Winding Temperature indicator on Transformer 1

[k0412d]

Hello all,

My question is as said in the Title about Temperature indicator on transformers, for both dry and liquid immersed transformers.
Just to be sure that I'm not missing any key point about the measurement here is my understanding for both types, please correct me if anything's wrong, simplistic or non-pertinent.

On liquid immersed transformers two ways are used to monitor winding temperature :
+ Indirect - by measuring oil temperature near the hottest stop and then adding the winding gradient by means of a current measurement.
+ Direct by means of an optical sensor.

On dry type transformers my undurstanding (but I'm not familiar at all) of the measurment was that a sensor could be placed into the resin and used alone to monitor the winding temperature (without adding any temp gradient).

So here are the questions:
I understood that placing the sensor directly on the paper (or enlameled) insulated winding in liquid immersed transformers was not done because it may put at voltage the sensor? (even though winding are coated?)

For dry type, putting sensor in the resin does not compromise insulation? or put sensor at voltage? and what about temp gradient?


Hope I've been intelligible enough, thanks you for your help.

 

[prc]

In oil immersed trfs, the winding temperature indication (ie average or hot spot) is achieved by indirect method. ie an oil temperature indicator will be programmed to show oil temperature( from sensing bulb at top of the tank) plus winding gradient ( by a heating coil which is fed from a CT feeding current proportional to winding current.) winding gradient will be found out at fcatory during tempertaure rise test and the heater coil will be adjusted to show the winding gradient.Hence you can say it is a slave programmed to show top oil plus winding gradient temperature.

In case of dry type trfs, a Pt-100 or similar sensor is embedded at neutral end of LV winding and indicates the winding temperature.

In case of direct measurement, which can be for oil filled or dry type, fibre optic sensors are embedded in winding and fibre optic cables are used to take insulted connections outside.Many companies supply such indicators-neo optix,fiso,luminex (now weidmann)

 

[k0412d]

Thank you very much for the info,
Just to be sure that I'm getting it right, direct measurment is done by optic means to ensure dielectric insulation (Sensor/T° controller device)?

And in dry type trfs, pt100 is embedded in neutral end when earthed or regardless of that?

THanks

 

[prc]

Optic cables are used to get insulation from High voltages. In case of dry type, sensor is put at LV earthed neutral end,in between LV and core touching the winding surface.During High voltage testing of winding meter has to be disconnected.

 

[k0412d]

ok, thank you very much.