does any one have a view of the reason for insulation failure of compensation cable in photo attached. analogue input module with k type compensation cable. insulation seems to be failing in many cores in random places.
We have two identical MV generators on ship, 9MW each, after long period of maintenance we return to service. On paralleling they both trip on over volts. Then we test one on its own, sometime it trips on over voltage when energise mv/lv transformer (no other load on generator or secondary of...
I’ve picked up an operating procedure implemented some years ago that recommends a period of 12hrs before a transformer is re-energised after in has been shut down. Nobody knows why this restriction is in place, I contacted manufacturer also they didn’t have any restrictions on how often and...
how would you calculate the time for a MV conductor to decay to voltage that is safe to touch, i.e. extra low voltage. i'm aware that all circuits must be earthed and proven dead before maintenance/work can take place. but if a feeder circuit breaker were to be opened and not its circuit earth...
Well everyday you learn something new as they say.
Today for me was brine tank load testing.
I remember when I was younger I listened to an old sea dog telling me how he could replicate fast acting action of a semi-conductor fuse with bucket of water of section of copper wire.
Today someone...
we have 6.6kv induction motor for bow thruster of ship (1.4MW), difficult access for cleaning and removal.
we conduct PI insulation resistance measurements and have low PI reading ratio. 1min IR reading is just over 100Mohm though (102Mohm) so not awful by any means.
We ran anti condensation...
We have a ship with 6.6kV system and dissimilar rated generators, one 30MVA GT and two 10MVA DGs. Each earthed via 3A resistor, not switched, only manual disconnector for maintenance purpose. I have info the GT alternator is 5/6 pitch, but still waiting on info of DG alternator winding design...
Im familiar with issues of 2speed motor and changing from high to low speed. But is also changing from low to high speed also problematic?
Fan starter has recently had impeller change (blade change and material change)but now protection trips on switch from low to high speed. Not sure if...
I’d like to gauge opinion on following, we have a MV motor (bow thruster on ship), 2MW 6.6kV. Due to poor original system design we have issue with voltage drop on starting across ship when on min generators. Temporary work around being bring more capacity online to start motor. Anyway we...
does anyone have a reference to website or good text book with internal motor winding of dahlander induction 2/4 pole (Y/YY) arrangement. I was trying to sketch it out and visualise how the motor winding is powered in the low speed and then subsequently the high speed arrangement and how the 6...
We have a couple of diesel generators and gas turbine on a ship. The class society guy wants us to prove the integrity of reverse power relays as part of his intermediate (2.5yr) survey. He suggested other operators choose to actually induce a real reverse power situation by taking load off...
Is there a standard (either IEC or NEMA / IEEE ) that defines the maximum shaft voltage when fed from non-sinusoidal supplies as when motor supplied by VSI drive?
I have looked at IEC 60034-25, AC electrical machines used in power drive systems - Application guide. This doesn't actually define...
We have a shaft grounding system for marine propulsion drive (electric VFD propulsion). The shaft grounding which is achieved by 4 shaft grounding brushes (brushes are of carbon-silver-carbon design, with silver segement strip being the centre of the brush and the carbon segments either side of...
We have measured quite high levels of even current harmonics in the input to our VSI npc drive system (24 pulse, obtain by two 12 pulse transformers shift by 7.5deg with respect to one another). Attached are the 6 pulse current waveforms on the secondary side of one of those transformers. Does...
Reading a past thread now closed "bearing insulation resistance test limits for INSTALLED motors"
Does anyone have the paper NETA paper that was given as a link. Is there any better guidance since this time on the subject.
We have marine electrical propulsion application where POD drive has...
I’m hoping to get some assistance with understanding some issues we are experience with our shore to ship power system and whether they could be having impact on corrosion of a ship. Basically our wharf structure sees noise potential when our shore power system is energised and this noise...
This relates to another recent thread i posted 238-414369
We measured circ current in installation with single corre cables laid in non-trefoil arrangement for 20% of cable run. Breaks out of trefoil then in to groups of three parallel phase conductors per phase with approx 6" between phase...
What would be the implications of not bonding an mv single core cable screen at all? Dont intend to do this but am trying to understand what consequences would be if this inadvertently happened. Would it be a concentration of electrical stress on the insulation at the isolated screen ends and/or...
i would like to get opionion on attached photo showing some damage to cable terminations. application vsd, secondary of 12 pulse transformer, 1.7kv, cable is 3.3/6kV grade. installation is 1yr in service
this was noticed as part of routine inspection.
terminations on one winding seem to be ok...
