Traditional synchrophasor measurement-based islanding detection techniques have primarily relied on voltage angle measurements and/or their derivatives for successfully detecting islands. However, relatively high instrumentation channel errors associated with phasor measurement unit (PMU) data, can significantly degrade islanding detection accuracies. In this paper, a new islanding detection scheme employing cumulative sum of change in voltage phase angle difference (CUSPAD) is proposed, which is immune to additive instrumentation channel errors in the PMU measurements. The robustness of the proposed islanding detection algorithm is established through application to an 18-bus test system and the IEEE 118-bus system having different wind energy penetration levels. Comparative analysis of the accuracies of the proposed approach (CUSPAD) and the conventional angle difference (AD) approach prove the former's superior performance when additive instrumentation channel errors are present.