New standards
for insulation monitoring devices (IMD)
Reliability of supply is a central task in electrical energy supply. In the event
of a fault, the main tasks of the protection and monitoring equipment include
the protection of humans and animals, the avoidance of unexpected interruptions in operation, as well as early information about impending hazards.
A particularly important aspect is the selection of power supply systems and
the related protection and monitoring devices. In unearthed power supplies (IT
systems), insulation monitoring devices have a crucial role. The characteristics
of these products have now been revised and re-written in a new edition of
the International and European product standards IEC/EN 61557-8, -9 and -15.
With the latest editions the increased requirements from practice and also new
metrological capabilities are addressed.
N E W S TAN DARDS
FOR INSULATION MONITORING DEVICES IMD
1. Historical development of the
standard for insulation monitoring
devices
As early as 1973 the first product standard for
insulation monitoring devices was published as
the German standard DIN 57413 Part 2 (VDE 0413
Part 2). In 1998 this standard was published as the
international standard IEC 61557-8:1998 for the
first time. The next milestone in 1999 was the independent product standard IEC 61557-9:1999 for
insulation fault location systems. New applications
in the area of functional safety resulted in the publication of IEC 61557-15:2014, the product standard
for IMDs, in 2014. The circle has been closed with
the third internationally available editions of IEC
61557-8 and -9 at the end of 2014. As such all three
editions of the product standards are harmonised
and are available in the latest version.
2. Clear marking of insulation
monitoring devices according
to EN 61557-8:2015
In unearthed power supplies (IT systems), insulation
monitoring devices have the task of signalling whenever the minimum insulation resistance RF level
falls below a minimum value . Insulation monitoring
devices according to EN 61557-8 [6] can also be
used to monitor offline TT, TN, and IT systems or
loads. This is a measure that has often been proven
in practice, e.g. to safeguard safety devices in the
event of a fault or as a preventive measure, e.g. in
fire-extinguishing systems. Compared to the following changes have been made:
• Terms and definitions have been complemented;
• Abbreviations are listed and explained;
• Requirements have been revised;
• Mandatory and optional functions and their terminology have been adapted from IEC 61557-15 [8];
• mechanical requirements have been added;
i
• information on the operating instructions has
been added;
• type tests and routine tests have been complemented;
• new annexes:
– Annex C:
"Insulation monitoring devices for photovoltaic
systems (PV-IMD)"
– Annex D:
"Insulation monitoring function of a photovoltaic inverter (PV-IMF) or in a charge controller".
The German edition DIN EN 61557-8 (VDE 04138) [6] is unpublished yet, but will be released
in 2015 with the title "Elektrische Sicherheit in
Niederspannungsnetzen bis AC 1 000 V und
DC 1 500 V – Geräte zum Prüfen, Messen oder
Überwachen von Schutzmaßnahmen – Teil 8:
Isolationsüberwachungsgeräte für IT-Systeme".
The standard specifies the requirements for operating insulation monitoring devices (IMD) that continuously monitor the insulation resistance to earth
of unearthed AC IT systems with galvanically connected d.c. circuits with nominal voltages up to 1
000 V a.c. as well as unearthed d.c. IT systems up
to 1 500 V d.c. independent from the measuring
method.
The design of IT systems is described in IEC
60364-1 / DIN VDE 0100-100 (VDE 0100-100)
[2] amongst other standards. Various installation
regulations and product standards require the
application of IMDs:
• DIN VDE 0100-410 (VDE 0100-410), "Protection
for safety - Protection against electric shock" [3]
• DIN VDE 0100-557 (VDE 0100-557), "Selection
and erection of electrical equipment – Auxiliary
circuits [4]i
German title is translated into English, this is not an International Standard (IEC)
2
N E W S TAN DARDS
FOR INSULATION MONITORING DEVICES IMD
3. Maximum response time
• DIN VDE 0100-710 (VDE 0100-710), "Lowvoltage electrical installations – Part 7-710:
Requirements for special installations or locations – Medical locations" [5]
• DIN EN 60204-1 (VDE 0113-1), Safety of machinery - Electrical equipment of machines - Part 1:
General requirements [10]
An obvious change is the marking of the devices
with corresponding pictograms. In principle, this
distinction is nothing new, but now the user can
also recognize visually which devices are suitable
for which IT systems (Figure 1). A differentiation is
made between the following types of IMD:
• type AC IMDs for pure AC IT systems;
• type AC/DC IMDs for AC IT systems with galvanically connected rectifiers and for pure DC IT
systems as well as for DC IT systems with directly
connected inverters;
• type DC IMDs for pure DC IT systems.
Unlike TN or TT systems which require a specific
disconnection time on the occurrence of a first fault
for the protection against electric shock, according to IEC 60364-4-41 / DIN VDE 0100-410 (VDE
0100-410) [3] this requirement is not necessary for
unearthed IT systems.
However, the response time tan for the system
leakage capacitance Ce and the defined frequency
range fn must be stated in the documentation for
the IMD. For this purpose two reference values for
Ce are required.
With a reference value of Ce = 1 uF the maximum
response times of ≤10 s for type AC IMDs, and ≤100
s for type AC/DC or type DC IMDs are specified.
The second reference value specifies the maximum system leakage capacitance Ce at which a
response time of ≤30 min must not be exceeded.
With this information a statement can be made on
the technical characteristics and quality of the measuring principle of the IMD or a comparable value is
specified for the user.
3.1 Insulation monitoring devices
for PV systems
FIGURE 1: Marking of insulation
monitoring devices for different types
of system EN 61557-8.
It is a general aim to no longer include specific
product requirements in the installation standards
of the IEC 60364 / the DIN VDE 0100 (VDE 0100)
[2] series of standards. For this reason, the requirements for insulation monitoring devices that monitor
medical locations according to IEC 60364-7-710
/ DIN VDE 0100-710 (VDE 0100-710) [5] were
defined for the first time in the second edition of
the product standard IEC 61557 / DIN EN 61557-8
(VDE 0413-8):2007-12. This successful practice has
3
N E W S TAN DARDS
FOR INSULATION MONITORING DEVICES IMD
been continued for photovoltaic installations in the
third edition of IEC 61557-8 / EN 61557-8 [6]. In the
new Annexes C and D the requirements are now
described for:
• Insulation monitoring devices for photovoltaic
systems (PV-IMD)
• Insulation monitoring functions of photovoltaic
inverters (PV-IMF).
A key aspect of photovoltaic installations is a continuous operation, as a shutdown is synonymous
to a financial loss. This issue has now also been
considered in IEC 61557-8 / EN 61557-8 [6] and the
necessary requirements for insulation monitoring
devices are defined in Annex C.
From a metrological point of view the possible high
system leakage capacitances and the dynamic
voltage changes represent a challenge for the IMD.
Therefore, even under the effect of the fluctuation in
the DC voltage as shown in Figure 2, an IMD may
• not trigger a false alarm;
The requirements for PV systems are complemented by Annex D that describes the requirements for the insulation monitoring function for
PV inverters taking into account the standard
IEC 62109-2 / DIN EN 62109-2 (VDE 0126-14-2)
[11]. Requirements similar to those for a PV-IMD
also apply here.
A corresponding marking has also been defined
for PV IMDs (Figure 3).
FIGURE 3: Marking of insulation
monitoring devices for photovoltaic
applicationsn
• not erroneously clear the alarm message from an
alarm status;
• detect and signal insulation faults within the specified response time;
• clear an alarm message if the insulation fault is
below the specified limit.
FIGURE 2:
Dynamic reference characteristics of photovoltaic
DC according to EN 61557-8
4. IMDs for applications with
functional safety according to
DIN EN 61557-15
The question of the functional safety of electrical
systems and respective monitoring devices is
arising in an increasing number of areas. The
requirements on these insulation monitoring
devices are defined in IEC 61557-15 / DIN EN
61557-15 (VDE 0413-15) [8] and can be applied
for example for applications according to the
comprehensive IEC 61508 / DIN EN 61508 (VDE
0803) [9] series of standards, which defines
the requirements for functional safety that are
of highest priority for safety-related systems.
Functional safety can be necessary in unearthed
IT systems if safety is based on insulation monitoring devices and on insulation fault location
systems as well as additional functions (for example switching).
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N E W S TAN DARDS
FOR INSULATION MONITORING DEVICES IMD
Although the fundamental requirements for these
devices are described in IEC 61557—8 / EN 615578 and IEC 61557-9 / EN 61557-9, these standards
however do not contain any requirements for the
consideration of functional safety according to
IEC 61557-15 / EN 61557-15 [8], for example the
degree of functional safety or how the related validation is to be undertaken.
To take into account requirements on the related
safety integrity level (SIL), the terminology and
the related systematologies were adapted in IEC
61557-8 / EN 61557-8 [6] and IEC 61557-9 / EN
61557-9 [7]. Ultimately, the simple adaptation of
these devices to the respective application is now
possible. Typical applications are for example
machines, cranes but also other installations with
high safety requirements. The title of IEC 6155715 is “Electrical safety in low-voltage distribution
systems up to 1 000 V a.c. and 1 500 V d.c. –
Equipment for testing, measuring or monitoring of
protective measures – Part 15: Functional safety
requirements for insulation monitoring devices in IT
systems and equipment for insulation fault location
in IT systems” [8].
Figure 4 shows a device in compliance with the
requirements on functional safety according to IEC
61557-15 / EN 61557-15.
5. Devices for insulation fault location
systems according to EN 61557-9
According to IEC 60364-4-41 / DIN VDE 0100-410
(VDE 0100-410) [3], it is a requirement that in IT
systems an insulation fault is eliminated within the
shortest practicable delay. Particularly in complex
and large installations however, this can become a
very time consuming affair. Here, the usage of insulation fault location systems provides a solution;
these devices locate the fault within a very short
time and without shutting-down the installation.
FIGURE 4: Insulation monitoring device
ISOMETER® type iso685 according to
IEC 61557-15 / EN 61557-8
[photograph supplied by Bender GmbH & Co KG]
IEC 61557-9 / EN 61557-9 describes the normative requirements on insulation fault location systems that can locate insulation faults
in unearthed a.c. IT systems or a.c. IT systems
with galvanically connected d.c. circuits with
nominal voltages up to 1 000 V a.c. as well as
unearthed d.c. IT systems up to 1 500 V d.c. [7].
An IFLS (Insulation Fault Location System)
must be able to locate both symmetrical and
asymmetrical insulation faults in an unearthed
IT system. The localisation message indicates
where the outgoing circuit or area with the insulation fault is.
5
N E W S TAN DARDS
FOR INSULATION MONITORING DEVICES IMD
The third edition of IEC 61557-9 / EN 61557-9
represents a comprehensive technical revision.
Compared to the second edition from 2009 the
following major changes have been made:
• the scope, normative references and terms and
definitions have been complemented;
• abbreviations are listed and explained;
• requirements, marking and operating instructions have been revised;
• mandatory and optional functions have been
defined and their terminology has been adapted
to IEC 61557-15;
• mechanical requirements have been added;
• Clause 6 "Tests" has been revised;
• Annexes A, B and C have been revised.
AUTHORS:
Dipl.-Ing. Harald Sellner
Head of Standardisation
Bender GmbH & Co. KG
35305 Gruenberg
Dipl.-Ing. Dieter Hackl
Head of T-MIS
Bender GmbH & Co. KG
35305 Gruenberg
Obmann DKE UK 964.1
SUMMARY
Already seven years have passed since the last
publication of the product standards for insulation monitoring devices and equipment for
insulation fault location in IT systems. With the
new editions of IEC 61557-8 and IEC 61557-9 the
rapid technological progress in the area of insulation monitoring for unearthed power supplies (IT
systems) has been addressed as has the trend
of describing more product requirements in
independent standards. These also include the
special requirements on the functional safety of
these devices in accordance with IEC 61557-15.
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N E W S TAN DARDS
REFERENCES:
FOR INSULATION MONITORING DEVICES IMD
[1]
Wolfgang Hofheinz
"Schutztechnik mit Isolationsüberwachung", VDE series volume 114, 3rd edition 2011
[2]
DIN VDE 0100-100 (VDE 0100-100):2009-06
„Errichten von Niederspannungsanlagen – Teil 1: Allgemeine Grundsätze, Bestimmungen allgemeiner Merkmale, Begriffe”
IEC 60364-1
"Low-voltage electrical installations – Part 1: Fundamental principles, assessment of general characteristics, definitions
[3]
DIN VDE 0100-410 (VDE 0100-410):2007-06
„Errichten von Niederspannungsanlagen – Teil 4-41: Schutzmaßnahmen - Schutz gegen elektrischen Schlag“
IEC 60364-4-41, "Low-voltage electrical installations – Part 4-41: Protection for safety - Protection against electric shock"
[4]
DIN VDE 0100-557 (VDE 0100-557):2014-10
“Errichten von Niederspannungsanlagen – Teil 5-557: Auswahl und Errichtung elektrischer Betriebsmittel – Hilfsstromkreise”
[English translation of the title: Low-voltage electrical installations - Part 5-557: Selection and erection of electrical equipment –
Auxiliary circuits]
[5]
DIN VDE 0100-710 (VDE 0100-710):2012-10
„Errichten von Niederspannungsanlagen Teil 7-710: Anforderungen für Betriebsstätten, Räume und Anlagen besonderer Art –
Medizinisch genutzte Bereiche“
IEC 60364-7-710, "Low-voltage electrical installations - Part 7-710: Requirements for special installations or locations – Medical locations"
[6]
EN 61557-8:2015-01
"Electrical safety in low voltage distribution systems up to 1 000 V a.c. and 1 500 V d.c. - Equipment for testing, measuring or
monitoring of protective measures - Part 8: Insulation monitoring devices for IT systems"
DIN EN 61557-8 (VDE 0413-8):2015-xx
„Elektrische Sicherheit in Niederspannungsnetzen bis AC 1 000 V und DC 1 500 V – Geräte zum Prüfen, Messen oder
Überwachen von Schutzmaßnahmen – Teil 8: Insulation monitoring devices for IT systems“ - the German adoption will be
published shortly.
[7]
EN 61557-9:2015-01
"Electrical safety in low voltage distribution systems up to 1 000 V a.c. and 1 500 V d.c. - Equipment for testing, measuring or
monitoring of protective measures - Part 9: Equipment for insulation fault location in IT systems"
DIN EN 61557-9 (VDE 0413-9)2015-xx
„Elektrische Sicherheit in Niederspannungsnetzen bis AC 1 000 V und DC 1 500 V – Geräte zum Prüfen, Messen oder
Überwachen von Schutzmaßnahmen – Teil 9: Einrichtungen zur Isolationsfehlersuche in IT-Systemen“ - the German adoption will
be published shortly.)
[8]
DIN EN 61557-15 (VDE 0413-15):2014-10
"Elektrische Sicherheit in Niederspannungsnetzen bis AC 1 000 V und DC 1 500 V – Geräte zum Prüfen, Messen oder
Überwachen von Schutzmaßnahmen - Teil 15: Anforderungen zur Funktionalen Sicherheit von Isolationsüberwachungsgeräten
in IT-Systemen und von Einrichtungen zur Isolationsfehlersuche in IT-Systemen"
IEC 61557-15:2014-02
“Electrical safety in low-voltage distribution systems up to 1 000 V a.c. and 1 500 V d.c. – Equipment for testing, measuring or
monitoring of protective measures – Part 15: Functional safety requirements for insulation monitoring devices in IT systems and
equipment for insulation fault location in IT systems”
[9]
DIN EN 61508 (VDE 0803):2011-02
„Funktionale Sicherheit sicherheitsbezogener elektrischer/elektronischer/programmierbarer elektronischer Systeme“
IEC 61508, "Functional safety of electrical/electronic/ programmable electronic safety-related systems
[10] DIN EN 60204-1 (VDE 0113-1):2007-06
„Sicherheit von Maschinen – Elektrische Ausrüstung von Maschinen – Teil 1: Allgemeine Anforderungen“
IEC 60204-1, "Safety of machinery. Electrical equipment of machines - Part 1: General requirements"
[11] DIN EN 62109-2 (VDE 0126-14-2):2012-04
„Sicherheit von Leistungsumrichtern zur Anwendung in photovoltaischen Energiesystemen – Teil 2: Besondere Anforderungen
an Wechselrichter“
IEC 62109-2, "Safety of power converters for use in photovoltaic power systems - Part 2: Particular requirements for inverters"
7