B 2 2 5 Hydropower system design Electronics

B 2. 2. 5 Hydropower system design Electronics and control: Why control? u 1 R 1 1 vr 1 1 Rotation v 2 2 vr 2 1 R 2 u 2 1

B 2. 2. 5 Hydropower system design Electronics and control: Why control? • Voltage regulation • Frequency regulation • Safety (turbine run-away) 2

B 2. 2. 5 Hydropower system design Electronics and control: Why control? Appliance Sensitivity to frequency fluctuations Sensitivity to voltage fluctuations Heating • None • Not a lot Lights (incandescent) • None • High V – bright and short lived • Low V – dim and long lived Motors • Low – Heat and Losses • Low – no problem • Transformers High can get away with +20% • High heat and losses (can get away with +20%) • Low – Heat and Losses • Low – Torque reduction • High can get away with +5 -10% • High heat and losses (can get away with +10%) • AC motors go the wrong speed • DC motors go the wrong speed Aim for V ± 7%; f +5%, -0% 3

B 2. 2. 5 Hydropower system design Electronics and control: Coupling 4

B 2. 2. 5 Hydropower system design Electronics and control: Coupling 5

B 2. 2. 5 Hydropower system design Electronics and control: Governing 6

B 2. 2. 5 Hydropower system design Electronics and control: Governing 7

B 2. 2. 5 Hydropower system design Electronics and control: Governing 8

B 2. 2. 5 Hydropower system design Electronics and control: Impulse turbine 9

B 2. 2. 5 Hydropower system design Electronics and control: Reaction turbine 10

B 2. 2. 5 Hydropower system design Electronics and control: Load controller generator Turbine Ballast load 11

B 2. 2. 5 Hydropower system design Electronics and control: Load controller 12

B 2. 2. 5 Hydropower system design Electronics and control: Load controller 13

B 2. 2. 5 Hydropower system design Electronics and control: Complexity? “We urge engineers who are specifying hydroelectric plant and particularly governors to beware of buying equipment which cannot reasonably be maintained by the staff available in the power stations in which they will be installed. A governor is a good servant but can be a bad master. A governor which operates with a number of sensitive relays and fine orifices may work beautifully in the temperate climate of south Germany where a skilled instrument engineer can be sent for at 2 a. m. to check a defective relay, but if the same governor is controlling a turbine in tropical Africa, the leg of a dead locust can play hell with a fine orifice or high humidity cause a breakdown in a relay which has ". . . been tested for many months in the manufacturer's research laboratory" under the eagle eye of young engineers in spotless white coats who know exactly what to do if anything goes wrong. We can only utter a warning: "It may look beautiful in colour in the manufacturer's catalogue, but can it be guaranteed to work beautifully in this particular power station? ” 14

B 2. 2. 5 Hydropower system design Electronics and control: Power curve (e. g. Pelton wheel) Runaway speed is usually 1. 8 – 2. 3 times operating speed 15

B 2. 2. 5 Hydropower system design Electronics and control: Large base load 16

B 2. 2. 5 Hydropower system design Electronics and control: Operating at the back side of the power curve 17

B 2. 2. 5 Hydropower system design Electronics and control: Flow control 18

B 2. 2. 5 Hydropower system design Electronics and control: Flow control 19

B 2. 2. 5 Hydropower system design Electronics and control: Flow control 20

B 2. 2. 5 Hydropower system design Electronics and control: To generate or not Mechanical power Electric power • Few losses • Losses in generation transmission and re-conversion to work (if used for motors) • Needs to be close to turbine • Can be distant from turbine • Speed not critical • Speed usually critical (more need for control – expense) • Servicing entirely mechanical so can be done by local technicians • Servicing can be electrical or electronic which needs specialise knowledge and equipment • Starting loads not important • Starting loads can dominate 21

B 2. 2. 5 Hydropower system design Electronics and control: To generate or not 22

B 2. 2. 5 Hydropower system design Electronics and control: Power conversion to electricity 23

B 2. 2. 5 Hydropower system design Electronics and control: AC or DC? AC DC • Needs specialised generating equipment • Generating equipment easily available (12 V alternators) • Must be converted to DC to be stored (in batteries) and then converted to AC for use • Battery charging simple • Governing critical • Governing not critical • Higher voltages transmit with few losses (L V 2) • Lower voltages need fat cables to avoid transmission losses • Appliances cheap and readily available • Appliances specialised 24

B 2. 2. 5 Hydropower system design Electronics and control DC generator Other DC sources Batteries Inverter Turbine 240 V distribution Local 240 V 12 V loads close to batteries 25

B 2. 2. 5 Hydropower system design Electronics and control: Two phase or Three phase? Single phase Three phase • Larger transmission losses • Smaller transmission losses (due to 415 v transmission) • Needs no load balancing • Needs a balanced load on all three phases • Switch gear and load control cheaper • Switch gear and load control more expensive • More powerful units larger and more expensive • More powerful units smaller and cheaper • Generally, good for <10 k. W • Generally, good for >5 k. W 26

B 2. 2. 5 Hydropower system design Electronics and control: Transmission losses System Short Long Single phase 2 wire, 240 V 1 1 3 phase 3 wire, 240 V (delta system) 0. 87 0. 75 Single phase 3 wire, 480/240 V 0. 62 0. 31 3 phase 4 wire, 415/240 V (star system) 0. 58 0. 29 27

B 2. 2. 5 Hydropower system design Electronics and control: Three phase power 28

B 2. 2. 5 Hydropower system design Electronics and control: Three phase power 29

B 2. 2. 5 Hydropower system design Electronics and control: Three phase power 30

B 2. 2. 5 Hydropower system design Electronics and control: Types of loads 31

B 2. 2. 5 Hydropower system design Electronics and control: Types of loads Resistive load Reactive load 32

B 2. 2. 5 Hydropower system design Electronics and control: Power factor P 0 E 0 = current f Filament lamp = EMF (Voltage) I 0 Type = effective power = power factor Power factor 1 Motors lightly loaded 0. 4 (lagging) Motors heavily loaded 0. 7 (lagging) Fluorescent lamps Overhead line 0. 5 – 0. 7 (lagging) 0. 9 (lagging) 33

B 2. 2. 5 Hydropower system design Electronics and control: Types of generator 34

B 2. 2. 5 Hydropower system design Electronics and control: Synchronous generator 35

B 2. 2. 5 Hydropower system design Electronics and control: Induction generators: Rotational speed with slip N = Rotor speed (rpm) f = frequency (Hz) p = number of pole pairs 36

B 2. 2. 5 Hydropower system design Electronics and control: Induction generators 37

B 2. 2. 5 Hydropower system design Electronics and control: Induction generators 38

B 2. 2. 5 Hydropower system design Electronics and control: Induction generators: Slip s = slip (tends to be around 5%) Ns = speed of the rotating field N = rotor speed 39

B 2. 2. 5 Hydropower system design Electronics and control: Induction generators: Rotational speed with slip N = Rotor speed (rpm) f = frequency (Hz) p = number of pole pairs s = slip 40

B 2. 2. 5 Hydropower system design Electronics and control: Induction generators 41

B 2. 2. 5 Hydropower system design Electronics and control: Induction generators Induction generator controller Induction generator Turbine Ballast load 42

B 2. 2. 5 Hydropower system design Electronics and control: Synchronous or induction? Synchronous Induction • Can start large motors and deal with large power factors • Large changes in voltage and power factor a problem • Can be destroyed by centripetal force during runaway • Safe up to runaway speeds (unless geared up) • Good stability under change in load • Poor stability under change in load • More expensive • Cheaper 43

B 2. 2. 5 Hydropower system design Electronics and control: Pumps as turbines Advantages Disadvantages • Very available and • Inefficient therefore cheaper than • Steep power curve turbine • Wear characteristics • All-in package unproven (monobloc) 44

B 2. 2. 5 Hydropower system design Electronics and control: Pumps as turbines 45

B 2. 2. 5 Hydropower system design Electronics and control: Pumps as turbines Nm = rated motor speed (rpm) Ng = generator speed e = efficiency f = rated frequency p = number of pole pairs 46

B 2. 2 Hydropower system design Summary • Inlet arrangements are the “last defence” for the turbine and should protect it against large flows and foreign material • Trashracks, entrances, bends, valves and contractions result in losses to the net head which can be calculated • Penstocks and penstock mountings are subject to forces such as expansion, bend forces and water hammer • Draft tubes provide a way of recovering velocity head but are limited by the vapour pressure of water and the turbine Thoma number • Turbines convert pressure head to mechanical power, this can be calculated using velocity triangles 47

B 2. 2 Hydropower system design Summary (cont’d) • A number of different turbines exist such as Pelton wheels, turgo and crossflow turbines (impulse turbines) and Francis, propeller and Kaplan turbines (reaction turbines). A number of turbine types are made in developing countries • Specific speed can be used as a simple specification for turbine selection – but beware dimensionality. • Governing of turbines can be critical. It can be archived in several “conventional” ways such as mechanical governors and load control. “Unconventional” methods such as employing a large base load, operating at the back of the load curve or flow control can save complexity 48

B 2. 2 Hydropower system design Summary (cont’d) • Electrical generation converts mechanical power to electrical power • AC or DC power can be used – each has trade offs. AC power can be single or three phase • AC generators can be synchronous or induction. Induction generators need capacitors across their phases and a low reactive load to effectively self excite • Pumps can also be used as turbines but with some trade-offs 49

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