Comments On Blog

[marke]

Hi

 

Here is an interesting "thread" in response to my Blog on energy saving with some fairly strong arguments against the tide.

http://www.lmpforum.com/inforum/Energy-Sav...3.html#comments

For 97% efficiency - I am also surprise that you are taking these manufacturers' claim seriously on the efficiency but do not study how (under what condition) that they claim 97%. In the matter of practical fact.. there is no way you can tranform energy from 1-form to another with 97% efficiency.

Your are right that Nola-type do control the voltage. However, because it allow the motor to rotate using the control & momentum (becase of the speed of motor), the freewheel effect is now taking the role in energy saving.

Any one got anything to add?

Please add it here rather than as a comment to the blog as it will not be seen there.

 

Best regards,

Mark.

[marke]

Hello STARS-5

 

This discussion should really be here, on the main forum rather than as comments on the blog, so I am continuing it here.

 

1

For 97% efficiency - I am also surprise that you are taking these manufacturers' claim seriously on the efficiency but do not study how (under what condition) that they claim 97%. In the matter of practical fact.. there is no way you can tranform energy from 1-form to another with 97% efficiency.

If you do some basic calculations as I showed previously, you will see that it is indeed possible and does infact occur.

There is a major danger in extrapolating figures from one technology to another. To claim it is not possible because you can not achieve this result on a battery charger, is not reasonable proof.

If the efficiency was around 80% as you have suggested, then there would be a very large amount of heat generated. There certainly is heat generated, but not the amount that would occur if the VFD was only 80% efficient. This is easily verified by the ventilation of enclosures where the airflow is designed for the efficiency to be better than 95%. If the heat losses were higher than 95%, the temperature rise inside the enclosure would be much higher than designed and problems would occur.

 

2.

You have a good indiction of calculating from AC to DC. However, you do not seem to take into consideration that huge amount of garbage power generated as the bi-products (ripples, harmonics etc) & electrical design has to take care of these garbage to minimse the operation impact. The circuit generate garbage & it needs another circuit design to clean these garbage.

The conversion from AC to DC is achieved as described before, by the use of a diode full wave bridge into a bank of capacitors with a DC bus choke or AC line reactor as an optional extra. Please explain to me what additional losses there are here? There are no extra circuits in VFD. There may well be extra in a battery charger, but not in a VFD.

 

3.

On inverter IGBT (or some use MOSFET, with lower in cost), what kind of inverter output signal (PWM) are we referring? Are we seeing a perfect Sine-wave? What is the cost of a inverter output with perfect Sine-wave?

The output voltage is a switched PMW waveform and is not filtered. The current through the motor resulting from this PWM waveform is a siewave, so the PWM waveform is designed to create a sinusoidal current through the motor.

 

4.

On FREEWHEEL - please make some study on the how a fix speed motor can achieve a freewheel effect. In Nola-tyep design, the rotation is vey much a momentum driven,

Have a look at the NOLA patent, or one of my patents on this energy saver method. No where is the momentum mentioned because it is not in any way relevent to the energy saving principle. The energy is reduced at light load because the voltage on the motor terminals is reduced. This reduces the flux in the iron, which in turn reduces the iron losses in the core of the motor.

 

5.

Talking about friction loss.. you are now drifting away... to includes pump & gear... If you talk about the impact of different types of load.. then you are adding more parameter into the design.. we are talking about the motor friction... not the external loading.

That is exactly the point. Re read the BLOG. The point is that if you are going to save energy, you must identify where the energy is being wasted and reduce that. There is little energy to be saved in the motor alone in many cases, but there is much to be saved in the machine. The used of a VFD is NOT to save energy in the motor, it is to save energy in the machine and this is achieved by slowing it down. If you can not slow the machine down during part of it's operation, DO NO use a VFD as you are wasting additional energy (about 3%).

 

Best regards,

Mark.