LVElectric Motors Basics

Transcription

1 LVElectric Motors Basics

2 Selection of electric motors has to be made using 3 different categories : By its electric design. By its mechanical design. By its insulation system

3 The most important features to define the electric design of a motor are : -No. of phases Single Phase Commonly found in domestic and very small applications Three Phase Found in industrial applications

4 -Voltage and Frequency The most common voltages for single phase motors in the US are 115/230 V. While for three phase motors is 230/460 V The standardized frequency in the US is 60 Hz. While in Europe it is 50 Hz.

5 -Power Defined in HP or kw. Power in HP = Power in kw In example : A customer requires a kw motor. What motor does the customer need in HP? HP = / = 0.5 HP

6 -RPM or Nominal speed Nominal speed depends on frequency and number of poles : Hz Hz Hz Hz RPM = 120 x Frequency No. of poles

7 -Service Factor Indicates an allowed increase in the load to the power of a motor without affecting its useful life (All three phase WEG motors have a service factor of 1.25; and all motors above 100 HP have a 1.15 service factor unless otherwise specified. In example ; A 10 HP can be used for an up to 12.5 HP application without affecting its useful life. -Inverter (Drive) application Due to the last trends in speed varation, it is very common to see motors used along with Variable Frequency Drives. It is important to know what will be the speed range that the motor will work in.

8 -Temperature Increase Each electric motor, depending in its particular electric design will increase its temperature while in operation. The temperature ranges/classes are as follows : : Green represents the temperature increase.

9 The most important features to define the mechanical design of a motor are : -Frame Size There is two world known standards that define the size of a motor. - NEMA sizes /5T 182/4T 213/5T 254/6T 284/6T (S) 324/6T (S) 364/5T (S) 404/5T (S) 444/5T (S) 504/5T (S) 586/7T (S) - IEC sizes (80) 90S/L (100) 112S/M 132S/M 160M/L 180M/L 200M/L 225S/M 250S/M 280S/M 315S/M 355M/L

10 -NEMA frame sizes In example. A 25 HP motor with a 284T frame /5T 182/4T 213/5T 254/6T 284/6T (S) 324/6T (S) 364/5T (S) 404/5T (S) 444/5T (S) 504/5T (S) 586/7T (S) B H T + S 1) 2) 3) 4) 1) 28 / 4 = distance H* ( = 7 = 177.8mm) (For frame 42 y 48 divide by 16; 56 frame is the same as 143T) 2) assigment B according to NEMA standards. A larger number represents a longer B distance. 3) T indicates that it is a NEMA standard frame 4) S indicates that the motor has a shorter shaft (Equal to a smaller size)

11 -IEC frame sizes (80) 90S/L (100) 112S/M 132S/M 160M/L 180M/L 200M/L 225S/M 250S/M 280S/M 315S/M 355M/L B H In example a 25 HP motor with a 180 frame M 1) 2) 1) distance H en mm = 180 = ) Assignment according to IEC standards L=long, M=medium, S=Short

12 -Enclosure against the environment It is important to define an enclosure IP (Internal Protection) as a motor operated in a non-suitable environment can easily be damaged or burnt. FIRST DIGIT (Against solids) I P - INTERNAL PROTECTION SECOND DIGIT (Against water or fluids) 0= no protection 1= machines protected against solids with a diamenter larger than a 2. 2= machine protected against solids with a diamenter larger than a = machine protected against solids with a diamenter larger than a = machine protected against solids with a diamenter larger than a = machine protected against dust 0= no protection 1= machine protected against water drip 2= machine protected against drip o with a 15 degrees inclination 3= machine protected against outside water condensation 4= machine protected against water sprinkle 5= machine protected against stream of water 6= machine protected against jetstream 7= machine protected for temporary water immersion 8= machine protected against continuous water immersion

13 - Mounting. It has to be specified wether the motor will be direct coupled with a flange or not. There is two types of standard flanges for NEMA and two for IEC : Flange NEMA: -Flange C (Small) ó Flange D (Large). NOTE: WEG has available C-Flanges for all NEMA frames; and D-Flanges for all NEMA- T frames. Flange IEC -Flange C-Din (Small) ó Flange FF (Large) NOTA: WEG has C-Din flanges available for frame 90,112 and 132. FF flange is available for all sizes.

14 Radial Loads Axial Loads

15 Ball Bearing Roller Bearing (For High axial load applications)

16 -Mounting / Type of bearings It is important to note what will be the mounting position of a motor : Horizontal Mounting (Direct Coupling) Vertical Mounting All WEG motors up to 60 HP can be mounted in any position when normal loads are applied to them. For maximum admited axial and radial loads you can consult the Electric Motor Manual. NOTE: In both cases (Shaftup or down the weight of the rotor is supported by the endbells. (The maximum supported loads are available in the Electric Motor Manual)

17 Use with belts For all motors 100 Hp and above (4,6, and 8 poles) it is recommended that they have roller bearings for belt applications due to very high radial loads. NOTE: 2 poles motores can never be used with belt applications. High Radial Loads

18 -Position of terminal box Superior (F3), on the left when seeing the motor from the drive end (F1), On the right side when seeing the motor from the drive end (F2) -Frame Material: Aluminum : Outstanding resistance to very humid and corrosive environments. Very light compared to cast iron. (Please note that all WEG aluminum motors are supplied with cast iron end bells and terminal box) Cast Iron: Most commercial motor for large applications. Excellent resistance / Severe duty Rolled Steel : Ideal for smaller applications due to lower cost and very low weight.