This document discusses fiber optic sensors for measuring the hot spot temperature of transformer windings. It begins by explaining that the winding temperature is not uniform, with hot spots limiting the transformer's loading capacity, and that conventional measurement methods make assumptions. It then discusses how fiber optic sensors were previously neglected due to fragility and cost but now offer advantages like reliability. Recent developments have created more robust fiber optic probes using GaAs technology. The document explains how the sensors work and details their specifications, installation process, and concludes that fiber optic sensors will likely be widely used for transformer monitoring.

1. Fiber Optic Sensors for
Transformers
Guided by: Mrs. Amruta Deshpande

2. Contents:

Introduction
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Negligence of FO Sensors
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Advantages of FO Sensors
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Recent development to measure Hot spot temperature.

Construction.

Operating Principle.

FO Probe Installation.

3. Introduction:

Transformer loading capacity is limited by winding
temperature which is not uniform.
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Winding Hotspot temperature.
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Conventional methods for measurement.
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Assumptions in conventional methods.

4. Negligence of FO Sensor:

Fragile- High percentage of fiber failures due to breakage in
industry.

Cost- high initial cost compared to a conventional product

5. Advantages of FO Sensors:

Reliable and do not cause delay during emergency
overloading.

Require less maintenance.

6. Recent Development:

Robust fiber optic sensors have been constructed.
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FO probe- 200 micron optical fiber with a permeable
protective PTFE sheath.
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Based on GaAs technology

8. 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.

10. Typical specifications/Characteristics:
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Temperature range: −40°C to 225°C
Resolution: 0.1°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.
resilient construction.
resistance to chemicals
completely immune to EMI and RFI environments

11. 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
insulation

12. Installation continued…

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.

13. 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%.

14. Practical installation:

15. Conclusion:

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.

16. Future Scope:

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.

17. References:
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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
department.
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