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Stray Voltage Problems with Dairy Cows

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Stray Voltage Problems with Dairy Cows AGRICULTURAL EXTENSION SERVICE Extension Folder 552-1980 UNIVERSITY OF MINNESOTA STRAY VOLTAGE PROBLEMS <- WITH DAIRY COWS R. D. Appleman and H. A. Cloud Many dairymen are losing milk pro­ dairymen. The number of cows Even when the stray voltage duction and experiencing cow affected and the severity of the problem has been corrected, milk health problems at milking time due milk let-down problem appear to production may remain abnor­ to small currents of electricity pass­ be dependent on the level of mally low for awhile because of ing through the cows' bodies. This stray voltage present. The mech­ the associated problems. condition may be caused by low anism of how this occurs is not It must be remembered that voltages existing on the grounded understood. When milk out is other factors such as mistreatment, neutrals of the farm electrical sys­ uneven, more machine stripping milking machine problems, disease, tem. Stray voltages can result from is required and longer milking sanitation, and nutritional disorders several electrical sources, but the time becomes apparent. can create problems which manifest major problem appears to be volt­ 2. Cows extremely nervous while in themselves in the above seven ages existing on the grounded neu­ the parlor. This trait often is char­ symptoms. A careful analysis of all tral network. acterized by the cows dancing or possible causes is necessary if the The prevalence of this problem stepping around almost continu­ proper corrective procedure is to be in Minnesota remains uncertain, but ously while in the parlor stall. found. the authors have been directly in­ However, dairymen are re­ volved on more than 50 farms in a 2- minded that cows may become WHAT CAUSES STRAY year period. Some experts feel that nervous for other reasons, such VOLTAGE? 20 percent or more of all parlor barn as malfunctioning milking equip­ All modern dairy facilities de­ dairy farms may be affected. ment or rough handling by the pend on electrical energy supplied The loss in milk production and operator. over rural distribution networks. The dairy farm income-combined with 3. Cows reluctant to enter the par­ primary distribution system together the aggravation, time, and cost of lor. When cows are subjected to with the secondary farmstead wiring correcting the problem-may be stray voltages in the parlor stalls, and all electrical equipment and substantial. One farmer with an 80- they soon become reluctant to grounded components form a com­ cow herd suffered a 3,000-pound enter the parlor. In extreme plex network. All parts of this net­ drop in annual milk production per cases, nearly all cows have had work are interconnected through an cow for a 2-year period and spent to be driven into the parlor and electrically conductive system con­ more than $15,000 to replace com­ there was a tendency to "stam­ sisting of the primary and secondary ponents of the milking system in an pede" out of the parlor upon re­ neutrals and all grounded equip­ attempt to correct the problem. lease. But again, this symptom is ment and facilities. The grounded not specific since cows may be neutral system is connected to earth TERMINOLOGY trained to expect the parlor oper­ through "ground rods" driven into The problem has been identi­ ator to chase them into the milk­ the soil and through electrically fied by several different names. ing stalls. grounded equipment and facilities in Among dairymen, stray voltage or 4. Increased mastitis. When milk contact with the soil. tingle voltage is the most common. out is incomplete, more mastitis Figure 1 shows a portion of the The most correct terminology, and is likely to occur. All that is re­ grounded neutral system containing that used by most power company quired is the presence of infec­ examples of neutral conductors and representatives, is neutral-to­ tious bacteria. This, in turn, will grounding conductors. All neutrals ground or neutral-to-earth voltage. result in an increased somatic and all grounding conductors are at­ Another name sometimes used, but cell count. tached to the grounding block at the one that has an altogether different 5. Reduced feed intake in the par­ service entrance of the barn which, meaning among electrical engi­ lor. If cows detect stray voltage in turn, is connected to the service neers, is transient voltage. The term while eating from the grain feed­ entrance ground rod. The grounding neutral-to-earth (N-E) voltage will be ers, a reluctance to eat and block is connected to the secondary used here and refers to the voltage reduced feed intake is almost neutral leading to the transformer. existing between the neutral system certain to occur. The secondary neutral is electrically and zero-potential earth. bonded to the primary neutral at the 6. Reluctance to drink water. Stray transformer. voltages may reach the cows in Figure 1 shows only the neutral SYMPTOMS OF STRAY stall barns through the water VOLTAGE PROBLEMS and grounding circuits. The dashed­ supply or metal drinking cups. line and arrows indicate the primary Animal reactions will vary de­ Thus, cows soon be.come reluc­ and secondary high voltage con­ tant to drink. pending upon the severity of the nections. This circuitry will have no problem. If one or more of the follow­ 7. Lowered milk production. Each direct effect on the grounded neutral ing symptoms persists, stray volt­ of the symptoms described previ­ system unless there is a "ground ages may be contributing to the ously is associated with stress, fault" electrically connecting the problem: reduced nutrient intake, or dis­ high voltage conductors to the 1. Uneven milk out. This is the most ease. In any case, a drop in daily grounded network. However, as we common symptom expressed by milk production is to be expected. will see later, loads added to the 2 Figure 1. The grounded neutral network on a single-phase distribution line TRANSFORMER FARM SERVICE ENTRANCE ---------PRIMARY "HOT" - -L~'HOT;;-- ---F-----~- - I SECONDARY NEUTRAL I PRIMARY NEUTRAL I I -~l I IL2 L 1 ,J- _'f_l ELECTRICAL BOND I • • I 240 VOLT BETWEEN PRIMARY 1 GROUND MOTOR AND SECONDARY BARN NEUTRAL SERVICE I ENTRANCE: NEUTRAL 120 VOLT MOTOR .----+--, I I ---~I-- - - - - _J PRIMARY GROUNDING NEUTRAL NEUTRAL GROUND TERMINAL ROD AT TRANSFORMER BLOCK __ I __ I __I __ J 120 VOLT CIRCUITS GROUNDED STANCHION PRIMARY NEUTRAL OR PARLOR PIPE GROUND RODS ALONG FARM r THE LINE SERVICE ENTRANCE GROUND system create various effects on the Figure 2. A dairy cow subjected to a neutral-to-earth (N-E) voltaQe grounded neutral network. SECONDARY NEUTRAL FROM Every part of the grounded THE TRANSFORMER neutral network including the con­ ductors, the connections, the earth, I -] and the contact between the ground I BA N I I SERVICE I rods and the earth, has some resist­ I ENTRANCE ance to the flow of electric current. l~+-~I ANY VOLTAGE ON THE GROUNDED GROUNDING NEUTRAL SYSTEM IS READ BY THE TERMINAL VOLTMETER AS A NEUTRAL- TO - Due to these resistances, whenever BLOCK-/ there is a current in the neutral sys­ EARTH VOLTAGE tem a voltage exists between it and earth. These voltages are reflected VOLT METER to all parts of the interconnected net­ STANCHION PIPE OR work and, if they are sufficiently ANYTHING ELSE THAT 1 IS "'ELECTRICALLY- _ high, may be detected by an animal. GROUNDED ) 1 -' \ I / \ They exist as neutral-to-earth (N-E) \,' \ (,. )\.__;\ ""ISOLATED"" voltages and will cause a current ~) I / • l GROUND ROD flow through the body of an animal AS A REFERENCE- bridging the gap between the neu­ ''"' "--.. I tral network and the earth, as shown SERVICE ENTRANCE in figure 2. In this case, the cow's GROUND ROD back feet provide a connection to "true ground" through the wet con­ crete and the wet soil underneath. The front portion of her body is in COW IN CONTACT· ~CK FEET IN contact with the grounded neutral WITH GROUNDED GOOD CONTACT NEUTRAL NETWORK WITH EARTH -'TRUE"' system through the pipe, wet con- GROUND 3 crete, feeder, etc. She may be sub­ Figure 3. Location of an "isolated" ground rod used as a reference in neutral-to­ jected to the same N-E voltage read earth voltage measurements by the voltmeter in figure 2. This voltage causes a current to flow through her body and can result in "ISOLATED" GROUND ROD USED serious problems when it is high AS A REFERENCE FOR NEUTRAL­ enough to cause discomfort. TO- EARTH VOLTAGE READINGS AT LEAST 25 FEET FROM ANY Neutral-to-earth voltages re­ UNDERGROUND PIPES, ELECTRICAL EQUIPMENT, OR GROUND RODS. sult from the voltage differential cre­ ated by current flowing in any part of the neutral network. The voltage de­ I pends on the resistance of and the YOUNG I STOCK ---_lt._41:§:R \ current flowing in all parts of the in­ ----, terconnected neutral system. Many I factors affect this: \ METER POLE \ 1. loads on all parts of the distribu­ tion system 2. length and size of the primary neutral SERVICE ENTRANCE 3. grounding resistances on the pri­ mary neutral HOUSE 4. resistances of all connections on SHOP 8 the primary neutral MACHINE SHED 5. grounding resistances on the farm 6. length and size of all secondary neutrals 7. current in the secondary neu­ trals, as affected by balancing of line-to-neutral loads (120 volts) 8. resistance of connections on the secondary neutrals the intermittent "here today, gone of this "isolated" ground rod and 9. ground fault currents tomorrow" nature of the problem. voltmeter will be discussed in the The cause of excessive N-E section entitled "Standardized Mea­ The effect of these voltages on voltages often is very difficult to lo­ surements." In this position the volt­ dairy cattle is influenced greatly by cate.
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