The integration of renewable energy has changed the fault characteristics of new power systems

leading to degradation of adaptability of traditional relay protection. Existing studies on protection adaptability boundaries of distributed generation implicitly assume that photovoltaic (PV) fault currents are in phase with the system-side currents

resulting in boundary inaccuracies. To address this issue

a quantitative method for protection adaptability based on phasor analysis is proposed. First

a PV generation fault model considering low-voltage ride-through (LVRT) control is established

and its fault characteristics are analyzed. Then

through theoretical derivation and phasor analysis

the influence mechanisms of PV integration on the magnitude and phase of the fault currents at the relay location under two typical infeed and outfeed scenarios are thoroughly investigated. On this basis

the critical conditions for Zone I protection mismatch under the infeed scenario and protection range reduction under the outfeed scenario are quantitatively derived. The results indicate that

under typical 10 kV distribution network parameters

protection mismatch due to PV infeed can be avoided when the PV capacity falls below 16% of the maximum system short-circuit capacity. Furthermore

an analytical expression for the degree of protection range reduction under the outfeed effect is derived. The derived protection adaptability boundaries provide a theoretical foundation for protection risk assessment and setting verification.