1 POWER QUALITY -- Bhanu Bhushan -- April, 2011

2 Simple examples around us : Ceiling fan regulators Tube lights Lap-tops & peripherals Domestic inverters

3 Ceiling fans ph Induction motors, shaded - pole or split - winding, inverted. Fan regulators -- Choke, Resistor or Electronic (wave - chopping) type. i) Weighty, costly, low PF; ii) Energy loss, heating; iii) Voltage & current distortion, harmful on both sides.

4 Tube lights : non-linear discharge lamps. Smoothening & PF improvement by choke and capacitor. Not a serious problem. Electronic ballasts : V & I distortions. Lap-tops & peripherals : AC / DC adapters draw non-sinusoidal current. Domestic inverters : Battery charging current is always non-sinusoidal.

5 POWER QUALITY in a wider, Indian perspective GRID - Level & CONSUMER - Level 1)SUPPLY CONTINUITY 2)FREQUENCY 3)VOLTAGE

6 SUPPLY INTERRUPTIONS a) LOAD - SHEDDING due to own or others’ over-drawal : Maximize generation, & Allow over-drawal, as long as grid can sustain it, and it is paid for. b) LOAD - SHEDDING to curtail over-loading or under-voltage : If too frequent, ask for system augmentation.

7 c) TRIPPING due to a fault or equipment failure : Minimize outage duration, : Reliable protection, Auto-reclosing, : Ask for building redundancies.

8 VOLTAGE PROBLEMS HIGH / LOW : Can be corrected by transformer tap-changing and reactive compensation : shunt / series capacitors, reactors, SVC, MVAR generation change. SWELLS & SAGS, SPIKES & DIPS, FLICKER : Caused by switching on / off of large loads, capacitor banks, electric furnaces, welding machines.

9 PHASE UNBALANCE : Caused by single - phase or unbalanced loads (e.g. railway traction), pole - discrepancy, break in a phase (conductor snapping), break in neutral, hanging faults, non-transposition. WAVE FORM DISTORTIONS (HARMONICS and DC offset) : caused by HVDC, SVC, FACTS, Converters, UPS, power / speed controllers, computers, TVs, chargers, printers, tube-lights, CFLs, fan regulators, electronic ballasts,

10 communication equipment, arc furnaces, welding, railway traction, etc. Circuit breaker and isolator operation (switching transients), L.A., transformer magnetizing current inrush, lightning, Faults and their clearance, insulator flash- over, corona, faulty grounding. Adverse effects : Over-heating & noise, resonance, telephone interference, hum, capacitor failure, control device maloperation.

11 Harmonic restraint in transformer differential relays. SOLUTION : Circuit segregation and Harmonic filters. INDUSTRIAL U.P.S.

12 SOLAR FLARES --- transient fluctuations in Earth’s magnetic field (geomagnetic storms) --- potential difference between different points on Earth’s surface --- DC enters one transformer neutral and exits at another -- half-cycle saturation of transformer cores --- unwanted trippings & grid disturbance.