Hi,
We have new ongoing project in our plant to upgrade the power by adding 2 frame5 generators to the network. Hence, the new generators are designed with 4 poles, 1500RPM. Whereby, the existing generators are designed with 2 poles , 3000 RPM. The frequency is maintained to 50Hz.
Can someone explains the benefits of increasing the number poles from 2 to 4?
Why the manufacturer didn't design like to like generator?
Will that change have negative impact to our network?

 

A 4-pole generator operates at half the speed of a 2-pole as you noted.
It allows the engine driving the generator to operate at a slower speed for quieter operation and longer life.
It does, however, require the engine to be physically larger for the same power output.

There is no change on the output waveform or impact on the network (as long as the two generator's outputs are synchronized).

 

the four pole generators run at lower rpm, its easier to ballance out vibration at lower rpm, and bearings will last longer. you will have to reduce speed to use the new generators, by reduction gears, belsts, or other means.

 

It works out this way:

(1) Changing Engine Speed to Vary Output FrequencyPresent-day generators consist of an engine directly connected to an alternator to produce electricity. One of the most common ways of changing the output frequency of a generator is to change the rotation speed of the engine.


The two factors are related as per the following formula –
Generator Frequency (f) = Number of revolutions per minute of the engine (N) * Number of magnetic poles (P) / 120
Conversely, P = 120*f/N


As per the above formula, a 2-pole generator producing an output frequency of 60 Hz has an engine speed of 3,600 rpm. To change the output frequency to 60 Hz for the same generator configuration, the engine speed needs to be reduced to 3,000 rpm. Similarly, for a 4-pole generator, an engine speed of 1,800 rpm produces output of 60 Hz. Reducing the engine speed to 1,500 rpm yields an output of 50 Hz.

In the case of small or residential generators, you can alter the engine rpm settings by making a few changes on the control panel of your unit. Follow the steps given below to alter your generator frequency from 60 Hz to 50 Hz:
(a) Run your generator engine and tune the frequency meter on your control panel to read 50 Hz.
(b) Check the AC voltmeter or potentiometer as the case may be and read the voltage output of the generator. The output voltage decreases as you reduce the frequency and may be lower than the desired value.
(c) Adjust the AC voltmeter or potentiometer on your control panel till you obtain the desired output voltage at 50 Hz.
(d) By making similar modifications on the control panel, you can increase the frequency from 50 Hz to 60 Hz.
(e) If the control panel does not display the frequency, you will need to first connect a device that will measure the frequency while the generator is in operation and then change the engine rpm.


Generator controller units undertake real-time monitoring and control of your unit. Built-in protective functions automatically shut down your generator in the case of excess engine rpm or very low output frequency. For additional information on the functionality of a generator please read the following article, How Generators Work.

Here in the US where 60 Hz is the mains power frequency my little 4,000 watt gasoline powered generator runs at 3600 RPM and is obviously a 2 pole generator, were I in a country with 50 Hz. mains it would run at 3,000 RPM. Rather than using gasoline if a diesel fuel engine were used diesel engines generally run at much slower engine speeds so the same generator using a diesel engine would likely be a 4 pole generator running at 1800 RPM here in the US. The horsepower of my engine is 8 HP (I think) and regardless of engine speed the amount of HP required to generate my 4,000 watts will remain the same.

The above quote was taken from here.

Ron

 

Thanks gents,

Do you think synchronizing the existing generator "3000rpm" with the new generator "1500rpm" will be a problem?
Note the frequency is 50Hz in both cases.

 

50 Hz is 50 Hz. no diff. in syncing them

 

Do you think synchronizing the existing generator "3000rpm" with the new generator "1500rpm" will be a problem?
Note the frequency is 50Hz in both cases.

Do you have a method for syncing them?

 

Yep, through Synch Panel.

 

Do you have a method for syncing them?

That would be my question? Sync does not just mean the frequency, it means to me each generators output is 50 Hz (in your case) and they are synchronized in phase as well as the same exact voltage out. Doing this is not an easy task and for small generators just about impossible. If I have a 4 KW generator and my needs grow to 8 KW the best solution is not to add another 4 KW generator unless each is kept isllated, the best solution is to remove and replace the 4 KW generator with an 8 KW generator.

Ron