Effects of 1-Phase loads on 3-Phase transformers 2

[transformerman]

hi everyone,
my name is tony, and am searching for information and possible case studies concerning:

EFFECTTS OF SINGLE PHASE LOADS ON THREE PHASE TEANSFORMERS
ESPECIALLY IN DEVELOPING COUNTRIES:

The effects i am most interested in include:
1:Heating effects and efficiency variation on 3-phase star connected transformers when consumer single phase trasformers coupled to them are overloaded.
2:Most common causes of overloading and times of the day when this occurs.
3etaroriation of the cables as a result of this.
4:Cost implications of this.
5:Legal implications of this if there are any(can the power supply companies be held legally liable by the consumers?}
6:Measures being taken to overcome this and in cases where it has been overcome,the measures that enabled the overcoming of the problem.

 

[alehman]

I assume you refer to a 3-phase substation transformer supplying distribution circuits with 1-phase transformers for customer loads? Is your concern with overloading the 1-phase transformers or overloading the 3-phase transformer, or both?

So long as none of the phases of the 3-phase transformer are overloaded, it should not have a problem with 1-phase loads. The 3-phase transformer doesn't care if the 1-phase transformers are overloaded. If the load is highly unbalanced, voltages may become unbalanced which can be a problem for 3-phase loads. Distribution transformers can handle a lot of overload for a short amount of time.

 

[tinfoil]

Most utilities use grounded-wye connections on the load side of the station transformers, so the inter-phase effects of one phase loads is not that much of a problem. As alehman stated, so long as no one phase is overloaded, then the xmfr itself should not experience any problems.

In addition, most utilities to phase balancing, where the single phase loads are evenly distirbuted across all phases as evenly as possible. Individual 1phase distrbution transformers may be overloaded, but disappear into the statistics when the hundreds (perhaps thousands) of distribution transformers connected to the station transformer are aggregated.

Utilities will do periodic studies and adjustments if the phases on the system are not well balanced.