Month: October 2017

Starting Chain Limits

It can be said that there are two ways to reduce the voltage at the start, the first of which consists of supplying the current to the normal voltage, thereby causing the motor to be temporarily connected to the grid, with the winding for a higher voltage , using the star-triangle starting system. The second method is to provide less than normal voltage current through resistors, inductors or autotransformer. All low voltage starting systems have, as opposed to the benefit of current reduction, the disadvantage that the starting torque or torque will be reduced in proportion to the square of the voltage reduction supplied to the electric motor Browning VF4S-232.

The connection of the motors to a public power grid needs to carefully analyze the prescriptions for this purpose, established by standard. Normally, it is necessary to start a motor at the moment of full voltage in order to make the most of the starting torque. When starting the full voltage of an electric motor causes a voltage drop greater than the maximum acceptable, a starting device with reduced voltage must be used, always being careful to check if the torque is enough to drive load.

Conjugate and Rated Speed

In case the required work of the driven machine will suffer temporary overloads, the motor power will need to be higher than the required power. It is extremely important to limit the significant increase of the losses, with proper maintenance of the machines and their mechanical components, such as adjustment of clearances, proper lubrication and verification of alignments, among others. An electric motor is designed so that it can provide a nominal torque Cn, at a nominal speed Nn.

This means that for a nominal power Pn, one must consider the expression Pn = CnxNn. It is noteworthy that the electrical losses, also known as thermal losses, change according to the square of the resistant conjugate, which is the load. On a well sized motor, this rugged torque must be less than the rated torque. If it is equal to or slightly higher, the resulting heating will be considerable. However, a motor considered under-loaded will have a noticeable reduction in efficiency. The ideal load should correspond to the workload that will be carried out, a factor not very simple to determine in most cases.