Mounting an European Paper Mill in South America 1

[petronila]

We are going to move a paper mill from Swiss to Perú, 30 % of motors are nameplated 380 V-50Hz and the rest are nameplated 500 V-50 Hz. We have to calculate the new power substation for 60 Hz. We think is better to use a 460 V with a tolerance of +/- 2 x 2.5 Volts and let all motors working with this voltage. The other idea is Rewound all 500 V motors.Another question is what to do with the contactors coils (220 V-50 Hz.)

What do you think fellows.

Thanks in advance for the help

Petronila

 

[Skogsgurra]

That's a challenge. I was once involved in the pre-study of a project in Peru. It turned out to be high up in the Andes - about 4000 metres above sea level. One of the problems was that we needed to derate equipment due to thin air and reduced cooling. But a paper mill is more likely to be at sea level. So that shouldn't be a problem. But keep an eye open for cooling problems if you are moving up the mountainside.

Running the 380 V motors on 460 V 60 Hz is just fine. But there is a risk that the 20 percent increase in speed will cause overload in pumps and fans.

The 500 V motors will not be happy at all with 460 V 60 Hz. They will be running at close to 25 percent undervoltage and that is not good. You will have a large slip and lots of rotor heat. A 500V/50Hz motor expects 600 V at 60 Hz.

Rewinding or not all depends on how many 500 V motors you have and how big they are. There is a reason for the 500 V - perhaps large units, perhaps because you usually run such systems with an isolated neutral. That underlying reason may also influence your choice of action. Is keeping the two systems separate totally unrealistic?

Contactor coils. If you feed the control transformers with 460 V 60 Hz, your AC coils will probably be happy with their new voltage/frequency combination. But you will have to be careful with your DC coils. They will have almost 50 percent more heat. And that may be a problem. A big problem, really.

You will also have to check other DC-fed things like proximity switches and such little devices. They usually have a maximum voltage equal to 30 V DC and since they already (in Europe) see about 27 V, you will be on the margin with a 20 percent higher voltage (1.2x27 = 32 - 33 V).

And there are the VSDs. They may be frequency inverters or DC drives. You will need to make sure they can operate with the voltage available.

Plus a few other things that you will find out on place - sometimes before, sometimes after something lets the smoke out.

Gunnar Englund

http://www.gke.org

 

[sacem1]

Contactors will work fine in 60 Hz even if they are 50 Hz, the problem will be the Amp load if you change voltages.

If you are out of Lima chances are high that the energy company will be able to supply you with 380 V - 60 Hz.

We use 220 V single phase, 220 V three phase in Lima with no N line, the rest of the country usually has 4 lines (RSTN) so you can get 380 V - 60 Hz

If you go the 440V route your 380 V will not work and the 500V units will be undervoltage by 24% and thats not acceptable.

Don't forget your motors will run at diferent speeds:
2 pole go 3600 instead of 3000 rpm
4 pole go 1800 instead of 1500 rpm
6 pole go 1200 instead of 1000 rpm
8 pole go 900 instead of 750 rpm, etc

If your motors where designed very close to maximun load at their original speed in 50 Hz they will be overloaded at 60 Hz at least by 20% in the blowers and pumps you will find that a 20% increase in speed will demand a 72.8% INCREASE in power demand.

HP increases at the CUBE of the speed variation, pressure at the square of the speed variation and displacement linearly with speed variation for air blowers and most centrifugal pumps.

Also take into account the altitude at which the plant will operate, here we have minning plants that have motors working at 4,000+ meters of altitude.

Regards

SACEM1

 

[petronila]

Thanks SACEM1 and SKOGS for the comments, and Yes Skogs, is a nice project because is complicate, the paper mill will run at sea level so no derrating will be necessary, but taking acount the paper mill works in swiss at mountain (alpes) Level the motors will be oversized. The pumps and fans problem could be fixed with VFD´s But the real problem are the 500 Volts motors,The power substation will be Rated 60 Hz totally new and the secundary connection will be WYE with NEUTRAL.

480 Volts-60 HZ COULD BE FINE???

Thanks again.

Petronila

 

[waross]

Hello petronila;
The problem with the 500 volt motors is not a big one. You may use two small transformers in open delta autotransformer boost service to power the 500 volt motors.
A 480v:120V transformer connected as an autotransformer will give you 575 volts. This is within 5% of rated voltage.
To size the transformers the 120 volt winding must have an ampacity sufficient for the motor full load current. If you can find a 480:120 volt or a 460:115 volt transformer with 5% taps you will be able to get the voltage exact.
We once serviced a plant with a mix of 480 volts and 600 volts. There was also a mix of 460 volt motors and 575 volt motors. It was common for a 575 volt motor to be installed on a 480 volt circuit and a 480 volt motor on a 600 volt circuit. We had pairs of small transformers all over the plant adjusting voltages. Only two transformers per motor are needed. Two transformers may also supply a panel feeding several 500/600 volt motors.
Also, although 460 volts is the standard motor voltage in North America, the standard system voltage is 480 volts and 460 volt rated motors are commonly used on 480 volt systems. You may verify this on the NEMA web site. You may want to consider using 480 volts rather than 460 volts. This will give you a little extra performance from the 380 volt motors and full voltage for the 500/600 volt motors.
respectfully