Basic Generator Setup Question

It's always a good idea to hook things up exactly as specified. Your problem lies within the things that were done differently. Redo them according to the manual.

PS- Your "electrician" might be nothing more than a residential wire puller.

1) Is the MCB tripping because of the generator in-rush initial currents? What is the inrush/staring current of everything powered by the generator?

2) Is the MCB tripping because it is a non-ideal wiring design? No way to tell. How long is the run?

I didn't mean to be hard on the OP, but I had a certified "electrician" come to my house to do some wiring. It took me 6 months to fix it.

I don't see it as a loss though. Knowledge gained.

...in which case it would be better to change the breaker for a 63A-trip-rating one.

Dear PWSlack

I think that it is the solution since with a 63Amp both conditions i.e. fault tripping one as well I<1.45Iz will be satisfied.

Dear Mr.RyanC83,

You have not indicated the connected load details, and which one you are starting first. From working point of you, the highest H.P motor, should be started first, and the small motors later.

When the Higher H.P. Motor is started last, the kick load, which depends upon the type of motor, starter etc., will be a limiting factor.

DHAYANANDHNA.S

As already pointed out by forum members, you have not indicated the voltage in order to arrive at the current rating.Probably the name plate detail will tell you the current rating.

I have not heard of start-up (inrush ) current for any generator though there may be inrush current for transformers and starting current for motors. I would suggest to keep tall the loads OFF during generator starting and and running.Switch on the loads one by one,the largest first and then the other loads in descending order allowing for few minutes in between each load.You will be able to locate the problem if any from the load side.For me it appears there is no problem with the rating of cable or the MCCB though they are rated critically assuming the voltage is 415 V, 3 phase and copper conductor cable

Further to the previous comments from the forum members, please be advised that the isolator does act as a non auto circuit breaker (MCCB or MCB) so it will not trip for an overload but it will protect the incoming cable for short circuit current.

How?

Check the technical catalogues of circuit breakers & Isolators such as ABB Group Schneider and others,

If You want to switch a generator to a f.ex 440 v grid, You must set the generator no load voltage to 445 V and then syncronize the generator and the grid before switching.

then there will be only a small current running.

You can then adjust the reactive current ( kVAr ) by raising og lowering the voltage.

And You can raise the kW by increasing speed on the diesel governor.

Dear Forum Members

Thanks for your response and apologize for not answering straight away, I was sleeping:) it was night here.

To answer your queries the terminal voltage is 415 V that's why I have told that the full load current out of generator is approximately 63 Amps (sorry for not telling).

The problem is that the electrician has replaced the 100 Amp MCB twice already and still the problem persists. to my understanding you need to multiply a factor of 1.45 to a type C MCB thus it is actuallyrated as 145 Amp for a specific amount of time.

Now having the following data:

Vt=415V

Genset = 45Kva

Ib (design current i.e. full load of generator)=63Amps

In (rating of MCB)=100 Amps

Ct (derating factor temperature of 45 deg. Cel.)= 0.71

thus Iz=141 Amps

From the above data a 4 x 16mm2 cable is not sufficient since such a cable delivers approx. 90-99Amps

Now taking the situation that 4 x 16 Amps are used

condition Ib<In< Iz is not satisfied.

Can anyone tell whether my understanding is correct? or I am confusing things.

With much appreciation

Ryan:)

Mr. Ryan,

A MCB tripps under two conditions:

1. Overload i.e. exceeding rated current

2. Short circuit

Overload at power on may be due to inrush current.It can be many time the actual load for a brief duration. During over load MCB trip by thermal action.Hence a delay.

When short circuit is MCB trips due to magnetic action hence instantaneous.

MCBs are two type: For normal electrical load

For Motor Load

Normal electrical load MCB operates faster under overload/inrush current than motor grade.

You can either select as 1.5 times calculated max. current or use motor grade MCB.

Detailed graphs are on manufacturer's data site.

D D Daga

Bubble Electronics

Dear Mr. dmdaga

I concur with all what you have said. :)

Ryan

What "type" of circuit breaker is it - B, C, or D-curve? Is it suitable for the load, ie. motors?

Dear Ryan,

Herewith is my answer to your questions:

1. MCB tripping has nothing to do with the in-rush current since you have just started the generator without load. In rush current occures only after your generator stabilized at no load and switching on the MCB with transformer load.

2. MCB tripping has nothing to do with wiring design since your generator has started only and no load.

3. It is not advisable to replace your MCB with Isolator since it is your main protection of the generator. I woul advise to install more protection on your generator such as overcurrent / overcurrent ground faulth relay, Over/Under Voltage relay, Over/under frequency relay and overload protection.

The possible caused of the MCB tripping is your generator AVR wherein the voltage is not stabilized. There are MCB with internal over voltage protection that possible caused the tripping at no load.

Regards

Arnulfo Palacio