U.S. patent application number 10/121558 was filed with the patent office on 2002-08-15 for uninterruptible power generation system.
Invention is credited to Alegria, Eduardo A., Potter, David S..
Application Number | 20020109411 10/121558 |
Document ID | / |
Family ID | 23925106 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020109411 |
Kind Code |
A1 |
Potter, David S. ; et
al. |
August 15, 2002 |
Uninterruptible power generation system
Abstract
A power delivery system is disclosed including a primary power
bus for transferring power to the facility from on-site generators,
and a secondary power bus for transferring power to the facility
from a utility. The system further includes a static disconnect
switch capable of quickly isolating the facility from the utility
power grid, and a controller for controlling the overall operation
of the power delivery system. In a normal mode of operation, the
utility supplies power approximately in the amount of the single
largest load in the facility, with the remaining power being
supplied by the on-site generators. If one or more of the
generators go off-line, the power supply from the utility may be
increased. Similarly, if the quality of the power supplied by the
utility drops below a predetermined level, the static disconnect
switch quickly opens and islands the facility, whereupon 100% of
the power is supplied by the generators.
Inventors: |
Potter, David S.; (Oakland,
CA) ; Alegria, Eduardo A.; (San Mateo, CA) |
Correspondence
Address: |
ChevronTexaco Corporation
Law Department
Intellectual Property Unit
P.O. Box 6006
San Ramon
CA
94583-0806
US
|
Family ID: |
23925106 |
Appl. No.: |
10/121558 |
Filed: |
April 11, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10121558 |
Apr 11, 2002 |
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09484669 |
Jan 18, 2000 |
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6404075 |
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Current U.S.
Class: |
307/64 |
Current CPC
Class: |
H02J 9/06 20130101 |
Class at
Publication: |
307/64 |
International
Class: |
H02J 007/00 |
Claims
We claim:
1. An uninterruptible power delivery system for supplying a power
load of a facility within a high quality power range, said high
quality power range being power within a predetermined voltage
range, a predetermined frequency range and not being interrupted
for more than a cycle, the uninterruptible power delivery system
comprising: a primary power supply from at least one generator
located on-site to the facility; and a secondary power supply from
a utility.
2. An uninterruptible power delivery system as recited in claim 1,
wherein said at least one generator is capable of supplying 100% of
the power load of the facility in the event said secondary power
supply from said utility deviates outside of said high quality
range.
3. An uninterruptible power delivery system as recited in claim 1,
wherein the facility islands in the event said secondary power
supply from said utility deviates outside of said high quality
range.
4. An uninterruptible power delivery system as recited in claim 3,
wherein said utility supplies power in a range large enough to
prevent power flow to a grid supplied by the utility in the event
of a drop in the power load of the facility, and small enough to
allow said at least one generator to supply 100% of the facility
load without tripping upon said islanding of said facility.
5. An uninterruptible power delivery system as recited in claim 1,
further including a switch capable of islanding the facility in
less than a cycle in the event said secondary power supply from
said utility deviates outside of said high quality range.
6. An uninterruptible power delivery system as recited in claim 1,
wherein said at least one generator supplies between 80% and 98% of
the power load of the facility and said utility supplies between
20% and 2% of the power load of the facility during normal
operation.
7. An uninterruptible power delivery system as recited in claim 6,
wherein said utility is capable of supplying more than 20% of the
power load of the facility in the event that one or more of said at
least one generator is off-line.
8. An uninterruptible power delivery system as recited in claim 6,
wherein said utility is capable of supplying 100% of the power load
of the facility in the event that one or more of said at least one
generator is off-line.
9. An uninterruptible power delivery system as recited in claim 1,
wherein the facility load is y kilowatts, and the single largest
load in the facility is x kilowatts, said at least one generator
supplying ((y-x)/y).times.(100%) of the power load of the facility
and said utility supplies (x/y).times.(100%) of the power load of
the facility during normal operation of the power delivery
system.
10. An uninterruptible power delivery system as recited in claim 9,
wherein said at least one generator supplies y kilowatts in the
event power from said utility drops outside of said high quality
range.
11. An uninterruptible power delivery system as recited in claim 9,
wherein said utility supplies y kilowatts in the event power from
said at least one generator drops outside of said high quality
range.
12. An uninterruptible power delivery system as recited in claim 1,
further comprising a controller for controlling the operation of
the power delivery system.
13. An uninterruptible power delivery system as recited in claim 1,
wherein said at least one generator generates waste heat in
addition to power, said waste heat being supplied to the facility
for use by the facility.
14. An uninterruptible power delivery system as recited in claim 1,
wherein the power delivery system does not include a short term
stored power supply.
15. An uninterruptible power delivery system for supplying a power
load of a facility within a high quality range, said high quality
range being power within a predetermined voltage range, a
predetermined frequency range and not being interrupted for more
than a cycle, the uninterruptible power delivery system comprising:
a primary power supply from at least one generator located on-site
to the facility; a secondary power supply from a utility; and a
static disconnect switch for isolating the facility from the power
supply from said utility in less than a cycle in the event power to
the facility from the utility is outside of said high quality
range.
16. An uninterruptible power delivery system as recited in claim
15, wherein said at least one generator is capable of supplying
100% of the power load of the facility in the event said secondary
power supply from said utility deviates outside of said high
quality range.
17. An uninterruptible power delivery system as recited in claim
15, wherein the facility islands in the event said secondary power
supply from said utility deviates outside of said high quality
range.
18. An uninterruptible power delivery system as recited in claim
17, wherein said utility supplies power in a range large enough to
prevent power flow to a grid supplied by the utility in the event
of a drop in the power load of the facility, and small enough to
allow said at least one generator to supply 100% of the facility
load without tripping upon said islanding of said facility.
19. An uninterruptible power delivery system as recited in claim
15, wherein said at least one generator supplies between 80% and
98% of the power load of the facility and said utility supplies
between 20% and 2% of the power load of the facility during normal
operation.
20. An uninterruptible power delivery system as recited in claim
19, wherein said utility is capable of supplying more than 20% of
the power load of the facility in the event that one or more of
said at least one generator is off-line.
21. An uninterruptible power delivery system as recited in claim
15, wherein the facility load is y kilowatts, and the single
largest load in the facility is x kilowatts, said at least one
generator supplying ((y-x)/y).times.(100%) of the power load of the
facility and said utility supplies (x/y).times.(100%) of the power
load of the facility during normal operation of the power delivery
system.
22. An uninterruptible power delivery system as recited in claim
21, wherein said at least one generator supplies y kilowatts in the
event power from said utility drops outside of said high quality
range.
23. An uninterruptible power delivery system as recited in claim
21, wherein said utility supplies y kilowatts in the event power
from said at least one generator drops outside of said high quality
range.
24. An uninterruptible power delivery system as recited in claim
15, further comprising a controller for controlling the operation
of the power delivery system.
25. An uninterruptible power delivery system as recited in claim
15, wherein said at least one generator generates waste heat in
addition to power, said waste heat being supplied to the facility
for use by the facility.
26. An uninterruptible power delivery system as recited in claim
15, wherein the power delivery system does not include a short term
stored power supply.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a large scale power supply
system, and in particular to an uninterruptible power supply system
providing high quality power through a system including a primary
on-site power supply, secondary utility power supply and a rapid
switching response to island the facility in the event of utility
power quality disruptions.
[0003] 2. Description of the Related Art
[0004] Primary power supply for facility operation and home usage
is conventionally provided by government regulated power utilities,
such as for example PG&E in northern and central California. It
is a goal of utilities to provide low cost, high quality power to
service subscribers' energy needs. High quality power is power that
is continuously available at a relatively constant voltage and
frequency. Most homes and some small facilities rely solely on
utilities for their power needs. However, it is more common, at
least in facilities, to employ some sort of emergency backup power
generation system in the event the voltage and/or frequency of the
utility supplied power fluctuates outside of acceptable ranges, or
fails entirely. Emergency backup systems in general minimize health
and safety risks to facility personnel and occupants, and ensure
continued satisfactory operation of the facility when power supply
from the utility is inadequate or fails. Moreover, certain
facilities require an uninterrupted supply of power to prevent
damage to facility systems and/or the loss of critical data. Such
facilities include semiconductor wafer fabs, automated
manufacturing plants and those employing data processing systems.
Uninterrupted power supplies are also often necessary m a wide
variety of facility control systems. Power failure to such facility
systems for even a second or two can be extremely disruptive,
damaging and dangerous.
[0005] There are several conventional emergency backup power supply
schemes. A first such system, shown in FIG. 1, employs a battery 10
(or battery bank), a battery rectifier/charger 12 and an emergency
AC bus 14. The rectifier/charger 12 is provided for converting the
current to the battery from AC to DC and for charging the battery.
An inverter 11 is also provided for converting the current leaving
the battery from DC back to AC. If power from the utility 16 is
inadequate or fails entirely, a control system 18 switches the
power feed to the battery. This type of system has the advantage
that the power supply may be switched over from the utility to the
battery in less than a cycle. However, such systems can only supply
power for short periods of time, and are not practical for long
term uninterrupted power supply (e.g., more than a few minutes).
Moreover, these systems themselves consume a relatively large
amount of power and are extremely expensive to operate in megawatt
power applications.
[0006] Another emergency backup power supply system, shown in FIG.
2, employs a generator 20. The generator includes a motor which
burns a working fluid, such as gasoline, natural gas or diesel oil,
to produce a mechanical output force. This mechanical output force
is then used to rotate conductive coils in the presence of a
stationary magnetic field, or visa-versa, to create electrical
energy in the windings. If power from the utility 16 is inadequate
or fails entirely, the engine runs the generator 20 to produce
power, and when the voltage and frequency of the output power
reaches acceptable levels, a control system 18 activates a transfer
switch 24 to supply the load from the generator. While such systems
may run for long periods of time, a significant drawback to backup
generators is that they take several seconds until the power can
properly supply the load. As such, use of a generator as a backup
power system is not feasible for facilities requiring
uninterruptible power supply.
[0007] Perhaps the most common emergency backup power supply system
for uninterruptible power applications is a combination of the
systems of FIGS. 1 and 2 to provide an uninterruptible power
supply. In particular, upon the voltage or frequency of the utility
power supply fluctuating outside of acceptable levels, power is
switched to a temporary power supply such as the battery system.
The battery system supplies the load until the output from the
backup generator is at acceptable levels, at which point the power
supply is switched over to the generator. Instead of the battery
system, it is also known to have a temporary power supply in the
form of a continuously running motor fed by the utility and
including a flywheel with a high moment of inertia. If the utility
power fails or falls below acceptable levels, the facility load is
switched to the motor, which supplies power from the kinetic energy
stored in the motor. As the kinetic energy is dissipated, the
backup generator is brought on-line, and once the power output from
the backup generator is at acceptable levels, the power supply is
switched over to the generator. Each of these combination systems
requires implementation, maintenance and control of additional
systems. Moreover emergency backup systems employing short term
supplies (such as the above-described battery and flywheel) are
expensive to operate. The short term supply system can often cost
approximately two-thirds of the overall cost of the power supply
system.
[0008] It is also known, as shown in FIG. 3, to have a primary feed
22 and secondary feed 24 to the power utilities. While this is
satisfactory for uninterrupted power supply, a second connection to
a power utility is expensive to implement and maintain. Moreover, a
second connection is often unavailable.
[0009] A common feature in known power supply systems is that the
primary facility load is supplied by the utility. Moreover, such
power supply systems employing emergency backup power supply for
megawatt applications conventionally include short term power
supply components, which as indicated above are expensive to
maintain. There is at present a need for an alternative power
supply system capable of supplying low cost, high quality power on
demand to facilities which require an uninterruptible power
supply.
SUMMARY OF THE INVENTION
[0010] It is therefore an advantage of the present invention to
provide a novel uninterruptible power supply system.
[0011] It is another advantage of the present invention to provide
low cost, high quality power for megawatt applications.
[0012] It is a further advantage of the present invention to
provide an uninterruptible power supply that includes no short term
power supply, together with an attendant reduction in cost.
[0013] It is a further advantage of the present invention that the
primary source of facility power supply is located on-site.
[0014] It is another advantage to provide a high level of power
quality in part through a rapid switching response to island the
facility in the event a power quality event degrades the power
received from the utility.
[0015] It is a still further advantage of the present invention to
provide significant cogeneration opportunities for servicing other
facility needs.
[0016] It is another advantage of the present invention is to allow
the power supply to be controlled by the facility instead of the
utility.
[0017] It is a still further advantage of the present invention
that conventional power delivery systems may be easily converted to
operate in accordance with the principals of the present
invention.
[0018] These and other advantages are provided by the present
invention which in preferred embodiments relates to a power
delivery system including a primary power bus for transferring
power to the facility from on-site generators, and a secondary
power bus for transferring power to the facility from a utility.
The system further includes a static disconnect switch capable of
quickly isolating, or "islanding", the facility from the utility
power grid, and a controller for controlling the overall operation
of the power delivery system.
[0019] The utility preferably provides a small, constant power flow
to supplement the primary generator power supply in a normal mode
of operation. In setting the precise relative contributions of the
on-site generators and utility in a normal mode of operation, the
utility power supply should be low enough that the generators can
handle the facility islanding at any time upon a drop in power
quality from the utility. At the same time however, the utility
power supply should be high enough to prevent frequent tripping of
the reverse power relay (at least in the United States) and to
prevent acceleration of the generators upon a drop in facility
load.
[0020] In a normal mode of operation, these factors are balanced by
the utility supplying power approximately in the amount of the
single largest load in the facility, with the remaining power being
supplied by the on-site generators. Setting the power draw from the
utility less than this presents the risk that power will attempt to
flow into the utility power grid in the event that high-load
facility component goes off-line. Setting the power draw from the
utility much higher than this presents the risk that the generators
will be unable handle the initial load upon a drop in power from
the utility and islanding of the facility.
[0021] If a generator goes off-line, the additional power may come
from the other generators, in the event a redundant generator
system is employed, or the additional power may come from the
utility. In the event a redundant generator system is used, the
controller controls the operation of the generators to make up the
power from the off-line generator. Where there are no redundant
generators, or during the time that the redundant generator or
generators are brought on-line, additional power is automatically
drawn from the utility to supply the load without separate
protocols in the controller. In the unlikely event that each of the
generators goes off-line, 100% of the facility load may be supplied
by the utility.
[0022] Should there be a drop in the quality of power from the
utility, this event is detected by sensors in communication with
the static disconnect switch controller, and the switch opens in
less than a cycle to thereby island the facility from the utility
power grid so that 100% of the facility load is supplied by the
on-site generators. This protects the facility against utility
power quality disruptions and the rapid switch over allows the
power supply system according to the present invention to
continuously provide a high level of power quality to the
facility.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present invention will now be described with reference
to the drawings in which:
[0024] FIG. 1 is a prior art schematic representation showing an
emergency backup power supply system including a primary feed from
a utility and a secondary feed from a battery;
[0025] FIG. 2 is a prior art schematic representation showing an
emergency backup power supply system including a primary feed from
a utility and a secondary feed from a generator;
[0026] FIG. 3 is a prior art schematic representation showing an
emergency backup power supply system including two feeds from a
utility;
[0027] FIG. 4 is a graphic representation of the power delivery
system according to the present invention operating in a normal
mode of operation;
[0028] FIG. 5 is a schematic representation of the power delivery
system shown in FIG. 4;
[0029] FIG. 6 is a schematic representation of a portion of the
power delivery system shown in FIG. 4;
[0030] FIG. 7 is a graphic representation of the power delivery
system according to the present invention operating under a utility
power grid event; and
[0031] FIG. 8 is a graphic representation of an alternative
embodiment of the power delivery system according to the present
invention where both the utility and the generator bank are
monitored for a power quality event.
DETAILED DESCRIPTION
[0032] The present invention will now be described with reference
to FIGS. 4-8 which in general relate to a low cost, high quality,
uninterruptible power delivery system employing parallel operation
of an on-site primary power supply and an emergency backup power
supply from a power utility. Referring specifically to the graphic
representation shown in FIG. 4, a facility 100 receives power from
a power delivery system 102 according to the present invention,
which includes a primary power bus 103 for transferring power to
the facility from on-site generators 104, and a secondary power bus
106 for transferring power to the facility from a utility 108. The
system further includes a static disconnect switch 110 capable of
quickly isolating the facility 100 from the utility power grid (a
condition known as islanding) and a controller 112 for controlling
the overall operation of power delivery system 102. In a preferred
embodiment of the present invention, power delivery system 102
supplies high power loads of approximately one or more
megawatts.
[0033] During normal operation of the system, the facility power
load is serviced primarily from the on-site generators 104 which
are run continuously. The remaining facility load is supplied by
power from the utility. The factors which determine the relative
contribution from the on-site generators 104 and utility 108 in a
normal mode of operation will be explained hereinafter.
[0034] The generators 104 for use with the present invention are
high efficiency generators of known construction, and may be for
example those produced by Caterpillar, Inc., 100 N.E. Adams, Peoria
Ill. 61629 under Model No. G3516 which run on natural gas and are
rated at 820 KW at 60 Hz. It is understood that a wide variety of
other generators may be used in accordance with the present
invention as the primary power supply for system 102. For example,
it is contemplated that on-site diesel or gasoline generators or
on-site gas turbines may used in alternative embodiments. The power
may alternatively be supplied by fuel cells. It is further
contemplated that a generator bank employing different types of
generators be used. The number and type of generators 104 used in a
given power delivery system 102 will depend on the size of the
facility receiving power from the system 102, as well as the
location of the facility and the availability of the various
generator fuels. It is also contemplated that redundant generators
104 be used so that, in the event of maintenance or failure of one
or more of the primary generators, the spare generators may be
brought on-line. As shown in FIG. 5, conventional generator
protection protocols may be employed for preventing electrical
faults, power surges and other conditions from damaging the
generators. Such generator protection protocols include for example
circuit breakers 113, grounding reactors 114, over-current and
over-voltage relays and directional/power relays.
[0035] Generators 104 preferably output power at the frequency
rating of the facility, for example 60 Hz in the United States. The
voltage output from generators 104 may match that received on
secondary bus 106 from the utility. Alternatively, one or more
transformers 118 may be employed for stepping up and/or down the
voltage to match that of the voltage received on secondary bus 106
from the utility. A transformer 118 may additionally or
alternatively be provided on secondary bus 106 for changing the
voltage from the utility 108.
[0036] Automatic electromechanical disconnect switches generally
take on the order of between 4 to 20 cycles to transfer power
supply. While this is acceptable for most facilities, it is not
acceptable for those which require an uninterruptible power supply.
In particular, it is a problem with conventional switches used in
high power applications that upon a grid related event such as an
electrical short, voltage in the grid drops drastically. As
conventional electromechanical switches are slow to respond, the
electrical short in the grid will drastically reduce the facility
voltage. In this event, the kinetic energy from the engines driving
the generators will exceed the power being drawn from the
generators by the facility load, and the generators will
accelerate. This acceleration will increase the frequency of the
power from the generators and may cause the generators to shut
down. Thus, when the conventional switch finally opens, it is too
late because the generators have already accelerated owing to the
drop in the facility voltage.
[0037] This problem is solved in the present invention by use of
the static disconnect switch 110 for quick islanding of the
facility. In the event of a grid related event such as a short, the
switch opens in less than a cycle. Thus, there is no power mismatch
in the generators and they remain in step with the facility load.
This rapid switching response in part accounts for the high level
of power quality provided by the present invention in that the
facility is protected against utility power quality
disruptions.
[0038] Static disconnect switch 110 is a solid state switch of
known construction, and is capable of switching in one-quarter
cycle or less from normal operation to an operational mode where
the facility load is supplied completely from generators 104. A
static disconnect switch 110 of a type for use with the present
invention is manufactured for example by Inverpower Controls Ltd.,
835 Harrington Court, Burlington, Ontario, Canada L7N-3P3, and
includes a number of thyristors and/or transistors 120 for
controlling current flow through the switch, and a static
disconnect controller (not shown) which preferably operates
independently of the overall controller 112 to open and close the
switch. It is understood that other switches exhibiting similar,
subcycle response times may be used instead of the static
disconnect switch in alternative embodiments.
[0039] In a normal mode of operation, the static disconnect switch
110 is closed and the facility load is supplied from both the
on-site generators 104 and the utility 108, with the generators
supplying the primary load. Several factors determine the precise
relative contribution between the on-site generators and utility
when operating in a normal mode. One factor is that in the United
States, only certain facilities are qualified to send power from
the facility into the power grid, i.e. in the direction of arrow A
on bus 106 in FIG. 5. If the generators provided 100% of the load,
upon a sudden decrease in the facility load (as where a facility
power-consuming component goes off-line), the generators would
initially be producing excess power before they adjusted to the
change in load. This excess power would flow back into the grid.
Where a facility is not qualified to send power to the grid, the
facility includes a reverse power relay 122 on bus 106, which relay
trips in the event the power supply system 102 attempts to supply
power to the grid. When the reverse power relay 122 trips, this
islands the facility so that 100% of the facility load is supplied
by the generators. When islanding, the facility load is fully
supplied by the generators, but has no backup power supply from the
utility.
[0040] Moreover, upon a sudden decrease in the facility load, in
addition to islanding, the electromotive power from the engines
driving the generators will exceed the power being drawn from the
generators by the facility load, which condition results in
acceleration of the generators. This acceleration can increase the
frequency of the power from the generators which may result in a
shut-down of the generators.
[0041] Additionally, if the power contribution from the utility is
set too low, then normal power fluctuations in the facility can
cause excess power from the generators to flow back to the grid,
resulting in frequent tripping of the reverse power relay and
islanding of the facility.
[0042] Even in situations where power is allowed to flow back to
the grid, there are advantages to having at least a small, constant
power flow from the utility. Referring to FIG. 6, if the generators
provide 100% of the power so that the power output from the
generators matches the power load of the facility, the voltage
potential between nodes 106A and 106B on the secondary bus 106 will
be zero with no current flow. However, in reality, the facility
load will fluctuate upwards and downwards slightly and the power
output from the generators will slightly trail the facility load.
This slight difference between the power generated in generators
104 and the facility load will result in power oscillations over
bus 106 as indicated by the arrows in FIG. 6, as excess power from
generators 104 flows to the grid in one instant and additional
power from the utility is drawn from the grid in the next. This
current flow oscillation can create noise and other disadvantageous
consequences.
[0043] On the other hand, if the utility is supplying too much of
the facility load in a normal mode of operation, then when the
utility goes off-line, the initial change in power draw on
generators may be too great causing the generator to decelerate and
the relays provided to protect the generators may trip and power
from the generators shut down.
[0044] Therefore, in setting the relative contributions of the
on-site generators and utility in a normal mode of operation, a
balance is struck. The utility power supply should be low enough
that the generators can handle the facility islanding at any time
upon a drop in power quality from the utility. At the same time
however, the utility power supply should be high enough to prevent
frequent tripping of the reverse power relay and to prevent
acceleration and potential shut-down of the generators upon a
decrease in the facility load.
[0045] In a normal mode of operation, this balance is struck both
in the United States and abroad by the utility supplying power
approximately in the amount of the single largest load in the
facility, with the remaining power being supplied by the onsite
generators. If the power from the utility is so small as to be
lower than individual facility component loads, then, should one of
those components go off-line, the facility load would be less than
the output of the generators and power would attempt to flow into
the grid. As discussed above, this can result in tripping of the
reverse power relays and/or acceleration of the generators to a
point where they shut down. Therefore, the utility preferably
provides an amount of power equal to or slightly greater than the
single largest load in the facility. In that way, if that facility
load goes off-line, there is still some power being drawn from the
utility.
[0046] As an example and in no way limiting on the present
invention, the generators may supply from 80% to 98% of the
facility load, with the utility supplying the rest. It is
understood however that the amount of power supplied respectively
by the generators and utility may vary outside of these percentages
in alternative embodiments. Additionally, it is understood that
factors other than those described above may be relevant in
determining the relative power contribution between the generators
and utility in a normal mode of operation.
[0047] While the utility provides a small constant flow of power in
a preferred embodiment for the above-explained reasons, it is
alternatively contemplated that the on-site generators provide 100%
of the load with the utility being available as a backup in the
event the power needs of facility are greater than the amount of
power provided by the on-site generators. (The facility load may
exceed the generator output if one or more of the generators go
off-line. This may also occur upon a sudden increase in facility
load, in which case the utility will supply the excess load until
the generators adjust to the facility power increase).
[0048] One role of the controller 112 is to continuously monitor
the facility load and adjust the power generated by the on-site
generators 104 accordingly. If the facility load drops, the
controller 112 decreases power output from the generators. In the
event that the facility load drops significantly, as discussed
above, the generators will initially be supplying excess power that
will have nowhere to go, and will attempt to flow into the grid.
There is a built in time delay in the reverse power relay 122 of a
few seconds. It is a goal of the controller 112 to reduce the power
output from the generators to match the reduced facility load
before the reverse power relay trips and islands the facility. On
the other hand, if the facility load increases, the controller 112
increases the power output from the generators. In this regard, the
utility acts as a buffer to supply any additional power necessary
while the generators are increasing the power output.
[0049] Up to this point, the power supply between the generators
104 and utility 108 to service the facility load has been described
under normal operating conditions, i.e., both the generators and
utility are supplying high quality power within acceptable voltage
and frequency ranges. However, it may happen that either the
generators or utility may experience problems. In such an event, it
is a feature of the present invention that the power output of the
properly functioning power supply can increase its power output to
maintain the supply of high quality power to the facility.
[0050] For example, if a generator 104 goes off-line, the
additional power may come from the other generators, in the event a
redundant generator system is employed, or the additional power may
come from the utility. In the event a redundant generator system is
used, the controller 112 controls the operation of the generators
to make up the power from the off-line generator. Where there are
no redundant generators, or during the time that the redundant
generator or generators are brought on-line, additional power is
automatically drawn from the utility to supply the load without
separate protocols in the controller. In the unlikely event that
each of the generators 104 goes off-line, 100% of the facility load
may be supplied by the utility 108.
[0051] Where one or more of the generators are down or where the
generator bank is otherwise unable to supply the facility load, the
controller 112 preferably disables the static disconnect switch 110
to prevent the facility from islanding. In this event, if the
quality of the power on the grid side also degrades, the facility
will receive the degraded utility power, as opposed to no power at
all.
[0052] Where the generators 104 are functioning properly, should a
grid related power quality event occur, this event is detected by
sensors in communication with the static disconnect switch
controller, and the switch 110 opens in less than a cycle to
thereby island the facility from the utility power grid. This
condition is shown in FIG. 7. Such power grid events include for
example, power interruptions, swells, sags, or where the frequency
fluctuates outside of acceptable levels (for example by a few hertz
in either direction). In this event, the switch 110 opens and 100%
of the facility load is supplied by the on-site generators 104. As
indicated above, the speed with which the facility islands in the
event of a utility power disruption allows the system of the
present invention to supply high quality, reliable power. In a
preferred embodiment, the subcycle response of the switch 110 is
between 1/4 and 1/2 cycle. It is understood that the subcycle
response may be lesser or greater than that in alternative
embodiments.
[0053] In a preferred embodiment, the system monitors power quality
only from the utility side. The generators will trip by their
associated relays as a protective measure only in the event of a
mechanical or electrical problem with the generators or their
associated bus. However, in an alternative embodiment, it is
contemplated that both the utility 108 and generators 104 are
monitored for power quality and that each include a static switch
which opens in the event of a power disruption or other power
quality event. This embodiment is shown in FIG. 8. As shown
therein, a static switch 140 may be located on bus 106, which
switch opens in the event of a power quality event in the grid, and
a static switch 142 may be located on bus 103, which switch opens
in the event of a power quality event in the generators. In this
embodiment, the switches collectively function as a static transfer
switch to transfer power away from whichever power supply is not
performing within the acceptable power ranges. Each of the switches
140 and 142 preferably responds to a sensed power quality event in
less than a cycle to provide the response time advantages discussed
above. In the unlikely event of a power disruption in both the grid
and the generators, the controller 112 will prevent the switch 140
and/or switch 142 from opening to ensure that the facility 100
receives some level of power.
[0054] In addition to supplying power to the facility 100, the
generators 104 generate waste heat which may also be utilized by
facility 100 for heating, cooling or facility processes. The use of
both power and heat from the generators is referred to as
cogeneration. In conventional cogeneration systems, the amount of
power and waste heat generated by the generator is dictated by the
facility heat load. This is in contrast to the present invention,
where the amount of power and waste heat generated by the generator
is dictated by the facility electrical load. As the generators 104
are the primary source of power for facility 100, and are
continuously running, a significant amount of heat energy is
created for use by the facility according to the present
invention.
[0055] The system according to the present invention is able to
provide an uninterruptible power supply to a facility where high
power quality is maintained by readily available backup power and
speedy subcycle switching in the event of a grid related power
quality event. Moreover, as the system operates without expensive
short term power supplies, it is inexpensive to operate. The ease
with which conventional power supply systems may be adapted to
operate in accordance with the principals of the present invention
is another attractive feature of the present invention. Moreover,
the facility is not subject to restrictions or changes in power
supply imposed by a utility. The power supply to the facility is
controlled by the facility.
[0056] Although the invention has been described in detail herein,
it should be understood that the invention is not limited to the
embodiments herein disclosed. Various changes, substitutions and
modifications may be made thereto by those skilled in the art
without departing from the spirit or scope of the invention as
described and defined by the appended claims.
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