Generator ATS transitions

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John120/240

Senior Member
Location
Olathe, Kansas
Joethemechanic, this might not apply but: with locomotives they use dynamic braking.

Going downhill switch off the generator, the resistance of the traction motors turning creates

electricity which is disspated in a dynamic brake grid. I'm sure there is a better explanition.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
Joethemechanic, this might not apply but: with locomotives they use dynamic braking.

Going downhill switch off the generator, the resistance of the traction motors turning creates

electricity which is disspated in a dynamic brake grid. I'm sure there is a better explanition.

Yeah but aren't most diesel electric locomotive systems DC? I know all the switchers I've worked on were DC
 

hurk27

Senior Member
Sorry I haven't responded in the last few days, been fighting a very bad head and chest cold and had a very fuzzy mind every time I have enough energy to log on, and that the Owner/Boss of the company I have worked for over 26 years till June of 2010 and who was a very close friend had passed way on Monday night, so it's been a lot to deal with.

I have thought about this a bit, I think I see where my thinking went wrong, as I was thinking for some crazy reason (must have been the cold) that you could never have over 60? out of phase with a 3-phase motor, but that was totally wrong as we must treat each set of poles as a single phase as they will always be connected between the same phases, and in fact can be 180? out of phase from source when the motor acts as a generator, it is when the motor is acting as a motor load that it can only be 60? out since it is only the slippage between the armature and the field poles that will cause the motor to speed up or slow down to return to sync. while I have had several systems that used a jog off to sync conveyors to keep the product from being pulled apart on production systems that didn't have a servo system to sync the conveyors, it never was a problem mostly because of no capacitors and long circuit runs limiting current to a level that didn't trip the OCPD's.

Well does this sound right? still a little fuzzy.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
I've built induction generators, I was a kid growing up around a repair shop, with a whole salvage yard full of parts to use. I used an old 5 HP 3600 rpm 3 phase motor and a Briggs & Stratton model 19 I took off of an old paving roller. I belt drove it about 125% overdrive so I could get the motor to spin at it's syncroness speed + the slip.

It put out nothing until I added some caps that I salvaged from some old high bay fixtures. ...

Joe - Your experment is fascinating. I've been around only a few induction alternators - all were connected to an external grid. I've never seen one driving into a load with no external source to stabilize the frequency. And since you actually have done this, seen this, I've got a few questions.

Here's my limited knowledge on induction alternators:
As mentioned earlier (by yourself and others): To act as an induction alternator, an induction motor requires reactive power, roughly the same as would be required to supply magnetizing current for operation as an induction motor. The reactive power is either supplied by an external source (such as the utility or a parallel synchronous generator) or can be supplied by capacitors.

In order for an induction alternator to generate, the rotor has to be turning faster than synchronous speed. It has to have slip - for a power output roughly equal to motor nameplate horsepower the slip would have to be about 5%. A two pole motor would have to turn about 3800rpm if it were driving into a 60hz grid.

If I am good up until now, here's my questions:
1. If the induction alternator is driving into a load, (no grid) what provides the 60hz for the alternator to slip against?

2. When you did this experiment were you connected to a load? Or were you just measuring the voltage output open circuit (open circuit except for the caps)?

3. Probably no chance you had a frequency meter connected - did you? I can't figure out how the alternator picked out what the output frequency would be. Induction motors don't have any inherent synchronous speed. A two pole, 60hz, 3450rpm motor is plenty happy at 30hz and 1750rpm.

I start looking at Torque-Speed curves, slip ratios, power output, voltage, current and it really gets confusing - Especially with no grid to stabilize the voltage or frequency.

Any insight you could throw my way will be graciously appreciated.

ice
 

jrvazzer

Member
generator tap box

generator tap box

Can someone help me. A generator tap box is located for the purpose of bringing a Food Store to life again after a storm. So rather than renting a portable gen and runing cables all over the floor back to the main board disconnecting the mains and connecting the generator cables. This box is already connected to the main board via taps and all the genrator company have to do is plug into the tap box near the loading doc with camlocks and open the main brker and away she blows.
The question is can you connect the conductor via conduit say 100' right to the main board without a disconnect means?
The main board is rated 2500A the conductors for the generator tap box is 800A. The tap box is kirk key with the MCB at the board.
This feeder is only used when their is a power failure the rest of the time is connectd hot to the tap box.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
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