Wye to low zig-zag on DELCO E-5399M2
Wye to low zig-zag on DELCO E-5399M2
(OP)
I purchased a rebuilt rail car genset with a 20kW/25kVA 3phase DELCO E-5399M2 (powered by a Detroit Diesel 2-71) as standby power for my home. I intended to use two lines (plus neutral) to provide 120V/208V to my split-phase 120V/240V panel through a transfer switch. I am concerned how the unbalanced load will affect the generator; therefore, I would prefer to rewire the output to single phase (zig-zag). Unfortunately, I received no documentation with the unit and when I removed the wiring panel I only viewed the four power and neutral wires coming from inside the generator outer shell. Does anyone have information on this unit that would enable me to rewire it from 3phase wye to single phase zig-zag? Thanks in advance for your assistance.






RE: Wye to low zig-zag on DELCO E-5399M2
RE: Wye to low zig-zag on DELCO E-5399M2
RE: Wye to low zig-zag on DELCO E-5399M2
If you have a single phase voltage regulator, put your load on the same lines as the voltage regulator.
It sounds as if your set has been rewound at some time and only four leads brought out.
Many of the old Delco sets used 10 lead connections and could not be reconnected for single phase.
Whether you use two phases of three phase, a zig-zag connection or a double delta connection, your KVA capacity on single phase will be 2/3 of the 3 phase capacity. The KW output will be limited by the maximum KVA.
When I say that it cannot be reconnected, I mean with the existing leads. A winding shop may be able to open the neutral star point and bring out three leads.
respectfully
RE: Wye to low zig-zag on DELCO E-5399M2
RE: Wye to low zig-zag on DELCO E-5399M2
The electric stove is slow heating but acceptable. The voltage is set for about 124/215. I have no problems, and I am probably the only one who is aware of the 208 volt connection.
I would suggest a similar voltage setting.
This is worth repeating.
Remember to take the power off the leads that supply the voltage regulator. If you don't you may experience severe voltage drops under load.
respectfully
RE: Wye to low zig-zag on DELCO E-5399M2
Mike Cole
RE: Wye to low zig-zag on DELCO E-5399M2
I always start designs of systems of this size by assuming a 100% neutral. I then only reduce the neutral if it can be justified. In this case the neutral must be 100% (or more if the load has a lot of harmonics.)
respectfully
RE: Wye to low zig-zag on DELCO E-5399M2
RE: Wye to low zig-zag on DELCO E-5399M2
However, most of your large loads will not use the neutral.
Water heater, electric stove, clothes drier, 230 volt air conditioners, will draw either no current or very little current on the neutral.
Estimate your single phase loads and compare to the size of your neutral conductor. The neutral should be large enough to support the single phase load on either line 1 or line 2.
I will be surprised if your neutral needs to be upgraded in North America.
I haven't done residential work in North America for a couple of decades now and I am not familiar with present neutral derating practices.
respectfully
RE: Wye to low zig-zag on DELCO E-5399M2
RE: Wye to low zig-zag on DELCO E-5399M2
However, in most electrical service applications the neutral size is not based on heating of the neutral but rather good voltage regulation for 120 volt loads as load balance is never perfect. You also need low enough neutral impedance so that when starting motor loads the shift in neutral voltage is not bad - too small of a neutral would cause lights on the same side of the line to dim when a motor starts and lights on the other side to brighten when a 120 volt motor starts.
Mike Cole
RE: Wye to low zig-zag on DELCO E-5399M2
RE: Wye to low zig-zag on DELCO E-5399M2
In any event, if it is sized for the unbalanced load it will still be adequate.
I think that mkteng was refering to neutral currents in a single phase installation compared to the neutral currents with two phases of a three phase system in use.
For example, if you have a resistive load of 40 amps on each leg of your main panel;
On single phase power from the utility the currents will cancel on the neutral and you will have zero current on the neutral.
When you switch the same load over to your generator, the neutral currents will not cancel but will add vectorilly and the neutral current will equal the phase or line currents.
Did I get that right, mteng?
respectfully
RE: Wye to low zig-zag on DELCO E-5399M2