Transcript chapter 6: earthing system tn systems

CHAPTER 6
EARTHING SYSTEM
CHAPTER 6: EARTHING SYSTEM
EARTHING SYSTEM
• Three earthing systems such as defined in IEC
364 are:
1) exposed-conductive parts connected to neutral
TN;
2) earthed neutral TT;
3) unearthed (or impedance-earthed) neutral IT
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PURPOSE OF EARTHING SYSTEM
• regards protection of persons and property:
mastery of insulation fault effects.
• They are considered to be equivalent with respect
to safety of persons against indirect contacts
CHAPTER 6: EARTHING SYSTEM
CLASSISFICATIONS
• The extent of the earth fault and the consequences
deriving from the touching of live exposedconductive-parts are specifically related to the
neutral condition of the power system and to the
types of system earthing.
• As a consequence, to select the proper device for
the protection against earth faults, it is necessary
to know the installation distribution system. The
International Standard IEC 60364-3 classifies the
electrical systems with the combination of two
letters.
CHAPTER 6: EARTHING SYSTEM
CLASSISFICATIONS
• The first letter indicates the relationship of the
power system to earth:
>> T = direct connection to earth of one point,
usually the neutral, in ac systems
>> I = all live parts isolated from earth or one point,
usually the neutral, connected to earth through an
impedance.
CHAPTER 6: EARTHING SYSTEM
CLASSISFICATIONS
• The second letter indicates the relationship of the
exposed-conductive- parts of the installation to
earth:
>> T = direct electrical connection of exposedconductive parts to earth
>> N = direct electrical connection of the exposedconductive parts to the earthed point of the power
system.
CHAPTER 6: EARTHING SYSTEM
CLASSISFICATIONS
• Subsequent letters, if any, indicates the
arrangement of neutral and protective conductors:
S = neutral and protective functions provided by
separate conductors
C = neutral and protective functions combined in a
single conductor (PEN conductor).
CHAPTER 6: EARTHING SYSTEM
CLASSISFICATIONS
• For TN-S, TN-C-S and TT systems the following
explanations should aid a full understanding of the
earthing arrangements and their scope of
application.
• The nomenclature of these system types is as
follows:
• T =Earth (from the French word Terre)
• N=Neutral
• S=Separate
• C=Combined
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TT SYSTEMS
• This arrangement covers installations not provided
with an earth terminal by the Electricity Supply
Company.
• Thus it is the method employed by most (usually
rural) installations fed by an overhead supply.
CHAPTER 6: EARTHING SYSTEM
TT SYSTEMS
• Neutral and earth (protective) conductors must be
kept quite separate throughout the installation, with
the final earth terminal connected to an earth
electrode by means of an earthing conductor.
CHAPTER 6: EARTHING SYSTEM
TT SYSTEMS
• The earth fault current returns to the power supply
node through the soil.
• In this type of electrical installations the neutral is
usually distributed and its function is making the
phase voltage (e.g. 240 V) available for the supply of
the single-phase loads of civil installations.
• Effective earth connection is sometimes difficult.
• Because of this, socket outlet circuits must be
protected by a residual current device (RCD) with an
operating current of 30 mA.
CHAPTER 6: EARTHING SYSTEM
TT SYSTEMS
• Effective earth connection is sometimes difficult.
• Because of this, socket outlet circuits must be
protected by a residual current device (RCD) with an
operating current of 30 mA.
CHAPTER 6: EARTHING SYSTEM
TT SYSTEMS
CHAPTER 6: EARTHING SYSTEM
TN SYSTEMS
• In TN systems, the neutral is directly earthed,
whereas the exposed-conductive-parts are
connected to the same earthing arrangement of
the neutral.
• TN electrical systems can be divided into three
types based on the fact that the neutral and
protective conductors are separate or not:
1) TN-S
2) TN-C
3) TN-C-S
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TN SYSTEMS: TN-S
• The neutral conductor N and the protective
conductor PE are separated
CHAPTER 6: EARTHING SYSTEM
TN SYSTEMS: TN-S
CHAPTER 6: EARTHING SYSTEM
TN SYSTEMS: TN-C
• TN-C: the neutral and protective functions are
combined into a single conductor, called PEN.
CHAPTER 6: EARTHING SYSTEM
TN SYSTEMS: TN-C-S
• TN-C-S: the neutral and protective functions are
partially combined into a single PEN conductor and
partially separated PE + N
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TN SYSTEMS: TN-C-S
CHAPTER 6: EARTHING SYSTEM
TN SYSTEMS
• In TN systems the earth fault current returns to the
power supply node through a direct metal
connection (PE or PEN conductor) without
practically affecting the earth electrode
CHAPTER 6: EARTHING SYSTEM
IT SYSTEMS
• The installation arrangements in the IT system are
the same for those of the TT system.
• However, the supply earthing is totally different.
• The IT system can have an unearthed supply, or one
which is not solidly earthed but is connected to earth
through a current limiting impedance.
CHAPTER 6: EARTHING SYSTEM
IT SYSTEMS
• The total lack of earth in some cases, or the
introduction of current limiting into the earth path,
means that the usual methods of protection will not
be effective.
• For this reason, IT systems are not allowed in the
public supply system.
• An exception is in medical situations such as
hospitals. Here it is recommended that an IT
system is used for circuits supplying medical
equipment that is intended to be used for lifesupport of patients.
• The method is also sometimes used where a
supply for special purposes is taken from a private
generator.
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IT SYSTEMS
• The earth fault current returns to the power supply
node through the earthing arrangement of the
exposed conductive parts and the capacities to earth
of the line conductors.
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Example Grounding System
• Let’s say Taman Jejawi, in Kangar Town, There is a
terrace house has two master bed room including a
small drawing room and total load consumption of
the house is 450 watts.
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Can you draw the grounding system for this house?
Can you estimate the length of copper conductors?
Can you estimate the number of copper connectors?
Can you calculate grounding resistance for this house?
Can you estimate the budget ?
CHAPTER 6: EARTHING SYSTEM
Drawing of Grounding System
•Try yourself
CHAPTER 6: EARTHING SYSTEM
Grounding Resistance
Calculation
•Try yourself
CHAPTER 6: EARTHING SYSTEM
Budget of Grounding System
•Try yourself
THANK YOU
Terima Kasih