EXPERIMENTAL INVESTIGATION OF EFFECTS OF VOLTAGE UNBALANCE ON THREE - PHASE INDUCTION MOTOR

A. F.

Nnachi

SAUPEC 2011

Outline of presentationq q q q q q q q q q Conclusion Laboratory test result Methods of quantifying Voltage unbalance Introduction

Outline of Presentation

Introductionq Voltage unbalance - the inequality of Voltage magnitudes &/ voltage angles among the three-phases of supply q Voltage unbalance is a common phenomenon in electrical grids and this occurs due to incomplete transposition of transmission lines open delta transformer connections unequal distribution of single phase loads blown fuses on capacitor banks railway traction loads adjustable speed drive operations q Induction motor is the most popular electric machine widely used in industrial, commercial and domestic applications. q q Effect of voltage unbalance on three phase induction motors considering variation in phase and voltage magnitude of supply q q In an attempt to incorporate voltage phase angle and magnitude variation in this investigation, a fully adjustable three-phase synchronous generator has been developed

Introduction

Voltage UnbalanceFour methods of quantifying voltage unbalance are: vPhase voltage unbalanced ratio v v v v v vLine voltage unbalance ratio v v v v v v vvoltage unbalanced factor v v v v vcomplex voltage unbalance factor

Voltage Unbalance: Methods of quantifying voltage unbalance

Laboratory test resultFully adjustable three-phase synchronous generator

Front view Rear view

Laboratory test result : Fully adjustable three-phase synchronous generator]

Effect of phase angle variationSingle phase angle variationvoltage unbalnce (%)

35 V UF LV UR

30

25

20

15

10

5

0 -170

-160

-150

-140 -130 -120 -110 P has e angle of Y -phas e (degrees )

-100

-90

Comparison of LVUR and VUF under variation in phase angle of Y-phase260 250 240 230 220 210 201

motor input power (W)

190

178 170 0 5 10 15 VUF (%) 20 25 30 35

variation of motor input power to changes in VUF

Effect of phase angle variation: Single phase angle variation]

Effect of single phase over voltage unbalance

motor input power due to the % voltage unbalance

Over-voltage unbalance often occurs in off-peak periods when there is not much load on the supply. In this part of the experiment, the blue and yellow phases were kept at 230 and the red phase varied from 230 and abovevariation of stator currents to changes in VUF (%)

Effect of single phase over-voltage unbalance

Two phase under voltage unbalance

motor input power due to the % voltage unbalance

Two phase under-voltage unbalance occurs when the two phases of a three-phase are heavily loaded compared to the third phase. In this case those two phases will have higher voltage drop than the third phase. In this part of the experiment, the red and yellow phases were varied below 230 V while the blue phase was kept constant at 230 V.

variation of motor stator current to changes in VUF (%)

Effect of two phase under voltage unbalance

Two phases under/over voltage unbalance

variation of motor input power to changes in VUF (%)

Phase voltage of the yellow phase is maintained at 230 V whereas Red phase and blue phase were varied below and above 230 V respectively

variation of motor stator current to changes in VUF (%)

Effect of two phases under/over voltage unbalance

ConclusionEffect of voltage unbalance on three phase induction motors considering variation in phase and voltage magnitude of supply In an attempt to utilize and incorporate phase angle variation in this investigation, a fully adjustable three-phase generator was developed which supplies the induction motor to be studied. From the experimental results, the following conclusions are derived: Unbalanced voltage source supplying a three-phase induction motor increases the motor input power, Increases stator current hence higher I2R losses therefore reduction in the overall efficiency. Change in the angle of any phase voltage causes voltage unbalance even though the magnitudes of all the phases are all equal. The positive-sequence voltages and negative-sequence voltages which are component of CVUF plays important role in voltage unbalance analysis.

Conclusion

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