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Transmission and Distribution Voltage Drop - SKM

Transmission and Distribution Voltage Drop - SKM

Transmission and Distribution Voltage Drop - SKM

(OP)
I am designing a 38kV transmission system that feeds delta wye transformers at from 2500kVA to 150kVA.  When I enter all of the data into SKM and perform the load flow and Voltage drop calculations the combined votlage drop from the point of connection to the secondary of the low voltage transformer total 6-8%.  

Q1) The NEC requires the voltage drop to be limited to 5%, but I am at the transmission level - are there any standars that govern the higher voltage levels?

Q2) To prevent my calculations from showing such a high voltage drop is it customary practice to utilize the transformer taps in the SKM project.  How else can this be fixed?

Q3)  Typically do voltage drop calculations restart at the secondary of the transformer?

RE: Transmission and Distribution Voltage Drop - SKM

Is this a transmission system or a distribution system?  If the secondary of the transformers is LV, then I would consider it distribution.  Distribution systems generally have voltage regulators.  Transmission systems usually don't.

ANSI C84.1 specifies voltag tolerance limits.  The ANSI C84.1 limits are also in the IEEE Red Book Std 141.

RE: Transmission and Distribution Voltage Drop - SKM

The NEC applies to the service or low voltage level.  If you back out the transformer drop, I suspect you'll be well within 5% for the drop for the conductors.

RE: Transmission and Distribution Voltage Drop - SKM

Q1. ANSI C84.1 specifies the allowable voltage ranges - http://www.powerqualityworld.com/2011/04/ansi-c84-1-voltage-ratings-60-hertz.html

Also, it is the utility's responsibility to make sure that voltages, both in the primary and secondary side of the distribution transformers to be within the Service Voltage limits set by ANSI.

Q2. First option is to change transformer tap setting. It won't cost you anything, except if transformer is already in service.

Q3. Question is not clear. Anyway, you can start voltage drop calculations at any point in the system as long as you know the voltage at that point.

RE: Transmission and Distribution Voltage Drop - SKM

(OP)
Thanks so much for your time and valuable answers.   

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