WO1996001522A1

WO1996001522A1 - Method for determining torque requirements

Info

Publication number: WO1996001522A1
Application number: PCT/SE1995/000757
Authority: WO
Inventors: Ulf Hagblom
Original assignee: Luossavaara Kiirunavaara Ab
Priority date: 1994-07-04
Filing date: 1995-06-21
Publication date: 1996-01-18
Also published as: AU2940395A; SE9402353L; SE9402353D0

Abstract

The present invention relates to a method of determining with the aid of an asynchronous electric motor the actual torque that is required to start-up and run a plant (1) that is driven by the electric motor (2). The method is characterized by measuring motor speed, voltage and current, and the phase angle between current and voltage, and comparing the measurement values obtained with known and mapped motor performance values, to establish the torque actually required with regard to the plant (1). The invention also relates to the use of the method.

Description

METHOD FOR DETERMINING TORQUE REQUIREMENTS

The present invention relates to a method of determining through the medium of an asynchronous electric motor a true torque requirement for starting-up and operating a plant driven by the motor. The invention also relates to the use of the method.

Asynchronous electric three-phase motors are used to a large extent in industry for operating different types of plants, such as conveyor belt systems, mills, etc.

In practice, it has been found particularly difficult to choose the smallest electric motor that will serve such plants and systems effectively, this difficulty often resulting in choosing for safety's sake an electric motor and associated peripheral devices and appliances, such as electrical installations and mechanical transmissions, that are unnecessarily large and expensive. Because many types of electric motor applications also involve large dynamic loads even during the actual start-up sequence, the electric motor must be capable of handling an initial start-up torque, and

■ a so-called jerk torque, which is the torque required to

"jerk" the apparatus or system into motion, these torques being much higher than the torque required in the normal running of the motor.

The object of the present invention is to provide a method which enables the actual torque required to start-up and to run the plant to be determined. This object is achieved with a method having the characteristic features set forth in the following Claims.

The following advantages are among those afforded by the invention.

The plant production capacity can be optimized in relation to the capacity of the electric motor.

Plant safety margins can be controlled.

When wishing to exchange or replace a drive motor, the inventive method enables the size of electric motor required to be established.

Experience is obtained regarding different operation require- ments, which enables future savings to be made, among other things.

The invention will now be described in more detail with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawing, wherein Fig. 1 illustrates schematically a plant driven by an electric motor in which the inventive method is applied.

The Figure shows a load 1 which derives from a plant or system of some kind or another, for instance from a conveyor belt. The load 1 is driven by an electric asynchronous three- phase motor 2. Current is delivered to the motor 2 through three electric conductors 3-5, each representing one phase.

In the illustrated exemplifying case, the non-drive end of the electric motor 2 carries a speedometer 6, which in this case has the form of a so-called tachometer generator which produces an electric voltage whose magnitude varies in accordance with the speed of the motor 2. As will be under- stood, the speedometer 6 may alternatively be placed at the drive end of the motor, when the transmission between the motor 2 and the plant 1 so permits.

A measuring means 7 which functions to measure voltage, current and phase angle between current and voltage when the motor is in operation is mounted adjacent the conductors 3-5.

The measuring values produced by the speedometer 6 and the measuring means 7 are passed continuously to a calculation and comparison unit 8, which compares continuously the input measurement values with the known and charted performance values of the motor, so as to determine the actual torque requirements of the plant 1 at different points in time. The actual torque requirement of the plant 1 is, of course, registered and stored in a suitable manner.

With regard to the performance and characteristics of the electric motor, it can be mentioned that the winding resis¬ tance of the motor stator and the rotational inertia of the rotor are of essential significance, as is also the torque curve and electrical performance of the motor.

The aforedescribed measuring procedure is continued for the length of time required to map or chart the motor loading conditions satisfactorily. Although the measuring procedure is normally carried out on all three phases, it may alterna¬ tively be carried out on only one phase when torque mapping is simplified.

The inventive method thus enables the actual torque required to start-up a plant or system 1 and to run the plant to be determined through the medium of the asynchronous electric motor 2.

The so-called jerk torque, start-up torque and running torque required by the plant 1 can be established and registered. This enables the load placed on the plant to be adapted so that the capacity of the motor 2 can be utilized in an economically optimal manner. Alternatively, a switch can be made to an electric motor that is more economical in opera¬ tion with regard to the plant concerned, in accordance with desired plant performance or plant loading capacity.

The inventive method thus provides disparate savings and optimizing possibilities over and above the knowledge attained with regard to the actual torque required to start¬ up and operate different types of plants and systems. The method also facilitates future choice of electric motors for operating similar types of plants.

It will be understood that variations can be made in the choice of devices for measuring speed, voltage, current and phase angle.

Naturally, the construction and design of the calculation and comparison unit may also be varied in accordance with requirements. The mapped actual torque requirement can, of course, also be registered and stored in many different ways within the scope of the invention.

The invention is therefore not restricted to the illustrated and described exemplifying embodiment thereof, since changes and modifications are possible within the scope of the following Claims.

Claims

1. A method of determining with the aid of an asynchronous electric motor the torque that is actually required primarily to start-up a plant (1) and secondarily to run a plant driven by the electric motor (2) , characterized by determining motor speed, voltage, current and phase angle between current and voltage, comparing the obtained measurement values with known and mapped motor performance values so as to establish the actual torque requirement of the plant (1).

2. A method according to Claim 1, characterized by adapting the loading of the plant (1) so that the actual torque requirement will conform with the economically optimal performance of the motor (2).

3. Use of the method according to Claim 1, characterized in that the method is used to establish a minimum or optimal requisite motor size for operating a plant or system on the basis of the actual operating conditions.

4. Use of the method according to Claim 1, characterized in that the method is used to establish the jerk torque required to start-up the plant.

5. Use of the method according to Claim 1, characterized in that the method is used to establish the requisite plant start-up torque.

6. Use of the method according to Claim 1, characterized in that the method is used to establish the torque actually required in the running of a plant.