Off grid Generator Imbalance

Industrial Toys · Apr 1, 2015

This is certainly not a straight forward situation with the inverters and all. What happened to draw attention to this imbalance? No matter what, I am still thinking that the output winding resistances should be closer in tolerence to each other.

As far as some other discussion here. The same guy that told be about the use of a transformer insisted that one should never switch a neutral. If the neutral switch fails in a split 110/220 system you get all those bad things happening tht have been mentioned in thee forums before. Lots of potential damage! Yet a friend who installed hundreds if not thousands of commercial inverters say they switch neutrals all the time in transfer switches, and their stuff gets inspected by the electrical authority. So I am a little confused on this one issue.

buickanddeere · Apr 1, 2015

Because floating generators don't switch the neutral in a transfer switch. A bonded generator is supposed to switch the neutral.

https://cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf

SPIKER · Apr 1, 2015

sodamo said:
...
Generator measurements

Resistance
Gen stopped, Outback or any other loads disconnected, Breakers off
Measured with Fluke 117
Measured at top of alternator, where windings connect to output
L1 / L2 - 1.0
L1 /N, - .7 (u5 winding)
L2/N, - .5 (w5 winding)



L2/N, - .5 (w5 winding)
L1/Earth - OL
L2/Earth - OL
 

L1/Gen case - OL
L2/Gen case - OL


N/Earth - OL
N/Gen case - 1.0

Note: no physical ground between system and generator
Earth is cable to bolt on engine block
Case is cable connected to bolt on rear of alternator
READINGS HAD TENDENCY TO FLUCTUATE BUT SEEMED TO SETTLE ABOUT 15 SECONDS

Voltage
Gen running, Outback or any other loads DISCONNECTED, Breakers OFF
On DSE7220 screen:
L1/L2 v- 232
L1-N - 115
L2 - N - 115

At alternator
L1 / L2 - 232
L1 /N - 116
L2/N - 116
L1/Earth - 109
L2/Earth - 116

N/Earth - 15.8


Voltage (AC on Fluke)
Gen running, Outback CONNECTED, Breaker ON
On DSE7220 screen:
L1-N - 110
L2 - N - 120

At alternator & MAIN BREAKER
L1 / L2 - 232
L1 /N - 111
L2/N - 121
L1/Earth - 110
L2/Earth - 120
N/Earth - 13.8

Maybe this is insightful?
David

David:

The N to GND (PE) is shown OPEN (no connection on the Generator when disconnected) which on most commercial generators is normally bonded at the source (N and PE bonded inside the Breaker Box or Main Connections.) If the Generator sets on a pad mounted then it should be bonded to a rod at the pad & to wire/rebar in the pad if concrete pour. That assures anyone working on the generator kneeling on the pad is protected via the bonding PE frame to ground.

Then with the Generator Connected you show 15 volts between N and PE/Ground which means you panel bond in the main panel in your home has a resistance that is high. There SHOULD be little to no voltage difference between your N and PE/Bond screw is rusted or missing. There should be a green screw in the N Bar inside the main breaker box. You should make sure all power is off and then pull the cover and remove clean & reinstall that bonding screw. You should also check ALL of the connections in the plugs and wires to make sure those are set tight and not corroded.

The resistance inside the L1 and L2 points to N are not too concerning as the voltages are OK between L & N.

Mark

grsthegreat · Apr 2, 2015

One final mix in the pot. Under 2014 NEC codes, if the neutral in a transfer switch ISNT switched, you are NOT supposed to set a ground rod at the generator.

In previous codes, all fixed generators reguardless were grounded. With this code change, you dont any longer. Generac has even eliminated the external ground point

buickanddeere · Apr 2, 2015

SPIKER said:
David:

The N to GND (PE) is shown OPEN (no connection on the Generator when disconnected) which on most commercial generators is normally bonded at the source (N and PE bonded inside the Breaker Box or Main Connections.) If the Generator sets on a pad mounted then it should be bonded to a rod at the pad & to wire/rebar in the pad if concrete pour. That assures anyone working on the generator kneeling on the pad is protected via the bonding PE frame to ground.

Then with the Generator Connected you show 15 volts between N and PE/Ground which means you panel bond in the main panel in your home has a resistance that is high. There SHOULD be little to no voltage difference between your N and PE/Bond screw is rusted or missing. There should be a green screw in the N Bar inside the main breaker box. You should make sure all power is off and then pull the cover and remove clean & reinstall that bonding screw. You should also check ALL of the connections in the plugs and wires to make sure those are set tight and not corroded.

The resistance inside the L1 and L2 points to N are not too concerning as the voltages are OK between L & N.

Mark

The 15 volts between ground/earth and neutral is because something is miss wired and neutral current is flowing in the ground system.
The neutral to earth bond must be open at the generator.
The generator chassis must be grounded .
The main distribution is the ONLY place where the ground is bonded to the neutral . The reason is only to keep the neutral and the live lines from floating above 0 and 120V true earth.
It appears that the distinction is not being made or an understanding of want the ground system and the neutral systems are and what they do.

sodamo · Apr 2, 2015

Thanks guys, back to investigating.

David Sent from my iPad Air using TractorByNet

SPIKER · Apr 4, 2015

David:

because you are using separately derived systems you need to read up on the grounding and neutral bonding methods for "Separately Derived Systems."

The Neutral and Bond in them are often made at transfer switches and not at the other locations. Generators are often wired for on board 120v plugs and as such are wired with Neutral and Ground (PE) bonded at them. The Solar system and different Generators all need to be done (wired) the same way.

Grounding and Bonding of Separately Derived Systems | Code Basics content from Electrical Construction & Maintenance (EC&M) Magazine

Having all the different methods of connection means you may have to bond at transfer switch rather than at main panel in the home with the Neutral being disconnected.

Again having a voltage reading greater than a volt or two between the Neutral and Ground (ANYWHERE) in the system means the main bonding bolt is not making a good connection.

I think you stated that there was no connection to the Neutral when the transfer switch is thrown means you are disconnecting the neutral so that points to it being wired as above "Separately Derived System."

Under some cases having a grounding electrode at the generator is needed it all depends on how the system is wired, number of wires and how far away it is located or if in a different building.
With PV panels in system the DC to AC inverters also need to be watched for proper grounding electrodes/wires and or distances from PEs. There may be a need for multiple ground rods all bonded with copper together to achieve proper PE connections (earth material moisture etc all makes a location dependent.)

M

sodamo · Apr 23, 2015

After fairly extensive load testing using heater elements as only load and directly connected to generator and seeing L1 vs L2 imbalance in all variations, took a deep breath and rewired the alternator from parallel zig zag to double delta. I think my electrician friend was impressed

So far all loads, initially the direct connect heater elements and eventually the house via Outback including 4 240v pumps, and L1-L2 were pretty balanced both voltage and amperage. So at this point, cautiously declaring success

Even ran the microwave oven without an error popping up.

Now to find someone with diesel injector pump governor experience to see if we can solve the run on situation.

David Sent from my iPad Air using TractorByNet