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Technical Note

Optimal utilisation of small-scale embedded generators in a developingcountry e A case study in Malaysia

Jianhui Wong a,*, Yun Seng Lim a, Phil Taylor b, Stella Morris a

a Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Jalan Genting Klang, 53300 Kuala Lumpur, Malaysiab School of Engineering, Durham University, South Road, Durham DH 1 3LE, UK

a r t i c l e i n f o

Article history:Received 3 August 2010Accepted 21 February 2011

Keywords:Building integrated photovoltaic systemsSmall-scale embedded generationLow voltage distribution networks ofMalaysia

a b s t r a c t

Building integrated photovoltaic (BIPV) systems are likely to become a dominant type of small-scaleembedded generator (SSEG) on public low voltage (LV) distribution network in Malaysia due to theenormous amount of initiatives and efforts taken by the government to promote the use of BIPV. Thegrowth of BIPV systems on LV distribution networks has the potential to alter the direction of power flowacross the distribution networks, hence imposing several serious technical issues relating to powerquality, distribution system efficiency and possible equipment overloading. Therefore, the utilitycompanies need to study the following technical issues: (i) voltage regulation, (ii) voltage rise, (iii)voltage unbalance, (iv) network power losses, and (v) cable and transformer thermal limits. This paperdescribes research carried out to investigate and quantify the impacts of BIPV on LV networks withparticular reference to developing countries striving to increase the utilisation of renewable energy. Thispaper presents and discusses the impacts of BIPV systems on two types of LV distribution network:a commercial LV distribution network and a residential LV distribution network in the state of Selangor,Malaysia. The results of these studies are compared with those from European networks to identify howthe differences in the electrical network characteristics influence the allowable penetration of small-scale embedded generators.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The Malaysian government has put in a great deal of effort toexplore and increase the utilisation of renewable energy sourcesover the past few years in order to reduce the dependence on fossilfuels and the emission of greenhouse gases [1e3]. For example, thegovernment reviewed its energy policy and implemented the FiveFuel Diversification Policy making renewable energy the fifthsource of energy in the country in 2000 [4]. The country is aiming tocapitalise on its abundant solar radiation by undertaking a nationalproject, namely Malaysia building integrated photovoltaic (MBIPV),aiming to create the necessary conditions which can lead toa sustainable and widespread application of BIPV from 2006 until2010 [5,6]. The MBIPV project aimed to induce the growth of BIPVinstallations by approximately 400% from 470 kW in 2006 toapproximately 2000 kW by 2010, with a unit cost reduction in theregion of 20%. Up to date, MBIPV has achieved 25% of cost reductionof BIPV system [7]. Currently, the government is considering a new

feed-in tariff scheme allowing the owners of BIPV systems to makeprofits after several years of system operations.

BIPV systems have the potential to be a dominant type of small-scale embedded generators (SSEG) to be installed in the public lowvoltage (LV) distribution networks in Malaysia. However, thecurrent strategies for designing, planning and operating lowvoltage distribution networks are used without taking into accountthe installation of BIPV systems. Hence, the direction of real powerflow is always assumed to be from the high voltage to low voltagenetworks. However, with the anticipated growth of PV systems onthe LV distribution network, power may flow from low voltage tohigh voltage networks under low load conditions and high PVpenetration levels. This future LV network configuration has thepotential to cause a number of serious technical issues related topower quality, distribution system efficiency and possible equip-ment overloading. Therefore, the utility companies, namely TenagaNasional Berhad (TNB), Sabah Electricity Sdn Bhd (SESB) and Sar-awak Electricity Supply Corporation (SESCO) need to study all theissues stated above.

In the past, research has been carried out to assess the technicalissues regarding the connection of distributed generators (DG) onMV distribution networks where the neutral line is absent and

* Corresponding author. Tel.: þ60 126217622.E-mail address: [email protected] (J. Wong).

Contents lists available at ScienceDirect

Renewable Energy

journal homepage: www.elsevier .com/locate/renene

0960-1481/$ e see front matter � 2011 Elsevier Ltd. All rights reserved.doi:10.1016/j.renene.2011.02.015

Renewable Energy 36 (2011) 2562e2572


balanced operation is assumed [8e14]. Recently, substantial studieshave been carried out to investigate the technical impacts of SSEGor DG on existing low voltage 3-phase 4-wire distribution networks[15e20]. However, most of the studies are based on the Europeancontext where the small-scale embedded generators are small-scale wind turbines and combined heat and power (CHP) type. Thenetworks are the European LV distribution networks where thevoltage level, earthing arrangement, cable types and networkconfiguration are different from that in Malaysia. Therefore, it isnecessary to perform the studies in a developing country inSoutheast Asia which strives to increase the utilisation of renew-able energy.

This paper presents and discusses the impacts of BIPV on twotypes of typical LV distribution network that are used in the study:a commercial LV distribution network and a residential LV

distribution network at Petaling Jaya in Selangor, Malaysia. The keyelectrical characteristics and load profiles of these two networks areunique and hence used to determine the response of the twonetworkswith respect to the installation of BIPV systems. This paperfocuses on 6 technical aspects of installing BIPV such as: (i) voltageregulation, (ii) voltage rise, (iii) voltage unbalance, (iv) networkpower losses, (v) power flow and (vi) thermal limits. The results ofthe studies are then used to compare with those of the UK and EUnetworks. The comparison allows identification of the differences inelectrical characteristics influencing the penetration of renewableenergy sources on developed and developing countries.

The paper is arranged in the following manner. Section 2describes the modeling approach, the details of the two LV distri-bution networks and modelling of PV systems. The results of thesimulation studies are presented and the various technical aspects

Fig. 1. Commercial LV distribution network diagram.

Fig. 2. Simulation model of Aman Jaya commercial LV distribution network.

J. Wong et al. / Renewable Energy 36 (2011) 2562e2572 2563


of BIPV installations are discussed in Section 3. Section 4 illustratesthe differences in practices and standards in the UK, EU andMalaysia, and hence the factors affecting the amount of SSEG thatcan be accommodated on their LV distribution networks. Section 5presents the conclusion of the studies.

2. Modeling approach

The two LV networks shown in Figs. 1 and 2 weremodeled usingthe simulation package PSCAD/EMTDC. Using appropriate equiva-lent models of network components, PSCAD is capable of repre-senting and simulating a power distribution system, with neutralwires and system grounding for the analysis of unbalanced multi-grounded 4- or 5-wire LV distribution systems under variousconditions of PV distribution.

2.1. Commercial distribution network

PSCAD/EMTDC was used to model two public distributionnetworks with a range of levels of penetration of PV systems. One isthe commercial LV distribution network at Petaling Jaya in Selan-gor, Malaysia. The commercial network is a three-phase four wiresystem. The LV public distribution networks are radial with a largenumber of LV feeders from the LV busbars of the �11 kV/415 Vtransformers. Consumers are connected at the remote end of thefeeders. The transformers are equipped with off-load taps at the HVside, providing a typical regulation range of �5%. The secondaryside of the 11 kV/415 V transformers are wye connected and are

solidly grounded. The earthing type used is known as t-t where theneutral line is not grounded throughout the network. The protec-tive earth of the customer is separated from the neutral line.Customers are responsible for grounding the protective earth. Thelength of the LV feeder, the cable emanating from the LV feederpillar, varies from 35 m to 80 m. Customers are not connected alongthe LV feeders. They are connected at the end of the LV feeders withthree-phase supply. Figs. 1 and 2 show the single-line diagram andPSCAD model of the commercial network respectively.

The commercial distribution network consists of 7 doublecircuits using 300MMP 4C XLPE Al cables from the low voltagedistribution board (LVDB) to a low voltage feeder pillar. The lengthof the double circuits varies from 65 m to 200 m. Fuses are used atthe out-going and in-coming points of the feeders with the currentrating of 1.6 kA. There are 47 low voltage feeders branching out

Table 1Parameters of the cables.

Type of equipment or cable Resistance(at 50 Hz at 90 �C)

Reactance(at 50 Hz)

11 kV/415V Transformer (1000 kVA)

0.00385 ohms 0.00807 ohms

300MMP 4C XLPE Al 0.13 ohms/km 0.072 ohms/km70MMP 4C XLPE Al 0.568 ohms/km 0.075 ohms/km

Fig. 3. Power demand (kW) of customers supplied by feeder FP 1e3 in the commercial network.

Fig. 4. Residential LV distribution network diagram.

J. Wong et al. / Renewable Energy 36 (2011) 2562e25722564


from the end of the double circuits. The LV feeders use 70 MMP 4CXLPE Al type underground cables to supply electricity to 47commercial shops. The parameters of these two types of cables aregiven in Table 1. The power factors vary within 0.88e0.92 lagging.The maximum demand is approximately 13 kW per shop that islikely to occur during business hours starting from 12pm to 5pm.Fig. 3 shows the power demand of customers supplied by feeder FP1e3 in the commercial network. The maximum voltage levelexperienced on these LV feeders is about 240 V. According to thedata obtained from the utility, minimum demand of the case studynetwork is recorded as 86.6 kW, while during peak hour themaximum demand tends to increase up to 530.0 kW.

2.2. Residential distribution network

The residential distributionnetworkhas fewer feeders comparedto that of the commercial network. The network is radial with anunderground cable of 300MMP 4C XLPE Al being used between thelow voltage distribution board (LVDB) and the end of the out-going

feeders. This network has 18 feederswhich are configured at the lowvoltage feeder pillar such that three-phase cables are provided tobungalows and semi-detached houses. Single-phase cables areprovided to terrace houses. Figs. 4 and 5 show the single-linediagram and the computer model of the residential networkrespectively.

The power factors are lagging varying within 0.88e0.92. Themaximum demand along a feeder is about 13 kW that may occurduring night between 9pm and 5am as shown in Fig. 6. The systemvoltage level is set at 240 V through selecting an appropriate settingof the off-load taps on the distribution transformer. Minimumdemand of the case study residential network is approximately18.9 kW while the maximum demand is recorded as 441.9 kW.

2.3. Modeling of single-phase photovoltaic inverter

The majority of the customers use single-phase inverters fortheir photovoltaic systems. At present, the inverter is installed atany of the three phases in the customers’ premises. Therefore,

Fig. 5. Simulation model of Aman Jaya residential LV distribution network.

Fig. 6. Power demand (kW) of customers supplied by feeder FP 3e4 in the residential network.



single-phase photovoltaic inverter is modeled in the distributionnetworks using PSCAD/EMTDC. The inverter circuit is made ofinsulated-gate bipolar transistor (IGBT). These IGBT models arenormally used as controlling switches in high voltage devices withlarge power ratings. The inverter was intended for use a batterythat acts as the supply to the circuit. This battery would representa photovoltaic panel [21] that supplies direct current to the circuit.Fig. 7 shows the computer model of the PV system.

Appropriate gate triggering pulses are generated and applied tothe terminals of the thyristors which results in a square waveoutput. The triggering pulses are generated by programming thecomponents in the requiredmanner. The inverter is then connectedto one of the three phases at the customers’ side via a couplingcircuit consisting of a resistor and an inductor. The value of theinductor is 67.35 mH and resistor is 0.001 ohms.

The real power output of the inverter is a function of the powerangle d between the fundamental component of the inverter outputvoltage and the grid voltage. A positive phase shift (d) of 20 isintroduced resulting in the inverter output voltage leading the gridvoltage by 20. During this leading mode of operation, real power isexported to the grid. The reactive power output of the inverter isa function of the voltage magnitude between the inverter outputand the grid voltage. If the magnitude of the fundamental

component of the inverter output voltage is set to 250 V rms andthe magnitude of the grid voltage to 230 V rms, then a current of1.3 A rms flows from the inverter to the grid. If themagnitude of theinverter output voltage is reduced to a value below 230 V rms, thenthe reactive power flows from the grid to the inverter.

The rating of this inverter depends on the capacity of the PVpanel being modeled. In Malaysia, the cost of PV system isapproximately USD 6.23 per Wp [7]. PV electricity is sold to theutility company at a rate of USD 0.092 per kWh. As described in[22], owners of PV systems may not be able to recover the invest-ment of their systems under the existing commercial framework.As a result, customers prefer the capacity of the PV systems in therange of 1 kWp to 5 kWp for residential and a range of 1 kWp to24 kWp for commercial. The average annual yield of PV in Malaysiais 1100 kWh/kWp [22]. The power output profile of a 5.25 kWp PVsystem in Malaysia is shown in Fig. 8. This PV system is installed ona bungalow in a township called Semenyih in Selangor. It can beseen that the PV system provides maximum power output at 1pmand that the hours of daylight vary only slightly throughout theyear due to Malaysia’s location close to the equator.

2.4. Description of the methodology

The computer models of the commercial and residentialnetworks were used to study how different aggregated volumes ofPV can influence the network voltage level, voltage unbalancedfactor, network losses, power flow and current flow. For eachnetwork, two extreme scenarios, namely uniform distribution andnon-uniform distribution of PV, were created as described below.

1. Uniform distribution of PV. All the customers coordinate witheach other such that they can install their PV systems in thephases in order to create the best possible balanced conditionfor the network.

2. Non-uniform distribution of PV. All the customers coordinatewith each other to install their PV systems in one phase only,say Phase A, in order to create the worst unbalanced conditionfor the network.

At present, customers install their PV systems under the plugand inform policy. The two extreme scenarios of PV distributionmay not happen. However, it is necessary to simulate these two

Fig. 7. Model of single-phase photovoltaic inverter.

Fig. 8. Daily power output of a 5.25 kW PV system on a bungalow in Semenyih atSelangor state.



scenarios in order to establish the possible range of negative effectscaused by the penetration of PV on the networks.

The computer models were to simulate the operating conditionsof the networks during which PV systems export the highestamount of real power to the networks. The PV systems export themaximum power at 12pm. Therefore, maximum demand was usedin the simulation model for the commercial network because thecommercial customers consume the highest power at 12pm. On theother hand, the residential customers consume the lowest power at12pm. Therefore, minimum demand was used in the computermodel of the residential network.

3. Simulation results and discussions

3.1. Voltage rise and voltage regulation

Voltage rise studies were carried out to determine the effects ofPV on the system voltage levels. The statutory tolerance for voltageexcursion on the low voltage distribution network isþ5% and�10%of the nominal value which is in the range of 252 V to 216 V [4]. Todetermine the total capacity of PV systems that can be accommo-dated at the connection points, the voltage rise magnitudes (%) atthe substations and loads are determined with respect to the totalcapacity of PV systems on the networks. Voltage regulation (VR) isalso determined with respect to the capacity of PV systems on thenetworks. VR is defined as the voltage magnitude deviationbetween the low voltage busbars of the MV/LV substation and theend of service. It is known that �5% is the VR limit in Malaysia [23].

The allowable PV volumes that can be accommodated on thenetworks before voltage magnitude and voltage regulation viola-tions occur were determined. For each network, the allowable PVvolumes are determined based on two scenarios of PV distribution:(i) uniform distribution of PV across the three phases of thenetwork and (ii) PV installed on Phase A of the networks only.

Fig. 9 shows the increase in the voltage magnitude at severalbuses of the commercial network when the capacity of PV isincreased. At the PV capacity of 100%, the voltage magnitude isabout 1.05 pu which is the upper limit of allowable voltage excur-sion. As a result, 100% of PV capacity is the allowable PV volume thatcan be accommodated by the commercial network as long askeeping the voltage magnitude below the upper limit.

Table 2 shows the allowable PV volumes that can be accom-modated by the commercial and residential networks before thevoltage magnitude at any points exceeds the limits. Table 3 is theallowable PV volumes on the two networks before the voltageregulation at any points exceeds the limits. It is shown that, foruniform distribution of PV, the total amount of PV that can beinstalled on the commercial and residential networks beforecausing any voltage rise violation is about 100% of the total loaddemand in both networks. However, if the PV systems are notuniformly distributed, then the amount of PV that can be accom-modated is reduced by 50% and 60% as compared to that of theuniform distribution of PV. The allowable PV volumes to beaccommodated on the networks before causing any voltage regu-lation violation is about 60% and 77% of the total load demands inthe commercial and residential networks, respectively. However, ifPV is not uniformly distributed, then the total allowable PV

Fig. 9. Voltage Magnitude (pu) with the increase in PV capacity in the commercial network under the uniform distribution of PV.

Table 2Allowable PV volumes (kW) on the networks before the violation of the voltage riselimit.

Scenarios Commercialnetwork (kW)

Residentialnetwork (kW)

Uniform distribution of PV 530 9.45Non-uniform distribution of PV 265.5 3.78

Table 3Allowable PV volumes (kW) on the networks before violating the voltage regulationlimit.



Uniform distribution of PV 530.9 14.17Non-uniform distribution of PV 265.5 5.67



volumes, with respect to voltage regulation, are reduced by 50% and60% as compared to that of the uniform distribution of PV.

3.2. Voltage unbalance

Themajority of PV systems are single-phase and their growth onthe LV distribution network is driven by customers and is notcentrally planned. Therefore, voltage unbalance level is likely toincrease as the amount of single-phase PV systems in the networksbecomes significant. The voltage unbalance factor (VUF) is used todefine the degree of unbalance as given below [23]:

VUFð%Þ ¼ V�

Vþ � 100 (1)

where VUF is the voltage unbalance factor; V� is the negative-sequence voltage (pu); and Vþ is the positive-sequence voltage (pu).

The statutory limit of the voltage unbalance factor is 1.0% inMalaysia [24]. The allowable PV volumes to be accommodated onthe networks before the voltage unbalance factor at any points onthe network exceed the limits are determined under uniformdistribution of PV across the phases of the network and non-uniform distribution of PV.

Fig. 10 shows the increase in voltage unbalanced factors atseveral feeders as the capacity of PV grows on the commercialnetwork under uniform distribution of PV. At about 60% of PVcapacity, the voltage unbalanced factors of the feeders are about 1.0which is the upper limits for the allowable voltage unbalancedfactor inMalaysia. This means that the allowable volume of PV to be

accommodated by the commercial network is 60% for maintainingthe voltage unbalanced factor below the upper limit. Table 4 showsthe allowable PV volumes to be accommodated on the networksbefore the voltage unbalance factor at any points of the networksexceeds the limit. It is shown that non-uniform distribution of PVcan cause the allowable volumes of PV to reduce by 80% and 87% inthe commercial and residential networks, respectively, comparedto that of the uniform distribution of PV.

3.3. Network losses

The line losses in the distribution networks are due to theresistance of the underground cables and overhead lines. The linelosses can be calculated as follows:

Plosses ¼ I2R ¼ ðPG � PLÞ2þðQG � QLÞ2V2 R (2)

where PG, and QG are the real (kW) and reactive (kVar) power of thePV systems, respectively; PL, and QL are the real (kW) and reactive(kVar) power of the loads, respectively; V is the line voltage at thePV connection point (V); I is the line current at the networksegment of PV connection point (A); R is the cable resistance (U)between the main substation and the PV connection point.

Fig. 11 shows the change in the total power loss as the PVcapacity grows from 0% to 200% on the commercial network underuniform distribution of PV. It is noticed that the power loss reducesas PV capacity increases from 10% to 75%. As the PV capacity grows,the amount of PV electricity available for the customers increases,hence minimising the electricity flow from the grid and the totalpower loss. However, the total network loss begins to rise as the PVcapacity grows from 75%. This is because the output of PV starts tobe higher than the customer demands. This causes the PV elec-tricity to be exported to the grid. As a result, 75% of PV capacity isthe allowable PV volumes that the network can accommodatebefore the increase in network loss.

Fig. 10. Voltage unbalanced factor at feeders versus the capacity of PV.

Table 4Allowable PV volumes (kW) on the networks before exceeding the limit of thevoltage unbalance factor.






Table 5 shows the allowable PV volumes to be accommodatedon the networks before the network losses increase. It is shownthat the allowable PV volumes on both networks under uniformdistribution of PV are higher than that under non-uniform distri-bution of PV. This is because, under non-uniform distribution of PV,additional power losses occur due to the imbalance current flowthrough the neutral lines, hencemaking network losses to rise evenat the low capacity of PV on the networks.

3.4. Thermal limits

Transformers and network line components have a thermalrating determined by the maximum current carrying capacity ofthe component. The presence of PV systems may increase theoverall current flow in the network, causing the equipment tooperate at or beyond their thermal limits. During low demand andhigh power output of PV systems, surplus power can be fed into thehigher voltage system through distribution transformers and mayexceed their nominal rating.

The growth of PV systems will affect the magnitude and direc-tion of the real power flow for varying levels of generation. Reverseflow of real and reactive powers may cause problems for the utilitycompany’s voltage control and protection systems as well asmetering systems. The 33/11 kV on load transformer tap changersmay not be adequately rated to accept significant flow of reversereal powers. The voltage control schemes for tap changers may alsobe affected by the flows of reverse real and reactive power. Boththese issues are largely dependent on the type of equipmentinstalled and their effects become significant on networks where

PV penetration levels could cause reverse power flow back up ontothe 11 kV system.

The current ratings of Tx1 and Tx2 of the commercial networkare 1.083 kA and 1.165 kA, respectively. The current ratings of Tx1and Tx2 of the residential network are 0.825 kA and 0.782 kA,respectively. The ratings of transformers Tx1 and Tx2 in thecommercial network are 1000 kVA. The power ratings of trans-formers Tx1 and Tx2 in the residential network are 750 kVA.

The current rating of the 70MMP 4C XLPE AL cable is 0.161 kA.The current rating of the 300MMP 4C XLPE AL cable is 0.434 kA.However, in both networks, such cables are used as double circuitsfor improving the reliability of electricity supply. Therefore, thecurrent rating of the double circuits is 0.868 kA. Tables 6 and 7show the allowable PV volumes to be accommodated on thenetworks before exceeding the power and current ratings oftransformers and cables.

It is shown that uniform distribution of PV allows the networksto accommodate higher volumes of PV than that of the non-distribution of PV. This is because uniform distribution of PVenables PV current to be evenly distributed across three phasesleading to reduced phase current.

It is shown that the non-uniform distribution of PV results in theallowable PV volumes being higher than that of the uniformdistribution of PV. This is because the network loss under non-uniform distribution of PV is higher than that under uniformdistribution of PV. Therefore, a large volume of PV can be accom-modated on the networks of non-uniform distribution of PV beforethe transformers are overloaded.

3.5. The total yields of the allowable PV volumes

The allowable PV volumes that can be installed on the commer-cial and residential networks with uniform distribution of PV andwithout violating any of the technical limits, determined by thevoltage unbalance constraint, are 318.58 and 14.74 kW, respectively.Assuming that the annual yield of a 1 kW PV system is 1100 kWh[22], then the total amount of electricity generated by the allowable

Fig. 11. Power loss on the commercial network with the increase in the capacity of PV.

Table 5Allowable PV volumes (kW) on the networks before the increase in network losses.






PV volumes on the commercial and residential networks are350 MWh and 16 MWh per year, respectively. It must be noted thatthese energy yields will only be realised if uniform distributions ofPV are achieved and that this would require some coordination bythe utility company.

Natural gas is the most likely fossil fuel to be replaced by PVsystems. As described in [22], the average amount of greenhousegases to be reduced by 1 kW PV over 30 years of PV lifespan are20.33 tones/kWp, then the total amount of greenhouse gases to bereduced by the allowable PV volumes are 6476 and 299 tonnes,respectively. These values are not only valuable to the governmentand environmentalists but also PV owners because they can use thedata to register their PV projects as a Clean Development

Mechanism (CDM) project [25]. Then, they are entitled to sell“Certified Emission Reduction (CERs)” to developed countriescreating additional income streams to the PV owners.

4. Comparison between UK, EU and Malaysian networks

Research has been carried out to identify the allowable volumesof small-scale embedded generators that can be installed on twonetworks: (i) Urban generic UK radial LV distribution network and(ii) typical European radial sub-urban LV network [15,19]. Thecharacteristics of these two networks are different from Malaysiannetworks in several aspects such as: (i) distribution of customersalong feeders, (ii) length of cables, (iii) earthing arrangement, (iv)combination of loads, (v) variation in power demand and (vi)technical constraints [26e30], Table 8 shows the differencesbetween the UK, EU and Malaysian LV distribution networks.Table 9 shows the allowable SSEG volumes that can be installed onthe UK, EU andMalaysian LV distribution networks before violatingany of the statutory limits. Table 9 shows the percentage of SSEGvolumes that can be accommodated on the UK, EU and MalaysianLV distribution networks against each of the technical constraints.The percentage is calculated by the following equation.

Table 6Allowable PV volumes (kW) on the networks before exceeding the current and power ratings of transformers.

Scenarios Transformers Violation of current ratings Violation of power ratings

Commercial network (kW) Residential network (kW) Commercial network (kW) Residential network (kW)

Uniform distribution of PV Tx 1 1609.9 38.74 1472.3 87.6Tx 2 1499.3 24.9 1509.1 58.1

Non-uniform distribution of PV Tx 1 794.9 12.0 1765.5 88.4Tx 2 515.4 8.13 1866.4 59.6

Table 7Allowable PV volumes (kW) in the networks before exceeding the current rating ofany cables.

Scenarios Cables Commercialnetwork (kW)


Uniformdistribution of PV

300MMP 4C XLPE AL 4858.3 32.1370MMP 4C XLPE AL 4657.1 30.24

Non-uniformdistribution of PV

300MMP 4C XLPE AL 2484.6 8.570MMP 4C XLPE AL 2317.3 8.5

Table 8Characteristics of LV distribution networks and electricity standards in the UK, EU and Malaysia.

UK generic LVdistribution network

European generic LV distribution network Malaysian LV distribution networks

Distribution of customers Customers distributed along an underground cable Customers >distributed alongan underground cable

Customers connectedto the remote end of the cables

Length of cable (km) 1.2 0.30 0.040e0.230Earthing arrangement T-T arrangement with multiple earthing points T-T arrangement with multiple earthing points T-T arrangementMixture of loads Three types of customers spread uniformly across

the network. Mixture of three-phase andsingle-phase oads in each cable

Three types of customers connected to theirindividual service cable. Mixture of three-phaseand single-phase loads in each cable.

Three types of customers connectedto their individual networks.Three-phase and single-phase loadsconnected at their individual feeders

Maximum and minimumdemands (kW)

Maximum demand¼ 499.2Minimum demand¼ 61.44

Maximum demand¼ 272Minimum demand¼ 85.2

For commercial network

Maximum demand¼ 530.0Minimum demand¼ 86.6For residential network

Maximum demand¼ 441.9Minimum demand¼ 18.9

Allowable voltage rise þ10, �6% �10% þ5% and �10%Allowable voltage

regulation�5% �5% �5%

Allowablevoltageunbalance

1.3% 2.0% 1.0%

TransformerRatings (kW) 500 400 For commercial network 1000 Forresidential network 750

Cable Thermal Limits (A) 185 mm2 CSA*: 355 A120 mm2 CSA*: 280 A70 mm2 CSA*: 205 A

300 mm2 CSA*: 465 A185 mm2 CSA*: 355 A120 mm2 CSA*: 280 A70 mm2 CSA*: 205 A

300MMP 4C XLPE AL**:434 A70MMP 4C XLPE AL: 166 A

*CSA: Cross Section Area.**Four-core armoured cables with aluminium conductor.



SSEGð%Þ ¼ SSEGðkWÞMDðkWÞ � 100 (3)

whereMD is the total maximum load demand of the network (kW).The percentage of SSEG volume indicates the maximum level of

PV which can be accommodated by each network without violatingthe technical constraints. The lower the percentage of SSEG volume,the sooner the network limits will be violated. For example, theMalaysian residential network has lowest percentage of SSEGunder voltage regulation, meaning that the residential network isthe easiest system to violate the voltage regulation constraint. It isshown that the UK generic LV distribution network has the lowestpercentage of SSEG volumes under voltage rise. Therefore, the UKnetwork is more susceptible to voltage rise issue. This may bebecause the off-load taps of the MV/LV transformers have beenadjusted to provide a voltage regulation of þ5% across the LVnetwork, hence reducing the margin for positive voltage excursion.

The Malaysian networks are very susceptible to voltage unbal-ance due to the tight voltage unbalance constraint and the T-T eartharrangement. Multiple earth arrangements implemented on the UKand EU distribution networks are an effective means of minimisingvoltage unbalance of the networks.

It is shown that none of the networks are vulnerable to trans-former and cable thermal limits. However, the power losses on theUK distribution network are easily influenced by the amount ofSSEG on the network. This is because the length of the cables usedin the UK distribution network is the greatest among all thenetworks. Therefore, the total resistance of the UK distributionnetwork is the highest, making the network losses easily increasedeven by a small volume of SSEG.

4.1. Fault tolerance

It is worth nothing that Malaysian networks have the ability ofmaintaining electricity supply to a proportion of the customers andto accommodate PV under n� 1 conditions. This is becauseMalaysian networks have double circuits made of 300MMP 4CXLPE AL. If one of the circuits is out of service, the utility companystill can maintain a proportion of the customers and SSEG on thenetworks. The UK and EU low voltage distribution networks maynot have such double circuits. Therefore, they may not be able to

accommodate any customers or SSEG during n� 1 conditions.Table 10 shows the percentage of allowable SSEG volumes on thefour networks during n� 1 conditions. It is shown that, duringn� 1 conditions, Malaysian commercial and residential networksare able to maintain PV with the capacity of 484% and 220.5% of themaximum demand. This shows that the fault tolerance of Malay-sian networks can be higher than that of the UK and EU distributionnetworks.

5. Conclusions

Three-phase four wire computer models of the commercial andresidential networks have been developed in PSCAD. Single-phasephotovoltaic inverters were modeled in the distribution networksusing PSCAD/EMTDC. The inverter circuit was made of insulated-gate bipolar transistor (IGBT) models. With the use of these twoPSCADmodels, studies were carried out to investigate the responseof voltage, network losses, current and power flow of bothnetworks with respect to the penetration of PV systems.

The differences in the characteristics and parameters of thecommercial and residential networks make these networksrespond differently to the penetration of PV systems. The responseof the networks was studied under two conditions: (i) uniformdistribution of PV and (ii) non-uniform distribution of PV. It wasshown that non-uniform distribution of PV can cause thecommercial and residential networks to reduce the amount of PVvolumes as compared to the uniform distribution of PV under mostof the categories of technical constraints. It was also noticed thatthe commercial and residential networks suffered from voltageunbalance problems relatively quickly which could limit thegrowth of PV systems. This is mainly because of the tight voltageunbalance limit imposed by the utility companies in Malaysia andthe type of earthing arrangement used. T-T arrangementmay not bean effective means of maintaining balanced networks in the pres-ence of significant levels of single-phase PV.

The allowable PV volumes that can be installed on thecommercial and residential networks without violating any of thetechnical limits were found to be 318.58 and 14.74 kW, respectively,for uniform distribution of PV systems. With such capacities of PVsystems, the total amount of electricity that can be generated by thePV systems are 350 MWh and 16 MWh per year, respectively. Theseamounts of solar electricity can reduce the emission of greenhousegas by 6476 and 299 tonnes, respectively. The PV owners cangenerate additional incomes by selling their “Certified EmissionReduction (CERs)”.

A comparison between the characteristics and parameters of theUK, EU and Malaysian networks was made to illustrate how thetechnical practices of the UK and EU may bring benefits tothe accommodation of PV systems on the LVnetworks inMalaysia. Itwas noticed that the UK generic LV distribution network is verysusceptible to voltage rise issue. This may be because the off-loadtaps of the MV/LV transformers were adjusted to increase the

Table 9Percentage of allowable SSEG volumes (%) on the UK, EU and Malaysia networks based on uniform distribution of SSEG.

Technical constraints UK generic LVdistribution network

EU generic LVdistribution network

Malaysia

Commercial network Residential network

Voltage regulation (%) 154 119 100 75Voltage rise (%) 37 196 100 60Voltage unbalance (%) 9.5/phase 9.9/phase 4.7/phase 3/phaseTransformer thermal limits (%) 122 185 303 463Cable thermal limits (%) 209 125 819 160Increases in losses (%) 16 66 75 20

Table 10Percentage of allowable SSEG volumes (%) on the UK, EU and Malaysia networksbased on uniform distribution of SSEG during n� 1 conditions.

Technicalconstraints

UK generic LVdistributionnetwork

EU generic LVdistributionnetwork

Malaysia

Commercialnetwork

Residentialnetwork

Cable thermallimits (%)

0 0 484 80



voltage levelbyþ5%across theLVnetwork. Therefore, themargin forpositive voltage excursion is significantly reduced. Apart from that,the fault toleranceof theMalaysiannetworks canbehigher than thatof theUK and EUnetworks because of the double circuit presence onthe Malaysia networks, hence making the networks being able toaccommodate a proportion of PV during n-1 conditions.

Malaysian networks are very susceptible to voltage unbalancedue to the tight voltage unbalance constraint and the T-T earthingarrangement. Multiple earth arrangements implemented in the UKand EU distribution networks are an effective means of minimisingvoltage unbalance of the networks.

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