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Commentator

Join Date: Jun 2008
Posts: 77

Selecting a 70-kva DG Set

01/29/2009 9:16 PM

We are planning to procure 70 kva DG set for the residence. Would be happy if someone can guide for proper selection speicifying tips for carrying better evaluation to avoid missing of salient points including the outside scope of suppliers.

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Guru
United States - Member - New Member

Join Date: Jun 2008
Location: Alabama
Posts: 1604
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#1

Re: Selecting a 70-kva DG Set

01/30/2009 11:28 AM

How did you arrive at the size of the generator? Seems a bit large for a residence.

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Associate

Join Date: May 2008
Location: City : Chandigarh, Country : India, Continent : Asia, Planet : Earth, Galaxy : Milky Way, Universe
Posts: 54
Good Answers: 1
#2

Re: Selecting a 70-kva DG Set

01/31/2009 12:00 AM

1. Have an AMF Panel installed with the DG

2. Have a Manual Changeover also installed for the possibility of AMF malfunction work.

3. Look for higher fuel efficiency and longer hours between subsequent maintenance.

Happy Buying..

Rgds

Sanjeev

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Anonymous Poster
#5
In reply to #2

Re: Selecting a 70-kva DG Set

01/31/2009 2:19 AM

Can the AMF be expalined in detail.Thanks for prompt response and guiding.

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Location: City : Chandigarh, Country : India, Continent : Asia, Planet : Earth, Galaxy : Milky Way, Universe
Posts: 54
Good Answers: 1
#7
In reply to #5

Re: Selecting a 70-kva DG Set

01/31/2009 3:01 AM

Automatic Mains Failure (AMF) Panel is for sensing the mains / grid failure, starting the DG and transferring the load to DG Supply... and the reverse process of DG Switch OFF in case of mains / grid restoration.

rgds

Sanjeev

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Anonymous Poster
#10
In reply to #2

Re: Selecting a 70-kva DG Set

02/01/2009 6:16 AM

Thank you very much.

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Active Contributor

Join Date: Nov 2008
Posts: 23
#3

Re: Selecting a 70-kva DG Set

01/31/2009 1:35 AM

70 KVA DG SET IS TOO BIG FOR A RESIDENCE AS PER MY EXPERIENCE. BUT BEFORE THAT PLEASE CONFIRM WHATS THE LOAD & MAX DEMAND AFTER CONSIDERING THE DIVERSITY FACTOR. THIS IS IMPORTANT FOR CALCULATING THE SIZE OF THE SET. FOR A DUPLEX VILLA YOU NEED A 25 KVA DG SET TO MEET THE DEMAND INCLUDING THE AIR CONDITIONERS & GEYSERS.

HOWEVER CALCULATE THE LOAD FIRST.

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Anonymous Poster
#4
In reply to #3

Re: Selecting a 70-kva DG Set

01/31/2009 2:18 AM

Thank you very much and I would be checking the details once again.The transformer rating selected is 100 kva and 70% loading of it is considered for DG set.However we would check the loads once again.

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Anonymous Poster
#6
In reply to #3

Re: Selecting a 70-kva DG Set

01/31/2009 2:21 AM

I appreciate if you can brief the meaning of diversity factor.

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Commentator
Engineering Fields - Power Engineering - Siswanto

Join Date: Mar 2008
Location: JAKARTA. INDONESIA
Posts: 73
Good Answers: 15
#8

Re: Selecting a 70-kva DG Set

01/31/2009 6:55 PM

Dear pokalasrao

This paper may can helping you to calculate of DG loading, its found from the website, but I forgot the web address...

Good Luck...

Rgds

Sis

Tables of contents

1. Legislation, statutory regulation in Hong Kong & relevant standard for electrical services

All of building services system is designed in accordance to legislation, statutory regulation in Hong Kong , relevant standards and guidance listed in the followings.

Services

Electrical

  • BS 7671 – Requirements for Electrical Installation.
  • Guide Books of Chartered Institute of Building Services Engineers.
  • General Specification for Electrical Installation in Government Buildings, Hong Kong and General Requirement for Electrical Contract/Sub-contract/Quotation let by Building Development Department, Hong Kong, 1984 edition. (E.G.S)
  • Code of Practice for the Electricity (Wiring) Regulations issued by EMSD 1997 edition.
  • Supply Rules of Hong Kong Electric Co., Ltd.
  • Code of Practice for Energy Efficiency of Electrical Installations (Draft)
Lighting
  • Chartered Institute of Building Services Engineers (CIBSE) Technical Memoranda TM12
  • Chartered Institute of Building Services Engineers (CIBSE) Technical Memorandum No.5
  • Chartered Institute of Building Services Engineers (CIBSE) Code for Interior Lighting
  • BS5266, Part 1, Code of Practice for Emergency Lighting.
  • Code of Practice for Energy Efficiency of Lighting Installations (Draft)
Emergency Generator
  • Code of Practice for minimum Fire Service Installations and Equipment and relevant circular letters issued by the Fire Service Department (COP/Fire)
  • Regulation of Environmental Protection Department.
Lightning Protection
  • BS6651, Code of Practice for Protection of Structures against lightning.
Lift and escalator
  • Code of Practice on the Design and Construction of Lifts and Escalators, EMSD 1993. (COP/Lift)
  • General Specification for Lift and Escalator Installation, in Government Buildings, Hong Kong, 1984 edition.
  • Building Regulation, CAP 123
Closed circuit television System (CCTV)
  • General Technical Specification for Monochrome closed circuit television systems, Specification No .ESG 14 Issue No. 2 – Electronics Division, EMSD.
  • General requirements for electronics contracts, Specification No. ESG01, Issue No. 6 – Electronics Division, EMSD
Security System
  • BS 4737 Intruder alarm systems.
Communal aerial broadcsat distribution system (CABD)
  • General Technical Specification for Communal aerial broadcast distribution systems and aerial distribution systems, Specification No. ESG 17 Issue No. 3-Electronics Division, EMSD
  • General requirements for electronics contracts, Specification No. ESG01, Issue No. 6 – Electronics Division, EMSD.
Building Management System (BMS)
  • General specification for Air Conditioning, Refrigeration, Ventilation and Central Monitoring and Control System Installation in Government Building, Hong Kong, 1988 Edition (A/C,\. G.S.)

2.Electrical load estimation

( a ). For flats

According to 'Code of practice for electricity (wiring) regulation), the electrical load demand for each flat is calculated as the following table:

Purpose of switchgearRating of switchgearEstimated

design current

Diversified factorDiversified current demand
Air-conditioning for living room (for summer)20A12A100%12A
Air-conditioning for bedroom (for summer)20A8A40%3.2A
Air-conditioning for bedroom (for summer)20A8A40%3.2A
Heater for living room

(for winter)

15A13A100%13A
Lighting for living room & terrace10A8A66%5.28A
Lighting for bedrooms, bathroom10A4A66%2.64A
Lighting for kitchen & entrance10A4A66%2.64A
Lighting for staircase & lav10A3A66%1.98A
Exhaust fan for kitchen10A4A100%4A
Washing machine15A7A100%7A
Socket outlet for living room30A-100%30A
Socket outlet for bedrooms30A-30%9A
Socket outlet for kitchen, entrance & staircase30A-30%9A
Overall89.14A

(for summer)

81.24A

(for winter)

The main switch for each flat shall be 100A single phase or 30A three phase. However, according to HEC's supply rule, 30A three phase is recommanded as the main switch rather than 100A single phase because meter for 100A single phase is not available.

The electrical load for all flat = 89.14A/3 per flat x 220V x 64 flats

= 418.4kVA

( b ). For shops and kindergarten

In reference to 'COMMERCIAL CODE OF PRACTICE 215 LOAD ASSESSMENT PROCEDURE (REVISION 2)' issued by China Light & Power Company Ltd., the electrical load is estimated as below:

Usage

Location

U.F.A.*1

(m2)

ADMD*2

(kVA/m2)

Estimated Load

(kVA)

Shops

*3

G/F2540.2358.42
Shops

*3

1/F2700.2362.1
Shops

*3

2/F3200.2373.6
Kindergarten3/F2120.05

*4

10.6

Total

1056

204.72

*1 means Usable Floor Area (U.F.A)

*2 means After Diversified Maximum Demand (ADMD) based on COP 215 by CLP

*3 Shops is assumed as light metal retail stores.

*4 ADMD is included central A/C.

( c ). For landlord Supply

Usage

Qty

Estimated Load

Estimated Load

(kVA)

AC System43.6TR1.85 kVA/TR80
Escalators6 Nos@30kVA180
P&D System1 Lot60
General Lighting & Power1000m

2 including Mech/F

20W/m

2*5

23.5
External Lighting, Atrium Lighting & Facade Lighting180m

2

40W/m

2*5

7.2

Total

350.7

*5 Data is based on Maximum Allowable Lighting Power Density extracted from Code of Practice for Energy Efficiency of Lighting Installation.

( d ). For essential Supply

Usage

Qty

Estimated Load

Estimated Load

(kVA)

Firemen's Lift2 Nos@40kVA80
FH/HR System1 Lot40
Sprinkler System1 Lot20
Sump pump1 Lot15
Essential Lighting & Power1 Lot10
Security & BMS System1 Lot10

Total

175

Overall electrical load = (418.4 + 204.72 + 350.7 + 175)kVA

= 1138.82kVA

However, two factors shall be considered as below:

Electrical load

1138.82kVA
Mixed development diversity factor (MDDF)1.14
Future extension15%

Total electrical load

1493.0kVA

Total usable floor area = 7600m2

Total demand density = 0.196kVA/m2

So, 1 No of 1500kVA HEC's transformer is required for the proposed residential building.

3. Generator loading

An emergency generator set is required to handle the following essential loads in case of power failure & fire conditions. If the equipment is started simultaneously, the starting current will be larger. So, in the building, the equipment of essential load is started in sequence and control by BMS to reduce the starting current so as to select a smaller generator.

The essential load estimated in (1) = 175kVA

Taking a safety factor of 10% for overload and a factor of 30% for future expansion,

The total essential load = 175kVA x 1.1 x 1.3

= 250kVA

So, a 300kVA generator set is selected. The generator should be operated normally within 15 seconds in case and the capacity of fuel tank should be capable to operate the generator for 6 hours.

Based on some manufacturer's catalogue, the capacity of fuel tank is about 400L.

4. Lightning hazards

Based on BS 6651:1992, Part 2, the overall lightning is calculated as the following to determine whether or not lightning protection is needed.

Probability of being struck, P = Ac x Ng x Ka x Kb x Kc x Kd x Ke x 10-6 ,where

Collection area, Ac = Area of roof + Area of perimeter of building + Area of four

rounded corners formed by quarter circles of building height

= LW + 2LH + 2WH + pH2

= 46x12 + 2x46x73 + 2x16x73 + px732

= 26.3 x 103 m2

No. of flash per km2 per year, Ng = 1.1

Factor for use of structure, K = 1.2

Factor for type of construction, Kb = 0.4

Factor for contents (or consequential effects), Kc = 0.3

Factor for degree of isolation, Kd = 0.4

Factor for type of terrain, Ke = 0.3

So, P = 26.3 x 103 x 1.1 x 1.2 x 0.4 x 0.3 x 0.4 x 0.3 x 10-6

= 5.0 x 10-3

The probability of risk (5.0x10-3) is greater than the critical risk (10-5) so that lightning protection is necessary. And, the actual design of the installation is illustrated by drawing no. EE-EP-RF

5. Earthing system

In accordance with BS 7671, the earthing loop impedance shall not be greater than 0.5 W Due to the site constraint, the plate electrode and tape electrode cannot be used as the earthing conductor. The most suitable and economic way is to use the rod electrode. The following calculation is to determine the no. of rod electrode and the size.

Resistance of rod electrode, where L = length of rod,

d = diameter of rod,

r = soil resistivity

Code 12C of COP electricity (wiring) regulation stated that the diameter of rod electrode should not be less than 12.5mm. The standard size of rod electrode in the market is 12.5mm & 15mm.

After site visit, the soil in the Wan Chai is marshland. The soil resistivity is around 4 W-m.

Consider a rod electrode of 4.5m length and 15mm diameter,

the resistance = = 0.9596 W

so that 2 rod electrodes in parallel is required to maintain 0.5 W earth loop impedance. And, the spacing between the earth pits shall be more than 9m (2x4.5m) to avoid the return loop.

6. Cable sizing

In this design report, the cable sizing procedure is referring to Code of Practice for Energy Efficiency of Electrical Installation (Draft).

  • To determine the design current Ib, nominal rating of protective device In
  • To calculate the min. tabulated value of current It(min) as the below formula:

,

Ca = Correction factor for ambient temperature

(Assume the ambient temp = 35 0C)

Cg = Corection factor for grouping

Ci = Correction factor for thermal insulation

Note that all correction factor is referring to Appendix 4 of IEE Wiring Regulation (16th Edition)

  • To select a suitable size It of conductor which satisfy It
  • To find effective current-carrying capacity Iz (Iz = It x Ca x Cg x Ci) and ensure that
  • To calculate the voltage drop along the conductor and determine whether or not cable size selected is acceptable. For sub-main circuit, the max. voltage drop is 1.5% and for final circuit, the max. voltage drop is 2.5%.

V.D. = r x p.f. x k x Ib x L , where

r = Voltage drop per ampere per metre at the conductor operating temperature

p.f. = Power factor (assume 0.85)

k = correction factor of operating temperature

, where tl = operating temperature

tp = max. permitted conductor operating temp

, ta = expected ambient temp. (assume 35 0C)

  • To calculate the percentage copper loss with respect to the total active active power transmitted.

The following table (EE-Table 1) shows the cable size.

7. Vertical transportation

( a ). Lift Performance

In accordance to the CIBSE Guide D, the lift performance is calculated as the following table:

Number of floor

9

Capacity of lift car

9 passengers

Number of passenger

7.2 passengers

Floor height

6m

Highest reversal floor

7.34

Probable number of stop

5.146

Total lift travel

54m

Contract speed

2.5m/s

Acceleration /deceleration

1m/s2

Upward running time

47.33 seconds

Downward running time

26.6 seconds

Door opening/closing time for centre door

2.5 seconds

Door operating time

30.73 seconds

Passenger transfer time

10.8 seconds

Round trip time (RTT)

115.46 seconds

No. of lift cars

2

Waiting interval

57.73

Handling capacity in 5 minutes

74.83

Total occupants

6 persons/flat x 64flats = 384

Peak arrival rate

19.49%

The lift performance is also simulated by computer software HEVACOMP (Results please refer to )

From the CIBSE Guide D, the recommended arrival rate and waiting interval are 5-7% and

40-90s for flats.

For the proposed building, the performance is satisfactory.

( b ). Escalator performance

According to CIBSE Guide D,

the escalator handling capacity, Cp = 60 v k s , where

v = horizontal speed (m/s)

k = average occupant density (people/step)

s = number of step (steps/m)

Due to architectural constraint, the physical data of escalator:

inclination of escalator = 300

height of escalalator = 4m

length of escalator = 6.9m

no. of step = 6900mm/400m = 17.25

width of step = 800mm

k = 1.5

h = height of step = 4000/17.25 = 231mm

s = 1000mm/231mm = 4.33

the speed = 0.5m/s (max. for 300)

the handling capacity = 60 x 0.5 x 1.5 x 4.33

= 194.85 person/min

From the CIBSE Guide D, the handling capacity for kindergarten is 92 person/min.

For the proposed building, the performance is satisfactory.

8. Lighting system

( a ). Shopping arcade corridor for G/F-2/F

Physical data of corridor, width = 2m, height = 4m

Data of luminaire: Manufacture = BEGA

Model no. = 6743

Type = Wall mounted discharge lamp with asymmetrical reflector

Lamp = 250W metal halide lamp (MBI-E)

Lumen output = 17000lm

Mounting height of luminaire = 3.5m

The angle of illuminating area = 300-00

The following calculation is based on technical data of BEGA 6743

the spacing between luminaires = 4m (obtained from cone diagram)

the average illuminance = 265 lx (obtained from cone diagram)

the luminous intensity (angle = 300) = 360 cd/klm x 17 lm = 6120 cd

the horizontal illuminance at the opposite side of corridor = 6120cd/(22+3.52)x0.8

= 302 lx

the luminous intensity (angle = 00) = 300 cd/klm x 17 lm = 5100 cd

the horizontal illuminance below the light fitting = 5100cd/(3.5)2x0.8

= 333 lx

(Assume the light loss factor = 0.8 & neglect the reflectance of walls due to open corridor)

( b ). Canopy

Physical data of corridor, width = 3m, height = 4m

Data of luminaire: Manufacture = BEGA

Model no. = 6180

Type = Recessed ceiling downlight c/w aluminium refelctor

Lamp = 80W metal halide lamp (MBF)

Lumen output = 4000lm

Mounting height of luminaire = 4m

The angle of illuminating area = -200-200

The following calculation is based on technical data of BEGA 6743

the spacing between luminaires = 4m (obtained from cone diagram)

the average illuminance = 80 lx (obtained from cone diagram)

the luminous intensity (angle = 300) = 360 cd/klm x 4 lm = 1440 cd

the horizontal illuminance at the side of canopy = 1440cd/(1.52+42)x0.8

= 63 lx

the luminous intensity (angle = 00) = 600 cd/klm x 4 lm = 2400 cd

the horizontal illuminance below the lighting fitting = 2400cd/(4)2x0.8

= 120 lx

(Assume the light loss factor = 0.8 & neglect the reflectance of walls due to open corridor)

( c ). Open atrium/corridor for L1-L5

Data of luminaire: Manufacture = THORN

Model no. = DLC 250/400

Type = Narrow bam medium bay lighting

Lamp = 250W/400W high pressure sodium lamp (SON-E)

Lumen output = 25500/45000 lm

Power input = 260W/410W per luminaire

The illuminance level is simulated by OPTILUME INTERIOR V3.03 by THORN LIGHTING LTD. And the results is summarised as below tables

FloorMounting height above floor levelDisplacement from corridorNos. of luminaireType of luminaireDirect illuminancePower
L112m3.5m52450W
L212m2.5m52450W
L312m2m52450W
L46m2m52450W
L56m1m52450W

( d ). Shops

Physical data of typical shop: 9m(L) x 6m(W) x 4m(H)

Data of luminaire: Manufacture = SIEMENS

Model no. = CR370SA-cent04-S70T

Type = Sealed-frame luminaire with dished triumph lens

Lamp = 70W high pressure sodium lamp (SON-T)

Lumen output = 5900lm

Mounting height of luminaire = 3.3m

By using lumen method,

According to CIBSE Lighting Guide LG1(The Industrial Environment), the standard illuminance is 500lx.

Assume UF = 0.5 & LLF = 0.7

nos. required

So, the decision is made to use N=15 luminaires. (3 columns of 5 pcs each).

The spacing between each luminaires = 1800mm

The power input = 15x87W = 1305W

Lighting power density = 24W/m2

The results is also simulated by manufacturer software SILICHT V4.1.

Appendix

Appendix - P.

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Anonymous Poster
#9
In reply to #8

Re: Selecting a 70-kva DG Set

02/01/2009 6:11 AM

Thanks a lot for giving a lot of informatin.

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Member

Join Date: Jan 2009
Posts: 5
#11

Re: Selecting a 70-kva DG Set

02/03/2009 1:12 PM

hi friends

for the proper selection of DG these points will help you

1. Rating selection:

the first ting is that you should calculate the total load and add 20% for the selection of DG because for best performance run the DG at 80% load.

2. brand selection:

select the DG by the performance of Engine brand there is most engines have good performance like CAT and CUMMINS but on my point of view CUMMINS have good fuel consumption Reta due to others.

3. Control system:

select the good and Essy to control system if you are using for residential, Must use ATS, AMF control system it will be help full to make automatic start and stop and switch over supply when utility fail.

thanks for study me

regards

sajid

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