Voltage drop problem

[Nestory Dismas]

Dear Team,
Please assist me as per the following explanations,

I spent last night and this morning stripping my systems apart to try and see if I could find any faults.


Can you please help me and advice testing/fault finding equipment to verify our equipment provided
1 X 33KV Ring Main Unit
1 X MVA Transformer
1 X 500KVA Transformer

Within the port we have a RMU distributing to 2 X Transformers, from these we have LV panels with a backup generator (change over switches in place).

When we are running through Utility
L1/N is showing 170V
L2 /N is showing 237V
L3/N is showing 359V
N/E is showing 117V

Running through generator
L1/N 241V
L2/N 237V
L3/N 239V
N/E 12V

This leads me to believe that there is a poor connection between our N and the incoming Transformers, this will mean our N is not held to our earth potential. This fault has only just developed, so we need to find the reason.
What can be the possible causes??

 

[Smart $]

...
This leads me to believe that there is a poor connection between our N and the incoming Transformers, this will mean our N is not held to our earth potential. This fault has only just developed, so we need to find the reason.
What can be the possible causes??

Looks to me you already suspect the correct cause... :happyyes:

Poor if not non-existent N-source connection will allow LN-load voltage to float, even when it has solid GE connection.

 

[Tony S]

I had the same thing happen but for a slightly bizarre reason.

Two electricians unfamiliar with the layout of the main panel disconnected the NE jumper to make way while they pulled a new cable in, they then reconnected the jumper and left. In the mean time all the office equipment had been toasted. As I’d installed the panel and 500kVA transformer I was sent to investigate, I couldn’t find anything wrong as the gruesome twosome had left. It took a chance conversation over lunch days later to find out what had happened.