effect of unbalance load on transformer and grid

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panthripu

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Hi
Let me ask all experts to understand few questions in my mind.
Assuming that a load 100MW is run intentionally with two phase.What effect is it going to make on the transformer which is feeding it and the complete network there after? I keep an electric arc furnace in mind while thinking of this question.
 
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GoldDigger

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panthripu said:
Hi
Let me ask all experts to understand few questions in my mind.
Assuming that a load 100MW is run intentionally with two phase.What effect is it going to make on the transformer which is feeding it and the complete network there after? I keep an electric arc furnace in mind while thinking of this question.
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Other than the details, following Phil's suggested calculations, the main effect will be:
Inefficient use of the transformer and wire resources if they are sized to take care of a balanced three phase load, one phase of which has the calculated power, compared to feeding only one phase (two phase wires.)
But if you have a three phase transformer and only use it to supply one phase you can get a little more current from its secondary than if it were fully loaded on all phases. For exact allowance, see manufacturer.

The effects upstream toward POCO are also waste of distribution and generating capacity if they cannot balance it with other customers' loads.
 
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Phil Corso

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Panthripu…

Reur 1st question (secondary effects):
The secondary system’s neural-current will double. Although the impact on the xfmr's secondary-winding is ‘nil’, the neutral circuit will be exposed to negative effects! One, is the arc itself, especially if the electrode’s are tre-foil arranged. Then too, the xfmr’s neutral connection will certainly suffer, as well as return-path components!

Reur 2nd question (primary effects):
If the grid’s capacity is at least 10x that of the xfmr there shouldn’t be any ill-effect to the grid!

Caveat: The above conclusions were based on several simple facts about EAF installations:

1) Load is predominately resistive in nature.

2) EAF operates close to short-circuit conditions

3) Xfmr impedance is quite small relative to the load, thus ignored

4) Harmonic and excitation effects were ignored!

5) Xfmr Windings configured as Delta-Wye.

6) Secondary-system load is 3ph, 4w.

Phil Corso
 
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