Negligence of FO Sensors
Advantages of FO Sensors
Recent development to measure Hot spot temperature.
FO Probe Installation.
Transformer loading capacity is limited by winding
temperature which is not uniform.
Winding Hotspot temperature.
Conventional methods for measurement.
Assumptions in conventional methods.
Negligence of FO Sensor:
Fragile- High percentage of fiber failures due to breakage in
Cost- high initial cost compared to a conventional product
Advantages of FO Sensors:
Reliable and do not cause delay during emergency
Require less maintenance.
Robust fiber optic sensors have been constructed.
FO probe- 200 micron optical fiber with a permeable
protective PTFE sheath.
Based on GaAs technology
Operating Principle of FO Sensor
Based on variation in absorption spectrum of GaAs with
respect to temperature
White light is incident on the crystal.
Depending on temperature light is more or less absorbed and
the less is reflected by a mirror.
Reflected light is analyzed electronically.
Temperature range: −40°C to 225°C
Accuracy : 2°C
Available sensor length: 1 to 15 meters
Fiber type: 200 μm silica fiber
Cable sheathing: Double PTFE sheathing (spiral wrap)
Sensor dimensions: 1.5 mm O.D.
resistance to chemicals
completely immune to EMI and RFI environments
FO Probe Installation
Sensor can be embedded in a spacer or attached directly to a
conductor whose temperature is to be measured.
Or it can be inserted in the spacer between successive
disks(a slot is cut in the spacer and glued)
The 2nd method avoids breaking and restoring the conductor
Installation of FO Probe and its handling during
manufacturing are challenging to avoid sharp bends.
This may break the fiber.
An improvement is a simplified through-wall connection.
This optical feed has a simple design, provides low loss optical
Connection and leak free operation. With this, survival rate of
FO sensors is better than 90%.
Hot spot measurement with fiber optic sensors is now being
accepted by many utilities and there are some drastic
improvements in their design and construction.
It is most likely fiber optic sensors will be used for transformer
cooling, loading etc., considering less maintenance, fast
response and accuracy.
With more and more development in FO technology, cost of
FO temperature monitoring systems can be fraction of 1% of
the cost associated with power transformer.
Long term benefits can be achieved.
Nasser a. Al-Qahtany*, Krishnan s. Balasubramanian, “Optic
Fiber Sensors for transformer winding hot-spot measurement
- Saudi electricity company specification” national grid SA –
Saudi electricity company, standards & specifications
Sheldon p. Kennedy, Thomas Gordner, “Hot spot studies for
sheet wound transformer windings” Doble engineering
company – 80th international conference of Doble clients.
Tpt-32 temperature sensor for oil-filled Transformers-PDF
Andersen, O.W. “Finite element solution of skin effect and
eddy current problems” IEEE paper A77 616-6, Mexico
City, July 1977