GENERATOR QUESTIONS FOR YOU EXPERT ELECTRICIANS

[Industrial Toys]

Still trying to understand this. Much information on the Internet and Youtube but mostly people just Parroting information they heard or read about, without any real technical understanding. Just take this wire off here and attach it here to make it work, kind of thing.

So forget about the derating for a moment. How can you take two legs of a three phase generator that are 120 degrees out of phase and use them to replace a single (split) phase 120/240 winding coming out of your utility transformer? It may work, but can't be the same????

As far as the 208 vs 240 goes. I just remembered a Fiasco from last summer. I was asked to provide the controls for a hydraulic pump on a tilting table for processing bagged fire wood. The pump was 240V as ordered by a friend for the friend I was working for, and as requested by the customer, or was it an assumption?

Anyway it kept tripping out when delivered to the customer. A lot of head scratching and wasted man hours, only to discover that the customer has 208 feeding his cord ended (240V) receptical. They ended up putting in a transformer.

 

[SPYDERLK]

208 is used all the time on 220/240 systems and is of no issue. A lot of apartments I worked on were supplied 3/0 to panels knowing everyone would have 208 volts. In the 100痴 of times I致e done this in over 35 years as an electrician I have had no issues. On average the only appliances using 208/240 in a residential panel are a/c, water heater, general heating and dryers. These are not effected by 208.

even if you rewire a 6 or 12 wire 3/0 to operate as single phase, you do get a loss in overall amperage available. Then again, I may be wrong Generator Phase Conversions: Electrical Conversion, Single Phase, Three Phase Power

It does get confusing.

An electric stove is pretty anemic on 208, motors run hotter and cannot support overload as well, etc. Essentially a continuous brownout on 240 equipment.

 

[grsthegreat]

An electric stove is pretty anemic on 208, motors run hotter and cannot support overload as well, etc. Essentially a continuous brownout on 240 equipment.

Beg to differ. Ive seen apartments full of electric stoves on 308 over the years. One company I do work for is using an old electrical stove on 208 as a powder coat oven for small parts. Very hot

As for motors, I’m talking about residential applications here. For industrial motors that’s a different ballywack, Not too many Residential units have 240 motors.

 

[CobyRupert]

Our Baldor generators at work can run single phase (120/240), 3 phase power and light (120/240/208 high leg), 3 phase power (120/208), and 3 phase power (277/480). Its changed via a switch and hooking up the leads at the transformer properly for the voltage required.

How can you take two legs of a three phase generator that are 120 degrees out of phase and use them to replace a single (split) phase 120/240 winding coming out of your utility transformer? It may work, but can't be the same????

Most of the time you can't. Most configurations will get you 120/208V.
As you probably know:
(3)-120V windings connected in a STAR (WYE (Y)) configuration give 3 phase 208V, and any 1 phase to neutral (center of the 'Y') is 120V.

HickoryFarm (above) indicates a generator that can give "3 phase power and light (120/240/208 high leg)".
This suggests a (3) 240V windings connected in a delta (triangle) configuration, where one 240V winding has a center tap (at the "120V", middle location). that gets grounded (referenced to 0 Volts).
Let's call the corners of the delta configuration (connection points of the 3 windings) phase "A", "B" and "C" and bring them to a 3 phase panel. We also bring the center tap of one winding, ground it and call that neutral. Let's say winding with center tap is between phase "A" & "B" terminals.

Voltages would be:
AB=AC=BC= 240V : 3 phase, 120 degrees out of phase with each other.
Voltage from 2 phase to neutral would be: AN = 120V; BN= 120V, 180 degrees out of phase with each other (because they're derived from one winding with a center tap, like the pole mounted 120/240V transformer).
The voltage from (Wild Leg/high leg) C to neutral: CN = 208V (1 phase).

Remember CN= 208V this way: 3 phases 120 degrees apart, connected in a delta (triangle) configuration. Draw a equilateral triangle where each side is 240V "long". 1/2 way (center tap) between corners "A" & "B" (at the 120V mark) call this "N". Draw a line from opposite corner "C" to "N". We now have a right angle triangle that we know 2 sides of (AN = 120V, AC = 240V, thus (Pythagoras of Samos (c. 570 c. 495 BC) says: ) CN MUST be 208V.

 

[Industrial Toys]

Thanks. I have to draw that out. But how much of the total rated power can you draw, single phase?

 

[CobyRupert]

Thanks. I have to draw that out. But how much of the total rated power can you draw, single phase?

Same if you draw out a star/wye ("Y") configuration, where each branch (leg) of the "Y" represents a winding and is 120V "long" and 120 degrees apart. It's easy to see (and reasonably easy to calculate) geometrically that the distance from one "Y" end "leg" to another would be 207.8V (208V).

These configurations DO make sense geometrically in accordance to the shape of their names. Greek letter D (Delta) which is shaped like a triangle and Wye (Y).

Have to get back to you on total rated power

 

[Industrial Toys]

You are one of the few that certainly understands what really makes this stuff work.

 

[aczlan]

Same if you draw out a star/wye ("Y") configuration, where each branch (leg) of the "Y" represents a winding and is 120V "long" and 120 degrees apart. It's easy to see (and reasonably easy to calculate) geometrically that the distance from one "Y" end "leg" to another would be 207.8V (208V).

These configurations DO make sense geometrically in accordance to the shape of their names. Greek letter D (Delta) which is shaped like a triangle and Wye (Y).

Have to get back to you on total rated power

Here are some diagrams of the different configurations, the T1 to T12 numbers are the leads coming off of the generator head, you can see the different options depending on how you wire them:
Single phase wiring:

3 phase wiring:

Here is another thread by sewerzuk detailing how he re-wired his 3 phase MEP-004 genset to single phase: MEP-004a re-wire for single phase operation, with video - SmokStak

Aaron Z

 

[cdaigle430]

Yeah this post went haywire....to the original posters question-no. You cannot hook them together and your best bet is to sell them and get the correct size from the money you make from them plus a little extra.
3 phase is nice, efficient but expensive. Most equipment will run on 208 to 240 no problem. A proper electrician will always check the voltage to make sure the mtor they are running will work....in the example above the electrician should have paid for his mistake.

 

[Industrial Toys]

Very, very interesting. 6600 Volts on Y ?? Are those for different versions of alternators?

Figuring the effects of the phase differences into the diagrams is not something I am capable of. I'm sure Nicola Tesla could look at them and say, "sure, that will work" lol