1. 1. Consider the simplified dc system shown in Fig. 1 . Only one converter is modeled, with the remote end represented by a dc source. 
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3. 2. The ac system is rated at 345 kV, with the converter transformer secondary voltage nominally set to 215 kV. 
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5. 3. Each transformer has an MVA rating of 600 MVA and has a leakage of 15%. Other system parameter values are indicated in the table. 
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7. 4.  The rectifier dc voltage is nominally 500 kV, and the nominal power at the rectifier end is 1000 MW.

Calculate the required transformer turns ratio and inverter side voltage 2 so that rated dc power and voltage are maintained with a firing angle α = 15°. Please note that although the transformer's voltage levels are given by 345kV:215kV, the transformer has a tap changer control which can vary the turns ratio. By calculating the required turns ratio, you are calculating the position of tap change.