ABUJA 5 Basics of Electrical Grounding

8/3/2019 ABUJA 5 Basics of Electrical Grounding

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Electrical Grounding

Grounding: the intentional andpermanent connection between

neutral and ground

Ground Fault: unintentional connection

between an energized conductor and

ground

90% electrical faults are ground faults



Grounding TerminologyGround

A conducting connection, whether intentional or

accidental, by which an electric circuit or

equipment is connected to the earth or to some

conducting body of relatively large extent that

serves in place of the earth.

Ground Potential Rise (GPR)

The maximum electrical potential that a

grounding grid may attain relative to a distant

grounding point assumed to be at the potential of remote earth. This voltage, GPR, is equal to

the maximum grid current times the grid

resistance.



Grounding Terminology

Grounding Grid

A system of horizontal ground electrodes that consists of a number of interconnected, bareconductors buried in the earth, providing a

common ground for electrical devices or metallic structures, usually in one specific location.

Touch Voltage

The potential difference between the ground potential rise (GPR) and the surface potential at

the point where a person is standing while at thesame time having a hand in contact with agrounded structure. [Also the potential differencebetween two different surfaces being touched with two hands.]



Grounding Terminology

Step Voltage

The difference in surface potential

experienced by a person bridging a distance

of 1 m with the feet without contacting any

grounded object.

Transferred Voltage

A special case of the touch voltage where a

voltage is transferred into or out of thesubstation from or to a remote point external

to the substation site.



Grounding TerminologyRemote Earth

A point on earth located at an

effectively infinite distance from

the location being analyzed. The

remote earth potential is thereference voltage for ground

potential rise and other voltages

developed during fault conditions.



Reasons for Grounding

Personnel (human) safety by limitingTouch Potential

Step Potential

Transferred Voltage

Tolerable Current through the body

Improve Equipment Protection and Performance

Reduce Liability Exposure



Substation Grounding Design

- IEEE 80In principle, a safe grounding design

has the following two objectives:

To provide means to carry electric currents

into the earth under normal and fault conditions without exceeding any operating and equipment limits or adversely affecting continuity of service.

To assure that a person in the vicinity of grounded facilities is not exposed to thedanger of critical electric shock.



Grounded power system



Grounding through zigzag transformer



Protective Earth Connection

(Earthing)

A protective earth (PE) connection ensuresthat all exposed conductive surfaces are at the

same electrical potential as the surface of the

Earth, to avoid the risk of electrical shock if aperson touches a device in which an insulation

fault has occurred. It ensures that in the case

of an insulation fault (a "short circuit"), a very

high current flows, which will trigger anovercurrent protection device (fuse, circuit

breaker ) that disconnects the power supply.



Functional Earth Connection

A functional earth connection serves apurpose other than providing protectionagainst electrical shock. In contrast to aprotective earth connection, a functional

earth connection may carry a current duringthe normal operation of a device. Functionalearth connections may be required bydevices such as surge suppression and

electromagnetic-compatibility filters, sometypes of antennas and various measurementinstruments. Generally the protective earth isalso used as a functional earth, though this

requires care in some situations



TN-S: separate protective earth (PE) and neutral (N)

conductors from transformer to consuming device,

which are not connected together at any point after the

building distribution point

TN-C: combined PE and N conductor all the way from

the transformer to the consuming device

TN-C-S earthing system: combined PEN conductor from transformer to building distribution point, but

separate PE and N conductors in fixed indoor wiring

and flexible power cords In a

TT earthing system, the protective earth connection of the consumer is provided by a local connection to

earth, independent of any earth connection at the

generator



IT Network



TT Network



TN-S earthing system



TN-C earthing system



TN-C-S earthing system

ABUJA 5 Basics of Electrical Grounding

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