s
IEC 62271 standards for medium-voltage
switchgear and controlgear
Precise classifications make planning easier
Author
Ansgar Müller
Siemens AG
PTD M SP
Mozartstrasse 31c
91052 Erlangen
Tel.
Fax
Mail
+49 9131 7-33619
+49 9131 8835-33619
ansgar.mueller@siemens.com
IEC 62271 standards for medium-voltage switchgear and controlgear
IEC 62271 standards for medium-voltage switchgear and controlgear
– Precise classifications make planning easier
Contents
1
Group of standards for high-voltage switchgear and controlgear
2
Classification of switchgear and controlgear
2.1
2.2
2.3
2.4
Switches
Circuit-breakers
Disconnectors
Grounding switches
IEC 60265-1
IEC 62271-100
IEC 62271-102
IEC 62271-102
3
Metal-enclosed switchgear and controlgear
IEC 62271-200
3.1
Reasons for and objectives of revising the old standard
3.2
Classifications
3.3
Compartments
3.3.1
Partition class
3.3.2
Insulating medium
3.3.3
Accessibility of compartments and access control
3.3.4
Loss of service continuity category LSC
3.3.5
Examples
3.4
3.4.1
3.4.2
3.4.3
3.4.4
3.4.5
Internal arc classification IAC
Test conditions
Ignition and energy flow direction
Testing arrangement
Assessment criteria
IAC designations
3.5
3.5.1
3.5.2
3.5.3
Gaps in the standards
LSC category
Cable testing
PD measurement
4
Outlook
2
IEC 62271 standards for medium-voltage switchgear and controlgear
1
Group of standards for high-voltage switchgear and controlgear
A few years ago, IEC decided to combine the standards of committees 17A and 17C for
high-voltage switchgear and controlgear with rated values in excess of 1kV in one group with
standardized numbering. This makes it easier for readers to find a standard. The new
numbers are not changed on a key date, but are only applied after revision of a standard,
and so the changeover period will extend until approximately the year 2010.
IEC 62271 HV Switchgear and controlgear standards
responsible
IEC committee
Parts
1 – 99 Generic standards
SC 17A / 17C
Parts 100 – 199 Switching devices
SC 17A
Parts 200 – 299 Switchgear installations
SC 17C
Parts 300 – 399 Guidelines, specifications
SC 17A / 17C
Fig. 1: New numbering structure
In relation to medium voltage, Table 1 shows a selection of the most important standards in
the new IEC 62271 group. The old IEC numbers did not indicate whether there were any
relationships between standards. By contrast, some national standardisation organisations
have been combining switchgear and controlgear standards for more than two decades now;
for example in the German VDE 0670 group.
IEC 62271
Title (short form)
Old number IEC
Part
1
Common specifications
60694
2007
Part
100
Circuit-breakers
60056
2001
Part
102
Disconnectors and earthing switches
60129
2001
Part
103
Switches
60265-1
Part
105
Switch-fuse combinations
60420
Part
106
Contactors
60470
Part
200
Metal-enclosed switchgear
60298
2003
Part
201
Insulation-enclosed switchgear
60466
2006
Part
202
Compact HV/LV stations
31330
2006
Table 1:
Transition
2002
Numbering of standards for switchgear and controlgear
in the medium voltage range (> 1 kV up to and including 52 kV)
3
IEC 62271 standards for medium-voltage switchgear and controlgear
2
Classification of switchgear and controlgear
Besides specification of the usual rated values for switchgear and controlgear, it has become
commonplace to specify a class that refers to a unit's useful life. Circuit-breakers are an
exception. In their case, an additional class designates their response to breaking of
capacitive currents.
Although the term “useful life” would be more appropriate to an object, the expression
"lifetime" has firmly established itself in the standards and so this term is also used below.
In 1998, the switches standard was the first to introduce the lifetime classification. The
lifetime is understood to be a minimum number of switching cycles that is possible without
noteworthy maintenance activities (e.g. greasing, topping up gas or cleaning exterior
surfaces). Classification encompasses the class "M" for the number of mechanical switching
cycles and the class "E" for the electrical switching cycles.
In the meantime, other equipment standards have also started defining such classifications.
Unfortunately, neither the ways in which the classes are enumerated nor the staggered
numbers of switching cycles given in the individual standards for switches are uniform and
careful attention has to be paid.
2.1
Switches to IEC 60265-1
The standard defines classes only for the so-called multi-purpose switches, although,
besides these, there are also "special purpose switches" and "limited purpose switches"1.
As the name suggests, multi-purpose switches must be capable of switching different kinds
of operating currents, for example load currents, ring currents, currents of unloaded
transformers, charging currents of unloaded cables and overhead lines, and also of making
short-circuit currents. Multi-purpose switches intended for use in networks with an isolated
star point or with earth fault compensation must also be capable of switching under earth
fault conditions. Their diversity is reflected in the fairly exact designations for the E classes.
Class
M
Description
M1
1000
Mechanical endurance
M2
5000
Increased mechanical endurance
E1
10 x I1
10 x I2a
2 x Ima
E2
30 x I1
20 x I2a
3 x Ima
E
E3
Table 2:
1
Switching
cycles
100 x I1
20 x I2a
5 x Ima
20 x 0.05 ⋅ I1
10 x I4a
10 x 0.2 to 0.4 ⋅ I4a
10 x I4b
I1
I2a
I4a
I4b
I6a
I6b
active load-breaking current
closed-loop breaking current
cable-charging breaking current
line-charging breaking current
earth fault breaking current
cable- and line-charging breaking
current under earth fault conditions
Ima
Short-circuit making current
10 x I6a
10 x I6b
Classes for multi-purpose switches
Limited purpose switches need only master a selection of a multi-purpose switch's duties. Special
purpose switches are intended for switching tasks such as those of single capacitor banks, parallel
switching of capacitor banks, ring circuits formed by parallel-connected transformers or motors (in
the normal or braked state).
4
IEC 62271 standards for medium-voltage switchgear and controlgear
2.2
Circuit-breakers to IEC 62271-100
While the numbers of mechanical switching cycles of the M classes are expressly mentioned,
the circuit-breaker standard does not define the electrical endurance of the E classes with
specific numbers of switching cycles, but unfortunately only vaguely with a verbal description.
The type test switching sequences of the short-circuit type tests provide some orientation as
to what is to be understood by "normal electrical endurance" and "extended electrical
endurance". The numbers of making and breaking operations are specified in the grayhighlighted boxes in the table.
It must also be said that modern vacuum circuit-breakers are generally capable of making
and breaking the rated normal current with the number of mechanical switching cycles.
Class
M
Description
M1
2,000 switching cycles
Normal mechanical endurance
M2
10,000 switching cycles
Extended mechanical endurance, low maintenance
E1
2 x C and 3 x O with 10%,
30%, 60% and 100% Isc
Normal electrical endurance (circuit-breaker not covered by
E2)
2 x C and 3 x O with 10%,
30%, 60% and 100% Isc
Without ARE 2
operation
E
E2
26 x C 130 x O 10% Isc
26 x C 130 x O 30% Isc
4xC
8 x O 60% Isc
4xC
6 x O 100% Isc
With ARE 2 operation
Extended electrical endurance
without maintenance of the arcing
chamber
C = closing, O = opening; Isc = rated short-circuit breaking current
Table 3:
Circuit-breaker classes
Above and beyond the lifetime data, the standard also describes capacitive switching
behavior by means of a class C, which summarizes the characteristics of three switching
tasks, namely the switching of
• Overhead lines
• Cables
• Capacitors (single and connected in parallel)
Class
Description
C1
Low restriking probability during breaking of capacitive currents
C2
Very low restriking probability during breaking of capacitive currents
C
Table 4:
2
Circuit-breaker classes in relation to capacitive switching behavior
ARE = automatic reclosing
5
IEC 62271 standards for medium-voltage switchgear and controlgear
Only at first glance does the definition of restriking probability as "low" and "very low" appear
imprecise. On the contrary, it is covered by an extremely complex type test. Two test
switching sequences have to be passed for each of the three test circuits (overhead line,
cable and capacitor), and the switching sequences and testing severity differ for the classes
C1 and C2. In the best and simplest case, during three-phase tests this signifies
C1:
144 breaking operations without restriking in accordance with conditions for class C1
C2:
200 breaking operations without restriking in accordance with conditions for class C2
However, this by no means reflects all definitions. The reason is that the occurrence of
restriking depends on marginal conditions (for example the condition of the switching
contacts, the load on the contacts due to previous switching operations, and the arcing time
during breaking) and, like many things in high-voltage physics, restriking is also a statistical
phenomenon. It would be unrealistic to expect a circuit-breaker that is completely and utterly
devoid of restriking. This is why restriking is allowed during the test series if subsequent
repetition of the test switching sequence concerned occurs without restriking. Repetition may
then call for about one hundred additional switching operations. This applies to three-phase
circuit-breaker tests; single-phase tests may call for more than five hundred switching
operations (with repetition). If a circuit-breaker does not pass the test for the desired class
C2, it can by reclassified in accordance with certain criteria as belonging to class C1.
There is no doubt that capacitive switching capacity is one of the indispensable
characteristics of a circuit-breaker in the network. In medium-voltage networks, according to
operating experience up to now, circuit-breakers have fully conformed to the demands. This
is why the question must be raised as to whether the intensified type testing procedure in the
standard is not too complex. A few hundred switching operations, in different test circuits and
with a large number of different parameter settings, take up a considerable amount of time
and therefore cost considerable amounts of money. Is the cost-benefit ratio still right?
Proponents of complex test procedures still get their money's worth, though.
6
IEC 62271 standards for medium-voltage switchgear and controlgear
2.3
Disconnectors to IEC 62271-102
Disconnectors do not have any switching capacity3, and so classes have only been defined
for the number of mechanical switching cycles.
Class
M
Switching
cycles
M0
1,000
M1
2,000
M2
10,000
Table 5:
2.4
Description
For general requirements
Extended mechanical endurance
Disconnector classes
Earthing switches to IEC 62271-102
In the case of earthing switches, the classes designate their short-circuit making capacity
(earthing to an applied voltage). E0 corresponds to a normal earthing switch and switches
belonging to classes E1 and E2 are also referred to as "make-proof earthing switches".
Class
E
Switching
cycles
E0
0 x Ima
E1
2 x Ima
E2
5 x Ima
Table 6:
Description
No short-circuit making capacity
Short-circuit making capacity
For general requirements
Reduced need for
maintenance
Classes for earthing switches
The standard does not define how often an earthing switch can be actuated mechanically.
There are no M classes for these switches.
3
Disconnectors up to 52 kV are only allowed to switch negligible currents up to 500 mA (e.g. voltage
transformers) or higher currents only if the voltage difference is insignificant (e.g. when changing
busbars with the bus coupling activated).
7
IEC 62271 standards for medium-voltage switchgear and controlgear
3
Metal-enclosed switchgear and controlgear
The new IEC 62271-200 standard superseded its predecessor IEC 60298 on November 1,
2003.
CENELEC ratified the IEC standard as the European standard EN 62271-200 on February 1,
2004. This date crucially influences the three-year transition period. Accordingly, the "old"
national standards corresponding to EN 60298 can still be used up to February 1, 2007.
3.1
Reasons for and objectives of revising the old standard
Medium-voltage switchgear and controlgear belong to the long-term capital investment
goods of the electricity supply company, and have useful lives extending over decades. This
is reflected in the standards and their revision cycles, which are oriented to the long term.
The predecessor standard IEC 60298 appeared in 1990 and an addition was made to its
subject matter in 1994, followed by a formal corrigendum in 19954. By the time of publication
of its now valid successor, the thirteen-year-old standard had reached an age when an
update had become absolutely essential. Following such a long time, the needs of the
market and the state of the art, both of which ought to be considered in a standard, had
evolved considerably. So, there were enough reasons for revising it.
•
In terms of its definitions and requirements, the previous standard was recognizably oriented to the design conditions of "removable" systems with switching devices on a truck
or a withdrawable part. Modern fixed mounting or gas-insulated systems (GIS) were under-represented.
•
Acording to their design, switchgear and controlgear were subdivided into three partition
types (Fig. 2): metal-clad, compartmented and cubicle. This subdivision, which was not
quite consistently defined, now only insufficiently described the attributes of current
switchgear and controlgear types.
Firstly, the boundary between metal-clad and compartmented was blurred because
insulator shutters were allowed in the case of metal-clad switchgear and controlgear.
Secondly, so many types of construction had now come into being that could be
classified as "cubicle" that this designation could no longer be used to describe clearly
defined attributes. And, thirdly, there is now a whole range of systems on the market that
hardly fits consistently into the patterns any more. Moreover, classification according to
the type of compartmentalisation could be misunderstood as an order of precedence in
terms of safety and reliability that does not reflect actual conditions.
•
Not least, there were also formal and editorial reasons for the update, e.g. the need for
adaptation to IEC 606945, the "generic standard" for all high-voltage switchgear and
controlgear above 1 kV.
4
IEC 60298:1990 +A1:1994 + Corrigendum:1995 - A.C. metal-enclosed switchgear and controlgear
for rated voltages above 1 kV and up to and including 52 kV
VDE 0670-6, Mai 1998 + Ber.1 März 1999 + Ber.2 Sept. 2001, Metallgekapselte WechselstromSchaltanlagen für Bemessungsspannungen über 1 kV bis einschließlich 52 kV
5
IEC 60694 Common specifications for high-voltage switchgear and controlgear standards
VDE 0670-1000 Gemeinsame Bestimmungen fuer Hochspannungs-Schaltgeräte-Normen
8
IEC 62271 standards for medium-voltage switchgear and controlgear
Metal enclosure – Designs acc. to IEC 60298
Function
Enclosure protects against
• external influences
• contact and shock
• internal arc faults (option)
Metal-clad
• Metal partitions
• Metal or insulating shutters
• Compartments for busbar,
„main switching device“, cable
Compartmentalisation
provides safe access to one
or more open compartments
while the adjacent compartments and functional units
can remain live
Compartmented („plastic-clad“)
• as „metal-clad, but
partitions of non-metal
Cubicle
• all other designs
User‘s benefit
Safety
Service
continuity
Maintainability
Fig. 2: Classification in the previous IEC 60298 standard according to design features
Standards are primarily a contractual basis for manufacturers and operators and this is why
they must reflect market needs. The market has undergone considerable transformation in
the past decade. Due to the liberalization of electricity markets and cost pressure in all
sectors of the economy, the requirements for switchgear and controlgear have also changed.
•
There was a wish for a type of classification that would be oriented to safety, availability
and maintainability, and thus to the "functionality" that stands behind the type of
construction.
•
Gas-insulated switchgear and controlgear and other types of construction with fixedmounted switching devices have accounted for a large proportion of new installations
and, at least in some countries, have driven back the share of "removable" systems.
•
Internal arc testing has become an attribute that has almost established itself worldwide
and which ought to be given more appreciation. A (still optional) genuine test with
defined test conditions and a "passed" or "failed" statement should take the place of a
mere "assessment of the effects".
•
The standard should be open to future developments. For example, nowadays many
functions that were once mechanical are now performed electrically or by software.
Specifications stipulating mechanical designs should be dispensed with.
3.2
Classifications in accordance with IEC 62271-200
To place the functionality of a switchgear and controlgear in the focus of classification, it was
only necessary to fall back on the functional attributes (on the right in Fig. 2) that already
existed in the previous structural subdivision of switchgear and controlgear, namely safety,
operational availability and maintainability.
The enclosure and compartmentalisation ensure protection against physical contact and
foreign matter. In an extreme case, the enclosure additionally protects persons outside the
system against the effects of an arcing fault.
The compartmentalisation also contributes to safety by protecting persons working inside an
open system against contact with live or other dangerous parts. Defined arcing fault
protection inside the system is not provided, however.
Breaking down switchgear and controlgear into compartments also makes it possible to work
in a functional unit and to at least maintain operation of the neighbouring units. Parts of the
open functional unit may even possibly remain live. This reduces the scope of switching over
9
IEC 62271 standards for medium-voltage switchgear and controlgear
and work activities. Ultimately, the number and design of the compartments define how
complex access to the parts of the switchgear and controlgear is without interrupting
operation in total, this being a measure of its operational availability and maintenancefriendliness.
Metal enclosure – Designs acc. to Part 200
Compartmentalisation features
Partition class
• PM (metal)
• PI (insulating material)
Insulation medium
• Ambient air
• Fluid (SF6, oil)
Non-accessible compartment
Accessible compartment
Access control
• interlock-controlled
• procedure-based
• tool-based
Loss of
service
continuity
• LSC 1
• LSC 2A
• LSC 2B
Internal Arc Classification
Option
Fig. 3: New classification structure in accordance with IEC 62271-200
3.3
Compartments
3.3.1
Partition class
While work is being done in open switchgear and controlgear, the partitions and shutters to
the next compartment or to the neighboring functional unit protect against high voltage. The
partition class specifies whether partitioning from high high-voltage parts is purely metallic or
whether it contains insulators. Although both of them achieve the same degree of protection
against electric shock, metal partitioning also screens off the electric field of the primary part.
The PM class stands for "Partition metallic" with earthed, continuously metallic partitions and
metallic shutters between the main circuit and the open compartment.
The PI class stands for "Partition of insulating material" whenever at least one part of the
partitioning is non-metallic, i.e. one or more partition(s) or shutter(s) is or are made of
insulating material. Note: partitioning made of insulating material is subjected to complex
tests and inspections to verify dielectric strength.
10
IEC 62271 standards for medium-voltage switchgear and controlgear
Partition classes
Class PM
Characteristics
• Metallic partitions and shutters between opened
compartment and live parts
( Partitions metallic )
• Dielectric conditions correspond to
metal enclosure
Class PI
• Non-metallic partitions and shutters between
( Partitions non-metallic;
i = insulating material )
opened compartment and live parts
Fig. 4: Dielectric classification of partitioning
The partition class clearly designates the actual dielectric conditions around the work
location. Previously, this was not the case because IEC 60298 also allowed insulating
material shutters for metal partitioning.
3.3.2
Insulating medium
Every compartment that does not use ambient air for insulation is considered to be a fluidfilled compartment.
Fluid is subdivided into
•
Gas
• Liquid
The term "fluid" describes liquids and gases neutrally. Apart from a few exceptions, in
practice the word fluid stands for oil or SF6. The standard, however, understands "gas" to be
any gas or gas mixture, but with the exception of ambient air.
All definitions, terms and formulations in the standard have been adapted according to this
generalization in terms of fluid. For example, the rating plate no longer speaks of the filling
pressure (instead, in the case of oil it would be a level), but generally of the filling level.
3.3.3
Accessibility of compartments and access control
There are four kinds of compartments, initially generally distinguished according to whether
they are accessible or not.
Accessible compartments are subdivided according to how access is controlled.
•
Interlock-controlled accessible compartment
The interlocks enable access only if all high-voltage parts are deenergized and earthed.
According to the manufacturer's specifications, opening has been conceived for normal
operation or for maintenance, e.g. to replace a fuse. By contrast, assembly, expansion
and repair are not deemed normal maintenance.
•
Procedure-based accessible compartment
Access is controlled via "work procedures" in combination with locking devices
(padlock). Organizational measures must ensure that access is possible only when highvoltage parts are deenergized and earthed. As before, opening was conceived for
normal operation or maintenance and not for assembly, expansion or repairs.
11
IEC 62271 standards for medium-voltage switchgear and controlgear
•
Tool-based accessible compartment
Such a compartment can only be opened using a tool, but not for normal operation and
maintenance. Defined work procedures (work instructions) are necessary as a safety
measure, but are not specified any further.
•
Non-accessible compartment
A non-accessible compartment (typical of gas-insulated systems) may not be opened by
the operator because opening can destroy the space or render it useless. An appropriate
notice for the operator must be placed on or in the proximity of the compartment.
Compartment
Interlock-controlled
accessible
Procedure-based
accessible
Characteristic of access
• Access enabled if HV
• Access for normal
parts are dead and
earthed
operation and
maintenance
• Access controlled by
e.g. to replace fuses
locking and work
instructions
• Not to be opened for
Tool-based
accessible
• Tools for opening,
normal operation /
maintenance
specific procedure for
access (instructions)
e.g. for cable testing
• Access not possible / not intended for user;
Non-accessible
opening may destroy compartment ( indication )
e.g. gas-insulated compartment
Fig. 5: Types of compartments and accessibility
3.3.4
Loss of service continuity category LSC
The loss of service continuity category describes the arrangement and design of
compartments. It depends on whether and which parts of the switchgear and controlgear
have to be deactivated or can remain live when a compartment is opened. This concerns
neighboring functional units and also other compartments of an opened functional unit.
LSC categories apply to switchgear and controlgear with accessible compartments. We have
to start with the highest category to understand the definitions.
•
Category LSC 2
This category applies to switchgear and controlgear that possess not only the
compartment of a single busbar, but also other, accessible, compartments.
When any one compartment of a functional unit is opened, all neighboring functional
units of the opened unit may remain live and can be operated as normally. The
compartment of a single busbar, which prevents system operation when it is opened, is
an exception to this rule. LSC 2 consists of two subdivisions:
•
Category LSC 2B
This category applies to switchgear and controlgear belonging to the category LSC 2 in
which the cable terminal compartment can also remain live if any other compartment in
the same functional unit is open.
12
IEC 62271 standards for medium-voltage switchgear and controlgear
•
Category LSC 2A
This category applies to switchgear and controlgear belonging to the category LSC 2
that does not conform to LSC 2B.
•
Category LSC 1
This category applies to switchgear and controlgear that does not conform to LSC 2.
Category of
Loss of Service
Continuity
If one accessible compartment
(e.g. circuit-breaker) in a
functional unit is opened …
LSC 1
z adjacent functional units must
be switched off
LSC 2A
z all other functional units
remain in service (energized)
LSC 2B
z all other functional units
remain in service (energized)
and the cable compartment of
the opened functional unit
LSC 2
Design
No partitions
between panels
Partitions between
panels +
disconnection and
partition to BB
As LSC 2A +
disconnection and
partition to cable
Fig. 6: Loss of service continuity categories
LSC 1:
The number "1" stands for the lowest service continuity and signifies that at least
one further functional unit, besides the open one, must be deactivated6.
Class 1 has no partitions between the functional units, for example.
LSC 2:
The number "2" means that no functional units apart from the one with the open
compartment need to be deactivated, i.e. the system remains available.
LSC 2A: "A" means that the functional unit with the open compartment must be taken out of
operation completely.
Class 2A requires:
- Partitions to neighboring functional units
- At least two compartments in a functional unit
- An isolation distance from the busbar
LSC 2B: "B" means that, even in the functional unit with an open compartment, the other
compartments may remain live. 2B offers the highest availability.
Class 2B requires:
- Partitions to neighboring functional units
- At least three compartments in a functional unit
- Isolation distances from the busbar and the cable
The LSC categories do not make any difference between fixed-mounted compartments with
shutters and temporary partitions (e.g. protective plates).
LSC categories only make sense for switchgear and controlgear in which other
compartments, with the exception of the busbar compartment, are accessible. This
6
If it is the busbar compartment, all other functional units belonging to this busbar section must be
deenergized.
13
IEC 62271 standards for medium-voltage switchgear and controlgear
categorization can therefore not be applied to gas-insulated switchgear and controlgear. This
may be irritating, but Section 6.1 of this paper discusses this issue in greater detail.
3.3.5
Examples
The following examples elucidate the new classifications.
a) Air-insulated switchgear and controlgear with three compartments and metallic shutters.
Old IEC 60298 designation: metal-clad
Accessibility of compartments
• BB:
tool-based
• CB:
interlock-controlled
or procedure-based
• Cable: tool-based
Loss of service continuity
• Category LSC 2B
Partitions and shutters
• Class PM (metallic)
Internal arc classification
• Classification IAC
Fig. 7: Air-insulated system with "metal-clad"
b) Air-insulated switchgear and controlgear, circuit-breaker/cable connection and
disconnector/earthing switch in separate compartments
Accessibility of compartments
• BB:
tool-based
• Disconnector and earthing
switch: non-accessible
• CB:
interlock-controlled
• Kabel: interlock-controlled
Loss of service continuity
• Category LSC 2A
Partitions and shutters
• Class PM
Internal arc classification
• Classification IAC
Fig. 8: Air-insulated system with "cubicle"
14
IEC 62271 standards for medium-voltage switchgear and controlgear
c) Gas-insulated switchgear and controlgear, circuit-breaker or switch and
disconnector/earthing switch and cable connection in separate compartments;
old IEC 60298 designation: metal-clad
Accessibility of compartments
• BB:
tool-based accessible
• CB/switch: non-accessible
• Cable:
interlock-controlled
Partitions and shutters
• Class PM
Internal arc classification
• Classification IAC
Fig. 9: "Metal-clad" gas-insulated switchgear and controlgear
d) Gas-insulated switchgear and controlgear, circuit-breaker and disconnector/earthing
switch in one compartment; old IEC 60298 designation: metal-clad
Accessibility of compartments
• BB:
tool-based
• CB:
non-accessible
• Cable: tool-based
Partitions and shutters
• Class PM (metallic)
Internal arc classification
• Classification IAC
Fig. 10: "Metal-clad" gas-insulated switchgear and controlgear
15
IEC 62271 standards for medium-voltage switchgear and controlgear
e) Gas-insulated switchgear and controlgear; old IEC 60298 designation: metal-clad
Accessibility of compartments
• BB:
non-accessible
• CB:
non-accessible
• Cable: tool-based / procedure-based
Partitions and shutters
• Class PM
Internal arc classification
• Classification IAC
Fig. 11: "Metal-clad" gas-insulated switchgear and controlgear
3.4
Internal arc classification IAC
IAC stands for "internal arc classification". Clearly greater importance has been attached to
internal arcing fault protection in IEC 60298 although, formally, the internal arc classification
remains an optional attribute that can be fulfilled voluntarily; in practice however, it would
hardly be possible to sell such an untested system. According to the new standard, testing is
now undertaken under specified conditions and in accordance with defined criteria.
Therefore, testing and its assessment are no longer a matter for negotiation.
Thus, the "IAC" classification applies only to switchgear and controlgear that fulfil all
prescribed assessment attributes for the protection of persons in the event of an internal arc,
verified by relevant tests and inspections.
• The test conditions are defined, and so they are no longer subject to an agreement
between the manufacturer and operator or test laboratory.
• Testing is passed only if all defined criteria are met. It is no longer possible to select
individual criteria.
3.4.1
Test conditions
The following defined test conditions are particularly important and worthy of emphasis:
• The test object must be fully equipped, but equivalents are possible if they conform to the
original in terms of volume and material.
• A test object consists of at least two functional units.
• Tests must be performed in each compartment (of the main circuit) and in the end unit.
• Only compartments that have not been previously burdened (with internal arcs) may be
tested, unless they are in a state that will not influence the result of testing.
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IEC 62271 standards for medium-voltage switchgear and controlgear
• SF6 may be replaced with air, but all other fluids must not be replaced for testing.
Ö This is intended to avoid SF6 decomposition products and unnecessary emissions and
is also for industrial safety reasons. However, it must be mentioned that the reaction
products of the materials resulting from an arc burning in air also pose problems.
• Degree of accessibility A, B or C
Degrees A (specialist personnel) and B (general public) remain unchanged. The degree of
accessibility C for devices and systems mounted on a pole is new.
3.4.2
Arc initiation and energy flow direction
• The manufacturer defines the testing duration, and 1.0 / 0.5 / 0.1 s are recommended
preferred values.
• Ignition is normally three-phase. Systems with single conductors partitioned from one
another that cannot influence each other are the exception to this rule. In their case, the
arc is ignited to earth.
• Ignition takes place in the tested compartment at the place furthest away from the
incoming supply.
Ö This is intended to make sure that the arc burns as long as possible there without the
duration of burning being shortened by the run time to this location. The tacit prerequisite
is that the arc travels to this point lest, in reality, it originates further towards the front at
the incoming supply point.
For ignition, the current flow direction (from the incoming supply to the ignition location) is:
• In the cable terminal compartment: through the busbar and the switching device
• In the busbar compartment without partitioning from unit to unit: through the busbar
• In the busbar compartment with partitioning from unit to unit: through the switching device
• In the switching device compartment – the switch is closed: through the busbar
• In a compartment with several switching devices – all switches are closed except for one
earthing switch: through a set of bushings
3.4.3
Testing arrangement
In future, defined distances will also apply to the test object setup in the room simulation (see
Fig. 12).
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IEC 62271 standards for medium-voltage switchgear and controlgear
• Specimen fully equipped
60 cm
(mock-ups permitted)
• Two functional units
• Test in each compartment,
10 cm
at end of the switchgear
• Accessibility A, B or C
80 cm
or
10 cm
• Arc initiation and direction
of power flow
Ö Other arrangements
are permitted
Fig. 12: Standardised arrangement for internal arc tests
The distance between the system and the ceiling is 60 cm, unless the system itself is less
than 1.50 m high. In this case, the ceiling is at least 2 m high (above the floor).
A distinction is made between whether or not the rear side is accessible, i.e. whether or not
the system is set up directly on the wall. Accessible rear sides must be tested with a distance
of 80 cm from the wall and rear panels directly on a wall must be tested with a distance of 10
cm.
Ö The 80 cm dimension is the result of the indicator rack's setup width.
Additional rules and regulations apply if a system is to be placed closer than 10 cm to the
wall than when tested. The distance from the wall must be greater than a lasting deformation
of the functional unit's enclosure as a result of the arc. Hot gases must not escape directly
towards the wall either.
Ö The wall must not support a system and must not hinder gas expulsion. Otherwise, the
wall could exert such an unfavorable influence on the pressure conditions in the system that
the result of testing (without the wall's influence) would no longer be representative of the
setup conditions.
If it is intended to bolt a system directly to the wall, internal arc resistance for this kind of
setup must be verified by a separate test.
Other heights and distances may be examined in additional tests for each separate case.
Installations mounted closer
to the wall than tested (10 cm)
require:
• the permanent deformation
must be less than the
distance to the wall
• exhausting gases are not
directed to the wall
Fig. 13: The deformation influences setting up against a wall
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IEC 62271 standards for medium-voltage switchgear and controlgear
3.4.4
Assessment criteria
The following list shows the assessment criteria, which have only been modified slightly, but
to which a few additional requirements have been added.
Criterion 1
• Doors and covers remain closed.
• Deformations are acceptable if no part reaches the indicators or walls
(depending on what is closer).
• The IP degree of protection no longer needs to be assured.
Additional conditions if the system is to be placed closer to the wall than during testing:
• Lasting deformation is less than the intended distance from the wall.
• Expelled gases are not pointed at the wall.
Criterion 2
• The enclosure does not break during testing.
• No parts up to a single weight of 60 g may fly off.
Criterion 3
• Up to a height of 2 m, holes must not be burned into the freely accessible
exterior parts of the enclosure
Criterion 4
• Indicators must not be ignited by hot gases. Permitted exception:
• ignition by burning paint coatings, adhesive labels or glowing particles is acceptable.
Criterion 5
• Earth connections remain effective.
• Verify by visual inspection or by measurement in cases of doubt.
3.4.5
IAC designations
If internal arc testing has been passed, switchgear and controlgear is assigned the following
designations on the rating plate:
Qualification:
IAC ("Internal Arc Classified")
Accessibility:
A, B or C
with details of the tested, accessible sides F, L, R
F = front, L = Side ("lateral"), R = rear
Tested values:
Current [kA] and duration [s]
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IEC 62271 standards for medium-voltage switchgear and controlgear
IAC A FLR
25 kA
1s
Switchgear accessible to
authorized personnel only
IAC BFL-AR 16 kA
1s
Switchgear e.g. in a workshop; front
and lateral side publicly accesible,
rear to authorized personnel only
Fig. 14: Internal arc classification examples
Degree of accessibility: The degrees A (authorized personnel) and B (general public), which
had already been defined previously, remain unchanged. The degree of accessibility C for
devices and systems mounted on a pole is new.
Hybrid forms of accessibility can also be declared, for example some sides accessible to the
public and others only to specialist personnel or not at all. For example, a system such as the
one shown on the right in Fig. 14 could serve as a load-center substation in a factory hall.
These designations are unusual and it remains to be seen whether they are absolutely
necessary on the rating plate. It must be said that, in total, as far as internal arc protection is
concerned, the test results have become more comparable due to the defined test conditions
and so users are able to assess safety with greater ease.
3.5
Gaps in the standards
Not all issues have been satisfactorily clarified in IEC 62271-200. A few of them are mentioned here without dealing with their causes in greater detail.
3.5.1
LSC category
Essentially, accessibility to the compartment of the main switching device (circuit-breaker)
during normal operation determines the LSC category. Thus, (almost) all air-insulated
systems can be described with an LSC category because the circuit-breaker compartment in
the systems is generally accessible.
Things are different in the case of gas-insulated systems, where the main switching device
(switch or circuit-breaker) is in a non-accessible compartment. It is not necessary to open the
gas compartments during normal operation and it is precisely for this reason that this is not
possible either. Nowadays, many systems are "sealed for life". This dispenses with the
prerequisite for assignment to an LSC category. This can cause confusion. For example,
how are users to compare air and gas-insulated systems if they do not obtain any LSC
information for a type of construction? Are GIS systems less reliable, for example? Of course
they are not. GIS systems do not need this categorization because they are inherently more
reliable and so the focus is not on accessibility and maintainability.
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IEC 62271 standards for medium-voltage switchgear and controlgear
One shortcoming of the standard is that this circumstance is not recognizable in an additional
LSC category. LSC incorporates the right concept, i.e. that the design of a system
determines its loss of service continuity category. Service continuity is inseparably linked with
reliability, though. However, the standard does not contain any stipulations and definitions
relating to reliability due to a lack of a secured – and internationally recognized – database.
3.5.2
Cable testing
If cable testing is performed during operation of switchgear and controlgear without isolating
the cable from the system, the isolation distance from the busbar is subjected to the total of
the test voltage on the cable and the operating voltage of the busbar.
UN
∆U
uTest
Beispiel: Schaltfeld mit Lasttrennschalter
In some cases, there is then no safety
margin left over for the withstand capability
of the isolation distance. It is also a problem
that, in some cases, the voltage stress
contains a DC component, although DC is
not a rated quantity for switchgear and
controlgear.
Due to a lack of uniformity of cable test
voltages, which are highly diverse on the
international scale, and also due to the
absence of international reference
standards, it was not possible to define any
provisions in this respect. What is left is the
reference to the hazard. Operators have to
know how to perform testing, what their
systems are capable of withstanding and
what precautions they have to take.
Fig. 15: Cable testing with cables that are not disconnected
3.5.3
PD measurement
Even the old standard included an informative attachment about measurement of partial
discharges (PD) which described measurement methods, but did not specify any permissible
PD limits. As the partial discharge rate says something about the dielectric state of the
insulation, it would be desirable for the standard to define testing. At the moment, though,
several prerequisites for this are missing. Up to now, there have been no internationally
established, generally valid assessment criteria to determine which PD levels are still
tolerable for functional units or entire systems. Limits would have to be coordinated with
those of individual components such as instrument transformers. Moreover, it is difficult to
include interfering influences on a PD measurement locally in standards definitions. This is
why the definition of permissible PD levels is still a matter for negotiation between operators
and manufacturers, who are best able to assess the characteristics of their products.
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IEC 62271 standards for medium-voltage switchgear and controlgear
4
Outlook
4.1
Switch standards
By classifying the endurances of switching devices, the standards have closed a gap in
recent years. The classes for the possible mechanical and electrical switching cycles provide
users with additional information about what tasks they can expediently use a switch for.
Endurance classes exist for switches and circuit-breakers and for disconnectors and earthing
switches. Thus, the most important maneuvering and safety switches are covered. The
contactor is still unaccounted for. It can be assumed that IEC 60470 will also introduce such
classes in the next revision, but a date has not yet been named.
The circuit-breaker standard IEC 62271-100, which is unfortunately not yet stable, is giving
cause for concern. Although it was not published until 2001, it has already been amended to
because of errors and two corrections have been implemented. A further, third amendment is
currently in the draft stage. There are fierce disputes in the IEC committee in relation to the
test procedures. It remains to be hoped that stability will return to this core standard.
4.2
Metal-enclosed switchgear and controlgear
IEC 62271-200 introduces new terms and definitions which might need getting used to at the
beginning, but which do better justice to the present-day requirements and types of
switchgear and controlgear construction. Especially the internal arc qualification conditions
are now defined more clearly and are declared unequivocally. Many, long overdue
clarifications and adjustments to the state of the art have been achieved. The fact that there
are still gaps has to do with the consensus without which no international standard would
come into being. Practice will have to show how the new definitions prove themselves.
Does the new standard influence types of switchgear and controlgear construction?
There was a need to adjust switchgear and controlgear technology to the market. Therefore,
it will not lead directly to new "designs", but will rather more pave the way for new types of
construction. Nevertheless, the standard may have an indirect influence on the mechanical
design of switchgear and controlgear. For example, the intensifying of internal arc testing
may compel manufacturers to adopt different approaches. No-one will want to bear the
expense of unnecessary tests to achieve qualification. This is why the characteristics of a
system must already be optimized before testing, to make the occurrence of an internal fault
(even) less probable, to limit the propagation and effect of an internal arc, and to ensure the
design stability of the functional units. CAD processes may help here.
Does switchgear and controlgear conform to the new standard and are old tests still
valid?
The new standard does not demand any design changes nor new safety requirements and
so switchgear and controlgear currently constructed in accordance with IEC 60298 may also
conform to IEC 62271-200. Rated values have not been changed and no new rated quantities have been introduced. This is why test verifications conforming to the old standard are
still valid. This fundamentally also applies to internal arc testing, which has undergone wideranging changes. Systems that met all criteria in accordance with the old standard still offer
solid protection against the effects of an internal arc. Specification of the new standard on
the rating plate depends on whether purely formal requirements are also met. This must
always be reviewed and documented in each individual case. These changeovers need time.
Therefore, many switchgear and controlgear assemblies will continue to be constructed in
accordance with the previous IEC 60298 standard during the current transition period up to
February 1, 2007. System operators will also be able to use this period to change over their
specifications.
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