|
Oil Immersed Manually Operated Auto Transformer Motor Starters
Bentex SKN Auto - Transformer Starters have been designed to provide control for A.C. squirrel cage motors upto 60 HP where it is found necessary to minimize the starting current and attain a higher starting torque. The starter reduces the line voltage by means of an Auto - Transformer and reduces proportionately the line current taken by the motor when starting.
An Auto-Transformer Starter is the obvious choice where supply companies regulations limit the use of direct on line starters for very small motors and starting conditions do not permit the use of star / delta starters.
The Auto-Transformers are provided with trappings for 40%, 60% and 80% of the line voltage to be applied to the motor while starting, as a standard practice. If necessary, other percentage trappings according to the requirements of the customer can be provided instead of the above. The trappings are brought to an easily accessible terminal board.
All Auto transformers leaving the works have the secondary connected to the 40% tapping. If the motor does not develop the correct starting torque the voltage can be altered by changing the tapping on the secondary of the auto transformer.
Construction
The starter and Auto-Transformer are enclosed in separate totally enclosed dust proof metal clad cases arranged for floor mounting. As can be seen from the illustration below, the starter is entirely separate from the auto transformer. This arrangement prevents carbonized oil from the starter depositing on the transformer mounted below, thus elimination electrical breakdowns in the transformer insulation.
Contacts
To ensure a trouble free life, these units are provided with heavy type copper contacts. these are made from hard drawn electrolytic copper section arcing contact and main contact. The arcing contacts make before and break after the main contacts, thus confining burning to the arching contacts. As such, the main contact scarcely calls for replacement. The arching contact, however, can be replaced very easily, with the removal of a screw.
Overload Protection
The overload is of magnetic direct acting type with oil dashpot time lag : under voltage protection is provided by closed type solenoid coil.
Accessories
The starters are generally provided with incoming and outgoing cable entry plates. Cable boxes for paper insulated cables, fully interlocked isolators can also be provided if required.
|
