Electrical Thumb Rules-(Part 10 & 11)

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%

Thumb Rule-11

AUGUST 19, 2014 15 COMMENTS

Size of Cable on Secondary Side of Transformer (11KV/433V)
Ref: KSEI Handbook
Rating of T/C (KVA)
Primary current (Amp)
Secondary Current (Amp)
Min. Size of Neutral Earthing Conductor (mm2)
Minimum Size of Cable (mm2)
63
3.3
84
25X3
50mm2
100
5.25
133.3
25X3
95mm2 or (2×50 mm2)
160
8.4
213.3
25X3
185mm2 or (2×95 mm2)
200
10.49
266.6
25X3
300mm2 or (2×120 mm2)
250
13.12
333
25X3
2×185 mm2
315
16.53
420
31X3 or 25X4
(2×300 mm2) or (3×185 mm2)
400
21.80
533
38X3
(3×300 mm2) or (2×400 mm2)
500
26.20
666.5
25X6
(3×400 mm2) or (4×240 mm2)
630
33
840
31X6
4×400 mm2
750
39.36
1000
50X4
Bus Bar Trucking (min. Isc 50KA)
1000
52.50
1333
210mm2
Bus Bar Trucking (min. Isc 50KA)
1250
65.50
1667
290mm2
Bus Bar Trucking (min. Isc 50KA)
1600
83.98
2133
380mm2
Bus Bar Trucking (min. Isc 50KA)
2000
105.00
2666
450mm2
Bus Bar Trucking (min. Isc 50KA)

HT Fuse on Primary Side of Transformer (11KV/433V)
Rating of T/C (KVA)
Primary current (Amp)
Secondary Current (Amp)
HT Fuse
Min (Amp)
Max(Amp)
63
3.3
84
10
16
100
5.25
133.3
16
25
160
8.4
213.3
16
40
200
10.49
266.6
25
40
250
13.12
333
32
40
315
16.53
420
40
63
400
21.80
533
40
63
500
26.20
666.5
50
100
630
33
840
63
100
750
39.36
1000
75
160
1000
52.50
1333
100
160
1250
65.50
1667
100
200
1600
83.98
2133
160
250
2000
105.00
2666
200
250

Capacitor Bank for Power Supply Voltage
System Voltage
Minimum rating of capacitor bank
3.3 KV , 6.6KV
75 Kvar
11 KV
200 Kvar
22 KV
400 Kvar
33 KV
600 Kvar

Capacities of PVC conduits
Nominal conductor Size mm
16 mm
20 mm
25 mm
32 mm
Number of Cables (maximum)
1.0
6
5
19
30
1.5
5
4
15
24
2.5
3
3
11
17
4
2
2
8
13
6
2
6
10
10
4
6
16
3
4
25
2
3
35
2

System Highest and Lower Voltage
Ref: NEC(India) :2011
System Voltage
Highest Voltage
Lowest Voltage
240 V
264 V
216 V
415 V
457 V
374 V
3.3 kV
3.6 kV
3.0 kV
6.6 kV
7.2 kV
6.0 kV
11 kV
12 kV
10 kV
22 kV
24 kV
20 kV
33 kV
36 kV
30 kV
66 kV
72.5 kV
60 kV
66 kV
72.5 kV
60 kV
132 kV
145 kV
120 kV
220
kV 245 kV
200 kV
400 kV
420 kV
380 kV

Number of Points for Dwelling Unit
Ref: NEC(India) :2011
No.
Description
Area for the Main Dwelling Unit (m2)
35 mm2
45 mm2
55 mm2
85 mm2
140 mm2
1
Light points
7 No
8 No
10 No
12 No
17 No
2
Ceiling fans Pont
2 No
3 No
4 No
5 No
7 No
3
Ceiling fans No’s
2 No
2 No
3 No
4 No
5 No
4
6A Socket outlets
2 No
3 No
4No
5 No
7 No
5
16A Socket outlets
1 No
2 No
3 No
4No
6
Call-bell (buzzer)
1 No
1 No
1 No

Recommended Schedule of Socket-Outlets
Ref: NEC(India) :2011
Description
Number of Socket
6A Socket
16A Socket
Bedroom
2
1
Living room
2
2
Kitchen
1
2
Dining room
2
1
Garage
1
1
For refrigerator
1
For air-conditioner
1 for each
Verandah
1 per 10mter2
1
Bathroom
1
1

Power requirements of the building
Ref: NEC(India) :2011
Part of ElectricalInstallation
Part of the Total Power Requirement in %
DiversityFactor
Ventilation, heating (air-conditioning)
45%
1.0
Power plant (drives)
52%
0.65
Lighting
30%
0.95
Lifts
20%
1.0
Kitchen
10%
0.6
Laundry
5%
0.6

Lift Car Speed
Ref: NEC(India) :2011
Occupancy
No. of Floors Served
Car Speed   m/s
Office building
4 to 5
0.5 to 0.75 m/sec
Office building
6 to 12
0.75 to 1.5 m/sec
Shops and departmental stores
13 to 20
More than 1.5 m/sec
Passenger lifts for low and medium lodging houses
0.5 m/sec
Hotels
4 to 5
0.5 to 0.75 m/sec
Normal load carrying lifts
2.0 to 2.5 m/sec
Hospital passenger Lift
4 to 5
0.5 to 0.75 m/sec
Hospital passenger Lift
13 to 20
More than 1.5 m/sec
Hospital bed lifts (Short travel lifts insmall hospitals)
0.25 m/sec
Hospital bed lifts (Normal)
0.5 m/sec
Hospital bed lifts (Long travel lifts inGeneral hospitals)

0.6 to 1.5 m/sec

Capacitor Ratings at Rated Voltage
Ref: NEC(India) :2011
Motor Rating(Kw)
Capacitor Rating in kVAR for Motor Speed
3 000rev/min
1 500rev/min
1 000rev/min
750rev/min
600rev/min
500rev/min
2.25
1
1
1.5
2
2.5
2.5
3.7
2
2
2.5
3.5
4
4
5.7
2
3
3.5
4.5
5
5.5
7.5
3
4
4.5
5.5
6
6.5
11.2
4
5
6
7.5
8.5
9
15
5
6
7
9
11
12
18.7
6
7
9
10.5
13
14.5
22.5
7
8
10
12
15
17
37
11
12.5
16
18
23
25
57
16
17
21
23
29
32
75
21
23
26
28
35
40
102
31
33
36
38
45
55
150
40
42
45
47
60
67
187
46
50
53
55
68
76

:Maximum Current Demand for Motor:
Ref: NEC(India) :2011
Nature of supply
Size of installation
Maximum current demand
Single phaseor Three phase
Up to and including 0.75 kW
Six times the full load current
Above 0.75 kW and up to 7.5 kW
Three times the full load current
Above 7.5 kW up to and up to11 kW
Two times the full load current
Above 11 kW
One and half times the full load current

Rated Basic Insulation Level (BIL)
Ref: NEC(India) :2011
Nominal System Voltage (kV)
Rated BIL (kVp)
33 KV
170
22 KV
125
11 KV
75
6.6 KV
60
3.3 KV
40

Illumination Level
Ref: NEC(India) :2011
Location
Illumination Level (Lux)
Residence
Entrance / Hallways
100
Living room
300
Dining Room
150
Bed Room (General)
300
Bed Room (Dressing , Bed Heads)
200
Kitchen
200
Kitchen sink
300
Bathroom
100
Sewing
700
Workshop
200
Staircase
100
Garage
70
Study Room
300
Office Building
Entrance hall / Reception
150
Conference Room / Executive Office
300
General Office Space
300
Business Machinery Operation
450
Drawing Office
450
Corridors
70
Stairs
100
Lift landing
150
Hospital Building
Reception & Waiting
150
General ward
100
Bed Side
150
Toilet
70
Stairs
100
Operation Theatre (General)
300
Operation Theatre (Operation Table)
Special
Laboratories
300
Radiology
100
Causality
150
Dispensaries
300
Laundry
200
Dry Cleaning
200
Ironing
300
General Office
450
Kitchen
200
Assembly & Concert Halls
Foyers
100 to 150
Auditoria
100 to 150
Platform
450
Corridors
70
Stairs
100
Cinema Halls
Foyers
150
Auditoria
50
Corridors
70
Stairs
100
Theatres
Foyers
150
Auditoria
70
Corridors
70
Stairs
100
School / College Building
Assembly Halls

General
150
Examination center
300
Platform
300
Classes

Desktop
300
Blackboard
200 to 300
Libraries

Shelves
70 to 150
Reading Room
150 to 300
Reading Table
300 to 700
Cataloguing
150 to 300
General

Office
300
Staff Room
150
Corridors
70
Stairs
100

Lamp’s Lumen Data
Rating (Watt)
Life (Hours)
Initial Lumens
Incandescent Lamp
60
1000
870
100
750
1750
150
2000
1740
200
2000
2300
500
2000
6500
Fluorescent Lamp
18
7000
1120
20
7000
1020
36
7000
2800
40
7000
2700
2X40
7000
4000
Compact Fluorescent Lamp
5
10000
220
7
7000
380
11
7000
560
13
7000
680
15
7000
810
18
7000
1050
23
7000
1500
26
7000
1800
32
7000
2400
Mercury Vapour Lamp
100
18000
3700
175
24000
8600
250
24000
12100
400
24000
22500
1000
24000
57000
Metal Halide Lamp
50
15000
3400
70
15000
5600
100
15000
9000
150
10000
13500
175
10000
15000
250
10000
20500
400
20000
36000
1000
12000
110000
High Pressure Sodium Vapour Lamps
35
16000
2250
50
24000
4000
70
24000
5800
100
24000
9500
150
24000
16000
250
24000
27500
400
24000
47500
1000
24000
140000
Pulse Start Metal Halide Lamp
50
15000
3400
70
15000
5600
100
15000
9000
150
15000
15000
175
15000
17500
200
15000
21000
250
15000
26300
320
20000
34000
400
20000
44000
450
20000
50000

:Duty Type of Motor:
Ref: IS-325
Duty Type Symbol
Duty Type
Application
S1
Continuous Duty
Pumps, Bowers, Compressors, Fans
S2
Short Time Duty
Siren, Flood relief Gates
S3
Intermittent Periodic Duty
Valve, Actuators, Wire drawing machine
S4
Intermittent Periodic Duty with starting
Hoist, Cranes, Lifts, Escalators
S5
Intermittent Periodic Duty with starting / Breaking
Hoist, Cranes (with electronics Breaks), Rolling mills
S6
Continuous Duty with Intermittent Periodic Duty
Machine tools, Conveyors
S7
Continuous Duty with starting / Breaking
Machine tools,
S8
Continuous Duty with periodic load changes
Pole Channing Applications

Type of Distribution System
As per IEC 60364-3
Unearthed System
Earthed System
IT
TT / TN (TN-S,TN-C,TN-C-S)
First Letter (the neutral point in relation to earth):T= directly earthed neutral (from the French word Terre)I =unearthed or high impedance-earthed neutral (e.g. 2,000 Ω)
Second letter (Exposed conductive parts of the electrical installation in relation to earth):T =directly earthed exposed conductive partsN =exposed conductive parts directly connected to the neutral conductor


1 comment:

  1. Totally copy past from www.electricalnotes.wordpress.com

    ReplyDelete

Thank you for comment...!!