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watdefak
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Paralleling Generators

10/21/2007 12:03 AM

Lets assume that we have one main Gen supplying a power grid with AC power. Somehow we need to parallel another Gen to the grid. Now, how would I do this without interrupting the power supply from the main Gen ?

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MarkTheHandyman
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#1

Re: Paralleling Generators

10/21/2007 3:47 AM

Your question is self-answering. If you are using a paralleling system, it will match the output of the two generators before you bring on the second, and since the two will be producing the exact same output, there will be no lag to cause any problems.

You have two choices:

1. Stay away from the thing until somebody who knows how to use it can show you how to operate it. (Highly recommended --even if you are impersonating an operating engineer who is already supposed to know all this [see #2]).

2. Read and memorize the manual, then refer to it constantly as you carefully do you your first few paralleling procedures. No operating engineer will fault you for doing that when you are unfamiliar with a new system, even if you are supposed to know what you are doing. And if you don't ask any questions that might give you away, you can probably get somebody to show you an unfamiliar system by just casually asking them for the manual and to give you a personal once-over review of it.

Try to not blow anything up! Those systems are kind of expensive.

Mark
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inayat hussain
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Join Date: Oct 2007
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#2

Re: Paralleling Generators

10/21/2007 6:51 AM

Simply by connecting existing bus bar with the new genertor through auto circuit breaker, the purpose can be achieved.

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Abbas
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#3

Re: Paralleling Generators

10/21/2007 8:00 AM

You should check at least the following before paralleling of new Generator and the existing one:

- Output voltage and frequency values shall be equal at the moment of paralleling

- synchronization shall be checked at the moment of paralleling

- System and switchgear shall be checked for increased short circuit value due to paralleling of two generator sets

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inayat hussain
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#4
In reply to #3

Re: Paralleling Generators

10/21/2007 8:27 AM

The question was the parallel operation of generator without disconnecting the originally installed generator; of course other aspects enumerated by u would have kept in view.

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Dragonfly
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#5

Re: Paralleling Generators

10/22/2007 2:08 AM

Been there, done that! MarkTheHandyman nailed it. Follow his advice.
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nascon
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#6

Re: Paralleling Generators

10/22/2007 2:46 AM

The proposed Alternator should be selected with auto mains failure, synchronising having auto load shredding and auto load sharing with PLC
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jdretired
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#7

Re: Paralleling Generators

10/22/2007 6:13 AM

"how would I do this without interrupting the power supply from the main gen ?"

If you have a single generator on line and a second generator is synchronised, when the seconded generator is matched to the system, cycles and voltage, and the CD closed at the correct position in the cycle, it will take a part of the load off the first generator, this will also effect system speed and voltage, Governor setting will then dictate which generator takes what load, it will then be necessary to adjust the governors to share load between them, for example you can not load up the second generator with out reducing the load on the first generator ( Governor setting), the reason as previously stated is the system speed or cycles.

Regards JD.

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Anonymous Poster
#8

Re: Paralleling Generators

10/22/2007 9:30 AM

Parall? simply hooking them together is counter productive, They must be syncronized to the same sine wave or they won't work. This can be achieved by using an SCR and using the main as your trigger. However to achieve maximum power it would be best to convert secondary to DC via a full wave bridge. in other words it will take a lot of thinking, which some of us are not known for!

Jay
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Garthh
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#9

Re: Paralleling Generators

10/22/2007 5:41 PM

Use the search function this question has been dealt with comprehensively in the past!
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olivinak
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#10

Re: Paralleling Generators

10/22/2007 6:19 PM

It's all about the synchro checks, if you have dat then u syncronise your genset but it also depends on what's the prime mover.For diseil gen set you will need one to lead (master) and the other to be the slave in that if the load reaches a certain percentage the slave will automatically come onto the system also a load sharing unit is necessary. For the hydro-type for example its all about the synchronism and its better you have electronic governors as they will affect the runnig gen less.

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jdretired
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#11

Re: Paralleling Generators

10/22/2007 8:24 PM

Synchronising alternators with incandescent lamps.

Voltage for synchronising purpose can be checked by connecting a voltmeter to each machine in turn. But this does not give any indication of polarities or phase relationships. Incandescent lamps can be used to indicate this as in the circuit shown above.

The voltage rating of the lamps needs to be twice the alternator phase voltage, and the simplest way to achieve this is to connect two lamps of equal wattage in series. The lamps can be observed as three pairs of lamps or three can be covered, leaving only three visible.

If the alternator is properly connected, the three lamps should all become bright and dim simultaneously. If they brighten and dim in sequence, it means that the phase rotation of the alternator is opposite to that on the distribution system, so the phase rotation of the incoming alternator must be reversed.

The lamps flicker at a rate equal to the difference in frequency between that of the incoming alternator and the bus bar leading to the distribution system. As the alternator frequency approaches that of the bus bar, the rate of flicker slows down, when the two frequencies are equal, the flicker stops. When the lamps are out (dark) the connecting switch can be closed and the two machines will remain synchronised. When all the lamps are dark, there is no potential across the lamps, indicating that the two voltages are in phase with each other.

The disadvantage of this connection is that the lamps can be dark even with a 'small' voltage across them. With smaller alternators the two a.c. sources can synchronise themselves if the difference is not too great, but with larger alternators the mechanical and electrical forces create by a phase displacement between the two sources can cause considerable damage.

Is this what your after.

Regards JD.
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watdefak
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#12

Re: Paralleling Generators

10/22/2007 9:02 PM

Thanks alot JD.

Does this method work on 60 Hz ? Will the lamps not flicker too fast ? If they dont, why ?

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jdretired
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#13

Re: Paralleling Generators

10/22/2007 10:53 PM

An incandescent lamp in your home is flickering at the system Hz, and only appears to be a constant brightness, it is only when the phases are close to matching that the flickering can be distinguished, and only when the phases are in step will they go out. To sum it up, yes the light will seem to be continually on at first, and secondly the flicker is not related to the system Hz but rather the relationship between the generators. It matters not if it 50Hz or 60Hz.

Regards JD.
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Haajee
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#14

Re: Paralleling Generators

10/24/2007 4:01 PM

My reply:
Incandescent lamps are not fast to response to zero-crossings.
Neon-lamps are.

However if Diode is connected in series it will flicker @ Mains freq.
But how to confirm that diodes are connected to the correct phases & correct in polarity.

Sophisticated Electronic circuits are used for this purpose in Large UPS Systems where more than on UPS modules are used [at least 3 in redundant systems] & Mains power is supplemented by generator(s).

Just Flickering of lights, I doubt very much, can do anything but a BANG !!!

My reply: to #1

Not only Voltage level but also Phase-Synch is UTMOST requirement.
The System had already have a system of Transferring-Load on Generators.
More over if the Load-Sharing is a must.

For more read also:
Paralleling of transformers <http://globalspec.ip09.com/rd/9z1zmpivhik4ta5ahvrd7ji332j9ghv8p0364v3d658> (

&

Combining portable generator output <http://globalspec.ip09.com/rd/9z1z4o4akgbccedogn3ca55c4ivu29tpnsnh7vgo1dg>
&

Parallel Running of Two Generators <http://globalspec.ip09.com/rd/9z1zvo7amkejrh0q2hq0r49plqc6dub3snuu33qkdtg>
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Garthh
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#15
In reply to #14

Re: Paralleling Generators

10/24/2007 4:50 PM

More generator relate threads,

Haajee, you can tell when your links are proper when the text changes color

http://cr4.globalspec.com/thread/9892/Generator-synchronising

http://cr4.globalspec.com/thread/11776/AC-generator

http://cr4.globalspec.com/thread/12814

http://cr4.globalspec.com/thread/6206/Tieing-Big-Bertha-to-big-Bert-Generator-to-Generator
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Haajee
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#17
In reply to #15

Re: Paralleling Generators

10/24/2007 6:36 PM

Thanks Garthh.
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Garthh
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#18
In reply to #17

Re: Paralleling Generators

10/24/2007 8:02 PM

No worries,

you always have coherent & logical posts.
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Haajee
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#19
In reply to #18

Re: Paralleling Generators

10/25/2007 3:34 PM

Thanks & regards
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Haajee
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Posts: 1758
Good Answers: 6
#16
In reply to #14

Re: Paralleling Generators

10/24/2007 6:32 PM

Sorry I forgot to activate URLs in my post:

Thanks Mr. Garthh for pointing out

Resubmitted:

My reply:
Incandescent lamps are not fast to response to zero-crossings.
Neon-lamps are.

However if Diode is connected in series it will flicker @ Mains freq.
But how to confirm that diodes are connected to the correct phases & correct in polarity.

Sophisticated Electronic circuits are used for this purpose in Large UPS Systems where more than on UPS modules are used [at least 3 in redundant systems] & Mains power is supplemented by generator(s).

Just Flickering of lights, I doubt very much, can do anything but a BANG !!!

My reply: to #1

Not only Voltage level but also Phase-Synch is UTMOST requirement.
The System had already have a system of Transferring-Load on Generators.
More over if the Load-Sharing is a must.

For more read also:
Paralleling of transformers <http://globalspec.ip09.com/rd/9z1zmpivhik4ta5ahvrd7ji332j9ghv8p0364v3d658> (

&

Combining portable generator output <http://globalspec.ip09.com/rd/9z1z4o4akgbccedogn3ca55c4ivu29tpnsnh7vgo1dg>
&

Parallel Running of Two Generators
http://globalspec.ip09.com/rd/9z1zvo7amkejrh0q2hq0r49plqc6dub3snuu33qkdtg
Register to Reply
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Users who posted comments:

Abbas (1); Anonymous Poster (1); Dragonfly (1); Garthh (3); Haajee (4); inayat hussain (2); jdretired (3); MarkTheHandyman (1); nascon (1); olivinak (1); watdefak (1)

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