Page 122 - Offshore Electrical Engineering Manual

Medium-Voltage Starters 109

The following checklist identifies key benefits available from integrated intel-
ligent MCC software.

1. Can be accessed at any network level: The user should be able to view the MCC
by plugging into any network level, such as DeviceNet, ControlNet or Ethernet.
This feature gives the user flexibility to locate the software on a maintenance
laptop, in a control room or at an engineer’s desk.
2. Operates in a familiar environment: The software will be easiest to use if it
behaves according to known operating environments, e.g., Windows.
3. Initiates network communication: Establishing devices as recognised entities
on a network can be the most time-consuming step. In the optimal situation,
the MCC manufacturer downloads user-specific information, such as node
addresses (per user specification or a standard scheme) and baud rate, and then
tests the entire system for accurate function and communication.
4. Display of preconfigured screens showing most common parameters: Intelligent
MCC software can be arranged to access the user’s specific data files and may
facilitate the generation of corresponding screen display windows.
5. Includes unique MCC documentation to initialise screens: The application
program, on installation, should access specific information to generate screens
containing data pertinent to that particular MCC.
6. Event logging: Alarms, faults and warnings should be logged as required.
7. Documentation database: Current wiring diagrams and schematics, user manu-
als and spare parts lists, available on-screen can be very useful for diagnosing
problems. However, it can be difficult to keep all this material up to date.

Please also refer to PART 2 Chapter 15.

MEDIUM-VOLTAGE STARTERS
DIRECT ON LINE STARTING
Vacuum contactors provide a reliable form of motor control for medium-voltage
motors. They are designed for routine starting of the motor and have insufficient
fault rating for fault clearance on most systems. This is because of the ‘softer’ met-
allurgy of the contacts, designed for more frequent operation than the equivalent
circuit breaker, and also to avoid current chopping transients which would damage
the motor insulation. Hence, they are protected from the higher prospective fault
currents with appropriately rated fuses. The fuses will also reduce the risk of contact
welding.

ELECTRONIC STARTERS

Electronic starters are often called ‘soft’ starters and use electronics to control voltage
and current during the motor starting. They are limited in use because of the effect on