U.S. patent application number 11/513517 was filed with the patent office on 2007-05-17 for current transformer test device and method.
Invention is credited to John S. Cook, Randall D. Davis.
Application Number | 20070108995 11/513517 |
Document ID | / |
Family ID | 37072425 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070108995 |
Kind Code |
A1 |
Cook; John S. ; et
al. |
May 17, 2007 |
CURRENT TRANSFORMER TEST DEVICE AND METHOD
Abstract
A current transformer test method implemented using a test
device, is useful to verify proper CT installation and operation,
and does not rely on the generator (or other system) to be in a
state of relatively high assembly. The test device allows a current
transformer to be tested by supplying an alternating current (AC)
signal to a primary winding of the current transformer to thereby
induce an AC signal in a secondary winding of the current
transformer. The test device is used to simultaneously monitor the
phases of the supplied AC signal and the induced AC signal so that
a determination can be made as to whether the current transformer
secondary winding is properly installed relative to the current
transformer primary winding, and to simultaneously monitor the
current magnitudes of the supplied AC signal and the induced AC
signal so that the turns ratio of the current transformer can be
determined.
Inventors: |
Cook; John S.; (Tulsa,
OK) ; Davis; Randall D.; (Claremore, OK) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Family ID: |
37072425 |
Appl. No.: |
11/513517 |
Filed: |
August 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11274073 |
Nov 14, 2005 |
7119548 |
|
|
11513517 |
Aug 30, 2006 |
|
|
|
Current U.S.
Class: |
324/726 |
Current CPC
Class: |
G01R 31/62 20200101;
G01R 35/02 20130101 |
Class at
Publication: |
324/726 |
International
Class: |
G01R 29/20 20060101
G01R029/20 |
Claims
1. A method of testing a current transformer, comprising the steps
of: supplying an alternating current (AC) signal to a primary
winding of the current transformer to thereby induce an AC signal
in a secondary winding of the current transformer, the supplied AC
signal and the induced AC signal each having at least a phase and a
current magnitude; simultaneously monitoring the phases of the
supplied AC signal and the induced AC signal to determine whether
the current transformer secondary winding is properly installed
relative to the current transformer primary winding; simultaneously
monitoring the current magnitudes of the supplied AC signal and the
induced AC signal to determine a turns ratio of the current
transformer; supplying the induced AC signal through a burden
resistor to thereby generate a voltage drop across the burden
resistor; measuring the voltage drop across the burden resistor;
and determining the turns ratio from the predetermined AC current
magnitude and the measured voltage drop.
2. The method of claim 1, further comprising: coupling a
multi-channel oscilloscope to at least receive signals
representative of the supplied AC signal and the induced AC signal;
and simultaneously monitoring the the phases of the supplied AC
signal and the induced AC signal on the oscilloscope.
3. (canceled)
4. A method of testing a plurality of stator current transformers,
each current transformer installed in and configured to monitor an
associated phase in a multi-phase stator, comprising the steps of:
supplying an alternating current (AC) signal to one of the
associated phases of the multi-phase stator to thereby induce an AC
signal in the current transformer installed in the associated
phase, the supplied AC signal and the induced AC signal each having
at least a phase and a current magnitude; simultaneously monitoring
the phases of the supplied AC signal and the induced AC signal to
determine whether the current transformer is properly installed
relative to the associated stator phase; simultaneously monitoring
the current magnitudes of the supplied AC signal and the induced AC
signal to determine a turns ratio of the current transformer;
supplying the induced AC signal through a burden resistor to
thereby generate a voltage drop across the burden resistor;
measuring the voltage drop across the burden resistor; determining
the turns ratio from the predetermined AC current magnitude and the
measured voltage drop; and repeating the previous steps for each of
the plurality of current transformers and associated phases.
5. The method of claim 4, further comprising: coupling a
multi-channel oscilloscope to at least receive signals
representative of the supplied AC signal and the induced AC signal;
and simultaneously monitoring the phases of the supplied AC signal
and the induced AC signal on the oscilloscope.
6. (canceled)
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
11/274,073 filed Nov. 11, 2005, now U.S. Pat. No. ______.
TECHNICAL FIELD
[0002] The present invention relates to alternating current (AC)
generators and AC electrical distribution systems and, more
particularly, to a device and method for testing current
transformers installed in AC generators and AC electrical
distribution systems.
BACKGROUND
[0003] Alternating current (AC) generators are used for myriad
applications, for example, in a gas turbine engine, such as that
found in aircraft, ships, and some terrestrial vehicles. These
generators may include three separate brushless generators, namely,
a permanent magnet generator (PMG), an exciter, and a main
generator. Each of these generators may include rotors and stators.
When the rotors rotate, AC current is induced in the associated
stators. The AC current induced in the main generator stator is
supplied to an electrical distribution system within, for example,
the aircraft, ship, or terrestrial vehicle.
[0004] Many AC generators, such as the one described above, include
one or more current transformers (CTs). The CTs sense, for example,
the AC current in the main generator stator windings, and supply a
signal representative of the AC current to a protection, monitor,
and/or control circuit. These one or more circuits, using the
signals from the CTs, may implement overload protection and/or
generator control. Thus, the generator CTs are subjected to various
tests upon installation to verify proper installation and
operation.
[0005] Although current devices and methods for verifying proper
installation and operation of generator CTs is safe, reliable, and
accurate, these current devices and methods do suffer certain
drawbacks. For example, with the exception of a "bench test" to
verify resistance, the current devices and methods only allow CT
verification testing to be conducted during generator functional
testing, which is typically conducted after the generator is in a
relatively high state of assembly. Thus, if the verification
testing indicates that one or more of the CTs may be faulty,
inoperable, or improperly installed, the generator may need to be
substantially disassembled to correct the CT installation or
replace the faulty CT, and then reassembled to once again conduct
the CT verification testing. This can potentially result in
increased labor time, which can concomitantly result in increased
costs.
[0006] Hence, there is a need for a device and method of verifying
proper CT installation and operation that does not rely on the
generator (or other system) to be in a state of relatively high
assembly. The present invention addresses at least this need.
BRIEF SUMMARY
[0007] The present invention provides a device and method of
verifying proper CT installation and operation that does not rely
on the generator (or other system) to be in a state of relatively
high assembly.
[0008] In one embodiment, and by way of example only, a method of
testing a current transformer includes supplying an alternating
current (AC) signal to a primary winding of the current transformer
to thereby induce an AC signal in a secondary winding of the
current transformer, wherein the supplied AC signal and the induced
AC signal each have at least a phase and a current magnitude. The
phases of the supplied AC signal and the induced AC signal are
simultaneously monitored to determine whether the current
transformer secondary winding is properly installed relative to the
current transformer primary winding, and the current magnitudes of
the supplied AC signal and the induced AC signal are simultaneously
monitored to determine a turns ratio of the current
transformer.
[0009] In yet another exemplary embodiment, a method of testing a
plurality of stator current transformers, each of which is
installed in and configured to monitor an associated phase in a
multi-phase stator, includes supplying an alternating current (AC)
signal to one of the associated phases of the multi-phase stator to
thereby induce an AC signal in the current transformer installed in
the associated phase, wherein the supplied AC signal and the
induced AC signal each having at least a phase and a current
magnitude. The phases of the supplied AC signal and the induced AC
signal are simultaneously monitored to determine whether the
current transformer is properly installed relative to the
associated stator phase, and the current magnitudes of the supplied
AC signal and the induced AC signal are simultaneously monitored to
determine a turns ratio of the current transformer. The previous
steps are repeated for each of the plurality of current
transformers and associated phases.
[0010] Other independent features and advantages of the preferred
current transformer test method will become apparent from the
following detailed description, taken in conjunction with the
accompanying drawings which illustrate, by way of example, the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1, a functional schematic block diagram of an exemplary
high speed generator system 100;
[0012] FIG. 2 is a functional block diagram of an exemplary test
device that may be used to verify proper installation and operation
of one or more current transformers installed, for example, in the
generator of FIG. 1;
[0013] FIG. 3 schematically depicts the test device of FIG. 2
electrically coupled to a stator and current transformers of the
exemplary generator of FIG. 1;
[0014] FIG. 4 is detailed schematic diagram of an exemplary
alternative embodiment of a test device that may be used to verify
proper installation and operation of one or more current
transformers installed, for example, in the generator of FIG. 1;
and
[0015] FIG. 5 depicts a front view of a particular physical
implementation of the test device that is schematically illustrated
in FIG. 4.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0016] Before proceeding with the detailed description, it is to be
appreciated that the present invention is not limited to use in
conjunction with a specific type of electrical machine. Thus,
although the present embodiment is, for convenience of explanation,
depicted and described as being employed with a brushless AC
(alternating current) generator, it will be appreciated that it can
be used with other AC generator designs that include one or more
current transformers (CTs), and may additionally be used with
various distribution systems and devices that use CTs to monitor AC
current flow through portions thereof.
[0017] Turning now to the description, and with reference first to
FIG. 1, a functional schematic block diagram of an exemplary high
speed generator system 100 for use with a gas turbine engine, such
as that in an aircraft, is depicted. This exemplary generator
system 100, which is commonly known as a brushless AC generator,
includes a permanent magnet generator (PMG) 110, an exciter 120, a
main generator 130, a generator control unit 140, and one or more
rectifier assemblies 150. During operation, a rotor 112 of the PMG
110, a rotor 124 of the exciter 120, and a rotor 132 of the main
generator 130 may all rotate at the same speed. In one embodiment,
the rotational speed may be, for example, in the range of about
12,000 to about 24,000 r.p.m., or greater. As the PMG rotor 112
rotates, the PMG 110 generates and supplies AC power to the
generator control unit 140, which in turn is rectified and supplied
as direct current (DC) power to a stator 122 of the exciter 120.
The exciter rotor 124 in turn supplies AC power to the rectifier
assemblies 150. The output from the rectifier assemblies 150 is DC
power and is supplied to the main generator rotor 132. As the main
generator rotor 132 rotates, magnetic flux lines are created about
alternating north and south poles which induce an AC voltage into
stator windings 135 of the main generator stator 134.
[0018] The generator system 100 is capable of providing output
power at a variety of power levels and over a variety of frequency
ranges. Further, typically the output power from the main generator
stator 134 is three-phase AC power. The generator control unit 140
can regulate the power output and/or provide various protective
functions based upon monitoring signals provided to it from a
plurality of current transformers (CTs)s 195. More specifically, at
least in the depicted embodiment, a CT 195 is provided and
configured to monitor the AC current in each of the three stator
windings 135. Thus, as was previously mentioned, it is desirable
that the CTs 195 be installed and operating properly when the
generator 100 is fully assembled. Moreover, as was also previously
mentioned, it is desirable that proper CT installation and
operation be verified before the generator 100 is in a relatively
high state of assembly. With reference to FIG. 2, a functional
block diagram of an exemplary test device 200 that may be used to
verify proper installation and operation of the CTs 195 is depicted
and will now be described.
[0019] The test device 200 includes a DC power source 202, a
variable AC power source 204, a current transformer primary winding
select switch 206, a current transformer primary winding test jack
208, and a current transformer secondary winding test jack 212. The
DC power source 202 and the variable AC power source 204 are both
adapted to receive AC power from a suitable non-illustrated
external electrical power source via, for example, a conventional
three-prong plug 214. When the plug 214 is coupled to a suitable AC
power source, the DC power source 202, which is preferably a fixed
DC power source, rectifies the AC power and supplies a fixed DC
voltage. The variable AC power source 204, when the plug 214 is
coupled to a suitable AC source, supplies an AC signal having a
voltage magnitude that is controlled and set via a user interface
216 such as, for example, a user input knob.
[0020] The current transformer primary winding select switch 206 is
a multi-position switch that is coupled between the DC power source
202 and a plurality of solenoids 218. The current transformer
primary winding select switch 206 is configured, depending on its
position, to selectively couple the DC power source 202 to, and
thus energize, one of the plurality of solenoids 218. In the
depicted embodiment, and as will be described in more detail
further below, the test device 200 is preferably configured to be
coupled to, and to selectively energize, three current
transformers. Thus, the current transformer primary winding select
switch 206 is a three-position switch, and the test device 200
includes three solenoids 218 (e.g., 218-1, 218-2, 218-3). It will
be appreciated, however, that this is merely exemplary of a
particular preferred embodiment, and that the current transformer
primary winding select switch 206 could include more or less than
this number of positions, and the test device 200 could be
implemented with more or less than this number of solenoids
218.
[0021] No matter the specific number of solenoids 218 that are
included, it is seen that each solenoid 218 includes a coil 222 and
an associated contactor 224. Each coil 222 controls the position of
its associated contactor 224. More specifically, when a coil 222 is
energized from the DC power source 202, its associated contactor
224 is moved to a closed position, and when a coil is de-energized,
its associated contactor 224 moves to an open position. It is seen
that, at least in the depicted embodiment, when a contactor 224 is
in the closed position, the AC signal from the AC power source 204
is coupled to the current transformer primary winding test jack
208.
[0022] The current transformer primary winding test jack 208 is
configured to be coupled, via a test cable 226, to a plurality of
current transformer primary windings (not shown). More
specifically, the current transformer primary winding test jack 208
is a multi-pin connector that includes at least one common pin 228
and a plurality of supply pins 232, one for each current
transformer to which the test device 200 is configured to be
coupled. Although the test device 200 may be configured to be
simultaneously coupled to various numbers of current transformers,
in the depicted embodiment, the test device 200 is configured to be
coupled to three current transformers. Therefore, the current
transformer primary winding test jack 208 includes three supply
pins 232-1, 232-2, 232-3. The common pin 228 is coupled to the
variable AC power source 204, whereas each supply pin 232 is
coupled to one of the solenoid contactors 224. Thus, the current
transformer winding test jack 208 is used to couple the AC signal
supplied from the variable AC power source 204 to the current
transformer primary winding that corresponds with the switch
position of the current transformer primary winding select switch
206.
[0023] The current transformer secondary winding test jack 212
configured to be coupled, via a second test cable 234, to a
plurality of current transformer secondary windings (also not
shown). The current transformer secondary winding test jack 212,
like the current transformer primary winding test jack 208, is a
multi-pin connector that includes a plurality of secondary winding
connection pin pairs 236. Each secondary winding connection pin
pair 234 is configured to receive a current transformer test signal
from a current transformer secondary winding when its associated
primary winding is supplied with an AC signal. Preferably, the
current transformer secondary winding test jack 212 is configured
to simultaneously couple the test device 200 to three current
transformer secondary windings, and thus includes three secondary
winding connection pin pairs 236-1, 236-2, 236-3. It will be
appreciated, however, that this is merely exemplary and that the
current transformer secondary winding test jack 212 could be
configured to coupled the test device 200 to more or less than this
number of current transformer secondary windings, and thus include
more or less than this number of secondary winding connection pin
pairs 236.
[0024] In addition to the above, it is seen that the test device
200 further includes a secondary winding test device node 238, a
current transformer secondary winding select switch 242, a primary
winding test device node 244, and an AC signal parameter select
switch 246. The secondary winding test device node 238 is coupled
to the current transformer secondary winding select switch 242 and
is adapted to be coupled to a test device 248. Although the
particular test device 248 may vary, the test device 248 is
preferably an oscilloscope. Moreover, the secondary winding test
device node 238 and the test device 248 may be configured to be
either releasably or permanently coupled together. In a preferred
embodiment, the secondary winding test device node 238 is
implemented as a releasable connector, such as a BNC connector,
that is configured to be releasably coupled to a test cable that is
in turn coupled to the test device 248.
[0025] No matter the specific implementation of the secondary
winding test device node 238 and the test device 248, it is seen
that the current transformer secondary winding select switch 242 is
coupled between the current transformer secondary winding test jack
212 and the secondary winding test device node 238. The current
transformer secondary winding select switch 242 is a multi-position
switch that is configured, depending on its position, to
selectively couple one of the current transformer secondary winding
test jack pin pairs 236 to the secondary winding test device node
238.
[0026] The primary winding test device node 244 is coupled to the
AC signal parameter select switch 246 and is also adapted to be
coupled to a test device. In the depicted embodiment, the primary
winding test device node 244 is adapted to be coupled to the same
test device 248 as the secondary winding test device node 238. It
will be appreciated, however, that this is merely exemplary of a
particular preferred embodiment, and that the test device nodes
238, 244 could, if so desired, be coupled to different test
devices. If, as is preferable, the two test device nodes 238, 244
are coupled to the same test device 248, the test device 248 is
preferably a multi-channel oscilloscope. In addition, similar to
the secondary winding test device node 238, the primary winding
test device node 244 may be configured to be either releasably or
permanently coupled to the test device 248. In a preferred
embodiment, the primary winding test device node 244 is also
implemented as a a releasable connector, such as a BNC connector,
that is configured to be releasably coupled to a test cable that is
in turn coupled to the test device 248.
[0027] The AC signal parameter select switch 246 is coupled between
the variable AC power source 204 and the primary winding test
device node 244. The AC signal parameter select switch 242 is a
multi-position switch that is configured, depending on its
position, to selectively couple a signal representative of either
the AC signal voltage or AC signal current that the variable AC
power source is supplying to a selected current transformer primary
winding. Both of these parameters are also visible on displays that
are mounted on the test device. In particular, a load voltage
indicator 252 and a load current indicator 254 are mounted on the
device and provide a visual indication of the AC signal voltage and
current magnitudes being drawn from the variable AC power source
204 by the selected current transformer primary winding. Although
the current and voltage displays 252, 254 could be implemented as
any one of numerous types of displays, preferably each is
implemented using a digital display meter.
[0028] Turning now to FIG. 3, a brief description of how the test
device 200 is connected to the CTs 195 of a 3-phase AC generator,
such as the one depicted in FIG. 1 and described above, will now be
provided. In doing so, reference should also be made, as needed or
desired, to FIG. 2. As FIG. 3 shows, the stator windings 135, which
function as current transformer primary windings, are coupled to
the current transformer primary winding test jack 208 via the test
cable 226, and the CTs 195 are each coupled to the current
transformer secondary winding test jack 212 via the test cable 234.
As FIG. 3 also shows, the main stator windings 135 are wound in a
three-phase wye configuration, and thus includes three CTs 195, one
CT 195 per phase 302. As is generally known, each phase 302 has a
load end 304 and is coupled to the other phases 302 at a neutral
node 306. Thus, as FIG. 3 also shows, the load end 304 of each
phase 302 is electrically coupled to one of the current transformer
primary winding test jack supply pins 232-1, 232-2, 232-3, and the
neutral node 306 is coupled to the current transformer primary
winding test jack common pin 228. Similarly, each of the CTs 195 is
separately coupled to one of the secondary winding connection pin
pairs 236-1, 236-2, 236-3.
[0029] With the above-described connections made, the test device
200 is preferably energized by coupling the plug 214 to a suitable
AC source. Upon energization, the DC power source 202 supplies
power to one of the solenoids 218, depending on the position of the
current transformer primary winding select switch 206. In addition,
the variable AC power source 204 supplies an AC signal to the
stator phase 302 selected by the current transformer primary
winding select switch 206, and at a voltage and current magnitude
set via the user interface 216. The load voltage and load current
magnitudes, as noted above, are displayed on the load voltage
indicator 252 and the load current indicator 254, respectively. It
will be appreciated that the user interface 216 is preferably
manually manipulated to supply a sufficient load current to the
selected stator winding phase 302 so that a sufficient current
magnitude is induced in the associated CT 195. It will be
appreciated that the specific load current magnitude that is
supplied to the selected stator winding phase 302 may vary, but in
a particular embodiment, it has been found that a current magnitude
of about 20 amps is sufficient.
[0030] No matter the specific load current magnitude that is found
sufficient, when the current is induced in the associated CT 195,
the induced current can be monitored. More specifically, one
channel of the test device 248, which as noted above is preferably
a multi-channel oscilloscope, is coupled to the secondary winding
test device node 238. Thus, when the current transformer secondary
winding select switch 242 is positioned to select the associated CT
195, the test device 248 will display the AC signal induced in the
associated CT 195. As was also noted above, a second channel of the
test device 248 is coupled to the primary winding test device node
244. Thus, depending on the position of AC signal parameter select
switch 246, either the AC load voltage signal or AC load current
signal supplied to the associated stator phase 302 will also be
displayed by the test device 248.
[0031] The test device 248 allows the AC voltage signal waveforms
of the stator winding phases 302 and the associated CTs 195 to be
monitored and compared. As a result, it is possible to determine if
each of the CTs 195 have been properly installed and whether the
installed CTs 195 have the proper turns ratio. In particular, by
comparing the waveforms displayed on the test device 248, a
determination can be made as to whether the stator winding phase
waveform and the associated CT waveform are in phase or out of
phase. If the waveforms are out of phase, this indicates that the
associated CT 195 has been improperly installed. Moreover, by
comparing the load current magnitude, using either the load current
display 254 or the test device 248, to the AC voltage signal from
the associated CT 195, the turns ratio of the CTs 195 can be
accurately determined. For example, if a 50 amp load current is
being supplied to a stator phase 302, and the associated CT 195 is
designed to have a turns ratio of 500:1, the output current from
the associated CT 195 should be 0.1 amps. If the current varies by
more than a predetermined amount, then it is likely that the turns
ratio of the CT 195 is incorrect.
[0032] The test device 200 depicted in FIG. 2 and described above
is merely exemplary of a particular, generalized functional
embodiment. It will be appreciated that the test device 200 may be
physically implemented according to any one of numerous
configurations. For example, FIG. 4 depicts a detailed schematic
representation of a particular physical implementation of the
generalized embodiment shown in FIG. 2, and FIG. 5 depicts an
actual physical implementation of a test device that is implemented
according to the schematic representation of FIG. 4. For
completeness, these actual physical implementations will now be
described. In doing so, it is noted that like reference numerals in
FIGS. 2, 4, and 5 refer to like parts. However, it is also noted
that the nomenclature used to describe the like parts of the two
different test device embodiments will, in many instances, differ.
For example, although the switch labeled using reference numeral
206 implements the same function in both test devices 200, 400,
this switch 206 is described using the nomenclature "current
transformer primary winding select switch" when referring to the
test device 200 of FIG. 2, whereas this switch 206 is described
using the nomenclature "PHASE SELECT switch" when referring to the
test device 400 of FIGS. 4 and 5.
[0033] In addition to the above, it may be seen from FIGS. 4 and 5
that the test device 400 depicted therein includes each of the
devices and components included in the generalized test device 200
of FIG. 2, plus a few additional components and devices. In
addition, some of the components and devices are depicted in FIGS.
4 and 5 in more detail than in FIG. 2. As such, the following
description will include only detailed descriptions of like
components that are illustrated in more detail in FIGS. 4 and 5,
and those components and devices depicted in the test device 400
shown in FIGS. 4 and 5 that are not included in the generalized
test device 200 of FIG. 2.
[0034] With the above background in mind, and with reference now to
FIGS. 4 and 5, it is seen that the physically implemented test
device 400 includes the DC power source 202, the variable AC power
source 204, the current transformer primary winding select (PHASE
SELECT) switch 206, the current transformer primary winding (STATOR
INPUT) test jack 208, the current transformer secondary winding (CT
INPUT) test jack 212, the plug 214, the user interface (VARIABLE
INPUT VOLTAGE) knob 216, the solenoids 218 and associated coils 222
and contactors 224, the secondary winding test device node (CT
OUTPUT) 238, the current transformer secondary winding select (CT
SELECT) switch 242, the primary winding test device node (STATOR
OUTPUT) 244, the AC signal parameter select (SENSE SELECT) switch
246, the load voltage (INPUT VOLTS) indicator 252, and the load
current (INPUT AMPS) indicator 254.
[0035] As shown most clearly in FIG. 4, the DC power source 202 is
preferably implemented as a conventional power supply device that,
when a MAIN POWER switch 402 is appropriately positioned, receives
and converts 120 VAC line voltage supplied to the plug 214 to about
+24 VDC. This +24 VDC power is used not only to selectively
energize the solenoids 218, but to also selectively energize an
input power relay 404. More specifically, the test device 400
includes an E-STOP switch 406, which is mounted on a side of the
test device 400 (see FIG. 5). When the MAIN POWER switch 402 is
closed, 120 VAC is supplied to the DC power source 202, which in
turn supplies +24 VDC. If the E-STOP switch 406 is open, then the
input power relay 404 will not be energized and a front-mounted
E-STOP indicator 408 will be illuminated with the 120 VAC. If,
however, the E-STOP switch 406 is closed, then the input power
relay 404 will be energized and a front-mounted MAIN POWER
indicator 412 will be illuminated with the 120 VAC. The E-STOP
switch 406 allows the test device 400 to be de-energized regardless
of the position of the MAIN POWER switch 402.
[0036] In addition to selectively coupling the 120 VAC main power
to the DC power source 202 and either the E-STOP indicator 408 or
the MAIN POWER indicator 412, the MAIN POWER switch 402
additionally selectively couples the 120 VAC main power to the
variable AC power source 204, the load voltage (INPUT VOLTS)
indicator 252, the load current (INPUT AMPS) indicator 254, and a
cooling fan 414 that is used to circulate air in and through the
test device chassis 502 (see FIG. 5). It will be appreciated that
the 120 VAC power to the indicators 252, 254 is operational
power.
[0037] The variable AC power source 204 functions as previously
described, but in the depicted embodiment is implemented using a
variable winding transformer 416. The variable winding transformer
416 includes a variable primary winding 418 and a secondary winding
422. The variable primary winding 418 is coupled to receive the 120
VAC main power via the input relay 404, and induces an AC signal in
the secondary winding 422. The voltage magnitude of the AC signal
in the secondary winding 422 will vary with the position of the
user interface (VARIABLE INPUT VOLTAGE) knob 216, which is coupled
to, and used to vary, the voltage across the variable primary
winding 418.
[0038] As in the generalized embodiment, the output of the AC power
source 204, which in FIG. 4 is the variable transformer secondary
winding 422, is coupled to the current transformer primary winding
(STATOR INPUT) test jack 208 common pin 228 and each of the
solenoid contactors 224. However, unlike the previous embodiment,
the test device 400 of FIG. 4 includes a plurality of load
resistors 424. In the depicted embodiment, the device 400 includes
four load resistors 424 (e.g., 424-1, 424-2, 424-3, 424-4). It will
nonetheless be appreciated that this is merely exemplary, and that
the test device 400 could be implemented with more or less than
this number of load resistors 424, so long as the resistance is
sufficient to limit the load current supplied to the stator
windings 135 or current transformer primary windings.
[0039] The current transformer secondary winding (CT INPUT) test
jack 212, the secondary winding test device node (CT OUTPUT) 238,
the current transformer secondary winding select (CT SELECT) switch
242, the primary winding test device node (STATOR OUTPUT) 244, the
AC signal parameter select (SENSE SELECT) switch 246, the load
voltage (INPUT VOLTS) indicator 252, and the load current (INPUT
AMPS) indicator 254 are each configured to function similar to the
test device 200 of FIG. 2. However, unlike the previous device 400,
a burden resistor 426 (e.g., 426-1, 426-2, 426-3) is coupled in
series between each pair of current transformer secondary winding
(CT INPUT) test jack 212 connection pin pairs 236 and the secondary
winding test device node (CT OUTPUT) 238. More specifically, a
burden resistor 426 is coupled between each of the current
transformer secondary winding (CT INPUT) test jack 212 connection
pin pairs 236and the current transformer secondary winding select
(CT SELECT) switch 242. The burden resistors 426 reduce the current
magnitude from the CTs 195 to the secondary winding test device
node (CT OUTPUT) 238.
[0040] As just mentioned, the secondary winding test device node
(CT OUTPUT) 238 and the primary winding test device node (STATOR
OUTPUT) 244 are configured to function similar to the previous
embodiment. Thus, in the depicted embodiment, and as shown most
clearly in FIG. 5, these nodes 238, 244 are preferably implemented
as BNC connectors that are configured to be releasably coupled to
the test device 248 via a non-illustrated test cable. With this
particular configuration, and with continued reference to FIG. 5,
the test device 248, which again is preferably a multi-channel
oscilloscope, may be placed atop the test device chassis 502. It
will be appreciated, as with the previous embodiment, that this
configuration is merely exemplary, and that the test device nodes
238, 244 and test device 248 could be non-releasably coupled
together. Moreover, the test device 248 could be permanently
mounted, if so desired, within the test device chassis 502.
[0041] In addition to the differences already described, it is seen
that the test device 400 of FIGS. 4 and 5 further includes a
plurality of chassis-mounted terminal boards 428, a plurality of
fuses 432, and an internal CT 434. The internal CT 434 is used to
sense the load current supplied to the stator windings 135 and that
is displayed on the load current (INPUT AMPS) indicator 254 and, if
selected using the AC signal parameter select (SENSE SELECT) switch
246, on the test device 248 via the primary winding test device
node (STATOR OUTPUT) 244.
[0042] The test device 400 depicted in FIGS. 4 and 5 and described
above operates substantially identically to the test device 200
depicted in FIG. 2. Thus, a description of the operation of the
test device 400 when it is coupled to a plurality of stator
windings 135 is not needed and will not be provided.
[0043] The test devices described herein, and the method
implemented by each for verifying proper CT installation and
operation, does not rely on the generator (or other system) to be
in a state of relatively high assembly. As a result, potentially
time consuming and costly disassembly and reassembly, in the event
of an improperly installed or operating CT, is avoided.
[0044] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt to a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
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