When bond graphs are generated from reasonable physical systems according to standard rules, there are only rare cases in which power loops arise that yield singular algebraic relations among effort and flow variables. On the other hand, if one assembles bond graphs from subsystem models, paradoxical situations may arise in which sign conventions and causality interact strangely and in which physically impossible situations seemingly occur. Some useful bond graph identities are shown which often eliminate such paradoxes. The general conclusion is that a bond graph containing a junction structure power loop should be carefully examined with respect to sign convention and to see whether a simplifying identity can be used before causality is applied and equations are formulated.

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