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RGarcia
February 6, 2021, 02:49 PM
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 ohms in each phase. How much is the secondary line current?

My answer is 9.6 Amps, I used 480V since it wont matter in the delta side (V line = V phase) and divide 50 ohms from it resulting 9.6 amps, however I got the question wrong. I know I line = 1.73 * I phase. I cant remember how to solve for it.
RGarcia
February 7, 2021, 12:34 AM
a watt-hour meter has a watt-hour constant, kh, of 1.2 it is used with 1200/5 ratio current transformers and 14,400/120 potential transformers. what is the primary watt-hour constant kh?

is it as simple as multiplying 1.2 by the CT Ratio and PT Ratio?
darinlamos
February 22, 2021, 02:52 PM
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 ohms in each phase. How much is the secondary line current?

My answer is 9.6 Amps, I used 480V since it wont matter in the delta side (V line = V phase) and divide 50 ohms from it resulting 9.6 amps, however I got the question wrong. I know I line = 1.73 * I phase. I cant remember how to solve for it.

You have to keep in mind the connection of the load. The load is connected Wye. Take the Delta secondary voltage and convert the phase voltage into line to ground. 480V/1.732 = 277V. 277V /50 ohms = 5.54A.
Izeldeen
November 7, 2021, 08:40 PM
a watt-hour meter has a watt-hour constant, kh, of 1.2 it is used with 1200/5 ratio current transformers and 14,400/120 potential transformers. what is the primary watt-hour constant kh?

is it as simple as multiplying 1.2 by the CT Ratio and PT Ratio?

yes
Izeldeen
November 7, 2021, 08:41 PM
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 ohms in each phase. How much is the secondary line current?

My answer is 9.6 Amps, I used 480V since it wont matter in the delta side (V line = V phase) and divide 50 ohms from it resulting 9.6 amps, however I got the question wrong. I know I line = 1.73 * I phase. I cant remember how to solve for it.

480/1.732=277
277/50=5.54A