In the mining industry the following machines are usually operated, for which we can configure our starters:
Fans / Blowers
Fans (sometimes also called blowers) usually have a very high moment of inertia; it is often many times higher than the moment of inertia of the driving motor. Therefore most of the fan drives start with a very long start time of up to app. 100 seconds. The torque speed curves (counter torque) of nearly all fans have a quadratic shape. Most fans can be started with reduced load by adjusting the blades. This adjustment provides a lower counter torque which results in a lower start current. Normal start currents for fans (Ia/In) are in the range of app. 1,5 - 3 times the motor rated current (In). Below you will find a characteristic example for a calculation. Due to the possibly high moment of inertia of the fan and the resulting very long start time the moment of inertia J [kgm2] (which can be estimated in the first step) should be present for an offer.
|motor rated power||Pn||2.000||kW|
|motor rated current||In||250||A|
|motor start current DOL||Ia||5||x In|
|motor rated speed (synchronous)||nn||1.000||rpm|
|moments of inertia|
|start voltage||Us||0,61||x Un|
The starter starts the motor with reduced voltage, 61% of the rated voltage, in this example (Us/Un = 0,61). The torque speed curve of the motor will be reduced by the factor Ts/TDOL = (Us/Un × F)2.
Ts/TDOL = (0,61 × 0,91)2 = 0,31 (F is a factor depending on the motor). The torque of the motor must always be higher than the counter torque. The start voltage Us/Un has been determined accordingly. The difference between the reduced motor torque Ts and the counter torque is the acceleration torque Ta.
The start time ts is calculated from the acceleration torque Ta and the total moment of inertia J = JM + JL = 150 + 2.500 kgm2 = 2.650 kgm2.
The motor current is IMot = Us/Un × IDOL × F = 0,61 × 5 × 0,91 = 2,8 × In
Mains start current:
A transformer has the same power at primary and secondary, which leads to the fact that the products of current and voltage are the same.
Un × Is = Us/Un × Imot => Is = Us/Un × IMot / Un
Is= 0,61 × 2,8 = 1,7 × In
The mains start current is therefore much lower than the motor start current.
For other start methods (electronic soft starter, starting reactor etc.) the following is valid: The mains current equals the motor current:
Is = IMot = 2,8 × In
For that reason these starting methods create a higher mains voltage drop.
Mills exist in a variety of different designs and types. We have prepared detailled information for the start procedure of a shredder. Needless to say, our starter can also be used for further mill types, if the start torque requirement of the mill is not too high. High moments of inertia and therefore long start times do not pose a problem for our starter. If a controlable (f. ex. hydraulic) coupling is mounted between mill and motor, the mill can be started with a very low start current (Ia/In) in the range of app. 1-2 times of the motor start current at direct on line (IDOL/In). We will gladly provide you with an offer and technical support.
Machines driven by electric motors exist in a variety of different designs and types. For the most common ones we have prepared detailled information for the start procedure. Needless to say, our starter can also be used for further types of machines. We will gladly provide you with an offer and technical support.