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9 GENERATINGELECTRICITY

9.1 Safety Warning9.2 Electrical Standards9.3 Earth-fault protection9.4 Generator Options9.5 Using 3-Phase Induction Motors as Single-PhaseGenerators.9.6 Electronic Load Control9.7 Alternatives to load control9.8 Selection and Sizing of Generator, Capacitors, Cable andProtection Equipment9.9 Installation and Connection

9.1 Safety WarningElectricity can be extremely dangerous. If aperson comes into contact with a live wire orfaulty equipment with a voltage higher than 50V,it is possible for them to receive a fatal electricshock. The electricity generating systemdescribed here is designed to operate at mainsvoltage (120V or 220V AC depending on thenational standards). Anyone carrying outelectrical installation work at these voltagesmust be supervised by a qualified andexperienced electrician. In addition the followingsafety instructions must be strictly followed:• Before attempting any installation or

maintenance, ensure that the generator isnot turning and that the flow control valve onthe penstock is firmly closed. Hang a label onthe valve to warn others if maintenance isdone outside the powerhouse (e.g.”Maintenance in progress – do not operate!”).

• Earth all metal cased equipment with asuitable earth connection (see 9.3)

• Never touch any electrical equipment withwet hands.

• Install all equipment according tomanufacturer’s instructions.

• Do not adjust or attempt to repair equipmentunless trained to do so.

• Notices that warn of the danger of highvoltages should be clearly positioned on thedoor of the powerhouse, on the case of thecontroller and on the front of each loadlimiter.

9.2 Electrical StandardsNational electrical standards should be followed.In some countries, special standards for microhydro and/or isolated village electrification havebeen agreed. These standards should be followedeven if they disagree with the recommendationsgiven here. Please read the disclaimer at thefront of this manual.

9.3 Earth-fault protectionAn earth fault occurs, for example, if a live wirebecomes loose inside a device and touches itsmetal case. An RCD (Residual Current Device)will disconnect the supply if a fault like thiscauses a large enough current to flow to theground (i.e. if the case is earthed or someonetouches the case and makes a path to earth). Itcan also disconnect the supply if someoneaccidentally touches a live wire causing currentto be conducted through them to the ground.This reduces the risk of fatal electric shocksthough these can still occur if someone touchesboth line and neutral and is insulated from theearth. The RCD required is one with a residualtripping current of 30mA. It should beconnected directly to the generator as shown inFigure 9-7.

Figure 9-1 3-phase RCD

In addition to an RCD, earth electrodes arerequired to allow the RCD to function. These aremetal conductors that are in close contact withthe soil and provide a low resistance path for thecurrent to the ground. Connection to an earthelectrode is required near the generator. Earthelectrodes are also required if any of theelectrical loads have metal cases (electriccookers, for example). The resistance of the

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earth should not be greater than 1kΩ if an RCDwith a 30mA tripping current is used.Measurement should be carried out with anearth tester. The manufacturer’s instructionsshould be carefully followed to ensure accurateresults. Earth testers are expensive (typically$600 to $1000). Consider hiring or borrowingunless you do a large number of schemes.

Three methods of installing an earth electrodeare described:Method 1 The easiest electrode to install isusually a 1 metre copper-coated steel rod that isdriven into the ground near to the powerhouse.The electrode is connected to the neutralterminal at the generator using a low-resistanceheavy-gauge copper cable (e.g. SWG 10mm²) anda brass, connecting nut that slides over the rodand allows the cable to be clamped in place. Twoshorter rods can be used and connectedtogether if it is notpossible to drive therod 1 metre into theground. They shouldbe spaced at leasttwo metres apartand connected withthe same earthcable.

Figure 9-2 A 1m copper-coated steel rod can provide asuitable earth electrode.

Method 2 A second method is to use a loose coilmade of about 10 metres of SWG 10 bare copperwire. This should be spread out and buried in ahole about one metre deep. If the soil is dampwhere the powerhouse is constructed, then the

coil of wire can be buried underneath thefoundations. Do not bury under the foundationsif the soil type is very dry as the resistance isunlikely to be low enough.Method 3 A third method is to use a copperplate measuring at least 500mm x 500mm. Thisshould be buried in a hole at least one metredeep in an area which remains moist.

Figure 9-3 Installation of a copper-plate earthelectrode, Multiple earth cables have been soldered inplace to reduce the resistance and increase thereliability.(Nepal)

9.4 Generator Options

Figure 9-4 3-Phase Induction Motor (7.5 kW) withdouble-ended shaft, used as a generator. (Nepal)

Induction generators and synchronousgenerators produce AC power. Alternatingcurrent (AC) and direct current (DC) areexplained in the Appendix. The main advantage ofAC is that the power can be transmitted overquite long distances. This makes AC suitable forvillage electrification projects because theelectrical loads (such as light bulbs) are usuallyquite spread out and often a long way from thegenerator.Induction generators are good for providingelectricity in remote areas because they are

1 m

etreCopper earth

rod driven intothe ground

Serviceable cable connectionmade to rod

to earth connected device

50 cm

Cover (e.g.large, flat stone )

Plasticdrainagepipe

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robust and very reliable. However, they are notthe only generators that are used for hydropower projects. Different generators have beencompared in Table 9-1. Situations where it maybe more practical to consider other generatorsin addition to the induction generator include thefollowing:1. Very low cost power systems for batterycharging or lighting only in a single dwelling nextto the powerhouse. Consider a DC generator.2. Schemes required to power motor loadsgreater than 15% of the generator rating arebest supplied by synchronous generators. Formore information about motor starting usinginduction generators, read Section 13.

9.5 Using 3-Phase Induction Motors asSingle-Phase Generators.

Purpose built induction generators are expensivebut three-phase induction motors can be used asgenerators when run in reverse. These are mass-produced and so are quite cheap and easilyavailable.For most small electrification projects, a single-phase supply is required. It is quite easy toproduce a single-phase supply from a three-phase motor. This is done by connecting unequalamounts of excitation capacitance across thewinding of the machine as shown in Figure 9-6.This is called C-2C because across the secondgenerator phase, twice the amount ofcapacitance is connected. On the third phase nocapacitors are connected.

It is important that capacitors of the correcttype are chosen and properly connectedotherwise the generator could fail to operate oroverheat. The manufacturer who supplies theturbine and generatorshould also supplycapacitors of thecorrect size. If theindividual componentsare bought separately,then follow the advicegiven in Section 9.8.

Figure 9-5 PowerCapacitors suitable forconnection to inductiongenerators

Figure 9-6 Single-phase supply from 3-phase motor

Type ofGenerator

Source Typical Cost for3kW Machine

Speed (rpm)Options

Disadvantages Advantages

Induction Standardindustrialmotor used as agenerator

Low:$200 - $250

1000, 1500,3000

Needs correctly sizedcapacitors connected tooperate as a generator. Poormotor starting ability

Widely available, slow speedranges, robust simpleconstruction. Can withstandoverspeed. Cheaper thansynchronous generators

Synchronous- Brushed

Commonly usedwith petrol ordiesel engines.

Low – medium:$300 - $500

3000,sometimes1500

Brushes and slip rings wear outand require replacement. Mustbe strengthened for over-speeding

Higher efficiency thaninduction at part-load andbetter motor startingcapability

Synchronous- Brushless

Occasionallyused withdiesel engines

High:$600 - $1000

1500, 3000 Not widely available. Repairsare often complex / expensive.Must be strengthened forover-speed

As synchronous-brushed butwith better reliability

DC Car or truckalternator

Not ApplicableMax. output ≈500W

Car > 2000,truck > 1200

Not suitable for villageelectrification. Restrictedrange of appliances. Brushesand slip rings wear out

Very low cost, no controllerrequired.

Table 9-1 Comparison of Generators suitable for use with Pico Hydro Turbines

InductionGeneratorWindings

Single PhaseSupply to Loads

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Figure 9-7 Connection of generator and controller

This switch is used todisconnect the

distribution systembefore the generator is

switched off.

The ballast load isswitched on and off bythe IGC. It uses the

power not required byother loads

The IGC keeps thevoltage constant

when the load on thegenerator changes.

The Residual CurrentDevice gives earth-

fault protectionimproving consumer

safety.

A copper earth electrode isrequired to allow RCD’s andlightning arrestors to work.

It is essential to have anearth connection near to

the powerhouse.

These capacitors areneeded to make the

induction motor workas a generator.

The ballast meterindicates how much

power is used by theballast load.

A MotorProtection Switch

protects thegenerator and

capacitors fromoverload.

A 3-phase inductionmotor is used as a

generator

L

N

User loadisolationswitch

Ballast Heater

Ballast trip lamp

Over-volt trip lamp

Capacitors

Motorprotectionswitch

3-PhaseRCD

Earthing Point

Induction Generator

2C N

L

I.G.C.

To user load

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9.6 Electronic Load ControlIf the voltage and frequency are not kept at theright level then the user loads connected to thegenerator can be damaged.

Too High Too LowVoltage Motors, televisions and

radios can be damaged.the lifetime oflightbulbs and heatersbecomes shorter.

Most applianceshave reducedperformance or failto operate

Frequency Will not usually causeproblems with mostconsumer loads. Exceptspeed dependant motorloads.

Can cause internalcircuits to overheatand fail in radios,TV’s and motors.

Table 9-2 Effect of voltage and frequency variation onloads

The speed of the turbine changes when the loadconnected to the generator changes. Forexample, if more lights are switched on then thespeed of the turbine will decrease. Since thischange of speed affects the voltage andfrequency, the load on the generator must bekept constant or the flow of water through thenozzle must be adjusted. The most reliablemethod of controlling the load and keeping thevoltage and frequency constant is by using anelectronic load controller.

The speed of an induction generator can be keptnear constant by using an IGC (InductionGenerator Controller). This device sends anyunused power to a ballast (or dump load) so thatthe total load on the generator remains constant.For example, if the generator produces 1000Watts and the total load connected by theconsumers is only 600W then the IGC willcontrol the switching on and off of the ballast sothat the remaining 400W is also dissipated. Ifthe consumer load changes at any time, the IGCwill automatically adjust the power diverted tothe ballast so that the voltage and frequency arekept constant.

The IGC cannot, however, prevent the generatorfrom becoming overloaded. For example, if thegenerator is producing 1000W but more than1000W of load is connected then the voltage willfall and the IGC is unable to prevent this. Toavoid overloading, the use of load limiters is

strongly recommended. This is explained in moredetail in Section 15.3.

Figure 9-8 Division of power between user load andballast

The BallastThe ballast is an essential part of the electroniccontrol system. Great care must be taken withthe choice and connection of the ballast. Themost common source of problems with inductiongenerator controllers is with the ballast.

Air heatersConvection heaters are the best type of ballastto use for pico hydro schemes. They are usuallyreliable and have the longest life. They are soldas electrical room-heaters. Designs that can bemounted on the wall are the safest type. A low-cost ‘DIY’ design of ballast using cooking rings isshown in Figure 9-9. This will work as a radiantheater when wall mounted on a suitable frame.The cable insulation and frame must be able towithstand very high temperatures. Radiantheaters generally have a shorter life thanconvection heaters because they operate at ahigher temperature.

Water heaters are often used as ballast loadsalthough experience has shown that these oftencause problems on small schemes and thereforethey are not recommended. Cheap water-heatingelements and steel ballast tanks often corroderapidly. The temperature requires monitoring andcold water must be introduced to the tankbefore the water boils. Automatic flow controlsystems can be designed to achieve this but theyare complicated and are not cost-effective forpico hydro.

Total Power1000W

User Loade.g. 600W

Power sent toBallast = 400W

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Figure 9-9 Low cost ballast using electric cooking rings

Low Cost Ballast Design

A ballast of this design should be mounted on thewall. The cables must be protected using a heat-resistant sheath and connections made to theheating elements from below.

Calculating the power dissipatedCooking rings are available with a range of powerratings and are cheap and robust. By connectingtwo rings in series the voltage is halved and thelifetime is considerably extended. Since thevoltage is halved with series connection, thecurrent is also halved and so the powerdissipation is therefore quartered. For example,a ballast to dissipate 3.0kW would require 8rings rated for 1.5kW. That is four pairs ofseries connected rings across the controller ortwo of the units shown in Figure 9-9.

V/2 x I/2 = P/4 = 375W dissipated per ring ifseries connected in pairs. 8 x 375W = 3.0kW.

The connection of the cooking rings for thisexample is shown in the circuit diagram below.

Figure 9-10 Electrical connection of cooking ring ballast(4 pairs of series connected rings)

Protection features of the IGCOver-voltage trip If the voltage rises too high,then the supply will automatically bedisconnected to protect the consumer loads. Theover-voltage trip lamp(s) will light to indicatethis condition.

Ballast trip: The ballast is automaticallydisconnected if the ballast is too large or if theballast connections are shorted out. The ballasttrip lamp(s) will light.Lightning protection: Many IGC designs containa varistor that minimises the risk of damage tothe controller due to indirect lightning strikes.MetersThe IGC will function without meters fitted.However, these enable the user to maximisetheir use of the power available and are helpfulfor identifying the cause of electrical problems.Ballast meter: This meter indicates thepercentage of power being dissipated in theballast load. It is the most useful meter becauseit indicates how much spare capacity there is andhow close the generator is to being overloaded(when the controller is functioning normally butthe meter reads zero).Voltmeter: This is useful for setting theoperating voltage on the controller and forobserving the voltage if the generator becomesoverloaded. It should be rated for 300V AC andconnected to the supply output terminals so thatit is protected by the over-voltage trip.

9.7 Alternatives to load controlIt is tempting to operate the generator with noload controller present. Two options areavailable.Fixing the LoadOne method of controlling the voltage andfrequency is to have a load connected thatexactly matches the output of the generator.However a fixed load is difficult to achieve ifmore than one consumer is connected andappliances, such as refrigerators, thatcontinually switch on and off cannot be used. Itis not recommendedManual Control of the Turbine SpeedManual control requires the presence of anoperator to correct the flow of water to theturbine and control its speed whenever the loadis changing. This method is not recommended forachieving good voltage and frequency regulationand is costly in the long term due to operatorwages.

1100mmWire mesh guard

Steel angleframe

CookingRing35

0mm

IGC Ballast Connections

3 kW ballast using 8 cooking ringsrated for 1.5 kW each.

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9.8 Selection and Sizing of Generator,Capacitors, Cable and ProtectionEquipment

Figure 9-7 shows how the generator, capacitorscontroller and ballast are connected. The are anumber of considerations when specifying amotor to use as a generator.

a) Voltage range: The voltage rating of thethree-phase induction motor to be used as asingle-phase generator must be carefullyselected. If the rating is too high, the generatorwill be unstable. If the rating is too low it willnot be possible to achieve the requiredgenerator voltage without overheating thewindings.

Motor Rating (kW)Type ofmotor

0.55 - 1.1 1.5 - 3.0 4.0 - 7.5

2 pole VGEN+6% VGEN+3% VGEN

4 pole VGEN+9% VGEN+6% VGEN+3%6 pole VGEN+12% VGEN+9% VGEN+6%

Table 9-3 Recommended motor voltage.

Note that the operating voltage of thegenerator (VGEN) is usually set slightly higherthan the national single-phase voltage to allowfor the voltage drop on the distribution system.Table 9-3 shows the recommended motorvoltage, in relation to the generator voltage, fordifferent motor sizes and speeds. This will givestable operation and a near optimum efficiency.The reason why smaller and slower speedgenerators require higher motor voltage ratingsis to compensate for their lower power factors.The acceptable limits for the voltage ratingare +/-6% of the recommended voltage.Example: If a 4-pole 3kW motor is to be used togenerate 245 Volts, using Table 9-3, therecommended motor voltage is 245V +6%, i.e.260 Volts. The acceptable limits of motorvoltage are 245V (recommended value –6%) and275V (recommended value +6%).The effect of increasing the voltage of themotor can be achieved by increasing thefrequency by the same percentage. Varying thefrequency has drawbacks as shown in Table 9-2.However, small increases of up to about 6% areacceptable. For example, if 230 Volts is astandard voltage available for the 3kW motordescribed above, this can be used at 6%

increased frequency in order to generate at 245Volts.The terminal box of many induction motorsallows connection in a star or delta pattern givingthe possibility of two voltage ranges. The voltagerange for star and delta is given on thenameplate. Either of the following is suitable fora 220V scheme:Either 380-415V star / 220-240V deltaOr 220-240V star / 127-139V delta

Note: Motors of 3kW and above are oftenwound for 660–720V star/ 380–415V delta.These are not suitable as 220–240V generators.Most manufacturers will supply motors wound tothe voltage you require, with a longer deliverytime.

Figure 9-11 The two voltage ranges are possible withmany induction motors by connecting the windings in'Star' or 'Delta'

b) Frequency: The frequency rating should bethe same as that required by the loads (i.e. 50Hzor 60Hz). For a direct drive system, thegenerator speed must be matched to the turbinespeed. Note that the generator speed is alwaysabout 10% higher than the motor speed. Shaftspeeds for common sizes of induction generatorare given in the table below. Select a machinewith the correct number of poles.

No. of poles 50 Hz 60Hz2 3.120 rpm 3,750 rpm4 1,560 rpm 1,875 rpm6 1,040 rpm 1,250 rpm

Table 9-4 Examples of induction generator shaft speeds

c) IP Number: Select a motor which is IP 55.The IP number is a measure of how easily liquidor dust (e.g. flour) can enter the machine. IP 55models are resistant to either and thereforesuitable for hydropower applications.

d) Insulation Class: Always select thehighest available winding insulation class. The

STARW1

U1

V1DELTA

W1V2

W2 U1

U2

V1

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two most common types are B and F. Class F hasa longer life than Class B. For the sameoperating temperature, Class F insulation will lastfour times as long as Class B.

d) Power Rating: Estimate the maximumelectrical power output, Pmax, by calculating thehydraulic power and assuming an overallefficiency of 50% (unless actual efficiencies areavailable). Use Pmax and the generator voltage(VGEN) to work out the operating current.

GENop V

PI max1.1 ×=

where Iop = maximum operating currentVGEN = generator voltage

The (rated) line current of the motor, Iline, mustbe greater than or equal to the operatingcurrent:

Iline ≥≥≥≥ Iop

Example: A 2-pole generator is to be used on apico hydro with a maximum electrical poweroutput of 1,500 Watts. The national voltage is220 Volts and the generating voltage 220V + 6%,i.e. 233V, calculate Iop:

Iop = 1.1 x 1500/233 = 7.1 Amps.

A 2.2kW 2-pole motor is available which, whendelta connected, has a voltage rating of 240Volts(the recommended voltage as given in Table 9-3),and a line current of 7.6 Amps. This motor isideal for use at this site.Over-current protectionThe generatorwindings andcables must beprotected fromexcessivecurrents. Thesecan cause them tooverheat and fail.High currentsalso damage thecapacitors.Figure 9-12 MotorProtection SwitchFor maximumprotection a motor protection switch should beused as the tripping current can be adjusted to

the precise current rating of the generator.Typical current ranges for motor protectionswitches are 2-4A, 4-6A, 6-10A, 10-16A, 16-20A,20-24A. For the 2.2kW motor in the example, a6-10A motor protection switch would be ideal.The alternative to the motor protection switch isthe Miniature Circuit Breaker (MCB). However,these have the disadvantage of being onlyavailable with fixed current ratings and socannot be set to the line current of the motor.

Figure 9-13 MiniatureCircuit Breaker

Current ratingof the cableThe cable currentrating should be atleast 40% greaterthan the maximumcurrent rating ofthe MotorProtection Switchor MCB. Conduit should be used for thepowerhouse wiring. The current ratings given,apply to single-core, PVC insulated cables whichconform to BS 6004, BS 6231 and BS6346.

CSA of coppercable (mm2)

Current capacity(Amps)

1.0 mm2 13.5A1.5 mm2 17.5A2.5 mm2 24A4.0 mm2 32A6.0 mm2 41A10.0 mm2 57A

Table 9-5 Current carrying capacity of single-coreelectric cables enclosed in conduit

Selection of CapacitorsThe excitation capacitors (C-2C) required toenable a 3-phase induction motor to work as asingle-phase generator will determine thefrequency of the electricity produced. Thecapacitance required to generate at a particularfrequency varies between one motor and anotherand depends on whether the motor voltage ratingis higher or lower than the recommended value inTable 9-3. The basic rule for calculating therequired capacitance C is as follows:

fVI

kFCGEN

line

πµ

2)(

××=

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where:π = 3.1416f = frequency of the generator (Hz)k depends on the voltage rating of the motorwhich is used. As described earlier, theacceptable limits for the motor voltage ratingare +/-6% of the recommended value (given inTable 9-3). The multiplying factor, k, can befound from Table 9-6:

Recommended voltage isused (as in Table 9-3)

k = 0.35

Recommended voltage+6% is used

k = 0.3

Recommended voltage-6% is used

k = 0.45

Table 9-6 Values of multiplying factor, k.

The value of C, as calculated above, should berounded up to the nearest 5µF and the 2C (2 xthe calculated value, C) rounded down to thenearest 5µF. It will probably be necessary toadjust these values further in order to obtainthe exact frequency required. The totalcapacitance C and 2C should be made up of anumber of individual capacitors. This will allowsome adjustment of the C-2C to be made duringinstallation. The voltage rating of the capacitorshould be comfortably greater than themaximum generator voltage, e.g. capacitorsshould be rated for 380V AC if generating ataround 220V. They should preferably have ascrew fitting underneath to allow them to besecurely mounted (see Figure 9-5). The ‘motor-run’ type of capacitors should be used as theseare rated for continuous use. ‘Motor-start’capacitors are only designed for intermittent useand are therefore not suitable. For informationabout connection of the capacitors, see Section9.9.

Selection of the IGCThe power rating for the controller must beequal to or greater than the maximum electricalpower output of the generator, Pmax. A goodquality IGC from a reputable manufacturer mustbe used as it cannot be repaired by the operator.

Additional electrical protection1. A lightning arrestor should be fitted close tothe powerhouse. This will protect the generatingequipment from high voltages caused by nearbylightning strikes and act in addition to thevaristor that protects the IGC (see Section 16).

2. The cables in the powerhouse must beprotected from mechanical damage by usingcable conduit. The conduit must be fixed to thegenerator connection box and to the controller/capacitor casing with threaded fittings. Thisprovides an additional layer of insulation,prevents the cables from being pulledaccidentally out of their connection boxes andprovides a watertight connection.

3. An isolation switch is needed to disconnectthe distribution system as the generator mustbe started and stopped without user loadconnected. Also it may be necessary todisconnect the user loads when drivingmechanical loads. A mains switch or an MCB canbe used as an isolation switch.

9.9 Installation and ConnectionIn addition to Figure 9-7 the following guidelinesshould be used when installing and connecting thegenerator and additional electrical equipment.Connecting the generatorAs described under “Generator Selection” inSection 9.8, an induction motor with either ofthe following connection possibilities is suitablefor a 220V scheme:

a) 380-415V star / 220-240V deltab) 220-240V star / 127-139V delta

Using motor a), the metal links should bearranged in the terminal box to give the deltaconnection. Using motor b), the links arearranged to give the star connection. This isillustrated in Figure 9-14. The three cables tothe RCD are tightened under the terminalwashers at the generator.

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Figure 9-14: Make sure the metal links are arrangedcorrectly in the terminal box to give STAR or DELTAconnection with the correct voltage range.

Connect the earth electrode to any of the threeterminals if the delta connection is used. For astar connected motor, use any of the threeseparate terminals but not the star pointattached to the metal links. The earthedterminal becomes the neutral (N) and theremaining two terminals are labelled live (L) and2C. It does not matter which way round L and 2Care as this will be determined when thegenerator is commissioned.

Figure 9-15 Connections inside generator terminal box.Several problems have been identified and solutions givenin the Table 9-7

Problem SolutionA IP 44 only

B No seal onconnection box

Use IP 55 which havebetter protection againstliquid and dust

C Loose connectionscausing over-heating

Tighten connections every 6months and use ‘shake-proof’ washers at terminals

D Lack of colour coding Cables of different coloursshould be used to avoidwiring errors.

E Pipe used as conduit Use cable conduit andconduit connectors toterminal box. (see photo)

Table 9-7 Problems with generator connections

Installation of the RCDThis should be mounted on the wall between thegenerator and controller. Ideally it should beenclosed in a purpose built housing with atransparent front allowing the operator to seewhen a trip occurs.

Connecting CapacitorsConnect the 3-phase RCD (2C, L, N) and motorprotection switch as shown in Figure 9-7. Thecapacitor connections will depend on the numberof capacitors that are used. For example, aparticular generator requires C=52µF, 2C=104µF.The capacitors available are 5µF, 15µF and 30µF.Rounding C up to 55µF and 2C down to 100µFallows these to be used and connected as shownin Figure 9-16. The 100kΩ / 2Watt resistors areused to discharge the capacitors if theprotection switch or RCD trip, preventing shock.

Figure 9-16 Suitable connection of capacitors if C= 52µF

Connecting several capacitors of different sizestogether, to make up the total values of C and2C, enables small adjustments to be made andallows the frequency to be corrected when thegenerator is commissioned. Removing smallamounts of capacitance increases the frequency.If the C capacitance is reduced by a certainvalue then 2C should be reduced byapproximately twice that value.

A

B

C

E

D

Terminal box of induction motor

Motor windings

STARW1

U1

V1

DELTA

W1V2

W2 U1

U2

V1

Metal links across herefor DELTA connection

Metal links here only for STAR connection

U2

V1

W2

U1

V2

W1

V2V2

V1

U2W2

U1

V2V2V2

W1

CConnectionfrom RCD

N

Connectionsfrom MCB

L

2C

2C

30µF

30µF

15µF

30µF

100K/2W

Connectto IGC

5µF5µF

30µF5µF

100K/2W5µF

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Most large capacitors have two connections oneach side and cables may either be soldered inplace or attached using suitable connectors thatare usually clamped onto the end of the wireswith the aid of crimping pliers. Connectors andthe appropriate tool should be used if they areavailable as soldering is impractical in isolatedlocations and prevents on site adjustment.Damaged capacitors are also difficult to replaceif the connections are soldered. When crimping,ensure that the connections are very tight, bothbetween the wire and crimp and crimp andcapacitor terminal.

Installing the IGC.The IGC is normally housed in a metal case thatis mounted on the powerhouse wall. The caseshould preferably have a hinged door and belarge enough to comfortably accommodate thecapacitors in addition to the IGC circuit board.

Figure 9-17 Correctly installed IGC and Capacitors

The trip lamps on the IGC may be mounted areusually mounted the circuit board and in the doorof the metal case.

Follow these instructions for IGC installation:• IGC must be installed vertically, in a well-

ventilated and dry location.• Connect according to labelling of terminals

and label all connecting wires.• The case must have ventilation holes that

allow a flow of cool air to pass over thefinned heat sinks of the IGC. The air ventsshould be above and below the IGC, coveredwith wire mesh and a solid protective coverraised above the surface that prevents entryof dripping water (as shown in Figure 9-18).

• Check that no cables are touching the heatsinks as the insulation could be damagedwhen the controller is operating.

• If housed in a metal case, then the case mustbe earthed.

• The ballast heater must not be installedunderneath the IGC but above or at the side.

The case must be locked, with a ‘high voltage’warning label on the door. A second label shouldstate that the box must not be opened unlessthe IGC has been isolated from the Generator

Figure 9-18 Suitable design of air vent for controller andcapacitor casing. A vent should also be provided at thebottom of the case to allow air-flow over the components

Controller Case

Water guard

Wire mesh