Transformer laoding 5

[H1H2N3F4]

I have a primary transformer that is a 1500 KVA, 69KV/13.8KV.

This transformer is supplying power to different loads total of ( 680 KVA).

A request for more power from this transformer was processed with the following specification:

Connected load is 1000KVA and the estimated total Demand Load is 600KVA.

The question is since I am a new to these terms (Connected and Demand), can any one explain what they mean and wither I can approve the request or not.



MMQ

 

[tinfoil]

The term 'connected load' usually refers to the SUM of ALL devices connected 'downstream', assuming every single device were using nameplate maximum power simultaneously.

The term 'demand load' usually refers to the largest momentary power that will be experienced under any reasonable scenario. This value is almost always less than the connected figure.

Looking at a typical home in North America, if you were to plug in and turn on every device and applicance available (i.e. washing machine, 2 hair dryers, water heater, furnace controller, TV's, VCRs, stereos, pool pump, clothes dryer, dishwasher, light bulbs, lawnmower, etc, etc), then you could easily THEORETICALLY reach 20-25kW even without electric space heating. But it is not reasonable to expect all of these things to be used at once.

However, utility planners usually use a lower demand load factor. If a transformer is supplying 6 or more homes, then a much lower number is assumed (due to load diversity). For example, we use 3kW as the worst-case, if no electric heat is present in a subdivision.

Getting back to your specific situation, it would appear that someone wishes to add ~600kVA to a load measured previously at 680kVA peak. If you add a 'pessimism factor' and assume the new peak load will be 600*1.33 (say), you get 680+600*1.33=1480kVA (ASSUMING that all of the customers' peaks will occur simultaneously, which usually doesn't happen).

In my area, we WOULD allow that load to be connected. However, your utility may have specific policies on these issues, which you should review before you make any decision.

 

[busbar]

One formal reference is IEEE Std C57.91-1995, guide for loading mineral-oil-immersed transformers.