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Wye-delta transformer secondary line current Jump to latest post
1.  Junior Member
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Reputation Wye-delta transformer secondary line current

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.  Reply With Quote

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Reputation NETA Level 2 Practice Exam

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?  Reply With Quote

3. Originally Posted by RGarcia 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.  Reply With Quote

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Reputation   Originally Posted by RGarcia 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  Reply With Quote

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Reputation   Originally Posted by RGarcia 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  Reply With Quote

electrical calculations, electrical theory, neta exam questions, neta level 2, neta level 3, transformers  