sfra typical results v1

8/10/2019 SFRA Typical Results v1

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Together We Power

The World

SFRA Training

Typical Results


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SFRA Typical Results

This presentation gives typical results fordifferent transformer windings and

configurations.


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SFRA Typical Results

Wye-wye transformer (delta-delta)

Delta-wye transformer (delta-star)

Measurement Sense (H1-H0 v H0-H1)Variation due to LTC

Effect of LTC Reversing Switch

Variation due to DETC

Effect of Oil results with and without

Effects of Poor Grounding

Effect of Magnetization

Sister UnitsShort Circuit Tests


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Wye-wye : HVs

Note low frequency variations


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Wye-wye: LVs

Less dB down than HV


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Wye-wye HV Short Circuit

LV windings shorted


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Another HV Wye

HV winding three phases one DETC positions


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Another HV Wye

Detail three phases

Center phaseTwo outer

phases


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Another HV Wye

Detail three phases

Center phase

Two outer

phases


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Delta-wye HVs

Typical response at low frequencies


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Delta-Wye: LVs

Less dB down than HV


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Delta-Wye HV Short Circuit

LV windings shorted together


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Another Delta-Wye HV

Note low frequency shape low MVA


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Autotransformer HV

HV Open Circuit


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Autotransformer LV

LV (common) winding typical result


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Autotransformer tertiary

Tertiary Open Circuit


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Autotransformer HV

HV LV and Tertiary compared

HV (series) winding

Tertiary winding

LV (common) winding


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Measurement Sense: H1-H0 v. H0-H1

Effect is smaller when the two bushings are

similar e.g. H1-H3 v H3-H1

H0-H1

H1-H0


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Variation with LTC position

16 Lower through 8 Lower for one winding


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Low frequency detail

16 Lower

8 Lower


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Mid frequency detail

16 Lower

8 Lower


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High frequency tap position variation


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Variation with Reversing Switch position

One winding neutral from raise & lower


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Variation with DETC position

HV winding one phase three DETC positions


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Position A Position E


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Position A Position E


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High frequency detail


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Variation with and without oil

LV winding

With oil

Lower

resonant

frequencies

Without oil

Higher

resonant

frequencies


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Effect of Bad grounds

Original and Bad Red lead ground

Original

Bad red lead

ground


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Original and Bad Black lead ground

Original

Bad red lead

ground


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Original and Bad Red & Black lead grounds

Original

Bad red and black

lead grounds


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Effect of Magnetization

Low frequency variation is severe but identifiable

Magnetization affects thecore response


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Magnetization & Grounding variation

HV winding

High frequency variationdue to grounding

Magnetization affects the

core response

Magnetized center phase


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Sister Units showing Magnetization

HV winding

Magnetization variation


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Sister Units showing Magnetization

HV winding same unit, more magnetization

Magnetization variation


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HV Wye winding: Open and Short


Open circuit wye windingVery similar at high

frequencies

Short circuit wye winding


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HV Delta winding: Open and Short


Open Circuit Similar at high

frequencies

Short Circuit


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Typical Results - Conclusions

Results vary between units depending onsize and type of unit

Results vary with magnetization &grounding

Results vary with tap changer positions Results vary with oil level

Know what to expect see next slide!!!


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One Transformer: HV, LV, SC & IW

IW = Interwinding measurement

HV Open Circuit

H-X interwinding

Short Circuit

LV Open Circuit

sfra typical results v1

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