Connection to the MV utility connection..

Connection to the MV utility connection

1. Connection to the MV Utility Network Big loads need big supply.

2. Why MV? LV works for homes, but factories need more. MV = higher voltage, lower current, smaller cables. Analogy: Supplying a city through a garden hose → LV = hose, MV = water main. Story: A shopping mall with 200 shops on LV would need tree-trunk cables → utilities insist on MV.

3. If Mall Takes LV Supply (400 V) 💡 Too much current = too many cables. Total load: 2 MW @ pf 0.9 → ≈ 3,200 A at 400 V. Each 400 mm² Cu cable ≈ 630 A. Needs 6 parallel cables per phase (≈ 18 + N + PE). Bulky cable bundles, high losses, expensive.

4. If Mall Takes MV Supply (11 kV) 💡 Smaller current, simpler supply. Same load: 2 MW @ pf 0.9 → ≈ 117 A at 11 kV. Only 1 MV feeder cable needed. On-site transformer (2.5–3.15 MVA) → LV bus. Compact, efficient, cheaper copper, easier protection.

5. Typical Voltages IEC defines MV = 1–52 kV. Common: 11, 22, 33 kV .

6. Single Line Diagram is the ID card of Main Switch Board (MSB)

7. MSB Contains MCCB (Molded Case Circuit Breakers)

8. Types of Breakers

9. Supply Architectures Radial = one line (cheap, less reliable). Ring = loop (more reliable). Meshed = city-style (most reliable, expensive).

10. Ring type MV

11. Radial VS Ring

12. First Steps (New Substation) Customer tells utility: load, power factor, reliability needs. Example: mall = 1500 kVA, PF 0.9.

13. Utility’s Role Utility says: voltage level, connection point, protection rules.

14. Commissioning Test insulation, grounding, protection. Only after passing tests: substation energized. Flowchart: Apply → Site → Transformer → Gear → Earthing → Test → Energize. Story: A factory skipped earthing; storm blew transformer → losses.

15. Why Protect? People: avoid shocks. Equipment: avoid damage.

16. Protection Methods Overload → breaker trips. Short circuit → relay + breaker. Earth fault → earthing + RCDs.

17. Extra Safety Interlocks: stop human mistakes (e.g., can’t open live cubicle).

18. LV Metering Substation Meter is on LV side (400 V). Typical for small sites.

19. Functions of LV Metering Substation Step down MV → LV. Protect system. Meter consumption.

20. MV Metering Substation Meter is on MV side. Used for big industrial loads.

21. Why MV Metering? LV currents too large → impractical. MV metering uses CT/PT to scale down. Story: Cement plant → LV meter would melt, CT/PTs make it possible.

22. MV Equipment Breakers: automatic cut. Isolators: manual cut. Relays: brain that commands breaker.

23. Transformers Size = load + margin. Oil cooled = outdoor, robust. Dry type = indoor, safer. Story: Hospital chose dry type → no oil fire risk.

24. Ventilation Transformers get hot → need cooling. Bad ventilation = risk of fire.

25. Stand-alone Generators Run only during blackout. Example: hospital backup genset.

26. Parallel with Utility Run with grid → must synchronize (same frequency, voltage).

27. Parallel Transformers Can share load if: same ratio, vector group, impedance. If mismatched → they fight each other.

28. Types of Substations Indoor (safe, costly). Outdoor (cheap, exposed). Prefab (ready-made). Underground (city centers).

29. Indoor vs Outdoor Indoor: hospitals, offices. Outdoor: rural, open factories.

30. Wrap-up MV is for big loads. Substations = heart of supply. Protection, metering, equipment choice = safety + efficiency.