Over-current protection delay time calculation method of urban rail transit power supply system

The invention provides an over-current protection delay time calculation method for an urban rail transit power supply system. The method comprises the following steps: S1, determining a superior and subordinate cooperation relationship among a plurality of protection devices; s2, determining the delay time tn of over-current protection of the lower-level protection device; s3, calculating the time level difference delta t of the delay time between the superior protection device and the subordinate protection device; and S4, calculating the delay time tn + 1 = tn + delta t of the over-current protection of the superior protection device. The invention provides a minimum time interval capable of reliably distinguishing over-current protection delay time of sequential actions of two switches for the whole process of protection from starting to outlet to tripping action of a circuit breaker. The problem that the number is limited under the condition that the maximum delay time of over-current protection is limit