With the rapid development of distributed generators， the impact on the power system is not to be neglected. Taking small hydro power as an example， this paper firstly analyzes the impact of distributed generators unit commitment on VQC relays. Then a method is proposed for computing the power penetration level taking into account the unit commitment of distributed generators. The above-mentioned model will become overoptimistic when multiple distributed generators are connected into a distribution network. So， the concept of the min-max penetration level is introduced， that is， the max penetration level under the worst generation pattern. And then， a leader-follower decision-making model based on bi-level optimization is proposed. Finally， a 112-bus test system is utilized to evaluate the proposed model and the results provided.