Typical Static Loads of Electric Drive

The electromagnetic torque (force) of a motor is the initial value of the computer-aided electric drive system and the input value of its mechanical part, while other moments and forces define its static loads

.

For any scheme being computed (one-, two-, three-mass) this loads for define electric drive remains the same.

All these moments (forces) of loads that applied to mechanical part of electric drive nay be divided into two groups:

- Useful loads of actuating part;

- Moments and forces of mechanical losses.

, [N^.m]

Where – total reduced moment of useful forces;

∆M – total reduced moment of losses (includes moment of mechanical losses of electric motor).

Useful load is one of the prime factor that connects electric drive with the production process of mechanism of facilities that makes electric drive moving.

Moments (forces) of useful load have different character in different production mechanisms (operating mechanisms). All variety of production mechanisms may be divided into four categories (classes) by the character of load moments (forces). The basic criterion of such classification is the dependence between load and speed, called the mechanical characteristic of manufacturing mechanism. For rotating electric drives it has view

, (2.5)

Where M_s – static resistance moment reduces to the motor shaft, [Nm];

ω - angular velocity reduced to the motor shaft (angular velocity of motor), [1/s].

Considering further particulars of forces and moments that actuate on the mechanical part of electric drive it was mentioning the following.

By its character of interaction with electric drive all forces and moments are divided into:

- Active;

- Reactive.

Active forces and moments are called forces and moments that are generated by external, relatively to electric motor, sources of mechanical energy irrespectively of electric drive motion, for example, potential energy of load that travels vertically or wind energy, etc. Demonstration of active forces and moments in lifting mechanisms are typical.

Reactive forces and moments are called forces and moments of resistance to motion that arise as the reaction to active motion moment that creates electric drive, or another any active motion moment that is not generated by electric motor, for example, reaction to the moment generated by inertia force. This loads are always acts in the opposite direction to the direction of electric drive motion and they are changes their direction at the reverse of motor speed.

All reactive forces and moments depend of speed. By the character of this dependence they are divided into:

- Dry friction load;

- Viscose friction load;

- Ventilation load.

Dry friction load is related to the values of friction factor (of material, character of production process, for example, machining with cutting, compression, and others).

Actually the viscose friction load is found rarely. This is found at dynamic processes significantly in mechanical system of electric drive when deformation of shafts, couplings, cables and other elements of mechanical parts of electric drive.

Ventilation load arises on rotating parts of mechanical part of electric drive as well as the drive itself.

Дата добавления: 2014-01-05