How to Design efficient Street lighting-(Part-1)


Introduction:

  • The basic idea of roadway and Highway lighting is to provide uniform level of illumination on road at horizontal and vertical level and provide a safe and comfortable environment for the night time driver.
  • Lighting design is basic idea of the selection and the location of lighting equipment to provide improved visibility and increased safety.
  • Street lighting systems should be designed in a way to avoid significant differences in luminance levels at the light source and on road areas. Furthermore, continuous variation of lighting levels can cause eye strain and should be avoided, in particular on long roads.
  • Road lighting provides visual conditions for safe, quick and comfortable movement of Road users.

 Designing Factor for Street Light:

  • The factors that are playing a vital role in the Road Lighting are following.

(A) Type of Road

  • Road Classification

(B) Street Light Pole

  • Street Light Pole Arrangements
  • Placement of Pole

(C) Lighting Fixture

  • Lighting Fixture Mounting Height
  • Lighting Fixture Classification
  • Lighting Fixture Distributor

(D) Lighting Factors

  • Maintenance Factor
  • Coefficient of Utilization

(E) Lighting Uniformity

  • Lighting Uniformity
  • Surrounding Ratio

(F) Lighting Pollution

  • Glare
  • Sky Glow
  • Trespass

(G) Selection of Luminas

  • Type of Light
  • Watt
  • Lumen
  • CRI
  • Efficiency

(A) Road Classification:

Table 4 : Road Classes as per SP 72 (Part 8), IS 1944 (Part 1) and IS 1970

Class A1 Important routes with rapid and dense traffic where safety, traffic speed, and driving comfort are the main considerations
Class A2 Main Roads with considerable volume of mixed traffic, such as main city streets, arterial roads and thoroughfares.
Class B1 Secondary roads with considerable traffic such as main local traffic routes, shopping streets
Class B2 Secondary roads, with light traffic
Class C Lighting for residential and unclassified roads not included in previous groups
Class D Lighting for bridges and flyovers
Class E Lighting for town and city centers
Class F Lighting for roads with special requirement such as roads near air fields, railways and docks

 

TYPE OF ROAD

TYPE OF ROAD DENSITY OF TRAFFIC TYPE EXAMPLE
A Heavy and high speed motorized traffic Road with fixed separators, No crossings for very long distance National highways or state highways or called interstate highways, express ways or motor ways
B Slightly lower density and lower speed traffic termed Road which is made for vehicular traffic with adjoining streets for slow traffic and pedestrians as we find in metros Trunk road or major road in a city
C Heavy and moderate speed traffic Important urban roads or rural roads. they do not interfere with the local traffic within the town Ring roads
D Slow traffic, pedestrians Linking to shopping areas and invariably the pedestrians, approach road Shopping street, trunk road
E Limited speed. Slow or mixed traffic predominantly pedestrians, Local streets, collectors road

(B) Street Light Pole:

(1) Street Light Arrangement:

  • There are four basic types of street lighting layout arrangements used for streets or highways illumination.

(A) One Side Pole Layout:

  • In One Side Pole Layout, all luminaries are located on one side of the road.
  • Road Width: For narrower roads.
  • Pole Height: The installation height of the lamp be equal to or less than the effective width of the road surface.

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  • Advantage: There are good indelibility and low manufacturing cost.
  • Disadvantage: The brightness (illuminance) of the road on the side where the lamp is not placed is lower than the on which side the light pole is placed.

(B) Both Side Staggered Pole Layout:

  • In the staggered arrangement, the luminaires are placed alternately on each side of the road in a “zig-zag” or staggered fashion.
  • Road Width: For Medium Size roads.
  • Pole Height: The installation height of the lamp is equal or 1.5 time the effective width of the road.

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  • Advantage: This type of arrangement is better than single side arrangement.
  • Disadvantage: Their longitudinal luminance uniformity is generally low and creates an alternating pattern of bright and dark patches. However, during wet weather they cover the whole road better than single-side arrangements.

(C) Both Side opposite Pole Layout:

  • In Both Side Opposite Pole Layout, the luminaries located on both sides of the road opposite to one another.
  • Road Width: For Medium Size roads.
  • Pole Height: The installation height of the lamp will be 2 to 2.5 time the effective width of the road.

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  • Advantage: opposite arrangements may provide slightly better lighting under wet conditions.
  • Disadvantage:
  • If the arrangement is used for a dual carriageway with a central reserve of at least one-third the carriageway with, or if the central reserve includes other significant visual obstructions (such as trees or screens), it effectively becomes two single-sided arrangements and must be treated as such.

 (D) Twin-central Pole Layout:

  • In Twin central arrangement, the luminaries are mounted on a T-shaped in the middle of the center island of the road. The central reserve is not too wide, both luminaires can contribute to the luminance of the road surface on either lane.
  • Road Width: For Large Size roads.
  • Pole Height: The installation height of the lamp be equal to the effective width of the road.

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  • Advantage: This arrangement generally more efficient than opposite arrangements. However, opposite arrangements may provide slightly better lighting under wet conditions.
  • Disadvantage:

Calculate Size of Pole Foundation & Wind Pressure on Pole


Example:

  • Calculate Pole foundation size and Wind pressure on Pole for following Details.
  • Tubular Street Light Pole (430V) height is 11 Meter which is in made with three different size of Tubular Pipe.
  • First Part is 2.7 meter height with 140mm diameter,
  • Second part of Pole is 2.7 meter height with 146 mm diameter and
  • Third part of Pole is 5.6 meter height with 194 mm diameter.
  • Weight of Pole is 241 kg and there is no any other Flood Light Fixtures Load on Pole.
  • Total Safety Factor is 2.
  • Wind zone category is 3.
  • The Pole is installed in open terrain with well scattered obstructions having height generally between 1.5 m to 10 m.
  • Foundation of pole is 700mm length, 700mm width and 1.95 meter depth. The Average weight of foundation concrete is 2500 Kg/M3.

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Calculation:

 Wind Pressure according to Location:

  • Wind Zone is 3 so Wind Speed as per following Table.
Basic Wind Speed-Vb (As per IS 802-Part1)
Wind Zone  Basic Wind Speed, vb m/s
1 33
2 39
3 44
4 47
5 50
6 55
  • Wind Speed (vb) = 44Mile/Second.
  • Co-efficient Factor (K0)=1.37
  • K0 is a factor to convert 3 seconds peak gust speed into average speed of wind during 10 minutes period at a level of 10 meters above ground. K0 may be taken as 1.375.
  • The Pole is used for 430Vand wind zone is 3 so Risk Co-efficient (K1) as per following Table
Table 2 Risk Coefficient K1 for Different Reliability Levels and Wind Zones (As per IS 802-Part1)
Reliability  Level Wind Zone-1 Wind Zone-2 Wind Zone-3 Wind Zone-4 Wind Zone-5 Wind Zone-6
1 (Up to 400KV) 1 1 1 1 1 1
2 (Above 400KV) 1.08 1.1 1.11 1.12 1.13 1.14
3 (River Crossing) 1.17 1.22 1.25 1.27 1.28 1.3
  • Risk Co-efficient (K1) =1
  • Terrain category (K2) for Open terrain with well scattered obstructions having height generally between 1.5 m to 10 m is 1 as per following Table
  • Terrain category (K2)=1
Terrain Roughness Coefficient, K2 (As per IS 802-Part1)
Terrain Category Category 1 Category 2 Category 3
Exposed open terrain with no obstruction and in which the average height of any object surrounding the structure is less than 1.5 m. Open terrain with well scattered obstructions having height generally between 1.5 m to 10 m. Terrain with numerous
closely spaced obstructions.
Coefficient, K2 1.08 1 0.85
  • Reference Wind Speed (Vr)= Vb / K0.
  • Reference Wind Speed (Vr)= 44 / 1.37 =32 Mile/Second.
  • Design wind Speed (vd)= Vr X K1 X K2.
  • Design wind Speed (vd)= 32 X 1 X 1 =32 Mile/Second.
  • Design Wind Pressure (Pd)=0.6 x vd2
  • Design Wind Pressure (Pd)=0.6 x (32)2 =614.4 N/m2
  • Design Wind Pressure (Pd)=614.4/10 =61.4 Kg/m2

Foundation Detail:

  • Total Weight =Pole Weight +Foundation Weight.
  • Total Weight = 241 +(0.7×0.7×1.95×2500) =2620.75 Kg
  • Stabilizing Moment = Total Weight X (Foundation Length/2)
  • Stabilizing Moment = 2620.75 X (0.7/2) = 920.41 Kg/Meter.

Pole Detail:

  • First Part of Pole (h1) = 2.7 meter
  • Diameter of First Part (d1) =140mm
  • Second Part of Pole (h2) = 2.7 meter
  • Diameter of Second Part (d2) =146mm
  • Third Part of Pole (h3) = 5.6 meter
  • Diameter of Third Part (d3) =194mm .

Wind Pressure on Pole:

  • Overturning Moment due to the wind on 1st Part of the pole=pdxh1xd1x(h1/2+h2+h3)x0.6
  • Overturning Moment due to the wind on 1st Part of the pole=61.4×2.7x(140/1000)x(2.7/2+2.7+5.61)x0.6
  • Overturning Moment due to the wind on 1st Part of the pole=134.47 Kg/meter—I
  • Overturning Moment due to the wind on 2nd Part of the pole=pdxh2xd2x(h2/2+h3)x0.6
  • Overturning Moment due to the wind on 2nd Part of the pole=61.4×2.7x(146/1000)x(2.7/2+5.61)x0.6
  • Overturning Moment due to the wind on 2nd Part of the pole=112.76 Kg/meter.—-II
  • Overturning Moment due to the wind on 3rd Part of the pole=pdxh3xd3x(h3/2)x0.6
  • Overturning Moment due to the wind on 3rd Part of the pole=61.4×5.6x(194/1000)x(5.6/2)x0.6
  • Overturning Moment due to the wind on 3rd Part of the pole=112.14 Kg/meter.—III
  • Total Overturning Moment on Pole due to Wind=134.47+112.76+112.14=359.36 Kg/meter.

 Safety Factor:

  • Calculated Safety Factor= Stabilizing Moment / Total Overturning Moment on Pole.
  • Calculated Safety Factor=920.41/ 359.36 =2.56.
  • For safe Design Calculated Safety Factor > Safety Factor
  • Here Calculated Safety Factor (2.56) > Safety Factor (2) hence
  • Design is OK
  • B : If Calculated Safety Factor < Safety Factor then Change Foundation Size (Length, width or depth)

 

Calculate Size of Circuit Breaker/ Fuse for Transformer (As per NEC)


  • Calculate Size of Circuit Breaker or Fuse on Primary and Secondary side of Transformer having following Detail
  • Transformer Details(P)= 1000KVA
  • Primary Voltage (Vp)= 11000 Volt
  • Secondary Voltage (Vs)= 430 Volt
  • Transformer Impedance= 5%
  • Transformer Connection = Delta / Star
  • Transformer is in unsupervised condition.

Calculations:

  • Transformer Primary Current (Ip)= P/1.732xVp
  • Transformer Primary Current (Ip)=1000000/1.732×11000=49Amp
  • Transformer Secondary Current (Is)= P/1.732xVs
  • Transformer Secondary Current (Is)=1000000/1.732×430=71Amp
  • AS per NEC 450.3, Max.Rating of C.B or Fuse is following % of its Current according to it’s Primary Voltage,% Impedance and Supervised/Unsupervised Condition.

Max Rating of Over current Protection for Unsupervised Transformer More than 600 Volts (As per NEC)

%Imp Primary secondary
>600Volt >600Volt <600Volt
C.B Fuse C.B Fuse C.B/Fuse
 Up to 6% 600% 300% 300% 250% 125%
More than 6% 400% 300% 250% 225% 125%

 

Max Rating of Over current Protection for Supervised Transformer More than 600 Volts (As per NEC)

%Imp Primary secondary
>600Volt >600Volt <600Volt
C.B Fuse C.B Fuse C.B/Fuse
 Up to 6% 600% 300% 300% 250% 250%
More than 6% 400% 300% 250% 225% 250%

 

Max Rating of Over current Protection for Transformers Primary Voltage Less than 600 Volts (As per NEC)

Protection Primary Protection Secondary Protection
Method More than 9A 2A to 9A Less than 2A More than 9A Less than 9A
Primary only protection 125% 167% 300% Not required Not required
Primary and secondary protection 250% 250% 250% 125% 167%

 

Size of Fuse / Inverse Time C.B as per NEC (Amp)

1 25 60 125 250 600 2000
3 30 70 150 300 700 2500
6 35 80 160 350 800 3000
10 40 90 175 400 1000 4000
15 45 100 200 450 1200 5000
20 50 110 225 500 1600 6000

For Primary Side:

  • Transformer Primary Current (Ip) =52.49Amp and impedance is 5%
  • As per above table in not supervised condition Size of Circuit Breaker= 600% of Primary Current
  • Size of Circuit Breaker = 52.49 x 600% =315Amp
  • If Transformer is in supervised condition then Select Circuit Breaker near that size but if Transformer is in unsupervised condition then Select Circuit Breaker next higher size.
  • Rating of Circuit Breaker =350Amp (Next Higher Size of 300Amp)
  • Size of Fuse = 52.49 x300% =157Amp
  • Rating of Fuse =160Amp (Next Higher Size of 150Amp)

For Secondary Side:

  • Transformer Secondary Current (Is) =1342.70Amp and impedance is 5%
  • As per above table in not supervised condition Size of Circuit Breaker= 125% of Secondary Current
  • Size of Circuit Breaker = 1342.70 x 125% =1678Amp
  • If Transformer is in supervised condition then Select Circuit Breaker near that size but if Transformer is in unsupervised condition then Select Circuit Breaker next higher size.
  • Rating of Circuit Breaker =2000Amp (Next Higher Size of 1600Amp)
  • Size of Fuse = 1342.70 x125% =1678Amp
  • Rating of Fuse =2000Amp (Next Higher Size of 1600Amp)

 Results:

  • Size of Circuit Breaker on Primary Side=350Amp
  • Size of Fuse on Primary Side=160Amp
  • Size of Circuit Breaker on Secondary Side=2000Amp
  • Size of Fuse on Secondary Side=2000Amp
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