Power at Work: How to check for and deal with stray voltage on the farm

Thursday, January 31, 2008

by RALPH WINFIELD

As I stated in an earlier article, what goes around comes around. Usually the time period is 20 to 30 years. Stray voltage is right on time.

I started hearing about this in the early 1970s when I worked as an agricultural applications engineer for Ontario Hydro. It was presumed at the time to be a greater problem in the United States, where they had many rural electrical co-operatives which did not have the quality of distribution line system we had in Ontario.

For example, in some remote rural areas, they only serviced customers with one line - the "hot line" - and all neutral current returned via the ground path. That single line system was also used in remote areas of rural Alberta, Manitoba and Saskatchewan, but never in Ontario.

By the early 1980s, it was becoming apparent that stray voltage could indeed be an issue on all rural electrical systems, but especially on long, single-phase service lines to more remote locations.

It was becoming evident that, as line loading increased, the voltage pressure to get current flow back to the initiating distribution transformer was increasing. It was that return voltage pressure which could give rise to "primary sourced" stray voltage.

To add a confounding effect, "secondary sourced" stray voltage could also be created on the farm - especially if 120-volt loads were not balanced, or nearly balanced, all the time.

In October 1984, the American Society of Agricultural Engineers sponsored a national symposium on stray voltage in Syracuse, NY. The choice of New York State was obvious. It has a high concentration of dairy farms, the primary applications where stray voltage can be of concern.

It should be noted here that the terms "stray voltage" and "tingle voltage" are often used interchangeably. Some research efforts use the word "tingle" because of the effects that stray voltage has on animals - primarily dairy animals which have to pass through milking parlours, where they can touch two metallic or wet surfaces that might be at different electrical potentials.

It was evident that dairy animals in particular will pick up the effects of voltages well below a level where we humans would even feel it. Remember that cows do not have rubber-soled shoes, stand on wet concrete slabs and frequently touch metallic items with a wet nose or tongue. Thus, dairy cows are often reported to respond to voltage differences of less than one volt.

Sources of stray voltage. As noted earlier, sources can be either "on-farm" or "off-farm." There is a tendency to blame the electrical supplier whenever stray voltage exists or is considered a problem, usually on dairy farms. But, before pointing fingers, it is absolutely critical that the property owner has confidence that the stray voltage is not created on the farm or is secondarily sourced.

On-farm causes can be unbalanced 120-volt loads at individual services which create current flow in the secondary (on-farm) neutral system. On-farm neutral current flow can also be caused by faulty wiring or faulty electrical equipment. Adding to this on-farm problem is the fact that neutral currents can come to your electrical service from a faulty neighbouring service.

It is critical to remember that all current flowing from a "distribution transformer," which can be located some kilometres from a farm, must and will flow back to that transformer. If you see a transmission line (usually towers) or a sub-transmission line serving the distribution station (usually a pole line with large insulators), you will note that a neutral wire does not exist. Those lines transmit three-phase electrical power.

It is and must be balanced by the power supplier.

When power leaves the distribution station via a number of three-phase distribution line bundles, each bundle will have a neutral conductor, always the lowest line of the four conductors on the pole.

Most rural residential or farm customers will only require single-phase power. Thus, attachment of the service transformer at the farm will only be to one of the three phases, plus that lower neutral conductor. If you look carefully you will note that your neighbour's transformer is very likely connected to a different phase than your own transformer, but to that same neutral conductor.

The power supplier will make every effort to balance the loading of the three phases. By doing so, the neutral current is kept to a minimum. However, power loading by individual customers will vary during the day and season, so getting a perfect balance is not possible.

In my case, being located on a three-phase line but only using single-phase power, my phase connection has been changed at least twice in 33 years by Ontario Hydro/Hydro One to try and maintain load balance.

Now for the greatest problem - location. As distances increase from the electrical distribution station, each of those three-phase bundles is broken down into single-phase lines with each one carrying that neutral conductor.

The neutral conductor is grounded at every transformer and service location on your farm as well as at intervals between, if long runs occur between customer services. But on these single-phase line sections, all outgoing current must return via that neutral conductor. If, for example, the neutral conductor has a corroded, high-resistance connector, neutral voltage will increase to push the current through the corroded connector or to bypass that connector by taking a ground path.

It is on these outlying single-phase service customer areas that most of the troublesome "primary source" stray voltages occur. Often, the stray voltage levels may be very low except during peak electrical use periods, such as milking times.

Measurement of neutral-to-earth (N-E) voltage should only be undertaken by knowledgeable and trained personnel. The process requires specialized test equipment and time available to determine intermittent - time of day - variations. In 1984, the rural service department of Ontario Hydro put together a "Tingle Voltage Manual" for Electrical Contractors. At the same time, the technicians of the Ontario agriculture ministry's engineering service were trained and equipped to do on-farm testing.

Corrective actions. If the primary sourced N-E voltage exceeded 10 volts, power supply personnel usually took immediate action. Some would even respond if it exceeded five volts. There was no known enforceable Canadian standard.

A variety of corrective actions were taken by the power supplier: improve load balance on three-phase feeders, improve neutral grounding, renew neutral splices or upgrade (upsize) neutral conductors.

As a last resort, the power supplier would temporarily separate the primary from the secondary on-farm neutral. This is not a safe permanent solution, but it aided in identifying the N-E voltage source.

Active suppression is also possible if the N-E voltage is coming from off or on the farm. The suppression device is located on the sensitive service. When this technique is used, all interconnected grounds between building services must be identified and cleared. The most common interconnections are metallic water pipes or sheathed telephone lines running between buildings.

After all other corrective actions to wiring, load balancing and faulty equipment have been applied on the farm, the installation of an equi-potential plane should be considered. This is most often done in milking parlours or around electrified frost-free waterers. The Ontario Electrical Code requires that equi-potential grid systems be installed in all new milking parlours, so that all metallic equipment can be bonded for electrical safety reasons. When equi-potential grids are installed, "step potential" must be considered where animals enter or exit the equi-potential grid.

Additional information. If you are convinced that you may have a problem with stray voltage and that it is transient or caused by the addition of your electrical load, then power your own service with a standby generator during peak use periods to determine if the stray voltage is reduced.

However, when you transfer power to the standby generator, do remember that the neutral connection to the electrical grid is not opened. Thus, the effect of a high primary neutral current can still occur - unless you get the power supplier to separate the neutral temporarily at your service entrance.

Lack of good grounding can occur in some areas of the province, especially in rocky areas, but this is rare in mostfarming areas.

Many beef producers and horse farms are using frost-free watering units to save energy. They are not connected to the electrical service and will not have neutral-to-earth voltage if plastic pipe is used.

Dairy operation sizes have increased very significantly in the last 20 years.

The number of 40-cow herds has decreased and is being replaced by herds of 100 or more. These farms will usually be served by upgraded hydro lines which have multiple phases to balance out the neutral currents, even if they only utilize single-phase power.
If neutral-to-earth stray voltage is a concern, suppression devices are available. They will solve the problem if properly installed and maintained, not bypassed. Electrical power suppliers have always co-operated to reduce neutral-to-earth voltages if they were at significant levels.

Can we expect the suppliers to keep all neutral-to-earth voltages at all service locations below 0.5 volts or even 2.0 volts? I don't think that is a practical or realistic expectation. The cost would be horrendous and most of us do not require the level to be below the generally accepted level of 10 volts for personal health or safety.

In summary, to the best of my knowledge, no human being has ever suffered directly from neutral to earth or stray voltages.

There was a time when people looked under high-voltage transmission lines which crossed farms and concluded that the "electric magnetic fields" (EMF) were affecting crop growth as crops were stunted under the lines. Well, it was soon established that the poor crop growth was due to soil compaction during line construction. It took many years to get that message out and accepted. Some people even believed that the presence of the EMF must be affecting cattle and humans. The only effect on humans was visual pollution and the frustration of TV signal interference.

Before we blame any EMFs from hydro lines for human health problems, we should be considering the possible effects of all the high-frequency communication signals which constantly surround us. Most of us now have more than one cell phone and multiple global positioning signals (GPS) in our homes, cars, trucks, tractors and combines. Remember, the signals are present even if you don't use them!

Instant communications and automatic steering of tractors are great high-tech achievements, but are we ultimately going to pay a higher price than we ever did for controllable stray voltage of a few volts?

For further information on stray voltage, please request a copy of: "Study of the Causes, Symptoms, Effects, Detection and Control of Stray Voltages in Barns" by R. G. Winfield and J. A. Munroe. It is an October 1986 research report 1-798 from the Engineering and Statistical Research Centre of Agriculture Canada in Ottawa. BF

Agricultural engineer Ralph Winfield farms at Belmont in Elgin County.