Transformer Efficiency and Load Capacity
1. Transformer Rating and Efficiency:
When a transformer is rated at 100 kVA
(kilovoltamperes), it means that it can
supply up to 100 kVA of apparent power
under ideal conditions.
However, the efficiency of a transformer
(the ratio of output power to input power)
is not always 100%. If a transformer has an
efficiency of 90%, it means that 90% of the
input power is converted to useful output
power, while 10% is lost as heat or other
forms of losses.
2. Understanding Derating:
Derating a transformer means reducing its
operating capacity to ensure it operates
efficiently without overheating or becoming overloaded. A derating factor of 0.9 means the transformer should operate at 90% of its rated capacity to ensure optimal performance.
For a 100 kVA transformer with a 0.9
derating factor, the effective capacity is 90
kVA. This is the maximum load you should
connect to the transformer to maintain its
efficiency and avoid overloading.
3. Calculating the Load Capacity:
If you connect a load higher than 90 kVA to
a 100 kVA transformer with 90% efficiency,
the transformer operates beyond its
derated capacity.
For example, if you connect a load of 95
kVA:
The load (95 kVA) exceeds the derated
capacity (90 kVA).
Operating at 95 kVA will cause the
transformer to run inefficiently and potentially overheat or experience higher
losses.
Conclusion: Importance of Selecting the
Correct Transformer Size
Why Choose a Transformer at 90% Efficiency?
When selecting a transformer, consider
both the rated capacity and its efficiency to
ensure it can handle the desired load
without issues.
Choosing a transformer with a capacity at
or below 90% of its rating ensures it
operates within its efficiency range,
minimizes losses, and prolongs its lifespan.
For a 100 kVA transformer with 90%
efficiency and a 0.9 derating factor, you
should ideally connect loads up to 90 kVA
and not exceed this limit to avoid overloading.