Working with a 4MW hospital account in Reno that's primary metered on NV Energy Schedule LGS. Both voltage and current transformers feeding the billing meter. CT ratio is 2000:5 and VT ratio should be 1000:1 but customer's bills seem high compared to similar facilities. How do you verify VT ratio errors on primary metered accounts? The VT cabinet is locked and NV Energy won't let us inspect without their rep present. Cliff W.
Primary Metered Account - VT Ratio Error on Hospital
Cliff, VT ratio errors are tricky because they affect both energy and demand calculations. First step is comparing the meter's voltage readings to actual line voltage measurements during peak load periods. If VT ratio is wrong, you'll see consistent percentage error between meter voltage and actual voltage. Also check power factor calculations - wrong VT ratio will throw off reactive power measurements. NV Energy should provide VT test results from last calibration. Randy D.
Had a VT ratio issue on a primary metered account with PNM. Hospital was being billed on 480V base when actual service was 4160V. Error was in the original engineering drawings that showed wrong VT ratio. Took six months to sort out but customer got $180,000 refund. Get copies of all original engineering specs and compare to actual installation. Frank S.
Update: Finally got NV Energy to do joint inspection. VTs are correct 1000:1 ratio but found the problem - one VT had failed internally and was reading low voltage on one phase. This created unbalanced voltage readings that threw off the total kWh calculation by about 8%. They're replacing the bad VT and will credit the customer for six months of overbilling. Cliff W.
Cliff that's a great outcome. VT failures are more common than people realize, especially in coastal areas with salt air. Duke Progress here in Raleigh recommends VT testing every 5 years on primary metered accounts but most customers don't know to request it. Steve Y.
Question for the group: how often should VTs be tested on primary metered accounts? Avista here in Spokane says every 8 years but that seems long for a 4MW load where billing errors could be huge. Nancy P.
Nancy, I recommend VT testing every 3-5 years on large primary metered accounts, especially above 1MW. The cost of testing is minimal compared to potential billing errors. Some utilities will do it annually if the customer requests and pays for it. Critical facilities like hospitals should definitely be on the shorter interval. Randy D.
Randy what's the typical cost for VT testing? TEP wants to charge our hospital client $2,800 for testing three VTs on a 2.5MW service. Seems high but might be worth it given the potential billing impact. Patricia W.