Conversion of Generator from 50Hz to 60 Hz 1

[MrVictor]

Hello fellow engineer,
Are all diesel synchronous generators able to be converted from 50 Hz to 60 Hz by simply increasing the speed of the rotor. i.e. f=Np/120.
If so, what effect will this have on the stability and performance of the diesel engine (prime mover).

 

[jtkirb]

most engines are designed for a specific RPM which, of course, is directly tied to frequency. The generators are also designed for the operational frequency.

Short answer- no. Long answer- ask the engine and generator MFG if it is OK. chances are they will say no.

engine wear and oil consumption are the two factors that pop in my head right off the bat.

JTK

 

[MrVictor]

JTK,
One manufacturer's technician told me that their generators (1 Mega Watt output)were 50/60 Hz. I questioned, but was told that this is standard with all diesel generators. I am still questioning.

 

[jtkirb]

standard? hardly. I only find generators of that size to be of a specific rating. What is the engine brand? It is dual speed rated? Is the gen nameplate dual speed rated (50/60)?

I doubt it, but it may have been designed to work both ways.

JTK

 

[powerwagon75]

As previously stated, you should definitely check with the MFR of the genset in question. I know, to use MrVictors 1-megawatt example, that there are instances where the camshafts, turbos, timing, electronic programming (if any) all need to be altered to produce efficient HP at the given frequencies(rpm's). You would need to know what components on the electrical control side are compatible with 50/60 Hz operation as well (AVR, metering,etc)

 

[edison123]

Other than the severe mechanical stress, which increases at speed squared, the generator voltage will increase by 20% - enough to send the winding to an early grave.

* If you have never succeeded in anything in first attempt, you better not try skydiving. *

 

[MrVictor]

The engines were made probably made by Cummings. I will check them out more thoroughly.

 

[rmw]

I would think it highly unlikely that a gen-set mfg'r would have an engine dedicated to either 50 or 60 Hz exclusively.

That said, however, I would also doubt that they use identical engines for both applications.

Turbos, injection pumps, inter-coolers, etc may be optimized for a particular RPM based on the requirement of the generator.

While the comment of the technician might be true with respect to the "frame" size of the engine/generator, it might not be so simple as monkeying with the governor settings.

Just my thoughts.

rmw

 

[MrVictor]

Thanks for your input fellows. I decided to visit google and search for cummins diesel genset 50/60 Hz. The results revealed that there are gensets being manufactured 50/60 hz switcable. I then decided to visit

http://www.agrekko.com,

which is the website of the company that uses the gensets that I was questioning. Turns out that they are a worldwide power rental company that build their generators for 50 or 60 Hz.
Thanks again.

 

[Plantbldr]

When purchasing a 1500kW genset recently, I noticed that the generator capacity exceeded the prime mover's capacity. In short, the generator may be switchable, but as has been previously mentioned, it is worthwhile to ensure that the prime mover can handle both speeds, as well.

 

[boo1]

The drive train must also be investigated, you may find a natural frequency or oscillation problem.

 

[MrVictor]

Plantbldr, that is a valuable piece of info. I will check that.
Good to hear from the mechy (boo1).

 

[waross]

Short answer;
1> Change the governor setting.
2> Change the Underfrequency Roll-of jumper on the Automatic voltage Regulator to the right frequency.
3> Reset the voltage if required. (50Hz is usualy 110v or a multiple, and 60Hz is usually 120v or a multiple.)
4> Reset the overspeed shutdown circuit. On perkins sets this may be in an Electronic Interface Module on the side of the engine. On some sets it's part of the circuitry inside the generator control box.
Very long answer.
I have had a lot of experience with diesel generators. I was selected to be party of a field test program by F.G. Wilson some years ago when they were in the final stages of bringing a new control card for an automatic transfer switch to market.
An extreme example of engine versatility was a 4 Cylinder Lister engine used by F.G. Wilson to power a range of generators. The outputs ranged from 15KW at 50Hz/1500 R.P.M. to 25 KW at 60 Hz. 3600 R.P.M.
F.G. Wilson was at the time the world's third largest manufacture of gensets. They manufactured the Olympian line For Caterpillar.
F.G Wilson has since been purchased by Caterpillar.

The same basic engine was used at 1500 R.P.M. for 50Hz.
It was used at 1800 R.P.M. for 60 Hz.
It was used at 3000 R.P.M. for 50 Hz.
It was used at 3600 R.P.M. for 60 Hz.
Same four pole alternator used for 1500 or 1800 R.P.M.
Same two pole alternator used for 3000/3600 R.P.M.
The only mechanical difference, 1500/1800 R.P.M. sets had a four weight governor. The 3000/3600 R.P.M. sets had a two weight governor.
The generator rating varied depending on service, (Standby, continous, or prime,) voltage (120/208, 220, 240) and speed.
For instance, a standby rated 4-pole set genset would use the same generator, but would have a higher output at 60 Hz.
Most F.G. Wilson Models are the same for 50Hz, or 60 Hz.
The conversion from 50Hz to 60 Hz is quite simple. Ratio 50:60 or 60:50. The current rating stays the same. Current causes heat and is one of the limiting factors. The voltage in an iron core winding (Motor, transformer, generator) may be increased in direct proportion to the frequency without flux saturation.
A 10 HP motor at 50 Hz becomes a 12 HP motor at 60 HZ.
10 x (60/50). The voltage may be safely increased from 220 to [220 x (60/50) = 264],- Quite safe at 240 volts.
As well as resetting the speed, you will probably have to change a jumper on the Automatic Voltage Regulator to configure the Underfrequency Roll-Off from 50Hz. to 60 Hz.
As to the voltage jumping 20% the voltage will stay at whatever the voltage regulator is set for. If you going from European settings to North American settings, you will probably want to increase it a little. 110 volts to 120 volts.
Most of my parts come direct from the UK. I usually have to change the jumper from 50Hz to 60 Hz., and reset the voltage.
If you run at 50 Hz with the UFR set for 60 Hz., the voltage will be unstable.
If you run at 60 Hz with the UFR set at 50 Hz you will not have the full benefit of the UFR circuit. In the event that an over-load slows the engine more than about 2 Hz below rated frequency, the Under Frequency Roll-off starts to shed the load by dropping the voltage. This gives the genset a better chance to recover. Most often comes into play starting large air conditioners in residential applications.
Another big advantage of UFR is that you could safely run the engine slowly without burning out the regulator. Diesel gensets used to have a switch to turn off the voltage regulator before stopping the set. If the set was run slowly for instance to check the valve clearances, the voltage regulator would quickly burn out. Every time the set was stopped or started with the regulator turned on, was a strain on the regulator. The advent of UFR regulators put an end to regulator burnout at low frequency.
Re the comments about natural frequency. Good point. Actually the first natural frequency is a few hundred RPM and affects both 50Hz and 60 Hz sets equally. I've never measured the actual speed but I've seen it hundreds of times. The sets usually start and accellerate through the critical speed so quickly that it isn't noticable, but when the set is coasting to a stop, as it passes the critical speed it will roll from side to side a few times. You better have enough play in the exhaust connection to "take the shake."
The second natural frequency of vibration is much higher than 1800 RPM and is not an issue.
I have rerated 50 Hz motors from Italy to 60 Hz for use in a Canadian Placer mine. I have rerated 60 Hz motors to 50Hz for use in a sawmill in Chile.
Current the same. Torque the same. Speed changes in the ratio of 50:60. Speed times torque equals Horse Power.
Higher frequenbcy allows higher voltage. Also, North American motors wil accept 15% over voltage Or 15% under voltage.
Standard motor voltages in North America are multiples of 115 volts. (Standard supply voltages are multiples of 120 volts)
That means that a 230 volt motor will work on anything from 197 volts to 264 volts.
If you look at the name plate of a commercial refrigeration compressor you will probably see "Min. Volts 197"
"Max. Volts 264"
460 volt motors work well on 416 volts, 440 volts or 480 volts.
575 volt motors work on 550 volts or 600 volts.

 

[MrVictor]

Waross, Thank you for that ueful BIT of information. Nothing beats experience. The rerating of the 50Hz motor to 60 Hz with current constant does not seem possible though. Voltage changes with frequency, and therefore current should change by the same ratio in order to produce the same torque.

 

[waross]

Actually speed changes with frequency. You have to change the voltage yourself.
Motor current has two components;
Current to supply losses, most of which will increase with increased voltage, and Current to supply usefull work which will decrease with rising current.
That is why motors run hotter on low voltage. With less volts, the motor has to draw more amps to produce the same watts of work.
Torque is related to current, not voltage or frequency. The same current will produce the same torque on 50 Hz or 60 Hz.

I don't know if I can share insider information here, but here goes.
When we re-rate from 50 Hz to 60 Hz. we use a ratio of 50:60.
This is correct for horsepower, because the same torque times higher RPM equalls more Horse Power.
However the voltage ratio is not 50:60, but 110:120, or 55:60.
Remember the statement, "Also, North American motors wil accept 15% over voltage Or 15% under voltage."? We have just fudged some of that tolerance for the voltage rating, but we will never say so.
Is this serious? Considering what Mother nature can do with the ambient on a motor from winter in the North to Summer in the South, I don't think so.

 

[itsmoked]

waross you want to correct your statement 2nd parragraph?

 

[waross]

itsmoked
Thank you for the heads up.
Yes I do want to correct my statment.
"Current to supply losses, most of which will increase with increased voltage, and Current to supply usefull work which will decrease with rising CURRENT."
Should read;
"Current to supply losses, most of which will increase with increased voltage, and Current to supply usefull work which will decrease with rising VOLTAGE."
Sorry