Grounding Objectives of Grounding Types and methods of grounding Substation Grounding Neutral Grounding Advantages Conclusion

1. Substation and Neutral
Grounding
A Presentation on

2. Contents
 Grounding
 Objectives of Grounding
 Types and methods of
grounding
 Substation Grounding
 Neutral Grounding
 Advantages
 Conclusion

3. Concept of Grounding or Earthing
 All the people living or working in
residential, commercial and industrial
installations, particularly the operators and
personnel who are in close operation and
contact with electrical systems and
machineries, should essentially be protected
against possible electrification. To achieve
this protection, Grounding system of an
installation is defined, designed and
installed according to the standard
requirements..

4. Grounding
 Electrical Grounding can be defined as the
process of transferring the immediate discharge
of the electrical energy directly to the Earth
with the help of the low-resistance wire.
or
 Connecting the neutral point of supply system
or the non current carrying parts of the
electrical apparatus to the general mass of
earth in such a manner that all times an
immediate discharge of electrical energy takes
place without danger.
Grounding

5. Objective
Of
Grounding
To provide safety to
personnel during normal
and fault conditions by
limiting step and touch
potential.
To assure correct
operation of
electrical/electronic
devices.
To prevent damage to
electrical/electronic
apparatus.
To stabilize voltage during
transient conditions and to
minimize the probability of
flashover during transients.
To divert stray RF energy
from sensitive audio, video,
control, and computer
equipment.
To dissipate
lightning strokes.

6. Why grounding.?
Personnel Safety Fault current to earth

7. Types of Circuits based on Grounding
Ungrounded System
An ungrounded system
is defined as a system
without an intentional
connection to ground,.
The neutral of an
ungrounded system
under reasonably
balanced load
conditions is usually
close to ground
potential.
Solid Grounding
A system is
considered to be
solidly grounded
when its neutral is
connected directly to
a station ground or
earth with no
intentional
impedance in that
connection.
Used in low voltage
system up to 600V
Resistance/Reactance
Grounding
A system is considered
to be grounded when its
neutral is connected
directly to a station
ground or earth with
intentional impedance
in that connection.
Used from 1000V to
33KV.
Resistive-grounded system

8. Methods of Grounding
Rod ground-electrode Grounding Plate Pipe grounding-electrode

9. Neutral Grounding
 The process of connecting the some electrical part of the
system (e.g. neutral point in a star connected system) to
earth (i.e. soil) is called grounding.
 Neutral can be grounded in different ways.
 Solid or effective Grounding
 Resistance Grounding
 Reactance Grounding
 Peter-son Coil Grounding
 The choice of the method of grounding depends upon many
factors including the size of the system, system voltage
and the scheme of protection to be used.
** Grounding also called Earthing.
** Fact: British terminology calls it earthing whereas the
American terminology refers to it as grounding.
Neutral Grounding resistor

10. Neutral Grounding
** solid grounding used below 11KV system, but resistance grounding used from 2.2KV to 33KV.

11. Reactance Grounding
 a reactance is inserted between
the neutral and ground as shown
in Fig. The purpose of reactance
is to limit the earth fault
current. By changing the
earthing reactance, the earth
fault current can to changed to
obtain the conditions similar to
that of solid grounding.
** High transient voltages appear
under fault conditions
Neutral Grounding
Peter-son Coil Grounding
 As the capacitive currents are responsible for
producing arcing grounds. These capacitive
currents flow because capacitance exists between
each line and earth. If inductance L of appropriate
value is connected in parallel with the
capacitance of the system, and L is so adjusted
that IL = IC, then resultant current in the fault will
be zero.
 “When the value of L of arc suppression coil is
such that the fault current IF exactly balances the
capacitive current IC, it is called resonant
grounding.”

12. Substation Grounding
 When a whole system is grounded properly at
common point or potential is called substation
grounding.
 Why substation grounded is needed?

13. Cont.
 The substation grounding system is
an essential part of the every
electrical system. The proper
grounding of a substation is
essential and very important for
the following two reasons. First, it
provides a means of dissipating
electric current into the earth
without exceeding the operating
limits of the equipment.
 **The ground grid consists of
horizontal interconnected bare
conductors (mat) and ground rods.
The design of the ground grid to
control voltage levels to safe
values should consider the total
grounding system to provide a safe
system at an economical cost.
 Safe grounding requires the
interaction of two grounding
systems:

14. Cont.
 The desired value is usually lesser than 1 Ohms.
For a little detailing,
 1. Maximum allowable earth resistance of a large
power station is 0.5 ohm
 2. Maximum allowable earth resistance of major
power station is 1.0 ohm
 3. Maximum allowable earth resistance of small
substations is 2.0 ohm
 4. Maximum allowable earth resistance for all
other cases is 5 ohm.
 The grounding value depends on the soil resistivity.
 Soil resistivity is resultant of variety of factors like
 Moisture content and retention quality
 size of the grains and the uniformity
 presence or absence of pebbles, rocks, quality of
soil, contaminants, plastic waste and other factors
that impede the flow of current
Grounding mat and mesh

15. Cont.
 The NFPA and IEEE recommend a ground resistance
value of 5 ohms or less while the NEC has stated to
“Make sure that system impedance to ground is less
than 5 ohms specified in NEC 50.56. In facilities with
sensitive equipment it should be 5ohms or less.”
 The intentional ground: consisting of grounding
systems buried at some depth below the earth’s
surface
 The accidental ground: temporarily established by a
person exposed to a potential gradient in the vicinity
of a grounded facility
 Purpose of grounding that any grounded
object can be safely touched..

16. Switchgear Body Ground
Outdoor
Substation
Grounding
Equipment Ground to main Bus

17. Comparison between different grounding
methods.

18. Advantages:
 It will be a stable neutral point.
 Life of the insulation will increase.
 Will get general safety to personnel and the equipment due to the operation
of the fuses.
 Overvoltage due to sudden lightning will be discharged to the earth.
 Earth fault relaying will relatively simple.
 Overload protection.
 Protect from sever damage to system of equipment during fault conditions.

19. Conclusion
 Ground is a source for unwanted currents and also as a return path for
main current. While Grounding is done not for return path but only for
protection of delicate equipment. It is an alternate low resistance path
for current. Earth is used for the safety of the human body in fault
conditions while Grounding (As neutral earth) is used for the protection
of equipment.
 It seems grounding is very necessary for personnel as well as for system
protection, and should be done for even a small equipment, while in
large systems proper grounding rules and codes must be followed.