new microsoft powerpoint presentation .ppt

8/14/2019 New Microsoft PowerPoint Presentation .ppt

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Grounding of Electrical

systems


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Grounded & Ungrounded Systems


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Grounded & Ungrounded Systems


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Grounding & Bonding

Grounding Neutral of power supply unit is attached to earth

Neutral of different utility sections is attached to

ground

Bonding Enclosures of two different equipments are

attached to each other with a solid conductor to

avoid static charge development


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Requirement of Grounding &

Bonding

To avoid electrocuting of living entities

To avoid transient over voltages To direct static charges to ground

To have an easy identification of faulty

conditions To protect electrical equipment


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Bonding


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Methods of Grounding


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Grounding Techniques


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Ungrounded Systems


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Solid Grounding

Neutral of the power supply is attached directly to ground

Neutral point is held at earth potential in all conditions

Advantages Faulty conditions could be identified easily

No over voltages on healthy phases occur

High safety of living entities

Disadvantages Large values of fault current

Possible equipment damage


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Solid Grounding


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Resistance Grounding

Neutral of the power supply is attached to ground

through a resistor

Value of R should neither be very low nor very high

Advantages Fault current magnitude is reduced

Improves the stability of the system under faulty

conditions

Disadvantages

Neutral is displaced during an earth fault

Large amount of energy is produced in the earthing

resistor for a fault


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Resistance Grounding


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Reactance Grounding

A reactor is attached between neutral and

ground

Higher fault currents would be required forinterruption

By adjusting the value of reactance we can

adjust the system to operate as any scheme ofgrounding


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Reactance Grounding


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Resonant Grounding

A variable inductance coil is used to avoidthe flow of charging current for faultconditions

If IL=IC fault current would be almost zero Reactor is provided with tapings to avoid

different values of charging current

A small magnitude of fault current flowswhich is in phase with the faulty phasevoltage


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Resonant Grounding


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Voltage Transformer Earthing

A single phase voltage transformer is used

to make a ground connection.

Primary is attached between neutral and

earth

A low resistance is attached in series with

a relay across the Secondary

Eliminates the condition of arcing grounds

and transient over voltages


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Voltage Transformer Earthing


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Grounding Techniques for Delta

Connected System

For system sections having delta

connections a virtual neutral is achieved to

facilitate the protection system Grounding transformers are used to create

this virtual neutral point

Grounding T/F Types Zig-Zag Transformers

Wye-Delta Transformers


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Zig-Zag Transformer


Connected System

G di T h i f D lt


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Zig-Zag Transformer

Behavior of Zig-Zag transformer durring a ground

fault


Connected System


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Wye-Delta Transformer

Primary is attached to the system for which

grounding is required

Neutral may be solidly or impedance

grounded

Secondary is delta connected or may be opendelta connected


Connected System


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Wye-Delta Transformer In normal conditions the transformer behaves like

an open circuited secondary and draws only a

small magnitude of magnetizing current


Connected System


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Wye-Delta Transformer Operation under ground fault conditions


Connected System


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Equipment Grounding

Equipment grounding is done to avoidelectrocuting of living entities

Fault current could flow through ground mass or

conductive path Usually low impedance or solid grounding is

used to avoid potential rise at the equipmentenclosure

For remote distances potential could developbetween different locations over the groundmass


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Equipment Grounding


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A conductive path is provided to minimizethe impedance for fault current

Equipment Grounding


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Ground Fault Current Detection


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Grounding Connection for Surge

Protective Equipment

Surge arrestors are used to direct any line

surge to ground

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