Conversion of 3PH 480V 60Hz Supply into 3PH+N 400V 50Hz Supply using Static Frequency Converter

[Roshan07]

In a project on an island offshore Abu Dhabi, UAE, the system voltage available is 3phase 480V 60 Hz. Due to the time constraints the HVAC equipment supplied & installed are of 3Phase+Neutral, 400 V 50 Hz.

A solution to convert the 3PH 480V 60 Hz into 3PH+N 400V 50 Hz was made through a VFD Panel, assuming the VFDs would convert the 3PH 480V 60 Hz into 3PH+N 400V 50 Hz. It did, of course. But after some time, some of the units failed. The reason being, the Output Voltage of the VFD varied corresponding to the varying HVAC Loads. (Though the VFDs could be considered as a converter, they should have been used as a source only for Inductive motor loads which form major part of the HVAC loads and not to supply auxiliary loads)

We are required to provide stable 400V Output supply at the AC DB/Panel which would not vary based on the variations of the HVAC Loads.

The current proposal that is being carried out is to use a Static Frequency Converter, which would provide 3PH+N 400V 60 Hz stable supply from an input of 3PH 480V 60 Hz supply.

We are going to do a trial run on the equipment, next week.

We propose to feed the SFC from a generator at 480V 60 Hz supply, feed the output of the SFC to a Inductive Load bank and test it.

We are apprehensive of the testing since our earlier trial run with the VFD panel was successful but in the long run, the solution failed.
Need your expert opinions on the above.

 

[alanElec]

So can I summarize your question as " Would the output Voltage of SFC change with varying HVAC load?" First You said about HVAC equipment.Can U specify like AHU,FCU,Split Units,chiller etc?

 

[Roshan07]

The AC Panel with the VFDs feeds

1. Two Closed Control units (CCUs) -one duty and the other Standby
2. two Outdoor Split Units (FCUs & CUs)- one duty and the other Standby
3. Tow Indoor Split Units (FCUs & CUs)- one duty and the other Standby

Each of the above 3 sets are fed from a single source (different source for each set) with contactor control to switch between the Duty & Standby.

Each VFD is fed via a MCCB in the AC Panel. Each VFD feeds an isolation transformer which in turn was feeding an RCCB the output of which was shared as described above.

We have modified the SLD , removing the VFD, isolation transformer &RCCB and added a MCB with Earth leakage relay after the contactor for the connection to the Duty Unit and the HVAC unit.

The concern , as you have stated is correct.
Would the output of the SFC be stable regardless of the variation of the HVAC Loads?

This is the first time I am using a Static frequency Converter. I suppose many of you have used similar Converters like shore to Ship Converters, Airplane power converters etc. What are you views on such a operation?

 

[mikekilroy]

Roshan,

I suggest you hire an electrical engineer to solve your problem; your solutions so far and proposed are no BAD.

But after some time, some of the units failed. The reason being, the Output Voltage of the VFD varied corresponding to the varying HVAC Loads.

No, the reason is you put 680v square waves into the equipment, with 1200v spikes on top of it! It HAD to fail, it could not have worked for long. This was a wrong decision from the get-go.

Now you want to put on a static converter? Wow. Don't go there.

Please hire a competent electric engineer. He will show you how and where to buy an off the shelf low cost buck boost 480->400v transformer and do the job as it should have been done on day 1.

http://www.KilroyWasHere<dot>com

 

[mikekilroy]

He will also check with the equipment mfgr and verify it is ok to run on 400v 60hz

http://www.KilroyWasHere<dot>com

 

[Roshan07]

'Now you want to put on a static converter? Wow. Don't go there."
Why not?
Any reasons? please clarify.

Could you explain the "No, the reason is you put 680v square waves into the equipment, with 1200v spikes on top of it!"

480V 60Hz is the system supply voltage. The output of the VFD is 400V 50 Hz. The voltage supplied to the HVAC Units is 400V 50 Hz. 480V 60 Hz is only up to the AC panel/VFD. there is no issue with the VFDs.

The Manufacturer of the VFD has provided a reply that the output of the particular VFD (The ATV212) can be used only for the Induction Motor Load and not supply other loads such as
a. heater banks
b. Control circuit Transformer for Humidifiers
c. Damper circuits
d. Transformers to supply another panel belonging to the client.
They had specifically stated that "The ATV212 can't be used just to get a 400V / 50 Hz output from the 480 V/ 60 Hz incomer in order to supply the other equipment's in the network. "

When the load in the circuit is mainly inductive motor loads, the output voltage of the VFD does indeed vary depending on the inductive loads.

The VFD issue is of the past. My concern is about the Static Frequency Converter.
If you have installed, commissioned and operated SFCs or marine shore to ship converters, please do provide inputs.

there is no requirement of a discussion on how the VFD set up failed.

 

[mikekilroy]

Thought you wrote you were next going to try a 'static phase converter;' that device does not change freq or voltage. You said The current proposal that is being carried out is to use a Static Frequency Converter, which would provide 3PH+N 400V 60 Hz stable supply from an input of 3PH 480V 60 Hz supply. Since you said you were not changing frequency anyway, I misread your device name as static phase converter, sorry.

If indeed you are only going to change voltage as you state and not freq, then a transformer is a LOT cheaper and more reliable - but again, you need an electrical engineer to verify with all the equipment manufactures that it is ok to run 400v 60hz (this is not a no brainer - it will make your motors run faster and be starved for voltage since they will expect 460vac. You may trade blowing up the controls for blowing up the motors with this scheme).

http://www.KilroyWasHere<dot>com

 

[waross]

Take a look at this FAQ:
Motors: Changing between a 50 and 60Hz supply. faq237-1224
Each type of equipment must be evaluated. Some will use transformers. Some may use small VFDs. Only a few will require a static convertor.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[alanElec]

It is highly recommended that you take support of the sfc manufacturer or their local agent in Abudhabi.Hope they are competent enough to solve this issue. Also consult the FCU factory of the possible effects of using 60 Hz instead of 50 Hz. You might be knowing the outcome, but better to ask the experts and get their advice in record.After all,another failure shouldn't be your responsibility alone..I am sorry I couldnt come up with a satisfactory answer..Keep trying..

 

[LionelHutz]

The VFD failed or components in the HVAC panel failed?

The VFD is probably in flux vector mode and that's why the output varies with the load. Using V/Hz mode would probably stabilize that. However, switching motors on the output of a running VFD is never a good idea.

The motors and auxiliary loads probably should have been split up with VFDs on the motors and transformers used for the other auxiliary loads.

It sounds like you are way too far down the static converter path to be changing direction now....

 

[sreid]

Why not use a rotary converter (MG Set).

 

[crshears]

Rotary converter definitely worth considering, in my opinion; relatively simple, reliable, repairable, probably can be designed to perform well in a hot, dry climate. Just be sure to filter ALL particulates from the cooling air supply, or the dust and sand will wreak havoc with the commutators and brushes. Such a machine at 600 rpm could almost certainly be designed with shaft-mounted fans and would not require auxiliary blowers.

Another handy feature: if provided with an appropriate excitation system, should have no issues coping with the starting or stopping of numerous connected loads.

Perhaps not as energy-efficient as some of the new electronics, but still...

CR