ends of the diverter base portion and the opposed
side walls of the frame member, and through the frame member back
to the opposite end of the permanent magnet member. The armature
member and the flux-diverter member are so proportioned that the
occurrence of an unusually high tripping signal through the trip
coil causes saturation of the armature member before saturation of
the flux-diverter base portion occurs. This, together with the air
gaps mentioned, assures that such extra high trip signal current
will not cause demagnetization of the permanent magnet.
The invention will be more fully understood from the following
detailed description, and its scope will be pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation view of a sensitive magnetic trip device
constructed in accordance with the invention.
FIG. 2 is a view similar to FIG. 1, but with certain of the parts
being shown in section to more clearly show the construction.
FIG. 3 is a side elevation view, partly in section, of another
embodiment of the invention.
Referring to FIGS. 1 and 2, the construction of a preferred
embodiment is shown, as including a generally rectangular frame of
highly magnetically permeable material and comprising two generally
L-shaped magnetically permeable members 10 and 12, interconnected
by suitable means, such as by having a reduced end of each of the
members 10 and 12 extending through a corresponding opening in the
opposite member and staked over as indicated at 13 and 14.
Alternatively, other forms of fastening, such, for instance, as
machine screws may be used. A generally cylindrical high induction
permanent magnet member 16 is supported in close engagement with an
end wall 17 of the frame member 12 by suitable means, not
shown.
A generally cylindrical armature 18 of high magnetically permeable
material is supported for reciprocal straight-line movement through
a corresponding circular opening in the end wall 19 of the frame
member 10. Movement of the armature 18 is guided in part by the end
wall 19 of the frame member 10, and in part by insulating bobbin
member 20, to be further described. The armature member 18 is
biased for movement outwardly through the frame member 10 by means
of a compression spring 21 which bears against a generally
cylindrical member 22 which is connected by a stem rod 23 to the
armature 18. Movement of the armature member 18 outwardly through
the frame member 10 is limited by suitable means, such as by a
generally hat-shaped stop member 24. The stop member 24 is affixed
to the outer surface of the frame member 10 by suitable means, such
as by screws 24A through the flange portion of the stop member 24.
The central portion of the stop member 24 is dimensioned so as to
receive the armature 18 when it is moved outwardly by the spring
21. Outward travel of the armature 18 is limited by its engagement
with the inner surface of the central portion of the stop member
24. The stop member 24 has a hole 24B in its central portion,
through which the stem rod 23 passes. The outer diameter of the
central portion of the stop member 24 is dimensioned to closely fit
inside the spring 21 to retain it in position.
A generally T-shaped flux-diverter member 25 is supported within
the frame 10, 12, and includes a generally rectangular transversely
extending base portion 26 which extends into closely spaced
relation with each of the side walls 28 and 29 of the frame members
10 and 12 providing small air gaps 26A and 26B. If desired,
suitable nonmagnetic spacer members, not shown, may be placed in
gaps 26A and 26B to aid in positioning flux-diverter 25. The
flux-diverter member is supported in position by being abutted
against an end portion of the permanent magnet member 16, and by
having a generally cylindrical extension 30 which extends into the
cylindrical central opening of the insulating bobbin 29.
In normal position, the armature 18 has one end thereof in abutting
engagement with the cylindrical extension 30 of the flux-diverter
25. The normal flux path, therefore, for flux produced by the
permanent magnet 16 is from one end surface thereof, into the
flux-diverter member 25, from thence into the armature 18, from
thence into the frame member 10, and through the opposed side walls
28, 29 of the frame members 10 and 12 respectively, to the end wall
17, to return to the opposed end wall of the permanent magnet
member 16. This holds the armature in retracted position against
the bias of the compression spring member 21.
For the purpose of causing release of the armature 18 from the
retracted position, a trip coil 35 is provided which is wound on
the bobbin member 20, so as to surround the interface of the
armature 18 and the extension 30 of the flux-diverter 25.
In operation, the occurrence of a trip signal current through the
coil 35 in the proper direction creates a magnetomotive force (MMF)
which acts in a direction to oppose the flux created by the
permanent magnet 16 across the interface of the armature 18 and the
projection 30 of the flux-diverter 25. This causes the flux
developed by the permanent magnet 16 to take the alternate path
through the flux-diverter transversely extending base 26 and across
the air gaps 26 and 26B and through a portion of each of the side
wall members 28, 29 of the frame, to the end wall 17 and to the
opposite end wall of the permanent magnet member 16. The decrease
of net flux across the interface of the armature 18 and the
projection 30 of the flux-diverter member 25, when the trip signal
current is of sufficient predetermined magnitude, causes release of
the armature 18, which moves outwardly under the force of the
compression spring 21, causing it to engage a trip member, such as
member 40, associated with an electric circuit breaker, not shown.
Following such tripping, and at a desired time, the armature 18 is
reset by suitable means, not shown, to return it to its normal
inactive position as shown in FIG. 1.
In accordance with the invention, the cross-sectional dimension of
the armature 18 is selected with respect to the cross-sectional
dimension of the base 26 of the flux-diverter member 25 so that the
armature member 18 and the cylindrical portion 30 of the
flux-diverter 25 are saturated by such flux associated with an
excessively high trip current.
The saturation of the armature 18 and the cylindrical portion 30 of
the flux-diverter 25 by such excessive currents prevents such
currents from causing demagnetization of the permanent magnet 16,
since the reluctance of the flux-path for flux generated by the
trip coil 35 becomes very high, thereby reducing the flux available
to flow through the permanent magnet 16 in a direction opposite to
the inherent flux of the magnet 16.
In one embodiment of the invention having a form as illustrated in
FIGS. 1 and 2, the device had the following characteristics:
Overall length of frame proper 10, 12 11/2" Thickness of frame
material 1/8" Width of frame material 3/8" Permeability of frame
material 16 2000 Diameter of permanent magnet 3/8" length of
permanent magnet 5/8" Strength of permanent magnet 11,000 gauss
Permanent magnet material Alnico 5 manufactured by General Electric
Co., Edmore, Michigan Diameter of armature 18 5/16" Length of
armature 3/8" Air gaps 26A and 26B .030" Tripping coil 35-- 750
turns of No. 31 copper wire, resistance, 17 ohms d.c., 60 Hz
impedance 42 ohms. Length of cylindrical portion of flux-diverter
25 (from end to plane of nearest surface of portion 26) 1/8"
Thickness of portion 26 of flux-diverter 25 1/8" Strength of spring
21 in compressed condition 5 lb.
Tests of the embodiment described above demonstrated that the
device tripped repeatedly by energy delivered from a capacitor of 5
microfarads charged to a potential of 14 volts, or about 0.0005
joules of energy. Allowing for manufacturing tolerance variations,
etc., it is planned that tripping signal energy of about 0.001
joules will be provided. This compares with trip energy of about
0.02 joules, or about 20 times as much energy required by a similar
functioning comparable device presently on the market.
Tests of the above described embodiment also revealed that driving
the tripping coil with excessively high trip current, such as 100
times the value required to trip, did not cause any measurable
demagnetization of the permanent magnet. Thus, a device constructed
as described above was mounted in a General Electric 1,200 ampere
frame size circuit breaker. The secondary of a current-transformer
having a secondary-to-primary current ratio of 200 to 5 was
connected to the tripping coil of the trip device. A current pulse
of 16,000 amperes (rms) was passed through the current transformer
primary numerous times, each time causing tripping of the circuit
breaker. No reduction in magnetic flux level of the permanent
magnet could be detected.
The significant operational characteristics demonstrated in such
tests were that an input trip signal having a power of only about
0.0005 joules produced release of the armature, delivering a
tripping force of 5.0 pounds.
The illustrated construction of the frame of the preferred
embodiment illustrated comprises two generally L-shaped members as
described. Other formations may be utilized if desired, however,
such, for instance, as a generally U-shaped frame member with a
however, bridging end member. See, for example, the embodiment of
FIG. 3, to be described. The construction illustrated, comprising
two generally L-shaped members, is preferred, however, since it
provides two similar members, simplifying manufacture and
assembly.
In FIG. 3 there is illustrated another embodiment of the invention.
This embodiment is essentially similar to that of FIGS. 1 and 2
except that the flux-diverter 125 is in contact with the opposed
side walls 128 and 129 of the frame and has a hole centrally
thereof providing a generally circular air gap 125A of
approximately one-sixteenth inch. The interface of the permanent
magnet 116 and the armature 118 is substantially co-planar with the
surface of the flux-diverter 125, as shown. Also, the tripping coil
135 consisted of 800 turns of No. 33 copper wire.
Tests on the embodiment of FIG. 3 showed the following results:
Tripping coil current 0.20 amperes, giving 160 ampere turns.
Energy required to cause tripping, 5 milli-joules (0.005
joules).
While this embodiment is quite satisfactory for many applications,
it will be observed that the form of FIGS. 1 and 2 provides an
increase of sensitivity (decrease of energy required to trip) of
about 10:1, or 10 times. This great improvement is believed to be
due primarily to two things; (1) the location of the air gap at the
outer ends of the diverter base (gaps 26A and 26B), and (2) the
location of the interface of the permanent magnet and armature
within the trip coil 35 as shown in FIGS. 1 and 2. These changes
greatly reduce stray flux paths and improve the efficiency of the
device accordingly.
While only two specific embodiments of the invention have been
shown and described, it will be obvious that many modifications
thereof may readily be made. I, therefore, intend by the appended
claims to cover all such modifications as fall within the true
spirit and scope of the invention.
* * * * *