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1. BENEFITS TO THE CONSUMERS DUE TO INSTALLATION OF SHUNT CAPACITORS: The main load of industrial consumers consists of induction motors which when lightly or partially loaded draw more current than what is actually required by that load to which they are connected. The ratio of useful to actual current drawn by the Motor is known as power factor.
The power factor of the induction motors can be improved by installation of shunt capacitors across the terminals of the motors. The main benefits to the consumers by installation of shunt capacitors are as under:- 1. Improvement in the voltage condition. 2. Improvement of power factor of load. 3. Saving in surcharge due to low power factor. 4. Saving in demand charges where maximum demand is recorded in KVA. PSEB system is a very vast net work and is designed for a power factor of 0.88 or even higher. At the time of peak load conditions it has been observed that the voltage available to the consumers is on the lower side. Low power factor of the consumers installation is one of the main causes for low voltage conditions. The low voltage conditions result in certain disadvantages such as the efficiency of the motor is lowered, the installed equipment is also subjected to over loads. Installation of shunt capacitors by the consumers will improve the voltage available to them and also lower maximum demands in KVA for the same load in KW. Besides improving the voltage, power factor of the motors is also improved resulting in better performance . Due to improvements of power factor the losses are reduced in the circuits between the load and the metering points thus some saving in energy bills is also effected. The improvement of power factors also helps the consumer in maintaining minimum stipulated power factor and thus saves him from surcharge which otherwise he will have to pay due to lower power factor of his installation. It also helps PSEB to serve its consumes in a better manner because improved power factor and voltage conditions reduce the overloading of its system. Capacitors are sensitive equipment and are liable to early damage if these are not maintained and operated properly. All the consumers on whose premises the capacitors are installed should observe the guidelines on following pages regarding selection, operation and maintenance of capacitors so that these can be utilized most effectively without premature damage.
2. CHOICE AND RATING OF CAPACITORS: 1, All the industrial consumers should ensure that capacitor units installed at their premises conform to ISI-2834. The capacitors can be applied across individual motor or for group connections. Where the load consists of a number of small or a fractional horse power motor operating at different interval it is economical to apply group connection. In case of large motors, the capacitors may be applied across each motor individually. 2. For choosing the proper value of shunt capacitors to be installed in a factory the guidance of local engineer of the firm supplying the capacitors or of PSEB should be sought. 3. In case of factories having large rectifiers or arc furnace loads harmonics are also present with basic load. The application of capacitors in such factories requires special consideration and therefore the type of the load should be specified while ordering the capacitors. Before and after installation of capacitors in such factories, the representative of the firm supplying the capacitors should be consulted because harmonics can damage the capacitors and can also cause higher voltage rise which will damage the other equipment. 4. In places where humidity is relatively high, the capacitors with a higher insulation level should be chosen. Insulation level should be of higher range than normally provided. This can be quoted in specification while placing an order with the supplying firm. 5. When it is desirable to improve the power factor of industrial motors or to have the capacitors also coming on and off with motors e.g. for factory where major load is of automatically controlled air compressors, the capacitors should be connected in such a way that its reactive out put is less than or equal to magnetizing KVAR of motor. Over capacity of capacitors is likely to damage motor and capacitor itself due to excitation of motors. 6. The following are generally recommended values of capacitors for different HP motors keeping in view the above considerations. 7. Rating of Capacitors of MS Consumers
8. Rating of Capacitors for Motors at different Speeds:
8.1. Rating of Capacitors for Submersible Pump Sets: The existing and prospective AP consumers those who have installed/proposed to install submersible motors on their tubewells, shall have to provide shunt capacitors duly ISI marked or purchased from the suppliers approved by Board from time to time conforming to following KVAR ratings as available in the market depending upon the rating of submersible pump sets.
9. Shunt Capacitor for Welding Sets:
10. Guidelines for installation of Capacitors: 10.1 Capacitors should be installed in well ventilated rooms so that there is adequate dissipation of heat produced by the capacitors. These should not be installed near source of heat such as arc furnaces and other heating devices etc. because they are liable to get damaged earlier. 10.1.1 The capacitors should be installed on raised dry platforms as dampness shortens the life of capacitors. 10.1.2 PSEB has specified that all motors above 5 BHP load should be connected through Star-Delta Starters. The arrangement should be such that no over voltage can occur during operation of Starter. For this ,a 6 terminal capacitor should be installed. The consumers while ordering capacitors should specially mention the requirement of 6 terminal capacitor, when the motor is provided with a star delta starter. 10.1.3 Proper earthing should be provided wherever capacitors are installed, otherwise these can be a source of danger. The outer metallic containers of the capacitors bank should be solidly earthed through independent earths. 10.1.4 It should also be ensured that no 'LIVE PARTS" make a contact with casing. 10.1.5 The switches, fuses and wherever some automatic circuit breaking gear is employed, should be of good quality and have proper contacts. Bad or worn out contacts cause damage to capacitors due to sparking on the contacts. 10.2 Recommended rating for fuses, cables etc: 10.2.1 Switches, Cables, CTs should have rating 1.5 times the current rating of capacitors. 10.2.2 Fuses should have rating 1.6 to 2 times the current of capacitors. 10.2.3 Where the rating of feeding transformer is 100 KVA or less, ordinary fuses maybe used. For higher rating of transformer HRC fuses maybe used. 10.3 The switches must be capable to disconnect the entire installation of Capacitors when the electric supply fails even momentarily. For this purpose switch gear having no voltage release devices should be provided. 10.4 Proper foundations should also be provided wherever necessary for capacitors. 11. Operation of Capacitors. 11.1 General 11.1.1 Temperature, voltage and current limits specified should be strictly adhered to and only in case of emergency should the capacitors be operated at maximum permissible voltage and maximum ambient temperature simultaneously. The maximum permissible voltage is 110% of the rated voltage specified on name plate. 11.1.2 When a capacitor is switched off, its residual voltage falls gradually through discharge resistance. This voltage must fall to 50 volts or less before some unit is switched on again. Therefore, it is necessary to wait for at least one minute before disconnected capacitor is again switched on otherwise capacitor is likely to fail. 11.1.3 Discharge resistances should be checked time and again to ensure that they are not damaged or burnt. In case of any damage they should be promptly replaced. 11.1.4 The cover boxes of capacitors should be occasionally opened to check loose connection, blown fuses and dust etc. 11.1.5 The capacitors should be saved from attack by insects and corrosive atmosphere. 11.22. For Capacitors provided in group for number of motors: 11.2.1 When the group correction is provided, it is essential that capacitors are put in circuit according to load requirement for which it is preferable to have two graded capacitors banks of 1/3, 2/3 capacity. This gradation can provide three step of ½, 2/3 and depending upon if No.1 and 2 or both banks are switched on. Each bank should have its separate controlling switch capable of switching on or off the bank according to the requirement. 11.2.2 When there are two or more units it should be taken care while switching on second unit in parallel with first unit, that there is sufficient load i.e. current through the mains. 11.2.3 The switches controlling the capacitors should have no volt release to switch off automatically when the supply fails even momentarily, otherwise the capacitors may be switched off immediately by manual operation and put in circuit when motors have been started and loaded. 12. Testing of L.T.Shunt Capacitors in case of SP and AP consumers: A very simple arrangement mentioned below for testing of LT capacitors in case of SP and AP consumers of PSEB(Diag No.4). 3 No. 400 volts Neon Lamps should be connected in star and the neutral be left floating. The other three terminals should be connected to three terminals of LT capacitors which is required to be tested. The healthiness of the units is checked by switching on the supply and switching it off. If the capacitors unit is healthy, the light of the neon lamp will take some time to go off because the capacitor takes some time to discharge. On the other hand, if the capacitors are damaged/defective, the neon light will go off as soon as the supply is switched off. This method can be conveniently applied in the field because three Neon Lamps can be easily fixed on wooden round block. The diagram of the arrangement is enclosed. The LT capacitors installed or to be installed at the SP/AP consumers premises may be checked by the field officers for their healthiness with above arrangements. 12.1 Checking with Battery operated Avometer(MEGGER): A good capacitor shows dead short between any two terminals at first and the resistance reading starts building up as the capacitor begins to charge up to the battery voltage. A good capacitor will show an almost infinite resistance between terminal and the earthing point from the very beginning. 12.2 Checking KVAR Rating of Capacitor: The reactive output in KVAR of the capacitors can be worked out from the following:- 12.2.1 Single Phase Circuit Voltage x line current KVAR 1000
12.2.2 Three Phase Circuit : Terminals( √ x voltage between line)x line current KVAR
(Star or Delta Connection) 3x Voltage between line x1000
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