GEH 230T

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GEH-230T
Supersedes
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INSTRUCTIONS
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INSTRUMENT TRANSFORMERS
DRY AND
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COMPOUND-FILLED TYPES
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GENERAL
. ELECTR.IC
GEH-230S
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TECHNICAL DATA
This book presents GENERAL INSTRUCTIONS which apply to all dry and compound-filled in­
strument transformers.
The descriptive bulletins listed below contain ADDITIONAL
TECHNICAL
DATA - such
characteristic ratio and phase-angle curves, and dimensions - for specific transformers.
can be obtained on request.
as
These bulletins
Information on instrument transformers not listed below, and on those with special features can also
be obtained on request.
Your letter should:
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a. Include all information on the transformer n ameplate;
b. Clearly state your specific questions.
Address all requests for bulletins and informatio n to your nearest General Electric apparatus sales
office.
TYPE NO.
BULLETIN
Indoor Current Transformers (cont.)
GEC-235
_
-4 69
-235
-4 69
JE-25
volts)
to 7200
JE-41 _(7200 to 14400
JE-42 _ (2400 volts)
JE-42 _(4200 to 7200
JE-42 _(7200 to 14400
JEF-5
JEG-5
YT-1557-M
Outdoor
JEB-3
JEB-4
-1200
KC-59
-60 6
-770
KC-74
-897
V)
V)
-666
-60 8
-770
V)
V)
-666
-60 8
GEC-419
JK-10
JK-12
-422
JKA-5
-813
JKB-1
-626
JKB-2
-769
-679
JKB-4
-41 8
JKB-5
-421
JKD-3
-680
JKD-4
-682
Transformers
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Outdoor Current Transformers
-769
JKD-5
-684
-891
JKH-3
-681
-925
JKH-4
-683
JKH-5
-688
Indoor Current Transformers
-814
JKP-0
_GEC-766
JKL-4
-765
JW-6
-627
JKL-5
-763
JW-14
-4 16
JKM-3
-497
JKP-0
-814
.E
JKL-3
JKR-0
JKR-1
__ ( 10 to 800
__ ( 1200 - 4000
JKR-2
-956
-328
A)
___
JKW-3
Portable
-1222
Potential
Transformers
GEC-755
E-6
-60 9
J E-9
Portable Current Transformers
-958
JP-1
GEC-929
JKR-2
A) __ -959
JKR-4
-872
JP-2
JKR-5
-762
JP-3
-980
JKR-6
-873
JP-6
-90 6
JL-9
-789
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332
-331
-890
JEB-1
-
-334
-955
GEC-448
JEA-3
JS-2
JY-9
-999
Potential
GEC-896
-333
JY-4
JE-41 _(2400
JE-41 _(4200
--
-
JS-5
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JE-2
JLF-5
JS-1
--771
-771
JE-1
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(240 to 2400 V)
to 4800 VL
E-22 _(240 to 2400 V)
E-22 _(4200 to 4800 V)
E-21
BULLETIN
TYPE NO.
Indoor Potential Transformers
E-21 _(4200
-1205
These mstructions do not purport to cover all details or variations in equipment nor to provide for every possible contingency to be met in connection with installation,
operation or momfenonce. Should further informafton be destred or should particular problems arise which ore not co'(ered sufficiently for the purchaser's purposes, the matter
should be referred to the General Electric Company.
2
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DRY AND COMPOUND-FILLED TYPES
The several types of transformers covered by
a winding temperature of
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INSTRUMENT TRANSFORMERS
80 C varies because
these instructions include indoor and outdoor
of the variations in losses and copper densities
instrument
in the different types of transformers.
instrument
and auxiliary transformers.
These instructions
It is ad­
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ls
transformers, portable
transformers, split-core current-measuring sets,
visa ble to start with a current not greater than
2 amperes in the secondary of a potential trans­
apply also to Type Y transformers, which are
former, or not greater than
not strictly standard but which utilize the mecha­
secondary of a current transformer.
nical construction
increase this current until the proper heating is
of standard
transformers.
5 amperes in the
Gradually
For information on the installation and care of
obtained.
transformers with unusual ratings of frequency,
cautiously with frequent checking of the rise in
secondary
temperature of the winding.
voltage, current, etc., consult
Electric
The temperature of the winding may be de­
When any special information is
termined conveniently by the resistance-change
sales
Company.
the
an
nearest
Increases of current should be made
office of
the
General
method.
order to indentify the transformer.
ing increases approximately one per cent for
Since the resistance of a copper wind­
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requested, give the complete nameplate data in
each
HANDLING
2-1/2 C, the temperature rise may be cal­
culated by measuring the " before" and "after"
When unpacking and handling the transfor­
resistances and finding the percentage increase
mer, exercise care not to damage the insulation.
in resistance.
Make an inspection to see
sistance is 0. 244 ohm and the resistance at the
mage
has
occured
during
whether any da­
shipment.
Trans­
formers that are reshipped to the point of in­
stallation, even though this be done by truck,
For example, if the "after" re­
starting (room) temperature is 0. 200 ohm, the
'
' 0. 244-0. 200
percentage mcrease ts -o.2oo--
=
"'
0. 22 =22 ,o,
should be supported only by the core or mount­
which corresponds to a temperature rise of
ing supports.
x 2-1/2 = 55 C (approximately).
Do
not use the bushings or leads
mate winding temperature at any time is the
as handles.
temperature rise at that time added to the start­
DRYING OUT
Transformers that have
ing (room) temperature.
been subjected to
When facilities for measuring resistance are
su bmersion or have been stored for some time
not available the temperature may
in a damp place should be dried out previous
by placing the
to installation.
When drying out is necessary
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the follo wing method should be used.
Allo w the transformer to stand not less than
12 hours in a room of an approximately even
temperature, and record that temperature.
Measure
winding.
the
resistance
of
the
secondary
.E
(do not use a mercury thermometer) on each
coil as close to the winding as the insulation
will
permit.
The
thermometer
In the case
the actual temperature of the primary wind­
ing can
flow in the winding to raise its temperature to
primary terminal .
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the
so that the bulb will have as nearly as possi ble
the
be quite closely o btained
TESTING
The winding
80 C until the transformer is dry.
The amount of current necessary to o btain
by placing
bulb of the thermometer directly on the
The rate of rise should
temperature should be held at approximately
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of
the actual temperature of the coil.
Adjust the voltage so that sufficient current will
6 C per half hour.
bulb
should be covered with clean dry cotton waste
of current transformers of high current ratings
Short-circuit the primary winding and apply
approximately 80 C.
be taken
bulb of a spirit thermometer
an adjusta ble voltage to the secondary winding.
not exceed
22
The approxi­
Dielectric Tests
If it is desired to make insulation tests after
the drying out period, or at any other time,
3
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GEH-230T
Instrument Transformers, Dry And Compound-Filled Types
these tests should be made in accordance with
the field of the primary conductors.
American Standard C- 5 7 for Transformers, Re­
necessary that the bus exactly fill the window,
Reactors
Standards No.
should
be
(superseding
4 and No.
stricty
14).
followed,
A.I.E.E.
These rules
both
as
to
the
value of test voltage and in the method of ap­
plication.
(Note that
periodic field tests of in­
sulation should not exceed
test voltage.
65% of the factory
Occasional tests should not exceed
but the bus or buses should be centralized.
For
ratings of 1000 amperes and less, these precau­
tions are generally unnecessary.
Ambient Temperature
Instrument transformers must not
be sub­
jected to an ambient temperature (temperature
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gulators, and
It is not
of the cooling air) higher than for which they
are designed unless certain precautions are taken.
75% of the factory test voltage.)
Most transformers are designed to operate
Polarity Tests
Convenient methods for testing polarity are
on a daily average ambient temperature not ex­
ceeding 30 C.
Metermen's
Edison
an am bient temperature up to 40 C for a few
Electric Institute, and General Electric Com­
hours a day, provided the average value does
Hand book
published
by
This rule permits rated load in
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given in American Standard C-57, the Electrical
pany's pu blication GET- 97.
not exceed 30 C.
Ratio and Phase-Angle Tests
use in enclosed switchgear, will operate satis­
Refer to Electrical Metermen's Handbook
factorily in an am bient temperature of
55 C.
Generally, the allowa ble am bient temperature
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and G-E publications GET- 172 5 and GET- 97.
A few designs, particularly for
for a particular transformer is marked on the
MOUNTING
nameplate.
When connecting instrument transformers in­
Application
of
instrument
transformers
in
to power or distribution lines, it is important
various ambient temperatures should be made
to make the connection in such a manner as to
in accordance with American Standard
avoid placing line strains upon the terminals of
the transformers.
Where the primary leads consist of cables, as
in the case of certain outdoor transformers, care
should be taken not to bend the leads sharply
The connection
where they enter the bushing.
should also be made so as to prevent swaying
of the ca bles.
Where the primary leads
are brought out
through stud-type bushings or so-called
fixed
tri
terminals, care should be exercised to prevent
either longitudinal or transverse strains upon
the bushings.
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Instrument transformers of the "window" type
(without primary winding) should be installed
CONNECTIONS
The resistance of all primary and secondary
connections should be kept as low as possible to
prevent overheating at the contacts, and particu­
larly in the case of current transformer secon­
dary circuits, to prevent an increase in the sec­
ondary burden.
WARNING: Always
consider
is connected, and do not touch the leads and
less they are properly grounded.
ing).
a current transformer while the transformer is
Secondary Connections
2 000
amperes and a bove, there may be some inter­
(See Ground­
Also, do not open the secondary circuit of
ried by the bus but by the mounting feet .
ratings,
instrument
terminals or other parts of the transformer un­
energized.
high-current transformer
an
transformer as a part of the circuit to which it
so that the weight of the transformer is not car­
For
C-57.
Current-transformer secondary circuits must
Break­
ing the secondary circuit while primary current
the bus centers are kept at a minimum distance
is flowing is especially to be avoided.
of 15 in. apart; for ratings a bove 5000 amperes
cases, the entire primary current becomes the
.E
ference from the field of the return bus unless
this distance should be not less than
2 4 in. In
case this type transformer is used with more than
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one primary turn, the loop should be at least
2 4 in. in diameter.
Care should
be taken to
not be open while primary current flows.
In both
exciting current which causes the core to satu­
induce voltage dangerous to human
life across the secondary terminals. Also, the
rate and may
transformer core may be damaged
(by being
magnetized;
together and carried out without passing through
fore, if it should be necessary to change second-
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see that the secondary leads are twisted closely
4
see
DEMAGNETIZING.)
There­
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Instrument Transformers, Dry And Compound-Filled Types
ary connections while primary current is flow­
tering
ing, the secondary terminals must be short-cir­
lead resistance is necessary.
cuited while the change is being made.
burdens.
For
such
GEH-230 T
transformers, lower
Take
In the case of potential transformers the volt­
care not to disturb ground connections.
Most indoor current transformers are sup-
age drop in the secondary leads may affect the
plied with an enclosed secondary terminal block
meters.
which can be sealed.
circuit-feet of No. 10 Awg copper wire (100 feet
tion because the short-circuiting device between
the secondary terminals is closed.
The procedure for making secondary connec­
to
the open-circuited position, and then retighten
Turn the cover 180 degrees
from the shipping position, and reinstall it on
after the service leads are in place until the
short-circuiting device is opened.
CAUTION: Do not short-circuit the secondary
of a potential transformer.
sidered as general.
instrument
In cases where instruments
transformers have
always
fur­
be made in the length or size of leads which
might change the volt-ampere burden in them.
If any change is needed consult the nearest
sales office of the Company.
Secondary Burdens
When calibrations are furnished with trans­
formers, it is important that the connected bur­
den be in agreement with the burden used in
calibration.
If it becomes necessary or desir­
there is any question
should
been
nished as a unit by the factory, no change should
able to change the connected burden, and if
The casings and frames of instrument trans­
formers
and
The above instructions regarding the length
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The cover cannot be replaced
Grounding
instrument
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the short-circuiting device by loosening
the screw or nut and turning the bridge
terminal block.
connected
of wire) are satisfactory.
and
Remove the cover, attach the service leads,
the screw or nut.
the
and size of the leads to be used should be con­
tions is as follows:
open
of
For the usual conditions, leads of 50
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When shipped, the cover
of the terminal block is in the reversed posi­
indications
be
grounded.
The
regarding the effect of
such a change on the accuracy of the transformer,
the nearest sales office of the Company should
secondaries should also be grounded close to the
be consulted.
transformers.
mum allowable burdens should also be referred
Grounding of instrument trans­
formers should
be made in accordance with
A.I.E.E. Standard No. 52, March 1951, Applica­
tion Guide for Grounding of Instrument Trans­
formers Secondary Circuits and Cases. On instru­
Questions regarding the maxi­
to the Company's nearest saleS office.
If transformer calibrations are required, it is
important that
complete
information
be
fur­
nished the Company, including the number of
ment transformers, the grounding of the feet
devices to be connected in the secondary of
also grounds the cores, casings, and frames.
each transformer, the rating of the device and
If it is necessary to change the secondary
type if the device has more than one current
connections, be careful not to disturb ground
or voltage, capacity, size, and length of leads
to be used, the frequency of the circuit, and
the method of connection.
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connections.
Secondary Leads
When planning installations of current trans­
Polarity
formers, the resistance voltage drop of the sec­
In wiring instrument-transformer circuits, it
ondary leads should be included in calculating
is necessary to maintain the correct polarity
.E
the secondary volt-ampere burden carried by
the transformer.
This total burden should be
relation between the line and the devices con­
nected to the secondaries.
For this reason, the
kept within limits suited to the transformers
relative polarity of each winding of a trans­
used.
For many conditions, secondary leads
former is indicated by a marker H 1 (or a white
whose resistance does not exceed that of 100
spot) on or near one primary terminal, and a
circuit-feet of No. 10 Awg copper wire
marker X 1
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feet of wire) are satisfactory.
(200
This resistance
is 0.2 ohm, requiring 5 volt-amperes at 5 am­
bushings.
peres. However, this burden is too great for
minals
transformers designed for low volt-ampere me-
will
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(or a white spot) near one secon­
dary terminal;
and
Where
will
be H1,
be
in
some
cases
taps
are
present,
marked.
The
H2, H,, etc., in
by
primary
order
white
all
ter­
leads
and
the
5
Instrument Tramformers, Dry And Compound-Filled Types
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GEH-230 T
secondary terminals X1, Xz, Xo, in order, and
be effective.
the tertiary, if present, Y1 , Y 2, Y,, in order.
of the above methods, wash the surface thorough­
H 1,
ly with clean water to avoid leaving foreign
always indicates the same instantaneous
polarity as X1, or Yt.
After cleaning a bushing by any
material.
Significance of Polarity Markings
FUSES
terminal having a polarity marking similar to a
given primary terminal, the polarity will be the
same as if the primary service conductor itself
were detached from the transformer and con­
nected directly to the secondary conductor.
In
other words, at the instant when the current is
flowing toward the transformer in a primary
lead of a certain polarity current will tend to
flow away from the transformer in the secondary
lead of similar polarity.
When
connecting
instrument
transformers
with meters or instruments, refer to the Instruc­
involoved.
transformer
protection
to
the
number of cases.
current-limiting
ways make certain that the secondary winding
transformer
fuse,
instrument
installation
have
transformers
been
for
indoor
installed, they
should
need no care other than seeing that they are
kept clean and dry. Transformers for outdoor
installation
should
receive
the
same care in
operation as power transformers of similar de­
sign and of similar voltage rating.
Considerable care should be exercised to make
and keep the resistance of all contacts in the
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secondary circuit as low as possible.
Cleaning of Bushings
Dirt or other contaminants on the surface of
a bushing may cause a decrease in the flashover
Danger of flashover occurs when the
.E
voltage.
surface coating is partly conducting, usually as
a result of moisture.
In some locations, operating conditions are
such that a periodic cleaning of the bushings is
desirable, at which time all foreign matter should
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be removed from the under, as well as the upper,
sides of the petticoats.
wet cloth may serve.
When the dirt is loose, a
If this method proves in­
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adequate, carbon tetrachloride or ammonia may
6
Type
EJ-1 ,
potential­
For this reason, current-limiting resistors should
be used in series with the fuse when necessary to
limit the current to a value which the fuse can
interrupt satisfactorily.
Replacing Fuses
potential transformers
are
equipped
However, when such transform­
ers are installed on a grounded circuit, it is com­
mon practice to substitute a brass tube (or a
"solid" connection) for the fuse in the grounded
ground at all times.
After
large
when a short circuit occurs in the transformer.
or that it is short-circuited at the terminals.
a current or a potential transformer.
a
maximum short-circuit currents which may flow
line.
so, do not disturb ground connections on either
in
With the exception of the
is either closed through the instrument circuit
Al­
intended
transformer fuses are not designed to open the
Many
MAINTENANCE
are
transformer, although the modern fuse will afford
with two fuses.
When working with current transformers, al­
fuses
primarily to protect the line rather than the
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tions furnished with the meters or instruments
Potential
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a secondary
an
When connection is made to
This is to establish a permanent unfused
Do not disturb this con­
nection when replacing a fuse.
The fuses of some types of potential trans­
formers, 3000 volts and below, are supported
by a hinged cover.
If it is necessary to replace
a fuse while the transformer is connected to an
operating circuit, the cover should be opened by
an insulated hook.
After the new fuse is insert­
ed, the cover should be closed also by means
of the insulated hook, which should be of suflic­
ient length to prevent the operator from being
burned in case a short circuit exists in the trans­
former.
The cartridge fuse may be replaced by
the Type EJ-1, Size A.
In testing fuses for continuity of circuit, not
more than 0.25 ampere should be used.
In replacing Type EJ-1 fuses or in substituting
the EJ-1 for the ES-1 or the cartridge fuse, care
-;hould be taken to select a fuse unit with the
nearest voltage rating above line-to-line voltage
of the circuit regardless of the rated voltage of
the transformer.
Do not use fuse units of higher
voltage ratings, as undesirable overvoltages may
result.
One permissible exception to this gen­
eral rule is the use of the Size A, Type EJ-1
fuse in Type JE-2 transformers.
In this case
0
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Instrument Transformers, Dr y And Compound-Filled Types
the size A fuse can be used on either 2400-volt
GEH-230T
Portable potential transformers have terminals
delta circuits or 2400/41 60-volt grounded "Y"
arranged with thumb nuts.
circuits.
formers have four primary terminals.
Double-rated trans­
Connect­
ing links are used to make connections for the
magnetized, it should be demagnetized in the
following manner before being used for precision
different ratios.
Care should be exercised to
clamp the links firmly in place in order to obtain
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DEMAGNETIZING
If by accident a current transformer becomes
good contacts.
Connect at least 50-ohms resistance in
Since certain portable current transformers
series with the meters or instruments in the
have no primary windings, the cable carrying the
secondary circuit.
current to be measured is threaded through the
work:
Bring the primary current
up to as near full load as possible and gradually
opening in the transformer.
reduce
a single-rated transformer is not tapped.
series
resistance
by
one-ohm
steps until it reaches zero, being careful not to
through the hole, and other ratings may be ob­
open the secondary circuit in the process.
tained by threading two or more turns through
DIFFERENTIAL PROTECTION
the hole.
may
be
plate.
The ratings are shown on the name­
The secondary of a multi-rated trans­
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Standard General Electric current transform­
ers
used
protection
former is tapped and the different ratios are ob­
through a considerable range of burden and
tained by connecting to the proper taps, as shown
overcurrent.
on the nameplate.
This
for
differential
The
rating is obtained by use of one turn of cable
an
the
The secondary of
range
is
limited
by
the
difference in burden, the maximum overcurrent,
and the mechanical and thermal short-time rat­
ing.
Information regarding these points may be
Other
types
have
self-contained
primary
windings as well as a hole in the core for higher
ratings.
The lower ratios are obtained by con­
obtained from G-E publication GET-97 or from
necting the current to be measured to the cor­
the nearest sales office of the Company.
rect binding posts as shown on the nameplate.
INDIVIDUAL TYPES OF TRANSFORMERS
Outdoor Instrument Transformers
Bushings of outdoor instrument transformers
sometimes become
broken.
For the replace­
ment of bushings on a compound-filled trans­
former it is recommended that the transformer
be returned to the factory.
For the replacement of bushings where the
casing is not filled with compound, access is gain­
a
portion of the transformer case.
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ed by removing
Conduit connections can be made to the sec­
ondary of a dry-type transformer having flexible
secondary leads, by loosening the screws which
hold the bushing in place, removing the bush­
.E
ing, and inserting conduit fitting in place of
the porcelain bushing.
Portable Transformers
When used under ordinary conditions, port­
able transformers, both potential and current,
except split-core current transformers, will not
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vary more than 1 per cent from their marked
ratio.
When better accuracy is required, the
ratio and phase angle certificate should be used.
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By means of this certificate corrections can be
made to within 0.1 per cent on ratio and to within
3 minutes on phase angle.
Other ratings may be obtained by threading the
c � ble, which carries the current to be measured,
through the hole in the core one or more times
as shown on the nameplate.
Still
others have all
ratings self-contained.
Changes in ratio are made by means of metal
links located on top of the transformer.
The
six-rated transformers also have a tap in the sec­
ondary.
Three of the ratios are obtained by
using the full secondary winding with the proper
arrangement of links on the primary winding;
the other three ratios are obtained by using the
tap in the secondary winding with the primary
links in the same positions as before.
All con­
nections are shown on the nameplate.
High-c.ccuracy laboratory standards are multi­
rated.
All ratings are obtained by connecting the
current to be measured to the proper terminals,
which are marked on the cover.
The lower cur­
rent ratings are protected by fuses inserted in
the cover adjacent to the corresponding termi­
nals.
Unscrew the cap in order to replace a fuse.
All portable current transformers, except the
split-core type, are provided with a short-circuit­
ing switch on the secondary.
This switch should
always be closed whenever it is necessary to
7
Instrument Transformers, Dry And Compound-Filled Types
open the secondary circuit with the transformer
between the two halves of the core will affect
connected
the calibration of the set.
in
the
line.
This
short-circuiting
Current-measuring
switch should always be opened after making
sets consisting of a split-core current transformer
connections.
calibrated with an indicating ammeter and leads
will have an accuracy of plus or minus 2 to 3
Split-core Current Measuring Sets
Certain split-core current transformers are in­
ua
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per cent of full scale, and with a recording am­
tended to be used only with the instrument and
meter and lt:uds, an accuracy of plus or minu�
3 to 5 per cent of full scale.
leads with which the transformer is calibrated.
A current adapter is used with the split-core
The scales on the ammeters are marked to read
transformer for measuring small currents. With
primary amperes directly, and the ammeters
the correct size of terminals attached to the
should not be used to measure current unless
adapter, insert it in place of the fuse in the cut­
used with the transformer with which they are
out.
calibrated.
round loop of the adapter and read the ammeter.
Clamp the split-core transformer into the
an
Changes in ratio are made by turn­
ing the rotating switch in the ammeter.
Compute the line current from the formula on
Split-core current transformers should not be
the nameplate of the adapter.
The use of the
current adapter does not affect the accuracy of
for the full voltage of the circuit.
the current measuring set, and it may be used
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ar
tM
used around any conductor which is not insulated
The butting core surfaces must be kept clean
with sets having either the indicating ammeter
or the recording ammeter.
ww
w
.E
lec
and free from any dirt as a very slight opening
3-54
.c
om
GEH-230T
{12M)
MET E R AN D
IN ST R U MENT
GENERAL
WEST
D EP A R T MEN T
fj ELECTRIC
lYNN,
MASS.
0