If I understood right, in a network, a PMU is conected in a link, instead of a node right? I would start with more important links, that is, the links with large betweenness centrality.
The betweenness centrality looks important in terms of optimally allocating PMUs.
I am new to the topic but, it seems that, rather than allocating them at lines, when they are allocated at optimal buses, they can function measuring more quantities including line flows. Please correct me if I went wrong. Great thanks.