INDUSTRIAL OR AGRICULTURAL STARTERS
An electric motor starter is a device that controls the use of electric power to various appliances with high energy demands. They are connected to electric motors and are operated through an on and off switches. They act as ‘safety switches’ on large motors with unmanageably high consumptions. However, these electric starters can be operated through automatic operation as well.
These starters, with suitable rating contactors and premium overload relays, provide complete protection to the motors from fault, hence are apt for industrial or agricultural purposes.
WHY INSTALL A STARTER?
1. Provides reliable overload relays.
2. Comes with a digital screen indicating “On” or “Trip” state of
3. Provides short circuit protection.
4. An ammeter with suppressed coil to withstand very high starting current.
5. An automated selector switch.
PROTECTIONS IT PROVIDES
• Overload protection
• Phase reversal protection
• Single phase protection
• Auto start with ON delay
• Phase unbalance protection
STARTERS APROPOS TO INDUSTRIAL OR AGRICULTURAL APPLICATIONS
DIRECT ON LINE STARTER
Direct On Line Starter is best suited for large starting current demands. It is compact, thus does not take up more space. Its construction is simple. It works best when connected to generators with a voltage dip ranging between 10-15%.
DOL is the most economic and popular method of starting squirrel cage induction, motors wherein the starter is directly connected to the supply. Generally, the magnitude of the starting current initially is as high as six to eight times that of the rated current.
• Shorter starting time
• Simple construction and wiring
• High starting torque
• Compact, hence space saving.
High starting current
The only operational condition for a DOL starter to work is that the high inrush current of the motor is not causing excessive voltage dip in the supply circuit.
Used for agricultural water pumps, compressors, conveyor belts, fans, etc.
A 3TS3 contactor wields a 10 HP DOL starter. The design of the contractor is such that it fits well for agricultural and industrial usage. A special wide band coil (voltage ranging from 200 V to 400 V) is designed to operate even under wide voltage fluctuations.
BI -METAL OVERLOAD RELAY
A 3UW5 bi-metal overload relay is fitted with a DOL starter. They are automatic and come with a fully graduated computer calibration. This feature ensures accurate protection to the motor. It has a built-in single phasing protection besides the overload protection. It also has an automatic reset function with a cooling time of about four seconds.
Generally a bi-metal overload relay system is coupled with a DOL starter. Once the starter is pushed ‘ON’, the contractor coils are energised switching on the circuit. When pushed ‘Off’, the contractor coils are de-energized and the circuit is switched off. The bi-metal overload relay has no role to play under normal circumstances. It works under overload, single phasing or locked rotor condition of the motor. When under the mentioned situations, the relay cuts off the power supply to the contractor coils, thus trips the circuit. The contractor slips into the “No voltage” mode in case of supply failure as the circuit switches off. To restart the power supply, the “On” push button is to be pressed again.
• Computer calibrated relays.
• Accurate protection under single phasing or overload.
• The contractor coils used in it ensures longer electrical and mechanical life of the starter.
• Unwanted operations are halted since resumption needs manual switching on of the push button.
• With 200 V to 400 V voltage range, the relay can easily handle huge voltage fluctuations.
AUTOMATIC STAR DELTA STARTER
Star Delta starters are apt for induction motors with a power capacity of about 10 kilowatts. They are even simpler in construction than DOL starter consisting only three electrical contactors, one overload protection device and a timer. The windings are Star connected reducing the starting current, voltage and starting torque leading to lower current inrush.
Low starting current.
• Low starting torque
• Longer starting time
• Needs more space
It consists of a star delta timer, contractor and an overload relay.
A timer manages the changeover from star to delta as per the pre-set time in the starter.
Brands To Look For
Click here to buy Siemens products.
Click here to buy Schneider products.