DEICING OF TRANSMISSION LINE

CONTENTS Introduction Methods Heating and mechanical deicing High frequency high voltage excitation Theory How to achieve uniform heating? Problems faced & methods of elimination Conclusion Reference

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INTRODUCTION

In many cold regions of the world, transmission lines are subjected to atmospheric ice accumulation

Collapse of transmission line Repair expenses-high Emergence of deicing

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PREVENTION OF ICE ACCUMULATION

METHODS

1)Heating and mechanical deicing [up to 245 kv]

2) High frequency, high voltage excitation [315-735 kv]

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METHOD 1

Heating and mechanical deicing

Using rollers, conductor heatingUp to 245 kvNot widely used

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METHOD 2

HIGH FREQUENCY HIGH VOLTAGE EXITATION

315-735 kv High frequency excitation of 8-200 KHz is

used for deicing Ice becomes a lossy dielectric & heats ice In addition skin effect causes resistive losses

&heating

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System used in two different ways

1)Lines with chronic icing-system permanently attached to a section of line

2)Mounted to a truck & dispatched in an emergency to rescue a section of line

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THEORY

Source of excitation current - high frequency high voltage power inverter 88

Coupling circuit connect inverter to transmission line

Functions of coupling circuit

o Low impedance path for high frequency excitation current

o Insulation between transmission line & inverter

Most appropriate configuration- series combination of capacitor & inductor

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Capacitor- Voltage Insulation

Inductor along with capacitor- low impedance

Capacitor and inductor work in resonance

Trap- omit high frequency current prior entering HV substation

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STANDING WAVE

Two waves- equal magnitude, wavelength, sped, frequency

Move in opposite direction

Displacement of two wave add

Non traveling vibration

Oscillate up & down1111

ACHIEVING UNIFORM HEATING

High frequency power excitation produce standing waves unless line is terminated

Ice dielectric heating / skin effect resistive heating act alone

Uneven heating

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SOLUTIONS

SOLUTION 1 Terminate the line

Running waves are produced

Entail large energy flow

Energy greater than energy dissipation in ice

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DISADVANTAGE

Power capability of source increases

Termination- capable of dissipating/recycling the power

Expensive

Not used

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SOLUTION 2 Use standing wave

Apply two heating effect in complementary fashion

If magnitude in proper ratio-total heating is uniform

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Total heating have ripple

Acceptable

Requires high total input power

Ripple free total heating- adjust frequency

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Frequency adjustment affects

1. Dielectric loss in ice2. Skin effect loss in conductor

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CONCLUSION

The application of high-frequency electric field to melting ice on power transmission lines appears promising. Combined dielectric heating & skin effect heating can be used to achieve uniform heating despite standing wave patterns.

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REFERENCE1. Sullivan C R “Breaking the ice driving power

transmission lines with high frequency, high voltage excitation”. IEEE Industrial Application Magazine vol.9 no”:5 PP 49-54

2. J.D. McCurdy, C.R. Sullivan, and V.F. Petrenko,“Using dielectric losses to de-ice power transmission lines with 100 khz high-voltage excitation,” in Conf. Rec. IEEE Industry Applications Society Annu. Meeting, 2001, pp. 2515-2519.Lawrence J “Frequency and time domain analysis” vol.32 Januvary 1996 IEEE .

3. J. Hu and C.R. Sullivan, “Optimization of shapes for round-wire high-frequency gapped-inducto windings,” in Conf. Rec. IEEE Industry Applications Society Annu. Meeting, 1998, pp. 900-906. 2121