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Case Study 31

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Case Study of HT Reactor failure- A Resonance Phenomenon in

11KV Water Pumping Station

Case Study 31

Case Study of HT Reactor failure- A Resonance

Phenomenon in 11KV Water Pumping Station

Abstract

A booster pumping station (BPS) in South India with high power HT pumping motors reported

sudden failures due to flashover of the current limiting reactors of the PF correction capacitor

circuit. The pumping circuit has its own power factor correction capacitor circuits. The failures were

reported repeatedly over three/ four days during December 2009. Extensive re-look on design

aspects and simulations studies pointed out no major design issues. Finally it was concluded that the

failures were due to the inherent design and workmanship limitations of the reactors itself to handle

transient over currents during switching. To find out the specific reasons for such failures (which

happened after three to four years’ of working), it was decided to undertake power quality studies.

The longer duration period of logging at identified points it was noted that at a certain random

periods , the voltage and current total harmonic distortions increases abnormally high. It was also

noted that the predominant in harmonic content. Detailed investigations provided the reason for

such random failures due to harmonic environment that too occurring at random intervals. This has

lead to shunt resonance situation for the LC circuit resulting into the failure of the reactor. Larger

sized current limiting reactors were found to be the best and economical solution in this case.

Background

The past six decades have witnessed phenomenal growth of urban population in India. At least 10

million people are being migrating to it each year. The services of municipal bodies and also utility

companies cover most basic needs like drinking water, street lighting, garbage handling, drainage and

sewage system etc.

Supplying potable quality piped drinking water to huge population has been one of the primary tasks

of the water utilities. Thus the reliable operation of the pumping station for 24x7 days has been the

top most priority for these water installations. There has been continuous attempt to follow the

“Best operating practices” at these places, though the money availability may not be adequate in

some cases.

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The basic equipment design takes care of the pump motor requirements including the requirement

of providing reactive power compensation at different station loads. However the reliability aspect of

such large equipment, the design itself should ensure adequacy of uninterrupted operation under

different conditions. It should also take care of unpredictable and / or peculiar failures of equipment

taking place all of a sudden, leading to disruption of the service. One of the major reasons for such

unpredictable failures in electrical systems could be due to the quality of the power supply and hence

enhanced awareness for the end users is essential. The power supply with harmonics could result in

a peculiar type of failures. It is always a challenging task to exactly pin point the reasons for such

failures as it requires special analysis of the equipment/system utilizing the advanced

technique/knowledge. The case study presented here highlights the necessity of visualizing such

problems at design stage itself as the equipment have to work under poorer power quality

environment. Only systematic Power and power quality study would help in identifying the reasons

for such unexpected and sudden failures and the best possible solution.

Demonstration Site

One of the southern India based water pumping installation has large water handling capacity of

180Million litres per day. This booster station has 3 numbers of 90 MLD capacity pumps, each one

being driven by 1800KW capacity motor at 11KV. A Fluid coupling box arrangement is made use for

speed reduction arrangement between motor and the pump .Normally, one pump operates

continuously but the second pump is also brought into operation few times in a week, based on the

consumer water supply requirements. The third pump is kept on standby. All the three pumps are

utilised in a planned schedule.

Details of Power/Distribution system at Booster station

The 11KV power supply is provided from a dedicated 110kV sub-station where there are 2x10MVA,

110/11KV power transformers. For enhancing the reliability of the power supply, the pumping station

has two 11KV feeders. The power supply arrangement is complete with two pole structures, main HT

panel, distribution panels with vacuum breakers and FCMA type starter panel (rotor side reactors

whose value is controlled to exhibit large value of impedance during staring to limit the starting

current and which subsequently gets saturated and exhibits low impedance when running) for

each of 11KV, 1800 kW slip ring induction motors. Each motor panel has its own power factor

correction HT capacitors’ bank of 500 KVAR, to improve the power factor from 0.88 to 0.98,along

with series connected current limiting iron core reactors.

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The reactors have been provided to achieve the required current limiting in the capacitor circuit

during motor starting and at the same time have reduced power loss. Normally the standard

recommended value of the series reactor for such requirements is 5% of the capacitor value.

However the reactor provided in the present case was only 0.2 % at the design stage possibly to

reduce the dimensions as well as the cost of the current limiting reactor. [Detailed as figure #1]

The design with the reduced reactor value had also worked for nearly three / four years before the

multiple failure of these reactors had taken place over couple of days in December 2009when the

second pump was getting started.

This case study is related to the analysis of this failure undertaken by the utility company,their

suppliers and finally (from May 2010) by the faculty of a leading institution. The original premise with

which the fault analysis was conducted, was to look for a possible reason for over voltage causing a

flash over and the resultant over current.

The electro-magnetic transient ( E M T )analysis conducted as part of the present case study

indicated that the selection of 0.2 % reactor would also serve the original purpose of limiting the

current through the PF capacitors during starting provided adequate design requirements to handle

larger transient currents during the short starting times are taken care of assuming that the input

supply is sinusoidal .It is to be mentioned that the starting requirements happen once in a while.

However when connected to a power system with harmonic voltages, the series filter circuit (

made up of a 0.2% reactor and 500 kVAR capacitor bank)could resonate at its tuned frequency,

which unfortunately, in the present case, happened to be one of the predominant harmonic

voltages ( 13th harmonic voltage )getting injected into the system at totally random times (not

always) from an external source connected to the grid.

The peculiarity of the present case was that, in the utility pumping station under consideration,there

is no non- linear load and hence the possibility of getting affected by power quality issue was not

considered at all. Also , as it was subsequently seen , the power quality problem comes as a

disturbance over certain durations( it is not present always )and hence was not identified until the

long time recording of parameters was conducted.

The station has also 2 x200KVA capacity auxiliary transformers of 200KVA rating for power supply to

other station LT loads.

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While, HT panel incomer is provided with Earth fault, over current and under voltage protections

each of the HT motor panels are with MRO (motor protection) relay for comprehensive protection to

the motors.

A typical wiring diagram of motor panel is illustrated below in Figure1

Figure 1: Wiring diagram for motor circuit

PQ issues at pumping installation

During December 2009, the water pumping installation had reported a series of failure of the current

limiting series reactors in the P.F correcting capacitor panel of motor, affecting severely their two

pump mode operation requirements. This was stated to be four times within a short span of four

days. The failure was observed only when the second pump was put into operation in parallel to the

already running first pump motor. The water utility had to organize urgent replacement/rewinding of

reactors and the replacements were used in the circuit after heating the same in oven. The failures

had also taken place randomly in any one of the phases but majority of the failures were in the

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second motor set capacitor current limiting reactors and also once of the first running motor’s

power factor capacitor reactor.

Further, during last event of failure,there was transformer tripping with Buchholz relay operation,

requiring removal of the transformer from site andfurther investigation and repairsat the

transformer manufacturer’s factory.

The photographs of the failed HT reactors and the incoming transformer are given as under :

Figure #2 HT Reactor ( 0.2% ) in series with PF capacitor Failure

Figure #3 Damaged10 MVA input Transformer under repair in the Factory

The physical inspection /photographs of the earlier failed reactors ( 4sets ) and the main input

transformer revealed the following:

a) Badly charred reactor indicated the flow path of a large quantity of current.

b) Minor inter-turn flashovers are observed for other three cases

c) Severe movement of LT coils alongwith their anchoring clamping /bolting arrangement indicated

the passage of heavy current on the secondary of the transformer.

After this fault the utility continued the operation with P.F correction for one pump motor only and

whenever the second pumping unit is brought into operation, the same was without the P F

correction unit.

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The above observations and the description of the faults observed required, a step–by –step study

of the entire system for identification of the possible reason(s) for the failure of these reactors

during two pump operation and then arrive at a solution to overcome the same .

The major studies, in the conventional approach, undertaken as part of the studies were:

Load flow analysis (to determine the equipment adequacy of the existing system).

Short circuit studies and fault level calculation (to determine the adequacy of the fault

rating of the existing system).

Review of the present relay settings (To determine improved recommendations for closer

coordination).

Adequacy of existing earthing and grounding system (for 110 / 11 kV switch yard ) and

finally

EMTP (Electromagnetic transient performance) related switching transient studies (to

determine the over voltages / over currents during the motor starting and capacitor

energisation.)

Preliminary findings

After the initial studies, analysis and findings by the college team , it was indicated to the utility

company during the month of Aug 2010 that the failure of the reactors are most probably due to

their inherent limitations in terms of their specification, design and workmanship to handle the

transient over currents.

This above decision was arrived at after all the other studies and analysis (as indicated above) did not

indicate any other definite and specific problems. The EMT (Electro Magnetic Transient) studies were

also carried out to find out the reason for the failure of the reactors under transient conditions (such

as starting of the motors). This was done for both the conditions -the existing reactor with an

impedance value of 0.2% and also for the normally recommended values (the standard value) of 5%

impedance. The studies only indicated that the transient currents are much larger with 0.2 % reactor

but there was no definite reason for the multiple failures of reactors after they were working for

number of years

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EMT Simulation studies with the existing 0.2 % Reactor for the PF compensation capacitor

circuit:

Figure-4(a)Transient switching current waveform-Inrush current through first pump reactor - 0.2%

reactor impedance value

Figure-4(b) Transient switching current waveform-Inrush current through second pump reactor -

0.2% reactor impedance value

EMT Simulation studies with the standard 5% Reactor for the PF compensation capacitor

circuit :

Figure-5(a)Transient switching current waveform-Inrush current through first pump reactor - 5%

reactor

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Figure-5(b)Transient switching current waveform-Inrush current through second pump reactor -

5% reactor impedance value

With 0.2% reactor, the transient currents observed were almost 15 times the rated currents; hence

this aspect must be specified while procuring the new reactors. The old specifications indicated only

the steady state values and not the transient currents which are actually encountered by the

reactors at the installation. Thus it was concluded that the reactors were inadequately specified and

manufactured.

With 5% impedance value, the transient currents for the reactor is found to be well within the

normal switching transient currents generally encountered for such application- about 3/ 4 times

for a short duration..

The above studies (EMT) also indicated that there was no occurrence of significant over voltages

which could cause flash-over during transient conditions.

The other possibility of over voltage considered was the pole discrepancy (of the closing contacts) of

any particular motor side breaker. This was also ruled out, since the failures were taking place

randomly in any of the three breakers which were in operation.

The earthing of the system was also tested (since poor earthing can result in system over voltages

under steady state or under switching modes) and no inadequacy was found.

Based on the above and after the physical inspection of two of the failed reactors it was concluded

that the design and manufacture of these reactors have major shortcomings which can be the

reasons for their failures. The original specification of these reactors received from the client,

considered only the steady state current and apparently the large transient currents experienced

during the starting of the pumps have not been considered.

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It is also noticed that the core of the reactors have got overheated ; the quality of the core

material also needed review from the point of view of losses and from the point of getting

saturated etc. Hence it was recommended to customer that the specification of the reactor should

consider the above aspects and an appropriate specification of the reactor be arrived at.

Causes for Multiple failures of reactors

After the preliminary report was submitted and discussed , it was decided as a last measure (

before the final report is submitted ) to monitor the various electrical parameters of the incoming

power system on a long time basis to find out the presence of any other random phenomena which

could have caused the problems and affect the system performance. In fact the team was looking

for supply voltage transients (over voltages due to switching of a short duration).

Customer was also looking for a more convincing explanation of the multiple failure of these

reactors all of a sudden and was not fully convinced that the failures were due to only the

inadequacy of the design and manufacturing of the reactors

Hence, a 24 hours continuous and simultaneous power quality monitoring recording was carried out

to record the various electrical parameters. Out of these recorded parameters, only the recordings

of voltage and current THD levels indicated an unexpected phenomenon not considered till then .All

other parameters were found to be of normal value.

The harmonics recording showed increased trend to a significant level during just a particular

interval, out of the total 24 hours . A typical recording of increased Harmonics levels for voltage and

current components on 6/7 September2010 is shown below as Figure6 (a)

It may be noted that the pump has been operating with steady loading for the total period of 24

hours both on 6/7 September and 7/8 October 2010 when the 24 hours long time recordings

were carried out.

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Figure 6(a) : Voltage and Current harmonics between 11:45 PM to 5:45 AM

This study was repeated again on 7th and 8th October 2010 with further continuous recording to

identify the individual harmonics also on another day after one month. These recordings indicated

significant presence of 13th harmonic components for both voltage and currents occurring at random

intervals.

Figure-6(b) below highlights the presence of high level of 13th level of harmonics for a typical day.

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The following Figure-6(c ), indicates the further increased values for both voltages and currents

(13th Harmonic) are seen

After this unexpected finding, the site Engineers had also confided the presence of increased reactor

noise during those random intervals, indicating the occurrence of high harmonic current levels.

Subsequently, harmonic analysis / study was conducted of the total electrical system to find its

natural frequency and which can result into series resonance conditions causing transient

amplification of the reactor currents.It was found that for the existing system the series resonance

condition sets in at 12.92 times the supply frequency. This was a startling finding as the major

harmonics which were noticed in the supply system when the power quality disturbance had

taken place was 13th harmonic.

The direct solution to this problem is to provide appropriate de-tuning filter circuit of appropriate

harmonic number and rating. However considering the randomness of the occurrence of the

harmonic voltage, it was recommended to go for shifting the resonance condition– occurrence of

minimum impedance- by modifying the values of the reactor (L) and capacitor(C).

Refer annexures for details of calculations to arrive at the final solution of Reactor designs.

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[Annexures contain exhibit#1 &2 and table #1 & 2]

The exhibit #1 provides the calculations for the 0.2 % reactor and exhibit #2 provides the

calculation for the 5 % reactor.

The minimum circuit impedance results with 0.2% reactor at 12.92ndharmonic frequency

corresponding to 646 HZ and the same is only 0.0393 Ohms. Considering the 13th harmonic which is

predominant as per measurement, the corresponding impedance is 0.1349 ohms . Also it is seen that

the minimum impedance occurs at the two pump operation due to the paralleling of the

impedances which also explains the failures taking place only at two pump operation.

The table #1 provides the results for 0.2 % reactors considering different values of X/R as well as

for different values for the capacitor bank. With this reactor even assuming smaller values of

X/R – i.e. larger resistance- the circuit impedance is still 0.1584 ohms at 13th harmonic and hence it

is still providing a low impedance path and hence is not safe.

The minimum circuit impedance results with 5% reactor at 2.6th harmonic frequency corresponding

to 130 HZ and the same is 1.279 Ohms even considering the two pump operation. At 13th harmonic,

the corresponding impedance will be even more .

The table #2 provides the result of the calculations with the other values of reactors , 0.5%, 1% and

5%. It is quite clear that with 5% reactor there is little possibility of series resonance.

From the above , it can be derived that at significant levels of 13th harmonic voltages (found to

be appearing randomly as per the recordings carried out), there will be large 13thharmonic reactor

circuit current. The cable reactance at 13th harmonic will however limit the reactor current to safe

values provided the 13th harmonic voltage are within the limits.

It is also seen that the harmonic voltage levels generally exhibit larger values during starting

conditions. Hence under a combined worst situation of starting the second pumpwith supply side

13th harmonic voltages at significant levels, large amplified reactor circuit currents would result .

The above condition, together with the above mentioned shortcomings( in the reactor

specification, design and workmanship), could have caused the failure of the reactors.

The solution considered is to shift the likely resonance condition to a frequency away from the

significant voltage harmonics noted, by adjusting the L and C values of the power factor

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compensation circuit. Shifting of the resonance frequency to a safe lower frequency value is possible

with increased value of the reactors. Calculations considering typical higher values of reactors at

0.5%, 1% and 5 % indicate shifting of the occurrence of minimum impedance at lower harmonic

values.

The simple and the most inexpensive solution for this sitewas to connect the power factor correction

capacitors in star connection instead of the existing delta connection ( by which the capacitor value is

effectively reduced by a factor of 3) even with the existing 0.2%reactor value. With this condition the

resonant frequency is shifted to a value more than 22, which is away from the present magnification

level of 13th harmonic number; this could be a safe value. But the problem is that the resultant kVAr

available would be less (as per the calculations done) and would result into poorer power factor of

0.92. Hence this was not recommended.

Thus the option to use different values of the reactors keeping the capacitor value the same only was

considered. The Calculations were done for higher values of reactors of 0.5 %, 1%, 5%.

With 0.5 % and 1% reactors, the series resonance conditions do occur but the resonance frequency

is only shifted to 8.2th and 5.6th harmonic numbers respectively. Even though in the actual

harmonic voltages noted (as per the recordings) the 5th, 7th and 9th harmonics are

comparatively low ( as compared to the 13th harmonic ), considering the randomness of the

supply harmonics , the solution of going for smaller values of the inductors may not be completely

fool-proof or safe.

It is seen that with 5% reactor, there is hardly any resonance condition and hence it is quite safe

to operate with this value. It is also seen under EMT ( simulations ) that with 5 % reactor, the

transient switching currents are lower and they are also in the range of the normal over current

capabilities of such current Limiting inductors.

Final Recommendations

It is noted that 5% reactor indicates almost no resonance condition. Thus , it was recommended to

opt for the standard value of the current limiting reactors ( normally recommended values as per

the literature for such current limiting applications ) , i.e. 5% impedance reactors. The rating was

also fixed at the steady state current values of 32A rating, as the reactor needs to withstand only

three times the normal steady state current during switching operation lasting for about 1.2

seconds.

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With the value of 5% reactor, the maximum inrush current value could be limited at 128 A (about 5

times to nominal current of capacitor). This is much less than the maximum inrush current of 374 A (

about 15 times ) expected to be occurring with the existing value of the reactor ( 0.2 % ) used in

the plant.

Thus this selection of 5% reactor not only limits the transient currents within the safe acceptable

values, and also the possibility of occurrence of resonance condition is also totally eliminated.

Post implementation

The recommended current Limiting reactor specification given to the reactor manufacturer is for

11KV , with 5% rating for Xc for 32A design. The other special requirements of reactor specification

were as follows:

i. The reactor needs to withstand 3 times the normal steady state current during

switching operation which happens occasionally .The switching transients last for about

1.2 seconds.

ii. The core and the windings to be appropriately designed

a. to avoid saturation of the core,

b. needs to withstand the resultant forces during transient currents and

c. to have appropriate insulation class to ensure non-deterioration of the same over its

life period.

iii. Iii A reactor has to be type testedfor switching transient currents.

Simulated Transient switching Current waveforms ( simulated ) with 5% reactor are given below :

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The Inrush current flowing through the first pump PF circuit series reactor considering 5% series

reactor

The Inrush current flowing through the second pump series reactor considering 5% series reactor

Cost benefit Analysis

Customer has already received offer for the purchase of these 5% reactors. The new reactor with

copper winding costs around Rs. 6.0 lacs(landed cost).The cost of repairs and transportation of

transformer was around Rs.5.00 lacs, while the failed reactor to be replaced cost around Rs. 1.10 lacs.

The simple payback period works out to less than an year. However, if cost of electricity bills due to

reduced consumption, is also considered, the pay back shall work out to 6-8 months, which is quite

attractive. The cost of missed billing of water supply during the shutdown of second pump, is not

considered. This itself was a huge revenue missed by the utility, as there was a demand of 120MLD ,

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10 days a month, for nearly 9-10 months, at the time of problem and the utility could supply only 90

MLD from one pump.

Current Status

The new reactor has not been as yet implemented as the demand for the water requirement –

feeding a industrial belt – has reduced to nearly 60 / 80 MLD- due to the industry recession- and

hence the customer is able to meet the demand at present, with one pump operating.

Conclusion

A Harmonic resonance condition may occur in the power factor correction capacitors and its current

limiting reactors for a large motor system. This interaction may lead to considerable magnification of

harmonic currents and voltages, causing disruption of the equipment operation. The predominant

harmonic frequencies normally fall in the vicinity of the 5th to the 13th harmonics. Care has to be

taken to ensure that the selected values of the PF capacitor and the reactor do not resonate at

these normal harmonic voltages. Detailed study of the impact of harmonics in this circuit, as has been

done in the present case, would help to properly design this apparently simple LC circuit

About the authors and institution

Authors : Prof.K.Narayanan

Dr.R.Meenakumari

Ms. A. Sheela

Company : 1. Professor , EEE department; Chief coordinator , Industry Institute Partnership

Cell,Kongu Engineering College, Perundurai, Erode-638052,Tamilnadu,India.

2. Professor and Head of the EEE department , Kongu Engineering College,

Perundurai, Erode-638052,Tamilnadu,India.

3. Assistant Professor( Senior Grade ), EEE department , Kongu Engineering College,

Perundurai, Erode-638052,Tamilnadu,India.

The simulation work was assisted by Dr.R.Nagaraja , PRDC, Bangalore.

M/s Kongu Engineering College (KEC) is a leading Institution, offering technical education and research with

state of the art facilities. It is an autonomous Institution affiliated to Anna University, Coimbatore and has

completed 27 years of dedicated service to the students of India and also from abroad.

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The Industry Institute Partnership Cell (IIPC) of Kongu Engineering College is in existence from 2002 started

with the grant in aid funding from All India Council of Technical Education (AICTE), New Delhi and it is

undertaking various consultancies for the nearby industries with the involvement of the expertise of the

appropriate departments of the college.

ANNEXURES GIVING DETAILS OF CALCULATIONS FOR REACTOR DESIGNS:

Exhibit:1RESULT OF RESONANCE FREQUENCY FOR X/R=20 ; 0.2 % reactor (2 Pumps )

Base MVA 100 Voltage 11 Base Z 1.21 Frequency 50

System data Filter data

Fault

MVA 94

X/R 10

C Delta 4.36E-06 C Star 1.31E-05

XL of Xc 0.002 XL 1.46E+00

p.u L 0.004648

Zsys 1.06383 X/R 20

Rsys 0.105855 R1 7.30E-02

Xsys 1.05855 Xl 1.46E+00

Xc 2.43E+02

Actual X/R 20

Zsys 1.287234 R2 7.30E-02

Rsys 0.128085 Xl 1.46E+00

Xsys 1.280846 Xc 2.43E+02

Zvalue Hz H.no Z value Hz H.no Z13

MinF_resonan

ce 0.039308 646 12.92 Max_resonance

602.79

31 389 7.78

0.1349

63

Hz Harmon

ic no Zsysinv

Zfilter1

Inv Zfilter2 Inv Zth zabs

38

9 7.78

0.0012-

0.10033i

0.00018+

0.05020i

0.000+

0.05020i

602.31-

24.042i 602.7931

64

6 12.92

0.00046-

0.0604i

11.79122-

4.740i

11.7912-

4.7408i

0.0364+

0.0147i

0.039308

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Exhibit 2 : RESULT OF RESONANCE FREQUENCY FOR X/R=12( 5 % reactor) (2 pumps )

Base MVA 100 Base Voltage 11 Base Z 1.21 Frequency 50

System data Filter data

Fault MVA 94

X/R 10

C Delta 4.36E-06 C Star 1.31E-05

XL of Xc 0.002 XL 3.65E+01

p.u L 0.116194

Zsys 1.06383

Rsys 0.105855

Xsys 1.05855 X/R of coil 12

R 3.04E+00

Actual Xl 3.65E+00

Zsys 1.287234 Xc 2.43E+02

Rsys 0.128085

Xsys 1.280846

Z value Hz H.no Z value Hz H.no Z 13

Min F_resonance 1.279639 130 2.6

Max

F_resonance 4.682827 126 2.52

z Harmonic no Zsysinv Zfilter1

Inv Zfilter2 Inv Zth Zabs

126 2.52 0.01227-

0.309324i

0.10058+

0.15143i

0.10058+

0.15143i

4.6807+

0.13926i

4.682827

130 2.6 0.01153-

0.29983i

0.2772-

0.11941i

0.27728-

0.119441i

0.92697+

0.882155i

1.279639

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Table 1: For the existing reactor value of 0.2 %

Calculation of minimum and Maximum impedances for both 1 filter and 2 filter for

various values of X/R ratio

Calculation of impedances for X/R=12

and C=4.36X10-6

(star connected) and

for C=8.72X10-6

(star connected)

S.N

o

Parameters X/R=20 X/R=12 X/R=10 X/R=8 C=4.36X10-6

(star

connected)

C=8.72X10-6

(star

connected)

(1

Fil

te

r)

(2

filter)

(1

Filter)

(2

filter)

(1

Filter)

(2

filter)

(1

Filter)

(2

filter)

(1

Filter)

(2

filter)

(1 Filter) (2

Filter)

1 Maximum

Impedance

72

3.

09

57

602.7

931

582.69

47

525.21

21

531.1

122

493.4

569

468.8

462

452.4

256

1749.

636

1559.

126

874.8585

780.314

2

1.1

Correspondin

g Harmonic

no.

9.

42 7.78 9.42

7.78

9.42

7.78

9.42

7.78

16.32

13.48

11.54

9.52

2 Minimum

Impedance

0.

07

85

44

0.039

308

0.1249

37

0.0625

27

0.148

655

0.074

398

0.184

508

0.092

344

0.121

699

0.060

849

0.124087

0.06208

4

2.1

Correspondin

g Harmonic

no.

12

.9

2

12.92 12.92 12.92

12.92

12.92

12.92

12.92

22.36

22.36

15.82

15.82

3 Impedance at

13th

Harmonic

0.

26

78

28

0.134

963

0.2844

5

0.1433

4

0.295

327

0.148

826

0.314

376

0.158

429

- - - -

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Table 2: Calculations for 5%, 1% and 0.5 % reactors :

Calculation of minimum and Maximum impedances for both 1 filter and 2 filter for various values of

X/R = 12 of 5%, 1% and 0.5%

S.No Parameters 5% 1% 0.5%

(1 Filter) (2 filter) (1 Filter) (2 filter) (1 Filter) (2 filter)

1 Maximum Impedance

5.1536 4.682827

63.66429

4.332184 186.9688

229.2909

1.1 Corresponding Harmonic no.

2.52 2.52 5.32 5.42 7.02 6.26

1.2 Hz 126 126 266 271 351 313

2 Minimum Impedance

1.964136 1.279639

0.605127

0.30544 0.307175

0.153397

2.1 Corresponding Harmonic no.

2.6 2.6 5.78 5.78 8.16 8.16

2.2 Hz 130 130 289 289 408 408

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The sole responsibility for the content of this document lies with the authors. It does not represent the opinion of the Asia

Power Quality Initiative and /or ICPCI/ICA network. APQI and ICA network are not responsible for any use that may be made

of the information contained therein.

APQI was initiated with support of Asia Invest Europe Aid Co-operation office. It is nurtured by ICA network and supported

by Leonardo Power Quality Initiative as knowledge partner

case study 31 - asia power quality initiativecase study 31 6 / 21 case study of ht reactor failure-...

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