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Theoretical foundations of electrical engineering

Calculation of the asynchronous motor

Problem situation:
"Construct a load diagram P = f (t) according to the load conditions of the production mechanism and chose the capacity of the asynchronous motor of any series. Check the selected motor on maximum power. Define the values of T and G shaped equivalent circuit in absolute units and put them on the equivalent circuits. Make mechanical characteristic according to the passport data and define the overload capacitance".

Given
t1=1 s;
t2=1,5 s;
t3=2,5 s;
t4=1,5 s;
t5=1,5 s;
P1=8 kW;
P2=6 kW;
P3=0 kW;
P4=4 kW;
P5=3,5 kW;
n=750 rpm;


Solution

Load diagram:
Calculation of the asynchronous motor, Load diagram

We define the duration of one working cycle of the motor:


We define the equivalent capacity developed by the asynchronous motor for the imbalance load:

We chose the motor 4A132S6Y3 with the following parameters:
Pnom=5,5 kW;
ωnom=1000 rpm;
Mstart. torque/Mnom=2;
Mmax/Mnom=2,5;
Scm=0,36;

We find the rating moment of the motor:


Maximum static torque developed in the loading cycle (in the section 1):


It is necessary to note that the maximum torque is developed in the first section of the load diagram. So, it is necessary to check the overload on the maximum allowable starting torque.


The motor is suitable for operation at a specified cycle.

We define the critical moment and make mechanical characteristic:


Mechanical characteristic of the asynchronous motor:
Calculation of the asynchronous motor, Mechanical characteristic

L and T shaped equivalent circuits of the asynchronous motor
We write out the values of the equivalent circuits from the information book, while taking into account that values are already listed.


L-shaped equivalent circuit of the asynchronous motor
L-shaped equivalent circuit of the asynchronous motor

T shaped equivalent circuit of the asynchronous motor
T shaped equivalent circuit of the asynchronous motor

T shaped equivalent circuit of the asynchronous motor

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