Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2000-03-17
2003-09-30
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C324S424000, C703S018000, C700S097000
Reexamination Certificate
active
06629044
ABSTRACT:
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
The present invention is directed to an electrical distribution selectivity analysis method and apparatus.
Power distribution devices are well known in the art. In typical power distribution systems, selectivity is desired generally to minimize nuisance tripping.
FIG. 1
generally shows a two tier selective system
40
. Selective system
40
comprises a source
41
, an upstream protection device
42
, a downstream protection device
44
coupled to a load
45
, and a downstream protection device
46
coupled to a load
47
. Any number of additional downstream protection devices
44
with corresponding loads
47
may be included in system
40
. Generally, each protection device
42
,
44
or
46
is a circuit interrupter (e.g., in a single phase power system) or a multiple pole circuit breaker (e.g., in a multiple phase power system). These circuit breakers can be any type, including but not limited to low voltage, medium voltage, high voltage, air, or vacuum breakers for residential, commercial or industrial uses. Source
41
is any power source or combination of power sources including but not limited to outside power feeds, generators, transformers, or uninterruptible power supplies. Loads
45
,
47
can be any load or combination of loads including but not limited to motors, lamps, ballasts.
A conventional circuit breaker includes a pair of contacts which allows circuit current to pass from one contact member to another contact member. An objective of these devices is to carry nominal rated current at very low loss and have momentary circuit current withstand levels, commonly referred to as “popping levels”. A withstand level is generally the level of circuit current that may pass through the circuit breaker before a fault condition is realized causing the contacts to open to prevent circuit current from passing through the contacts. When the contacts open, circuit current is prevented from flowing from one contact member to the other and therefore, circuit current is prevented from flowing to a load which is connected to the device. By having these momentary circuit current withstand levels, operation under high inrush loads, common with motors and transformers, is permitted. Accordingly, these devices need to have momentary circuit current withstand levels so that they may be properly used with such high inrush loads to protect the loads and the overall electrical system.
Downstream device
44
is rated to meet the demands of load
45
, e.g., 20×(twenty times) rated circuit current maximum. When load
45
exceeds this rating, which is likely only when a fault occurs, device
44
would then rapidly transition to a current limiting position. In the current limiting position, downstream device
44
has a reduced circuit current let-thru which in turn reduces stresses on the entire system
40
. By reducing these stresses on system
40
, the devices of load
45
are also protected and this is of particular interest if load
45
has a motor starter in the circuit thereof.
FIG. 2
is a plot of peak let-thru current versus prospective current of downstream device
44
and upstream device
42
in a current limiting position in accordance with the present invention. Downstream device
44
is in a current limiting position when device
44
is under fault conditions which are circuit current conditions substantially above the withstand level. In this position, downstream device
44
keeps the let-thru circuit current below the withstand level of the upstream device
42
, as shown in FIG.
2
. Because upstream device
42
can be of the same design as downstream device
44
and have a high withstand, it does not trip and the remainder of the system
40
remains in service. If upstream device
42
did not have a sufficiently high withstand level, then upstream device
42
would be prone to tripping and such tripping would cause the remainder of the system
40
to be out of service. By reducing the circuit current let-thru, downstream device
44
reduces the stresses on the entire system
40
and thereby protects the devices of load
47
as well. The plots represented on
FIG. 2
represent ideal system behavior. Even if the ideal behavior is not attained, selectivity is still possible generally as long as the let-through of downstream device
44
remains below the trip response of upstream device
42
. However, in non-ideal systems, the behavior cannot be analyzed with conventional techniques because the current through downstream device
46
will also be effected by the voltage generated by the upstream device.
Turning now to
FIGS. 3 and 4
, an exemplary multi-pole circuit breaker
50
that can be an upstream protection device
42
, a downstream protection device
44
, and/or a downstream protection device
44
are shown. Circuit breaker
50
generally includes a molded case including a top cover
52
, a mid cover
54
and a base
56
. A plurality of cassettes
58
,
60
and
62
are disposed within base
56
. An operating mechanism
64
is disposed atop cassette
60
. Cassettes
58
,
60
and
62
are commonly operated via a set of cross bars
66
,
68
. The crossbar
66
is disposed through an opening
70
in a portion of operating mechanism
64
.
A line side contact strap
72
and a load side contact strap
74
extends from each cassette
58
,
60
and
62
for connection with a power source and a protected circuit and/or load, respectively. A current transformer
76
is arranged relative to each line side contact strap
72
. Current transformer
76
is coupled (not shown) to a trip unit
78
positioned within mid cover
54
. Optionally, a rating plug (not shown) can be interfaced with trip unit
78
to change the settings of circuit breaker
50
.
Trip unit
78
includes an actuator
80
. Actuator
80
can be, for example, a flux actuator that operates substantially as described in U.S. Pat. No. 6,211,758 entitled “Circuit Breaker Accessory Gap Control Mechanism”, U.S. Pat. No. 6,172,584 entitled “Circuit Breaker Accessory Reset System”, and in U.S. Pat. No. 6,211,757 entitled “Flux Actuator”.
Operating mechanism
64
includes a toggle handle
82
extends through openings within top cover
52
and mid cover
54
. Toggle handle
82
provides external operation of operating mechanism
64
. Operating mechanism
64
operates substantially as described in U.S. Pat. No. 6,346,868 entitled “Circuit Interrupter Operating Mechanism” and in U.S. Pat. No. 6,087,913 entitled “Circuit Breaker Mechanism for a Rotary Contact Assembly”.
Cassettes
58
,
60
,
62
are typically formed of high strength plastic material and each include opposing sidewalls
84
,
86
. Sidewalls
84
,
86
have a pair of arcuate slots
88
,
90
positioned and configured to receive and allow the motion of cross bars
66
,
68
by operating mechanism
64
. Examples of a rotary contact structures that may be operated by operating mechanism
64
are described in more detail in U.S. Pat. No. 6,114,641 entitled “Rotary Contact Assembly For High-Ampere Rated Circuit Breakers” and U.S. Pat. No. 6,396,369, entitled “Laterally Moving Line Strap”, U.S. Pat. No. 6,175,288 entitled “Magnetic Supplemental Trip For A Rotary Circuit Breaker”, and U.S. Pat. No. 6,366,438 entitled “Rotary Contact Arm”.
Referring now to
FIG. 5
, a partial view of the inside of a cassette similar to cassettes
58
,
60
,
62
is shown. Each cassette
58
,
60
,
62
includes a rotary contact assembly
92
. Rotary contact assembly
92
is disposed intermediate to line side contact strap
72
and load side contact strap
74
. Line side contact strap
72
and load side contact strap
74
are configured as U-shaped reverse loop conductor straps. Line side contact
Elasser Ahmed
Papallo, Jr. Thomas F.
Ramakrishnan Sriram
Barlow John
Cantor & Colburn LLP
General Electric Company
Le John
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