800hp auto synchronous motor fault
800hp auto synchronous motor fault
(OP)
new boy here,hope someone could help with a problem thats got our team stumped!
motor runs a ball mill,motor runs up fine thru first and second stage resistances but nine times out of ten hunts badly with large current swings after shorting of rotor resistances and changing to exciter control
any ideas would be appreceated.
motor runs a ball mill,motor runs up fine thru first and second stage resistances but nine times out of ten hunts badly with large current swings after shorting of rotor resistances and changing to exciter control
any ideas would be appreceated.





RE: 800hp auto synchronous motor fault
RE: 800hp auto synchronous motor fault
RE: 800hp auto synchronous motor fault
I measured run up times of the outher drive [witch is fine]
and this made it to 690 rpm [60rpm short of 750 rated]
before it changed to dc control;this machine seems to stay in it's accelleration stage for longer than the problem drive,i cannot turn it off for four days as it is critical plant.
the rotor resistors are liquid and appear to have been mismaintained so this could prevent motor reaching a
high enough speed prior to going to dc if extending run up time does not improve matters.
RE: 800hp auto synchronous motor fault
"Venditori de oleum-vipera non vigere excordis populi"
RE: 800hp auto synchronous motor fault
There are two types synchronous motors that I have rewound.
First one was the synchronous induction motor, where a normal slipring motor, at minimum slip, pulled into step by applying dc to the star connected rotor winding and shorting two sliprings. The dc current was I in one phase and I/2 in the other phases of the rotor winding.
The second one was more intesresting salient pole type synchronous induction motor where a separate normal 3 - phase start winding is located in the slots cut into pole faces of the salient poles and is connected through its own sliprings to the LRS during start up.
RE: 800hp auto synchronous motor fault
Difference is First and second starts with out load, synchronize and then you couple the load (pneumatic or magnetic coupling type).
Third starts with load (common used in mining an cement industry)
RE: 800hp auto synchronous motor fault
"Venditori de oleum-vipera non vigere excordis populi"
RE: 800hp auto synchronous motor fault
RE: 800hp auto synchronous motor fault
rotor and exciter being tested on thursday as i have had tacho on shaft at start up and it only got to 600 rpm befor dc applied.
changed timers and got to 700rpm,big improvement but still fails to synch 3 or 4 times out of ten
RE: 800hp auto synchronous motor fault
RE: 800hp auto synchronous motor fault
when the rotor is being tested i should be able to compare
the resistors to makers spec
by the way when the drive was new would the lrs have allowed the motor to get that close to synchronous speed?
RE: 800hp auto synchronous motor fault
If possible, use a separate three phase contactor in parallel with the rotor external resistance, which will short out all the three phases of the rotor winding. After the last contactor in your rotor external resistance is closed, close this shorting contactor and see if the speed goes above 700 RPM. This additional shorting contactor should be opened again prior to application of dc to the sliprings. Bit of co-ordination reqd here. Good luck
RE: 800hp auto synchronous motor fault
I am suspicious of the rotor starting induction winding condition. Make winding resistance, insulation resistance, PI and surge Test the three phases. If your winding is not good and balanced the motor will not accelerate close to 750 rpm even if the resistors and final short circuit of the rotor are in good shape and/or you increase the allowed acceleration time .
RE: 800hp auto synchronous motor fault
RE: 800hp auto synchronous motor fault
things to check when the specialist motor guy comes on thursday.
still waiting for original lrs spec however an operatve says aguy from the starter makers drained refilled the lrs
need to speak with him soon.
RE: 800hp auto synchronous motor fault
RE: 800hp auto synchronous motor fault
ok as did stator.
motor has been starting ok since I increased start up timer
but still only reaches 690 rpm before pulling in so iam now going to really look closer at lrs as I assume if rotor
ok lrs limit final speed befor synch.
could being too slow at synch demand to much current from
exciter at change over