17.Nov.2007- Sweden
Variable speed drive (VSD)
AC Induction Motor
C0nversation between AC induction motor- (1) and his owner(or consultant)- (2)
1)Hello , this is me , i am going to work for you ! are you going to buy me?
2)Yes , yes , but I am not sure in which application ,from the following below to use you!
Fans ,Pumps, compressors and conveyors , cranes or elevators, material handling or machine tools ,and many others.
1) Oh , sir ,don’t worry, no problem , in all those applications I can start to work and you will be happy !!
After a period of time anew changes happened , the AC induction motor (1) started to shout !!
1)Hello , this is me , i am going to work for you ! are you going to buy me?
2)Yes , yes , but I am not sure in which application ,from the following below to use you!
Fans ,Pumps, compressors and conveyors , cranes or elevators, material handling or machine tools ,and many others.
1) Oh , sir ,don’t worry, no problem , in all those applications I can start to work and you will be happy !!
After a period of time anew changes happened , the AC induction motor (1) started to shout !!
(1) AC motor - Help !! Help!! Help!!
(2) The owner ( consultant) -Hello , what’s wrong with you? what’s going on ? what’s happening?
1) OOH Sir, I am sorry , I feel my self very bad , I am over heated , I think I have flu !! Actually I am going to die soon!!
2)Don’t be afraid , you are still young , just few years ago you started to work for me , usually you are living 10- 15 years .
1) I agree with you , but 10 C of overheating me will reduce my life to 50% ! and I am very hot. All that started after that moment, when you connected me to PWM frequency converter
! I was happy before that time , working at full speed with full load fed with clean power from the network 400V / 50 Hz.
But ,at that time, you were not satisfied , crying all the time that I am consuming a lot of energy and always running at full speed or standing .You wanted me to start walk instead of running (even some times very slow) !!
2) yes, my friend , because a lot of applications want to start and stop smoothly and to change their speed according to their needs , like Fans , Pumps and elevators for example ,supplying you with full voltage and nominal current reflected in inrush spikes of voltage and current in the network and you could not handle a lot of important application – that was the reason to connect you to a Frequency Converter ! Do you understand?
1)It is true that your ideas were the reason of my illness and possible close death !!
2) No , no , my friend , don’t worry , I will solve all your problems , but first tell me about them ? I have an idea to call a Doctor from NFO DRIVES AB in Sweden . What do you think?
INFO?? I don’t need information , I know my situation very well , and beside that , how info could help me ?
2) Oh , I am sorry , seems to be you did not hear it well , it is not info ! It is NFO – natural field orientation – it is a patent registered to NFO Drives in Sweden , it helps you to work in a very accurate way !
1)Really ! There was a far talk about it , but no body applied it to me .
May be not to you , personally , but more than 8000 AC motors of your brothers in Sweden are working with it( NFO).
1)Really , I like it , but let me first tell you a bout my illness and troubles which started with PWM – FC
2) Ok . I am listening to you carefully .
1) First of all , you are giving me infected food ( a choppy squared off wave -voltage pulses) full of harmonics , please see the drawings below :
Harmonic content in such wave
Distortion of 5 th harmonic 
Distortion of 5 th harmonic 
Motor’s Voltage near nominal speed
2)Ok , In which way those harmonics are like infection to you ?
1) Ah , I see , did not you know that ? Ok , for example 5th harmonic is trying to rotate my shaft in the opposite direction to my movement , and that’s cost me effort to spend part of my food ( energy) to compensate its negative action , and that’s make me more warm and become overheated .
2) Don’t make me laugh ! Areyou trying to tell me that small 5th harmonic , will make you ( kaboot) !!
1) Not only 5th harmonic, but you can add the effect of its brothers to that !! ; 11 , 17 ,23 and so on…. , all those are trying to rotate me in the opposite direction , and you are paying for them and for there compensation.
In addition , their energy is wasted in heating and did not give any useful work ! even more , other harmonics like 7th , 13 ,19 , 25 and so on… are making my movement pulsating and not smooth.
2)Ok , In which way those harmonics are like infection to you ?1) Ah , I see , did not you know that ? Ok , for example 5th harmonic is trying to rotate my shaft in the opposite direction to my movement , and that’s cost me effort to spend part of my food ( energy) to compensate its negative action , and that’s make me more warm and become overheated .
2) Don’t make me laugh ! Areyou trying to tell me that small 5th harmonic , will make you ( kaboot) !!
1) Not only 5th harmonic, but you can add the effect of its brothers to that !! ; 11 , 17 ,23 and so on…. , all those are trying to rotate me in the opposite direction , and you are paying for them and for there compensation.
In addition , their energy is wasted in heating and did not give any useful work ! even more , other harmonics like 7th , 13 ,19 , 25 and so on… are making my movement pulsating and not smooth.
Motor’s current near nominal speed
2) Ok , for such infection , I will ask to get less useful work from you , or in other words I must to derate you !
1) not only for the harmonics reason , actually , my stators windings ends are becoming very hot , because I am receiving high voltage spikes ,some times double of the DC link voltage 1130 V in 400v system.
My insulation , will not withstand such over voltages spikes , especially when I am located far away ( more than 100feets -35 m) from your friend “ PWM” F.C, or when I am used as a second hand AC motor in any retrofitting project , standard B insulation type !
2)As , I mentioned before , I can derate you ,and use your brother NEMA MG1 Part 31.40.4.2 standards - Inverter grade motor ,insulation systems which are designed to meet and exceed resistance to spikes of 2 times nominal voltage .
1) Of course , you could do that ,but you will continue to pay for the negative effect of high harmonics (5-10)% of the energy fed to me ,it costs you a lot of money ! Take for example my brother 15 kW AC motor and calculate the losses for it, you will pay for 650W wasted energy in every hour of its work, and the efficiency of oversized motor is very poor when you are regulating the speed under 50% of its nominal value ,which always takes place in pumps and fans ,…….. so you are saving from one side and loosing from another !!
Please see an example of efficiency curves of AC induction motors
2) Ok , for such infection , I will ask to get less useful work from you , or in other words I must to derate you !1) not only for the harmonics reason , actually , my stators windings ends are becoming very hot , because I am receiving high voltage spikes ,some times double of the DC link voltage 1130 V in 400v system.
My insulation , will not withstand such over voltages spikes , especially when I am located far away ( more than 100feets -35 m) from your friend “ PWM” F.C, or when I am used as a second hand AC motor in any retrofitting project , standard B insulation type !
2)As , I mentioned before , I can derate you ,and use your brother NEMA MG1 Part 31.40.4.2 standards - Inverter grade motor ,insulation systems which are designed to meet and exceed resistance to spikes of 2 times nominal voltage .
1) Of course , you could do that ,but you will continue to pay for the negative effect of high harmonics (5-10)% of the energy fed to me ,it costs you a lot of money ! Take for example my brother 15 kW AC motor and calculate the losses for it, you will pay for 650W wasted energy in every hour of its work, and the efficiency of oversized motor is very poor when you are regulating the speed under 50% of its nominal value ,which always takes place in pumps and fans ,…….. so you are saving from one side and loosing from another !!
Please see an example of efficiency curves of AC induction motors
The efficiency of the motor is close to its max. value between 75% and 100% of the full rated load
But for the 10% load, the efficiency plummets to 55%. For a 15 kW motor.
2) Ok ,OK ….. I have another solution, it will make you happy!!
1) really , what is it?
2) I will connect you to PWM conventional type - FC through a filter
But for the 10% load, the efficiency plummets to 55%. For a 15 kW motor.
2) Ok ,OK ….. I have another solution, it will make you happy!!
1) really , what is it?
2) I will connect you to PWM conventional type - FC through a filter
In Europe some times , they called it ( Sine Former) 
Elevators
- Pumps
- Traction and conveyer systems
- HVAC systems (heating, ventilation and air conditioning)
But it consumes a lot of energy , comparing that with other solution comes from NFO DRIVES AB by using NFO SINUS Inverter.
- Pumps
- Traction and conveyer systems
- HVAC systems (heating, ventilation and air conditioning)
But it consumes a lot of energy , comparing that with other solution comes from NFO DRIVES AB by using NFO SINUS Inverter.
For PWM – FC connected to a 15 kW motor
Voltage drop = 8% X400 V= 32 V
Losses = 33A X 32V = 1056 W ! it is too much !! ( for VSD with motor Power rating 15kW)
And the ( sine former) is limited up to 100Hz speed change,
In North America , they called it (Motor guard)
Voltage drop = 8% X400 V= 32 V
Losses = 33A X 32V = 1056 W ! it is too much !! ( for VSD with motor Power rating 15kW)
And the ( sine former) is limited up to 100Hz speed change,
In North America , they called it (Motor guard)
It called NFO SINUS Inverter ! and it looks like :
It includes:
1- MOSFET transistors , with switching frequency between (30- 220) kHz …………..IGBT=( 800Hz-15kHz)
2-Sine switch , registered patent to NFO Drives AB, which is forming the output current wave shape and make it pure sine type , some times ,even better than the wave form from the grid !!
It includes:
1- MOSFET transistors , with switching frequency between (30- 220) kHz …………..IGBT=( 800Hz-15kHz)
2-Sine switch , registered patent to NFO Drives AB, which is forming the output current wave shape and make it pure sine type , some times ,even better than the wave form from the grid !!
Please note that NFO Sinus is acting to eliminate the output harmonics content to protect the motor and not to decrease them on the input of the drive
It is a fact that PWM- FC s can damage the insulation system of your motor. However, with better understanding, you should be able to prevent the infant mortality that so many have seen. Unless you’re looking for a reason to replace the motor, you should not install a PWM FC to an aged class B insulation system. Drive manufacturers of PWM- FC have increased effectiveness through PWM technology to deliver close to a clean current waveform to your motor. But that current comes with the expense of very fast rise time (dV/dT) and harmonics content.
Looking for a patched solution by adding sine wave output filter will protect the motor , but it will result in more capital investment and continuous additional consumption of electric energy , which could cost, in one year, more than 35% of the total purchasing price of the drive.
To avoid all above mentioned headaches and to save your money , NFO Drives AB offer you the solution by using NFO Sinus Inverter, and the particular, expensive part in it is the (NFO Sinus- Switch) which delivers a clean sine (pure sine waveform) voltage to your motor.
Weather your project is new or retrofitting type , your motor premium or standard one . In all cases with NFO Sinus Inverter , your application will work in perfect way for long time with minimum preventive maintenance and saving your money and effort !!
Have a nice time
2) Are you satisfied with us ?
1) Sure , with NFO SINUS Inverter, I am happy .
It is a fact that PWM- FC s can damage the insulation system of your motor. However, with better understanding, you should be able to prevent the infant mortality that so many have seen. Unless you’re looking for a reason to replace the motor, you should not install a PWM FC to an aged class B insulation system. Drive manufacturers of PWM- FC have increased effectiveness through PWM technology to deliver close to a clean current waveform to your motor. But that current comes with the expense of very fast rise time (dV/dT) and harmonics content.
Looking for a patched solution by adding sine wave output filter will protect the motor , but it will result in more capital investment and continuous additional consumption of electric energy , which could cost, in one year, more than 35% of the total purchasing price of the drive.
To avoid all above mentioned headaches and to save your money , NFO Drives AB offer you the solution by using NFO Sinus Inverter, and the particular, expensive part in it is the (NFO Sinus- Switch) which delivers a clean sine (pure sine waveform) voltage to your motor.
Weather your project is new or retrofitting type , your motor premium or standard one . In all cases with NFO Sinus Inverter , your application will work in perfect way for long time with minimum preventive maintenance and saving your money and effort !!
Have a nice time
