NPU, SW Version 1.8, ©ComAp, September 2003
NPU-1.8r2.PDF 13
As shown in the timing diagram the voltage jumps to an other value and the phase position changes. This
procedure is named phase or vector surge. NPU continuously measures the cycles, starting each zero up
ward slope. The time cycle is internally compared to the quartz table reference time. In case of vector
surge the zero up ward is delayed and the device trips instantaneously. The trip angle ∆ϑ and
consequently the sensitivity of the vector surge detection is adjustable.
Measuring principle
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