Ground%20Fault%20Protection[1].ppt

8/19/2019 Ground%20Fault%20Protection[1].ppt

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Grounding

Ground Fault Protection


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Course Objectives:Upon completion of this course, you will be

able to:• Define the ground fault protective schemes

utilized in the industry today for simple radial schemes• Define the ground fault protective schemes

utilized in the industry today for complex

systems


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Ground-Fault Systems

Types of Ground Fault Protective Schemes Ground Strap

Zero Sequence

Residual


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Ground Strap System


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Ground Strap Operation


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Ground Strap System

Disadvantages

* Can only be used on main disconnect

* ust be the only neutral ground ! " can lead to nuisance trippings

" desensiti#ed tripping under an actual

faulted condition


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Ground Strap System

Disadvantages

* desensiti#ed tripping due to groundedneutrals


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Zero Sequence System


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Zero Sequence System Operation


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Zero Sequence System Operation


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Advantages

**can be used on both the main and feeder brea$ers

Disadvantages**do%nstream grounds can cause nuisance trippings

**improperly centered conductors can also causenuisance trippings


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Residual System


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Residual System


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Residual System


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Residual System Operation


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Residual System

Advantages

&sed on main and feeder brea$ers

'eutral grounds on line side have no effect

'o control po%er required

(ne)pensive if purchased %ith brea$er

'eutral C only e)ternal device

Disadvantages

'o do%nstream grounds

'ot economical for fused s%itches


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Complex Systems



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Multi-Leel Ground Fault- ProtectionSystems



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!ou"le-#nded Su"station


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!ou"le-#nded Su"station $it% Fault


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Single Point Ground System


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Modi&ied !i&&erential Sc%eme


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Modi&ied !i&&erential $it% Residual System


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#mergency Systems


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#mergency Systems $it% S$itc%ed 'eutral

irst !lternative

Utilize four"pole

#ransfer $witch


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#mergency Systems

$econd !lternative

%emove the &ain

'onding (umper


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#mergency Systems

#hird !lternative

)mploy a Differential

$cheme


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Ground Fault

*+ hat are the two schemes often employed to provide

ground"fault protection on double"ended substations-

.+ hat is the major disadvantage of the

single"point"grounding scheme for ground" fault

protection when the tiebrea/er is closed-0+ hat are the three different types of ground"fault systems-

1+ here is the ground"fault sensor located for a ground

strap system-

2+ hat is the only disconnect device that can use a ground strap system-


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Ground Fault

*+ hat are the two schemes often employed to provide

ground"fault protection on double"ended substations-

3source ground sensing

3modified differential scheme

.+ hat is the major disadvantage of the

single"point"grounding scheme for ground" fault

protection when the tiebrea/er is closed-

++!ll unbalanced single"phased loads from the remote halfof the switchboard are 4seen5 as fault current 6 which may

cause nuisance trippings+


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Ground Fault

0+ hat are the three different types of ground"fault systems-

3ground strap 7also called neutral ground strap8

3zero se9uence

3residual

1+ here is the ground"fault sensor located for a ground

strap system-

3located on the main bonding jumper


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Ground Fault

2+ hat is the only disconnect device that can use a

ground strap system-

3ground strap system can only be used on the main

disconnect


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Ground Fault

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Ground%20Fault%20Protection[1].ppt