Today we are testing a summation transformer arrangement with an electricity meter for overall kWh errors for utility meter verification.
Summation current transformers are used to add up secondary currents of multiple main current transformers to measure with one instrument only. This method will eliminate the need for having multiple electricity meters for ct metering applications.
Our kWh accuracy testing concludes summation type of arrangements are ok when the load is in unity power factor. However, when the load is leading or lagging the summation transformers can induce additional kWh % errors to the metering installation. This is because transformer construction and electromagnetic flux coupling between transformers introduced additional phase error.
A careful consideration for current transformer selection and routing of cables required for obtaining the overall error requirements specified in Chapter 7 National electricity rules.