Help with a transformer

[Royston87]

I have a 110 5kva transformer. Run it off a 30 meter exstension lead running from the house into the Work shop. The transformer works and powers all machines
I've now installed a 6 mm armoured cable running length 30 meters on a 32amp breaker to the woek shop. When plug the transformer into the work shop sockets it trips the breaker. But socckets runs every thing else with out tripping. What could be the problem ?

 

[Chivers]

Can you check polarity in the 1st instance, and just for clarity is it an MCB tripping or RCD?

 

[Royston87]

Can you check polarity in the 1st instance, and just for clarity is it an MCB tripping or RCD?

Hi. Yes it's tripping the mcb. Only happens running from the sockets in the workshop. But nothing else trips it

 

[Chivers]

Have you tested the ZS at the end of the SWA? Only thing I can think of personally is when it's initially powered up there's a slight surge but does sound a little odd.

 

[Royston87]

Have you tested the ZS at the end of the SWA? Only thing I can think of personally is when it's initially powered up there's a slight surge but does sound a little odd.

Just tried a exstension lead in the work shop. Now that powers the transformer Fine. Just a direct plug to sockets to the sockets trips. Just cant think why

 

[westward10]

It is almost certainly surge from the transformer. Different Type of mcb supplying the shed, can you show the consumer unit.

 

[pc1966]

Just tried a extension lead in the work shop. Now that powers the transformer Fine. Just a direct plug to sockets to the sockets trips. Just cant think why

The added resistance of the extension lead (probably 1.5mm at most) is much more than the 6mm SWA, so any surge from the transformer now lacks that extra mitigation.

As @westward10 says you need to tell us more about the type of MCB, etc. Often for transformers a D-curve is used to avoid such trips, but that also has issues of achieving low enough Zs to meet disconnection times.

For a 5kVA transformer at 230V Hager recommend wither 63A C-curve or 32A D-curve. A 32A BS88 fuse has easier-to-meet Zs for similar surge capacity, but not nearly as convenient as a MCB.

 

[pc1966]

For a 5kVA transformer at 230V Hager recommend wither 63A C-curve or 32A D-curve. A 32A BS88 fuse has easier-to-meet Zs for similar surge capacity, but not nearly as convenient as a MCB.

I would add that those MCB recommendations are for fault protection, not for overload protection of the transformer. It might have its own protection on the primary (230V) or on the secondary (110V) sides, but check the manufacturer's recommendation for supply protection first.