High-Altitude Consideration For Electrical Power System and Components

Nawaraj Kumar Mahato

Roll No: 120104024

B.Tech(EEE) 5th Sem

School of Engineering and Technology

Sharda University

In Guidance of Dhiraj Sinha

What is Power System?• Network which deals with the generation, distribution, transmission

and utilization of electric power and electrical power and electrical devices connected to the system including generators, motors and transformers.

Why do we need to Consider High-Altitude?

The main constraints are :-

• Temperature

• Barometric pressure.

• Humidity

• Relative air density

Relative Air Density

• Air is used as the dielectric in majority for distribution lines and practically all transmission lines.

• Another dielectric which is commonly used is vacuum.

• Air is good insulator and vacuum is even better.

• The dielectric strength varies directly with the pressure until the pressure is low enough that a “good” vacuum is created.

• The better the vacuum the higher the dielectric strength.

Pressure-spacing dependence of dielectric of air.

Relative Air Density

𝑅𝐴𝐷 =(0.392𝐵)

(273 + 𝑇)

• Where

• RAD = relative air density,

• B = barometric pressure (mm of Hg),

• T = temperature (°C).

The standard temperature and barometric pressure are 25 °C and 760mm of hg respectively

Here, RAD varies directly with the barometric pressure and inversely with the absolute temperature. RAD will vary from summer to winter, with the summer RAD normally being lower value.

Humidity

• Humidity also effects dielectric strength of air.

• The humidity factor of a dry climate will have a tendency to lower the insulating quality of air while that of the moist climate will have tendency to increase it.

• The standard humidity is 11g/𝑚2.

Power Supplies (Live Wire)

• Transmission and distribution lines, substation busses and other electrical equipment depend on air for means of insulation.

• The density and dielectric strength of air is good at sea level but at higher altitudes, the thinner air loses some of its dielectric strength.

• It needs to be insulated to prevent high voltage arching or breakdown within the supply, and to protect end to end-equipment and to operating personnel.

• For this, National Electricity Safety Code (NESC) has designated minimum clearances for the electrical supply stations and overhead lines.

Power supplies at high altitude

Power Transformers

• The standard does not speak about the operation of any equipmentbetween sea level to 1000m as no correction for the temperature risecorrection factor is applied.

• Therefore, the derating factor for dielectric strength are unity from sea level to 1000m.

• Above 1000m, the dielectric strength is derated at a rate of approximately one percent per 100m (three percent per 1000ft).

𝑇𝑎 = 𝑇𝑒 𝐴 − 1000 𝐹

• Where

• Ta = increase in temperature rise at altitude A meters (°C),

• Te = observed temperature rise (°C),

• F =4 ∗ 10−5, Self-cooled node,

• F =6 ∗ 10−5, forced-air cooled mode.

Motors and Generators

• Motors and generators having Class A and B insulation and air temperature rises provided that the ambient temperature compensated for increased temperature due to the reduced cooling at higher altitude.

Kulekhani Hydropower Plant

• Hydropower Plant of capacity 144 Mw at the height of 1530m.

Conclusion

It was concluded that the design of an electrical power system isaffected by the altitude of the system, therefore it is necessary to designthe system considering the factor. Many of the standards indicate that anelectrical devices will operate satisfactorily at elevations between sealevel to 1000m. Usually a derating is applied on equipment operatedabove 1000m.

Thank You

?Any Query