Neutral current compensation in three phase, four wire systems a review

Review Neutral current compensation in three-phase, four-wire systems: A review Available online 26 January 2012 Keywords: Transformers Inmanyresidentialandofficebuildings,powerisdistribu

Review

Neutral current compensation in three-phase, four-wire systems: A review

Available online 26 January 2012

Keywords:

Transformers

Inmanyresidentialandofficebuildings,powerisdistributedthroughathree-phase,four-wire(3P4W) systems.Thenon-linearandunbalancedloadsinthesesystemsmayresultinexcessiveneutralcurrents, whichmaypotentiallydamagetheneutralconductoranddistributiontransformerwhileaffectingthe safetyoftheconsumers.Severaltechniqueshavebeenreportedinliteraturetoovercomethisproblem Thispaperpresentsacomprehensivereviewofneutralcurrentcompensationmethods,theirtopologies, andtheirtechnicalandeconomicallimitations.SimulationsarealsocarriedoutinMATLAB/SIMULINK environmentforcomparingtheexistingmethods

© 2011 Elsevier B.V All rights reserved

Contents

1 Introduction 171

2 Problemsofhighneutralcurrents 171

3 Recommendedpracticesforhandlingexcessneutralcurrents 171

4 Passiveharmonicfilters 171

5 Synchronousmachineasafilter 172

6 Transformerbasedtopologies 172

6.1 Zigzagtransformer 172

6.1.1 Operationofzigzagtransformerwithunbalanced/distortedsupplyvoltages 172

6.2 Star-deltatransformer 173

6.3 T-connectedtransformer 173

6.4 Star-hexagontransformer 173

6.4.1 Zigzagtransformerwithsingle-phaseshuntAPF 174

6.4.2 Zigzagtransformerwithsingle-phaseseriesAPF 175

6.4.3 Star-deltatransformerwithsingle-phasehalf-bridgePWMAPF 175

7 Three-phase,four-wireactivepowerfilters 176

7.1 ThreeH-bridgeshuntAPFtopology 176

7.2 Three-phase,four-wirecapacitormidpointAPFtopology 176

7.3 Three-phase,four-wirefour-legAPFtopology 177

8 Conclusion 178

References 178

1 Introduction

2 Problems of high neutral currents

3 Recommended practices for handling excess neutral

currents

4 Passive harmonic filters

Fig 2. Schematic diagram for neutral current compensation with synchronous

machine.

5 Synchronous machine as a filter

6 Transformer based topologies

Table 1

Source neutral current without compensator (rms, A) 19.3

Source neutral current after compensation

with inserted inductor (Zn) (rms, A)

[41–43]

same

same

under:

stringent

inTable3.ThekVAratingofthetransformerisprimarilydecided

are:[28,29]

location

◦ ,

◦ & −240

◦ )

Table 3

Transformer type Zigzag ( Fig 3 ) Star-delta ( Fig 4 ) T-connected

Star-hexagon

two-winding)

two-winding)

single-phase two-winding)

three-winding)

3

√

3

√

2

√

3

3

√

V √lI n

star-hexagon

star-hexagon

Good

APF

[28,29,34–36].Theseapproachesgreatlyreducetheratingofthe

7 Three-phase, four-wire active power filters

[48–55,103]

in[80,81]

Fig 12.The 3P4W four-leg topology.

capacitors:

[51,52].Inthistopologythreeoftheswitchlegsareconnectedto

[51,52]

Table 4

Active filter topology Three H-bridge ( Fig 10 ) Capacitor midpoint ( Fig 11 ) Four-leg APF ( Fig 12 )

currents

H-bridge

requirement

devices

devices

devices

currents.

Table 5

Transformer based solutions Three-phase, four-wire active power filters Basic principle Provideslowimpedancepathforzero-sequenceharmonics

currents.

Compensate by injecting equal-but-opposite compensating current.

Depending upon the selection of transformer, these currents may circulate in the secondary winding of the transformer or may circulate between load and transformer.

Effectiveness of neutral current

compensation

Compensates only zero-sequence harmonics (complete compensation is possible with addition of 1-␸ APF)

Completely compensates neutral current Operation under unbalanced and/or

distorted utility voltage conditions

Degrades and causes uneven raise of neutral and line currents (but with addition of 1-␸ APF this problem can be alleviated to some extent)

Degrades (with proper design of controller this problem can be alleviated to some extent) Phase harmonic compensation,

reactive power compensation and

flicker mitigation

Not possible (possible only with addition of three-phase, three-wire compensator)

Possible (this is the native feature of 3P4W APFs)

Rating of the compensator Very less (low kVA rating of the compensator reduces cost,

power losses and the generated electromagnetic interference)

Very high Robustness of compensator High because of passive compensation Less

Effect of location on compensating

characteristics

Effect of source impedance on

compensating characteristics

impedance is less than source impedance) Effect of buffer reactor (Zn) on

compensating characteristics

Dependent (but no buffer reactor is required with addition of 1-␸ APF)

No buffer reactor is required

Application and topology selection Suitableforhighvoltage,mediumtohighpowerapplications Suitable for low to medium power applications

Not suitable with unbalanced and/or distorted utilities voltages

appli-cations

8 Conclusion

References

[15] IEEE Recommended Practices and Requirements for Harmonics Control in

249–259.

2848–2853.

41–48.

164–173.

1649–1656.

1263–1270.

[77] M.C Benhabib, S Saadate, New control approach for four-wire active power

4643–4649.

1139–1149.

538–544.

633–638.

1935–1944.

1–6.