Western Electric 30KVA / Detroit Diesel 353

I have a retired Bell System generator set installed as a whole house generator. The spec # is KS20523 L-1 8 11.
It is manual start / manual transfer with a DD353 operating at 1,800 RPM. It does not have a block heater.
It has a 12 lead generator presently set up in a parallel Wye for 120/208v 3 phase power.
I am using it for single phase 120/208v and hope I am not hurting anything by having an imbalance condition with no load on L3. I'm also hoping that my 240v appliances don't kick about operating at 208v. I would prefer single phase 120/240v. I realize that either way, the usable output is then only 20 kva, but that is plenty for my needs.

I believe that I could rewire the generator output leads into a double Delta for 120/240v but some of the leads are presently monitored for control / instrumentation and I don't want to mess anything up. Is there anything I should know or avoid before making this wiring change?

Also, the operating instructions say to lower the speed to 58 cycles during cool down before shutting the engine down.
This means that I am starting a cold engine at 1,740 RPM. It seems to work fine and has probably been started this way for its entire life (50+) years, but it is always in the back of my mind that it would be better to slow the engine much more, so that it starts at a much lower speed when cold on the next run.
I don't have a tach, but I do have a frequency meter. At some point while lowering the engine speed, the meter shows 60 cycles again (maybe 900 rpm? I'm not sure). Would anything concerning the generator itself be adversely affected by lowering the engine speed during cool down and then starting the engine at the lower speed. I would not transfer the load until the engine is warmed up and brought up to 1800 rpm, but I don't know what, if anything, detrimental may happen to the excitation or output voltage during these times below 1800 rpm. Also I don't know what the optimal starting rpm should be, maybe that point where it shows 60 cycles again on the meter?

Thanks for any help. Info on these old sets is hard to come by and actually finding someone with hands-on experience is even more difficult.
 
RS. . .
Q1) When you say "no load on L3" do you mean there is no load connected between L1-L3, nor between L2-L3, nor between L3 and neutral ? In other words, only single-phase 208V load connected between L1-L2 ?

Q2) Can you provide a photo of the nameplate?
Regards, Phil Corso
 
RS. . .
Q1) When you say "no load on L3" do you mean there is no load connected between L1-L3, nor between L2-L3, nor between L3 and neutral ? In other words, only single-phase 208V load connected between L1-L2 ?

Q2) Can you provide a photo of the nameplate?
Regards, Phil Corso
Phil,
Thanks for the reply.
Correct.
The present wiring configuration is a 120/208v parallel Wye with connections at L1, L2, L3 and T0 or neutral.
Since I am using this as a backup generator for my house which has 120/240 single phase service, I am connected to L1, L2 and neutral with no connection on L3. I know that 3 phase generators should have balanced load if possible, but in this case I have no load connected to L3. that's why I'm considering changing the generator leads to a double Delta configuration.
 
Phil,
Thanks for the reply.
Correct.
The present wiring configuration is a 120/208v parallel Wye with connections at L1, L2, L3 and T0 or neutral.
Since I am using this as a backup generator for my house which has 120/240 single phase service, I am connected to L1, L2 and neutral with no connection on L3. I know that 3 phase generators should have balanced load if possible, but in this case I have no load connected to L3. that's why I'm considering changing the generator leads to a double Delta configuration.
 
RS...
Label the House Source Terminals L1h, L2h, and Nh. Then, your House's single-phase Load-voltages, that is, voltages between L1h-Nh and L2h-Nh are both 120V. The two are additive meaning the Voltage between L1h and L2h is 240V. It can be said their phasor's are 0 degrees apart.

Now label Generator Source Terminals L1g-Ng and L2g-Ng. But, their phasor's are not 0 degrees apart. Instead, they are 120 degrees apart making the Load-voltage equal to 208V between L1g-L2g, not 240V. Thus, any house-load connected between L1g and L2g would operate at 86.7% of it's nominal Voltage! Note: the 208 value is derived from 120V x Sqrt(3) !

Without knowledge of the 12-Lead tagging I can't readily determine if reconnecting the 6 coils is possible!

Phil
 
Your observed load of 12-kW exceeds the Rule-of-Thumb, i.e., a single-phase load should be limited to 30% of the 3-ph rating or 9-kW.
Furthermore, a phase-phase winding actually has 4 sub-coils in series... 2-associated with the positive and 2 with the negative stator poles!
Re-wiring for 120/240 requires access to each of the 4-sub coils ! A real messy job, worsened by the fact the slot-to-pole ratio may not be symmetrical !
 
RS...
Expanding on the Hi-Leg Xfmr approach, are you capable, or have someone capable, of re-configuring the 6-winding's, now connected as a parallel 120/208V Wye, into a 240V Delta?
Phil
 
RS...
Re-configuration involves knowing the magnitude of phase-current unbalance. It can be determined using a math-tool called "Symmetrical Components" ! The procedure reveals an undesirable parameter called "Negative-Sequence Ampere Ratio !

Short of operating the Gen-set, there are at least 2 ways to determine Negative-Sequence Amperes. One is by contacting the Mfg. The other, is with some simple components, simple instruments , and a single, isolated, phase-winding, as listed below below:

Step 1: Energize the winding with a 6-12 AC source and measure Volts & Amperes.
Step 2: Energize the winding with a 6-12 DC source and measure Volts & Amperes.

Please note... the "method" is not perfect, but it can provide a "Figure-of Merit" for at least 3 possible re-configurations, i.e., 4-lead, 8-lead, or 12-lead !

Regards, Phil Corso
 
Phil,
Thanks for the additional info.
Sorry it took me so long to reply.
To recap a bit and bring you up to speed:

I have a Bell System - AC Delco KS 20523 Gen Set.
It is rated 120/208v or 139/240v 3 phase 4 wire 30kw and was factory wired in a parallel Wye configuration. It has a 12 lead generator and all the leads have the original factory tags from T1 to T12.

Attached please find the wiring diagram that I used. The existing wiring matched the Parallel Wye diagram and the new wiring matches the Double Delta diagram.

For 20+ years I have been using this setup as a whole house standby generator to back up my single phase 120/240 residential service.
It has never had a problem, but I have always been concerned that I was unevenly loading the generator with no load on L3 and I also didn't like the idea of running my AC compressors and well pump at 208v.

So, with Covid 19 time on my hands, I decided to bite the bullet and change the generator connections to Double-Delta in order to load the generator more evenly and to derive 120/240v single phase 3 wire.

I have double checked my connections. But my voltage is now 155/311v.
Operating in Parallel Wye, the normal excitation current of 1.0 dc amps resulted in 120/208v.
The excitation current is now 2.65a and the alternator voltage rheostat will not adjust the field current.
I cleaned the rheostat and tested its function with an ohm meter.
It tests steady and linear.

I wonder if this may have to do with three CTs that had generator leads double wrapped around their exteriors?
Coil 1 had T6 and T12
Coil 2 had T5 and T11
Coil 3 had T4 and T12
These were the six leads going to T0 or N.
With the Double Delta,
I double wrapped coil 3 with T2 and T4 and coil 2 with T7 and T12 with both sets going to N.

I believe the winding connections are correct because the 155/311v that I am reading is the same ratio or proportion as 120/240, just too high.
I think the voltage regulator doesn't like seeing 0 voltage now on L3 and is raising the DC field voltage to 2.65a.

I'm pretty sure that I need to reduce the field current.
If the voltage regulator is monitoring all three phases, and I now have no voltage on L3, it might be overcompensating. I tried a jumper from L1 to L3 in the hopes that the voltage regulator would accept that, but it didn't.
I measured the voltage from the T9,T11 splice hoping for a usable voltage for L3, but the measurements are:
T9,T11 splice to L1 255v
T9,T11 splice to L2 149v
T9,T11 splice to N 149v
So that won't work.
I think I'm close, but I may need to return everything back to normal and just live with it the way it was.
 

Attachments

RP...
I don't know why, but I can't down-load your diagram. Please send it directly to [email protected]!
Are you sure the original configuration was a parallel 'Y'? And not a double-delta? Or even the Zig-Zag? Frankly, I don't a think a parallel 'Y' will be successful!
If you can obtain the phase-impedance from the gen-set's mfgr, or determine it by test (I presented it earlier), I can send you my "Negative-Sequence" calculation in Excel!
But, in the end, unless the exciter is working properly, you won't be successful!
Regards, Phil
 
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