DOCNO:

CoreI:

CTsizingcalculationfor33kV‐DefiniteTimeGroundO/CProtection(51NS)

BasicData:

Ratio = /1A

Accuracyclass =

Burden(VA) = VA

Burdensofrelaysconnected:

IDMTOvercurrentRelay = VA

CableLength(m) = m

CableSizeofCTconnected = Sqmm

Leadresistanceat75ºCfor4mm2coppercable = Ω/km

LoopResistance(RL)(Ω) = (Ω)

LoopBurden(VA) = VA

TotalMeterBurden(VA) = VA

TotalBurdenonCT(VA) = VA

Selectedburdenismorethanrequired. HENCESAFE.

CoreII:

CTsizingcalculationfor33kV‐RestrictedEarthFaultProtection(64R)

BasicData:

Ratio = /1A

PrimaryVoltage(kV) = kV

SecondarVoltage(kV) = kV

AccuracyClass =

Transformerrating = MVA

Impedenceoftransformer = %

Maximumthroughfault,MVA = (8x100)/8.35

= MVA

ThroughFaultcurrentatprimaryIf = (95.81x1000)/(√3x33)

If = A

ThroughFaultcurrentatsecondaryIfs = (95.81x1000)/(√3x6.6x900)

Ifs = A

1.1

PS

8.35

6.6

33

900

1.863

8

95.81

1676.29

1.72

15

1.62

0.1

1.0

1.62

1.3

TRANSFORMERSECONDARYSIDENEUTRALCT

1.0

1.2

150

5.41

0.1

4

1.1

900

5P10

1 of 18

DOCNO:

TRANSFORMERSECONDARYSIDENEUTRALCT

BurdensofRelaysconnected:

RestrictedEarthFaultRelay = VA

CableLength(m) = m

CableSizeofCTconnected(Sqmm) = Sqmm

Leadresistanceat75ºCfor4mm2coppercable = Ω/km

LoopResistance(RL)(Ω) = Ω

LoopBurden(VA) RL = VA

InternalresistanceofCTsecondary(Ω) Rct = Ω

RequiredKneepointVoltage

≥ (2xIfs(Rct+2RL))volt

≥ 2x1.87x(2+2x1.623)

≥ V

≥ V

1.2

1.3

1.00

Vk

Vk

19.55

500

150

5.41

1.6230

1.6230

2

4

2 of 18