6 low voltage

7/29/2019 6 Low Voltage

1/15

Copyright Siemens AG 2008. All rights reserved.

Sector Energy PTI NCTheodor Connor

Neutral earthing in low voltage


2/15

Page 1 01.2008

For internal use only. / Copyright Siemens AG 2008. All rights reserved.

PTD SE PTITh. Connor

Content

Neutral earthing principle

Load flow

Fault conditions


3/15

Page 2 01.2008



Types of system earthing (Fault Protection)

according to IEC 60364-1 (2005-11) (part1)

Earth

L1

L3

L2

N

Source

Installation

The systemearthing is a essentialpartof protectionagainst faults

(Protection against indirect contact)

Exposed conductive

parts of installation


4/15Page 3 01.2008



The types of systemearthing are defined via the relationship of power systemand of

exposed conductive parts to earth.

The first letter shows the relationship of power systemto earth.

T: Direct connection of one point to earth

I: All live parts isolated fromearth

The second letter shows the relationship of exposed conductive parts to earth

T: Direct electrical connection of exposed conductive parts of the installation to

earth, independently of the earthing of any point of the power system

N: Directelectrical connection of the exposed conductive parts to the earthed pointof the power system.

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)

Types of system earthing

according to IEC 60364-1 (2005-11) (part2)


5/15Page 4 01.2008



Low voltage systems

TN-S-System

IT-System

TT-System

L2

L3

N

L1

Earthing of system

Exposed conductive part

PE

Impedance1)

Definitions according IEC 60364-3


6/15Page 5 01.2008



Low voltage systems

Separated PE and Neutral conductorin the whole interconnected LV-system

PE- and Neutral conductor combined

in the feeding part of LV- system

TN-S-System

TN-C-S-

System


7/15Page 6 01.2008




according to IEC 60364-1 (2005-11) (TN-S System)

Source

Installation

Exposed conductive


: Load current

PE

Three phase load


8/15Page 7 01.2008





Source

Installation

Exposed conductive


: Load current

PE

Single phase load


9/15Page 8 01.2008





Source

Installation

Exposed conductive


: Fault current

PE

Single phase short circuit


10/15

Page 9 01.2008




according to IEC 60364-1 (2005-11) (TN-C-S System)

Source

Exposed conductive


: Fault currentSingle phase short circuit


11/15

Page 10 01.2008




according to IEC 60364-1 (2005-11) (TT System)

Source

Exposed conductive


: Fault current

Local earth


12/15

Page 11 01.2008




according to IEC 60364-1 (2005-11) (IT System)

Source

Exposed conductive


: Fault current

Local earth


13/15

Page 12 01.2008



Low voltage supply by TN-C

Socket

PEN

Transformer

Structure of building,pipe

Socket

Screen

Tokenring

L1

I L1I N

I PENIL1 = phase current

IN = neutral conductor current

IPEN = PEN conductor current


14/15

Page 13 01.2008



Low voltage supply by TN-C

Socket

PEN

Transformer


Socket

Screen

Tokenring

IL1 = phase current


Istru = part returning via structure

IStray= stray current via communication cable

U = voltage drop

L1

On I L1I N

Istru

IPEN

U>

0

Istray

Istray

Istray

I L1

I L1


15/15

Page 14 01.2008



Low voltage supply by TN-S

Socket

PEN

Transformer


Socket

Screen

Tokenring

IL1 = phase current


U = voltage drop

L1

On I L1I N

IPEN

U=

0

6 low voltage

Documents