Power supply systems and protective measures · Exercise 5: Customer installation project: handing...

WorkbookTP 1111

With CD-ROM

Festo Didactic

567309 en

Power supply systemsand protective measures

RCD

M3

RCD

N

L3

L2

L1

N

PE

L3

L2

L1

M3

PEN

L3

L2

L1

M3

Order no. 567309

Revision level: 10/2012

Authors: Jürgen Stumpp

Edited by: Frank Ebel

Graphics: Remo Jedelhauser, Thomas Ocker, Jürgen Stumpp

Layout: 10/2012, Susanne Durz, Frank Ebel

© Festo Didactic GmbH & Co. KG, D-73770 Denkendorf, Germany, 2013

Internet: www.festo-didactic.com

E-mail: [email protected]

The purchaser shall receive a single right of use which is non-exclusive, non-time-limited and limited

geographically to use at the purchaser's site/location as follows.

The purchaser shall be entitled to use the work to train his/her staff at the purchaser's site/location and

shall also be entitled to use parts of the copyright material as the basis for the production of his/her own

training documentation for the training of his/her staff at the purchaser's site/location with

acknowledgement of source and to make copies for this purpose. In the case of schools/technical colleges

and training centres, the right of use shall also include use by school and college students and trainees at

the purchaser's site/location for teaching purposes.

The right of use shall in all cases exclude the right to publish the copyright material or to make this available

for use on intranet, Internet and LMS platforms and databases such as Moodle, which allow access by a

wide variety of users, including those outside of the purchaser's site/location.

Entitlement to other rights relating to reproductions, copies, adaptations, translations, microfilming and

transfer to and storage and processing in electronic systems, no matter whether in whole or in part, shall

require the prior consent of Festo Didactic GmbH & Co. KG.

© Festo Didactic GmbH & Co. KG 567309 III

Table of Contents

Use for intended purpose __________________________________________________________________ IV

Preface ______________________________________________________________________________ V

Introduction ____________________________________________________________________________ VII

Work and safety instructions ______________________________________________________________ VIII

Training package for “Power supply systems and protective measures” (TP 1111) ___________________ IX

Learning objectives ________________________________________________________________________X

Equipment set ___________________________________________________________________________ XI

Notes for the teacher/trainer _______________________________________________________________ XII

Structure of the exercises _________________________________________________________________ XIII

CD-ROM contents ________________________________________________________________________ XIII

Exercises and solutions

Overview of power supply systems ____________________________________________________________ 3

Exercise 1: Measurements at power supply systems ____________________________________________ 5

Overview of protection against electrical shock ________________________________________________ 29

Exercise 2: Protection against electrical shock – protection during normal operation ________________ 31

Exercise 3: Protection against electrical shock – protection in case of fault ________________________ 43

Exercise 4: Protection against electrical shock during normal operation and in case of fault __________ 65

Exercise 5: Customer installation project: handing over a service installation to a customer __________ 71

Exercises and worksheets








IV © Festo Didactic GmbH & Co. KG 567309

Use for intended purpose

The training package for “Power supply systems and protective measures” may only be used:

For its intended purpose in teaching and training applications

When its safety functions are in flawless condition

The components included in the training package are designed in accordance with the latest technology as

well as recognised safety rules. However, life and limb of the user and third parties may be endangered, and

the components may be impaired, if they are used incorrectly.

The learning system from Festo Didactic has been developed and produced exclusively for training and

continuing vocational education in the field of automation technology. The training companies and/or

trainers must ensure that all trainees observe the safety instructions described in this workbook.

Festo Didactic hereby excludes any and all liability for damages suffered by trainees, the training company

and/or any third parties, which occur during use of the equipment sets in situations which serve any

purpose other than training and/or vocational education, unless such damages have been caused by Festo

Didactic due to malicious intent or gross negligence.

© Festo Didactic GmbH & Co. KG 567309 V

Preface

Festo Didactic’s training system for automation and technology is geared towards various educational

backgrounds and vocational requirements. The learning system is therefore broken down as follows:

Technology-oriented training packages

Mechatronics and factory automation

Process automation and control technology

Robotino® – training and research with mobile robots

Hybrid learning factories

The technology packages deal with various technologies including pneumatics, electro-pneumatics,

hydraulics, electro-hydraulics, proportional hydraulics, programmable logic controllers, sensor technology,

electrical engineering and electric drives.

The modular design of the training system allows for applications which go above and beyond the

limitations of the individual packages. For example, PLC actuation of pneumatic, hydraulic and electric

drives is possible.

VI © Festo Didactic GmbH & Co. KG 567309

All training packages feature the following elements:

Hardware

Media

Seminars

Hardware

The hardware in the training packages is comprised of industrial components and systems that are specially

designed for training purposes. The components contained in the training packages are specifically

designed and selected for the projects in the accompanying media.

Media

The media provided for the individual topics consist of a mixture of courseware and software. The

courseware includes:

Technical literature and textbooks (standard works for teaching basic knowledge)

Workbooks (practical exercises with supplementary instructions and sample solutions)

Lexicons, manuals and technical books (which provide technical information on groups of topics for

further exploration)

Transparencies and videos (for easy-to-follow, dynamic instruction)

Posters (for presenting information in a clear-cut way)

Within the software, the following programmes are available:

Digital training programmes (learning content specifically designed for virtual training)

Simulation software

Visualisation software

Software for acquiring measurement data

Project engineering and design engineering software

Programming software for programmable logic controllers

The teaching and learning media are available in several languages. They are intended for use in classroom

instruction, but are also suitable for self-study.

Seminars

A wide range of seminars covering the contents of the training packages round off the system for training

and vocational education.

Do you have suggestions or criticism regarding this manual?

If so, send us an e-mail at [email protected].

The authors and Festo Didactic look forward to your comments.

© Festo Didactic GmbH & Co. KG 567309 VII

Introduction

This workbook is part of the training system for automation technology from Festo Didactic GmbH & Co. KG.

The system provides a solid basis for practice oriented training and vocational education. The training

package for “Power supply systems and protective measures” (TP 1111) covers the following topics:

Mains supply

– Power supply systems (TN, TT and IT systems)

– Protective measures in the various types of power supply systems

Service connection

– Components of a service connection system

– Additional designations in the TN system (TN-C, TN-S, TN-C-S)

– Selection of protective measures and protective devices

– Measuring instruments for protective measures

– Planning and performance of initial testing per IEC 60364-6 and

Periodic testing per EN 50110

– Preparation of test reports

Subdistributor

– Dealing with protective measures and measuring instruments

– Planning and performance of initial and periodic testing

– Evaluation of measurement results and preparation of test reports

– Recognising, describing and measuring danger due to faults

– Systematic troubleshooting

The workbook for power supply systems and protective measures covers the issue of the safety of electrical

systems in accordance with IEC in a targeted fashion. Special circumstances and measures for preventing

dangerous satiations are addressed on the basis of realistic situations. Knowledge regarding protection

against direct and indirect contact, protection against electrical shock (also in the event of a fault) and

protection by means of RCD, as well as initial and periodic testing of electrical systems and devices is

imparted in project format for various types of power supply systems (TN-C, TN-CS, TT and IT).

A laboratory workstation equipped with fused mains supply power, two digital multimeters and laboratory

safety cables are prerequisites for setting up and evaluating the circuits.

All of the circuits for the 5 tasks are set up using the TP 1111 equipment set.

VIII © Festo Didactic GmbH & Co. KG 567309

Work and safety instructions

General

Trainees should only work with the circuits under the supervision of a trainer.

Observe specifications included in the technical data for the individual components, and in particular all

safety instructions!

Malfunctions which may impair safety must not be generated in the training environment, and must be

eliminated immediately.

Electrical components

Risk of death in case of interrupted protective earth conductor!

– The protective earth conductor (yellow/green) must never be interrupted, either inside or outside a

device.

– The insulation of the protective earth conductor must never be damaged or removed.

In schools and training facilities, the operation of power supply units must be responsibly monitored by

trained personnel.

Caution!

The capacitors in the device may still carry a charge even after it has been disconnected from all power

sources.

When replacing fuses, use specified fuses only with the correct current rating.

Never switch the power supply unit on immediately after it has been moved from a cold room to a warm

room. Under unfavourable conditions, the condensate which forms as a result may damage the device.

Leave the device switched off until it has reached room temperature.

Use only extra-low voltage (max. 25 V DC) as operating voltage for the control circuits in the various

exercises.

Electrical connections may only be established in the absence of voltage.

Electrical connections may only be interrupted in the absence of voltage.

Use only connecting cables with safety plugs for electrical connections.

Pull the plug only when disconnecting connector cables – never pull the cable.

© Festo Didactic GmbH & Co. KG 567309 IX

Training package for “Power supply systems and protective measures”

(TP 1111)

Training package TP 1111 consists of a multitude of individual training materials. The subject of this portion

of training package TP 1111 is the fundamentals of electrical protective measures.

Important components of TP 1111

EduTrainer® mains supply

EduTrainer® service connection

EduTrainer® subdistributor

Media

The courseware for training package TP 1111 consists of a workbook. The workbook include exercise sheets

for each exercise, the solutions to each individual worksheet and a CD-ROM. A set of ready-to-use exercise

sheets and worksheets is included in each workbook for all of the exercises.

Data sheets for the hardware components are made available along with the training package.

Media

Workbooks Power supply systems and protective measures

Digital training programmes WBT electrical protective measures

Overview of media for training package TP 1111

Available software for use in combination with training package TP 1111 includes the digital training

programme for electrical protective measures. This training programme offers an introduction to the subject

matter of protective measures. The leaner also finds out everything about legal regulations.

The media are offered in several languages. Further training materials can be found in our catalogues and on

the Internet.

X © Festo Didactic GmbH & Co. KG 567309

Learning objectives

Exercise 1: Measurements at power supply systems

You will be familiar with the TN-C system.

You will know how the TN-C system is used in actual practice.

You will be familiar with the TN-C-S system.

You will know how the TN-C-S system is used in actual practice.

You will be familiar with the TT system.

You will know how the TT system is used in actual practice.

You will be familiar with the IT system.

You will know how the IT system is used in actual practice.

You will be familiar with the stipulated protective measures for the individual systems.

Exercise 2: Protection against electrical shock – protection during normal operation

You will be familiar with the term “insulation of active parts”.

You will be familiar with the term “cover or enclosure”.

You will be familiar with the term “protection by obstacle”.

You will be familiar with the term “protection by clearance”.

You will be familiar with the additional protection provided by residual current circuit breakers (RCCBs).

You will be familiar with the various types of RCCB.

Exercise 3: Protection against electrical shock – protection in case of fault

You will be familiar with the term “fault type”.

You will be familiar with the terms “fault resistance” and “fault current path”.

You will be familiar with the terms “fault voltage” and maximum permissible “contact voltage”.

You will be familiar with the term “loop impedance” (loop resistance).

You will be familiar with protection by means of automatic shutdown of supply power in the TN system.

You will be familiar with protection by means of automatic shutdown of supply power in the TT system.

You will be familiar with protection by means of automatic shutdown of supply power in the IT system.

You will be familiar with protection by means of equipotential bonding.

You will be familiar with protection by means of non-conducting locations.

You will be familiar with protection by means of earth-free local equipotential bonding.

You will be familiar with protection by means of electrical separation.

© Festo Didactic GmbH & Co. KG 567309 XI

Exercise 4: Protection against electrical shock during normal operation and in case of fault

You will be familiar with the term “SELV”.

You will be familiar with the layout of a SELV circuit.

You will know how SELV circuits are used in actual practice.

You will be familiar with the term “PELV”.

You will be familiar with the layout of a PELV circuit.

You will know how PELV circuits are used in actual practice.

Exercise5: Customer installation project: handing over a service installation to a customer

You will be familiar with the procedure for testing protective measures in accordance with

IEC 60364-6.

You will be familiar with the procedure for visually inspecting the system.

You will be familiar with the procedure for testing the system.

You will be familiar with hook-up and operation of the utilised measuring instruments.

You will be familiar with the procedures for the individually specified measurements.

You will be familiar with test reports and handover reports for electrical systems.

You will be familiar with troubleshooting and eliminating faults in the CEE outlet circuit.

You will be familiar with troubleshooting and eliminating faults in the earthing contact outlet circuit.

You will be familiar with troubleshooting and eliminating faults in lighting circuits.

Equipment set

The equipment set for “Power supply systems and protective measures” (TP 1111) includes all of the

components which are necessary for mastering the predefined learning objectives. Two digital multimeters

and safety laboratory cables are also required for setting up and evaluating functional circuits.

Equipment set for “Power supply systems and protective measures”, order no. 571824

Component Order no. Quantity

EduTrainer® mains supply 571825 1

EduTrainer® service connection 571826 1

EduTrainer® subdistributor 571827 1

XII © Festo Didactic GmbH & Co. KG 567309

Notes for the teacher/trainer

Learning objectives

The basic learning goal of this workbook is the analysis and evaluation of measurement results obtained

from power supply systems. Electrical protective measures are deduced on the basis of these measurement

results This direct interplay of theory and practice ensures fast progress and long-lasting learning. Concrete,

individual learning objectives are assigned to each exercise.

Required time

The time required for working through the exercises depends on the learner’s previous knowledge of the

subject matter. Roughly 1 to 1½ hours should be scheduled for each exercise.

Equipment set components

The workbook and the equipment set are designed to be used together. All 5 exercises can be completed

using components from one TP 1111 equipment set.

Standards

The following standards apply in this workbook:

EN 60617-2 to EN 60617-8 Graphic symbols for diagrams

EN 81346-2 Industrial systems, installations and equipment and industrial products;

structuring principles and reference designations

IEC 60364-1 Low-voltage electrical installations – Fundamental principles,

(DIN VDE 0100-100) Assessment of general characteristics, definitions

IEC 60346-4-41 Low-voltage electrical installations – Protective measures –

(DIN VDE 0100-410) Protection against electric shock

Identification in the workbook

Solutions and supplements in graphics or diagrams appear in red.

Exception: Information and evaluations regarding current are always in red; information and evaluations

regarding voltage are always in blue.

Identification in the worksheets

Texts which require completion are identified with a grid or grey table cells.

Graphics and diagrams which require completion include a grid.

Solutions

The solutions specified in this workbook result from test measurements. The results of your measurements

may deviate from these.

© Festo Didactic GmbH & Co. KG 567309 XIII

Structure of the exercises

All 5 exercises have the same structure and are broken down into:

Title

Learning objectives

Problem description

Circuit or layout

Project assignment

Work aids

Worksheets

The workbook contains the solutions to each worksheet included in the exercise book.

CD-ROM contents

The workbook is included on the CD-ROM as a PDF file. The CD-ROM also provides you with additional

media.

The CD-ROM contains the following folders:

Images

Product information

Images

Photos and graphics of components and industrial applications are made available. These can be used to

illustrate individual tasks or to supplement project presentations.

Product information

Contains product information from the manufacturers of selected components. The representations and

descriptions of the components in this format are intended to show how they would appear in an industrial

catalogue. Additional information regarding the components is also included.

XIV © Festo Didactic GmbH & Co. KG 567309

© Festo Didactic GmbH & Co. KG 567309 1

Table of Contents

Exercises and solutions

Overview of power supply systems ___________________________________________________________ 3







2 © Festo Didactic GmbH & Co. KG 567309


Overview of power supply systems

Power supply systems

TT system IT systemTN system

T N C S

1 32

Power supply systems, 1: grounding at the power utility, 2: grounding at the consumer; 3: N and PE conductor at the consumer

RB

PEN

RA

PEN PE

L3

L2

L1

RA

PEN PE

N

L3

L2

L1

First letter

Relationship of the power supply system to

ground

Second letter

Relationship of the frame of the electrical

operating equipment in the electrical

installation to ground

Additional letters

Configuration of the neutral conductor and

the protective conductor

T

Direct connection of a point to ground.

T

Direct connection of the frame to ground,

regardless of any existing grounding of a

point within the power supply system.

S

Protective function which is furnished by

means of a conductor which is isolated

from the neutral conductor or the

grounded phase conductor.

I

Either all active parts isolated from ground,

or a point connected to ground via a high

impedance.

N

Direct electrical connection of the bodies

with the grounded point of the power

supply system.

C

Neutral conductor and protective

conductor functions combined into a single

conductor (PEN conductor).

Meanings of the letters



Exercise 1

Measurements at power supply systems

Learning objectives

After completing this exercise:










Problem description

Various power supply systems need to be examined with suitable measuring instruments.

The various systems can be represented by switching or repatching on a mains connection board.

,

Mains connection board

Exercise 1 – Measurements at power supply systems


1. TN-C system

Project assignments

1. Set up a TN-C system at your mains connection board.

2. Complete the entries in the worksheet so that a TN-C system is created.

3. Measure all possible voltages in the TN-C system with a suitable measuring instrument.

4. Enter the measured values to the table furnished to this end.

5. Evaluate the measured values.

6. When is a TN-C system used in actual practice?

Documentation

Textbooks, table manuals

Operating instructions

Data sheets

Internet

Equipment overview

Quantity Component

1 Mains supply

1 Service connection

1 Suitable measuring instrument (e.g. multimeter)

2 Laboratory safety cables

a) Complete the diagram so that a TN-C system is created.

Designate the individual conductors.

PEN

L3

L2

L1

M3



b) Measuring circuit layout

GNDPE

L1

L1

L2

L2

L3

L3

N

PE/PEN

N

VCC

PE

L1

L2

L3

N

L1

L2

L3

N

PE/PEN

GND

Probe

GND

L1 L2 L3 N PE

L1 L2 L3 N PE

kWh

20m

1,5Ω 47Ω 470Ω 1kΩ 2,7kΩ

N

PE

L

PE

VCCVCC

4

5

mS

UL= 50

VACmAMΩ

N PE L

battery test

L-NL-PEN-PE

VDCVACkDΩHz

TEST

RCD

RLORE

ZLRISO ΔTIΔ

select

clear

recall

store

ZRZLZS

PSC

UN

IK

UF

REPEFC

IKRE

ZERO

Var

AUTOx1/2x1x5

mA300

180°

500

VOLTS2500

1000

1000

0~ S

memory recall +!

ZERO

MEMORY

TEST

F1

F2

F3

F4

V

1,5Ω

Performing the measurement – measuring voltage and frequency

1. Set the rotary switch to the V position.

2. Use the L (red) and PE (green) sockets for this test.

Use the laboratory safety cables.

• The main display (top) indicates alternating voltage.

• The secondary display (bottom) indicates line frequency.

• Press F1 in order to switch the displayed voltage to L-PE.

• Repatch the laboratory safety cables in order to perform the required measurements.



c) Measure the voltages in the TN-C system

Attention

You will be working with line voltage while performing the measurements.

Do not switch on until the entire circuit has been completely wired!

Conductors Standard value Measured value

L1 – L2 400 V 398 V

L1 – L3 400 V 398 V

L2 – L3 400 V 396 V

L1 – PEN 230 V 230.8 V

L2 – PEN 230 V 230.8 V

L3 – PEN 230 V 231.2 V

Voltages in the TN-C system

d) Evaluate the measured values.

The measured values correspond with the standard values. Minimal deviations can be traced back to

differing loads within the system.

e) What needs to be observed in actual practice in the case of the TN-C system?

In the TN-C system, a PEN conductor is used which functions simultaneously as protective conductor

(PE) und neutral conductor (N).

In the event that the phase conductors are not uniformly loaded, compensating current flows via the

neutral conductor. As a rule, this results in the presence of a voltage between conductive housings of

operating equipment which are connected to PEN, and ground. In accordance with Ohm’s law, this is

the result of cable resistance and flowing current.



If the PEN conductor is interrupted in an installation, full voltage to ground, i.e. up to 230 V, is applied

to the conductive housings of the operating equipment downstream from the point at which PEN is

interrupted.

TN-C systems are only permissible with copper conductors with a cross-section of at least

10 square mm, or aluminium conductors with a cross-section of at least 16 square mm. This restriction

was specified in order to reduce the likelihood of a broken PEN conductor to a minimum.

2. TN-C-S system

Project assignments

1. Set up a TN-C-S system at your mains connection board.

2. Complete the entries in the worksheet so that a TN-C-S system is created.

3. Measure all possible voltages in the TN-C-S system with a suitable measuring instrument.



6. When is a TN-C-S system used in actual practice?

Documentation



Data sheets

Internet

Equipment overview

Quantity Component

1 Mains supply






a) Complete the diagram so that a TN-C-S system is created.


N

PE

L3

L2

L1

M3

b) Sketch the fault loop in the event of a fault to frame into the graphic below.

N

PEPEN

L3

L2

L1

RARB

IK

IK

IK

IK



c) Measuring circuit layout

GNDPE

L1

L1

L2

L2

L3

L3

N

PE/PEN

N

VCC

PE

L1

L2

L3

N

L1

L2

L3

N

PE/PEN

GND

Probe

GND

L1 L2 L3 N PE

L1 L2 L3 N PE

kWh

20m

1,5Ω 47Ω 470Ω 1kΩ 2,7kΩ

N

PE

L

PE

VCCVCC

4

5

UL= 50

V

N PE L

battery test

L-N

Hz

TEST

ZERO

MEMORY

TEST

F1

F2

F3

F4

V

1,5Ω



2. Use all sockets for this test (red, blue and green).




• Press F1 in order to switch displayed voltage back and forth amongst L-PE, L-N and N-PE.




d) Measure the voltages in the TN-C-S system

Attention




L1 – L2 400 V 398 V

L2 – L3 400 V 396 V

L1 – N 230 V 230.8 V

L2 – N 230 V 230.8 V

L3 – N 230 V 231.2 V

L1 – PE 230 V 230.4 V

L2 – PE 230 V 229.8 V

L3 – PE 230 V 231.6 V

Voltages in the TN-C-S system

e) Evaluate the measured values.

Except for minimal deviation, the measured values correspond with the standard values.

Voltage between the phase conductors and neutral conductor N has the same value as between the

phase conductors and protective conductor PE.

These voltage values were expected, because the two conductors are connected upstream from

physical separation into neutral conductor and protective conductor.



f) What needs to be observed in actual practice in the case of the TN-C-S system?

As of the transformer, the TN-C-S initially has the same layout as the TN-C system. At a given point, no

later than as of the point at which the required minimum cross-section of 10 square mm will be fallen

short of, the PEN conductor is split into neutral conductor and protective conductor. These continue

on separately and may not be brought back together again.

The TN-C-S system is widespread in building applications in Germany. The protective conductor and

the neutral conductor are split in the main distributor inside the building.

The PEN conductor is split into the PE conductor (protective function, green-yellow) and neutral

conductor N (operating current circuit, light blue).

The protective conductor may not be used for any purpose other than implementation of the safety

measure which involves connection of all conductive system components, housings etc. to each other

and to the transformer’s neutral point.



3. TT system

Project assignments

1. Set up a TT system at your mains connection board.

2. Complete the entries in the worksheet so that a TT system is created.

3. Measure all possible voltages in the TT system with a suitable measuring instrument.



6. When is a TT system used in actual practice?

7. Why are residual current devices (RCDs) mandatorily stipulated in TT systems?

8. Examine the dependence of contact voltage on grounding resistance and fault current.

Documentation



Data sheets

Internet

Equipment overview

Quantity Component

1 Mains supply






Information

Residual current devices (RCDs) are mandatorily stipulated in TT systems!

N

N

PE

L3

L3

L2

L2

L1

L1

M

RCD RCDRCD

RARARB RA

Connection of consumers via RCDs in the TT system



a) Complete the diagram so that a TT system is created.


RCD RCD

M3

N

L3

L2

L1


GNDPE

L1

L1

L2

L2

L3

L3

N

PE/PEN

N

VCC

PE

L1

L2

L3

N

L1

L2

L3

N

PE/PEN

GND

Probe

GND

L1 L2 L3 N PE

L1 L2 L3 N PE

kWh

20m

1,5Ω 47Ω 470Ω 1kΩ 2,7kΩ

N

PE

L

PE

VCCVCC

4

5

mS

UL= 50

VACmAMΩ

N PE L

battery test

L-NL-PEN-PE

VDCVACkDΩHz

TEST

RCD

RLORE

ZLRISO ΔTIΔ

select

clear

recall

store

ZRZLZS

PSC

UN

IK

UF

REPEFC

IKRE

ZERO

Var

AUTOx1/2x1x5

mA300

180°

500

VOLTS2500

1000

1000

0~ S

memory recall +!

ZERO

MEMORY

TEST

F1

F2

F3

F4

V

1,5Ω





2. Use the L (red) and N (blue) sockets for this test.






c) Measure the voltages in the TT system

Attention




L1 – L2 400 V 399 V

L2 – L3 400 V 398 V

L3 – L1 400 V 401 V

L1 – N 230 V 230.5 V

L2 – N 230 V 229 V

L3 – N 230 V 230.8 V

Voltages in the TT system




Except for minimal deviation, the measured values correspond with the standard values.

e) What needs to be observed in actual practice in the case of the TT system?

The use of the TT system in combination with residual current circuit-breakers is stipulated, for

example in agricultural and horticultural applications, as well as for distributors at construction sites.

The TT system is also stipulated for portable distributor systems, for example for temporary structures

such as fair ground vehicles.

f) Why are residual current devices (RCDs) mandatorily stipulated in TT systems?

The earth electrode’s grounding resistance must be small enough that maximum permissible contact

voltage is not exceeded and the overcurrent protection device is tripped in the event of a fault.

If fuses or circuit breakers are used, this results in small grounding resistance values which cannot be

achieved economically at nominal current values of greater than 6 A.

If the RCD has a nominal fault current of 30 mA and maximum permissible contact voltage is 50 V,

grounding resistance may amount to 1665 .

If maximum permissible contact voltage is cut in half to 25 V, grounding resistance is also cut in half to

832 .

L A A U R I

Solved for RA

LA

A

U

RI

UL= maximum permissible contact voltage

RA= grounding resistance

IA= nominal fault current of the RCD



g) Fault current is shown in the following table as measured for various grounding resistance values.

Use these values to calculate the respective contact voltages.

Grounding resistance Fault current Contact voltage

1 k 0.21 A 210 V

400 0.48 A 192 V

200 0.82 A 164 V

100 1.42 A 142 V

40 2.15 A 86 V

20 2.5 A 50 V

h) Evaluate the individual values.

The smaller the grounding resistance, the greater the fault current. If fault current is increased, contact

voltage rises as well in accordance with Ohm’s law. If fault resistance is neglected, contact voltages

occur which exceed the maximum permissible value.

On the basis of contact voltage, grounding resistance would have to be less than 20 . Earthing

resistance values which should be less than 20 are difficult to achieve in actual practice with

individual earth electrodes.

With a maximum permissible contact voltage of 25 V, the required grounding resistance value is

nearly impossible to achieve with individual earth electrodes. RCDs are used in order to fulfil

shutdown conditions in the event of a fault.

Consequently, RCDs are used where specified grounding resistance values cannot be achieved.



4. IT system

Project assignments

1. Complete the entries in the worksheet so that an IT system is created.

2. Set up an IT system with the help of the mains connection board and the IT board.

3. Measure all possible voltages in the IT system with a multimeter, and enter the values to the table

provided for this purpose.


5. The transformer in the IT board is designated Dyn5. Explain this designation.

6. Explain when and where the IT system is used in actual practice.

7. Why are insulation monitoring devices (IMDs) mandatorily stipulated in IT systems?

8. Describe the insulation monitoring function.

9. Start up the IT system. Set the IMD to a threshold value of approximately 60 k. Generate an earth fault

with the potentiometer (500 k) and select various resistance values at the ohmmeter (500 k,

200 k, 100 k, 50 k). Describe the reaction of the IMD.

10. Two RCDs (30 mA and 300 mA) are used for shutting down the IT system.

Supplement the IT system with the two RCD boards. Simulate an earth fault from L to PE at the 300 mA

RCD via the potentiometer (500 k) (first fault). Reset the acoustic signal and simulate an earth fault

from L2 to PE downstream from the 30 mA RCD (second fault). Explain how the IT system reacts.

11. Which tasks have to be completed when testing the IT system in accordance with IEC?

Documentation



Data sheets

Internet

Equipment overview

Quantity Component

1 Mains supply

1 IT system

1 RCD board (300 mA, 30 mA)





Attention

There is no connection between active conductors and grounded parts in the IT system.

The bodies included in the electrical system are grounded.

Insulation monitoring devices (IMDs) are mandatorily stipulated in IT systems.

a) Complete the entries in the worksheet so that an IT system is created. Designate the individual

conductors.

Z < RCD

N

L1

L2

L3

RA RARA

M3

Z: impedance



b) Set up an IT system with the help of the mains connection board and the IT board.

GNDPE

L1

L1

L2

L2

L3

L3

N

PE/PEN

N

VCC

1,5Ω

PE

L1

L2

L3

N

L1

L2

L3

GNDGND

10k�

500k�

1,5�

1,5�

1,5�

1,5�

VCC VCC

L3L2L1N

5 4

+

ONTest

Reset

AL

RAL

mS

UL= 50

VACmAMΩ

N PE L

battery test

L-NL-PEN-PE

VDCVACkDΩHz

TEST

RCD

RLORE

ZLRISO ΔTIΔ

select

clear

recall

store

ZRZLZS

PSC

UN

IK

UF

REPEFC

IKRE

ZERO

Var

AUTOx1/2x1x5

mA300

180°

500

VOLTS2500

1000

1000

0~ S

memory recall +!

ZERO

MEMORY

TEST

F1

F2

F3

F4

V











c) Measure all possible voltages in the IT system with a multimeter, and enter the values to the table


Attention




L1 – L2 400 V 410 V

L2 – L3 400 V 410 V

L3 – L1 400 V 410 V

L1 – N 230 V 236 V

L2 – N 230 V 236 V

L3 – N 230 V 236 V

L1 – PE 0 V Not measurable



Voltages in the IT system




Except for minimal deviation, the measured values correspond with the standard values. The values

are a bit higher, because they were measured while the transformer was overloaded.

A voltage of 400 V prevails between the phase conductors. A voltage of 230 V prevails between the

phase and neutral conductors. These voltages correspond to a 3-phase, 4-wire system.

Due to the fact that all active conductors are isolated from ground in the IT system, there is no

measurable voltage between phase conductor and ground. No point within the IT system may be

directly grounded!

e) The transformer in the IT board is designated Dyn5. Explain this designation.

The designation makes reference to the 3-phase transformer. As is the case with all transformers,

there is a primary winding and a secondary winding.

Letter D: The primary winding is wired in delta connection.

Letter y: The secondary winding is wired in star connection.

Letter n: The neutral conductor is led out at the secondary winding.

Number 5: Primary winding voltage stays ahead of secondary winding voltage by 5 x 30°.

f) Explain when and where the IT system is used in actual practice.

In actual practice, IT systems are only permissible in limited installations with separate transformer or

generator.

IT systems demonstrate single fault security, which significantly increases their reliability. IT system

are used for facilities in intensive care units and operating rooms, in explosion protected areas, in

mining and in smelting plants.

In production facilities, for instance in the chemicals industry, the IT system is used when considerable

economic loss can be expected in the event of a power failure with a TN system.

IT systems are also used by fire departments and disaster control services (generators).



g) Why are insulation monitoring devices (IMDs) mandatorily stipulated in IT systems?

Due to the fact that no point within the IT system may be directly grounded, no voltage can occur

between phase conductor and ground.

If a fault occurs within the IT system (earth fault), it must be reported immediately and then

eliminated. An insulation monitoring device is used to generate the required message.

A second fault would result in shutdown of the system.

h) Describe the insulation monitoring function.

Insulation monitoring device (IMD)

Insulation resistance in the IT system is continuously monitored by the insulation monitoring function.

The normal operating state (fault-free) is indicated by a green indicator lamp.

The IMD’s threshold value can be adjusted, for example to a value of 50 k. If insulation resistance

falls below the minimum value of 50 k, this state is indicated by means of a yellow lamp and an

acoustic signal. The acoustic signal can be cleared, but optical indication cannot be switched off until

after the fault has been eliminated.

If a second fault occurs, the system is shut down immediately.



i) Reaction of the IMD

The IT system is started up. A threshold value of 60 k is selected at the IMD. Earth faults are

generated via the potentiometer with different resistance values, and the reaction of the IMD is

observed.

• 500 k: No reaction



• 50 k: The IMD indicates the fault both optically and acoustically.

If the threshold value selected at the IMD is fallen short of, optical and acoustic fault indication

ensues.

j) Reaction of the IT system to fault 1 and fault 2

Two RCDs (30 mA and 300 mA) are used to shut down the system.

Setting at the IMD = 50 k. An earth fault is simulated at the 300 mA RCD (L1 to PE via the

potentiometer – first fault).

The IMD indicates the fault both optically and acoustically.

The 300 mA RCD does not shut the system down.

The acoustic signal is reset and a second fault is simulated at the 30 mA RCD

(L2 to PE – second fault).

The 30 mA RCD shuts the system down, and the 300 mA RCD is still switched on.



k) Which tasks have to be completed for initial testing of the IT system in accordance with IEC?

1. Visual inspection

General condition of the system, equipotential bonding, cable types, wire identification,

protection class adequate for the system, system documentation available.

2. Visual inspection and testing

Protective conductor connections, main equipotential bonding, auxiliary equipotential bonding.

3. Insulation resistance measurement

Not required for repeat measurement, measurement without IMD

4. Measurement or calculation of leakage current

Leakage current from the conductor, leakage current from the consuming devices, addition of

individual current values.

5. Grounding resistance measurement

6. Measurement or calculation of contact voltage when first fault occurs.

7. Measurement for verification of the protective measure, shut down when second fault occurs.

8. Testing of the IMD and any included RCDs.

9. Evaluation of results

Preparation of documentation.

Note

IEC regulations concerning insulation monitoring:

• IEC 60364-1: Protection against indirect contact with shut-down and indication

• IEC 60364-7-710: Electrical safety in medical locations




Table of Contents

Exercises and worksheets










Overview of power supply systems

Power supply systems

TT system IT systemTN system

T N C S

1 32

Power supply systems, 1: grounding at the power utility, 2: grounding at the consumer; 3: N and PE conductor at the consumer

RB

PEN

RA

PEN PE

L3

L2

L1

RA

PEN PE

N

L3

L2

L1

First letter

Relationship of the power supply system to

ground

Second letter

Relationship of the frame of the electrical

operating equipment in the electrical

installation to ground

Additional letters

Configuration of the neutral conductor and

the protective conductor

T

Direct connection of a point to ground.

T

Direct connection of the frame to ground,

regardless of any existing grounding of a

point within the power supply system.

S

Protective function which is furnished by

means of a conductor which is isolated

from the neutral conductor or the

grounded phase conductor.

I

Either all active parts isolated from ground,

or a point connected to ground via a high

impedance.

N

Direct electrical connection of the bodies

with the grounded point of the power

supply system.

C

Neutral conductor and protective

conductor functions combined into a single

conductor (PEN conductor).

Meanings of the letters



Exercise 1

Measurements at power supply systems

Learning objectives

After completing this exercise:










Problem description

Various power supply systems need to be examined with suitable measuring instruments.

The various systems can be represented by switching or repatching on a mains connection board.

,

Mains connection board


6 Name: __________________________________ Date: ____________ © Festo Didactic GmbH & Co. KG 567309

1. TN-C system

Project assignments

1. Set up a TN-C system at your mains connection board.

2. Complete the entries in the worksheet so that a TN-C system is created.

3. Measure all possible voltages in the TN-C system with a suitable measuring instrument.



6. When is a TN-C system used in actual practice?

Documentation



Data sheets

Internet

Equipment overview

Quantity Component

1 Mains supply




a) Complete the diagram so that a TN-C system is created.


M3


© Festo Didactic GmbH & Co. KG 567309 Name: __________________________________ Date: ____________ 7


GNDPE

L1

L1

L2

L2

L3

L3

N

PE/PEN

N

VCC

PE

L1

L2

L3

N

L1

L2

L3

N

PE/PEN

GND

Probe

GND

L1 L2 L3 N PE

L1 L2 L3 N PE

kWh

20m

1,5Ω 47Ω 470Ω 1kΩ 2,7kΩ

N

PE

L

PE

VCCVCC

4

5

mS

UL= 50

VACmAMΩ

N PE L

battery test

L-NL-PEN-PE

VDCVACkDΩHz

TEST

RCD

RLORE

ZLRISO ΔTIΔ

select

clear

recall

store

ZRZLZS

PSC

UN

IK

UF

REPEFC

IKRE

ZERO

Var

AUTOx1/2x1x5

mA300

180°

500

VOLTS2500

1000

1000

0~ S

memory recall +!

ZERO

MEMORY

TEST

F1

F2

F3

F4

V

1,5Ω



2. Use the L (red) and PE (green) sockets for this test.




• Press F1 in order to switch the displayed voltage to L-PE.




c) Measure the voltages in the TN-C system

Attention




L1 – L2

L1 – L3

L2 – L3

L1 – PEN

L2 – PEN

L3 – PEN

Voltages in the TN-C system


e) What needs to be observed in actual practice in the case of the TN-C system?



2. TN-C-S system

Project assignments

1. Set up a TN-C-S system at your mains connection board.

2. Complete the entries in the worksheet so that a TN-C-S system is created.

3. Measure all possible voltages in the TN-C-S system with a suitable measuring instrument.



6. When is a TN-C-S system used in actual practice?

Documentation



Data sheets

Internet

Equipment overview

Quantity Component

1 Mains supply






a) Complete the diagram so that a TN-C-S system is created.


M3

b) Sketch the fault loop in the event of a fault to frame into the graphic below.

N

PEPEN

L3

L2

L1

RARB



c) Measuring circuit layout

GNDPE

L1

L1

L2

L2

L3

L3

N

PE/PEN

N

VCC

PE

L1

L2

L3

N

L1

L2

L3

N

PE/PEN

GND

Probe

GND

L1 L2 L3 N PE

L1 L2 L3 N PE

kWh

20m

1,5Ω 47Ω 470Ω 1kΩ 2,7kΩ

N

PE

L

PE

VCCVCC

4

5

UL= 50

V

N PE L

battery test

L-N

Hz

TEST

ZERO

MEMORY

TEST

F1

F2

F3

F4

V

1,5Ω











d) Measure the voltages in the TN-C-S system

Attention




L1 – L2

L2 – L3

L1 – N

L2 – N

L3 – N

L1 – PE

L2 – PE

L3 – PE

Voltages in the TN-C-S system

e) Evaluate the measured values.



f) What needs to be observed in actual practice in the case of the TN-C-S system?



3. TT system

Project assignments

1. Set up a TT system at your mains connection board.

2. Complete the entries in the worksheet so that a TT system is created.

3. Measure all possible voltages in the TT system with a suitable measuring instrument.



6. When is a TT system used in actual practice?

7. Why are residual current devices (RCDs) mandatorily stipulated in TT systems?

8. Examine the dependence of contact voltage on grounding resistance and fault current.

Documentation



Data sheets

Internet

Equipment overview

Quantity Component

1 Mains supply






Information

Residual current devices (RCDs) are mandatorily stipulated in TT systems!

N

N

PE

L3

L3

L2

L2

L1

L1

M

RCD RCDRCD

RARARB RA

Connection of consumers via RCDs in the TT system



a) Complete the diagram so that a TT system is created.


M3


GNDPE

L1

L1

L2

L2

L3

L3

N

PE/PEN

N

VCC

PE

L1

L2

L3

N

L1

L2

L3

N

PE/PEN

GND

Probe

GND

L1 L2 L3 N PE

L1 L2 L3 N PE

kWh

20m

1,5Ω 47Ω 470Ω 1kΩ 2,7kΩ

N

PE

L

PE

VCCVCC

4

5

mS

UL= 50

VACmAMΩ

N PE L

battery test

L-NL-PEN-PE

VDCVACkDΩHz

TEST

RCD

RLORE

ZLRISO ΔTIΔ

select

clear

recall

store

ZRZLZS

PSC

UN

IK

UF

REPEFC

IKRE

ZERO

Var

AUTOx1/2x1x5

mA300

180°

500

VOLTS2500

1000

1000

0~ S

memory recall +!

ZERO

MEMORY

TEST

F1

F2

F3

F4

V

1,5Ω





2. Use the L (red) and N (blue) sockets for this test.






c) Measure the voltages in the TT system

Attention




L1 – L2

L2 – L3

L3 – L1

L1 – N

L2 – N

L3 – N

Voltages in the TT system




e) What needs to be observed in actual practice in the case of the TT system?

f) Why are residual current devices (RCDs) mandatorily stipulated in TT systems?



g) Fault current is shown in the following table as measured for various grounding resistance values.

Use these values to calculate the respective contact voltages.

Grounding resistance Fault current Contact voltage

1 k 0.21 A

400 0.48 A

200 0.82 A

100 1.42 A

40 2.15 A

20 2.5 A

h) Evaluate the individual values.



4. IT system

Project assignments

1. Complete the entries in the worksheet so that an IT system is created.

2. Set up an IT system with the help of the mains connection board and the IT board.

3. Measure all possible voltages in the IT system with a multimeter, and enter the values to the table



5. The transformer in the IT board is designated Dyn5. Explain this designation.

6. Explain when and where the IT system is used in actual practice.

7. Why are insulation monitoring devices (IMDs) mandatorily stipulated in IT systems?

8. Describe the insulation monitoring function.

9. Start up the IT system. Set the IMD to a threshold value of approximately 60 k. Generate an earth fault

with the potentiometer (500 k) and select various resistance values at the ohmmeter

(500 k, 200 k, 100 k, 50 k). Describe the reaction of the IMD.

10. Two RCDs (30 mA and 300 mA) are used for shutting down the IT system.

Supplement the IT system with the two RCD boards. Simulate an earth fault from L to PE at the 300 mA

RCD via the potentiometer (500 k) (first fault). Reset the acoustic signal and simulate an earth fault

from L2 to PE downstream from the 30 mA RCD (second fault). Explain how the IT system reacts.

11. Which tasks have to be completed when testing the IT system in accordance with IEC?

Documentation



Data sheets

Internet

Equipment overview

Quantity Component

1 Mains supply

1 IT system

1 RCD board (300 mA, 30 mA)





Attention

There is no connection between active conductors and grounded parts in the IT system.

The bodies included in the electrical system are grounded.

Insulation monitoring devices (IMDs) are mandatorily stipulated in IT systems.

a) Complete the entries in the worksheet so that an IT system is created. Designate the individual

conductors.

Z <

M3

Z: impedance



b) Set up an IT system with the help of the mains connection board and the IT board.

GNDPE

L1

L1

L2

L2

L3

L3

N

PE/PEN

N

VCC

1,5Ω

PE

L1

L2

L3

N

L1

L2

L3

GNDGND

10k�

500k�

1,5�

1,5�

1,5�

1,5�

VCC VCC

L3L2L1N

5 4

+

ONTest

Reset

AL

RAL

mS

UL= 50

VACmAMΩ

N PE L

battery test

L-NL-PEN-PE

VDCVACkDΩHz

TEST

RCD

RLORE

ZLRISO ΔTIΔ

select

clear

recall

store

ZRZLZS

PSC

UN

IK

UF

REPEFC

IKRE

ZERO

Var

AUTOx1/2x1x5

mA300

180°

500

VOLTS2500

1000

1000

0~ S

memory recall +!

ZERO

MEMORY

TEST

F1

F2

F3

F4

V











c) Measure all possible voltages in the IT system with a multimeter, and enter the values to the table


Attention




L1 – L2

L2 – L3

L3 – L1

L1 – N

L2 – N

L3 – N

L1 – PE

L2 – PE

L3 – PE

Voltages in the IT system




e) The transformer in the IT board is designated Dyn5. Explain this designation.

f) Explain when and where the IT system is used in actual practice.



g) Why are insulation monitoring devices (IMDs) mandatorily stipulated in IT systems?

h) Describe the insulation monitoring function.

Insulation monitoring device (IMD)



i) Reaction of the IMD

j) Reaction of the IT system to fault 1 and fault 2



k) Which tasks have to be completed for initial testing of the IT system in accordance with IEC?

Note

IEC regulations concerning insulation monitoring:

• IEC 60364-1: Protection against indirect contact with shut-down and indication

• IEC 60364-7-710: Electrical safety in medical locations



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