Primary Transformer Compatability Problem
Primary Transformer Compatability Problem
(OP)
In checking into power problems in (2) differant rural schools. They both suffer a grea deal of electronic equipment failure (typically after a power outage or primary phase loss). I have found that both had delta wye configurations on the primary transformers. This is unusual in our area as the utility is a wye configured system. I feel that this is causing the problems but I am having trouble finding the documentation I need to support this. Any help would be appreciated.






RE: Primary Transformer Compatability Problem
If you get lightning in your area, you might also ask utility to check the transformer grounding to make sure it is intact. Surges on the primary can create problems on the secondary side if you don't have a good local ground reference.
Aside from the ferro-resonance problem, which can be solved by using three-pole switching and protection, a delta-wye configuration is really to be preferred over a wye-wye, at least for the customer.
RE: Primary Transformer Compatability Problem
One of the top electrical inspectors in northeast Ohio says tht only the bottom 2 feet of an 8 foot rod driven from the surface will act as a grounding electrode. Most soils around here are clay that retains moisture. He liked to drive ground rods below basement floors when he was an electrical contractor.
If the rod is installed in the backfill around the pole or is within 3 feet of the pole ground resistance will be increased by loose soil. Even if you use power compacting equipment the soil will take 20 years to compact enough to work well.
One time a cable plant technician for Ohio Bell told me that 97% of their lightning damage comes from silent lightning and invisible lightning. He then said that when a Big One strikes it has about 100 side strikes over a 100 yard radius.
We have also installed copper foil underneath floor tile to provide a static electricity path using the equipment grounding wires in the electrical outlets. If a person has a 100,000 volt or even 25,000 volt electric charge on them that is just like silent lightning.
RE: Primary Transformer Compatability Problem
Can you elaborate “primary transformers” ? Do you have your own secondary transformers?
Do you attribute the failure to lightening, Overvoltage and grounding ?
Is the primary side high voltage and Delta? And secondary Wye?
Is the secondary Wye 4 wires?
Do they have TVSS, Movs and other overvoltage protection devices on the Load side? You have more scope to work on Load side.
Marvin
RE: Primary Transformer Compatability Problem
One of the few things that Cleveland Public Power does right is to use 4 primary fuses on delta-delta transformer banks.
RE: Primary Transformer Compatability Problem
There are TVSS units on and MOV on the service as well as all of the building panels. In the older building (10 yrs) the Cutler Hammer MOV TVSS unit has expired and needs to be replaced. After an outage on the Max/Min panel meter that when they lost 2 of the phases the other phase increased to 528 volts. They did not lose equipment in this event, but it may illustrate what could be happening.
As far as load on the secondary side it is a school. It is overbuilt, lightly loaded and probably never a balanced load.