Refined_Week3_Slides.................pptx

Refined_Week3_Slides.................pptx

1. Week 3 – Load Estimation & Supply Characteristics Sub-topics: Connected load, maximum demand, demand factor factors. Tariffs and metering basics. Supply characteristics: voltage levels, fault levels & Earthing arrangements (TN, TT, IT) Case study: residential vs commercial loads

2. Why Design Matters Ensures SAFETY – prevents shocks, fires, hazards. Ensures EFFICIENCY – correct cable sizes, minimal losses. Ensures COMPLIANCE – must follow BS 7671 / IEC 60364. Analogy: Building a house – if you don’t plan, sockets may end up behind the fridge!

3. The Design Sequence 1. Assess demand (loads, demand factor ). 2. Determine supply characteristics (voltage, fault levels). 3 . Choose distribution system (radial, ring, busway ). 4. Select cable sizes and check voltage drop 5 . Protective devices and Overload protection. 6. Verify compliance with regulations.

4. Basic Tools & Standards BS 7671 (IET Wiring Regulations). IET Electrical Installation Design Guide. Cable tables, correction factors, demand factor factors. Manufacturer data for breakers, RCDs, SPDs.

5. System Sketch Grid → Meter → Main Distribution Board → Final Circuits → Loads Example: • Grid supplies 400/230 V. • Meter measures consumption. • DB distributes to lighting, sockets, HVAC, etc.

6. Step 1 – Maximum Demand & demand factor Why It Matters: • Safety (avoid overload) • Cost (avoid oversizing) • Correct equipment sizing ( We must size supply & equipment for the expected maximum demand .) Analogy: Water pipes – too small = burst, too large = waste.

7. Story Example Case: A new office designed without proper load estimation. Result: Frequent breaker trips due to undersized circuits. Lesson: Always follow the design sequence before installation.

8. Worked Example – Small House Lighting: 2 kW (90% demand factor → 1.8 kW) Sockets: 5 kW (70% demand factor → 3.5 kW) Cooker: 7 kW (100% demand) EV Charger: 7 kW (100% demand) Total = 19 kW → 12.5 kVA Lesson: demand factor reduces final design load.

9. Worked Example – Office Lighting: 10 kW (90% demand factor → 9 kW) Sockets: 12 kW (70% demand factor → 8.4 kW) HVAC: 15 kW (100% demand) Total = 32.4 kW → 3 6 kVA Key Lesson: Commercial loads are more steady : Unlike residential demand (where users switch things on/off at random), commercial spaces (offices, shops, clinics) have longer operating hours, centralized HVAC, and continuous lighting , which keeps the diversified load factor higher . This means maximum demand is closer to connected load , so utilities and designers size supplies closer to the actual connected power.

10. In a hotel, which loads are likely to run all the time? Continuous / base loads: Emergency lighting. Fire alarms, security systems, CCTV. Reception/servers (IT backbone). Central HVAC (in many hotels, it runs nearly continuously). Refrigerators/freezers in kitchens. Water pumps (especially domestic water circulation and firefighting). 👉 Other loads (room lights, kettles, TVs, lifts) are intermittent and subject to demand factor.

11. Each MDB has MD Value E.G 25KVA

12. Why do we need load estimation? Architect needs to know what I need as an electrical engineer such as electricity room for panels, generator room and transformer room. We also need to know the voltage required, LV/MV. Which means if TRANSFORMER is needed. If load is less than 400KVA , LV connection and no transformer needed. Otherwise , if load is greater than 400kVA, MV connection is needed.

13. Building Area Method

14. Load Estimation Steps (Load Break Down Method) 1. Know the building type. 2. List categories of loads. 3. Estimate each (per m² or equipment). 4. Apply demand factor . 5. Add = Maximum Demand. 6. Convert to kVA for supply size .

15. 📊 Load Estimation Reference Table Building Type Category Typical Load (W/m²) demand factor Factor Residential 🏠 Lighting 7–10 100% Sockets 15–20 (or 500 W/room) 30–40% Kitchen Appliances By nameplate (5–10 kW cookers, etc.) 30–50% Air Conditioning 80–120 70% Commercial 🏢 Lighting 10–15 100% Sockets 20–30 60–80% HVAC 100–150 100% Industrial 🏭 Lighting 10–12 (20 for task) 100% Small Power 10–15 50–60% Motors By nameplate 70–80%

16. ✅ Key Notes for Designers - W/m² values are for initial estimation only — always confirm with datasheets. - demand factor reflects realistic operation: • Lighting = 100% (all can be ON) • Sockets = reduced (not all used at once) • Motors = not all running together at full load - Power Factor ( pf ): • Residential ≈ 0.95 • Commercial ≈ 0.9 • Industrial ≈ 0.85 ⚡ Analogy: Load density = appetite per square metre , demand factor = how many are actually eating.

17. By Illumination (More Accurate) Formula: No. of fixtures = (E × A) ÷ (F × UF × MF) E = required lux (illumination level, e.g., 300 lux for offices) A = area in m² F = lumens per lamp UF = utilization factor (≈ 0.6–0.8) MF = maintenance factor (≈ 0.8) 👉 Example: Office, 40 m², need 300 lux, lamp 2500 lm, UF=0.7, MF=0.8: = (300 × 40) ÷ (2500 × 0.7 × 0.8) ≈ 8 light fittings

18. Illumination Standards (Typical Lux Levels) Space / Room Lux Level (Recommended) Living Room 100–150 lux Bedroom 50–100 lux Kitchen (general) 200–300 lux Kitchen (task areas – worktop, stove) 300–500 lux Bathroom / Toilet 100–150 lux Stairs / Corridors 100–150 lux Classroom 300–500 lux Office (general work) 300–500 lux Reading / Study Area 500 lux Workshops / Labs 300–750 lux (depending on task) Supermarket / Retail 500–1000 lux Hospital Operating Theatre 1000–2000 lux

19. LED Wattage vs Lumen Output & Suitable Rooms LED Wattage (W) Approx. Lumens (lm) Typical Use / Room Suitability 5 W 400–500 lm Toilet, corridor, night light 7 W 600–700 lm Bedroom (1–2 lamps), stairwell 10 W 800–900 lm Living room (general light), bathroom 15 W 1200–1400 lm Kitchen (general lighting), study desk 20 W 1600–1800 lm Kitchen worktop, small office 30 W 2400–2800 lm Large living room, classroom 50 W 4000–5000 lm Workshops, retail shops 100 W 9000–10000 lm Industrial halls, warehouses

20. Classroom Activity For this classroom find the no. of lighting fixtures?

21. Example 1 — 3-Bedroom Apartment (120 m²) 1 ) Building type: Residential apartment 2) Load categories: Lighting, sockets, kitchen appliances, A/C, water heater 3) Estimate each: Lighting: 7 W/m² × 120 = 0.84 kW Sockets (general): 15 W/m² × 120 = 1.80 kW Kitchen appliances (cooker 5, kettle 2, fridge 0.2, washer 2) = 9.2 kW A/C: 2 rooms × 1.2 kW = 2.4 kW Water heater = 2.0 kW Connected load = 16.24 kW 4) Apply demand factor (residential): Lighting 100% → 0.84 Sockets 40% → 0.72 Kitchen group 40% → 3.68 A/C 70% → 1.68 Water heater 100% → 2.00 5) Maximum Demand (kW): 0.84 + 0.72 + 3.68 + 1.68 + 2.00 = 8.92 kW ≈ 9 kW 6) Convert to kVA ( pf 0.95): 9 ÷ 0.9 = 10 kVA ➡️ Ask the utility for ~10–12 kVA single-phase service (fits typical flats).

22. Example 2 — Small Office Floor (500 m²) 1) Building type: Commercial office 2) Load categories: Lighting, sockets, HVAC, server 3) Estimate each (rules of thumb): Lighting: 12 W/m² × 500 = 6 kW Sockets: 25 W/m² × 500 = 12.5 kW HVAC: 100 W/m² × 500 = 50 kW Server/IT room = 5 kW Connected load = 73.5 kW 4) demand factor (office): Lighting 100% → 6.0 Sockets 70% → 8.75 HVAC 100% → 50.0 Server 100% → 5.0 5) Maximum Demand: 6 + 8.75 + 50 + 5 = 69.75 kW ≈ 70 kW 6) kVA ( pf 0.9): 70 ÷ 0.9 = 77.8 kVA → add 15% margin ≈ 90 kVA ➡️ Specify a 100 kVA LV transformer / supply allocation.

23. Example 3 — Light Industrial Workshop (800 m²) 1) Building type: Industrial (motors + tools) 2) Load categories: Lighting, small power, motors, compressor, welding, HVAC 3) Estimate each: Lighting: 10 W/m² × 800 = 8 kW Small power: 10 W/m² × 800 = 8 kW Motors: 4 × 15 kW = 60 kW Air compressor = 7.5 kW Welding sockets = 10 kW HVAC/ventilation = 10 kW Connected load = 103.5 kW 4) demand factor (industrial): Lighting 100% → 8.0 Small power 60% → 4.8 Motors 80% → 48.0 Compressor 100% → 7.5 Welding 60% → 6.0 HVAC 80% → 8.0 5) Maximum Demand: 8 + 4.8 + 48 + 7.5 + 6 + 8 = 82.3 kW 6) kVA ( pf 0.85 typical with motors): 82.3 ÷ 0.85 = 96.8 kVA → add 20% margin ≈ 116 kVA ➡️ Select a 125 kVA transformer. (Note: check motor starting—VFDs or soft-starters may be needed if voltage dip is tight.)

24. Backup Generator Sizing Decide the load → Full building or essential circuits only. Convert kW → kVA → kVA= kW÷PFkVA = kW ÷ PFkVA = kW÷PF (PF ≈ 0.85–0.9). Allow for motor starting → Add 20–30% (big inrush currents). Add growth margin → 10–20% future-proofing. Round up → Choose next standard generator rating (e.g., 250, 315, 400 kVA). 👉 Worked Example (Hotel): Essential load = 150 kW. PF = 0.85 → 176 kVA. Add motor margin → 220 kVA. Add growth margin → 253 kVA. Final choice = 315 kVA generator

25. Tariffs & Metering Tariffs: Domestic vs Industrial (different unit rates) Metering: Analog vs Smart Case Study: Prepaid meters – help budgeting but can disconnect supply instantly.

26. Supply Characteristics – Voltage LV: 230 V (1-phase) or 400 V (3-phase) MV: 10–35 kV (utility supply) Analogy: Voltage = Water pressure – too low = weak flow, too high = damage.

27. Remember SLD and MSB Protection and isolation at the building/service entry point.

28. Electrical Installation Certificate External loop impedance ( Ze ) is a critical test value. It ensures fault currents are high enough to trip breakers and protect people & property .

29. Supply Characteristics – Fault Level Fault levels = short-circuit currents Must know to size switchgear & breakers Analogy: Pipe burst → sudden high flow High fault levels = stronger equipment needed.

30. Methods to Obtain Fault Level 1. By enquiry – ask the utility provider for fault level at point of supply. 2. By calculation – use transformer kVA and % impedance. Example: 1000 kVA, 6% Z, gives ≈ 24 kA fault at LV terminals.

31. Fault Current Example – 1000 kVA, 6% Z Given: 1000 kVA transformer, 6% impedance, 400 V Method 1: I_FL = 1000kVA / (√3 × 400V) ≈ 1443 A I_SC = I_FL / 0.06 ≈ 24 kA Method 2: Fault MVA = 1.0 / 0.06 = 16.7 MVA I_SC = 16.7 / (√3 × 0.4) ≈ 24 kA Result: ~24 kA at LV terminals.

32. Supply Characteristics – Earthing Types: TN-S, TN-C-S, TT, IT Purpose: Safety – fault current goes to earth, not people Analogy: Safety net under a trapeze – catches faults instantly.

33. 1. TT Earthing System What it is: Supply neutral is earthed at the source. Installation has its own earth electrode (separate from supply). PE (Protective Earth) conductor connects exposed metal parts to this local earth. TT is the most commonly used earthing system in Somaliland and East Africa. How it works: In a fault, current flows from equipment → local earth electrode → ground → source earth → back to supply. RCDs are mandatory , since fault current may be too small for fuses/breakers to trip.

34. 2- TN-S Earthing System What it is: Neutral (N) and Protective Earth (PE) conductors are separate from the supply point. Source neutral is earthed at the transformer. PE conductor runs all the way from the source to the installation. How it works: Fault current flows through PE back to the transformer neutral. This gives a low impedance fault loop , so breakers trip quickly without relying on earth electrodes. Analogy: ⚡ Think of TN-S like a dedicated return road : neutral carries normal current, PE carries only fault current

35. 3- TN-C-S Earthing System (PME) What it is: Neutral and Protective Earth are combined into one conductor (PEN) from the source up to the supply point. Inside the installation, PEN splits into separate Neutral (N) and PE conductors . Commonly used in UK. How it works: Fault current returns via the PEN conductor back to the source. Multiple earth connections are often made along the PEN for reliability. Provides a low-impedance fault path, so protective devices trip quickly.

36. Quick Quiz Q1: Why apply demand factor ? Q2: What is the role of earthing? Q3: What does a 6% transformer impedance mean? Answers: 1. To avoid oversizing 2. Provides safety path for fault currents 3. Limits short-circuit current