Answer / ambat

The transformer winding temperature measurement is a
complicated procedure since we cannnot place any sensor on
the surphase of the winding.So normally a WTI CT is
connected with suitable ratio and the secondary current is
used to heat a resiistance kept inside the thermowell
filled with the same oil.the resistance used for this will
be of the same thermal characteristic of the transformer
winding wire to get the thermal image.Then temperature of
the heated oil is measured by using RTD or any other
temperature measuring device.SO many other elctronic
devises are also now available. but in all devices WTI CT
are essential

Answer / mohamed

how to select the CT ratio for WTI
the answer :
SCIENTIFIC CONTROLS Mechanical Instruments are incorporates
proven design features acquired from many years of
experience in providing Temperature Indicators/Controllers
for Power & Distribution Transformers.
Oil Temperature Indicator: The Oil Temperature Indicator
(OTI) measures the Top oil Temperature. It is used for
control and protection for all transformers.
Winding Temperature Indicator: The Winding is the component
with highest temperature within the transformer and, above
all, the one subject to the fastest temperature increase as
the load increases. Thus to have total control of the
temperature parameter within transformer, the temperature
of the winding as well as top oil, must be measured. An
indirect system is used to measure winding temperature,
since it is dangerous to place a sensor close to winding
due to the high voltage. The indirect measurement is done
by means of a Built-in Thermal Image.
Winding Temperature Indicator is equipped with a specially
designed Heater which is placed around the operating
bellows through which passes a current proportional to the
current passing through the transformer winding subject to
a given load. Winding Temperature is measured by connecting
the CT Secondary of the Transformer through a shunt
resistor inside the Winding Temperature Indicator to the
Heater Coil around the operating Bellows. It is possible to
adjust gradient by means of Shunt Resistor.
In this way the value of the winding temperature indicated
by the instrument will be equal to the one planned by the
transformer manufacturer for a given transformer load.

Answer / arvind

if the transformer is oil cooled then temperature is
measured by dipping thermometer to the top oil.And if ithe
xformer is aircooled then it is measured by resistance
method.

Answer / shiva

sumpenrs test is also used to find the temp rise of the
transfrmers.

Answer / vikram

it is easy to find the temperature of the transformer
winding by BUCHHOLZ RELAY and also with the THERMAL RELAY.
ALSO WE CAN SET THE LIMITS OF THE TEMPERATURE FOR SAFETY.

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