Monday, December 31, 2012
Friday, December 21, 2012
Motor starters
Star-delta starter
This is the most popular and commonly
used starting method for motor ratings
> 4 kW (400 V).
• Electronic motor starter (EMS) and soft
starter
These enable the soft and low-noise
starting of the motor. This eliminates
interference producing current peaks
and jerks during switching. The startup
and deceleration phase of the motor can
also be time-controlled depending on the
load.
• Frequency inverter
This enables time-controlled motor
starting, motor braking and operation
with infinitely variable motor speeds.
Depending on the application, different
types of frequency inverters are used:
– with the voltage/frequency control
(U/f) or vector control for
frequency-controlled motor operation,
– with vector control or servo control for
high speed accuracy and additional
torque adjustment.
Associated circuit diagrams
Direct on line starter
Direct-on-line starter
In the simplest case the motor is
connected directly with a contactor. The
combination of motor protection and
cable protection (fuse) is called a motor
starter (MSC = Motor Starter
Combination).
By applying the full mains voltage to the
motor windings, DOL starting may
produce large starting currents which
may result in troublesome voltage
changes. Direct-on-line starting
three-phase motors must not cause
interference voltage changes in the
public utility grid. This requirement is
generally fulfilled if the apparent power
of a three-phase asynchronous motor
does not exceed 5.2 kVA or its startup
current does not exceed 60 A.
With a mains voltage of 400 V and 8 times
the starting current, this corresponds to
a rated motor current of around 7.5 A and
thus a motor rating of 4 kW.
The motor rating denotes the mechanical
output of the motor at the shaft.
Thursday, December 20, 2012
Wednesday, December 12, 2012
Standards
CE
The CE conformity marking shall indicate conformity to all the obligations imposed
on the manufacturer, as regards his products, by virtue of the European
Community directives providing for the affixing of the CE marking.
When the CE marking is affixed on a product, it represents a declaration of the
manufacturer or of his authorized representative that the product in question
conforms to all the applicable provisions including the conformity assessment
procedures. This prevents the Member States from limiting the marketing and
putting into service of products bearing the CE marking, unless this measure
is justified by the proved non-conformity of the product.
Flow diagram for the conformity assessment procedures established by the Directive
2006/95/CE on electrical equipment designed for use within particular voltage range:
Manufacturer
Technical file
The manufacturer
draw up the technical
documentation
covering the design,
manufacture and
operation of the
product
EC declaration of
conformity
The manufacturer
guarantees and declares
that his products are in
conformity to the technical
documentation and to the
directive requirements
Naval type approval
The environmental conditions which characterize the use of circuit breakers for
on-board installations can be different from the service conditions in standard
industrial environments; as a matter of fact, marine applications can require
installation under particular conditions, such as:
- environments characterized by high temperature and humidity, including saltmist
atmosphere (damp-heat, salt-mist environment);
- on board environments (engine room) where the apparatus operate in the
presence of vibrations characterized by considerable amplitude and duration.
In order to ensure the proper function in such environments, the shipping registers
require that the apparatus has to be tested according to specific type
approval tests, the most significant of which are vibration, dynamic inclination,
humidity and dry-heat tests.
Standards
“Low Voltage” Directive 2006/95/CE
The Low Voltage Directive refers to any electrical equipment designed for use
at a rated voltage from 50 to 1000 V for alternating current and from 75 to
1500 V for direct current.
In particular, it is applicable to any apparatus used for production, conversion,
transmission, distribution and use of electrical power, such as machines,
transformers, devices, measuring instruments, protection devices and wiring
materials.
The following categories are outside the scope of this Directive:
• electrical equipment for use in an explosive atmosphere;
• electrical equipment for radiology and medical purposes;
• electrical parts for goods and passenger lifts;
• electrical energy meters;
• plugs and socket outlets for domestic use;
• electric fence controllers;
• radio-electrical interference;
• specialized electrical equipment, for use on ships, aircraft or railways, which
complies with the safety provisions drawn up by international bodies in which
the Member States participate.
Directive EMC 2004/108/CE (“Electromagnetic Compatibility”)
The Directive on electromagnetic compatibility regards all the electrical and electronic
apparatus as well as systems and installations containing electrical and/
or electronic components. In particular, the apparatus covered by this Directive
are divided into the following categories according to their characteristics:
• domestic radio and TV receivers;
• industrial manufacturing equipment;
• mobile radio equipment;
• mobile radio and commercial radio telephone equipment;
• medical and scientific apparatus;
• information technology equipment (ITE);
• domestic appliances and household electronic equipment;
• aeronautical and marine radio apparatus;
• educational electronic equipment;
• telecommunications networks and apparatus;
• radio and television broadcast transmitters;
• lights and fluorescent lamps.
The apparatus shall be so constructed that:
a) the electromagnetic disturbance it generates does not exceed a level allowing
radio and telecommunications equipment and other apparatus to operate
as intended;
b) the apparatus has an adequate level of intrinsic immunity to electromagnetic
disturbance to enable it to operate as intended.
An apparatus is declared in conformity to the provisions at points a) and b) when
the apparatus complies with the harmonized standards relevant to its product
family or, in case there aren’t any, with the general standards.
ABB MCC
Friday, August 10, 2012
Control Circuits
Control Circuits
Control Control components are used in a wide variety of applications with varying degrees of complexity. One example of a simple control circuit is a circuit that turns a light on and off. In this circuit, the control component is often a single-pole switch.
Control circuits used in commercial and industrial applications tend to be more complex than this simple circuit and employ a broader variety of components. However, the function of these circuits is often the same, to turn something on and off. In some cases, manual control is used. More often, automatic control circuits or circuits that combine manual and automatic control are used.
Tuesday, August 7, 2012
Thursday, August 2, 2012
Pollution Degree
The level of pollution in the environment in which the Assembly is intended to be
installed. Four categories are defined in the Standard as follows:
Pollution degree 1 : No pollution or only dry, non-conductive pollution occurs.
Pollution degree 2 : Normally, only non-conductive pollution occurs. Occasionally, however, a temporary
conductivity caused by condensation may be expected.
Pollution degree 3 : Conductive pollution occurs, or dry, non-conductive pollution occurs which becomes
conductive due to condensation.
Pollution degree 4 : The pollution generates persistent conductivity caused, for instance, by conductive dust or by
rain or snow.
Unless advised otherwise, the Standard and the manufacturer will assume
pollution degree 3 is applicable for industrial applications.
Wednesday, August 1, 2012
ROUTINE TESTS
These tests have a totally different function to Type Tests, BS EN 60439-1, states:
‘Routine tests are intended to detect faults in materials and workmanship. They are carried
out on every ASSEMBLY after its assembly or on each transport unit. Another routine test
at the place of installation is not required.’
Hence, Routine Tests on Assemblies are normally undertaken at the
manufacturer’s premises, and are:
• part of the quality control activity. They are intended to ensure materials and
workmanship included in every assembly produced meet the standards required
by the design.
• carried out on every assembly or transportable unit to be put into service. It is
recognized that it is unnecessary, with modern modular designs, to fully couple
assemblies for routine test, if they are subsequently to be shipped in several
sections.
• of a non-destructive nature having minimal effect on the service life of the
equipment.
• not intended to duplicate routine tests, previously carried out on components as
part of their manufacturing process.
• not intended to be repeated on site. This does not remove the onus of the
installer to ensure the assembly’s correct installation and obligation to test under
BS 7671. Before tests under BS 7671, or other testing is undertaken, the effects
of these tests on voltage sensitive components should be established.
(BEAMA Installation)
Tuesday, July 31, 2012
PARTIALLY TYPE TESTED ASSEMBLY (PTTA)
IEC 60439-1, defines a PTTA as:
‘A low-voltage switchgear and controlgear assembly, containing both type-tested and nontype-
tested arrangements provided the latter are derived (e.g. by calculation) from type tested
arrangements which have complied with the relevant tests’.
This means:
• The assembly will be derived from a Type Tested Assembly.
• Deviations from the tested configuration are only permitted provided they can
be verified by calculation or equivalent methods. Such methods have their
limitations which must be fully understood and, where appropriate, allowed for
through safety factors in the analysis.
• As a means of demonstrating design compliance with the Standard,
manufacturers must have available Type Test documentation for the original
design and any calculations relating to modified elements.
• The Assembly will consist, as far as practical, of a series of standard elements
configured to suit a particular application. Customisation should be restricted to
situations where it cannot be avoided, e.g. facilities for terminating over size
cables, use of an alternative tested component, etc.
• All components and devices will be fully Type Tested to their respective product
standards. Documentation will be available for examination.
• Combinations of Type Tested components and devices installed in an otherwise
untested Assembly are not covered by this definition and the Standard.
(BEAMA Installation)