45kw motor and generator problem

[Rocboni]

Hi all,

Got a bit of a problem with a new generator when starting a 60hp motor.

It's a 250kva generator with a 125A mounted plug, the plug is protected by a C125 A Merlin gerin c120h MCB with combined 300mA RCD, the motor starts fine but when it changes over to delta it trips the 125A mcb (I temporarily removed the rcd to prove it wasn't that as the are coupled together)

The motor is a 45KW 60hp motor, it is driving a hydraulic pump (tripping with no real load on the motor). After a few goes it will eventually hold, I'm guessing the oil heats up a bit and isn't as thick.

I have done an insulation test between the windings and to earth and all is good, all phases are balanced aswell, the motor is only 2 years old, full load current is 82A if I remember correctly, timer set at 5sec with an 80ms delay between star and delta

So I am putting this purely down to inrush current, will putting a D125 on it resolve this problem of tripping, I have tested using a clamp meter and under some circumstances the current peaks at 150amps for a split second.

None of this was an issue with he old generator however the plug was protected by a 150A MCCB no rcd.

 

[timbobelfast]

No sure if I would be selecting an RCD for this application TBH. Is this a client requirement ?

 

[telectrix]

is yourZs low enough for a type D? i'd be inclined to check it first and maybe try a type C first.

 

[westward10]

I doubt it is an IR problem if in runs in star. It is possible the oil density is retarding the motor as it should reach 75 - 80% of its full speed before the transition to delta where for a fraction of time you get a current spike so the slower the star run speed the higher the spike. Can you increase the time at the starter before the delta transition occurs.

 

[Rocboni]

No sure if I would be selecting an RCD for this application TBH. Is this a client requirement ?

An rcd is required as flexible cables h07rnf are being used, it is an amusement ride.

is yourZs low enough for a type D? i'd be inclined to check it first and maybe try a type C first.

It is a short 35mm 5 core always supplying the same ride, I have tried a type c and this is what it is tripping.

I doubt it is an IR problem if in runs in star. It is possible the oil density is retarding the motor as it should reach 75 - 80% of its full speed before the transition to delta where for a fraction of time you get a current spike so the slower the star run speed the higher the spike. Can you increase the time at the starter before the delta transition occurs.

Timer set at 5Seconds at the moment, I can try increasing this but motor sounds like it is up to speed.

Do you think it should be holding on an a 125A type C?

 

[westward10]

I suspect the mcb is the problem if you never had such an occurrence with the mccb. You could increase the time to say 10 sec and see what happens. This method of starting may reduce start up currents but there will always be a current spike on the transition to delta and mcbs are not ideal devices for motor protection.

 

[Andy-1960]

The C120 range comes with B, C & D tripping curves, don't assume that because it says C120 it's a C type, it could be anything.

 

[davesparks]

No sure if I would be selecting an RCD for this application TBH. Is this a client requirement ?

How else would you provide fault protection? A 250kVA generator will not be capable of providing the fault current necessary to operate the mcb in time

 

[davesparks]

is yourZs low enough for a type D? i'd be inclined to check it first and maybe try a type C first.

Zs is irrelevant, a 250kVA generator will not be able to deliver enough fault current, the engine will stall first.

 

[davesparks]

An rcd is required as flexible cables h07rnf are being used, it is an amusement ride.

Why does the type of cable require a 300mA RCD?
It is there to provide fault protection

 

[Rocboni]

The C120 range comes with B, C & D tripping curves, don't assume that because it says C120 it's a C type, it could be anything.

I know C120H is the range, well aware of that, it is a C125 MCB, you don't get 120Amp MCB.

Why does the type of cable require a 300mA RCD?
It is there to provide fault protection

If it was an armoured to the machine you wouldn't require an RCD.

I understand that it is a requirement under regulation 740.410.3


I agree the MCb is the problem, but harder to intigrate RCD protection with an mCCB

I have been down turned up the star delta change over time, helped a bit, but he said it also tripped once mid ride, far from ideal. So reluctant to keep the C125, measured it with my clamp meter with max function and it peaked at 175A, also measured earth leakage, it was around 30mA until the motor was started, meter maxed out then dropped to 120mA while motor was running, but I'm unsure if he meter would accurately read when the motor starts as there's such a high inrush. The next question is the RCD time delayed, I don't know it doesn't say type S. See picture this is what they have at the moment, as you can see not easy to fit anything other than this set up. This box supplies a 63A, 2x 16A and 32A. There is an main RCD on the generator but have this turned off as a fault in one ride cannot shut the whole lot down when they are open.

I'm not sure what to suggest.

 

[westward10]

A very much doubt the rcd is the problem.

 

[Rocboni]

A very much doubt the rcd is the problem.

I'm going to ask them to try the C125 now that I have increased the time and see how they get on, if not they'll have to try the type but not cheap, just wanted to here everyone else's thoughts.

 

[westward10]

So the trip during mid ride occurred when the motor was up to speed not during the transition to delta.

 

[davesparks]

I

If it was an armoured to the machine you wouldn't require an RCD.

I understand that it is a requirement under regulation 740.410.3

[H]

Yes you would require an RCD whatever type of cable it is, it is needed for fault protection due to the generator being incapable of delivering enough current under fault conditions to operate the mcb within the required time.