Some of those called in to help estimate up to 90% of farmers can have problems when installing a new electronic identification system, because wiring on existing equipment may not have been put in place correctly or a minor interference problem that was already there causes much more trouble as more sophisticated and updated gadgetry is added.
This can leave farmers frustrated and out of pocket as they struggle to find a solution to their particular issue or, more often than not, multiple issues. They don’t see the efficiencies they’ve been promised, resulting in some of the more extreme cases in farmers being advised to move to a different herd tagging system at considerable cost.
So what’s the problem, or perhaps more importantly, what isn’t the problem?
Stray voltage is where a small voltage might be present between two conductive surfaces that could be simultaneously contacted by the cow (Dairy Exporter, May 2014, page 116).
“There are well-understood reasons as to the cause and remedy of these voltages, with cow behaviour being altered at lower current levels moving on to involuntary muscle spasms at higher currents,” Craig Burrows, director of Dairymaster Milking Systems in Stratford, said. Burrows is the New Zealand Milking and Pumping Trades Association (NZMPTA) spokesman on the issue.
Burrows said he’s put a lot of work into dispelling the myths around stray voltage, because some farmers believed it was a possible cause of mastitis, and became distracted from finding the real cause or causes.
He said the NZMPTA, which offers online stray voltage testing courses, tried to help with farmer education. More recently it had more success educating rural professionals such as milking technicians, vets, DairyNZ and electricians so information could filter down to farmers that way.
He stressed stray voltage and electromagnetic interference (EMI) were two completely different things. EMI was responsible for interference with EID systems, which he said was also a well-understood, but complex issue.
“Anyone selling EID equipment should have a full understanding of EMI and what can interfere,” he said.
But it was hard to give complete advice to farmers because something as common as the computer they used could be the cause of the problem. Electricians dealing with equipment with the potential to give off EMI should be following manufacturers’ instructions, he said.
Many people immediately thought of variable speed drives (VSDs) as the cause of EMI, but there were many other things that could cause interference. It was well-established what drives or filters were required to meet electromagnetic compliance (EMC).
“Electricians are trained in their installation, so there is no excuse for them not to be installed according to electrical code and manufacturers’ recommendation.”
Mark Empson, the owner and manager of Advanced Motor Control which has seven staff around the country, imports VSDs for a range of different industries. But he’s increasingly being called on by farmers to first find the source of their EMI problems, then install the filters his company sells.
He has published a guide to minimising EMC with VSDs which is freely available. It emphasises that VSDs approved for use in NZ must have a CTick and that industrial installations are more tolerant of EMC than domestic or dairy installations. Any need for a filter should be included with documentation that comes with the VSD.
These were generally needed for European and Asian-manufactured VSDs for domestic and sensitive installations.
Empson said it was common to find VSD installations that didn’t minimise EMI, and he believed the allowable level in the Standards NZ handbook covering dairies (see shaded box) was too high at up to one volt.
“We generally work to a voltage level of 0.3 volts to ensure no problems.”
He said he had approached both Federated Farmers and DairyNZ about the issue but they’ve declined to get involved. Eventually he believes NZ regulations
will be changed in line with those in Europe.
Burrows said there were regulatory measures in place with the Radio Communications Act 1989 and Radio Communications Regulations 2001 managed by Radio Spectrum Management, a division of the Ministry of Economic Development. Again anyone selling or installing an EID system should be aware of these and use compliant equipment.
“They should have the skills and equipment necessary to find and resolve any interference when encountered,” he said.
“I guess like with anything if the farmer is not getting results, find someone who can and do your research before you buy.”
Reaching for the standard
A new Standards NZ handbook, SNZ HB 6117:2014 Electrical installations in dairy sheds, was published in March last year. Its development was funded by Energy Safety – Worksafe NZ with the main objective of providing guidance on minimising stray voltage in dairies.
It looks at the effect on cows during milking and provides a number of recommendations including the type of supply system, general earthing arrangements in dairies, connections to electric fences, and installation of VSDs.
It was intended to provide guidance and additional information to AS/NZS 3000 Electrical installations (known as the Australian-NZ Wiring Rules), the primary standard used in the electrical industry, and is cited in the Electricity (Safety) Regulations 2010.
The handbook allows for the alternative use of the Terra-Terra (TT) earthing system, which can help reduce stray voltage. Under this system a protective earth connection is provided by a local earth electrode, and there’s another independently installed at the generator. The big advantage of the TT earthing system is that it’s clear of high-and-low frequency noises that come through the neutral wire from connected equipment. It’s used in Japan, but it can impose added requirements on VSDs that often have substantial filters passing high-frequency noise to the ground conductor.
While the TT system isn’t currently permitted by the Electricity (Safety) regulations it is being considered, and if it was approved amendments would be required to the handbook.
Representatives from the Electrical Contractors Association, Electrical Safety NZ, the Electrical Workers Registration Board, Electricity Engineers’ Association, Energy Safety – Ministry of Business, Innovation and Employment, the NZ Electrical Institute, the NZ Manufacturers and Exporters’ Association and Federated Farmers worked on the handbook. They recommended it be considered for publication as a full standard when revised in the future, but that’s unlikely to happen in the next few years unless new information comes to light.
Looking for trouble?
Brian Rickard, pictured, is a trouble-shooter who spends his time finding out where dairy farmers have electrical interference issues on their properties.
He’s an inspector technician with Electricity Ashburton Networks but through word of mouth has been called in to look at these problems all over the country on an independent basis.
He’s sent out more than 1680 reports to farmers since he started this work in the 1980s. While cow behaviour alerted farmers to stray voltage problems in the past, he said in the past few years he’d been called out more frequently to look at EMI issues which could be often traced back to VSDs.
He often finds some of components used and VSDs will comply with regulations in overseas countries.
“But they don’t comply in NZ and shouldn’t be used.”
The issue can be compounded by wholesalers selling large quantities of components for VSDs without knowing the finished piece of equipment would be used in dairies.
Some farmers’ problems can be so complex he needs to return a number of times.
“There can be some glaring great problems but they may be masking other problems as well,” he said.
The situation could be compounded by local electricians called in to fix one particular issue. They might not have been employed when wiring was previously installed so weren’t aware that by adding a new component the old wiring would no longer be suitable.
Rickard believed the solution to the issue would be for all the information available to be put together in one paper which would point out exactly what problems can and have occurred.
Another independent contractor, Peter Dewes, performs a similar role in Waikato.
“A lot of farmers don’t know they’ve got an issue,” he said.
He agreed that previous installation work was often at the root of the problem but said many electricians had upskilled themselves over recent years and now knew where to find the cause of the problems they encountered.
He gave details of a recent onfarm visit where there was cabling between a VSD controller and a vacuum pump which wasn’t screened and didn’t have electromagnetic compliance (EMC) glands installed.
With the correct screened cable and EMC glands in place leakage dropped from 0.12 volts to 0.03 volts when the VSD was idle and from 23.6 volts to 0.61 volts when it was running.
Rickard has dealt with an increasing number of issues with irrigation systems in Mid Canterbury over recent years and Dewes believed he could be looking at more of these problems as irrigation systems were installed further north.
