Multicast is proposed as a preferred communication mechanism for many power grid applications. One of the biggest challenges for multicast in smart grid is ensuring source authentication without violating the stringent time requirement. The research community and standardization bodies have proposed several authentication mechanisms for smart grid multicast applications. In this paper, we evaluate different authentication schemes and identify the best candidates for phasor data communication in wide area monitoring systems (WAMS). We first do an extensive literature review of existing solutions and establish a short list of schemes to evaluate. Second we make an experimental comparison of the chosen schemes in an operational smart grid pilot and evaluate the performance of these schemes by using the following metrics: computation, communication and key management overheads. The best candidates we consider are two variants of ECDSA, TV-HORS and three variants of Incomplete-key-set. We find ECDSA without pre-computed tokens and all the Incomplete-key-set variants are inapplicable for WAMS due to their high computation overhead. The ECDSA variant that uses pre-computed tokens and TV-HORS perform well in all metrics; however, TV-HORS has potential drawbacks due to a large key management overhead as a result of the frequent distribution of a large public key per source.