Running Load or Peak Load?
Running Load or Peak Load?
(OP)
In determining generator or transformer sizes which type of load to be considered (industrial application): Maximum Running Load or Peak Load.
In our calculations,
Running Load = 100% x Continuous Load + 50% Intermittent Loads
Peak Load = 100% x Continuous Load + 50% Intermittent Loads +
20% Standby Loads
The loads above are base loads based on individual MCC load calculations (with load factor considered for each utilization equipment). The percent factors above are diversity (to consider non-coincidence). It does not include any projected future load and contingency factor.
In our calculations,
Running Load = 100% x Continuous Load + 50% Intermittent Loads
Peak Load = 100% x Continuous Load + 50% Intermittent Loads +
20% Standby Loads
The loads above are base loads based on individual MCC load calculations (with load factor considered for each utilization equipment). The percent factors above are diversity (to consider non-coincidence). It does not include any projected future load and contingency factor.






RE: Running Load or Peak Load?
- Client standards: really, this is the first port of call since many clients will actually stipulate _exactly_ how they want you to size equipment. For example, Shell DEP 33.64.10.10-Gen calls for switchgear, generators, transformers, etc to be able to continuously supply 125% of the peak load.
- Redundancy / operational considerations: if you're running in a completely redundant configuration (e.g. 2 x 100% transformers), then in normal operation, the transformers will be loaded at 50% or less.
- Type of generator: some generators such as gas engine generators have low turndown capability and need to be operated at >50% load to avoid excessive CO and NOx emissions. On the other hand, these generators typically also have high transient reactance, so you may want lots of spinning reserve for large motor starting.
- Equipment lifetime considerations: transformers can potentially last much longer if they're lightly loaded, especially in high temperature environments.
- Standard unit sizes: if the running load is 1550kVA and the peak load is 1620kVA, would it be more reasonable to specify a 1600kVA or 2000kVA transformer (assuming allowances for future loads and design contingencies have been captured)? Perhaps you might consider 2000kVA to be oversized. Or perhaps all of your other transformers are 2MVA and you can standardise and keep maintenance spares.
- Client preferences: are they conservative or would they prefer to operate more on the margins (but cut costs)?
Ultimately, unless the client has specific instructions on how to size the equipment, it will come down to "engineering judgement". As nebulous as that sounds, as long as you can justify your decisions and get client buy-in, then it should would out fine.