60Hz vs. 50Hz 1

[bozkirkurdu]

Hello Everybody,

I am working in a construction site in Kazakhstan where it is extremely cold outside and therefore the mobile heaters are used to heat the construction area. Lately we received two new 2million BTU heaters from USA, but they are delivered without their own generator on it which should generate 460VAC, 3 phase, 60Hz in order to run the heater. The only energy we have at site is coming from our diesel generators (no utility supply yet) and it is 380VAC, 3 phase and 50Hz.

After a close look at the heaters, I realized that I can run the fan motor and the burner motor with 380VAC at 50 Hz just by changing their winding connections from wye to delta which will cost a 20% power reduction at their output acc. to the manual. I have also a transformer which accepts 380VAC at 50Hz instead of 460VAC in order to give 120VAC needed (but at 50 Hz of course)for the motor contactors.

But the burner has an electronic controller and an ignition coil both of which require 120VAC at 60 Hertz acc.to the labels on them.

My questions are:
1. Does it make any harm to the burner controller if I apply 120VAC,50Hz instead of 120VAC,60Hz?
2. If this is not good, what else can I do?

regards,

 

[itsmoked]

The electronics probably will work with 50Hz with a hitch.

Doesn't say anywhere on a label???

One concern would be the electronics actually including some relays that run on 120V 60Hz, as any coil unless specified on it would probably fry. If you can look in the controls see any relays look for their coil voltages. If they say things like 5VDC or 12VDC then you'd be okay. If they say 12VAC or 120VAC then they better say 50/60Hz or it won't be okay.

 

[Skogsgurra]

I wouldn't be concerned about relay and small contactor coils running at 50 Hz instead of 60. The resistive part of the coil is relatively high and they can usually take a dirty air gap (less inductivity - more current) without getting overly hot. Big contactors (the 100+ ampere ones) may be more sensitive. But, as Smoked says, DC coils don't care.

Gunnar Englund

http://www.gke.org

 

[jtkirb]

The fan may run slower, electronics shouldn't care unless there is a control power transformer in there somewhere (it might not have enough iron for 50hz).

JTK

 

[Vladpl]

I wouldn't be concerned about the electronics as well unless there is as jtkirb said a control transformer.

All your transformers, motors, fans if they are designed for 60Hz only will run 20% harder if you connect them to 50Hz. This may result in transformer/motor burn out if it is run at the rated voltage (it depends how they were designed)

One alternative is to have a stepdown transformer and reduce the voltage by 20% to compenstate for 50Hz. The bad side is that the fans/motors would be slower.

These days most of the motors built have a 50/60Hz rating.I would check to see if they have been designed for that.

Since you talk about the cotroller part only that shouldn't use too much power. You can certanly buy speed controllers. When you input 50Hz on the output you can change it to 60Hz. These units can go up to 3kW. 1kw units cost around $300.

 

[waross]

Hi bozkirkurdu,
May I suggest a rethink about rewiring the NEMA motors in a Delta configuration?
1> It is probably not possible. NEMA motors typically have an internal, unaccessible Wye connection. It would be the 10,11,12 connection in a 12 lead machine, but the standard is 9 leads and an internal Wye point.
2> It probably is not nescesary. The optimum voltage for a 460 Volt, 60 Hz. machine on 50 Hz. is 383.3 volts. 460 x 50/60 = 383.3 Volts. You're within 1% of the optimum voltage at 380 Volts, 50 Hz.
Just hook it up.
The maximum allowable current will be the same so you don't have to change or adjust the Overload Relays. The reduction in power will be 1 - 50/60 = 16.7%
The reduction in the load with fans will be more. No worry about overloading at the new rating.

YOUR GAS MIXTURE IS OF MORE CONCERN.
If the burner motor is supplying combustion air, it will be supplying quite a bit less, and your burner may be running quite rich.
If you are not familiar with gas combustion systems, it may be prudent to look for a gas forum.
Some of the posters here may be able to help.
For the 120 volt electronics, the optimum voltage for 120 Volt 60 Hz motors and transformers used on 50 Hz. is 100 Volts, but a very common dual rating for coils is 110/120 Volts, 50/60 Hz.
If you can find a 110 volt transformer you will probably be a little safer with the coils and transformers in the controls.
The electronics probably have a transformer and rectifier for DC. If the transformer is OK, the electronics should work fine.
I would look for some way to drop the control voltage to 110 volts. This is a good compromise and will keep the DC voltages in the electronics from dropping too far.
If this was not possible, I would probably try one heater on 120 volt controls. If it ran ok, i would do the other heater tomorrow.
Good luck and watch the gas mixture.
yours

 

[d23]

bozkirkurdu

First and foremost I recommend that you contact the manufacture to get their recommendation.

Frequency should not have any bearing on your question.

If you have a blower motor rated at 460 volt and you input 380 volt you should not need to change any connection. The speed the motor will rotate will be:
(380 / 460) * full load speed.
The problem with this is that the motor expects “X” amount of air passing over it to cool it. At the lower speed the fan (like a pump) will only produce head (velocity) at the rate of
(380/460)^2.
The low air flow could result in a premature motor winding failure.
You should not require any re-connection of the motor for this application.

In general terms the igniter is purely resistive. The 380 volt verses 460 volt should only bring conductor size into question. Being a resistive circuit the igniter should work with the lower volts.

Please check with the manufacture on this. It will save you warranty questions in the long run.

D23

 

[bozkirkurdu]

Thank you all. Your answers are very helpful.

Waross,
Both the fan motor and the burner motor has nameplates on them on which I can read two different ratings, one with 460VAC at 60Hz and the other with 380VAC at 50Hz. I think, the motors are designed for both 50 and 60Hz as Vladpl suggests.

The control electronics HAS a transformer and rectifier for DC. I should check the transformer but finding a way to reduce the voltage to 110V seems to be an applicable solution. I should check whether we have an appropriate transformer in warehouse.

The combustion mixture is another concern which I did not think of it before. But we have good mechanical people at site who can adjust the mixture properly.

I will not pay too much attention for the cooling of the motors since the temperatures outside are about -20 to -30F.

I really appreciate your help. Best regards.