Hydro elevator tripping main breaker at top floor once a day

Ok.

Sounds like the lift is cavatating and low on oil at the top floor potentially. Check this first.

Check 3 phase mainline voltage. Had same problem (during summer heat though). When all the air conditioners at the complex would be on at the same time the car happened to be leveling in at the top. The Boss wanted me to change the packing, thought it was tight but the power company had to come out and resize the power transformers.

So with out any further information we'll just simply wing it. Is this one of your jobs and this problem just started? Or...?
Any chance the unit is bumping the up stop limit before coming off of LU? Ya know, something to get the pump into a rapid start/stop cycle or the starter to chatter. You'd think the MOL would trip out first though, but...you never know. Packing's good? All seems well with the selector/vanes/magnets etc.? What type of controller are you dealing with?

Found out there main breaker was bad and it being at the top floor everytime was irrelevant

In that case, Charlie's response wins!