Phân tích đáp ứng tần số trong thí nghiệm Máy Biến Áp

Why SFRA ?4  To assess mechanical integrity of a transformer  To detect core displacement and winding deformation due to :  Large electromagnetic forces from fault current  Transform

Benefits of SFRA - Case Studies

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Transformers- Modern Trends

B B Ahir

Gujarat Energy Transmission Corporation Limited

 Condition Monitoring in GETCO

 Why SFRA ?

 Case study (1):SFRA - How it helped to find a fault in winding

 Case study (2): SFRA - How it helped to find a fault in core

 Case study (3): SFRA - How it helped to find a fault in core

 Conclusion

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Condition Monitoring in GETCO

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Insulation Resistance and Polarisation Index √

Capacitance & Tan δ measurements √

Measurement moisture content in active parts of Transformer √

Transformer

Why SFRA ?

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 To assess mechanical integrity of a transformer

 To detect core displacement and winding deformation

due to :

 Large electromagnetic forces from fault current

 Transformer transportation and relocation

 Winding shrinkage causing release of clamping structure

 To detect broken or loosened clamping structure

 Hoop Buckling

 Shorted turns and open winding

Initially SFRA along with Low Voltage Test and DGA

OSR relay operated due to LV side Isolator support insulator flash over

DGA Results ( Post Tripping )

Nature of incipient fault Major Key

Gas

Minor Key Gas

Low voltage magnetic balance test found abnormal in R phase and DGA indicates arcing

Case study (1):

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HV – N at Tap No.1 ( Post fault - Abnormal)

500Hz to 2MHz with +/- 3 dB: Tap and Main winding

HV R Phase

HV R phase shifted -3dB with reference to other phase in main and tap winding portion

Case study (1):

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LV – N at Tap No.17 ( Post fault - Abnormal)

500Hz to 2MHz with +/- 3 dB: Tap and Main winding

LV R Phase

20Hz – 10KHz – Core deformation/open ckt./

Shorted turns / residual

magnetism

LV R phase shifted widely with reference to other phase in main and tap winding portion

It seems like open circuit.

Case study (1):

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 SFRA LV R phase found abnormal – defect in

tapped winding ( 500Hz to 2 MHz) and open winding ( 5Hz to 100kHz ) with +/- 3 dB

variation.

 Problem reflected in low voltage magnetic

balance and DGA ( Arcing ) also.

 Based on above abnormal results, decided to

internal inspection of this transformer.

Analysis

Case study (1): Internal Inspection

 Drying process with oil filtration

 Take SFRA and other supporting test

Burned connecting leads

Case study (1):

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HV – N at Tap No.1 ( Normal – After rectification )

HV R Phase

All phases are identical after rectification of problem

Case study (1):

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LV – N at Tap No.17 ( Normal – After rectification)

LV R Phase

All phases are identical after rectification of problem

Case study (1):

LV MAGNETIC BALANCE ( Normal – After rectification )

APPLIED VOLTAGE

 SFRA plays a role as a supporting test to confirm thefault with other test.

High key gases in routine DGA test

355 2988 13928 472 <1 538 214 57 1085

DGA Results ( on 21.04.08 , Abnormal )

DGA indicates thermal fault as per high key gases method

Case study (2): Low voltage Test

MAGNETIZING CURRENT ( Post fault - Normal)

Case study (2): Low voltage Test

SHORT CIRCUIT CURRENT ( Post fault - Normal )

HV - N ( Post fault - Abnormal)

Case study (2):

20Hz – 10KHz – Core deformation/open ckt./ Shorted turns / residual

magnetism

HV B Phase

B phase curve differ in core area in compare with other two phases which shows core related issue

B phase curve differ in core dominated area, which shows problem in core area

Case study (2):

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 SFRA showed abnormality in the core

 IR between core , frame and earth was measured

Analysis

Case study (2): Schematic Diagram

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Case study (2): Analysis

Case study (2):

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HV - N ( LV Shorted ) ( Normal – After rectification )

After attending the problem all phase curves found identical

Case study (2):

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LV – N ( Normal – After rectification)

After attending the problem all phase curves found identical

 Such kind of unbelievable fault can be identified bySFRA.

 In this case SFRA played a vital role as a supporting toolwith DGA to detect the faulty area and to reach up to theroot cause of the fault

Tripped on differential relay due to failure of 66kV class

Y phase bushing with reflected of 11kV feeder

Case study (3): Low voltage Test

MAGNETIZING CURRENT ( Post fault - Abnormal )

HV PH – PH ( Post fault - Abnormal )

Case study (3):

20Hz – 10KHz – Core deformation/open ckt./ Shorted turns / residual

LV PH – N ( Post fault - Abnormal )

Case study (3):

20Hz – 10KHz – Core deformation/open ckt./ Shorted turns / residual

magnetism

All three phases response are differ in core related area as mentioned frequency

Case study (2): Analysis

Case study (2): Internal Inspection

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 After attending the problem, SFRA was taken

Yoke Bolt

Yoke Channel

Case study (3): Low voltage Test

MAGNETIC BALANCE ( Normal – After rectification)

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 SFRA responses clearly indicate faulty conditions of transformer and it

helped for root cause analysis.

 SFRA helps to detect fault by just compare with different phase with

different task without having a initial results of same transformer or same design transformer.

 SFRA plays vital role as supporting test for final conclusion as its

deliver diversity of information in only one test.

 SFRA is very useful tool to detect heavy through fault current leads to

mechanical deformation of core or winding, internal connections and contacts inside transformer.

 GETCO has adopted such diagnosis tool while fault as well as in

routine practice while shifting of transformer.

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