PREAMBLE (NOT PART OF THE STANDARD)

In order to promote public education and public safety, equal justice for all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to know and speak the laws that govern them.

END OF PREAMBLE (NOT PART OF THE STANDARD)

IS:7752(Part I) – 1975

(Reaffirmed 2006)

Indian Standard
GUIDE FOR IMPROVEMENT OF POWER FACTOR IN CONSUMERS’ INSTALLATIONS
PART I LOW AND MEDIUM SUPPLY VOLTAGES

(Sixth Reprint DECEMBER 2007)

UDC 621.316.727.027.2

© Copyright 1975

BUREAU OF INDIAN STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002

Gr 4

December 1975

i ii

Indian Standard

GUIDE FOR IMPROVEMENT OF POWER
FACTOR IN CONSUMERS’
INSTALLATIONS

PART I LOW AND MEDIUM SUPPLY VOLTAGES

Code of Practice for Power Installation and Maintenance Sectional Committee; ETDC 20

Chairman Representing
Shri K. S. Subrahmanyam Central Electricity Authority, New Delhi
Members  
Shri N. S. S. Arokiaswamy Tamil Nadu Electricity Board, Madras
     Shri N. Tyagarajan (Alternate)
Shri V. G. Bapat Electrical Engineer to the Government of Maharashtra, Bombay
Shri B. L. Deshpande (Alternate)
Shri V. S. Bhatia Siemens India Ltd, Bombay
     Shri M. A. Noorudin (Alternate)
Shri K. K. Bose The Calcutta Electric Supply Corporation Ltd, Calcutta
     Shri A. Chatterjee (Alternate)  
Shri N. N. Chakraborty Government of West Bengal, Calcutta
Shri K. V. Chaubal Federation of Electricity Undertakings of India, Bombay
     Shri B. C. Amin (Alternate)  
Shri Ranes Ray Chaudhuri Engineering Construction Corporation Ltd, Bombay
     Shri L. E. D.’ Cruz (Alternate)  
Chief Engineer (Electricity) General Mysore State Electricity Board, Bangalore
Chief Electrical Engineer, Northern Railway Railway Board (Ministry of Railways), New Delhi
     Deputy Director Standards (Electrical II, RDSO) (Alternate)
Shri H. M. Desai The Bombay Electric Supply and Transport Undertaking, Bombay
     Shri D. M. Vatcha (Alternate)  
Director (HED 1) Central Electricity Authority, New Delhi
     Deputy Director (HED 1) (Alternate)
Shri K. K. Gupta Jyoti Limited, Baroda
     Shri K. W. Dharmadhikari (Alternate)

 

® Copyright 1975
BUREAU OF INDIAN STANDARDS

This publication is protected under the Indian Copyright Act (XIV of 1957) and reproduction in whole or in part by any means except with written, permission of the publisher shall be deemed to be an infringement of copyright under the said Act.

1
Members Representing
Shri Mohamed Hameed Chief Electrical Inspector to the Government of Tamil Nadu, Madras
Shri R. T. Harihar Maharashtra State Electricity Board, Bombay
Shri R. D. Jain Rural Electrification Corporation, New Delhi
Shri V. A. Krishnamurthi Central Public Works Department, New Delhi
     Shri A. Rajagopal (Alternate)  
Shri V. G. Kulkarni Tata Consulting Engineers, Bombay
     Shri R. C. Bajpai (Alternate)  
Shri J. D. Malhotra Punjab State Electricity Board, Patiala
Shri S. V. Marfatia Tariff Advisory Committee (Insurance Association of India), Bombay
Shri M. L. Mittal Bharat Heavy Electricals Ltd, Bhopal
     Shri K. C. Lahiri (Alternate)  
Shri K. P. R. Pillai The Fact Engineering and Design Organization, Udyogamandal
     Shri T. K. Mathew Vaidyan (Alternate)
Shri S. S. Raghawan Engineer-in-Chief’s Branch, Army Headquarters, New Delhi
     Shri K. N. Nadgir (Alternate)  
Shri I. G. Sanger Delhi Electric Supply Undertaking, Delhi
     Shri P. S. Sawhney (Alternate)  
Shri Sardul Singh Chief Electrical Inspector to the Government of Punjab, Patiala
     Senior Assistant to Chief Electrical Inspector (Alternate)
Shri K. G. Shanmukhappa NGEF Ltd, Bangalore
     Shri A. N. Srivathsa (Alternate)
Dr T. C. Sidhan Chief Electrical Inspector to the Government of Kerala, Trivandrum
Shri K. Sudhakaran Nair Kerala State Electricity Board, Trivandrum
     Shri R. A. Subramonia Iyer (Alternate)
Shri G. N. Thadani Engineers India Ltd, New Delhi
     Shri S. K. Sharma (Alternate)  
Shri N. Srinivasan, Director General, ISI (Ex-officio Member)
     Director (Elec tech)  

Secretary
Shri R. C. Jain
Deputy Director (Elec tech), ISI

2

Indian Standard

GUIDE FOR IMPROVEMENT OF POWER
FACTOR IN CONSUMERS’
INSTALLATIONS

PART I LOW AND MEDIUM SUPPLY VOLTAGES

0. FOREWORD

0.1

This Indian Standard (Part I) was adopted by the Indian Standards Institution on 14 August 1975, after the draft finalized by the Code of Practice for Power Installations and Maintenance Sectional Committee had been approved by the Electrotechnical Division Council.

0.2

This standard (Part I) has been prepared with a view to providing guidance to the. consumers of electrical energy who take supply at low and medium voltage for improvement of power factor of the installations in their premises. The subsequent part of this standard will cover installations of consumers of electrical energy who take supply at high voltage.

0.3

The various advantages of maintaining a high power factor of a system reflects on the national economy of a country. The available resources are utilized to its fullest possible extent. More useful power is available for transmission and utilisation without any extra cost. Also the life of individual apparatus is considerably increased and the energy losses reduced.

1. SCOPE

1.1

This standard (Part I) provides guidance to the consumers of electric energy who take supply at low and medium voltages for improvement of power factor of the installations in their premises.

2. TERMINOLOGY

2.1

For the purpose of this standard, the definitions given in IS: 28341964* shall apply.

3. GENERAL

3.1

Conditions of supply of Electricity Boards or Licensees stipulate the lower limit of power factor which is generally 0.85 and consumer is obliged

*Specification for shunt capacitors for power systems.

3

to improve and maintain the power factor of his installation to conform to this conditions.

3.1.1

When the tariffs of Electricity Boards and the Licensees are based on kVA demand or kW demand with suitable penalty/rebate for low/high power factor, improvement in the power factor would effect savings in the energy bills.

3.2

Power factor is dependant largely on consumers’ apparatus and partly on system components such as transformers, cables, transmission lines, etc. System components have fixed parameters of inductance, capacitance and resistance. The choice of these components to bring up the power factor depends on economics.

3.3

In case of ac supply, the total current taken by almost every item of electrical equipment, except that of incendescent lighting and most forms of resistance heating, is made up of two parts, namely:

  1. the in-phase component of the current (active or useful current) which is utilized for doing work or producing heat, and
  2. the quadrature component of the current (also called ‘idle’ or ‘reactive’ current) and used for creating magnetic field in the machinery or apparatus. This component is not convertible into useful output.

4. POWER FACTOR

4.1

The majority of ac electrical machines and equipment draw from the supply and apparent power (kVA) which exceeds the required useful power (kW). This is due to the reactive power (WAR) necessary for alternating magnetic field. The ratio of useful power (kW) to apparent power (kVA) is termed the power factor of the load. The reactive power is indispensable and constitutes an additional demand on the system.

4.2

The power factor indicates the portion of the current in the system performing useful work. A power factor of unity (100 percent) denotes 100 percent utilisation of the total current for useful work whereas a power factor of 0.70 shows that only 70 percent of the current is performing useful work.

4.3 Economics of Power Factor Improvement

4.3.1

Static capacitors, also called static condensers, when installed at or near the point of consumption, provide necessary capacitive reactive power and relieve distribution system before the point of its installation from carrying the inductive reactive power to that extent.

4.3.2

The use of static capacitors is an economical way. of improving power factor on account of their comparatively low cost, ease of installation, less maintenance, low losses and the advantage of extension by addition of

4

requisite units to meet the load growth. Installation of capacitors also improves the voltage regulation and reduces amperes loading and energy losses in the supply apparatus and lines.

4.3.3

When considering the economics connected with power factor correction, it is most important to remember that any power factor improving equipment will, in general, compensate for losses and lower the loadings on supply equipment, that is, cables, transformers, switchgear, generating plant, etc.

4.3.4

The minimum permissible power factor prescribed in the conditions of supply of Electricity Boards or Licensees and the reduction in charges offered in supply tariffs for further improvement of power factor shall, along with other considerations such as reduction of losses, etc, determine the. kVAR capacity of the capacitors to be installed.

4.3.5

In case of two part tariff with kVA demand charged, the value of economic improved power factor (Cos ϕ2) may be obtained as follows:

Let the tariff be Rs A per kVA of maximum demand per annum plus Rs P per kWh
Cos ϕ1 is the initial power factor,
Cos ϕ2 is the improved power factor after installing the capacitors
The economic power factor Cos ϕ2 is obtained from the expression

Image

where

B is the total cost per kVAR per year of capacitor installation inclusive of interest, depreciation and maintenance.

Note—The explanation for the derivation of the formula for economic power factor Cos ϕ2 is given in Appendix A.

4.4 Principal Causes of Low Power Factor

4.4.1

The following electrical equipment and apparatus have a low power factor:

  1. Induction motors of all types particularly when they are underloaded;
  2. Power transformers and voltage regulators;
  3. Arc welders;
  4. Induction furnaces and heating coils;
  5. Choke coils and magnetic systems;
  6. Fluorescent and discharge lamps, neon signs, etc.,
5

4.4.2

The principal cause of a low power factor is due to the reactive power flowing in the circuit. The reactive power depends on the inductance and capacitance of the apparatus.

4.4.3

The relationship between the voltage and current and the effect of use of capacitor is expressed graphically as below:

Image

4.4.4

In the diagram, OV represents the mains voltage, and OI the current flowing in an inductive ac circuit such as one supplying a motor or transformer. The current vector OI is displaced from the voltage vector OV by the angle ϕ1, This is designated as the angle of lag of the current. This angle increases as the inductance of the load circuit is increased. The larger this angle of lag becomes, the lower is the power factor of the circuit, the power factor being equal to the cosine of the angle of lag (Cos ϕ1).

4.4.5

If now a capacitor is connected across the same circuit, it will draw a current which leads the voltage in phase. This is represented by vector OC drawn at 90° to OV since the capacitors take a leading current of 90°.

4.4.6

The resultant line current is the vector sum of the two currents OI and OC which is the vector OT. Vector OT is smaller than vector OI which means that the total current drawn from the mains is reduced by connecting the capacitor across the circuit. And since the angle of lag ϕ2 is smaller than ϕ1 the Cos ϕ2 is greater than Cos ϕ1, the power factor has been improved by adding the capacitor.

4.5 Effect of Power Factor to Consumer

4.5.1

The disadvantages of low power factor are as follows:

  1. Overloading of cables and transformers, 6
  2. Decresed line voltage at point of application,
  3. Inefficient operation of plant, and
  4. Penal power rates.

4.5.2

The advantages of high power factor are as follows:

  1. Reduction in the current;
  2. Reduction in power cost;
  3. Reduced losses in the transformers and cables;
  4. Lower loading of transformers, switchgears, cables, etc;
  5. Increased capability of the power system (additional load can be met without additional equipment);
  6. Improvement in voltage conditions and apparatus performance; and
  7. Reduction in voltage dips caused by welding and similar equipment.

5. USE OF CAPACITORS

5.1

In order to improve the power factor, the consumer shall install capacitors where the natural power factor of his installation is low.

5.2

The average values of the power factor for different types of 3-phase electrical installations as measured by one of the major utilities in the country is given in Table 1 for information.

5.2.1

The average values of power factors for electrical appliances and equipment used on single phase supply are also given in Table 2 for information.

5.3

Capacitors for power factor improvement may be arranged as described in 6.4 to 6.7. The successful operation of power factor improvement depends very largely on the positioning of the capacitor on the system. Ideal conditions are achieved when the highest power factor is maintained under all load conditions.

5.4

Individual Compensation—Wherever possible the capacitor should be connected directly across the terminals of the low power factor appliance or equipment. This ensures the control to be automatic through the same switching devices of the apparatus or appliance.

5.5

Group Compensation—In industries where a large number of small motors or other appliances and machines are installed and whose operation is periodical it is economical to dispense with individual installation of capacitors. A bank of capacitors may be installed to connect them to the distribution centre or main bus-bars of the group of machines.

7
TABLE 1 POWER FACTOR FOR THREE PHASE ELECTRICAL INSTALLATIONS
(Clause 5.2)
Sl No. Type of Installation Natural Power Factor
(1) (2) (3)
1. Cold storage and fisheries 0.76 to 0.80
2. Cinemas 0.78 to 0.80
3. Metal pressing 0.57 to 0.72
4. Confectionery 0.77
5. Dyeing and printing (Textile) 0.60 to 0.87
6. Plastic moulding 0.57 to 0.73
7. Film studios 0.65 to 0.74
8. Newspapers 0.58
9. Heavy engineering works 0.48 to 0.75
10. Rubber extrusion and moulding 0.48
11. Pharmaceuticals 0.75 to 0.86
12. Oil and paint manufacturing 0.51 to 0.69
13. Silk mills 0.58 to 0.68
14. Biscuit factory 0.60
15. Printing press 0.65 to 0.75
16. Food products 0.63
17. Laundries 0.92
18. Flour Mill 0.61
19. Gas works 0.87
20. Textile mills 0.86
21. Oil mill 0.51 to 0.59
22. Woollen mills 0.70
23. Potteries 0.61
24. Cigarette manufacturing 0.80
25. Cotton press 0.63 to 0.68
26. Foundries 0.59
27. Tiles and Mosaic 0.61
28. Structural engineering 0.53 to 0.68
29. Chemicals 0.72 to 0.87
30. Municipal pumping stations 0.65 to 0.75
31. Oil terminals 0.64 to 0.83
32. Telephone exchange 0.66 to 0.80
33. Rolling mills 0.72 to 0.60
34. Irrigation pumps 0.50 to 0.70
8
TABLE 2 POWER FACTOR FOR SINGLE PHASE ELECTRICAL
APPLIANCES AND EQUIPMENT
(Clause 5.2.1)
Sl No. Appliance/Equipment Power Output Average Natural Power Factor
    Minimum Maximum  
(1) (2) (3) (4) (5)
    (W) (W)  
1. Neon sign 500 5 000 0.5 to 0.55
2. Window type air conditioners 750 2 000* 0.75 to 0.85
        0.68 to 0.82
        0.62 to 0.65
3. Hair dryers 150 2 000 0.7 to 0.8
4. Liquidiser 150 450 0.8
5. Mixer 150 350 0.8
6. Coffee grinder 200 400 0.75
7. Refrigerator 200 800 0.65
8. Freezer 600 1 000 0.7
9. Shaver 80 250 0.6
10. Table fan 25 120 0.5 to 0.6
11. Ceiling fan 60 100 0.5 to 0.7
12. Cabin fan 75 100 0.5 to 0.6
13. Exhaust fan 150 350 0.6 to 0.7
14. Sewing machine 80 120 0.7 to 0.8
15. Washing machine 300 450 0.6 to 0.7
16. Radio 25 100 0.8
17. Night lamp 10 15 0.6
18. Vacuum cleaner 200 450 0.7
19. Tube light 40 100 0.5
20. Clock 5 10 0.9
* Start dropping when compressor motor not in circuit.

5.6

Central Compensation—Capacitors may also be installed at a central point, that is, at the incoming supply or service position. In order to overcome problems of drawing leading currents on light loads, these capacitors may be operated manually or automatically as required. The automatic control is preferred as it eliminates human errors. Automatic operation may be arranged by means of suitable relays in which a contactor controls the capacitor bank and maintains the correct amount of kVAR in the circuit.

5.7

The methods of connecting power factor capacitors to supply line and motors is given in Fig. 1 and 2.

9

Image

Fig. 1 Methods of Connecting Capacitors for Improvement of Power Factor to Motors

Image

Fig. 2 Methods of Connecting Capacitors for Improvement of Power Factor to Supply Line

10

5.8

The recommended capacitor rating for direct connection to ac (50 Hz) induction motors is given in Table 3.

TABLE 3 CAPACITOR RATINGS AT RATED VOLTAGE
Rated Output of Motors Capacitor Rating in kVAR When Motor Speed is
  3 000 1 500 1 000 750 600 500
  rev/min rev/min rev/min rev/min rev/min rev/min
(1) (2) (3) (4) (5) (6) (7)
(kW)            
2.25 1 1 1.5 2 2.5 2.5
3.7 2 2 2.5 3.5 4 4
5.7 2.5 3 3.5 4.5 5 5.5
7.5 3 4 4.5 5.5 6 6.5
11.2 4 5 ‘ 6 7.5 8.5 9
15 5 6 7 9 11 12
18.7 6 7 9 10.5 13 14.5
22.5 7 8 10 12 15 17
37 11 12.5 16 18 23 25
57 16 17 21 23 29 32
75 21 23 26 28 35 40
102 31 33 36 38 48 55
150 40 42 45 47 60 67
187 46 50 53 55 68 76
Note 1—The reference to speed of motor has been made since the manufacturers provide information on that basis.
Note 2—The capacitive current supplied by condensers directly connected across induction motor terminals should not exceed the magnetising current of the induction motors, to guard against excess transient torques and over-voltages.
Note 3—Should a consumer desires to improve the power factor beyond a value which is limited by considerations of magnetising kVAR of the motor as stated in Note 2, then he may install the calculated capacitor kVAR as a separate circuit with its independent controlgear.

6. POWER FACTOR IMPROVEMENT AND CAPACITOR RATING

6.1

For calculating the size of capacitor for power, factor improvement, reference should be made to Table 4 and Fig. 3.

Note—An example illustrating the reference to Table 4 is given below:

The value of capacitor kVAR required to improve the power factor of a 100 kW load from 0.7 to 0.95 is found from the table as follows:

From the table the multiplying factor for improving the power factor from 0.7 to 0.95 is 0.691.

Therefore capacitor rating = 100 × 0.691 = 69.1 kVAR.

11

Image

Fig. 3 Curves for Obtaining Capacitor Size in kVAR per kW of Load for Power Factor Improvement

TABLE 4 CAPACITOR SIZES FOR POWER FACTOR IMPROVEMENT
(Clause 6.1)
Existing Power Factor Improved Power Factor
  0.80 0.85 0.90 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1.00
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)
            Multiplying Factor          
0.40 1.537 1.668 1.805 1.832 1.861 1.895 1.924 1.959 1.998 2.037 2.085 2.146 2.228
0.41 1.474 1.605 1.742 1.769 1.798 1.831 1.860 1.896 1.935 1.973 2.021 2.082 2.225
0.42 1.413 1.544 1.681 1.709 1.738 1.771 1.800 1.836 1.874 1.913 1.961 2.022 2.164
0.43 1.356 1.487 1.624 1.651 1.680 1.713 1.742 1.778 1.816 1.855 1.903 1.964 2.107
0.44 1.290 1.421 1.558 1.585 1.614 1.647 1.677 1.712 1.751 1.790 1.837 1.899 2.041
0.45 1.230 1.360 1.501 1.532 1.561 1.592 1.626 1.659 1.695 1.737 1.784 1.846 1.988
0.46 1.179 1.309 1.446 1.473 1.502 1.533 1.567 1.600 1.636 1.677 1.725 1.786 1.929
0.47 1.130 1.260 1.397 1.425 1.454 1.485 1.519 1.552 1.588 1.629 1.677 1.758 1.881
0.48 1.076 1.206 1.343 1.370 1.400 1.430 1.464 1.497 1.534 1.575 1.623 1.684 1.826
0.49 1.030 1.160 1.297 1.326 1.355 1.386 1.420 1.453 1.489 1.530 1.578 1.639 1.782
0.50 0.982 1.112 1.248 1.276 1.303 1.337 1.369 1.403 1.441 1.481 1.529 1.590 1.732
0.51 0.936 1.066 1.202 1.230 1.257 1.291 1.323 1.357 1.395 1.435 1.483 1.544 1.686
0.52 0.894 1.024 1.160 1.188 1.215 1.249 1.281 1.315 1.353 1.393 1.441 1.502 1.644
0.53 0.850 0.980 1.116 1.144 1.171 1.205 1.237 1.271 1.309 1.349 1.397 1.458 1.600
0.54 0.809 0.939 1.075 1.103 1.130 1.164 1.196 1.230 1.268 1.308 1.356 1.417 1.559
0.55 0.769 0.899 1.035 1.063 1.090 1.124 1.136 1.190 1.228 1.268 1.316 1.377 1.519
0.56 0.730 0.860 0.996 1.024 1.051 1.085 1.117 1.151 1.189 1.229 1.277 1.338 1.480
0.57 0.692 0.822 0.958 0.986 1.013 1.047 1.079 1.113 1.151 1.191 1.239 1.300 1.442
0.58 0.655 0.785 0.921 0.949 0.976 1.010 1.042 1.076 1.114 1.154 1.202 1.263 1.405
0.59 0.618 0.748 0.884 0.912 0.939 0.973 1.005 1.039 1.077 1.117 1.165 1.226 1.368
0.60 0.584 0.714 0.849 0.878 0.905 0.939 0.971 1.005 1.043 1.083 1.131 1.192 1.334
0.61 0.549 0.679 0.815 0.843 0.870 0.904 0.936 0.970 1.008 1.048 1.096 1.157 1.299
0.62 0.515 0.645 0.781 0.809 0.836 0.870 0.902 0.936 0.974 1.014 1.062 1.123 1.265
0.63 0.483 0.613 0.749 0.777 0.804 0.838 0.870 0.904 0.942 0.982 1.030 1.091 1.233
0.64 0.450 0.580 0.716 0.744 0.771 0.805 0.837 0.871 0.909 0.949 0.997 1.058 1.200
0.65 0.419 0.549 0.685 0.713 0740 0.774 0.806 0.840 0.878 0918 0.966 1.027 1.169
0.66 0.388 0.518 0.654 0.682 0.709 0.743 0.775 0.809 0.847 0.887 0.935 0.996 1.138
0.67 0.358 0.488 0.624 0.652 0.679 0.713 0.745 0.779 0.817 0.857 0.905 0.966 1.108
0.68 0.329 0.459 0.595 0.623 0.650 0.684 0.716 0.750 0.788 0.828 0.876 0.937 1.079 12
0.69 0.299 0.429 0.565 0.593 0.620 0.654 0.686 0.720 0.758 0.798 0.840 0.907 1.049
0.70 0.270 0.400 0.536 0.564 0.591 0.625 0.657 0.691 0.729 0.769 0.811 0.878 1.020
0.71 0.242 0.372 0.508 0.536 0.563 0.597 0.629 0.663 0.701 0.741 0.785 0.850 0.992
0.72 0.213 0.343 0.479 0.507 0.534 0.568 0.600 0.634 0.672 0.712 0.754 0.821 0.963
0.73 0.186 0.316 0.452” 0.480 0.507 0.541 0.573 0.607 0.648 0.685 0.727 0.794 0.936
0.74. 0.159 0.289 0.425 0.453 0.480 0.514 0.546 0.580 0.618 0.658 0.700 0.740 0.909
0.75 0.132 0.262 0.398 0.426 0.453 0.487 0.519 0.553 0.591 0.631 0.673 0.713 0.882
0.76 0.105 0.235 0.371 0.399 0.426 0.460 0.492 0.526 0.564 0.604 0.652 0.687 0.855
0.77 0.079 0.209 0.345 0.373 0.400 0.434 0.466 0.500 0.538 0.578 0.620 0.661 0.829
0.78 0.053 0.183 0.319 0.347 0.374 0.408 0.440 0.474 0.512 0.552 0.594 0.634 0.803
0.79. 0.026 0.156 0.292 0.320 0.347 0.381 0.413 0.447 0.485 0.525 0.567 0.608 0.776
0.80 0.130 0.266 0.294 0.321 0.355 0.387 0.421 0.459 0.499 0.541 0.582 0.750
0.81 0.104 0.240 0.268 0.295 0.329 0.361 0.395 0.433 0.473 0.515 0.556 0.724
0.82 0.078 0.214 0.242 0.269 0.303 0.335 0.369 0.407 0.447 0.489 0.530 0.698
0.83 0.052 0.188 0.216 0.243 0.277 0.309 0.343 0.381 0.421 0.463 0.504 0.672
0.84 0.026 0.162 0.190 0.217 0.251 0.283 0.317 0.355 0.395 0.437 0.478 0.645
0.85 0.136 0.164 0.191 0.225 0.257 0.291 0.329 0.369 0.417 0.450 0.620
0.86 0.109 0.140 0.167 0.198 0.230 0.264 0.301 0.343 0.390 0.424 0.593
0.87 0.083 0.114 0.141 0.172 0.204 0.238 0.275 0.317 0.364 0.395 0.567
0.88 0.054 0.085 0.112 0.143 0.175 0.209 0.246 0.288 0.335 0.395 0.538
0.89 0.028 0.059 0.086 0.117 0.149 0.183 0.230 0.262 0.309 0.369 0.512
0.90 0.031 0.058 0.089 0.121 0.155 0.192 0.234 0.281 0.341 0.484
0.91 0.027 0.058 0.090 0.124 0.161 0.203 0.250 0.310 0.453
0.92 0.027 0.063 0.097 0.134 0.176 0.223 0.283 0.426
0.93 0.032 0 066 0.103 0.145 0.192 0.252 0.395
0.94 0.034 0.071 0.113 0.160 0.220 0.363
0.95 0.037 0.079 0.126 0.186 0.329
0.96 0.042 0.089 0.149 0.292
0.97 0.047 0.107 0.250
0.98 0.060 0.203
0.99 0.143
Note—The consumer is advised to make proper allowance for lower supply voltages where these exist during the working hours arid may choose slightly higher kVAR than recommended in the table for such cases.
13

Image

Fig. 3 Curves for Obtaining Capacitor Size in kVAR per kW of Load for Power Factor Improvement

6.2

For information to be supplied to manufacturers for supply of suitable capacitors reference should be made to Appendix G of IS : 2834.1964*.

7. INSTALLATION AND MAINTENANCE

7.1

The following factors should be kept in mind for proper installation and operation of capacitors:

  1. Selection of control switchgear which should be adequately rated and designed for capacitor switching duty;
  2. Proper ventilation of the capacitor bank;
  3. Arcing free joints and contacts;
  4. Derating of switchgear, cables and fuses; and
  5. Overvoltages (see B.5 of IS; 2834.1964*).

7.1.1

For detailed information on these factors, reference shall be made to IS: 2834.1964*.

*Specification for shunt capacitors for power systems.

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7.2

For the maintenance of capacitors the following points shall be borne in mind:

  1. Capacitors, being static apparatus are not usually given the same care as rotating machinery but, nevertheless require regular maintenance. Normally, a power factor correction capacitor should be inspected at least every 12 months, preferably every 6 months. The time interval between inspection is, however, governed mainly by the conditions on site. Where capacitors are installed in humid atmosphere or subjected to chemical fumes or exposed to dirt and dust, more frequent attention should be given.
  2. Before examination, always ensure that the apparatus is switched off. After switching off, allow time for the capacitor to discharge completely as stated on the rating plate. The terminals shall be permanently connected to earth during inspection.

7.3

The following points are to be observed for maintenance of a power factor correction capacitor:

  1. Condition of exterior finish, protective paint should be maintained in good condition by repainting when necessary. Observe oil leakage through pin holes or cracks in the body. The leak should be repaired by soldering or plugging it by epoxy compound.
  2. Remove the terminal box cover and note any abnormality, special care being taken of the following points:
    1. Condition of cables,
    2. Condition of interior paint work, repaint if necessary.
    3. Tightness of nuts and bolts especially earth connections,
    4. Removal of dust and other foreign matter,
    5. Clean any surface that needs attention, particularly insulators and terminals,
    6. Check the soldering of terminals of cables. These terminals should not cause sparking and heating, and
    7. External discharge resistance shall be intact.
  3. The following points shall also be checked:
    1. The surface temperature of the unit to be measured periodically and remedial measures taken (see IS: 2834.1964*).
    2. The controlgear to be inspected to detect any possibility of arcing or pitting of contacts, etc.
    3. The capacitor current to be measured periodically so as to ascertain if any of the internal fuses have blown.

*Specification for shunt capacitors for power systems.

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It is recommended that a record should be kept of inspection made and details of maintenance carried out. Any correspondence concerning power factor correction capacitors or auxiliary gear or both should quote original order number, rating details, serial number and date supplied.

Note—Askarels insulators which are used in the capacitor are health hazards and should be handled with special care.

APPENDIX A
FORMULA FOR ECONOMIC POWER FACTOR Cos ϕ2

(Clause 4.3.5)

A.1.

The formula for economic power factor has been obtained as follows:

Image

kVAR for improvement of power factor = ACBC
  = BA
  = kW tan ϕ1—kW tan2

Image

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