selection criteria for induction motors for vfd applications · selection criteria for induction...
TRANSCRIPT
VFD ensures energy saving, process control, lower starting
current and long service life for mechanical components
VFDS OFFER EXCELLENT ENERGY SAVING OPPORTUNITIES.
BUT THE MOTOR RELIABILITY HAS TO BE ENSURED
THROUGH PROPER SELECTION
Two learning experiences
400 kW, 1485 rpm motor failed on overload
Application: FD Fan in 135 TPH Boiler x 2 nos, Fan BkW- 358 kW- VFD
• 1. As per the process requirement, at 60% of Boiler MCR condition,
(One Fan Operating condition) Fan shaft power- 335 kW at 1330 RPM.
• 2. Two Fan Operating Condition, Fan shaft Power- 358 kW at 1485 RPM.
Problem faced:Problem faced:
• Winding burnout due to overload in 2 nos
• VFD failed once- all 3 on different occasions
Why?
• Selection of 400 kW for this application was wrong!!!!!
Speed in
RPM Power in kW
0 0
150 1
300 4
450 13
600 30
Fan Power increases in cube proportion to speed
600 30
750 59
900 103
1050 163
1200 243
1350 346
1500 475
The right selection is 475 kW rated at rated speed of 1492 rpm
Hoisting winch application
The motors would not lift!!!
• 132 kW, 6 pole- 6 nos • Identical everything, except
the motor brand
• Upon close comparison of
the data sheets, and after a
study at site, Pull out
• Brand A was successful
• Brand B did not hoist
• Identical components
study at site, Pull out
torque TPO of Brand B was
found to be 30% lower than
Brand A.
• Final solution was given
with higher size gearbox
Selection criteria for VFD driven motors
Efficiency
• VFD driven motors have
higher losses
• High efficiency motor keeps
it efficiency high
Reliability
• Torque characteristics
• Insulation stressa) Impulse voltage
b) Cable lengthit efficiency high
• Cumulative efficiency is
more important
b) Cable length
• Temperature rise
• Bearing current
• Noise level
• Vibration level
Additional joule losses under PWM
IEC:60034-17 / IS: 15880 – “Application guide- Cage
induction motors when fed from converters”
“IE” class-New efficiency standard
• North America with the core
regions US, Canada and
Mexico• Dimensions in inches
IEC 60034-30
Applicable the World over!
IEC: 60034-30 for efficiency & IEC: 60034-2-1 for testing of efficiencyIndian standard IS: 12615/2011 for efficiency & IS: 15999 for Testing of efficiency
MEPS for India is IE2- To become IE3 from January, 2014!!!
IE3 will have IE2 & IE2 will have IE1 efficiencies,
when operated through VFD
Output Output Output
kW 2 4 6 kW 2 4 6 kW 2 4 60.37 66.1 65.1 63.0 0.37 72.2 70.1 69.0 0.37 75.5 73.0 71.9
0.55 69.1 69.1 67.0 0.55 74.8 75.1 72.9 0.55 78.1 78.0 75.9
0.75 72.1 72.1 70.0 0.75 77.4 79.6 75.9 0.75 80.7 82.5 78.9
1.1 75.0 75.0 72.9 1.1 79.6 81.4 78.1 1.1 82.7 84.1 81.0
1.5 77.2 77.2 75.2 1.5 81.3 82.8 79.8 1.5 84.2 85.3 82.5
2.2 79.7 79.7 77.7 2.2 83.2 84.3 81.8 2.2 85.9 86.7 84.3
3.7 82.7 82.7 80.9 3.7 85.5 86.3 84.3 3.7 87.8 88.4 86.5
5.5 84.7 84.7 83.1 5.5 87.0 87.7 86.0 5.5 89.2 89.6 88.0
7.5 86.0 86.0 84.7 7.5 88.1 88.7 87.2 7.5 90.1 90.4 89.1
11 87.6 87.6 86.4 11 89.4 89.8 88.7 11 91.2 91.4 90.3
No. of Poles No. of Poles No. of Poles
IE1 IE2 IE3
1. The standard
stipulates that motors
must meet at least IE2
to be labeled Energy
Efficient.
15 88.7 88.7 87.7 15 90.3 90.6 89.7 15 91.9 92.1 91.2
18.5 89.3 89.3 88.6 18.5 90.9 91.2 90.4 18.5 92.4 92.6 91.7
22 89.9 89.9 89.2 22 91.3 91.6 90.9 22 92.7 93.0 92.2
30 90.7 90.7 90.2 30 92.0 92.3 91.7 30 93.3 93.6 92.9
37 91.2 91.2 90.8 37 92.5 92.7 92.2 37 93.7 93.9 93.3
45 91.7 91.7 91.4 45 92.9 93.1 92.7 45 94.0 94.2 93.7
55 92.1 92.1 91.9 55 93.2 93.5 93.1 55 94.3 94.6 94.1
75 92.7 92.7 92.6 75 93.8 94.0 93.7 75 94.7 95.0 94.6
90 93.0 93.0 92.9 90 94.1 94.2 94.0 90 95.0 95.2 94.9
110 93.3 93.3 93.3 110 94.3 94.5 94.3 110 95.2 95.4 95.1
125 93.5 93.5 93.5 125 94.5 94.7 94.5 125 95.3 95.6 95.3
132 93.5 93.5 93.5 132 94.6 94.7 94.6 132 95.4 95.6 95.4
160 93.8 93.8 93.8 160 94.8 94.9 94.8 160 95.6 95.8 95.6
200 94.0 94.0 94.0 200 95.0 95.1 95.0 200 95.8 96.0 95.8
250 94.0 94.0 94.0 250 95.0 95.1 95.0 250 95.8 96.0 95.8
315 94.0 94.0 94.0 315 95.0 95.1 95.0 315 95.8 96.0 95.8
355 94.0 94.0 94.0 355 95.0 95.1 95.0 355 95.8 96.0 95.8
375 94.0 94.0 94.0 375 95.0 95.1 95.0 375 95.8 96.0 95.8
2. IE1 tables are
given for
comparing the
efficiency of an IE2
motor when driven
by a VFD.
Cumulative efficiency
VFD speed variation
offers, nearly, 50%
more saving than the more saving than the
mechanical controls
Load torques & Power
Selecting for constant torque with VFDMixing, Mills, Cranes, Conveyors etc
Required
constant Torque
should be
available from
the motor, the motor,
throughout the
speed range.
Please always
specify the
Torque
Impulse voltage
Switching under PWM results in high dV/dt and the
rise time (tr) has direct influence on insulation life
Extra features for VFD duty Motors1. Magnet wire with increased dielectric strength- Dual coat wire
2. Additional cycles of varnish dip or Vacuum-pressure impregnated
3. heavy-duty lacing or taping of end-turns
Cable for VFD loads
The length of the cable connecting the VFD to the motor, the
rise time of the VFD output voltage pulse and the size of the
motor are the main variables affecting the winding insulation
� For retrofit applications, VFDs having a rise time of at least 0.5ms
should be chosen and the switching frequency for VFDs should be
selected below 5 kHz.
� The cable length should be restricted below 30 meters
Temperature rise of winding
Voltage harmonic distortion causes additional joule
heating in the lamination steel and operations at low
speeds causes ventilation reduction. Hence Torque
derating or oversizing of self cooled motor should be done
When a stray current in an electric motor uses a bearing
as its path to ground, bearing damage can occur. The most
common causes of stray electric currents are: asymmetry
in the motor’s magnetic circuit, unshielded power cables,
and fast switching pulse width modulated (PWM)
frequency converters used in modern variable frequency
drives (VFDs).
Insulated bearing
drives (VFDs).
Noise- IS: 12065 is the Indian standard
IEC 60034-17states:
A-weighted noise level increase in the range of 1 dB to 6 dB occurs for
operation with I-converters up to rated frequency compared with
operation on a sinusoidal voltage at rated frequency, and in the range of
5 dB to 15 dB for operation from U-converters. The actual values depend
upon the number of motor poles, the pulse pattern of the converter
Vibration- IS: 12075 is the Indian standard
Procedures recommended by IEC 60034-14 confirmed that
the vibration levels of induction motors increase when
these are fed by frequency converters
• VFD Duty
• NEMA / IEC
• Dual coat
Class F to F• Constant Torque
• Variable Torque
Torque derating for
Features for selection
High dV / dt
• Dual coat
• VPI/IGT
Torque derating for Constant Torque
or higher frame for Variable
Torque for F/B
PWM
Existing motor & New purchase
Existing motor
• Use with double shielded cables
• Limit the cable length below 10
meters
• Include a line reactor 3% or 5%
• Replace with VFD-duty when
motor fails
VFD-duty motor
• Comply with IS: 15880/2009, IEC
60034-17- “guide for selection of
cage induction motors for VFD”
• Torque derating or higher frame
size for temperature limiting
selection should be addressedmotor fails
selection should be addressed
• Insulated bearing at NDE, if
required
• Winding & Bearing protection
accessories, if specified
• Encoder provision, if required
• Forced cooling arrangement
