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If the reactive power (var) supply capability is not constrained; the transmission line loadability may be limited by the angle or thermal static stability. Once the reactive power supply is limited or not great enough to support the operation, the transmission line loadability will be limited by voltage. The reactive power supply capability has great influence on the transmission line loadability. While the reactive power supply capability reaches its maximum, the transmission line loadability may be reach the maximum or others, which is decided by reactive power supply capability value and load type. This paper presents a method to compute the transmission line loadability that is consistent with the reactive power supply limits, voltage magnitude and voltage static stability limit. The voltage static stability limit is determined by considering the singularity of the Jacobin matrix in which different constituents of load and the different load compositions are used. And the load voltage characteristic is also considered here.