Preventing ground loops

[ktm400sx]

A dairy facility has a problem with ground loops...I guess stray voltage might be a better term. To try and eliminate these issues, is there something we can do with the ground electrode? A diode has been suggested, but I think that would also prevent the ground electrode from doing its job.....because if there was a ground fault, the diode would prevent current from flowing through the ground back up through the rod.

So I'm not sure there is anything I can do. Anyone else run into this?

 

[brian john]

Keep all neutrals from being grounded down stream from their neutral ground bond.

Megger all circuits and verify there is a high resistance between neutral and ground at all points except the service or SDS.

Verify all equipment is clear of shorts on the neutral conductor.

 

[tom baker]

Many stray voltage issues are caused by wiring issues and mistakes.
However, stray voltage commonly is due to utilites practice of mutipoint grounding of the primary neutral. There is a voltage drop along the lenght of the primary neutral causing stray voltage in the earh, no ground rods will ever make it go away.
For this reason there are special wiring methods required in dairy barns in particular a voltage graident ramp.
Check the Mike Holt Web site under this link
http://www.mikeholt.com/newslettersArchive.php?list=SV-HTML&back=newslettersCategories.php

 

[iceworm]

A dairy facility has a problem with ground loops...I guess stray voltage might be a better term. To try and eliminate these issues, is there something we can do with the ground electrode? A diode has been suggested, but I think that would also prevent the ground electrode from doing its job.....because if there was a ground fault, the diode would prevent current from flowing through the ground back up through the rod.

http://www.ronkelectrical.com/blocker.html

I'm pretty sure they are back-to-back Zeners.

I have not personally installed any of these. I've seen them installed at remote cathodic protection sites. These sites always have an elevated neutral voltage (above local ground potential - its a long ways from the substation - they're "remote", remember :roll. With the blocker installed, the local neutral is at local earth potential.

There was a thread some years back - maybe 5 years.

ice

 

[GoldDigger]

http://www.ronkelectrical.com/blocker.html
I'm pretty sure they are back-to-back Zeners.

Nope. One problem with back to back zeners is that they will end up having to carry lots of current in the event of a really poor primary neutral connection and may also fail open when they are needed to conduct for fault clearing.

The BLOCKER? is installed between the primary and secondary
neutrals of the distribution transformer. The BLOCKER? has
a very low impedance (less than .5 ohms) for a voltage level
above 12 volts. This provides the fault current path in the event
of a primary to secondary short in the distribution transformer
(with a 7,200 volt primary, the voltage drop of 12 volts across
the BLOCKER? is less than 0.2% and is, therefore, negligible).
The device operates directly on the principle of magnetic saturation
and does not depend on external controls or internal
logic signals, therefore, it reacts instantaneously, providing
immediate, continuous protection at all times.
In the normal operation of a system, the primary to second-
ary neutral voltage seldom exceeds several volts
(unless, of course, faults, poor grounds, or other problems
exist). At these voltage levels, the BLOCKER? has very high
impedance, effectively "blocking" the primary neutral voltage
and current from entering the secondary neutral circuit and
subsequently the system grounding conductors.

The idea is apparently similar to a swinging choke. The DC resistance of the blocker is small, but there is an inductance which is dependent on a ferromagnetic core. At 60 Hz that impedance is normally high, so the grounds are isolated. Once the voltage rises above a certain limit, the core saturates and the inductance effectively goes away. That keeps it from carrying current at low voltages, allowing the secondary neutral to stay at ground, while providing a low enough impedance to higher fault currents that it can provide a fault clearing path in those situations.
Very clever.

All you have to do is persuade POCO to install it.

 

[iceworm]

Nope. .

Did not know that. The only blocker I've been near was a 100a unit for marina shore power to a sailboat. it was b-t-b zeners.

ice

 

[iceworm]

One problem with back to back zeners is that they will end up having to carry lots of current in the event of a really poor primary neutral connection .

I thought that blockers were connected between the secondary CT (neutral) and the primary NG. If so, how would a poor primary connection cause high current in the blocker (that is, if the blocker were a zener)?

View attachment blocker connection.pdf

ice

 

[ptonsparky]

A dairy facility has a problem with ground loops...I guess stray voltage might be a better term. To try and eliminate these issues, is there something we can do with the ground electrode? A diode has been suggested, but I think that would also prevent the ground electrode from doing its job.....because if there was a ground fault, the diode would prevent current from flowing through the ground back up through the rod.

So I'm not sure there is anything I can do. Anyone else run into this?

One of the hardest things to do is convince the owner that most likely most of problems are from on farm.

We work with a dairy that, even though we can show him where problems are, they attempt all sorts of unorthodox solutions, vs pay to have things fixed properly. Good luck. Start with the basics as suggested. The Ronk Blocker and others should be thought about afterwards, not first.