## Calculate Size of Neutral Earthing Transformer (NET)(Excel)

• Calculate Total Capacitive charging current (It).
• Calculate Neutral Earthing Transformer  Secondary Current.
• Calculate Required Grounding Resistor value at primary side (Rp).
• Calculate Required Resistance value at secondary side (Rsec).
• Calculate Neutral Earthing Transformer X/R Ratio
• Calculate Fault current through Neutral (single line to ground fault) (If)
• Calculate Rating of Neutral Earthing Transformer (P).

## (1) Calculate Distance between each Street Light Pole:

Example: Calculate Distance between each streetlight pole having following Details,

• Road Details: The width of road is 11.5 Foot.
• Pole Details: The height of Pole is 26.5 Foot.
• Luminaire of each Pole: Wattage of Luminaries is 250 Watt, Lamp Out Put (LL) is 33200 Lumen, Required Lux Level (Eh) is 5 Lux, Coefficient of Utilization Factor (Cu) is 0.18, Lamp Lumen Depreciation Factor (LLD) is 0.8, Lamp Lumen Depreciation Factor (LLD) is 0.9.
• Space Height Ratio should be less than 3.

Calculation:

• Spacing between each Pole=(LL*CU*LLD*LDD) / Eh*W
• Spacing between each Pole=(33200×0.18×0.8×0.9) / (5×11.5)
• Spacing between each Pole= 75 Foot.
• Space Height Ratio = Distance between Pole / Road width
• Space Height Ratio = 3. Which is less than define value.

## (2) Calculate Street Light Luminaire Watt:

Example: Calculate Streetlight Watt of each Luminaire of Street Light Pole having following Details,

• Road Details: The width of road is 7 Meter. Distance between each Pole (D) is 50 Meter.
• Required Illumination Level for Street Light (L) is 6.46 Lux per Square Meter. Luminous efficacy is 24 Lumen/Watt.
• Maintenance Factor (mf) 0.29, Coefficient of Utilization Factor (Cu) is 0.9.

Calculation:

• Average Lumen of Lamp (Al) = 8663 Lumen.
• Average Lumen of Lamp (Al) =(LxWxD) / (mfxcu)
• Average Lumen of Lamp (Al)= (6.46x7x50) / (0.29×0.9)
• Average Lumen of Lamp (Al)=8663 Lumen.
• Watt of Each Street Light Luminar = Average Lumen of Lamp / Luminous efficacy
• Watt of Each Street Light Laminar = 8663 / 24

## (3) Calculate Required Power for Street Light Area:

Example: Calculate Streetlight Watt of following Street Light Area,

• Required Illumination Level for Street Light (L) is 6 Lux per Square Meter.
• Luminous efficacy (En) is 20 Lumen per Watt.
• Required Street Light Area to be illuminated (A) is 1 Square Meter.

Calculation:

• Required Streetlight Watt = (Lux per Sq.Meter X Surface Area of Street Light) / Lumen per Watt.
• Required Streetlight Watt = (6 X 1) / 20.