A police operation at Redfern station that sparked widespread delays to trains across the city highlighted the critical junction's status as a "choke point" and a "major vulnerability" of Sydney's rail system, a transport expert said.

An alleged trespasser on the station's power lines forced authorities to halt trains and cut electricity on Thursday morning, triggering delays of more than an hour on some Sydney train lines.

Serious situation: A man climbs on the the power lines at Redfern station. Credit:Matthew Beck

Services were restored by noon but the delays continued through the afternoon as commuters prepared to head home before the Easter long weekend.

University of Sydney senior transport lecturer Geoffrey Clifton said that only an incident at Central or Town Hall station would have a similarly severe impact on trains across the city.