U.S. patent application number 11/106139 was filed with the patent office on 2005-09-08 for method and a connector arrangement for connecting and disconnecting a generator to a circuit with an existing alternating current.
Invention is credited to Aldridge, Wayne Kenneth, Francis, George McChesney, Rea, Isobel Dorothy.
Application Number | 20050194940 11/106139 |
Document ID | / |
Family ID | 9887587 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050194940 |
Kind Code |
A1 |
Aldridge, Wayne Kenneth ; et
al. |
September 8, 2005 |
Method and a connector arrangement for connecting and disconnecting
a generator to a circuit with an existing alternating current
Abstract
A method and a connector arrangement for connecting and
disconnecting an electrical generator, such as a prime mover driven
alternator (10), to a circuit with an existing alternating current
such as the mains electricity supply (20).
Inventors: |
Aldridge, Wayne Kenneth;
(Nottingham, GB) ; Francis, George McChesney;
(West Midlands, GB) ; Rea, Isobel Dorothy;
(Leicestershire, GB) |
Correspondence
Address: |
KENNEDY COVINGTON LOBDELL & HICKMAN, LLP
214 N. TRYON STREET
HEARST TOWER, 47TH FLOOR
CHARLOTTE
NC
28202
US
|
Family ID: |
9887587 |
Appl. No.: |
11/106139 |
Filed: |
April 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11106139 |
Apr 14, 2005 |
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10221876 |
Dec 20, 2002 |
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10221876 |
Dec 20, 2002 |
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PCT/GB01/00840 |
Feb 27, 2001 |
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Current U.S.
Class: |
322/23 |
Current CPC
Class: |
Y10T 29/49105 20150115;
H02J 3/40 20130101; Y10T 29/49169 20150115; F02G 1/043
20130101 |
Class at
Publication: |
322/023 |
International
Class: |
H02H 007/06; H02P
009/00; H02P 011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2000 |
GB |
0006114.3 |
Claims
1: A method of connecting a prime mover driven electrical
alternator arranged to generate a current between two terminals to
a circuit with an existing alternating current, the method
comprising connecting an impedance of such a value between the
terminals of the alternator that the prime mover arranged to drive
the alternator substantially cannot move and cannot make the
alternator generate a current, initializing the prime mover so that
it is in a suitable condition to drive the alternator at the
frequency of the alternating current in the circuit to which it is
to be connected and connecting the terminals of the alternator to a
circuit with an existing alternating current to cause the
alternator to start movement of the prime mover.
2: A method according to claim 1, wherein the prime mover is a
Stirling engine and the alternator is a linear alternator.
3: A method according to claim 2, in which the Stirling engine is
initialized by supplying heat to one end of its piston chamber.
4: A method according to claim 1, in which the circuit with an
existing current is the mains electricity supply.
5. A method according to claim 1, in which the terminals of the
alternator are connected to a circuit with an existing alternating
current through an impedance.
6: A method according to claim 5, in which the impedance through
which the terminals of the alternator are connected to a circuit
with an existing alternating current is subsequently short
circuited.
7: A method according to claim 1, in which after the terminals of
the alternator are connected to a circuit with an existing
alternating current, the characteristics of the current passing
through that connection are checked to determine whether they are
within expected parameters.
8: A method according to claim 6, in which the characteristics of
the current passing through the short circuit are checked to
determine whether they are within expected parameters.
9: A method according to claim 7, wherein if the characteristics of
the current are outside expected parameters the alternator is
disconnected from the circuit with an existing alternating
current.
10-15. (canceled)
16: An apparatus for connecting a prime mover driven alternator to
a circuit with an existing alternating current comprising an
impedance switchable into and out of a parallel arrangement with
the alternator, the impedance being of sufficiently low value that
the prime mover cannot drive the alternator to produce a current
around the impedance when connected in parallel with the
alternator, and a switch to connect the alternator to a circuit
with an existing alternating current.
17: An apparatus according to claim 16, including a control means
arranged to connect the impedance into a parallel arrangement with
the alternator, arranged to disconnect the alternator from a
parallel arrangement with the alternator and arranged to connect
the alternator to a circuit with an existing alternating
current.
18: An apparatus according to claim 17, wherein the control means
is arranged to disconnect the impedance from a parallel arrangement
with the alternator before it connects the alternator to a circuit
with an existing alternating current.
19: An apparatus according to claim 17, wherein the control means
is arranged to disconnect the impedance from a parallel arrangement
with the alternator after it connects the alternator to a circuit
with an existing alternating current.
20: An apparatus according to claim 16, wherein the alternator is
connected to a circuit with an existing alternating current through
an impedance.
21: An apparatus according to claim 20, including means to monitor
the characteristics of the current passing through the impedance
connected between the alternator and a circuit with an existing
alternating current.
22: An apparatus according to claim 21, wherein the control means
is arranged to short circuit the impedance connected between the
alternator and a circuit with an existing alternating current if
the characteristics of the current passing through the impedance
are within desired parameters
23-28. (canceled)
Description
CROSS REFERENCE TO RELATED DOCUMENT
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/221,876, filed Dec. 20, 2002, which in turn is a 371 of
PCT/GB01/00840, filed on Feb. 27, 2001 and claiming priority of
United Kingdom Application No. 0006114.3, filed on Mar. 15, 2000.
The entirety of each of the foregoing applications is incorporated
herein by reference, and this application is entitled to the
benefit of, and claims priority to, each such application.
FIELD OF THE INVENTION
[0002] The present invention relates to a method and a connector
arrangement for connecting and disconnecting an electrical
generator such as a prime mover driven alternator to a circuit with
an existing alternating current such as the main electricity
supply.
BACKGROUND OF THE INVENTION
[0003] A number of problems are encountered when connecting and
disconnecting an electrical generator to a circuit carrying an
existing alternating current such as the main electricity
supply.
[0004] An electrical generator can be started in isolation until it
reaches suitable power quality and the appropriate frequency and
phase, and then connected to the main electricity supply. However,
the provision of a control device to monitor the power quality of a
generator and then connect the generator to the main electricity
supply when the appropriate power quality has been achieved is
expensive, increases the complexity of the device and is liable to
error.
[0005] When disconnecting the electrical generator from the main
electricity supply, arcing is produced between the contacts of the
switch used for disconnection. This arcing wears out the contacts
of the switch impairing performance and necessitating regular
replacement which is inconvenient and expensive. Arcing also
disturbs the quality of the main electricity signal which is
prohibited. Arcing can also cause damage to other components and
the starting of fires and its prevention by for example the
provision of an inert gas atmosphere is expensive.
SUMMARY OF THE INVENTION
[0006] It is an object of the present invention to overcome one or
more of the above problems.
[0007] According to a first aspect of the present invention a
method of connecting a prime mover driven electrical alternator
having two terminals to a circuit with an existing alternating
current comprises connecting the two terminals of a prime mover
driven alternator together through a suitably low impedance such
that the prime mover arranged to drive the alternator does not move
substantially and cannot make the alternator generate a current,
initializing the prime mover arranged to drive the alternator so
that it is in a suitable condition to drive the alternator at the
frequency of the alternating current in the circuit to which it is
to be connected and connecting the terminals of the alternator to a
circuit with an existing alternating current to cause the
alternator to start movement of the prime mover for the prime mover
to drive the alternator to generate an alternating current with a
suitable power quality for the circuit thereafter.
[0008] A Stirling engine is preferably used as the prime mover as
it can be initialised by being heated by an external heat source
and then remain in a state ready to be brought into operation
extremely quickly. Starting the Stirling engine only requires a
small amount of energy since the pistons, which are the moving
part, are relatively light and can be accelerated from rest very
easily. The acceleration of the pistons from rest is continued in
the normal operation of the engine, by linear simple harmonic
motion.
[0009] The starting energy is provided by applying the alternating
current from the circuit to which the prime mover driven alternator
is to be connected, which is usually main power, to the stator of
the alternator through a suitable impedance to bring the inrush and
to bring the alternator closely into phase with the main.
[0010] According to a second aspect of the present invention a
method of disconnecting a prime mover driven electrical alternator
from a circuit with an existing alternating current comprises
connecting an impedance in parallel with the prime mover driven
electrical alternator, the impedance having a sufficiently low
impedance to require a current in excess of that which the
alternator is able to deliver to prevent the prime mover from
driving the alternator and thus stalling the alternator and
disconnecting the alternator from the circuit with an existing
alternating current.
[0011] By stalling the alternator before disconnecting it from the
main, the arcing caused when it is disconnected is substantially
reduced.
[0012] According to a third aspect of the present invention an
apparatus for connecting a prime mover driven alternator to a
circuit with an existing alternating current comprises an impedance
switchable into and out of a parallel arrangement with the
alternator, the impedance being of sufficiently low value that the
prime mover cannot drive the alternator to produce a current around
the parallel impedance and a switch to connect the prime mover
driven alternator to the circuit with an existing alternating
current.
[0013] According to a fourth aspect of the present invention an
apparatus for disconnecting a prime mover driven alternator from a
circuit with an existing alternating current comprises an impedance
switchable into a parallel arrangement with the alternator, the
impedance being of sufficiently low value that the prime mover
cannot drive the alternator to produce a current around the
parallel impedance and a switch to disconnect the prime mover
driven alternator from the circuit with an existing alternating
current.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] An example illustrating the present invention will now be
described with reference to the accompanying drawings in which:
[0015] FIG. 1 shows a connector arrangement for connecting a prime
mover driven alternator to a circuit with an existing alternating
current,
[0016] FIGS. 2 to 7 show the effective state of that circuit at
various intervals,
[0017] FIG. 8 shows a control system for controlling switches in
the connector arrangement,
[0018] FIG. 9 shows the sequence of steps followed by the control
system to connect a prime mover driven alternator to a circuit with
an existing alternating current and
[0019] FIG. 10 shows the sequence of steps followed by the control
system to disconnect a prime mover driven alternator from a circuit
with an existing alternating current.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] The prime mover which drives the alternator 10 in the
present example shown in FIG. 1 is a Stirling engine as is well
known in the art, such as the one described in WO 94/04878 for
example. However, any other suitable prime mover such as a gas
engine, an internal combustion engine or a steam turbine for
example would be suitable. Any suitable alternator may be used but
in the present example a linear alternator has been found to work
particularly well with the reciprocating Stirling engine. In the
present example shown in FIG. 1 the main electricity supply 20
between neutral 21 a live terminal 22 acts as the circuit with an
existing alternating current. The alternator has two terminals 11,
12 one of which 11 is connected to neutral. The other terminal 12
of the alternator 10 is connectable to the live main supply 2 by
two parallel paths 30, 40. The first electrical path 30 has a
switch 31 and a meter 32 in series and the second electrical path
40 has a first impedance 41, which in the present example is 10
ohms, a second impedance 42, which in the present example is 27
ohms, a switch 43 and a meter 44 in series.
[0021] Between impedances 41 and 42 a line 50 connected to neutral
21 is provided. The line 50 has two switches 51, 52 in series.
[0022] Before starting the Stirling engine and connecting the
alternator to the main supply, switches 31 and 43 are opened and
switches 51 and 52 are closed to produce the effective circuit
shown in FIG. 2 with resistor 41 connected around the alternator
10. The impedance of resistor 41 is selected to be sufficiently low
such that the prime mover driven alternator 10 cannot produce a
current required to pass through the resistor 41 so that the engine
is stalled and kept in a stationary condition. The engine (not
shown), which in this case is a Stirling engine, is then brought
into a condition ready for use by applying heat to one end of its
piston chamber and cooling the other end. When the engine is
sufficiently "warmed up" to achieve steady state operation and it
is desired to connect the alternator 10 to the main electricity
supply 20, switch 52 is opened and switch 43 is closed. Switches 52
and 43 are provided by a "break before make" switching arrangement
as is well known in the art to ensure that switch 52 is open before
switch 43 is closed. The connector arrangement is then effectively
in the configuration shown in FIG. 3 with the alternator 10
connected to the main 20 through the two impedances 41 and 42 in
series. The particular total value of the impedances 41 and 42 is
selected dependent upon the particular prime mover and alternator
combination that is used. In the present example, the sum of the
series impedances has been selected at 37 ohms which dictates the
current which passes through the coils of the alternator and which
in turn dictates the force applied to the moving portion of the
alternator within the coils which in this case is a piston. The
force must be sufficient to start movement of the piston and yet
must not be so excessive that it produces so much force that the
piston damages the alternator or prime mover. As can be seen, the
particular impedance value selected would be dependent upon the
particular type of prime mover and alternator used. The connector
arrangement 1 of the present invention is particularly suitable for
use with a Stirling engine as the prime mover of the alternator as
the Stirling engine can be powered by an external heat source and
then remain in a steady state ready to be brought into operation
extremely quickly. Furthermore, starting the engine only requires a
small amount of energy since the piston is relatively light and can
be accelerated from rest very easily. The acceleration of the
piston from rest is continued in the normal operation of the engine
by linear simple harmonic motion.
[0023] Starting the prime mover driven alternator in this manner
ensures that the alternator 10 produces electricity of a suitable
power quality for the main electricity supply with the same
frequency and in phase.
[0024] The connector arrangement 1 of the present invention is
provided with a meter 44 which provides an indication of the
current passing through line 40. After switch 43 is closed the
current measured by meter 44 is checked to ensure that it is within
expected parameters. This check provides an indication that the
impedances 41, 42 and contacts of the switches 31, 43, 51, 52 are
working satisfactorily. The current measured by meter 44 is read by
a controller 101 which compares it with expected values to ensure
that the connector arrangement 1 is functioning correctly. If the
measured value is outside the desired values the control means
performs an emergency shut down procedure as described later.
However, under normal circumstances, the reading of meter 44 will
be within expected parameters and so switch 31 is closed and switch
51 is opened to produce the effective circuit shown in FIG. 4.
Switches 31 and 51 are provided in a "make before break"
configuration as is well known in the art. After a suitable period
of time has elapsed for the current through line 30 to settle, for
example 100 ms, the current through meter 32 is checked to see
whether it is within normal operating parameters. If it is not then
the connector arrangement undergoes emergency shut down procedures
as are described later. However, under normal circumstances the
current will be within normal parameters and switch 43 is then
opened to eliminate the impedance provided by impedances 41 and 42
such that the prime mover driven alternator is directly connected
to the main as shown in FIG. 5. Since in the present example
switches 43 and 52 are formed together in a "break before make"
arrangement the opening of switch 43 also closes switch 52.
However, no current passes through line 50 because switch 51
remains open. The prime mover driven alternator 10 continues to be
directly connected to the main supply 20 as shown in FIG. 5 until
it is desired to turn off the prime mover. During normal operation
the current passing through meter 32 is monitored at regular
intervals to ensure that the connector arrangement 1 is working
satisfactorily and to ensure that the prime mover driven alternator
is operating within its normal specification.
[0025] When it is desired to disconnect the prime mover driven
alternator 10 from the main supply 20 the heater of the Stirling
engine which is used in the present example is turned off and the
remaining heat in the Stirling engine is used up. When the Stirling
engine drops below a critical temperature it starts drawing power
from the main 20 rather than supplying it as is well known in
Stirling engine operation. A temperature detector 15 provided on
the Stirling engine is connected to a controller 101 (see FIG. 8)
and when this critical temperature is reached, which for the
Stirling engine used in the present example is 300.degree. C.,
switch 51 is closed to produce the effective circuit shown in FIG.
6 for a few milliseconds as the "make before break" switch
arrangement of switches 31 and 52 changes state. In this
arrangement the engine stalls because it cannot produce sufficient
current to be driven through the impedance 41. The value of
impedance 41 is selected for the particular type of prime mover
driven alternator 10 used such that the prime mover driven
alternator cannot produce sufficient current to be driven through
the resistor 41 so that the engine stalls.
[0026] After alternator a suitable period of time for the prime
mover driven alternator to stall, in this example 1.5 ms, switch 31
of the "make before break" switch arrangement of switches 31 and 51
is opened to disconnect the prime mover driven alternator from the
main 20 to produce the effective circuit shown in FIG. 7.
Substantially less or no arcing is produced as the prime mover
driven alternator is already stopped before it is disconnected from
the main supply 20.
[0027] When the prime mover driven alternator is disconnected from
the main 20 in an emergency situation, for example because the
current detected at meters 32 or 44 is outside normal parameters,
then switch 51 is closed and switch 31 is opened without waiting
for the remaining heat in the Stirling engine to be used up. This
should prevent the prime mover driven alternator from suffering any
damage due to operation outside its normal conditions.
[0028] The arrangement of the control system for controlling
switches 31, 51, 43, 52 in the manner described above is shown in
FIG. 8.
[0029] The controller 101 which may be a microprocessor or a
computer for example has data links 110, 111 to meters 32 and 44
respectively and a data link 112 to, temperature detector 15 on the
Stirling engine. The controller 101 also has actuating links 115,
116 to "make before break" switch arrangement 31, 51 and "break
before make" switch arrangement 43, 52 respectively.
[0030] The sequence of operations followed by the control system
for connecting the prime mover driven alternator 10 to the main
electricity supply 20 is shown in FIG. 9.
[0031] At step 201 the connector arrangement 1 is initially put
into the condition in which:
[0032] SWITCH 31 is OPEN
[0033] SWITCH 43 is OPEN
[0034] SWITCH 51 is CLOSED
[0035] SWITCH 52 is CLOSED
[0036] At step 202
[0037] SWITCH 52 is OPENED and
[0038] SWITCH 43 is CLOSED
[0039] At step 203
[0040] A reading is taken from meter 44 and if it is outside
expected conditions emergency shut down is activated at step 208.
If the reading is inside expected conditions the control means
proceeds to step 204.
[0041] At step 204
[0042] SWITCH 31 is CLOSED and
[0043] SWITCH 51 is OPENED
[0044] At step 205
[0045] A reading is taken from meter 32 and if it is outside
expected conditions emergency shut down is activated at step 208.
If the reading is within expected conditions the control means
proceeds to step 206.
[0046] At step 206
[0047] SWITCH 43 if OPENED and
[0048] SWITCH 52 is CLOSED
[0049] At step 207
[0050] Meter 32 is monitored and if a reading is taken which is
outside expected conditions emergency shut down is activated at
step 208. Otherwise the system continues with this switch
arrangement until disconnection is required as shown in FIG. 9.
[0051] The sequence of operations followed by the control system
for disconnecting the prime mover driven alternator 10 from the
main electricity supply is shown in FIG. 10.
[0052] Initially
[0053] SWITCH 31 will be CLOSED
[0054] SWITCH 43 will be OPEN
[0055] SWITCH 51 will be OPEN and
[0056] SWITCH 52 will be CLOSED
[0057] At step 301 the heater for the Stirling engine is turned off
and the temperature of the Stirling engine is monitored on line 112
until it reaches a critical temperature at which the engine begins
drawing or is about to draw power from the main. When this
temperature is reached the control means proceeds to step 302.
[0058] At step 302 "make before break" switch arrangement 31, 51 is
activated such that
[0059] SWITCH 51 is CLOSED and then
[0060] SWITCH 31 is OPENED
[0061] For emergency shut down the control system proceeds directly
to step 302.
[0062] A Stirling engine driven alternator 10 and connector
arrangement 1 can be transported with the connector arrangement 1
arranged with switches 31 and 43 open and switches 51 and 52 closed
to produce the effective circuit shown in FIGS. 2 and 7. In this
condition the piston of the Stirling engine is held substantially
stationary so that no damage will be caused to the Stirling engine
by movement or vibration during transportation.
[0063] The use of mechanical switches to perform the shutdown
sequence rather than an external timing device enables shutdown to
be performed even in the event of loss of the power supply. The
connector arrangement 1 is able to provide both connection and
disconnection from the main power supply with the same components
thus lowering the component count by providing dual
functionality.
[0064] The connector arrangement 1 provides both a reliable main
supply connection and a safe instant disconnection in the event of
loss of main electricity supply. The method relies on connection to
a circuit with an existing alternating current such as the
main.
[0065] As well as using the full circuit design, part of the
circuit may be used for a particular connection or disconnection
application. For example the disconnection circuit could be used
for a stand alone generator and the connection circuit could be
used for grid independent starting.
* * * * *