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.

 

[davesparks]

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.

It's not too hard to integrate earth leakage protection into an MCCB, just fit a shunt trip operated by an earth leakage relay.

How does the generator behave when the mcb trips? Does it throw up any faults, lose speed, send up a cloud of black smoke etc?

Switching out the main RCD on the generator may not be a very sensible idea, and may not be compliant with the requirements of bs7909. You should adjust the tripping current and time delay in order to achieve discrimination.

 

[Rocboni]

You would also need to Integrate CT coil and earth leaks the relay as well as the MCcb, and there is no extra space.

The generator does noticeably change speed when the motor changes over but no smoke

The generator came from an sound and lighting company so I would imagine it implies with bs7909

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

Apparently it did once but I am notsurprised as I have measured peaks of 175A for a few seconds.

The particular ride is a Miami,they are notoriously had to drive as the motor is subject to high load then very little very frequently.

 

[Andy-1960]

Still don't seem to know what protection curve the MCB is....

 

[westward10]

When did you measure these peaks during change over or when it was up and running.

 

[davesparks]

You would also need to Integrate CT coil and earth leaks the relay as well as the MCcb, and there is no extra space.

The generator does noticeably change speed when the motor changes over but no smoke

The generator came from an sound and lighting company so I would imagine it implies with bs7909



Apparently it did once but I am notsurprised as I have measured peaks of 175A for a few seconds.

The particular ride is a Miami,they are notoriously had to drive as the motor is subject to high load then very little very frequently.

The generator cannot comply with bs7909 on its own! Bs7909 is the standard which covers your whole installation from generator through to the ride.

If the generator is noticeably slowing down then the output voltage and frequency will also dropping, this will have a knock on effect on everything it is powering.
Are you running this whilst other loads are on the generator, or is it the only load?

 

[Rocboni]

Still don't seem to know what protection curve the MCB is....

See pitcture

When did you measure these peaks during change over or when it was up and running.

When up and running, it wasn't this high when changing over,

The generator cannot comply with bs7909 on its own! Bs7909 is the standard which covers your whole installation from generator through to the ride.

If the generator is noticeably slowing down then the output voltage and frequency will also dropping, this will have a knock on effect on everything it is powering.
Are you running this whilst other loads are on the generator, or is it the only load?

I admit i am not familiar with the standard but all the leads over 32A are covered by 300ma RCD and correct overcutrent protective devises and anything under this 30mA double pole rcbo, I'm sure there is more to it, it's not somign I am involved with every day, just been asked to look at this for them.

The voltage and frequency do not change, there are meters on the machine so you can watch them while transferring.

There are other loads about another 75 amps/ phase on at the same time.

 

[westward10]

Those measurements are more than double its expected flc and it sounds like the other loads are also contributing. Sounds like this new generator maybe inadequate for the expected loading.

 

[Rocboni]

It all used to run off a 200kva with no issues, this was captured by my clamp meter with the max function it may have only existed for a second, the whole ride with motor running but no load (lights ect) was only drawing about 50amps/phase.

It has been designed to run off a 125A socket from day one, the machine itself has a 160Amp Mccb albeit someone has fiddled with it and turned it up to its max, the adjustment screw is chewed to bits.

 

[davesparks]

The voltage and frequency do not change, there are meters on the machine so you can watch them while transferring.

There are other loads about another 75 amps/ phase on at the same time.

[]

You said the generator slowed down, but you are also saying that the voltage and frequency do not change. This is not possible, The frequency is governed by the generator speed, if one drops then the other must.
Also when you apply or remove a load on a generator it has to react to compensate, the speed and frequency will change. How big a change this is will depend on the magnitude of the change in load.

 

[Rocboni]

I was wrong to say it slowed down, you could tell it Was working harder but it was coping fine, it drives the machine easily

 

[westward10]

Is it possible to ditch the ancillary loads and just run the motor.

 

[Rocboni]

Do you mean the lighting on that ride or the other loads on the generator, the other main loads are run from other plugs with their own protection all of which are fine, it's just when the motor changes to delta and the very odd time while the ride is operating, I am confident the generation is well capable of driving it, as well as other rides at the same time.

 

[westward10]

Yes ignore my last post I misthought the ancillary loads were affecting the motor load. I think the mcb tripping on the delta transition is down to the fact it is an mcb. Tripping when it is running could be down to a number of factors such as poor maintenance placing additional loading on the motor through poor lubrication, worn bearings etc.. Is the passenger capacity being exceeded.

 

[Rocboni]

So you don't think changing to a D curve would make a difference?

You cannot really exceed the ride capacity as there are a fixed number of seats. There is also counter weights to off set the "boat" so I can't see where the load is really.

 

[westward10]

It may do but it also sounds like is is prone to an overcurrent issue and changing the type may not resolve it.

 

[Rocboni]

Trouble is it's £250 to find out.

 

[westward10]

Think you need to explain to the owner this and that there is no guarantees it will resolve it. Why did they replace the old generator.

 

[Rocboni]

I will do, this is a vast improvement in terms of protection on the usual set up, the sockets are usually straight onto the bus bars of the generators and the older ones don't have RCDs built in! So this is all quite hard to explain and hard to get them to understand why you need all this.

They will also want suggestions how to overcome this but there's space to fit a Mccb.

How would you normally supply this size of motor?

 

[westward10]

BS88 fuses or a suitable mccb.

 

[Rocboni]

The motor is actually supplied buy 2x 100 A and an 80amp bs88 fuses (not ideal) before the star/delta contractors and these are holding up, by the looks of it the 80amp is an original.

 

[westward10]

The mcb I feel is the Achilles heel as they are not suitable for large size motor protection.

 

[Cadgey123]

The motor is actually supplied buy 2x 100 A and an 80amp bs88 fuses (not ideal) before the star/delta contractors and these are holding up, by the looks of it the 80amp is an original.

Link the MCB out the equation to see what happens?...

You said you had added protection in regards to the other fuses.

 

[Rocboni]

They have fitted a 4 pole isolator at the moment so that can operate, but ther is no protection for the cable and socket other than the MCcb in the generator with is about 400Amps

 

[westward10]

Link the MCB out the equation to see what happens?...

You said you had added protection in regards to the other fuses.

Link out the mcb is just removing the problem not solving it plus you remove circuit protection for the socket.

 

[davesparks]

what is the overload trip on the starter doing during all of this? Assuming it is set correctly then that should be providing the overload protection so the mcb or whatever will only be needed for fault protection.

 

[westward10]

The relay would be more tolerant to current peaks whereas the mcb is not and that is the problem. The same goes for the BS88 fuses.

 

[Dozer 73]

A handy little tool for selecting gen set sizes etc
Macfarlane Generators Power Calculator - https://www.macfarlanegenerators.com.au/power-calculator.php

 

[Dozer 73]

A handy little tool for selecting gen set sizes etc
Macfarlane Generators Power Calculator - https://www.macfarlanegenerators.com.au/power-calculator.php

Know it's the the solution to your post , just a good tool to have

 

[Rocboni]

I turned the changeover time up to 10 seconds and it's been fine ever since however I have ordered a D type so will fit that for piece of mind.

 

[westward10]

That is what I suggested way back in #6, glad it seems to have resolved it.

 

[Rocboni]

I know you did westward, just didn't get the opportunity to test during operation as I had to leave the isolator in place until their busy days were over and they could afford the inconvience of it possibly tripping. Understandably it doesn't look good if it cuts out mid ride.

I think the C125 is operating right on its limit though with the regular however short current spikes so I think a D would be more suitable. The RCD is holding fine as well so all good.

 

[MikeM3]

Normal delay in a star delta setup should
be around 9 seconds.

Mike.

 

[davesparks]

Normal delay in a star delta setup should
be around 9 seconds.

Mike.

How can you have a 'normal' delay when each machine is going to be different and take a different length of time to start?

 

[Cadgey123]

How can you have a 'normal' delay when each machine is going to be different and take a different length of time to start?

I agree depends on the motor application and loading

 

[Rocboni]

Further update on this, MCB was holding fine until the colder nights set in, the MCB began to trip when transitioning to delta due to the oil viscosity, the D type was fitted and there have been no other issues.

It's such an unusual load, I was observing the display on the generator at the weekend where it was going non stop for 2-3hrs riding full, the load peaks to 132kw for a second then down to about 60kw, somtimes read minus 10Kw.

It's an interesting industry

Anyway if there was going to be an issue it wouldn't have happened that night!