Sunday, 31 August 2014

Solar Powered Wheelchair

Haidar Taleb, a 47 year old man from UAE, displayed a rare combination of human spirit and willpower when he took up a 200-mile long journey on a wheel chair that he has built for himself which runs on solar power. Being a person with polio since the age of 4 has not stopped him from taking up this challenge on this wheelchair, a piece of technological innovation.

https://www.youtube.com/watch?feature=player_embedded&v=fV4D3CGiYXQ


World Records In Haidar’s Name.
Since this is not the first time Haider has taken up such journey on his solar powered wheel chair, he will have more than one record in his name once he finishes this tour. These include,
  • Entering Guinness Book of World Records by traveling 80 miles during a 14-hour trip from Abu Dhabi to Sharjah at a speed of 12 mph on a solar-powered wheelchair.
  • Making his own record better by 200 miles, mentioned above on the same wheel chair.
Aim of the journey
Haider says, “By taking-up this journey, I want to raise awareness about disability and tell people that we, despite our disability can achieve anything as an individual, if we are determined to try and have courage to do so.” With this journey Haider also wants to send out a message to other persons with disabilities like him, who have mobility problem. He wants to tell them, “There are no obstructions because you can do as you think. Given a chance, persons with disabilities can perform miracles.”
During the course of his journey, Haider will share the above message to inspire everyone when he talks to both disabled and non-disabled people in schools, colleges and centers working for the disabled.
Promoting eco friendly wheelchairs 
With this journey, Haidar has helped to promote eco friendly wheelchairs. He says, “This journey was important in the sense that through it, apart from encouraging persons with disabilities in general, I have shown the world that solar-powered wheel-chair are important and they can change the lives of persons with mobility problems.”
The journey that Haider took on with the help of the eco-friendly device was sponsored byMasdar. It is a project to encourage detailed research into alternative energy solutions. It is hoped that the invention of solar-powered wheelchair and the message Haidar has given, will have a far reaching effects.

Sunday, 17 August 2014

Cabel Sizing Calculations and considerations



Input information

Electrical details:

Electrical load of 80KW, distance between source and load is 200 meters, system voltage415V three phase, power factor is 0.8, permissible voltage drop is 5%, demand factor is 1.
Cable laying details:

Cable is directed buried in ground in trench at the depth of 1 meter. Ground temperature is approximate 35 Deg. Number of cable per trench is 1. Number of run of cable is 1 run.
Soil details:

Thermal resistivity of soil is not known. Nature of soil is damp soil.

Ok, let’s dive into calculations…
Consumed Load = Total Load · Demand Factor:
Consumed Load in KW = 80 · 1 = 80 KW
Consumed Load in KVA = KW/P.F.:
Consumed Load in KVA = 80/0.8 = 100 KVA
Full Load Current = (KVA · 1000) / (1.732 · Voltage):
Full Load Current = (100 · 1000) / (1.732 · 415) = 139 Amp.

Calculating Correction Factor of Cable from following data:

Temperature Correction Factor (K1) When Cable is in the Air

Temperature Correction Factor in Air: K1
Ambient TemperatureInsulation
PVCXLPE/EPR
101.221.15
151.171.12
201.121.08
251.061.04
350.940.96
400.870.91
450.790.87
500.710.82
550.610.76
600.50.71
6500.65
7000.58
7500.5
8000.41

Ground Temperature Correction Factor (K2)

Ground Temperature Correction Factor: K2
Ground TemperatureInsulation
PVCXLPE/EPR
101.11.07
151.051.04
200.950.96
250.890.93
350.770.89
400.710.85
450.630.8
500.550.76
550.450.71
6000.65
6500.6
7000.53
7500.46
8000.38

Thermal Resistance Correction Factor (K4) for Soil (When Thermal Resistance of Soil is known)

Soil Thermal Resistivity: 2.5 KM/W
ResistivityK3
11.18
1.51.1
21.05
2.51
30.96

Soil Correction Factor (K4) of Soil (When Thermal Resistance of Soil is not known)

Nature of SoilK3
Very Wet Soil1.21
Wet Soil1.13
Damp Soil1.05
Dry Soil1
Very Dry Soil0.86

Cable Depth Correction Factor (K5)

Laying Depth (Meter)Rating Factor
0.51.1
0.71.05
0.91.01
11
1.20.98
1.50.96

Cable Distance correction Factor (K6)

No of CircuitNilCable diameter0.125m0.25m0.5m
111111
20.750.80.850.90.9
30.650.70.750.80.85
40.60.60.70.750.8
50.550.550.650.70.8
60.50.550.60.70.8

Cable Grouping Factor (No of Tray Factor) (K7)

No of Cable/Tray123468
1111111
20.840.80.780.770.760.75
30.80.760.740.730.720.71
40.780.740.720.710.70.69
50.770.730.70.690.680.67
60.750.710.70.680.680.66
70.740.690.6750.660.660.64
80.730.690.680.670.660.64

According to above detail correction factors:

- Ground temperature correction factor (K2) = 0.89
- Soil correction factor (K4) = 1.05
- Cable depth correction factor (K5) = 1.0
- Cable distance correction factor (K6) = 1.0

Total derating factor = k1 · k2 · k3 · K4 · K5 · K6 · K7

- Total derating factor = 0.93

Selection of Cable


For selection of proper cable following conditions should be satisfied:
Cable derating amp should be higher than full load current of load.
Cable voltage drop should be less than defined voltage drop.
No. of cable runs ≥ (Full load current / Cable derating current).
Cable short circuit capacity should be higher than system short circuit capacity at that point.

Selection of cable – Case #1

Let’s select 3.5 core 70 Sq.mm cable for single run.
Current capacity of 70 Sq.mm cable is: 170 Amp,
Resistance = 0.57 Ω/Km and
Reactance = 0.077 mho/Km
Total derating current of 70 Sq.mm cable = 170 · 0.93 = 159 Amp.
Voltage Drop of Cable =
(1.732 · Current · (RcosǾ + jsinǾ) · Cable length · 100) / (Line voltage · No of run · 1000) =
(1.732 · 139 · (0.57 · 0.8 + 0.077 · 0.6) · 200 · 100) / (415 · 1 · 1000) = 5.8%

Voltage drop of cable = 5.8%

Here voltage drop for 70 Sq.mm Cable (5.8 %) is higher than define voltage drop (5%) so either select higher size of cable or increase no of cable runs.
If we select 2 runs, than voltage drop is 2.8% which is within limit (5%) but to use 2 runs of cable of 70 Sq.mm cable is not economical, so it’s necessary to use next higher size of cable.

Selection of cable – Case #2


Let’s select 3.5 core 95 Sq.mm cable for single run, short circuit capacity = 8.2 KA.
Current capacity of 95 Sq.mm cable is 200 Amp,
Resistance = 0.41 Ω/Km and
Reactance = 0.074 mho/Km
Total derating current of 70 Sq.mm Cable = 200 · 0.93 = 187 Amp.
Voltage drop of cable =
(1.732 · 139 · (0.41 · 0.8 + 0.074 · 0.6) · 200 · 100) / (415 · 1 · 1000) = 2.2%


To decide 95 Sq.mm cable, cable selection condition should be checked.
Cable derating Amp (187 Amp) is higher than full load current of load (139 Amp) = O.K
Cable voltage Drop (2.2%) is less than defined voltage drop (5%) = O.K
Number of cable runs (1) ≥ (139A / 187A = 0.78) = O.K
Cable short circuit capacity (8.2KA) is higher than system short circuit capacity at that point (6.0KA) = O.K



95 Sq.mm cable satisfied all three condition, so it is advisable to use 3.5 Core 95 Sq.mm cable.