Current
Transformer Burden Ammeter is a rugged, portable instrument, designed to
field-test current transformer installations for:
_
short-circuited secondary turns
_
short-circuited primary turns
_
short-circuited secondary wiring
_
high-resistance connections in the secondary circuit
_
grounding of secondary winding when mounted on a grounded structure
_
grounding of a normally ungrounded wire
APPLICATIONS
Within
the accuracy limits of the CT, a good current transformer should not have a
noticeable change in ratio when a secondary burden is added. This is because
the primary effect of additional burden on a good CT is a rise in the secondary
voltage.
However,
if one or more turns of a CT are shorted, a substantial amount of the total
available ampere-turns is diverted into the shunt path created by the short.
Thus, the current to the circuit connected to the CT is less than
the
CT’s total secondary current.
Therefore,
when the proper burden within the ammeter is added in series with the circuit
connected to a good CT, the current indicated by the ammeter should only
decrease a few percent.
However,
in a bad CT, the additional burden will cause even more current to be diverted
into the shorted turn(s). This will cause the current indicated on the ammeter
to decrease significantly. This sudden and large decrease in the ammeter
reading will be seen immediately whenever the burden is added by using the
switch.
FEATURES
AND BENEFITS
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Multi range ammeter incorporating switch-selected burdens
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The burdens are normally shorted out, but can be put in series with the ammeter
by a spring-loaded momentary switch
_
Designed to ensure that the secondary of the CT under test will not be
accidentally opened; make-before-break construction used for ammeter range and
burden selector switches
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