Generator Syncing

Are these synchronous motors? If they are induction motors, how do you get the reactive excitation current?
Bill

Yes I believe they are synchronous motors.
Jim Rojas

It would be nice to know for sure- water pump motors are likely to be induction machines- check the nameplate data- rated speed in particular. Do they generate without the backup genset? In that case do they always operate them with no connection to the genset (no synchronising with the genset)? The capacitors may provide some of the reactive needs but how much conditioning they do is unclear and such conditioning may not actually be needed other than reactive support. More information is needed- including the capacitor rating.
By the way 700KW/month is meaningless. I assume that you mean 700KWH a month. -- Don Kelly cross out to reply

Ok. I will take a look on the nameplate tomorrow.
700KWH is correct.
Jim Rojas

Jim Rojas is in over his head. I personally will not help him get into deeper problems. He needs to hire competent help.
Bill

I stand corrected. It is an induction motor.
The info below comes from an overseas friend who help me set it up:
The motor is 3 phase. In order to reduce it to single-phase, 3 capacitors, one 70 ?F and the other 140 ?F (two 70 ?F capacitors wired in parallel) were wired in a ?C-2C? configuration, this process provides excitation. 70 ?F is on one phase, 140 ?F is on the other, and the third phase having none. We have plans to add a newer controller and a better ballast load, but this will have to wait until I return to Florida in the spring. Manually synchronizing these motors is pretty straight forward, but I would like to do it automatically when I am away. Either with an electronic circuit or even with a relays...either way it must be something any homeowner can handle without too much difficulty.
Jim Rojas

My expertise is in electronic security. This is why I am asking for some help.
Thank you
Jim Rojas

Induction motors can be used as generators, sometimes there's enough residual magnetism to get them going. I recall reading that if you load them past a certain point, the output just falls to zero and you have to start over. I've never actually tried using one for that myself though. I don't think they're very efficient generators, but they are cheap.

The county I live in has a 5KW per single motor size limit before a laundry list of special permitting, engineers drawings, and inspections are required. They do allow paralleling of motors, up to 4, as long as they are all under 5KW each. I really need 10-15KW in the summer months. Everything in my home is electric. A 10+KW motor can easily weigh in at a couple of hundred pounds, to a ton. If a motor goes bad, I want to be able to replace it easily in a day, and not rent a bobcat, and start a huge permitting issue just on motor change out.
It took me 3 years, and many letters to get the county to allow me to use water to power the motor. Once they saw that the diverted water quickly worked its way back into the water table, without any pollution, they signed off on it.
Jim Rojas

This looks like what I need.
Thank you all for your assistance.
Jim Rojas

I found this one as well...far less complicated and far less to purchase.
Jim Rojas

I sure wish there was something of that nature around me, there's no flowing water anywhere on my property though.
Can you just wire them up in parallel? Certainly connecting a large generator out of sync to the grid is disastrous, but something of this nature I would have thought would sync up on its own just by switching it in, they are motors afterall.

I am no expert. But just paralleling AC motors would probably break the armature on one or both. I can also see the motor coils frying. You can easily parallel with DC motors. But DC motors require expensive controllers and inverters which makes it alot less appealing dollar wise.
Jim Rojas

It could be a real problem if the generators were driven by something with a lot of torque and rotational mass, like a reciprocating engine, but I would think a generator in that power range driven by a small hydro turbine would not have any problems. Remember that in normal use they are abruptly connected to the AC line when used as a motor, and they spin up to speed on their own driving a load. The only difference here is that the motor is already spinning when you connect it to the grid. You certainly won't fry the coils.

What you're saying about AC synchronous generators could be true, depending on the sizes and such.
But if I understand you so far, these are really induction generators (AC induction motors driven at greater than synchronous speed). Induction generators don't 'lock' in to synch with the running supply.
The nature of induction generators can make operating them in parallel a bit tricky as well. When unloaded, the AC output is very close in frequency to the synchronous output (f= N*P/120 where N is RPM and P is number of poles). But as they are loaded, the speed must be raised if you want to maintain a constant frequency output. This is because the % slip between output frequency and rotor speed rises with load.
Because induction generators don't have their own internal excitation, you might find it easiest to connect the incoming machine by just running it at synchronous speed without any capacitors and connect it to the line. This is equivalent to connecting an induction motor across the line when it's already spinning at rated speed. No large surge currents.
After it's on the line, then connect the capacitors to provide the excitation needed.
daestrom

Thank you for the advice.
Jim Rojas

As Daestrom indicates, induction motors are easy and synchronization is not needed. However, for best operation, they should be connected to the system as the system must provide reactive (and this will be appreciable). With the system connection, the system dictates the frequency independently of the speed of the motor but, if it can't supply the needed reactive, the voltage will be low. Capacitors in parallel will help provide this reactive. Parallel operation shouldn't be a problem if there is sufficient capacity, system + capacitors to supply the reactive. In more remote parts of Scotland, induction motors have been used in that way. Daestrom's statements appear to be based on stand-alone setups and there could be problems there as you then do get into control of the sources driving the two motors to try and maintain the same frequency (if not quite the same, there will be some messy circulating currents as one motor may try to accelerate the other until they are at the same speed This may not fit the conditions imposed by the prime movers and water flow). In your case it appears that you do have a standby generator (substitute for the grid system and governed to control frequency which can provide the necessary frequency control and take care of excitation and load reactive with the assistance of parallel capacitors. How much? As a rough measure- the no load current and KVA (volt-amps) which would be near 50% of the motor rating.
In any case the more information available - the better an answer can be. For example, you don't specify how much of your load is single phase nor the rating of your backup generator. What is the maximum power load that you want to deal with? Do you run the two induction generators independently of this backup generator? If so, how well do they hold frequency? It all boils down to what you actually have and how you are using this at present.

It is intended for synchronous machines- both phase (speed of prime mover) and voltage control. On the basis of the description given- don't bother wasting your money.
You don't have either when dealing with induction motors. If you are connected to the grid, and they allow it, then you can simply open the gates to let the water run and then connect the induction machine to the grid. The amount of power produced is at grid frequency and is dependent on the "slip speed" of the machine. This also means that excess is fed back to the grid. For example, a motor rated at 10KW (input) at 5% slip (say 1710 rpm for a 60 Hz 4 pole machine) will produce something near (but under) 10KW at 1890 rpm. What you actually get is dependent on the prime mover as well as the motor/generator used. - Don Kelly cross out to reply

Yes. But your biggest problem will be throttle control. Once you figure out how to control the no load speed of a generator, a PID controller with an error frequency input will bring them into sync.
Your next problem will be voltage control, particularly if these are PM generators. The way generators are brought into sync is as follows:
Gen 1 is running and possibly under load.
Gen 2 is started unloaded and brought close to gen 1's speed. Gen 2 voltage is set to be the same as gen 1.
As the phase of the two generators slowly changes (they are not quite running at the same speed), a voltage sensing relay enables the gen 2 breaker to close when the phase difference drops below some desired level.
At this point, the gen 2 throttle setting switches from speed control to load sharing, where the generator throttles are biased up or down based on the difference between their output power and the average output power.
The generators' voltage regulators should be biased up or down based upon reactive load sharing when in parallel.