Monday, December 30, 2013
Friday, December 13, 2013
Dead-front panels
Dead front is defined in Article 100 of the NEC as being “without live parts exposed to a person on the operating side of the equipment.” Section 408.38 requires that panel boards be mounted in cabinets, cutout boxes or enclosures designed for the purpose and shall be dead front. The term “dead front” is used in other places in the NEC, but basically, the NEC requires distribution panels, panel boards (load centers), switchboards (stage and theater) be constructed so that switches, circuit breakers and other electrical components can be operated without the user being exposed to live parts.
Tuesday, December 10, 2013
Circuit breaker accessories - Service releases
Shunt opening release
This allows circuit-breaker opening by
means of an electric command. Release
operation is guaranteed for a voltage
between 70% and 110% of the rated
power supply voltage Un, both in AC and
in DC. It is always fitted with an auxiliary
limit contact.
Under voltage release
This opens the circuit-breaker due to a
power supply failure to the release, or
voltage drops to minimum values of 0.7
x Un with a trip range from 0.7 to 0.35 x Un.
After tripping, the circuit-breaker can be
closed again, starting with a voltage
higher than 0.85 x Un. With the undervoltage
release de-energised, neither
circuit-breaker nor main contact closure
is possible.
Time-delayed undervoltage release
The undervoltage release can be combined
with an external electronic power
supply time-delay device, which allows
circuit-breaker opening to be delayed in
the case of a power cut to the release
itself, according to fixed time-delays of
0.5-1-2-3 [s], so as to avoid unwarranted
trips caused by temporary malfunctions.
It is available for the SACE S3, S4, S5,
S6, and S7 circuit-breakers with power
supply voltages at 110-220 V (50-60 Hz)
only coupled with an undervoltage release
at 310 V DC.
Shunt closing release
This allows circuit-breaker closure by
means of an electric command. Operation
of the release is guaranteed for a
voltage between 80% and 110% of the
rated power supply voltage Un, both in
AC and in DC.
ABB SASE
Information included in the design verification
The design verification serves to document compliance with the specifications
of this standard. It is comprised of 13 individual verifications.
For selected individual verifications, additional sub-verifications in subcategories
may be required. If selected verifications are not required
due to the application, the respective verification should, as a minimum
requirement, state that verification on the basis of the standard is not
required in this instance.
1. Strength of materials
Verification of material strength is divided into seven sub-points. If
an empty enclosure pursuant to IEC 62208 was used and no modifications
have been made which could influence the functioning
of the enclosure, no further strength testing of the materials for this
enclosure is required. Compliance with standard IEC 62208 should
then be confirmed in the design verification. However, verification
of the resistance of the insulating materials to abnormal heat and
fire for the components used in the busbar system and other insulating
materials should additionally be provided.
a. Resistance to corrosion
Resistance to corrosion can only be verified by testing. For resistance
to corrosion, the verification should stipulate the "testing"
method, the degree of severity and the test report number.
2. Properties of insulating materials – Thermal stability of
Enclosures
This evidence is only required for enclosures made from insulating
materials, or parts made from insulating materials mounted on the
outside of the enclosure, and which are relevant to the protection
category. Verification should state that the test was passed at a
temperature of 70 °C, for a duration of 168 h, and with a recovery
time of 96 h, and should also include the method and the test
report number/report number.
3. Properties of insulating materials – Resistance to abnormal
heat and fire due to internal electric effects
These properties should be verified using the "testing" method on
the material used, or using the "assessment" method with the data
sheets for the basic plastic material. Verification should state that
the properties of the insulating materials meet the requirements of
the glow-wire test depending on the three intended applications:
960 °C for parts necessary to retain current-carrying parts
in position
850 °C for enclosures intended for mounting in hollow walls
650 °C for all other parts
The design verification should include the test method, the result of
the test, and the test report or report number.
4. Resistance to ultra-violet (UV) radiation
Resistance to UV radiation only applies to enclosures and external
parts of switchgear and controlgear assemblies for outdoor installation.
Verification may be provided by testing or by assessing the
data from the original material manufacturer. The design verification
should include the test method, the result of the test method,
and the test report or report number.
5. Lifting
Verification for lifting can only be provided by testing. Verification
should state that the test was passed, indicating the maximum
number of sections that can be lifted and the maximum weight,
together with the test report number.
6. Mechanical impact
The impact resistance of a switchgear and controlgear assembly is
verified by testing. The design verification should state the method,
the tested IK protection category, and the corresponding test
report number.
7. Marking
There is no requirement to test markings made by moulding, pressing,
engraving or similar, as well as labels with a laminated plastic
surface. In such cases, it is sufficient to state the chosen technique
in the design verification. For all other types of marking, testing is
mandatory. The test outcome should be documented, stating the
test report number.
RITTAL (Standard compliant switchgear & controlgear production)
Tuesday, December 3, 2013
Calculation of the temperature rises in compliance with the Std. IEC 60890
Calculation of the powers generated by the different
components and dissipated inside the assembly
The calculation of the power losses reported in the
configurations shown is carried out by taking into account
the effective powers dissipated by the different
components.
Circuit-breakers
Given the power losses at the rated current (In) shown in
the following tables and the current which actually flows
through the circuit-breakers (Ib), it is possible to calculate
the effective power losses of the equipment:
The values thus obtained must be increasde by a factor
depending on the circuit-breaker type.
This coefficient is used to take into account the connections
which carry current to the circuit-breakers
Open-type and enclosed assemblies
According to the constructional typology the Standard
IEC 61439-1 distinguishes between open-type and enclosed
assemblies.
- Enclosed assembly
An assembly is enclosed when there are protected
panels on all its sides so as to provide a degree of
protection against direct contact not lower than IPXXB
(see Chapter 4). Assemblies intended to be installed
in common environments shall be of enclosed type
- Open-type assembly
An assembly, with or without front covering, in which
the live parts of the electrical equipment are accessible.
Such assemblies can be used only in places
where skilled persons have access for their use.
Monday, December 2, 2013
Rated electrical characteristics of an assembly
Rated voltage (Un)
Highest nominal value of the a.c. (r.m.s) or d.c. voltage,
declared by the assembly manufacturer, to which the
main circuit(s) of the assembly is (are) designed to be
connected. In three-phase circuits, it is the voltage
between phases.
Rated operational voltage (Ue)
it is the rated voltage of a circuit of an assembly which
combined with the rated current of this circuit determines
its application. For three-phase circuits such voltage corresponds
to the voltage between phases.
In an assembly there are usually a main circuit with its
own rated voltage and one or more auxiliary circuits with
their own rated voltages.
The manufacturer of the assembly shall state the limits of
voltage necessary for correct functioning of the circuits
inside the assembly.
Rated insulation voltage (Ui)
it is the voltage value of a circuit of an assembly to which test voltages
(power frequency withstand voltage) andthe creepage distances are referred.
The rated voltage of each circuit shall not exceed its
rated insulation voltage.
Rated impulse withstand voltage (Uimp)
it is the peak value of an impulse voltage which the circuit
of an assembly is capable of withstanding under specified
conditions and to which the values of clearances
are referred. It shall be equal to or higher than the values
of the transient overvoltages occurring in the system in
which the assembly is inserted.
Rated current of the assembly (InA)
It is a new characteristic introduced by the Std. IEC
61439 and normally indicates the maximum incoming
permanent and allowable load current or the maximum
current which an assembly is capable of withstanding.
The rated current shall be withstood in any case, provided
that the temperature-rise limits stated by the Standard
are complied with.
Rated current of a circuit (InC)
It is the current value to be carried out by a circuit without
the temperature-rise of the various parts of the assembly
exceeding the limits specified according to the testing
conditions of Clause 7.
Rated short-time current (Icw)
it is the r.m.s. value of the current for the short-circuit test
for 1 s time; such value, declared by the manufacturer
does not imply the opening of the protective device
and is the value which the assembly can carry without
damage under specified conditions, defined in terms of
current and time. Different Icw values can be assigned to
an assembly for different times (e.g. 0.2 s; 3 s). Manufacturer,
can withstand satisfactorily for the operating
time of the device under the specified test conditions.
Rated diversity factor (RDF)
it is the per unit value of the rated current, assigned by
the assembly manufacturer, to which outgoing circuits
of an assembly can be continuously and simultaneously
loaded taking into account the mutual thermal influences.
The rated diversity factor can be stated:
- for groups of circuits;
- for the whole assembly.
The rated diversity factor is:
The rated diversity factor multiplied by the rated current
of the circuits (In) shall be equal to or higher than the
assumed loading of the outgoing circuits (Ib).
The rated diversity factor is applicable to the outgoing
circuits of the assembly and demonstrates that multiple
functional units can be partially loaded.
When the manufacturer states a rated diversity factor,
this factor shall be used for the temperature-rise test,
otherwise reference shall be made to the values recommended
by the Standard 61439-1 in Annex E.
Rated frequency
value of frequency to which the operating conditions are
referred. If the circuits of an assembly are designed for
different values of frequency, the rated frequency of each
circuit shall be given.
-ABB technical application papers
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