When generation is insufficient to support all loads in a power system under emergencies, effective and efficient load shedding needs to be deployed in order to prevent system collapse. This paper presents a ratio consensus based distributed algorithm to discover the system overload after disturbance. In the proposed algorithm, the agent at each bus only communicates with its neighboring agents via directed communication links possibly with arbitrarily large but bounded time-varying communication delays. Simulation results are used to validate the proposed method.