OTI- Oil Temperature Indicator Safety Connection diagram, Working principle, alarm & trip setting.
1- OTI- Oil Temp Indicator:
Winding is the important parts of transformer which is costly part so for winding safety, the oil temp indictor relay is used for protection. A more temp increases due to over load and short circuit then the oil temp also increases. Due to high temp, the winding may be failure or oil tank may be damage. During load condition the current is circulated through winding then oil temp increases.
The main purpose of OTI is to indicate the oil temp of transformer oil tank. default temp setting of OTI is 70 and 75 degree centigrade. Fist alarm setting is 70 degree centigrade and 2nd tripping setting is 75 degree centigrade.
2- Construction of OTI:
According above figure the black needle shows to the current temp and red needle shows the highest temp of the day. After 24 hrs the red needle is reset manually.
The green and red, two knobs are used for temp setting. The green knob is used for alarm temp setting and red knob is used for temp trip setting.
Oil temp sensor is installed on tank for receiving temp signal into OTI instrument through heat resistance.
3- Connection diagram:
4- Working principle:
A oil temp sensor is used for measuring the oil temp. Thermal temp sensor is used through tank space.
A liquid is filled in measuring equipment and heating resistance is connected to the temp sensor. It is proportional to the oil temp. When oil temp is rises then heating resistance temp also increases resultant the instrument liquid volume is increase and needle moves.
WTI instrument liquid volume is increase according default setting if the temp in 70 degree centigrade then alarm contact will be closed resultant hooter will be activate on HT panel. If the temp is 75 degree centigrade then the trip contact will be close resultant HT panel circuit breaker will be tripped.
5 - Why OTI is used?
Oil Transformer is a costly equipment. Due to over heating, overload or short circuit in the oil tank,
resultant winding insulation may be failure or explosion in oil tank. Due to this condition a lot of temp is
produced in oil tank So prevention for winding and explosion in tank, The OTI instrument is
installed in the middle of tank.
When a fault is occurred in a tank then due to high temp WTI instrument is activated and a signal
of alarm and tripping is sent to the transformer incomer breaker. So in this way the oil transformer can be
prevented
by OTI.
Oil temp indicator has two important features which is mentioned in below.
- Due to any fault or overload condition in transformer oil tank and after crossing 70 degree centigrade temp setting then it provides alarm signal for protection on the HT panel.
- Due to any fault or overload condition in transformer oil tank and after crossing 75 degree centigrade temp setting then it provides trip signal for protection on the HT panel.
