Saturday, January 18, 2014
Enclosure for potentially explosive atmospheres
What is ATEX?
It is a term commonly used to describe potentially explosive atmospheres
(ATmosphères EXplosibles in French) and standards for protection systems
and equipment.
Two European directives, ATEX 99/92/CE and ATEX 94/9/CE, and
international standards IEC 60079 and IEC 61241, harmonized with
EN European standards, apply to this field.
How is an potentially explosive atmosphere defined
according to ATEX?
An potentially explosive atmosphere is defined as a mix of flammable
substances in the form of gas, vapour, dust (cloud or deposit) which, in air
and under normal atmospheric conditions, can completely or partially catch
fire in the form of an explosion when exposed to a source of ignition.
Equipment for potentially explosive atmospheres
Degree of protection In hazardous areas, equipment is required to
offer a minimum degree of protection of IP54, but it can be tested or
certified with a higher degree of protection.The final solution must be certified by a notified body
Since 1st July 2003, European directive ATEX 94/9/CE has made it compulsory to use certified electric or
non-electric equipment when it must be installed in zones with explosive atmospheres (gas or dust).
Certification must be provided by a body which is notified according to the same directive.
The body notifies its assessment of the quality of the production and certifies that the product complies
with the health and safety demands defined in the directive and the international standards.
The certificate shows the category of the product by marking, and thus the zone and atmosphere in
which it can be used.
The standards define the following types of protection for electric equipment:
Enclosures are certified as components. They will be assembled with other ATEX electrical, pneumatic
and hydraulic components, among others to form a final solution which, in turn, must be ATEX-certified
and subject to a declaration of conformity
More info.
http://www.schneiderelectric.pt/documents/product-services/involucros-universais/ATEX.pdf
Thursday, January 16, 2014
Monday, January 13, 2014
ASTA Type Test Certification
ASTA Type Test Certificates provide authoritative objective evidence that your bespoke equipment is compliant to relevant safety standards. The certificate can be used for supporting technical files related to CE Marking for the European Union.
ASTA Type Test Certification is best suited for low volume or ‘bespoke’ equipment. ASTA Type Test Certification provides you with an independent compliance test certificate for one or a number of samples when tested against the requirements of the product safety standard. The document issued is known now as an ‘ASTA Type Test Certificate.’
Type test certification does not involve inspection of the manufacturing facility and the production processes. In some markets type test certification may be sufficient to satisfy the legislative or commercial requirements but in others, particularly where the safety and compliance of mass-produced products is concerned, additional guarantees may be required i.e. full certification. All test reports and certificates are verified by independent Intertek engineers. The ASTA Type Test Certificate issued is sealed and bound to prevent misuse.
Network of Global ASTA Recognized Laboratories
Shipping heavy bespoke equipment to testing laboratories can be a costly exercise. In order to assist our customers, Intertek has a global network of ASTA recognized laboratories. These recognized laboratories may carry out tests to support the issue of ASTA Certificates and Test Reports in accordance with ASTA’s rules and regulations. Mandated ASTA Observers witness the type tests on behalf of ASTA and the ASTA Observers draft the ASTA reports and certificates which are then sent to the ASTA office for verification and issue.
Products for which ASTA Type Test Certificates can be issued include:
| Product | Standard |
| LV Assemblies | IEC 60439-1 / IEC 61439-2 |
| LV Busbar Trunking Systems | IEC 60439-2 |
| LV Distribution Boards | IEC 60439-3 |
| LV Fuses / Fuse holders | IEC 60269 Series |
| LV Circuit Breakers | IEC 60947-2 |
| LV Fuse Switches | IEC 60947-3 |
| LV Starters / Contactors | IEC 60947-4-1 |
| Miniature Circuit Breakers | IEC 60898 |
| Power Transformers | IEC 60076 Series |
| HV Circuit Breakers | IEC 62271-100 |
| HV Metal Enclosed Switchgear & Controlgear | IEC 62271-200 |
| Internal Fault (Arc) Tests | IEC 62271-200 Annex A |
Copyright :
Friday, January 10, 2014
Salt mist test
This test serves to demonstrate that under the influence
of a saline atmosphere no damage (corrosion) is caused
to the components of the equipment under test and no
functional affections occur. This test is only performed
on products which are to be installed on the open deck
area.
Cold & Damp Heat test
Cold
This test serves to demonstrate that under the influence
of cold no damage is caused to the equipment under
test and no permanent or temporary malfunctions occur.
5.1 Test procedure
Basis: IEC publication 60068-2-1
– Test A): for products inside the ship
– Test B): for products on the open deck or in
cold areas.
5.2 Test conditions
The functional tests are performed at the rated operational
voltage Ue.
Damp heat
This test serves to demonstrate that under the influence
of damp heat no damage is caused to the equipment
under test and no permanent or temporary malfunctions
occur.
7.1 Test procedure
Basis: IEC publication 60068-2-30
– Test Db
7.2 Test conditions
The functional tests are performed at the rated operational
voltage Ue.
Tuesday, January 7, 2014
Design verification
Design verification is a prerequisite for all assemblies
provided. It is fundamental to ensuring every assembly
meets its defined design requirements. There is flexibility
in the way in which this is achieved within the new standard,
and some new concepts have been introduced, but the
options are defined and where necessary their use is
restricted and a design margin applied.
Examples of the limitations and margins applied to verification without type test include;
All assemblies connected to a supply with a prospective short circuit current in excess of 10kA
rms or having a cut-off current of 17kA peak must be of a type-tested design or the verification
must be an interpolation from a reference design. Under no circumstances can the assigned
short circuit current rating be higher than that of the reference design.
So as to take account of the air temperature within the enclosure, thermal interactions and
possible hot spots; components within a circuit that has not been temperature rise tested,
must be de-rated to 80% of their free air current rating.
Comparison of the power loss of the components within an assembly with the known heat
dissipation capability of an enclosure, is restricted to assemblies having a rating of 630A.
Confirmation of temperature rise performance by calculation is limited to assemblies with a
rating not exceeding 1600A. Test or interpolation from a tested design must be used to verify
higher ratings.
EMC Environment
Assemblies can emit and the must be immune to external
electromagnetic disturbances. IEC defines two categories
a) Environment A - relates to low-voltage non-public or industrial
networks / locations / installations including highly disturbing sources.
b) Environment B - relates to low-voltage public networks such as
domestic commercial and light industrial locations / installations.
This environment does not cover highly disturbing sources such as
arc welders.
The specifier should detail a requirement for either Environment A or B.
In exceptional applications, for example, some rail applications, it is
necessary to specify a higher level of immunity.
Rated diversity factor
In reality all circuits within an assembly will not be called upon to carry
their rated current simultaneously and continuously. Diversity is the
proportion of their rated current each circuit within a group of outgoing
circuits or all outgoing circuits within the assembly can carry,
continuously and simultaneously, without the assembly overheating. In
the absence of any other information in the assembly specification the
manufacturer will assume the standard diversity factors for the whole
assembly.
Typical RDF
| Number of main |
|
| 2 and 3 | 0.9 |
| 4 and 5 | 0.8 |
| 6 to 9 inclusive | 0.7 |
| 10 and more | 0.6 |
| SCHNEIDER ELECTRIC |
Defined IP ratings for different type of environment
Type of assemblies / Type of environment Standards and sub-clause Minimum degree of protection
Switchgear and control gear assembly: enclosed switchboard IEC 60439-1 sub-clause 2.3.3 Not defined
Assemblies for outdoor installation IEC 60439-1 sub-clause 7.2.1.3 IPX3
Assemblies with protection by total insulation IEC 60439-1 sub-clause 7.4.3.2.2 IP2XC
Installations in normal environments
Live parts which are not be touched intentionally IEC 60364-4 sub-clause 412.2.1 IPXXB (IP2X)
Live parts which are readily accessible (horizontal top) IEC 60364-4 sub-clause 412.2.2 IPXXD (IP4X)
Installations in locations containing a bath tube or shower basin
Zones 1 and 2 IEC 60364-7 sub-clause 701.512.2 IPX4
Zone 3 IEC 60364-7 sub-clause 701.512.2 IPX1
Zones 1–2–3 public baths where water jets are used for
cleaning purposes IEC 60364-7 sub-clause 701.512.2 IPX5
Installations for swimming-pools
Zone 0 IEC 60364-7 sub-clause 702.512.2 IPX8
Zone 1 IEC 60364-7 sub-clause 702.512.2 IPX5
Zone 2 for indoor locations IEC 60364-7 sub-clause 702.512.2 IPX2
Zone 2 for outdoor location IEC 60364-7 sub-clause 702.512.2 IPX4
Zone 2 where water jets are used for cleaning purposes IEC 60364-7 sub-clause 702.512.2 IPX5
Installations for rooms and cabins containing sauna heaters IEC 60364-7 sub-clause 703.512.2 IP24
Assemblies for construction sites (ACS) IEC 60439-4 sub-clause 7.2.1.1 IP44
Heat Dissipation in Electrical Enclosures
The accumulation of heat in an
enclosure is potentially damaging
to electrical and electronic devices.
Overheating can shorten the life
expectancy of costly electrical
components or lead to catastrophic
failure. It is therefore important that
system designers are aware of the
temperature implications of their
designs prior to implementation.
Enclosure Temperature Rise The
temperature rise illustrated by the curve in the
graph below is the temperature difference
between the air inside the enclosure and the
air outside the enclosure (or ambient air
temperature).This value is described in the
graph as a function of input power in watts per
square foot. In order to predict the
temperature inside the enclosure, the
temperature rise indicated in the graph must
be added to the ambient temperature where
the enclosure is located.
The enclosure temperature rise is not
dependent on the ambient temperature; rather,
the temperature rise for a given enclosure and
heat input are constant. For example, if the
graph indicates a temperature rise of 30° F, the
interior of the enclosure will be 30° F warmer
than the temperature in the surrounding area.
If the temperature in the surrounding area
reaches a maximum of 100° F then the
enclosure interior will reach a maximum
of 130° F.
Since temperatures in an environment often
vary widely, temperatures within enclosures
will also vary. In general, industrial
environments are warmer in the summer than
in the winter.Therefore, when calculating the
warmest enclosure temperature, use the
maximum ambient temperature that is attained
in a given environment.
Enclosure Heat Input For any temperature
rise calculation, the heat generated within the
enclosure must be known.This information
can be obtained from the supplier of the
components mounted in the enclosure. Heat
input values are usually given in watts, but may
also appear in BTU/hour. BTU/hour can be
converted to watts by dividing the value by
3.414 (for example, 341 BTU/hour = 100 watts).
It is not possible to approximate the heat input
for a particular application based on enclosure
size. Heat input varies from application to
application for all enclosure sizes.The system
designer must obtain estimates of heat
input from the information that is available.
Safety factors should be considered if any
uncertainty exists.
Enclosure Surface Area The physical size
of the enclosure will be the primary factor in
determining its ability to dissipate heat.
The larger the surface area of the enclosure,
the lower the temperature rise due to the heat
generated within it.
To determine the surface area of an enclosure
in square feet, use the following equation:
Surface Area = 2[(A x B) + (A x C) + (B x C)]÷
144 where the enclosure size is AxBxC
This equation includes all six surfaces of the
enclosure. If any surface is not available for
transferring heat (for example, an enclosure
surface mounted against a wall), it should not
be included in the calculation. It is also
noteworthy that enclosure volume cannot be
used in place of surface area
Other Enclosure Materials The graph
below applies to enclosures that are gasketed,
non-ventilated, and constructed of painted
steel. Paint color has little effect on enclosure
temperature rise, except when exposed to sun
(see “Outdoor Applications”). Higher
temperature rises can be expected with
aluminum and stainless steel enclosures due to
the poor radiant heat transfer effects of their
metallic finishes.To find the temperature rise of
these enclosures, multiply the results found in
the graph by 1.5. Non-metallic enclosures have
similar heat transfer characteristics to those
constructed of painted steel, so the graph can
be used directly despite the difference in
material.
Subscribe to:
Posts (Atom)
