The advanced electric power grid is a complex real-time system having both Cyber and Physical components. While each component may function correctly, independently, their composition may yield incorrectness due to interference. One specific type of interference is in the frequency domain, essentially, violations of the Nyquist rate. The challenge is to encode these signal processing problem characteristics into a form that can be model checked. To verify the correctness of the cyber-physical composition using model-checking techniques requires that a model be constructed that can represent frequency interference. In this paper, RT-PROMELA was used to construct the model, which was checked in RT-SPIN. In order to reduce the state explosion problem, the model was decomposed into multiple sub-models, each with a smaller state space that can be checked individually, and then the proofs checked for noninterference. Cooperation among multiple clock variables due to their lack of notion of urgency and their asynchronous interactions, are also addressed. Type of Submission: Research Paper Keywords: Interference, Model Checking, Decomposition, Real-time System, Frequency Domain Relevant Topics: Formal methods: program analysis, model checking, model construction, formal process models, noninterference. Evaluation of software products and components: static and dynamic analysis, validation and verification.