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Cigré 2005, SC B5 Colloquium in Calgary Preferential Subject 1Question 7

Zoran GajićABB

Sweden

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SC B5: PS1, Q7 Transformer Inrush Currents

EFFECT OF TRANSFORMER INRUSH CURRENTS ON PROTECTION FUNCTIONS

Where to Look,

Security,

Dependability

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Transformer Inrush Currents – Where to look?

Measured in Phase Currents or in Differential Currents? 2nd harmonic

4th harmonic

5th harmonic

DC offset

Wave shape recognition

etc.

Set block level depends on position where measurement is taken

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Transformer Inrush Currents – Security?

Security? Block for all inrush cases

Not good practice to put burden on the end user to completely set this logic

15% or 7%?

Adaptive 2nd harmonic + WaveBlock good results

Correct and easy to use design is manufacturer responsibility

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Transformer Inrush Currents – Dependability?

Dependability? Trip for all internal faults

Insure that restraint level will trip in spite of CT saturation

Use of adaptive second harmonic blocking insures that

Paper in IEE DPSP 2001