This paper investigates retrofit technology without outage to address the problem that the 10 kV busbar cannot be powered off during main transformer protection retrofit in substations. By adopting techniques such as conductor selection and potential measurement

installation of trip output links

addition of intermediate relays

use of maintenance links

and digital simulation testers

the correctness of the low voltage side backup protection of the main transformer and the tripping and blocking circuits of the bus-tie breaker is verified without physically operating the bus-tie breaker. Meanwhile

for the difficulty of accessing the TV secondary voltage circuit

the advantages

disadvantages

and risks of two schemes

namely TV outage transfer and voltage acquisition from the fault recorder panel

are compared. Through scheme comparison and optimization

a safe and efficient typical work procedure and corresponding risk management system for retrofit without outage are finally developed.