In the direct-online starter, NO-VOLT release is to
Right Answer is:
Safeguard the motor against the failure of the supply
In case of small capacity motors having a rating of less than 5 hp. The starting current is not very high and such motors can withstand such starting current without any starter. Thus there is no need to reduce the applied voltage, to control the starting current. Such motors use a type of starter which is used to connect the stator directly to the supply lines without any reduction in voltage. Hence the &starter is known as the direct online starter.
Though this starter does not reduce the applied voltage, it is used because it protects the motor from various severe abnormal conditions like overloading, low voltage, single Chasing etc.
The NO contact is normally open and NC is normally closed. At the start, NO is pushed for fraction of a second due to which the coil gets energized and attracts the contractor. So stators directly get supply. The additional contact provided ensures that as long as the supply is ON, the coil gets supply and keeps the contactor in ON position. When NC is pressed, the coil circuit gets opened due to which coil gets de-energized and the motor gets switched OFF from the supply.
Under overload conditions, the current drawn by the motor increases due to which there is an excessive heat produced, which increases temperature beyond the limit. Thermal relays go open due to high temperature, protecting the motor from overload conditions.
Hence from the above it is clear that No Volt Coil ensures that whenever supply resumes after switching off or supply failure, the motor does not start on its own, but starts only after the user starts it and that too through current limiting resistors. When the supply voltage is below 85% of its rated voltage or it suddenly fails, the no volt-coil becomes demagnetized