Tres de los problemas más comunes en los motores trifásicos por los que somos consultados son:

1. “El motor toma mucha corriente en vacío”
2. “La corriente en las tres líneas no está balanceada”
3. “ El motor trabaja caliente”

Incluso si nunca te has enfrentado a uno de estos problemas, sigue leyendo porque es casi inevitable que lo hagas y querrás saber qué hacer al respecto.

Three of the most common three-phase motor problems we receive inquiries about are:

1. “The motor is drawing high no-load current.”
2. “The current of the three line leads is not balanced.”
3. “The motor is running hot.”

Even if you have never faced one of these issues, read on because it is almost inevitable that you will, and you will want to know what to do about it.

Here is a random collection of some relatively common misconceptions about three-phase squirrel cage motor performance characteristics.

Aquí tenemos una colección de algunos de los conceptos errados más comunes acerca de las características de desempeño de los motores eléctricos tipo jaula.

Although the earliest practical DC motor was built by Moritz Jacobi in 1834, it was over the next 40 years that men like Thomas Davenport, Emil Stohrer and George Westinghouse brought DC machines into industrial use.  It’s inspiring to realize that work-ing DC motors have been around for over 160 years. For the past century, DC machines over 30 or 40 kW have been cooled in the same manner – by mounting a squirrel cage blower directly over the commutator.

We know that excessive temperature and moisture are the largest contributors to bearing and winding failures. Understanding the source of the increased temperature will help us to correct the problem and improve the machine’s life expectancy.

The most stressful time for electric motors is during starting. At starting, the motor current is the highest it will ever be. This is referred to as starting or locked rotor current. These different terms describe that when the shaft speed is zero, the current is maximum. Once the motor has been successfully started, the load current level is reached and the cooling circuit of the motor is able to dissipate the additional heat produced by the starting current. Restarting the motor before this additional heat has been dissipated means more heat in the form of kW•h will be added on top of that which is there. Each subsequent start before the additional heat has been dissipated will add more heat — raising the temperature until some component in the motor reaches its failure point. This article looks at safe starting practices for electric motors.

Thermistors, derived from the term thermally sensitive resistors, are a very accurate and cost effective method for measuring temperature. Thermistors are usually two-terminal semiconductor devices made from semi-conductor materials that have an electrical resistance that varies non-linearly with temperature. Some materials provide better stability while others have higher resistance ranges and are fabricated into smaller thermistors. Each specificthermistor has its own unique resistance versus temperature characteristic. 

Whether an old or new design, lowering temperatures is based on the same principles. I've often commented on how fortunate we are to work on such a variety of electric motor designs. One day, you are working on a new design some designer has recently created, and the next day you are repairing a motor that could be in a museum. It's fascinating to see the different ways engineers have devised to do the same thing, and yet reassuring to see how many things remain unchanged even after a century of electric motors. One aspect of electric motors that could be placed in both categories is the way an electric motor is cooled. This article takes a look at how motors are cooled and how we can improve cooling for some of the special applications we encounter.