Why 11kV, 22kV, 33kV, 66kV, and 132kV

 Electricity transmission and distribution voltages are often multiples of 11, such as 11kV, 22kV, 33kV, 66kV, and 132kV, due to a combination of historical, technical, and practical factors.

The main reason behind this pattern is to compensate for voltage drops during transmission. When electricity travels long distances, it encounters resistance and impedance, leading to energy losses. To mitigate these losses, engineers design systems with voltage levels that allow a buffer for losses during transmission .

Key Factors Influencing Voltage Levels:

- Voltage Drop Compensation: Transmitting electricity at a slightly higher voltage (e.g., 11kV instead of 10kV) ensures that the actual delivered voltage remains within an acceptable range.
- Standardization: Using standardized voltage levels like 11kV, 22kV, and 33kV simplifies equipment design and production, reducing costs and improving interoperability.
- Efficient Power Transmission: Higher voltage levels minimize energy losses due to resistance in transmission lines .

1️⃣ Historical standardization

• Early power systems were developed at certain voltages that matched the limitations of insulation technology at the time.

• Once a voltage became standard, utilities and manufacturers adopted it widely, making it economical to continue using.

---

2️⃣ Economics and efficiency

• Higher voltages allow transmitting more power over longer distances with less current, which reduces I²R losses (heat losses in conductors).

• The chosen levels represent a balance between efficiency and cost—going higher in voltage increases insulation and equipment cost.

---

3️⃣ Insulation rating steps

• Equipment insulation is manufactured in specific classes (e.g., up to 1 kV, 11–15 kV, 22 kV, 33 kV, etc.).

• These steps correspond to practical insulation design and standard Basic Insulation Levels (BIL) set by IEC and IEEE.

---

4️⃣ Multiples of 11 or close to it

• Many medium voltage levels (11 kV, 22 kV, 33 kV, 66 kV, 132 kV) are multiples of 11 because:

  • Early transformers had ~10% voltage drop under full load, so an “11 kV” generator would still deliver ~10 kV at the far end.

  • Engineers standardized on “slightly higher” nominal voltages to ensure the load end got the required minimum.

  • Why Multiples of 11?

    The "multiple of 11" pattern likely originated from adding 10% to the desired voltage level to account for transmission losses. For example ³:

    - 10kV + 10% = 11kV

    - 20kV + 10% = 22kV

    - 30kV + 10% = 33kV

    - 60kV + 10% = 66kV

    - 120kV + 10% = 132kV

---

5️⃣ Practical transmission & distribution segmentation

• 1 kV – Upper limit for Low Voltage (LV) systems.

• 11–33 kV – Medium Voltage (MV) for distribution feeders.

• 66–132 kV – High Voltage (HV) for sub-transmission between substations.

• Above 220 kV – Extra High Voltage (EHV) for long-distance transmission.

---

If you want, I can also make a clear infographic showing where each voltage fits in the power system and why it’s chosen. That would make this much easier to remember. Thanks