Question

Two six pulse converters used for bipolar HVDC transmission system, are rated at 1000 MW, +- 200 kV. Find the rms current rating required for the SCRs.

(a) 2500 A

(b) 1350 A

(c) 1445 A

(d) none of the mentioned

The question was posed to me during an internship interview.

I'm obligated to ask this question of Applications of Power Electronics-2 topic in chapter Applications, Cycloconverters and  Miscellaneous of Power Electronics

Answer 1

Right answer is (c) 1445 A

The explanation is: Transmission voltage = 200 + 200 = 400 kV.

I = P/V = 1000 mW/ 400 kV = 2500 A.

As in 3-phase full converter each SCR conducts for 120° for a total period of 360°.

Irms = 2500 x √(120/360) = 1443.4 A. Nearly about 1445 A as it is a standard current rating.