Two & Three Winding Transformers and Circulating Fault Currents - - PowerPoint PPT Presentation

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Two & Three Winding Transformers and Circulating Fault Currents

By: Abdur Rehman 2019 Hands on Relay School

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Purpose at the 2019 HRS

• Intention is to share our knowledge and passion for Power

Systems Engineering & Protection

• NOT intended to replace any lecture…
• Intention is to supplement other lectures

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Assumed Knowledge

• Basic understanding of symmetrical components - Phase &

Ground faults

• Working knowledge of Transformer Phase Shifts
• Fundamental understanding of power systems

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Outcomes & Takeaways

• Better understanding of transformers under faulted conditions
• Practical application of sequence network diagrams
• Visual display of circulating sequence currents for 2 & 3

winding transformers

• Introduction to help better understand the handouts

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Outcomes & Takeaways

• Sit back… Relax… and Enjoy the show.
• The step-by-step details are in the accompanying PDF for your

review… Presentation = Introduction

• Make sure to send me an email for the accompanying PDF

document, presentation, and videos… abdur.rehman@pse.com

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Video Tutorial available on Youtube

• Search for “General PAC” or visit generalpac.com
• Topic “Fault Analysis in Power System”

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2 Winding Transformer Example

DABY-G 30 MVA 115 kV 13.8 kV

MVASC = 600 MVA

Line A Line B Line C Line a Line b Line c

Y

AB PSE.com // GeneralPAC.com

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6 Step Process to calculate fault current

Step 1: Convert the system quantities into per-unit quantities Step 2: Identify the type of fault Step 3: Draw the unfaulted sequence networks Step 4: Interconnect the faulted sequence networks Step 5: Hand Calculate Sequence Currents & Voltages Step 6: Convert to Phase currents & voltages

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`

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ZG

(1)

1pu ZG

(2)

ZG

(0)

ZT

(0)

ZG

(1)

1pu ZT

(1)

ZG

(0)

ZT

(0)

Open Open

ZT

(1)

ZT

(2)

Positive Sequence Negative Sequence Zero Sequence

115kV 13.8kV

ZG

(2)

ZT

(2) 115kV 13.8kV 115kV 13.8kV

+ + + = = =

Generator Transformer System

j0.05 j0.05 j0.05 j0.10 j0.10 j0.10 j0.05 j0.05 j0.05 j0.10 j0.10 j0.10

Sequence Components

Source

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ZG

(1)

1 pu

ZT

(1) 115kV 13.8kV

ZG

(1)

1 PU

ZT

(1) 115kV 13.8kV

ZG

(2)

ZT

(2) 115kV 13.8kV

ZG

(0)

ZT

(0) 115kV 13.8kV

Open

3PH Fault 1LG Fault

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Big Picture 1 of 5

3 Phase Fault

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Big Picture Comparison

3 Phase Fault

8367|-90 8367|150 8367| 30 1004|-60 1004|180 1004| 60

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Big Picture

1LG Fault

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Step #4

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Step #5

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Big Picture Comparison

1LG Fault

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Big Picture 1 of 1

LL Fault

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Big Picture 1 of 1

2LG Fault

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3 Winding Transformer Example

Y-D-YG 30 MVA 115 kV 13.8 kV

MVASC = 600 MVA

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Sequence Components

ZG

(1)

1pu ZG

(2)

ZG

(0)

ZG

(0)

ZT

(0)

Open

ZH

(1)

Positive Sequence Negative Sequence Zero Sequence

ZG

(2) 115kV 13.8kV 115kV 13.8kV

+ + + = = =

Generator Transformer System

ZM

(1)

ZL

(1)

ZH

(2)

ZM

(2)

ZL

(2)

ZH

(0)

ZM

(0)

ZL

(0)

T

Open

T T

ZM

(0)

ZL

(0)

T

13.8kV

ZH

(2)

ZM

(2)

ZL

(2)

T

ZG

(1)) 115kV 13.8kV

ZH

(1)

ZM

(1)

ZL

(1)

T

1pu

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Big Picture 1 of 1

3 Phase Fault

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Big Picture 1 of 1

1LG Fault

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Big Picture 1 of 1

LL Fault

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Questions? Abdur.rehman@pse.com Generalpac.com

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