Uncovering the hidden capacity in your medium voltage AC motors

An inevitable part of any major paper mill expansion or modernization project is the need to provide additional horsepower for several loads in excess of that which the vendor recommended and the engineers selected. Classic examples of this problem are such things as pressure screens, pulpers and some large pumps. After exhausting all other "normal" remedies, such as correcting mechanical problems or adjusting operating conditions, the usual result is that a new motor of a higher rating is ordered and eventually installed. This decision is then usually followed by the ordering of a new spare since the spare previously ordered will not be of the correct rating. The problem is further compounded by the fact that one may also be stuck with at least two motors that one no longer needs. The total cost is, of course, dependent on the horsepower involved and the number of applications requiring correction, but these situations are generally very expensive by anyone's standards. Although this is the usual scenario, it need not be the only option in all cases. The introduction a few years ago of reliable, solid state, temperature-based overload devices has opened up another avenue for those applications where the motor is just a "little bit" undersized. In order to do this, however, it is necessary to redefine the thinking of a lot of engineering, maintenance, and operating personnel with respect to motor overload protection.