Gas Turbine Generator Configuration: Basic Sizing and Selection
During engineering phase, sizing Gas Turbine Generator (GTG) is started from electrical load calculation. When the electrical load is confirmed then it will basis for GTG selection, normally it will use Electrical Design Load which is 1.2 Peak Load.
It will be based on the project specific requirement how electrical load margin (contingency, growth allowance, etc..) is calculated, i.e., Total Load, Normal Load, Peak Load and Design load. For example, Normal Load is calculated by Total Continuous + (50% x Total intermittent Load, Peak Load is calculated by Normal Load + (10% x Total Standby Loads or any one biggest Standby Loads), then Design load is 1.2 x Peak Load.
When the Design Load is confirmed, we will go to the vendor/manufacturer to get the quotation for actual arrangement/configuration available in the market. Each manufacturer like GE, Siemens, SOLAR Turbine and others has their product range which possibly meet with our power demand.
As each manufacturer has specific ISO rating which may different to the other it will be challenging to see the best configuration that meet our power demand.
Fig-1 Sample GTG configuration Lay Out
The following table is summary what GTG model is available in the market comparing to our design load and their possible configuration. Please note that this is only sample and GTG ISO rating may not exactly match with any GTG model on the actual market.
Let we assume we require 17,000 KW Design Load in this sample case.
Fig-2 GTG configuration selection
In this sample we consider degradation to the site rating which directly impact to the aged condition we assume that GTG is still able to cover the electrical load in the several year after Plant is running. We may add some another assumption as a basis during engineering as required on project requirement, of course.
As per above Table we can see the optimum configuration that technically acceptable which is in this case N+1=3 GTG configuration. N is number of GTG running and 1 is number of standby GTG.
It mean that, in this sample case both above vendor proposal with N+1=3 configuration can go further to the commercial evaluation and finally purchased the GTG.