Neutral earthing in low voltage
Sector Energy PTI NC
Theodor Connor
Copyright © Siemens AG 2008. All rights reserved.
Content
Neutral earthing principle
Load flow
Fault conditions
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 1
01.2008
Th. Connor
PTD SE PTI
Types of system earthing (Fault Protection)
according to IEC 60364-1 (2005-11) (part1)
The system earthing is a essential
part of protection against faults
Source
(Protection against indirect contact)
L1
L2
L3
Exposed conductive
parts of installation
N
Installation
Earth
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 2
01.2008
Th. Connor
PTD SE PTI
Types of system earthing
according to IEC 60364-1 (2005-11) (part2)
The types of system earthing are defined via the relationship of power system and of
exposed conductive parts to earth.
ƒ The first letter shows the relationship of power system to earth.
ƒ T: Direct connection of one point to earth
ƒ I: All live parts isolated from earth
ƒ
ƒ The second letter shows the relationship of exposed conductive parts to earth
ƒ T: Direct electrical connection of exposed conductive parts of the installation to
earth, independently of the earthing of any point of the power system
ƒ N: Direct electrical connection of the exposed conductive parts to the earthed point
of the power system.
ƒ Subsequent letter if any shows the arrangement of neutral and protective
conductor: S: separated protective and neutral conductor (5wire); C: Neutral and
protective function combined in a single conductor (4wire)
ƒ
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 3
01.2008
Th. Connor
PTD SE PTI
Low voltage systems
TN-S-System
IT-System
L1
L2
L3
N
Impedance1)
PE
Exposed conductive part
Earthing of system
TT-System
Definitions according IEC 60364-3
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 4
01.2008
Th. Connor
PTD SE PTI
Low voltage systems
Separated PE – and Neutral conductor
in the whole interconnected LV-system
TN-S-System
TN-C-SSystem
PE- and Neutral conductor combined
in the feeding part of LV- system
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 5
01.2008
Th. Connor
PTD SE PTI
Types of system earthing
according to IEC 60364-1 (2005-11) (TN-S System)
Three phase load
: Load current
Source
PE
Installation
Exposed conductive
parts of installation
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 6
01.2008
Th. Connor
PTD SE PTI
Types of system earthing
according to IEC 60364-1 (2005-11) (TN-S System)
Single phase load
: Load current
Source
PE
Installation
Exposed conductive
parts of installation
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 7
01.2008
Th. Connor
PTD SE PTI
Types of system earthing
according to IEC 60364-1 (2005-11) (TN-S System)
Single phase short circuit
: Fault current
Source
PE
Installation
Exposed conductive
parts of installation
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 8
01.2008
Th. Connor
PTD SE PTI
Types of system earthing
according to IEC 60364-1 (2005-11) (TN-C-S System)
Single phase short circuit
: Fault current
Source
Exposed conductive
parts of installation
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 9
01.2008
Th. Connor
PTD SE PTI
Types of system earthing
according to IEC 60364-1 (2005-11) (TT System)
: Fault current
Source
Exposed conductive
parts of installation
Local earth
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 10
01.2008
Th. Connor
PTD SE PTI
Types of system earthing
according to IEC 60364-1 (2005-11) (IT System)
: Fault current
Source
Exposed conductive
parts of installation
Local earth
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 11
01.2008
Th. Connor
PTD SE PTI
Low voltage supply by TN-C
PEN
L1
Socket
I L1
IN
Screen
Tokenring
Socket
I PEN
Transformer
IL1
= phase current
IN
= neutral conductor current
IPEN = PEN conductor current
Structure of building,
pipe
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 12
01.2008
Th. Connor
PTD SE PTI
Low voltage supply by TN-C
PEN
L1
Socket
On
I L1
IN
Istray
Screen
I L1
Istray
Tokenring
>0
Socket
ΔU
Istru
Istray
IPEN
I L1
IL1 = phase current
Transformer
IN = neutral conductor current
Istru = part returning via structure
IStray= stray current via communication cable
ΔU = voltage drop
Structure of building,
pipe
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 13
01.2008
Th. Connor
PTD SE PTI
Low voltage supply by TN-S
PEN
L1
Socket
IN
On
I L1
Screen
Tokenring
ΔU
=0
Socket
IPEN
IL1 = phase current
Transformer
IN = neutral conductor current
ΔU = voltage drop
Structure of building,
pipe
For internal use only. / Copyright © Siemens AG 2008. All rights reserved.
Page 14
01.2008
Th. Connor
PTD SE PTI