Induction Motors Performance under Symmetrical ... - IEEE Xplore

2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June 2013

Induction Motors Performance under Symmetrical Voltage Sags and Interruption - Test Result Surya Hardi a), Syafruddin Hs a), Muhd. Hafizi a), Z. Pane b) , R. Chan b) a)

School of Electrical System Engineering, University Malaysia Perlis (UniMAP), Malaysia b) Department of Electrical Engineering, University of North Sumatra (USU), Indonesia References [4, 5] explained that effects resulted by voltage sag on behavior induction motor depends on some characteristics of voltage sags, such as sag magnitude and sag duration, types of voltage sag, phase shift, point on wave of sag initiation and recovery voltage. Many studies have been developed to investigate effects of voltage sags on induction motor in also experimental and simulation. An experimental study and some calculation specific energy have carried out in reference [6]. Induction motor performance caused by symmetrical voltage sags and interruption was analyzed. The motor behavior is studied in during and at the end of voltage sag instant. By using a three phase squirrel cage induction motor of 5.5 kW, 1500 rpm, 380 volt. Shallow and deep voltage sags were introduced in this experiment i.e., 85% and 20% of nominal voltage to investigate the current and specific energy. For shallow sag the current is 20% higher than the normal current and specific energy slight higher at beginning voltage sag and at end of the voltage sag, the current is higher than normal of 25%. The currents are higher when the motor was subjected to deeper voltage sag. Influence of sag magnitude and sag duration on the current peak, torque peak and speed loss was also investigated [4]. From simulation result shows the current peak and torque peak produced in different sag duration is not significant and they always occur at the beginning of voltage sag. From previous several reports related to effect of voltage sag on induction motor have been published, but not show the effect caused by other characteristics such as repetitive sag and multiple sag. This paper presents an experimental test to investigate effect caused by others characteristics of voltage sags on performance of induction motors beside sag magnitude and sag duration as the main characteristics.

Abstract- Main source voltage sags are short circuit faults in power systems. These fault currents propagate entire the circuits connected with them. After the fault is removed by circuit breaker opened, the system voltage may recover to its normal value, the motor will reaccelerate during recovering process accompanied by high transient currents. This paper presents an experimental test to investigate effect of various characteristics of voltage sags such as magnitude, duration, repetitive and multistage of voltage sags on performance of induction motors. Several small induction motors were used to this purpose. Sag magnitude significantly influenced on the current peaks and speed variation whereas sag duration significantly influenced only on the speed. The motor responses to magnitude and sag duration in repetitive and multistage events are different. Index Terms—Voltage sags, current peak, speed variation. I. INTRODUCTION Induction motors are one of the most common pieces of equipment used in industrial application. They are can either directly connected to power supply or through a contactor or an adjustable speed drive. It is depending on requirement of the industrial. Induction motors are one of sensitive industry equipment against to voltage sags. When the terminal motor is subjected voltage sag, high current peaks and torque peak produced at the beginning and the end of voltage sags (voltage recover) instants and speed loss. They values are very depending on the sag magnitude, sag duration and others sag characteristics. Commonly the motors are completed by protection systems i.e., overcurrent or undervoltage protections. The large torque peaks may cause damage to the shaft or equipment connected to the shaft. The large inrush current at recovery voltage instant may triger overcurrent protection to trip and then the motors become stall, thus causing a stop in production with noticeable associated costs [1, 2]. Reference [3] has investigated effect of system recovery voltage due to severe sags or interruption on protection system of induction motor. High current produced at the end of the voltage sag instant can stress the motor protection such as fuses. This is identified as specific energy value, (I2t) cause fuse aging and motor winding overheating. There are many interrelated factors which determine this performance.

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II. CHARACTERISTICS OF VOLTAGE SAGS IEEE Std. 1250, 1995 define that sag magnitude has range from 10% to 90% of nominal voltage and sag duration from one half cycles to one minute (magnitude less than 10% are classified as interruptions) [7]. Some types of fault on the power system usually cause voltage sag but can also be caused by energizing of heavy loads or starting of large motors. Although duration of voltage sag caused by motor starting is generally longer, but voltage drops are usually small and do not cause serious problems at the customer locations [1].

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Regarding to continuity of the power supply, the voltage sag is different from the interruption. An interruption is characterized as a complete loss of voltage due to the opening of the circuit breaker between the sources and the load. Duration of voltage sags is described as the total time interval between the point on wave of sag initiation and voltage recovery point. It is determined by fault clearing time, which highly depends on protective devices. The main causes of repetitive voltage sags are lightning strokes and re-closer operations. Automatic circuit re-closer is an over current protective device that trips and reclose a preset number of times to clear transient fault or to isolate permanent fault. Multi stage sags are voltage sag due to faults but they present different levels of magnitude before voltage returns back to normal. Magnitude and duration are main characteristics of the voltage sags which influenced on behaviour of equipment [1]. Fig. 1 shows several sag characteristics produced by Schaffner Profline 2100 EMC. The others characteristics such as symmetrical and unsymmetrical voltage sags, phase angle shift, point on wave of sag initiation, recovery voltage, repetitive sag, multi sag have been found to influence significantly the equipment’s sensitivity to the voltage sags [1]. All the characteristics may occur when a power system experience short circuit faults.

(c). Multi stage voltage sags Fig. 1. Characteristics of voltage sag

III. TEST SET-UP To investigate the performance of induction motors due to voltage sag, an experimental test is developed such as in Fig. 2. It consists of five major parts: a Schaffner Profline 2100 EMC tester used for generating voltage sags, personal computer for adjusting the sag characteristic desired, induction motor (under test), generator as load, a digital tachometer RS 232 (as output data-logger) is used to measure the rotation of the shaft on the induction motor. Several small induction motors ranging 0.17 up to 1 kW are used for testing. Specifications data of the induction motors available on their name plate have voltage 415/240 volt as in Table I.

(a). Voltage sag described by magnitude and duration

(b). Repetitive voltage sag event Fig. 2. Test set up for testing an induction motor

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TABLE I SPECIFICATION DATA MOTORS USED No.

No. of Phase

No. of Pole

Power

Rpm

P.f

M1

Single phase

4

1 kW

1450

0.92

M2

Three phase

2

1 kW

2770

0.83

M3

Three phase

4

1 kW

1400

0.79

M4

Three phase

4

0.37 kW

1400

0.8

4

0.186 kW

1345

0.8

M5

Three phase

From Fig. 5, it can be observed that for sag magnitude of 40% and below and values of the current peak produced are almost similar, whereas for deeper sag their values are different. The currents are also large increasing in this range. The single-phase motor (motor 1) draws current is highest than two other motors (motors 2 and 3) and can reach about 10 p.u in interruption event. The two-pole motor draws current is higher than the four-pole motor. All values of the current peak show are higher for deeper sag.

The motors were subjected to symmetrical voltage sags with various sag characteristics namely, sag magnitude, sag duration, repetitive sag and multi sag. The sags magnitude was set to start from 90% to 0% of the nominal voltage in step of 10% increments. IV. RESULTS AND DISCUSSION Fig. 3 shows an example experimental test result for motors (M4) was subjected to voltage sag (sag magnitude of 20% and sag duration of 100 ms). This figure shows three-phase line currents of the motor before, during and after voltage sag. From this figure can be observed that transient currents occur at drop point and recovery voltage instant. The current peaks always occur at this point. The peak current in phase A is higher than two other phases. This is also according to some experiment tests have carried out on others motors (is not displayed in this paper) which current in phase A is always higher two others phases. The current peaks are designated in per unit (p.u) which is ratio between the current peak at recovery voltage (end of the voltage sag) and normal instants.

Fig. 4. Voltage and currents waveform of the motor was subjected to voltage sag (50%; 6 cycles).

Fig. 5. Influence of sag magnitude on the current peaks for three different motors

Fig. 3. Three-phase line currents waveform of the motor was subjected to voltage sag (20%; 100 ms).

A.

Influence of Sag Magnitude on the Current Peak Experimental test was carried out on for three different motors (different phase number and different pole number) and they have similar rating of 1.1 kW. Fig. 4 is an example performance of the voltage and current waveform for motor 2 caused by voltage sag (sag magnitude of 50% and sag duration 6 cycles). In this condition the current peak can reach about four times current normal. Test result for all the voltage sag with 6 cycles in duration is displayed such as in Fig. 5.

Fig. 6. The current peaks of 0.37 kW induction motor in different sag duration

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Fig. 6 shows influence of sag magnitudes in different sag duration. An small induction motor of 370 watt was subjected to voltage sag with diferrent duration (50, 100, 150, 200, 300, …, 500 milliseconds). This figure can explain that increasingly voltage sag (more deeper), the current peaks are higher for all duration. This figure explain also that the highest current for deeper voltage sag. This proves that values of the current peak are great influenced by sag magnitudes. B. Influence of Sag Duration on the Current Peak Fig. 7 shows influence of sag duration on the current peak for different sag magnitude for a 0.37 kW induction motor (M4). Sag durations are not significant different on the current peaks for voltage sag of 50% and above. But the sag duration influence start occurred for sag of 20% and below. This is clearly visible for interruption event and it occurs in ranging around 75 up to 200 milliseconds. The current peaks can reach higher than others.

Fig. 8. Influence of sag duration on the speed variation

D. Performance of the current peak caused by repetitive voltage sag A 0.37 kW induction motor was subjected to repetitive voltage sag with sag magnitude of first voltage sag and second voltage sag is similar, i.e., 50%. Difference sag durations were set for first sag only (50, 100, 300 ms), whereas for second sag duration is constant (100 ms). The purpose this experiment is to investigate performance on the current peak in second sag caused by first sag duration. Performances of the current peaks in various first sag durations are displayed in Fig. 9.

Fig. 7. Influence of Sag duration on the current peaks for different sag magnitude

C. Influence of Sag Duration on the Speed Fig. 8 shows influence of the sag duration on the motor speed variation in different sag magnitude on motor (M5). This Figure shows minimum speed occurs for different sag magnitude at certain sag duration (1 to 10 seconds with interval 1 second). The motor speed performances during voltage sag in period 1 second to 10 seconds. Motor speed reduction depends on the sag duration and magnitude of voltage sag. For sag magnitude to 70%, speed drop does not significant influenced. For deeper sags i.e., sag magnitude of 30%, 20% and 10% results in a significant speed loss. For example, speed drops rapidly approximately 15% of its nominal value for 20% sag depth in period 4 to 5 seconds and even for sag magnitude of 10%, the motor shorter to reach stalling condition voltage sag occurs 2 seconds and above in duration.

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(a)

V1=V2 = 50%, t1= 50 ms, t2 = 100 ms

(b)

V1=V2 = 50%, t1= 100 ms, t2 = 100 ms


(c)

V1=V2 = 50%, t1= 300 ms, t2 = 100 ms

(a)

Multistage voltage waveform applied to terminal voltage

Fig.9. Current waveform of the motor caused by repetitive voltage sag in different sag duration. (V1 and V2: value of sag magnitudes for first and second sag respectively; t1 and t2 : value of sag durations)

From Figure 9 can be observed that there is no different significant occurred on the current peak in second sag caused by duration of the first voltage sag. The current peak was produced around 3.2 A, therefore repetitive voltage sags are not influenced on the current peaks for this sag duration period. E. Performance of the current peak caused by multistage voltage sag The motor was also subjected to multistage sag namely, sag magnitude of 80% (shallow sag) and 20% (severe sag) with sag duration of 73 milliseconds for first sag and second sag.

(c) The current wafeform caused by multistage sag Fig. 11. Multistage voltage sag waveform ((V1= 20%; V2 = 80% with 73 ms duration).

Performance of the current peak is displayed in Fig. 10 and Fig. 11. From Fig. 10 can be seen that the current peak on the second sag caused by magnitude sag of 20% can reach over 5 A. As comparison, the current peak caused by sag magnitude of 20% in the first sag is 4 A (in Fig. 11). This can explain that value of the current peak in second sag is influenced by first voltage sag magnitude which the current is increase. CONCLUSSIONS (a)

A study has conducted using experimental test to investigate effect of various characteristics of voltage sags on performance of induction motors. Magnitude of voltage sags have greatly influence to induction motors performances. The current peak is higher for lower sag magnitude whereas influence sag duration on the current peaks virtually for severe sag only. Both sag magnitude and sag duration have influence in speed loss. Even the motor may stall when it was subjected to severe voltage sag in short duration. The motor has different response to others characteristics such as repetitive and multistage of voltage sag. In repetitive sag event, sag duration of the first voltage sag do not influenced on the current peak in second sag. In multistage voltage sag event, value of the current peak in the second sag is influenced by first sag and the current become increase.

Multistage voltage waveform applied to terminal voltage

(b)

The current wafeform caused by multistage sag

Fig. 10. Multistag voltage sag waveform (V1= 80%; V2 = 20% with 73 ms duration).

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REFERENCES [1] [2] [3]

[4] [5]

[6]

[7]

M. H. J. Bollen, Understanding Power Quality Problems, “Voltage Sags and Interruptions”. IEEE Press Series on Power Engineering, New York. 2000. F. Carlson, “Before and during voltage sags: the relationship between the voltages and the tripping level for line-operated machines,” IEEE Industry Applications Magazine, Mar/Apr 2005. D. H. Tourn, J. C. Gomez,.“ Effect of system recovery on induction motor protection using HBC fuses, following a short circuit fault, Industry Applications Conference, 2001. Thirty-Sixth IAS Annual Meeting. Conference Record of The 2001 IEEE Volume:3. L. Guash, , F. Corcoles and J. Pedra.“Effect of Symmetrical and Unsymmetrical Voltage Sags on Induction Machines,”IEEE Trans. On Power Delivery, vol. 19.,N0. 2, April, 2004. M. T Llerena, R. P. Homrich,.F. F. Filho, A. “Estimation of the induction machine behaviour subjected to voltage sags. Power Electronics , Machines and Drives, 2006. PEMD 2006. The 3rd IET International Conference. J. C Gomez, Medhat M. Morcos, Claudio A. Reineri an Gabriel N. Campetelli,”Behaviour of Induction Motor Due to Voltage Sag and Short Interruption”, IEEE Transaction on Power Delivery, Vol. 17, No. 2, April 2002. IEEE Guide for Service to Equipment Sensitive to Momentary Voltage Disturbances, IEEE Std. 1250, 1995.

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