Electrical Thumbs Rules (Part-10)


Economical Voltage for Power Transmission:

  •  Economic generation voltage is generally limited to following values (CBIP Manual).

Economic generation voltage (CBIP Manual)

Total Load

Economical Voltage

Up to 750 KVA

415 V

750 KVA to 2500 KVA

3.3 KV

2500 KVA to 5000 KVA

6.6 KV

Above 5000 KVA

11 KV or Higher

  •  Generally terminal voltage of large generators is 11 kV in India. Step up voltage depends upon Length of transmission line for interconnection with the power system and Power to be transmitted.
  • High voltage increases cost of insulation and support structures for increased clearance for air insulation but decreases size and hence Cost of conductors and line losses.
  • Many empirical relations have been evolved to approximately determine economic voltages for power evacuation. An important component in transmission lines is labor costs which are country specific.
  • An empirical relation is given below.
  • Voltage in kV (line to line) = 5.5x√0.62L + kVA/150

  • where kVA is total power to be transmitted;
  • L is length of transmission line in km.
  • American practice for economic line to line voltage kV (based on empirical formulation) is
  • Voltage in kV line to line = 5.5x√0.62L + 3P/100

  • For the purpose of standardization in India transmission lines may be classified for operating at 66 kV and above. 33 kV is sub transmission, 11 kV and below may be classified as distribution.
  • Higher voltage system is used for transmitting higher amounts of power and longer lengths and its protection is important for power system security and requires complex relay systems.

Required Power Transfer (MW)

Distance (KM)

Economical Voltage Level (KM)

3500

500

765

500

400

400

120

150

220

80

50

132

 Factor affected on Voltage Level of system:

  • Power carrying capability of transmission lines increases roughly as the square of the voltage. Accordingly disconnection of higher voltage class equipment from bus bars get increasingly less desirable with increase in voltage levels.
  • High structures are not desirable in earthquake prone areas. Therefore in order to obtain lower structures and facilitate maintenance it is important to design such sub-stations preferably with not more than two levels of bus bars.

 Size of Cable according to Short circuit (for 11kV,3.3kV only)

  • Short circuit verification is performed by using following formula:
  • Cross Section area of Cable (mm2)S = I x√t / K

  • Where:
  • t = fault duration (S)
  • I = effective short circuit current (kA)
  • K = 0.094 for aluminum conductor insulated with XLPE
  • Example: Fault duration(t)= 0.25sec,Fault Current (I) = 26.24 kA
  • Cross Section area of Cable = 26.24 x √ (0.25) / 0.094= 139.6 sq. mm
  • The selected cross sectional area is 185 sq. mm.

Ground Clearance:

  • Ground Clearance in Meter = 5.812 + 0.305 X K

  • Where K= (Volt-33) / 33
Voltage Level Ground Clearance
<=33KV 5.2  Meter
66KV 5.49 Meter
132KV 6.10 Meter
220KV 7.0   Meter
400KV 8.84  Meter

 Voltage Rise in Transformers due to Capacitor Bank:

  • The voltage drop and rise on the power line and drop in the transformers. Every transformer will also experience a voltage rise from generating source to the capacitors. This rise is independent of load or power factor and may be determined as follows:
  • % Voltage Rise in Transformer=(Kvar / Kva)x Z

  • Kvar =Applied Kvar
  • Kva = Kva of the transformer
  • z = Transformer Reactance in %
  • Example: 300 Kvar bank given to 1200 KVA transformer with 5.75% reactance.
  • % Voltage Rise in Transformer=(300/1200)x 5.75 =1.43%

Electrical Thumbs Rules (Part-9)


 

Load in Multi-storied Building (Madhyanchal Vidyut Vitran Nigam)

Type of Load

Calculation

Diversity

Domestic  (Without Common Area)

50 watt / sq. meters

0.5

Commercial  (Without Common Area) 150 watt / sq. meters

0.75

Lift, Water Pump, Streetlight ,Campus Lighting ,Common Facilities,

Actual load shall be calculated

0.75

 

Load in Multi-storied Building (Noida Power Company Limited)

Type of Load

Calculation

Diversity

Domestic (Constructed area) 15 watt / sq. Foot

0.4

Commercial(Constructed area) 30 watt / sq. Foot

0.8

Industrial (Constructed area) 100 watt/ 1 sq. Foot

0.5

Lift, Water Pump, Streetlight ,Campus Lighting ,Common Facilities, 0.5Kw / Flat

 

Voltage Drop: 2% Voltage drop from Transformer to Consumer end.

T&D Losses: 2% T&D Losses from Transformer to Consumer end.

 

Approximate % Cost or Sq.Foot Cost

Project Item

% of Total Project Cost

Rs per Sq.Foot

Articheture (Consultancy)

0.7%

13.1 Rs / Sq.Foot

Structural (Consultancy)

1.2%

21.8 Rs / Sq.Foot

Service Design (Consultancy)

0.4%

7.2 Rs / Sq.Foot

Fire Fighting Work

1.3%

23 Rs / Sq.Foot

Electrical Work (Internal)

4.1%

76 Rs / Sq.Foot

Lift Work

4.4%

82 Rs / Sq.Foot

 

Street Light Costing (CPWD-2012)

Fluorescent Lamp

95 Rs/Sq.Meter

With HPMV Lamp

130 Rs/Sq.Meter

With HPSV Lamp

165 Rs/Sq.Meter

Electrical Sinage

85 Rs/Sq.Meter

 

Other Electrical Cost

Area Required for Solar Light

10 Watt/Sq.Foot

Solar Power Installation

1.5 Lacs Rs/1Kw

HVAC Cost

18 Watt/Sq.Foot

 

Distribution Losses (Gujarat Electricity Board)

Voltage (Point of Injection)

At 11 KV

Point of Energy Delivered

11KV / 22KV / 33KV

10%

1082%

400 Volt

16.77%

 

Rate Analysis (CPWD-2012)

Description

Amount
Sub Station Equipment 7000 Rs/ KVA
D.G Set with installation 1000 Rs / KVA
UPS with 30min Breakup 20000 Rs / KVA add 8000 Rs / KVA additional each 30 min
Solar Power Generation 1.25 Lacs / KW
Solar Water System (200Liter/Day) 46000 Rs
Solar Water System (300Liter/Day) 64000 Rs
Solar Water System (1000Liter/Day) 210000 Rs
Central AC Plant 75000 RS / Ton
VRF / VRV System 55000 Rs / HP
Air condition System 11000 Rs / Ton
CCTV System 300 Rs / Sq Meter
Access Control system 200 Rs / Sq Meter
Hydropenumatic Water system 2000 Rs / LPM
Building Management System 300 Rs /  Sq Meter add 100 Rs / Sq Meter additional area beyond 10000 Sq Meter

 

Rate Analysis (Rs per Sq. Meter) (CPWD-2012)

Work

Office/College/Hospital

School

Hostel

Residence

Fire Fighting (with Wet Riser)

500

500

500

500

Fire Fighting (with Sprinkler)

750

750

750

750

Fire Alarm (Manually)

300

Fire Alarm (Automatic)

500

500

500

500

Pressurized  Mechanical Ventilation

650

650

650

650

 

Rate Analysis (% of Total Project Cost) (CPWD-2012)

Work

Office/College/Hospital

School

Hostel

Residence

Internal Water Supply & Sanitary

4%

10%

5%

12%

Internal Electrical Installation

12.5%

12.5% 12.5% 12.5%

 

Lift Speed (Indian Army Manual)

No of Floor

Lift Speed

4 to 5

0.5 to 0.7 meter/Sec

6 to 12

0.75 to 1.5 meter/Sec

3 to 20

1.5 to 2.5 meter/Sec

Above 20

 Above 2.5 meter/Sec

 

Lift  Details (CPWD-2012)

Type of Lift 

Persons

Weight

Speed  M/Sec

Travel

Price

Add Rs /Floor

Passenger Lift 

8 Person 544 Kg 1.0 G+4 18 Lacs 1.25 Lacs

Passenger Lift 

13 Person 844 Kg 1.5 G+4 22 Lacs 1.25 Lacs

Passenger Lift 

16 Person 1088 Kg 1.0 G+4 28 Lacs 1.50 Lacs

Passenger Lift 

20 Person 1360 Kg 1.5 G+4 30 Lacs 1.50 Lacs

 

MCB Class according to Appliances

Appliance

Capacity / watt

MCB Rating

MCB Class

Air Conditioner

1.0 Tone

10A

C Class

1.5 Tone

16A

C Class

2.0 Tone

20A

C Class

Freeze

165 Liter

3 A

C Class

350 Liter

4 A

C Class

Oven /Grill

4500 Watt

32 A

B Class

1750 Watt

10 A

B Class

Oven / Hotplate

750 Watt

6 A

B Class

2000 Watt

10 A

B Class

Room Heater

1000 Watt

6 A

B Class

2000 Watt

10 A

B Class

Washing Machine

300 Watt

2 A

C Class

1300 Watt

8 A

C Class

Water Heater

1000 Watt

6 A

B Class

2000 Watt

10 A

B Class

3000 Watt

16 A

B Class

6000 Watt

32 A

B Class

Iron

750 Watt

6 A

B Class

1250 Watt

8 A

B Class

Toaster

1200 Watt

8 A

B Class

1500 Watt

10 A

B Class

Calculate Technical Losses of Transmission / Distribution Line:


Introduction:

  • There are two types of Losses in transmission and distribution Line.
  • (1) Technical Losses and
  • (2) Commercial Losses.
  • It is necessary to calculate technical and commercial losses.Normally Technical Losses and Commercial Losses are calculated separately .Transmission (Technical) Losses are directly effected on electrical  tariff but  Commercial losses are not implemented to all consumers.
  • Technical Losses of the Distribution line mostly depend upon Electrical Load, type and size of conductor, length of line etc.
  • Let’s try to calculate Technical Losses of one of following 11 KV Distribution Line

Example:

  • 11 KV Distribution Line have following parameter.
  • Main length of 11 KV Line is 6.18 Kms.
  • Total nos. of Distribution Transformer on Feeder 25 KVA= 3 No, 63 KVA =3 No,100KVA=1No.
  • 25KVA Transformer Iron Losses = 100 W, Copper Losses= 720 W, Average LT Line Loss= 63W.
  • 63KVA Transformer Iron Losses = 200 W, Copper Losses= 1300 W, Average LT Line Loss= 260W.
  • 100KVA Transformer Iron Losses = 290 W, Copper Losses= 1850 W, LT Line Loss= 1380W.
  • Maximum Amp is12 Amps.
  • Unit sent out during to feeder is  490335 Kwh
  • Unit sold out during from Feeder is 353592 Kwh
  • Normative Load diversity Factor for Urban feeder is 1.5 and for Rural Feeder is 2.0

Calculation:

Total Connected Load=No’s of Connected Transformer.

  • Total Connected Load= (25×3) + (63×3) + (100×1).
  • Total Connected Load=364 KVA.

 Peak Load = 1.732 x Line Voltage x Max Amp

  • Peak Load = 1.732x11x12
  • Peak Load =228 KVA.

 Diversity Factor (DF) = Connected Load (In KVA) / Peak Load.

  • Diversity Factor (DF) = 364 /228
  • Diversity Factor (DF) =1.15

 Load Factor (LF)= Unit Sent Out (In Kwh) / 1.732 x Line Voltage x Max Amp. x P.F. x 8760

  • Load Factor (LF)=490335 / 1.732x11x12x0.8×8760
  • Load Factor (LF)=0.3060

 Loss Load Factor (LLF)= (0.8 x LFx LF)+ (0.2 x LF)

  • Loss Load Factor (LLF)= ( 0.8 x 0.3060 x 0.3060 ) + (0.2 x 0.306)
  • Loss Load Factor (LLF)= 0.1361

 Calculation of Iron losses:

  • Total Annual Iron loss in Kwh =Iron Loss in Watts X Nos of TC on the feeder X8760 / 1000
  • Total Annual Iron loss (25KVA TC)=100x3x8760 /1000 =2628 Kwh
  • Total Annual Iron loss (63KVA TC)=200x3x8760 /1000 =5256 Kwh
  • Total Annual Iron loss (100KVA TC)=290x3x8760 /1000 =2540 Kwh
  • Total Annual Iron loss =2628+5256+2540 =10424Kwh

 Calculation of Copper losses:

  • Total Annual Copper loss in Kwh =Cu Loss in Watts XNos of TC on the feeder LFX LF X8760 / 1000
  • Total Annual Copper loss (25KVA TC)=720x3x0.3×0.3×8760 /1000 =1771 Kwh
  • Total Annual Copper loss (63KVA TC)=1300x3x0.3×0.3×8760 /1000 =3199 Kwh
  • Total Annual Copper loss (100KVA TC)=1850x1x0.3×0.3×8760 /1000 =1458 Kwh
  • Total Annual Copper loss =1771+3199+1458=6490Kwh

 HT Line Losses (Kwh)=0.105 x (Conn. Load x 2) x Length x Resistance x LLF /( LDF x DF x DF x 2 )

  • HT Line Losses= 1.05 x(265×2) x 6.18 x 0.54 x 0.1361 /1.5 x 1.15 x1.15 x 2
  • HT Line Losses = 831 Kwh

 Peak Power Losses= (3 x Total LT Line Losses) / (PPLxDFxDFx 1000)

  • Peak Power Losses= 3 x (3×63+3×260+1×1380) /1.15 x 1.15 x 1000
  • Peak Power Losses= 3.0

 LT Line Losses (Kwh)= (PPL.) x (LLF) x 8760

  • LT Line Losses = 3 x 0.1361 x 8760
  • LT Line Losses = 3315 Kwh

 Total Technical Losses= (HT Line Losses + LT Line Losses + Annual Cu Losses + Annual Iron Losses)

  • Total Technical Losses = ( 831+ 3315 + 10424 + 6490)
  • Total Technical Losses = 21061 Kwh

% Technical Loss= (Total Losses) / (Unit Sent Out Annually) x 100

  • % Technical Loss= (21061/490335) x100= 4.30%

% Technical Loss=4.30%

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