Calculation of Electrical Maximum Demand Abstract:
The Electricity provider does charge the fixed charges on the basis of consumer’s maximum Electrical Demand. Consumer shall restrict restrict the power consumption under under the contracted maximum demand. This article furnishes calculation for Maximum Contract Demand. 1. Introduction:
The Electricity provider does record maximum demand in pre-defined interval e.g. !" minutes or #$ minutes% through duly sealed and calibrated energy meter. &enerally Maximum Demand denotes in '() for billing purpose. Consumer need to sanction Maximum demand from Electricity *rovider considering type of industry and operation pattern pattern of the e+uipments. Consumer shall pay fixed charges charges on the basis of Maximum Demand obtained from the provider i.e. the maximum rate at which an electrical power has been consumed during any period of defined consecutive minutes in the billing month. 2. Analysis: General Formula to calculate the Maximum Demand is described below: Maximum Demand= Connected Load * Load Factor / Power Factor. Factor. Where Connected Load = !otal Connected load in the "a cilit# in $W. Load Factor = %tilit# Factor * Di&ersit# Factor. Power Factor = '#stem a&era(e Power Factor. )xamle: !otal connected load o" "acilit#: +,-- $W !otal Load Factor: -. Considerin( steel lant t#e0 Power Factor: -.1, Maximum Demand= +,-- * -. / -.1, = 2343 $56 %tilit# Factor and Di&ersit# Factor Factor can be "indin( out b# the !ime Pro"ile o" load and usa(e o" the e7uiment. 6ll e7uiments o" "acilit# ma# not oerate at similar time and also ma# not run with "ull load. 8ence Di&ersit# Factor in ercenta(e = 9nstalled load / runnin( load.
3. Conclusion:
Consumer should sanction Maximum Demand after studying the load pattern of the electrical installation. ,btaining higher Maximum Demand shall result higher minimum fixed charges plus higher deposit and if sanctioned Maximum Demand exceed than consumer shall confront penalty.
Transformer testing and fault rectification. Power transformer failure results in production loss, unavailability of critical services, and loss of revenue. Routine testing and performing diagnostics can minimie loss and down time. Reliable and continual performance of power transformers is t!e "ey to beneficial generation and transmission of electric power. #enerally, reasons for failure include external factors suc! as lig!tning stri"es, system overload, s!ort circuits, and internal factors suc! as insulation deterioration, winding failure, over!eating, and t!e presence of oxygen, moisture, and solids in t!e transformer oil. To minimie unexpected outages, periodic transformer testing and diagnostics is necessary. T!ree categories can be defined for transformer testing$ •
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Performance acceptance test after installation and commissioning of t!e transformer. Predictive maintenance plan%based test during normal operation of t!e transformer to verify t!at electrical properties !ave not c!anged from design specifications. &ailure test for identify brea"down cause of t!e transformer. T!ese tests are re'uired to determine electrical, t!ermal, and mec!anical c!aracteristics.
Visual Inspection ( daily c!ec"list procedure s!ould be establis!ed to perform t!e visual routine test. )t s!ould contain oil temperature, winding temperature, oil level, !umming *noisy operation+, and oil lea"age c!ec"s. (n annunciation window *an indicator t!at announces w!ic! electrical circuit !as been active+ displays alarm and trip signals generated from t!e load. Buchholz Relay ( uc!!ol relay is a safety device normally mounted at t!e middle of t!e pipe connecting t!e transformer tan" to t!e conservator. )t is a gas detection relay used to detect minor and ma-or faults in t!e transformer. ( uc!!ol relay operates by detecting t!e volume of gas generated in t!e transformer tan". #as produced by faults accumulates over time wit!in t!e relay c!amber. !enever t!e volume of gas exceeds a certain safe level, t!e float moves lower, closes t!e contact, and generates an alarm. T!e fault alarm can be displayed on an annunciation window and t!e master trip relay will cause t!e circuit brea"er to open.
Thermal Imaging (Thermography) T!ermal imagers capture images of infrared energy or temperature. T!ey can detect !eat patterns or temperature c!anges in e'uipment. T!e engineer can determine problems prior to an expensive down time by analying t!ese temperature c!anges. Conveniently, one can measure and compare !eat readings for eac! part of t!e e'uipment wit!out disrupting t!e transformer/s operation. Prevention, diagnosis, and repair benefits can be obtained for transformers by introducing )nfrared t!ermograp!y into your predictive maintenance plan.
Insulation Resistance Test )nsulation ages and deteriorates because of moisture, dust, and electrostatic stress. )nsulation s!ould be monitored continually to avoid sudden failure of t!e e'uipment. (n insulation resistance test detects insulation 'uality wit!in t!e transformer. T!e conductive impurities or mec!anical flaws in t!e dielectric can be analysis based on t!is test. T!e instrument used to measure insulation resistance is "nown as t!e 0megger.0 1ormally meggers !ave a test voltage of 2334, 52334, or 23334. Eac! winding s!ould be s!ort circuited at t!e bus!ing terminals. T!e resistance value s!ould be measured between eac! winding and wit! respect to ground also. T!e winding s!ould be disc!arged
after t!e test is completed by connecting to t!e ground. T!e insulation resistance value measured is usually in t!e order of mega%o!ms. #enerally t!e value s!ould be greater t!an 6 mego!m for every 6"4 rating of t!e e'uipment. )nsulation resistance values decrease wit! increase in t!e temperature. T!erefore t!e values s!ould be normalied for a standard temperature. )t is necessary to !ave t!e insulation resistance as !ig! as possible.
Transformer Turns Ratio Test Eac! winding of a transformer contains a certain number of turns of wire. T!e 0transformer turns ratio0 is t!e ratio of t!e number of turns in t!e !ig! voltage winding to t!at in t!e low voltage winding. T!e ratio is calculated under no%load conditions. T!e transformer ratio can c!ange due to several factors li"e p!ysical damage because of faults, deteriorated insulation, contamination of oil etc. )f a transformer ratio c!anges more t!an 3.2 percent from t!e rated voltage ratio, it needs immediate attention. T!e turns ratio will establis! t!e proper relations!ip between t!e primary and secondary winding impedances. T!e turns ratio is t!e s'uare root of t!e impedance ratio, i.e. i7pri87sec 9 *1pri81sec+5 7pri 9 Primary )mpedance 7sec 9 :econdary )mpedance 1pri 9 1umber of turns on t!e primary coil 1sec 9 1umber of turns on t!e secondary coil
Dissolved Gas Analysis (DGA) Transformer overloading, over!eating, corona, spar"ing, and arcing can cause t!ermal degradation of t!e oil and paper insulation wit!in t!e tan". T!ermal and electrical faults can accelerate t!e decomposition of dielectric fluid and solid insulation. #ases generated by t!is process include !ydrogen, met!ane, et!ane, acetylene, carbon monoxide, and carbon dioxide, all w!ic! will dissolve in t!e transformer oil. T!e D#( test involves extracting t!e gases from t!e oil and in-ecting it into a gas c!romatograp!. #as concentrations are detected using a flame ioniation detector and a t!ermal conductivity detector. Diagnostic and analysis of t!e specific proportions of eac! gas s!all !elp to identify t!e fault type *t!ermal conditions involving t!e oil or t!e paper, partial disc!arge, sustained arcing, etc.+. ( D#( test study can minimie damage by ta"ing precautionary actions at an early stage.
agnetic Balance Test T!e magnetic balance test is conducted on transformers to detect inter%turn faults and magnetic imbalance. )t gives an idea about t!e flux distribution in t!e core. )t is only an indicative test and does not reduce t!e need for ot!er tests in diagnostics. T!e magnetic balance test is carried out on a t!ree p!ase transformer by applying a two p!ase supply across t!e p!ases *i.e. one winding say ; and 4+ wit! a lower t!an rated voltage.
Tan Delta Test Degradation of t!e insulation ta"es place because of mec!anical vibration, over temperature operation, and gaseous and metallic impurities in t!e transformer. T!is may cause insulation ageing and brea"down. )t is very important to study t!e insulation 'uality of t!e mac!ine. T!e dissipation factor Tan or Power &actor Cos = is considered to indicate t!e 'uality of insulation. )t is also "nown as t!e loss angle test or t!e dissipation factor test. ( clean insulation acts as a capacitor. T!e current s!ould lead t!e voltage by >3 degrees in a pure capacitor. T!e pure insulation s!ould also conduct similarly. )f t!e insulation is deteriorated, t!e current will also !ave resistive factor. T!is will cause t!e angle of t!e current to be less t!an >3 degrees. T!is measured difference in t!e angle is described as t!e loss angle. T!e tangent of t!e angle *i.e. opposite8ad-acent+ indicates t!e condition of t!e insulation. ( greater loss angle value points to a !ig! contamination of t!e insulation.
Transformer !il Brea" Do#n Test T!e D4 test measures t!e dielectric strengt! of t!e oil using an oil tester. During t!is test, sp!erical electrodes !aving a 5.2 mm gap s!all be gradually applied voltage until t!e oil loses its dielectric strengt!. T!is test s!ould be performed for one minute, and t!e brea"down voltage displayed on t!e oil tester meter s!ould be considered t!e D4. 1ormally it may be ?3 "4 and over for one minute or as per (:TM D@AA%@5 or ):%BB2. ( low value in t!is test indicates t!e presence of impurities in t!e oil. )n t!is case it s!ould be filtered to remove impurities and moisture.
&ollowings are ot!er tests t!at can be used to detect oil based faults$ •
(cidity test
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Electric strengt! test
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Color test
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Polyc!lorinated ip!enyl (nalysis *PC+ test
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&iber estimation
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&urfuralde!yde analysis test
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Metal in oil test
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Resistivity test
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&uran analysis
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&re'uency Response (nalysis
