Alternator Paralleling

Both.

Actually, for alternators in parallel you should match speed, voltage, AND phase angle.

GA from me.

To OP:-

Also the "oncoming" alternator must have a tiny bit more speed, so that as the phases lock in together, some load is taken, otherwise the reverse power relay (which of course you DO have, don't you???) will drop it off immediately.

The oncoming should be in manual control, the running in auto....

Load balancing electronics are needed to keep both running in auto later, otherwise you need one in manual and one in auto, but keep a close eye on them just in case a radical load change happens....the manual alternator is usually set for 50% of the whole load and the auto one takes up the rest and readjusts to a degree for load changes.....not completely safe though without a watchkeeper......

Remember, if you synchronize out of phase, one or both alternators will be severely damaged, one may even fly through the air, mowing down anything in its path!!!!

They have "jumped" through the sides of ships before now!!!

So be warned, this is not something to do while reading instructions, you need also to see it done by a fully competent person as well......at least once, more is better.

I really have to give Andy more of a good answer on this rather than msamad since some things brought up should be pretty self evident. First who would ever think it's OK to parallel two different voltage systems or connect a single to a 3 phase system or a 50 to a 60 cycle system. If they have these thoughts then get them out of the engine room or the power plant as fast as possible. Do not pass GO. Do not collect 200 dollars.

Aboard ship, your main generators are "generally" (since there no absolute truisms) always identical in design and output for both spare parts and training-operational issues. 'Oh gee, that's how the other one is brought up but not this one."

You start it up unloaded and disconnected electrically, bring it up to speed and for a 60 cycle system that would generally be 3600 RPM or 3000RPM for 50cycle since 2 pole generators are the most common. Your governor will hold the speed once you're online. Watch your phase meter and bring them into as close phase alignment as possible. Connect your oncoming machine to the system by closing its circuit breaker. Increase its "field excitation" and decrease that of the unit you're shutting down unless you need the extra capacity and plan on running them in parallel in which case increase the oncoming units field and decrease the other till they each have about 50% capacity. The speed governors will pretty much keep them at equal loads and there are load balancing controls to keep them equally loaded. If you're taking the one offline then increase the oncoming and keep decreasing the other till it has minimal load. Then throw off its breaker. As Andy pointed out you do that at too high a load and things could go bump in the night.

Andy, I don't know if a "reverse power relay" would come into the picture. That's often more of a shore side item where if you're generating power internally and the local grid goes down you disconnect so it doesn't suck out your power, overload your generator and pop it off leaving you high and dry.

As Andy said, not a job for amateurs. Although it has been a few years since last doing it I'm pretty sure that it's got to be similar except of course now there are probably several more bells and whistles to make it more idiot proof.

We had RP Relays to knock off and alternator or generator on all the RN ships that I worked on, both on DC220v and AC440 3 Ph 60Hz, NATO standard ships.....

I must admit I only know RN equipment.......(and that was many years ago now!)

Same here as far as USN and USA Merchant Marine ships, AC and DC. There may well have been such a feature but would not really come into play except before/after dry dock when powering up or down since there would be no other power system to feed into except your own. It would also require that your one generator try to drive the other as a motor which when I think of it could happen if some body goofed up and threw the breaker and connected the idle generator. Then you could have a motoring situation of disastrous proportion to the system and a reverse power safety system would be advantageous

Absolutely correct!!

The voltage should always be the same.

RPM will affect both voltage and current output. This: http://www.plane-power.com/R1224B.htm is the solution used on twin engine aircraft with two alternators. It will keep the current and voltage in synchronization by adjusting the output to the field and make up for some RPM difference so that the alternators will load-share.

Sorry,

Did not realize this was about AC generation. My comments above apply only to DC power generation.

for parell operation the below is must

1. Phase sequence sholud be same ( for sigle phase phase alternator phase sequence is not required)

2.Sycronisation will be done for same phasing machines (both machines should be three pahse)

3. frequency should be same (here the speed is not the criteria we will get 50Hz on 1500 rpm Alternator, the same 50Hz we will get on 750 rpm Alternator also, the speed is based on the prime mover RPM, Ultimately the frequency is depending on Speed (RPM).

4.Phase angle for alternator may be required, if not the sycronisation will be done at 6 'O' clock position. If PT's are connected for voltage monitoring to the sycroscope the PT : S1,S2 connection should not be changed.Some times for new generator commissioning this will appear.Due to this Sycronisation will be done at 6 'O' Clock position.

To the best of my memory, oncoming generator slighly high, synchroscope turning clockwise (in the fast direction), and close the breaker at five to midnight.

Sounds familiar but then it has been over 30 years since actually standing there doing it. It makes sense that a slightly higher speed would be necessary since it did slow down as it accepted some load, I think I remember the phase meter was rotating slowly clockwise and the 5 to 12 rings a bell, standing there waiting for the correct moment to throw the breaker so you didn't black out the plant. I'm sure that that is probably completely automated these days. It probably amounts to "Press Start" on the screen, after it comes up to speed there's probably "Do you wish to parallel?" "Please Press Again to Confirm" Takes all the fun and excitement out of it.

That is the same way as we practised in the RN.....