https://edis.ifas.ufl.edu/ae019 by:

Stray Voltages In Dairies 1

R.A. Bucklin, M.T. Talbot, W.J. Becker and D.R. Bray2

A stray electrical current passing through a cow's body may cause reduced milk production and health problems. The electrical current can be caused by poor or faulty wiring, faulty equipment, improper grounding, or originate off the farm and be introduced through the grounded neutral wiring network. Stray voltages are usually low alternating current voltages on the grounded neutral wires of the farm wiring system. Power suppliers may use the terms neutral-to ground voltage and neutral-to earth voltage to refer to the problem. Lost milk production and the costs for treatment of the cow's health problems can lead to substantial losses for dairymen.

• Cows often hesitate to enter the parlor. They may stampede or rush out of the parlor when released.

• Cows often dance or step around constantly while in the milking parlor. Nervousness can also be caused by other sources such as malfunctioning milking equipment or rough handling.

• Normal milk letdown is interrupted, thus requiring more time for milking and machine stripping. This adds more time and money into the production process.

• Udder irritation can be caused by incomplete milkout, which increases the incidence of mastitis.

• If cows are exposed to stray voltages while eating, they will be reluctant to eat and feed intake will be reduced.

• Stray voltages may enter the parlor through the water supply or metal drinking cups. Animals will hesitate to drink and may lap the water. Each of these symptoms is associated with stress, reduced nutrient intake or disease. All of these will cause a drop in milk production.

• my Case/several Energy Audits 50kW and 80 kW PV Plants checked:(240VAC/400VAC) system Single Phase inverters been used 2010"

• I was forwarded from Plant Owner to the next Plant Owner with "similar problems"

    - Showers were introduced for the cows , to cool down in a dessert  environment/ reaching up to 50 degrees C outside for several months-

  Cows were standing towards wind in the shelter after showering, some areas not been occupied , mostly next to Earthing Points and Steel columns.

After the Energy Audit I could pinpoint the areas with the least and the most earth leakage currents - sure enough the cows were standing away from the severly "high earth leakage points" after the installation of the PV system.

Some of the "most liked spots before" were not been occupied anymore , from the cows - the owner was thinkin of removing the whole PV Systems as he thought the reason for the stress on the cows was "PV related".

In actual fact it was a combination of "Loss of the Main Earthing Point" of the House Installation and stray currents without / One common Earthing Point...

After the Remedy took place the places were occupied once again and production from PV System increased , stray currents "disappeared".

Step Voltage with "wet feet " - only 1 Volt is enough to feel it  , OHM s LAW            1 V/1 O = 1 A ( assuming a body resistance of 1000 Ohm normally can be reduced once wet towards 1 Ohm only )

• The PV System was unusually for that area producing with similar equipment (inverter/module/Angles/East_West Roof) 10-15% less production in kWh/kWp installed 50kW small holding or/and 80kW
• First of All there was no Bonding in between Roof/Earthing - Earthing Rod- Grid Earth at the incoming line - resolved / day 1
• 5 core cabling introduced , no combined PEN anymore TN C S from DB Board towards PV Plant
• Immediate recovery of  +10% in production
• + side effect Monitoring system had no data losses anymore ; due to leakage currents inside datacabling of 600- 800 mA !!! went down to ZERO or less than 5 mA
• Second Earthing of inverter were introduced ( transformerless inverters) with less than 10mm wired / in here it was 5x6 mm 
• Inverters upgraded towards 5 x 10mm way better Impedance and Earth loop 
• Voltage AC side went down during production significantly before 250- 252 VAC now "in full swing " stays at 245 VAC max , before it triggered at Noon several times to shut down the inverter ( stops at 255 VAC )
• Other inverters "see" a brownout and reduce production or search unnecessarily new MPPT settings several times a day - production losses
• The high resistance and the Earth loop as well Impedance triggered every day several inverters - always different ones to shut down during production / peak time
• No frequency fluctuation anymore ~ roughly at 49,95 Hz at production, before it was floating in between 49,9 - 50 Hz sometimes "triggering" to shut down the inverter several times a day -> loss of production 1-3 hrs a day ( worst case ) some days just for measuring cycle 180 sec. off

Remedies as explained are :

Isolating Transformers

Upgrade of wiring , not the Phase but rather Neutral should be thought of

3 1/2 wiring should never be used for inverters 

Bonding of several independent Earthing structures ( at one point only ) 

Check cabling and Earth Loop , as well in LV the Impedance "How far away is the Transformer" to avoid High Voltage 250 VAC and above , in one case during Noon I could measure 258 VAC - which will damage installed equipment on side like compressor units , light bulbs or computer equipment - just because the cabling was not well designed upfront

All in All a + 15 % in kWh/kWp was achieved after the investigation on site.

No modules needed to be replaced or inverters , later one I heard that 3 inverters were changed already / the cause was the "shutdown and less production " of the PV Plant, as well 1 string was tested with new modules.

Needless to say :

As this "phenomena" was selfmade the "cure" didn t work at All