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## Full text

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MECH3005 – Building Servicesg http://www.hku.hk/bse/mech3005/

### Electrical Supply

Dr. Sam C M Hui

Department of Mechanical Engineering Department of Mechanical Engineering

The University of Hong Kong E-mail: cmhui@hku hk

E mail: cmhui@hku.hk

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## Basic Terms

### (useful or real power)

• Time average of instantaneous power when the

i k l l f A/C

average is taken over a complete cycle of an A/C waveform, expressed in Watt (W)

• For single phase, P = V I cos ø

• For balanced three phase P √3 V I cos ø

• For balanced three-phase, P = √3 Vph-ph I cos ø

### p

• For single phase, AP = V I

h h √

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## Basic Terms

### •

• Sum of all the loads connected to the electrical

ll d i

system, usually expressed in watts

### Demand factor

• = Maximum demand / Connection load

### the maximum demand over a defined interval

• In commercial buildings, between the hours 9:00 to 18:00 the load factor is usually close to unity

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Typical load profile for an office building

M Max.

Average

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## Basic Terms

### Power factor

• The ratio of the apparent power in a circuit (V.A)

h f l (W) if h l d

to the useful power (W) if the voltage and current are sinusoidal

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### :

• Non-essential supply: plumbing and drainage, pp y p g g passenger lifts, air-conditioning plant, public lightingg g

• Essential supply: fire protection/detection system, fireman’s lifts, essential lighting, PABX system, fireman s lifts, essential lighting, PABX system, building management system, important computer room

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### Objectives

• Ensure loading demands are estimated accurately • What happens if they are “under-estimated”?

• What happens if they are “over-estimated”?

### Important factors

• Load research data (from power company)

• Design marginDesign margin

• Checking & monitoring at each design stage

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### Preliminary stage

• Plan the transformer (Tx) & main switch room

• Apply to power company for supply

• Based on rough info or past experience

I t t t k th l d f th BSE t

• Important to know the loads of other BSE systems

### g

• Update the estimate w/ more accurate info

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### Load evaluation by power company

• Architect/Engineer/Developer submit application

• For typical categories, planning engineer of power company assesses the load estimation using the p y g

• After finalising the total load, determine the nos. of transformer and transformer bays

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## Assessment Guidelines

### General

• Usable floor area (UFA)

• Development informationp

• Floor area usage, public services, any special loads

• Standard load estimation sheet (see handouts)

• Standard load estimation sheet (see handouts)

• Public services

• Assessed independently

• Public lighting, lift, water pump, fire services, lobby air g g, , p p, , y conditioning

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Minimum design load capacities for lighting and small power g p g g p requirement for various types of building

(W/m2) (W/m2) Office 60 School 30 Residential building 30 Hospital 25 Hospital 25 Hotel 25 Church 15

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## Assessment Guidelines

### After diversity maximum demand (ADMD)

• Load densities derived by dividing the aggregate

l d b h di UFA fl

load by the corresponding UFA or flat nos.

• Cover most typical cases; for special situation, yp ; p ,

designer/planning engineer may exercise his own discretion to adjust the load estimates

• ADMD is for planning supply Tx capacity, it may not be suitable for designing customer raising

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## Assessment Guidelines

• Load assessment data (see handouts)( ) • Residential development

• Commercial development

• Commercial development

• Industrial development

• Municipal development

• Mixed development diversity factor (MDDF)

• Reference (from CLP Power)

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60.0

50.0

30.0 40.0

A

/Flat

20.0 30.0 kV A 0 0 10.0 0.0 1 6 11 16 21 26 31 36 41 46 51 No. of Flats

What is the effect of load diversity on the kVA/flat data?

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## Assessment Guidelines

### •

• For central air conditioning load

• For general development

### Example of electrical load estimation

• Electrical supply arrangement

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## Assessment Guidelines

### i

• LightingLighting

• Small power and special user equipment

• HVAC equipment

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## Legal Framework

• Typical legal system in Hong Kong (statutory)yp g y g g ( y) • Ordinance (Laws of Hong Kong)

• Regulations

• Regulations

• Code of Practice

• Supporting documents (non-statutory) • Technical Guidelines

• Technical Notes or Technical Memoranda

• Circular letters

• Circular letters

• Reference standards (usually from other countries)

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## Legal Framework

### Electricity Ordinance & subsidiary regulations

• Electricity Ordinance (Cap. 406) * • Electricity (Exemption) Regulations

• Electricity (Registration) Regulations

• Electricity Supply Regulations

Electricity (Wiring) RegulationsElectricity (Wiring) Regulations Most important

• Electricity Supply (Special Areas) Regulations El t i l P d t (S f t ) R l ti

• Electrical Products (Safety) Regulation

• Electricity Supply Lines (Protection) Regulation (* can be read from the website www.justice.gov.hk)

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## Legal Framework

• Relevant codes and guides to g statutoryy regulationsg • Code of Practice for the Electricity (Wring) Regulations

• Code of Practice for Minimum Fire Services Installations

• Code of Practice for Minimum Fire Services Installations and Equipments

N l i / d d

• Non-statutory regulations/standards

• IEE Regulations for Electrical Installation, 15th edition and/or 16th edition *

• Supply Rules (from power companies)pp y ( p p )

• British Standards Specifications & Codes of Practice or other equivalent national standards and publications

ot e equ va e t at o a sta da ds a d pub cat o s (* IEE = Institution of Electrical Engineers, now IET)

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## Legal Framework

### Electrical Contractors and Workers

• Registered Electrical Contractors (REC)

• Registered Electrical Workers (REW) • Grade A Electrical Work (≤ 400 A)Grade A Electrical Work (≤ 400 A)

• Grade B Electrical Work (≤ 2500 A)

• Grade C Electrical Work (any capacity)

• Grade C Electrical Work (any capacity)

• Grade H Electrical Work (high voltage)

• Grade R Electrical Work (special, e.g. neon sign)

• NS: neon light; WH = water heaters; AC = air-conditioners

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## Legal Framework

### Registered Electrical Workers (REW)

• Permitted work: code • 0 = any categories

• 1 = only issue design certificate

• 2 = only perform installation & repair works

• 3 = only perform repair works3 only perform repair works

• Example:

• “B0” means REW grade B (≤ 2500 A) who can design, install and repair electrical works

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## Legal Framework

### )

• Completion of an installation • Certification on the design

• Certification on the design

• Certification on the installation

W k l i ifi

• Work completion certificates

• Form WR1 – a complete installation

• Form WR1(A) – Part of an installation (e.g. for a repair)

• Periodic test certificates

• Form WR2 – a complete installation

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## References

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