Goal
b Present MV products and equipment and their environment.
b Facilitate their choice, according to a normative system of
reference.
b Provide design rules used to calculate the dimensions
or characteristics of an MV switchboard.
How?
b By proposing simple and clear calculation outlines to guide
the designer step by step.
b By showing actual calculation examples.
b By providing information on units of measure and international
standards.
b By comparing some of the main international standards.
In summary
This guide helps you to carry out the calculations required
to define and determine equipment dimensions and provides
useful information enabling you to design your MV switchboard.
General contents
Presentation 5
Design rules 13
Switchgear defi nition 47
Units of measure 71
Standards 75
References
Introduction
In order to design a medium-voltage cubicle, you need to know the following basic magnitudes:
Voltage
Current
Frequency
Short-circuit power.
The voltage, the rated current and the rated frequency are often known
or can easily be defined, but how can we calculate the short-circuit power
or the short-circuit current at a given point in an installation?
Knowing the short-circuit power of the network allows us to choose
the various parts of a switchboard which must withstand significant temperature rises and electrodynamic constraints. Knowing the voltage (kV) will allow us to define the dielectric withstand of the components.
E.g.: circuit breakers, insulators, CT.
Disconnection, control and protection of electrical networks are achieved by using switchgear.
The classification of metal-enclosed switchgear is defined in the IEC
standard 62271-200 with a functional approach, using several criteria.
Accessibility to compartments by persons
Level of Loss of Service Continuity when a main circuit compartment is opened
Type of metallic or insulated barriers, between live parts and opened accessible compartment Level of internal arc withstand in normal operating conditions.
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