SFRA Typical Results This presentation gives typical results for different transformer windings and configurations.
SFRA Typical Results This presentation gives typical results for different transformer windings and configurations.
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 Effect of of Oil – result resultss with with and with without out Effects of Poor Grounding Effect of Magnetization Sister Units Short Circuit Tests
Wye-wye : HV’s Note low frequency variations
Wye-wye: LV’s Less dB down than HV
Wye-wye HV Short Circuit LV windings shorted
Another HV Wye HV winding – three phases one DETC positions
Another HV Wye Detail – three phases Center phase Two outer phases
Another HV Wye Detail – three phases
Center phase
Two outer phases
Delta-wye HV’s Typical response at low frequencies
Delta-Wye: LV’s Less dB down than HV
Delta-Wye HV Short Circuit LV windings shorted together
Another Delta-Wye HV Note low frequency shape – low MVA
Autotransformer HV HV Open Circuit
Autotransformer LV LV (common) winding – typical result
Autotransformer tertiary Tertiary Open Circuit
Autotransformer HV HV LV and Tertiary compared
Tertiary winding
LV (common) winding
HV (series) winding
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
Variation with LTC position 16 Lower through 8 Lower for one winding
Variation with LTC position Low frequency detail
16 Lower
8 Lower
Variation with LTC position Mid frequency detail
16 Lower
8 Lower
Variation with LTC position High frequency tap position variation
Variation with Reversing Switch position
One winding – neutral from raise & lower
Variation with DETC position HV winding – one phase three DETC positions
Variation with DETC position Low frequency detail
Position A
Position E
Variation with DETC position Low frequency detail
Position A
Position E
Variation with DETC position High frequency detail
Variation with and without oil LV winding
With oil – Lower resonant frequencies
Without oil Higher resonant frequencies
Effect of Bad grounds Original and Bad Red lead ground
Bad red lead ground
Original
Effect of Bad grounds Original and Bad Black lead ground
Original
Bad red lead ground
Effect of Bad grounds Original and Bad Red & Black lead grounds
Bad red and black lead grounds
Original
Effect of Magnetization Low frequency variation is severe – but identifiable Magnetization affects the core response
Magnetization & Grounding variation
HV winding High frequency variation due to grounding
Magnetized center phase
Magnetization affects the core response
Sister Units showing Magnetization HV winding
Magnetization variation
Sister Units showing Magnetization HV winding – same unit, more magnetization
Magnetization variation
HV Wye winding: Open and Short HV winding – same unit, more magnetization
Short circuit wye winding
Open circuit wye winding Very similar at high frequencies
HV Delta winding: Open and Short HV winding – same unit, more magnetization
Short Circuit
Open Circuit
Similar at high frequencies
Typical Results - Conclusions
• Results vary between units – depending on size 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!!!
