1 v r1 v r2 B2.2.5 Hydropower system design Electronics and control: Why control? Rotation u1u1 u2u2 v1v1 v2v2 R1R1 R2R2 11 11 11 22

2 B2.2.5 Hydropower system design Electronics and control: Why control? Voltage regulation Frequency regulation Safety (turbine run-away)

3 B2.2.5 Hydropower system design Electronics and control: Why control? ApplianceSensitivity to frequency fluctuations Sensitivity to voltage fluctuations HeatingNoneNot a lot Lights (incandescent) NoneHigh V – bright and short lived Low V – dim and long lived TransformersLow – Heat and Losses High can get away with +20% Low – no problem High heat and losses (can get away with +20%) MotorsLow – Heat and Losses High can get away with +5-10% AC motors go the wrong speed Low – Torque reduction High heat and losses (can get away with +10%) DC motors go the wrong speed Aim for V ± 7%; f +5%, -0%

4 B2.2.5 Hydropower system design Electronics and control: Coupling

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6 B2.2.5 Hydropower system design Electronics and control: Governing

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9 B2.2.5 Hydropower system design Electronics and control: Impulse turbine

10 B2.2.5 Hydropower system design Electronics and control: Reaction turbine

11 B2.2.5 Hydropower system design Electronics and control: Load controller Ballast load generator controller generator Turbine

12 B2.2.5 Hydropower system design Electronics and control: Load controller

13 B2.2.5 Hydropower system design Electronics and control: Load controller

14 B2.2.5 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?”

15 B2.2.5 Hydropower system design Electronics and control: Power curve (e.g. Pelton wheel) Runaway speed is usually 1.8 – 2.3 times operating speed

16 B2.2.5 Hydropower system design Electronics and control: Large base load

17 B2.2.5 Hydropower system design Electronics and control: Operating at the back side of the power curve

18 B2.2.5 Hydropower system design Electronics and control: Flow control

19 B2.2.5 Hydropower system design Electronics and control: Flow control

20 B2.2.5 Hydropower system design Electronics and control: Flow control

21 B2.2.5 Hydropower system design Electronics and control: To generate or not Mechanical powerElectric power Few lossesLosses 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 criticalSpeed 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

22 B2.2.5 Hydropower system design Electronics and control: To generate or not

23 B2.2.5 Hydropower system design Electronics and control: Power conversion to electricity

24 B2.2.5 Hydropower system design Electronics and control: AC or DC? ACDC 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 criticalGoverning 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

25 B2.2.5 Hydropower system design Electronics and control Turbine DC generator Batteries Inverter 240 V distribution Local 240V12V loads close to batteries Other DC sources

26 B2.2.5 Hydropower system design Electronics and control: Two phase or Three phase? Single phaseThree phase Larger transmission lossesSmaller transmission losses (due to 415v transmission) Needs no load balancingNeeds 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 <10kWGenerally, good for >5kW

27 SystemShortLong Single phase 2 wire, 240V 11 3 phase 3 wire, 240V (delta system) Single phase 3 wire, 480/240V phase 4 wire, 415/240V (star system) B2.2.5 Hydropower system design Electronics and control: Transmission losses

28 B2.2.5 Hydropower system design Electronics and control: Three phase power

29 B2.2.5 Hydropower system design Electronics and control: Three phase power

30 B2.2.5 Hydropower system design Electronics and control: Three phase power

31 B2.2.5 Hydropower system design Electronics and control: Types of loads

32 B2.2.5 Hydropower system design Electronics and control: Types of loads Resistive loadReactive load

33 TypePower factor Filament lamp1 Motors lightly loaded0.4 (lagging) Motors heavily loaded0.7 (lagging) Fluorescent lamps0.5 – 0.7 (lagging) Overhead line0.9 (lagging) B2.2.5 Hydropower system design Electronics and control: Power factor P 0 = effective power E 0 = EMF (Voltage) I 0 = current f = power factor

34 B2.2.5 Hydropower system design Electronics and control: Types of generator

35 B2.2.5 Hydropower system design Electronics and control: Synchronous generator

36 N = Rotor speed (rpm) f = frequency (Hz) p = number of pole pairs B2.2.5 Hydropower system design Electronics and control: Induction generators: Rotational speed with slip

37 B2.2.5 Hydropower system design Electronics and control: Induction generators

38 B2.2.5 Hydropower system design Electronics and control: Induction generators

39 s = slip (tends to be around 5%) N s = speed of the rotating field N = rotor speed B2.2.5 Hydropower system design Electronics and control: Induction generators: Slip

40 N = Rotor speed (rpm) f = frequency (Hz) p = number of pole pairs s = slip B2.2.5 Hydropower system design Electronics and control: Induction generators: Rotational speed with slip

41 B2.2.5 Hydropower system design Electronics and control: Induction generators

42 B2.2.5 Hydropower system design Electronics and control: Induction generators Ballast load Induction generator controller Induction generator Turbine

43 B2.2.5 Hydropower system design Electronics and control: Synchronous or induction? SynchronousInduction 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 expensiveCheaper

44 B2.2.5 Hydropower system design Electronics and control: Pumps as turbines AdvantagesDisadvantages Very available and therefore cheaper than turbine All-in package (monobloc) Inefficient Steep power curve Wear characteristics unproven

45 B2.2.5 Hydropower system design Electronics and control: Pumps as turbines

46 N m = rated motor speed (rpm) N g = generator speed e = efficiency f = rated frequency p = number of pole pairs B2.2.5 Hydropower system design Electronics and control: Pumps as turbines

47 B2.2Hydropower 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

48 B2.2Hydropower 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

49 B2.2Hydropower 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

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