POWER TRANSFORMER TEMPERATURE RISE
TEST AT LOAD BEYOND NAMEPLATE RATING BASIC INFORMATION
How To Conduct Temperature Rise Test
For Power Transformer Beyond Nameplate Rating?
After completing the hot resistance
tests data recorded during tests may be evaluated to determine
preliminary exponents. The preliminary exponents may be used to
evaluate whether an excessive top oil temperature or winding hottest
spot temperature may occur during this test.
It is suggested that the winding
hottest spot temperature be limited to 140 ˚C and top oil be limited
to 110 ˚C, unless other values are agreed upon by the manufacturer
and user. The top oil temperature and the measured rate of change of
the oil level with temperature may be used to evaluate whether
excessive oil levels may occur during this test.
If it becomes apparent that excessive
values may be obtained, the load may be reduced from the 125% value,
so the top oil temperature, winding hottest spot temperature, and oil
level are limited to acceptable values.
After the evaluation of risk and the
load beyond nameplate to be applied has been determined, proceed with
the test as follows:
a) Short-circuit one or more windings,
and circulate a constant current , at rated frequency, equal to
125% of rated current (1.25 x IR), plus
additional current to produce losses equal to the rated no-load loss.
The current to be circulated may be
determined using Equation (3). Continue applying this current until
the top oil temperature does not vary by more than 2.5% or 1 ˚C,
whichever is greater, in a time period of three consecutive hours.
b) Record all data listed in Clause 6
and Clause 7 after the top oil temperature rise has stabilized and
while is being applied:
c) Reduce the current to 125% of rated
current ( ) and hold for a minimum time period of one hour. Calculate
and record as measured current/ for later use in 9.8.5.
d) At the end of the one-hour period,
while the current equal to 125% of rated ( ) is being applied, record
all data.
e) Remove the load current, and measure
a series of hot resistances of the windings at appropriate time
intervals to determine the average winding temperatures using the
cooling curve method in IEEE Std C57.12.90-1999. Only those windings
found to be the hottest windings in item e) of 9.5 need be measured.
No comments:
Post a Comment