Strange behavior of an Electrical Crane

[umery2k75]

clamp meter

This is the electrical over head crain, it is at floor but it will go up at the column around 35ft high above the ground, you can see the relay logic diagram of the system in the picture.I was astonished to see that the electrician had used the 4 core cable in which two wires were used for input and other two for output.It's bad practice, I believe. I was busy for almost a month and unfortunately I couldn't used the internet and I was missing EDABoard alot especially postings of Fvm and topics of discussion going on, this sunday I will read all the previous postings from the last month.

 

[umery2k75]

cranes for electric post

I have encountered a problem. This 30 ton crane wasn't able to pickup the load of greater than 18ton of weight. A 16 sqr.mm, 4 core cable was available as a spare. So this cable was used, you can see the old arrangement as in this picture.Unfortunately, I took the picture late, it has been opened up and wires have got free.



It was opened up and the cable was doubled, new picture is not shown, crane was then able to pickup the mechanical load of 18 ton easily.Just imagine a right breaker having 6 cables attach to 3 poles of breakers. Two RED,Two Yellow,Two Green.
Things that I observed.
The current capacity of that cable per core, accroding to catalog of cable=79A
The current reading through clamp meter per core=132A
STILL THE CIRCUIT BREAKER OF 100A DIDN'T TRIP
By doubling the cable 79x2=158A, per phase crane will get 158A.


Things that are still on my wind
1)Why the breaker of 100A didn't trip at readings of 100A,132A?
2)Why the crane didn't pickup the load when cable was single?
As a side effect, it should have got heaten up, but it must support currents of 100A.A cable that has maximum current per core=79A, why wasn't it able to flow up more than 79A at a cost of it's depriciation/destruction. I used to think before, that if i allow more current from 79A to let it flow, it will self destroy itself, but will allow to carry the current. But what I observed was that this crane wasn't able to pickup heavy load, as you can see in the picture.



The Electrical Over head crane is not able to lift this piece of steel on a single cable and the hoist motor(the top motor, that picks up load) was producing a great hum.When cable was doubled, crane operators said in the following words, it appears as if this crane has got a new life and it's more quick and powerful than before.

 

[jorgito]

crane electrical datasheet

Hello umery2k75,

Can you please provide more data on your circuit breakers?
I can not see clearly your photo, Specifically: Are the breakers actuated by thermal action only, or they also have magnetic action?
If they are thermal only, How much time have you measured the 130+ A current?
Regarding the cable size, when you speek about cable capacity, you only refers to cable self heating and not IR drop along the line, so you also need to consider cable length.
I remember having a similar problem as you, that I finally traced to a cable that started in the main cabinet as 16mm2, but was "converted" to 4mm2 in a undocumented junction box a couple of meters from the main cabinet!

Hope this helps!

 

[umery2k75]

german engineers 30 t crane

This is page#8, The MODEL = XE100NS on first column.



Here's the PDF, I can't find a dedicated datasheet of this breaker.This is from TERASAKI a chineese company :|

www.bchindia.com/products/Cat_PDF/MCCB.pdf

I talked with my friend right now on messenger. He told me that triping switch might be out of order inside the breaker. He added that , incomming 3 phase MAINS mostly have these sorts of problems.

How much time have you measured the 130+ A current?

I measured for more than 2 seconds. I guess. It was measured by Current Clamp Meter.

 

[jorgito]

what is electrical cranes?

Hello umery2k75,

Saddly, the specs do not have trip curves for your circuit breaker. Assuming a similar mag trip than others models (adjustable from 5 to 10 times In) you are not going to get instant trip at 130 A.
The thermal trip may be delayed more than 2 seconds. For example a Z curve may delay a 3 * In overcurrent more than 10 seconds.

Hope this helps you.
Best regards!

P.S.: Have you done some investigation on IR drop in your installation?

 

[umery2k75]

can clamping 2 wires at a time destroy clampmeter

No I haven't check up the IR drop of the cable.