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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
Grounding Techniques for Delta
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
Grounding Techniques for Delta
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
Grounding Techniques for Delta
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
Grounding Techniques for Delta
Connected System
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Wye-Delta Transformer Operation under ground fault conditions
Grounding Techniques for Delta
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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