U.S. patent application number 12/610541 was filed with the patent office on 2010-02-25 for ac power distribution system with transient suppression and harmonic attenuation.
Invention is credited to Ullrich Joseph Arnold.
Application Number | 20100045109 12/610541 |
Document ID | / |
Family ID | 36073771 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100045109 |
Kind Code |
A1 |
Arnold; Ullrich Joseph |
February 25, 2010 |
AC Power Distribution System with Transient Suppression and
Harmonic Attenuation
Abstract
An AC power distribution unit for coupling AC power having a
fundamental frequency to a plurality of electrical loads has an
enclosure. A power input feed is retained by the enclosure for
coupling to a source of the AC power. A plurality of power output
feeds is retained by the enclosure for coupling to the plurality of
electrical loads. A harmonic mitigation module is retained in the
enclosure and is connected in series between the power input feed
and the plurality of power output feeds. The harmonic mitigation
module bilaterally reduces harmonic current distortion above a
predetermined frequency between the power input feed and the
plurality of power output feeds.
Inventors: |
Arnold; Ullrich Joseph;
(Northville, MI) |
Correspondence
Address: |
MACMILLAN SOBANSKI & TODD, LLC
ONE MARITIME PLAZA FIFTH FLOOR, 720 WATER STREET
TOLEDO
OH
43604-1619
US
|
Family ID: |
36073771 |
Appl. No.: |
12/610541 |
Filed: |
November 2, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10945420 |
Sep 20, 2004 |
7633772 |
|
|
12610541 |
|
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Current U.S.
Class: |
307/31 ;
307/105 |
Current CPC
Class: |
Y02E 40/40 20130101;
H02J 3/01 20130101 |
Class at
Publication: |
307/31 ;
307/105 |
International
Class: |
H02J 3/00 20060101
H02J003/00 |
Claims
1. An AC power distribution unit for coupling AC power having a
fundamental frequency to a plurality of electrical loads,
comprising: a wall-mounted enclosure; a power input feed in said
enclosure for coupling to a source of said AC power; a plurality of
power output feeds in said enclosure for coupling to said plurality
of electrical loads; and a harmonic mitigation module retained in
said enclosure and connected in series between said power input
feed and said plurality of power output feeds, said harmonic
mitigation module bilaterally reducing harmonic current distortion
with respect to said plurality of electrical loads above a
predetermined frequency between said power input feed and said
plurality of power output feeds while harmonic current is
distortion at said predetermined odd harmonic is substantially
unreduced.
2. The unit of claim 1 wherein said predetermined frequency is
comprised of a third harmonic of said fundamental frequency.
3. The unit of claim 1 further comprising: a surge suppression
device mounted within said enclosure and coupled to said power
output feeds for operating with said electrical loads.
4. The unit of claim 1 in a panelboard configuration further
comprising: a plurality of overcurrent protection elements mounted
within said enclosure, each overcurrent protection element
providing a respective power output feed.
5. The unit of claim 1 wherein said predetermined frequency is
comprised of a third harmonic of said fundamental frequency, and
wherein said unit further comprises: an isolating transformer
mounted within said enclosure and coupled between said power input
feed and said plurality of power output feeds, wherein said
isolating transformer substantially reduces said third
harmonic.
6. The unit of claim 1 in a point-of-use configuration further
comprising: a plurality of receptacles supported on said enclosure
and connected to respective power output feeds.
7. The unit of claim 6 further comprising: an isolating transformer
mounted within said enclosure and coupled between said power input
feed and said plurality of power output feeds, wherein said
isolating transformer is selected from the group comprising a
K-rated type transformer, and isolation type transformer, a zig-zag
type transformer, and a ferroresonant voltage regulator type
transformer.
8. The unit of claim 6 further comprising: a surge suppression
device mounted within said enclosure and coupled to said power
output feeds for operating with said electrical loads.
9. The unit of claim 1 wherein said harmonic mitigation module
comprises a line reactor.
10. The unit of claim 1 wherein said harmonic mitigation module
comprises a lowpass filter.
11. The unit of claim 1 wherein said harmonic mitigation module
comprises a choke filter.
12. An electrical panelboard for supplying AC power having a
fundamental frequency from an input power feed to electrical loads
on a plurality of branch circuits, said panelboard comprising: a
wall-mount enclosure; a phase bus in said enclosure; a plurality of
circuit breakers in said enclosure connected to said phase bus and
having an output terminal for coupling to a respective branch
circuit; a TVSS module in said enclosure coupled with said branch
circuits for lo suppressing transient voltages and surges to said
branch circuits; and a harmonic mitigation module in said enclosure
coupled with said branch circuits for bilaterally reducing harmonic
current distortion with respect to said electrical loads above a
predetermined frequency while harmonic current distortion at said
predetermined odd harmonic is substantially unreduced.
13. The electrical panelboard of claim 12 wherein said wall-mount
enclosure is adapted for flush mounting between standard wall
studs.
14. The electrical panelboard of claim 12 wherein said wall-mount
enclosure is adapted for surface mounting.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending application
Ser. No. 10/945,420, filed Sep. 20, 2004.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] The present invention relates in general to power
distribution systems, and, more specifically, to integrated
harmonic distortion cancellation and transient voltage surge
suppression within wall-mounted electrical distribution panelboards
and point-of-use devices.
[0004] In supplying electricity to a building, AC power from a
utility is connected via a service entrance to various types of
feeder panels and then on to electrical loads connected to branch
circuits. Many of the loads that may be supplied on the branch
circuits such as computers, electronic ballasts, variable frequency
drives, telecommunications equipment, and laboratory equipment, are
non-linear loads. It is known that such non-linear loads create a
power quality problem known as harmonic distortion because they
draw current at other than the frequency of the input AC voltage.
Total harmonic distortion, expressed as THD, is measured as a
percentage amount of distortion present on the current or voltage
sinewave.
[0005] Voltage transients or surges are a major problem affecting
sensitive electronics including microprocessor-controlled
equipment. Power conditioning devices known as transient voltage
surge suppression (TVSS) units or surge protection devices (SPDs)
are widely used to reduce this problem. SPDs, however, do not
remedy harmonic distortion. As the number of non-linear loads in
closely coupled electrical circuits increases, the increasing
amount of harmonic distortion can lead to malfunctions of sensitive
electronics. The problem of harmonic distortion is discussed in
I.E.E.E. Standard 519, "Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems".
[0006] Increased levels of harmonic current distortion contribute
to adverse thermal effects on electrical equipment. Examples of
this problem include premature failure of transformers and nuisance
tripping of breakers and fuses. This can even occur on circuits
where the actual load current would indicate that the circuit is
not overloaded.
[0007] Harmonic distortion causes current to flow on the neutral
conductor. In a balanced three-phase power system supporting linear
loads, very little current is normally present on the neutral
conductor. However, power systems that supply electrical power to
non-linear loads will always have current flowing on the neutral
conductor. The amount of current flowing in the neutral conductor
can potentially exceed the amount of current flowing in the phase
conductor with the most current load. Since there is no overcurrent
device on the neutral conductor this can create a serious problem.
In severe cases, harmonic distortion has been found to be the cause
of electrical fires in buildings.
[0008] Harmonic current distortion also causes distortion of the
voltage waveshape. This voltage distortion is measured as a
percentage of voltage THD. Excessive voltage THD can cause
microprocessor-controlled equipment to malfunction. IEEE Standard
519 states that voltage THD must be kept to less than 5% in order
to avoid such malfunctions.
[0009] For electrical loads such as variable frequency motor
drives, which create significant harmonic distortion, it is known
to reduce the distortion flowing back to the distribution system or
other loads by coupling a harmonic mitigation device in series with
the drive. Standalone components such as K-rated transformers and
zig-zag transformers are available for this purpose. For other
loads such as the switching DC power supplies in computers and
other electronics, the level of harmonic distortion created does
not justify the expense of deploying a harmonic mitigating
transformer with each load since the distortion from one such load
is unlikely to cause noticeable problems even though that
distortion propagates back up the branch circuit through its feeder
panel and then to loads in other branch circuits. When a greater
number of such loads are supplied by a feeder panel, however, the
cumulative harmonic current distortion of all the devices can
easily cause disruptive overheating problems and if left unchecked
will cause voltage harmonic distortion levels to approach and
exceed the 5% limit. The TVSS module often attached to or
integrated into a feeder panel only protects the loads from
transients and is ineffective in controlling the harmonic
distortion.
SUMMARY OF THE INVENTION
[0010] The present invention provides a cost effective and robust
solution to the problem of harmonic distortion within the
electrical distribution systems of buildings and other facilities
by integrating a harmonic attenuation function within feeder
panels. Thus, harmonic distortion from loads that may be connected
within any particular branch circuit will be substantially confined
to that branch circuit, and loads in that branch circuit will be
protected from harmonic distortion created in other branch
circuits.
[0011] In one aspect of the invention, an AC power distribution
unit for coupling AC power having a fundamental frequency to a
plurality of electrical loads comprises an enclosure. A power input
feed is retained by the enclosure for coupling to a source of the
AC power. A plurality of power output feeds is retained by the
enclosure for coupling to the plurality of electrical loads. A
harmonic mitigation module is retained in the enclosure and is
connected in series between the power input feed and the plurality
of power output feeds. The harmonic mitigation module bilaterally
reduces harmonic current distortion above a predetermined frequency
between the power input feed and the plurality of power output
feeds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram showing nonlinear loads coupled
with an electrical distribution panelboard or circuit breaker
panel.
[0013] FIG. 2 is a block diagram showing an example of an
electrical power distribution system for deploying the present
invention.
[0014] FIG. 3 is a diagrammatic view of a panelboard according to a
first embodiment of the invention.
[0015] FIG. 4 is a perspective view of the panelboard of FIG.
3.
[0016] FIG. 5 is a schematic view of a panelboard of the
invention.
[0017] FIG. 6 is a partially broken-away plan view of a
point-of-use unit of the present invention.
[0018] FIG. 7 is a block diagram showing a power conditioning unit
of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0019] Referring now to FIG. 1, an electrical distribution system
subject to harmonic distortion problems includes a panelboard 10
coupled to nonlinear loads 11-15. The nonlinear loads can be any
arbitrary loads such as electronic lighting ballasts, switching
power supplies for computers or other electronic equipment. Another
nonlinear load comprises a variable frequency drive (VFD) 16
powered by panelboard 10. It is known to limit harmonic distortion
that propagates from a VFD to other devices by introducing a
harmonic mitigating device 17 to the electrical distribution system
between VFD 16 and panelboard 10. Harmonic mitigating device 17 may
typically comprise a transformer (such as a zig-zag transformer for
canceling harmonic distortion) or a load reactor or a line reactor,
for example. Although the known harmonic mitigating device 17
reduces harmonic distortion that propagates from VFD 16 to other
devices, harmonic distortion to or from nonlinear loads 11-15 is
not addressed by the prior art electrical distribution systems. The
problems associated with harmonic distortion are especially severe
in distribution systems with multiple panelboards having many
branch circuits or in multiple phase systems that supply nonlinear
loads and that also supply power to a large number of unprotected
sensitive electronic loads.
[0020] FIG. 2 shows an overall electrical distribution system
architecture in which the present invention may be employed.
Utility power is provided to a switchgear 20, which in turn
supplies electrical power to a building 21. The building service
entrance comprises a disconnect 22, a transformer 23, and a
switchboard 24. Switchboard 24 supplies panelboards 25 and 26.
[0021] One configuration of the present invention incorporates an
electrical distribution panelboard or circuit breaker panel with
harmonic mitigation (e.g., harmonic filtering) at the branch supply
level for plug-in or hardwired single or 3-phase loads. An
integrated harmonic mitigation module is placed in series with all
loads supplied by the respective distribution unit of the
invention, as described in more detail below.
[0022] The present invention is especially advantageous when
implemented within a panelboard (e.g., load control center), such
as panelboard 25 in FIG. 2. Panelboard 25 has a first branch
circuit to which loads 27-29 are connected and a second branch
circuit to which loads 30 and 31 are connected. The loads may
comprise any combination of linear or nonlinear loads. Conventional
wiring and receptacles are provided for connecting any arbitrary
loads as is known in the art.
[0023] The present invention may also be implemented at a
distribution level below that of the panelboard, either alone or in
combination with harmonic mitigation also being obtained at the
panelboard level. Thus, panelboard 26 has a first branch circuit
connected to a point-of-use (POU) device which contains plug-in
receptacles for connecting with loads 33 and 34. POU device 32
includes a harmonic mitigation module for use in connecting with
electrical devices which may not themselves provide harmonic
distortion mitigation, may be a source of harmonic distortion, or
may be sensitive electronic devices requiring protection from
harmonic distortion created by other devices located elsewhere on
the electrical distribution system. Panelboard 26 has a second
branch circuit to which loads 35 and 36 are connected. Yet another
embodiment of the invention is depicted by power conditioner 37
which is also connected to panelboard 26 in this branch circuit and
drives a nonlinear load 38. Power conditioner 37 incorporates a
harmonic mitigation module and is similar to POU device 32 except
that it lacks receptacles (i.e., load 38 is hardwired to power
conditioner 37).
[0024] Panelboards have certain size limitations because of their
typical wall mounting (e.g., flush or surface mounting to wall
studs). In addition to the normal function of providing overcurrent
protection using circuit breakers or fuses, panelboards frequently
incorporate an integral surge protection device within its
enclosure. By locating the surge protection device closer to the
input power feeds and farther from the loads, enhanced surge
protection can be obtained. In contrast, the prior art has sought
to place harmonic mitigation devices as close as possible to the
nonlinear loads generating the harmonic distortion. In addition,
harmonic mitigating devices such as transformers tend to be rather
bulky and have been placed in their own enclosure or in the same
enclosure as the protected device.
[0025] FIG. 3 shows one preferred embodiment of the present
invention in greater detail wherein a harmonic mitigation module 40
is integrated in a panelboard 41. Panelboard 41 is mounted to studs
42 and 43 within a wall. Three-phase power is provided to a main
circuit breaker 44 (e.g., by wires routed into panelboard 41) and
to harmonic mitigation module 40. Harmonic mitigation module 40 is
a three-phase device which couples the three phases to load line
feeders (or phase busses) 45, 46, and 47. Load line feeders 45-47
may comprise busbars, for example. A plurality of overcurrent
devices (e.g., circuit breakers) 50 are coupled to respective ones
of load line feeders 45-47 for connection to separate branch
circuits in a conventional manner. A TVSS module 51 is also coupled
to each load line feeder. Neutral and ground structures 52 and 53
are also deployed in panelboard 41 as is known in the art.
[0026] Input power is provided to panelboard 41 typically having a
fundamental frequency of 60 Hertz. The nonlinear loads create
harmonic distortion mainly at odd harmonics of this fundamental
frequency. Depending upon the types of loads, significant
distortion may or may not be created at the third harmonic. In a
single-phase uninterruptable power supply, for example, the third
harmonic may be the largest component of the current distortion. In
some cases, overall total harmonic current may be nearly equal in
magnitude or exceed the fundamental current. In some three-phase
devices, on the other hand, the greatest harmonic component may be
at the fifth harmonic. Although certain types of line reactors or
other lowpass filters can be provided for mitigating the fifth
harmonic and above without requiring a large package size,
mitigating the third harmonic typically requires bulky components
such as a transformer.
[0027] In one preferred embodiment of the invention, harmonic
mitigation module 40 is comprised of a filter such as a choke, a
line reactor, or other lowpass filter impedance in a configuration
that greatly reduces odd order harmonic current distortion at above
the third harmonic frequency (i.e., at the fifth harmonic and
above) but that leaves harmonic current at the third harmonic
frequency substantially unreduced. Thus, problems of harmonic
current distortion propagating within an electrical distribution
system and creating harmonic voltage distortion may be greatly
reduced with a device that can be packaged within a normal
panelboard enclosure suitable for wall mounting. Most commercially
available line reactors are dimensioned such that packaging within
the depth of a standard enclosure may not be feasible. However,
high volume production designs are easily modifiable to provide the
same electrical properties in a package size that can be
accommodated in a standard enclosure. A line reactor can be used
having the electrical performance of the Guard-AC line reactor from
MTE Corporation or similar line reactors from suppliers such as
Mag-Tran Equipment Corporation, L/C Magnetics, Trans-Coil, Inc.,
and Myron Zucker, Inc. The line reactor is preferably hardwired
between a power input feed and the power busbars of a conventional
panelboard enclosure. The height of an enclosure may need to be
increased in order to package the harmonic mitigation module, but
the enclosure thickness and width are unmodified so that the
enclosure can still be located between the studs of a standard
framed wall.
[0028] FIG. 4 shows a perspective view of panelboard 41 wherein the
enclosure includes a dead front 55 connected to a box 56. An access
door 57 is mounted to dead front 55 and may be opened to gain
access to overcurrent devices 50. Harmonic mitigation module 40,
main breaker 44, and TVSS module 51 are all mounted in box 56
behind dead front 55. Thus, panelboard provides front only
access.
[0029] Referring now to FIG. 5, a schematic view of the invention
illustrates input power feeds being coupled to main breaker 44 in a
three-phase, four-wire system. By way of example, harmonic
mitigation module 40 could be comprised of a three-phase line
reactor with individual inductors connected in series in each phase
to a respective phase bus 45, 46, and 47. A circuit breaker 50
mounts to phase bus 45 and provides an output feed to a respective
branch circuit.
[0030] Since harmonic mitigation module 40 is connected in series
with any loads connected to panelboard 41, harmonic current
distortion is bilaterally reduced and prevented from spreading
within the electrical distribution system. As previously described,
line reactors are one preferred type of harmonic mitigation device
in view of their ability to reduce fifth order harmonics and higher
in a package size that is easily accommodated in a panelboard
enclosure. In addition, other types of lowpass filters can be
employed, either active or passive. Furthermore, the present
invention may be employed in other distribution enclosures such as
a point-of-use device with output receptacles or a hardwired output
for specific loads.
[0031] FIG. 6 shows a point-of-use (POU) device 60 including an
enclosure 61 which preferably may be wall mounted (e.g., surface
mounted) but may also be floor mounted or suspended in a ceiling,
for example. A power input feed 62 is coupled to an optional
isolating transformer 63 connected to harmonic filter 64. Isolating
transformer 63 may comprise a K-rated type transformer, a shielded
isolation type transformer, a zig-zag type transformer, or a
ferroresonant voltage regulator type transformer, for example.
Among other things, isolating transformer 63 may attenuate noise
energy propagating through the point-of-use unit and reduce the
harmonic current distortion at the third harmonic frequency. An
optional TVSS module 65 is connected to the output of harmonic
filter 64 in parallel with a plurality of receptacles 66-68. An
overcurrent device (e.g., fuse block or circuit breaker) for TVSS
module 65 may also be included depending upon the type of TVSS
module used.
[0032] FIG. 7 shows an alternative embodiment of a power
conditioning device 70 similar to POU 60, but lacking output
receptacles. Instead, a dedicated hardwired output 71 is
employed.
* * * * *