Diagnosing a power quality problem

I ran into an interesting problem a couple of weeks ago. Around 6 pm one evening, a utility transformer that serves three users -- a small apartment complex, a diary farm and a golf course clubhouse -- failed. The farm owner said his milk processing equipment was running when the outage occurred. The apartment manager said his tenants were home cooking dinner as usual. The golf course superintendent said the club had sponsored a tournament that day and rented several battery- operated carts to supplement their normal fleet. These were all plugged in for recharging when the transformer failed. Checking the battery charger current with a Fluke 43B power quality analyzer showed that the total harmonic distortion was 37%, well above an acceptable

20% level. A heavily loaded transformer can overheat is a large portion of the load current contains harmonics. In this case, all three users experienced peak loads at the same time and the sudden addition of the battery charger loaded caused the transformer to fail. To prevent future failures, the golf club supervisor agreed to restrict the use of battery chargers during peak load times.