This is a starting method that reduces the starting current and starting torque. The Motor must be delta connected during a normal run, in order to be able to use this starting method. L start. They are used in an attempt to reduce the start current applied to the motor during start as a means of reducing the disturbances and interference on the electrical supply. The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only.
The starting current is reduced to one third of the direct starting current. There are two contactors that are close during run, often referred to as the main contactor and the delta contactor. The third contactor is the star contactor and that only carries star current while the motor is connected in star. The current in star is one third of the current in delta, so this contactor can be AC3 rated at one third of the motor rating.
In operation, the Main Contactor KM3 and the Star Contactor KM1 are closed initially, and then after a period of time, the star contactor is opened, and then the delta contactor KM2 is closed. The control of the contactors is by the timer K1T built into the starter.
These two contactors are the main contactor and delta contactor. Hence contactor rating is one-third of motor rated current. In star delta starter 3 contactors are used. Main contactor, star contactor, and delta contactor. A contactor is a heavy-duty relay with the high current rating, used for power up the electrical motor. The current rating for contactor varies from 10 amps to several hundred amps.
High current contactor is made from an alloy containing silver. Arcing during the switching operation of the contactor causes the contact to oxidize. However, silver oxide still a good conductor.
Overload protection is provided along with the contactors to start the motor. A contactor is not used to interrupt a short circuit current, Unlike the circuit breaker used. Contactor size varies from small to large for high current appliances. The majority of winding failure is because of overloading, Operation on unbalance supply voltage or single phasing due to phase loss which leads to excessive heating to degradation of winding insulation, due to this electrical motor required overload protection, to prevent damage from over-loading the motor, or to protect form sort circuit or internal winding fault of electric motor.
All these conditions are prevented by using a thermal overload relay. Fuse unit is used to protect the motor from over current or short circuit conditions.
The main purpose of the fuse is to protect the motor and is composed of an alloy which has a low melting point. A strip of a fuse is placed in series with the motor circuit. The working principle is that if the current in excess then the strip would melt and break the circuit and isolate the motor from the supply. So, how are soft starters and star-delta starters similar, and how are they different? And which should you use for starting your motor? Both types of starters serve the same general purpose.
They decrease the voltage supplied to a motor during startup to prevent a sudden jump in power that can damage the motor and cause various other issues.
However, the main differences are:. Browse Motor Starters. Which kind of starter should you use with your motor? Soft starters offer more features and easier installation, but star-delta starters offer the advantage of lower cost. Here are some additional reasons to use each type of starter:.
Soft starters are used more often than star-delta starters today because of their enhanced capabilities and additional features. Soft starters are also more flexible than star-delta starters and easier to install.
You might also choose a soft starter for the additional capabilities it offers, such as the ability to accommodate varying load conditions, enable soft stops, and adjust the starting time and torque.
Soft starters also offer advantages through improved functionality, such as a smooth progressive start, no power loss, built-in protection and long life due to a lack of moving parts. The main advantage of star-delta starters is their lower cost, although the cost difference is less than it once was. Because of the lower cost, a star-delta starter may be the right choice for a motor that you rarely start or an especially small motor.
A star-delta starter may be the best choice for extremely light loads, as it may be able to lower the voltage more than a soft starter could. At Global Electronic Services, our experienced team can provide the expert repair and maintenance services your company needs for your motor starters, as well as a wide range of other industrial equipment types.
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