Transformer Selection Example

In reviewing how Design Optimization uses algorithms to select the optimum transformer, let’s consider a URD with eight connected service points for a single-family, high density development as shown in the following example:

The load profile for this design is shown in the following example:

The two parameters of interest in the load profile are the Building Floor Area (2000) and Peak kVA Per Area (0.004). Using these parameters, Design Optimization calculates the peak kVA load for each service point:

2000 x 0.004 = 8 kVA

Design Optimization calculates the kVA peak load and displays it in a list in the Design Optimization Group Parcels window as shown in the following example:

Design Optimization can now calculate the diversified kVA peak load. For this example, let’s assume the coincidence factor (based on eight service points) is 0.609375. Therefore, the diversified load kVA for all eight connected service points is:

8 kVA(0.609375) + 8 kVA(0.609375) + 8 kVA(0.609375) + 8 kVA(0.609375) + 8 kVA(0.609375) + 8 kVA(0.609375) = 39 kVA

Now that we know the diversified kVA peak load for the selected parcels, Design Optimization can choose the transformer that will meet the load demand. Design Optimization selects the transformer from a list of available transformers stored in the transformer catalog as shown in the following example:

In selecting the optimum transformer, Design Optimization considers the maximum allowable overload on a transformer as specified in the electrical policy settings. For this example, let’s assume the maximum allowable overload is 120% of the transformers kVA rating as exemplified in the following graphic:

Based on this scenario, the 25 kVA and 50 kVA transformers are two potential choices for servicing a diversified peak load of 39 kVA. The 50 kVA transfomer falls within the 120% maximum transformer overload factor, while servicing a diversified peak load with a 25 kVA transformer exceeds the 120% maximum overload factor. Therefore, Design Optimization selects the 50 kVA transformer as shown in the following example:

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