Specifications

6
Selection
criteria
Introduction
2-Selection phase
Principle
This chapter presents the various steps required to select the most appropriate starter components as well as
the automation architecture which will ensure control.
Each process control project has specic requirements and constraints that inuence the selection of a motor
control solution.
The project specication present the characteristics that determine the selection criteria to be used in the selec-
tion steps.
The diagram on the next page summarizes the selection phase:
Project specications b
It sets out the broad outline of the architecture. The size of the plant, process complexity and other customer
requirements decide the PLC topology, distributed I/Os architecture and connection types (see next pages).
It also covers related constraints, which can be divided into two groups:
Functional constraints b
The process characteristics impose constraints in terms of power, load types and process power supply that
must be complied with. This subject is introduced in the following chapter without going deeply into the calcula-
tions or protection details of LV and MV networks. Readers are advised to refer to the specic selection guides
published by Schneider Electric.
Operational constraints b
The project characteristics impose constraints such as:
Plant productivity: Traceabilty, environmental constraints,
Process quality: Diagnostic information required, standard to apply,
Design Cost: centralized or distributed architecture
Operation cost: operator proles, energy monitoring,
These processes and project constraints are the inputs for the three following selection steps.
Selecting starter mode: b
Three solutions are proposed to realize a motor control function:
Direct On Line starter with contactor - the simplest solution that is appropriate for low and medium power motors
that do not need frequent start-up. Depending on requirements, elaborate protection and monitoring devices can
be associated here.
Soft starter - it enjoys the advantage of reducing the peak starting current which can avoid water hammer
and respect mechanical parts in pump applications.
Variable speed drive - the most powerful solution with an ability to regulate ows in pump applications.
It can also facilitate the optimization of energy consumption.
The starter structure is detailed on page 8 and 9. A selection guide is provided on page 10.
Selecting motor control devices: b
The most appropriate device is selected based on requested control functions that must be provided by the
starter. Those functions are categorized into three types:
Motor protection: overload and short-circuit
Metering functions: measurement of power, current, etc … .
Monitoring functions: alarms, histories, …
A table on pages 12 and 13 summarizes the various starter functions.
Selecting architecture: b
All selected motor control devices have to be connected to the global system architecture. Therefore, the
communication link offered by the device must be selected in a consistent manner and in compliance with the
chosen global architecture.