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Why Power Transmission / Distribution Voltage is always 11KV, 33KV, 66KV, and 132KV?

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Why are the electric power transmission distribution voltage of only 11KV, 33KV, 66KV, and 132KV? Just why are they multiples of 11? Why not 10, 30, 60, 120? Let’s find the explanation.

Many say the idea is that the form factor is 1.11, the voltage pattern is like that.

• 10 × 1.11 = 11.1
• 30 × 1.11 = 33.3
• 60 × 1.11 = 66.6
• 120 × 1.11 = 133.2

In reality this idea is not correct because multiplying 120 volts by 1.11 does not give 132 KV.

Again, the form factor is the ratio of RMS & the Average value. There is no point in multiplying it. So, which one is right?

Let me give you an example before that. Suppose, you got a contract to send 500 mangoes from Rajshahi to Chittagong. Then will you send only 500 mangoes along? Of course not.

Because there may be snatching on the way or the mango may rot. So, they keep some backup. They provide 50 extra mangoes. Similarly, power transmission/distribution companies send 10% more voltage than the actual voltage. Because they know very well that there will be system loss along the way.

Now let’s calculate,

• 10 + 10 × 10% = 11 KV
• 30 + 30 × 10% = 33 KV
• 60 + 60 × 10% = 66 KV
• 120 + 120 × 10% = 132 KV

Now, many people are wondering why electric power transmission distribution voltage is only calculated using 10, 30, 60, 120?

Generating & distribution stations in our country mainly generate this voltage. The latter transmits the said voltages along with the back-up. Yes, it may be a little less. However, this calculation is on average.

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