Static Frequency Converter to Provide Stable Power Supply To Inductive HVAC Load

There wasn't time to order the correct equipment yet there is time available to solve a problem based on the arrival of the incorrect equipment and to hang around on CR4 for proverbial straws at which to clutch. How does that work?

OK. What has been the original equipment manufacturer's input to this problem so far?

The original equipment manufacturer of the AC panel which has the VFDs in it is at fault that they suggested that the VFDs could provide a stable Supply. They have refused to rectify the issue and we are dealing with them separately, by litigation etc., which is taking time.

In the meanwhile, to save costs (we are running the AC Panel feeding the HVAC Loads, from generator supply), we had an engineering consultant evaluate the situation and they have come up with the Solution of using a Static frequency Converter.

I was wondering whether any of you have worked with SFCs or Marine Shore to Ship Converters or converters for Aircraft power supplies which function similarly.

this is a first for me, using a Static Frequency converter and I would appreciate all inputs.

It's just that VFDs are designed each to turn a single motor.

Please post the single line diagram for the equipment to be powered on this supply using the camera button.

...and because of the intended litigation indicated in #4 above, any further Customer Care from that quarter is unlikely to be forthcoming, for both this and any future prospects.

One wonders if this project has become a victim of its own, over-ambitious and unrealistic Gantt Chart.

I absolutelly agree with RamConsult, the motor should be inverter grade, otherwise the insulation will fail, but that's not all, the motor will receive electro micro-abrasion as well (unless you permanently swipe the shaft with a conductive brush connected to the shell.

Anyway, most of the 3 phase induction motors for 200 or 400 V 50Hz. can be run in 230 or 440 VAC 60Hz. with no need for extra equipment. I have done it myself; but I'm not sure that yours will withstand the full 480, specially after being ran with an inverter wich might have already derated the insulation; are you sure it is 480?.

If it is 480, you can arrange three single phase stepdown transformers (480v to 48v) as backbust, thus subtracting 48 volts from every phase, which will give you 432Vac 60Hz. perfect for your 400Vac 50Hz system.

What size the transformers ? Oh, you'll have to figure that.

Regards

That could work if the load wasn't made of compressors. Using the step down transformers will work for the voltage and should be reliable but the 20% higher frequency will increase the pumping capacity of the compressors.

This will most likely produce an overload for the compressors.

I would go for dynamic converter consisting of 600 rpm motor generator set.

Motor will be 10 poles 60Hz and Alternator coupled to it 12 pole 60HZ.

Combined Efficiency of MG set can be between 94.5 to 95%. You can not expect similar from static converter. Moreover you do not have any problem of electrical noise from MG set.

I have supplied may such units for industry, ships and air port for 50/60Hz and 50/400Hz applications in 90s and are very reliable.

Most members have suggested cause of failure of previous trials as harmonics - same will be expected from Static Frequency Converter.

Moreover it will not be easy to filter the harmonics for HVAC plant - as harmonics in supply will vary with change in load - expecting higher harmonics when SFC is lightly loaded (due to chopping of AC curve much earlier at low load).

In my opinion MG frequency converter can be better solution. To save cost instead of Synchronous motor + Synchronous Alternator combination, you can opt for Induction motor + Synchronous Alternator combination. Maximum expected slip is 3% - which is within the range of permissible frequency variation of motors.

You mean to say all the equipment's are like chiller,condenser pumps ,chill water pumps and AHU's are 480 Volts or only main control panel working voltage is 480V?

How about using Delta Star transformer of suitable voltage ratio! Performance of motor with 60 Hz or 50 Hz is raleted to corresponding cooling. Supplying 60 Hz to 50 Hz motor may cause marginal overheating, and corresponding derating, or additional cooling provision may resolve the issue.

KM

Further to my suggestion of yesterday suggesting MG set, I read your inputs again and noticed that within a week you are going for trial with Static Frequency Converter -

One important point - have you specified to Static Frequency Converter supplier that his equipment shall be suitable to cater for heavy starting current of AC motors which is inductive (Power Factor of starting current 0.2 to 0.25). If not again you may find problems.