Current Transformer Accuracy on Pulse-Burst-Modulated Circuits

The performance of metering-type current transformers connected in circuits with Pulse-Burst Modulation was studied. Measurements for Integral-Cycle and Half-Cycle Control are presented. Test results show that, when Integral-Cycle Control is used to regulate loads with power factors less than 0.95 lag, the recurrent transient component of the current could cause unacceptable increases in the current transformer phase-angle error. This paper considers four distinctive operation modes of Integral-Half- Cycle Control. It is shown that for only one of these modes the phase-angle error can be kept within acceptable limits. For this case the thyristor is turned on during an odd number of half- cycles and is off during an even number of half-cycles. A simple mathematical model explains the experimental results.