21. WHAT IS METER ?A device which measures, indicates and records certain measurable quantity.2. WHAT IS ENERGY METER ?A device which measures, indicates and records electrical power flow (energy) in a specified time between two points.3. Pre Requisites of a MeterPurpose : Catering to Commercial needsFuturistic : Catering to foreseen needsReliable : RepeatabilityAccurate : Good amount of money at stake
3Classification of meters Interface Meter :Installed at interconnecting points betweenGenerating company to Inter-state systemGenerating company to Intra-state systemcovered under ABT2. Consumer Meter :Electrical utility to consumer not covered under INTERFACE meters3. Energy Accounting and Audit Meters :Used between Gen Stns to different segments of electrical system determinesConsumption of powerLossOur focus is on SEMs which are interface meters
4What is Special Energy Meter(SEM)? SEM is an Application specific Microprocessor base solid state energy meter. This together with a data collecting device (DCD) and a local Computer forms a powerful system of metering and data logging.This arrangement of metering and data logging gives a unique method for measurement of all relevant electrical quantities.
5Why metering is required? ABT, three part tariff :Capacity charge (a)Energy charge / Scheduled Energy charges (b)Adjustment for deviation/ Unscheduled Interchanges (c)Total payment for the day = a + b (+/-) cReason of metering
6What is Metering? Meter data handling Converting meter data into useful informationFeeder wiseStation wiseState wiseRegion wiseIts a challenging task for the utilities due to huge volume of data logged by these meters
7Area covered by meters ISGS Sub Stations ICTS Feeders Any other drawl or injection points spread over the state, region and the country as a whole
8Metering Management Initial/one time activities Choose the category of meterSelection of meterInstallation of meters in strategic locationsDeciding status of meters as Main, Check and Stand-by metersPeriodic/maintenance activitiesMaintaining healthinessPeriodic checkingTime correctionPeriodic testingReplacement of meter (as and when required)Regular/routine activitiesCollection of dataTransmittal of data to a central location for processingProcessing meter data into useful informationArchiving final processed data
9Metering StandardsCompliance with the relevant standards of Bureau of Indian Standards (BIS)If BIS Standards are not available for a particular equipment or material, the relevant British Standards (BS), International Electro-technical Commission (IEC) StandardsWhenever an international Standard or IEC Standard is followed, necessary corrections or modifications shall be made for nominal system frequency, nominal system voltage, ambient temperature, humidity and other conditions prevailing in India before actual adoption of the said StandardAt the time of commissioning, each interface meter shall be tested by the owner at site for accuracy using standard reference meter of better accuracy class than the meter under test.
10Metering StandardsAll interface meters shall be tested at least once in five yearsThe meters may be tested using NABL accredited mobile laboratory or at any accredited laboratory and recalibrated if required at manufacturer’s works.Active energy Wh as per class 0.2 S of IEC-687/IECVar/Reactive energy class 2 of IEC or betterIS standards to be followed w.r.t voltage range, frequency, power factor range, impulse voltage withstand test, power ferquency withstand voltage, power consumption etc
13Features of Special Energy Meter(SEM) Works on 3 phase 4 wire principleStatic meterWorking voltage of 63.5VAccuracy class of 0.2SShow time stampingMeasures:Average frequencyNet active energy transmitted in 15 mins block wiseDaily reactive energy transmitted in high / low voltage conditions
14Features of Special Energy Meter(SEM) -ve sign if net Wh exportMeter continuously integrates and can display on demand the net cumulative active energy sent out from the substation bus bars upto that time.The cumulative Wh reading at each midnight is stored in the meter’s memory.The register moves backwards when active power flows back to substation bus barsMeter counts the number of cycles in VT output during each successive 15-minutes block, and divides the same by 900 to arrive at the average frequencyThis is stored in the meter’s memory as a 2-digit code which is arrived at by subtracting 49 from the average frequency, multiplying by 50 and neglecting all decimals.E.g Hz is recorded as 44. In case the average frequency is less than 49.0 Hz, it is recorded as 00. In case it is 51.0 Hz or higher, it is recorded as 99.
15Features of SEMThe meter continuously computes the average of the RMS values of the three line-to-neutral VT secondary voltages as a percentage of V, and displays the same on demand.The meter also computes the reactive power (VAR) on 3-phase, 4-wire principle, with Class 2 accuracy, and integrates the reactive energy (VARh) algebraically into two separate registers => 103% & <= 97%When reactive power is being sent out from substation bus bars, VAR display have a plus sign or no sign and VARh registers move forwardWhen reactive power flows into the substation busbars, VAR display have negative sign and VARh registers move backwards.All 15 minute Wh figures is however be rounded off to the nearest last decimal but no rounding off for frequency/voltage displays
16Features of SEMThe three line-to-neutral voltage is continuously monitored and in case any of these falls below about 70%, a normally flashing lamp provided on meter’s front become steady.It go off it all three voltages fall below 70%. The time blocks in which such a voltage failure occurs/persists is recorded in the meter’s memory.The lamp automatically resumes flashing when all VT secondary voltages are healthy again.The meters normally operates with the power drawn from the VT secondary circuits.The meters are supplied duly fitted with the batteries, which shall not require to be changed for at least 10 years, as long as total VT supply interruption does not exceed two years.The battery mounting is designed to facilitate easy battery replacement without affecting PCB of the meterThe meters don’t require any separate auxiliary supply for their operation. All displays may disappear on loss of VT supply.
17Features of SEMEach meter has a built-in calendar and clock, having an accuracy of 30 seconds per month or better. The calendar and clock are correctly set at the manufacturer’s worksOnly limited clock adjustment is possible at site, using the DCD.When an advance or retard command is given, six subsequent time blocks is contracted or elongated by ten seconds each. The meter does not accept another clock correction command for seven days. All clock corrections are registered in the meter’s memory and suitably shown on print out of collected data.Each meter has a unique identification code, which is marked permanently on its front, as well as in its memory.
18Features of SEMIdentification code:: NP-four digit running serial number-A OR B e.g. NP-6060-A“A” for Model-A, and “B”, for the use with CT secondaries of 1 A and 5 A respectively.A touch key or push button is provided on the meter front for switching on the display and for changing from one indication to the nextEach meter has an optical port on its front for tapping all data stored in its memoryEach meter is provided with a RS-485 port on one of it’s sides, from where all the data stored in the meter’s memory can also be tapped.Data stored in the meter’s memories is tapped once a week from any of the two ports mentioned above and transmitted to RLDCs by e_mail generallyMeters are totally sealed and tamper proof, with no possibility of any adjustment at site, except for clock correction.
19Features of SEMMeters continue to function for the remaining healthy phase(s), in case one or two phases of VT supply fails with recording of a lower reading corresponding to number of phases under outageIn case of a complete VT supply failure, the computation of average frequency shall be done only for the period during which the VT supply was available in the 15-minute block
20SEM Technical Specifications Standard : IEC-687 / IECAccuracy Class : 0.2SInterface (Compatible with DCD) : With RS 485Reference Voltage(Vref) : 110V.(P-P)Rated Current : 5A or 1A.Operating Voltage : +20% to -30% of Vref.Operating Current : 0.2% to 200% of Rated current
21Types of SEM SEMs are of following two types : A-TYPE : Connected to VT having rated secondary line-line voltage of 110V and CT having rated secondary current of 1A.B-TYPE: Connected to VT having rated secondary line-line voltage of 110V and CT having rated secondary current of 5A.It operates with power drawn from the secondary circuits and no auxiliary power supply required.
22Operating section of (SEM) a) Analog Section: High precision Current transformer and voltage transformer step down input currents and voltages which are fed to an Analog to Digital converter. b) Digital Section: A powerful microprocessor controls the Analog and Digital sections. Analog to Digital converters are fed from high precision instrument transformers. The Digital samples from Analog to Digital converter are used to process the metering data. The sampling rate is 3000 samples per second which gives the meter an exceptional accuracy and results. c) Power supply Section: A switch mode power supply (SMPs) unit supplies power to the meter’s internal circuit.
23Data stored in a SEMEach meter has a non-volatile memory in which the following is automatically stored:i) Average frequency for each successive 15-minute block, as a 2-digit codeii) Net Wh transmittal during each successive 15-minute block, upto second decimal, with plus/minus signiii) Cumulative Wh transmittal at each midnight, in six digits including one decimaliv) Cumulative VARh transmittal for voltage high condition, at each midnight in six digits including one decimalv) Cumulative VARh transmittal for voltage low condition, at each midnight, in six digits including one decimalvi) Date and time blocks of failure of VT supply on any phase, as a star (*) markThe meters store all the above listed data in their memories for a period of ten (10) daysData older than ten (10) days get erased automatically.
24Display parameters of SEM Display Parameter Indication Display format Meter identification code A NP1234A Date (day, date, month, year) d dd-mm-yy Time (hour, min, sec) t hh:mm:ss Cumulative Wh reading c xxxx.x Wh Reactive Power Pr xxx:x VAr Average freq. of previous block F xx:xx Net Wh transmittal-previous block E xx:xx Average % voltage U xx:xx Voltage high VArh register reading H xxxx:x VArh Voltage low VArh register reading L xxxx:x VArh Real time indication rtC Fit Low battery indication Low Bat
25Classification of SEMs Main Meter : means a meter, which would primarily be used for accounting and billing of electricity.Check Meter : means a meter, which shall be connected to the same core of CT and PT to which main meter is connected and shall be used for accounting and billing of electricity in case of failure of main meter.Standby Meter : means a meter connected to CT and VT, other than those used for main meter and check meter and shall be used for accounting and billing of electricity in case of failure of both main meter and check meter;
26Location of Meters Location Main meter Check meter Standby meter Generating SystemOn all outgoingfeedersHV side of GTHV side of StationAux. TransformersTransmission SystemAt one end of the line between the S/Ss of the same licensee and at the both ends of the line between S/Ss of two different licensees. Meters at both ends shall be considered as main meter.There shall be noseparate standbymeter. Meter installed at other ends of the lines in case two different licensees shall work as standbymeter.ICTHV side of ICTLV side of ICT
27Location of Meters Philosophy of installation For GENERATING Stations Out going feedersCHECK METERMAIN METER400 KV BUSSTAND BYMETERSTN TRANSFORMERGENERATOR
28Location of Meters For ICTS 400 KV BUS MAIN METER ICT STAND BY METER Main meter is provided on EHV side of ICT and stand by meter on LV side of ICT.400 KV BUSMAIN METERICTSTAND BY METER220 KV BUS
29Location of Meters For Inter-state lines. SEB-B SEB-A A B MAIN METER STAND BY METERSTAND BY METER
30Location of Meters Metering arrangement for POWERGRID lines. On POWERGRID lines, unless an end is regional energy accounting point, an Energy Meter is provided only at one end of each line. The readings recorded by these meters are being used for information and analysis only, and not for the energy accounting purposes.
31Measurement principle of SEM Net Wh Transmittal during each successive 15-min time block up to second decimal, with plus/minus sign.Cumulative Wh transmittal at each midnight in 6-digits including one decimalIt works in real time with the help of an in-built clock.Average frequency of 15 mins block as 2 digit code ( 00 to 99 )Actual freq = ( 2digit code / 50 )e.g. If, SEM shows 2 digit code of 55 as frequency code,The actual frequency = 49 + (55 / 50) = 50.1 HzCumulative VARh transmittal for high voltage condition at each midnight( V > 103% of Rated Voltage)Cumulative VARh transmittal for low voltage condition at each midnight(V < 97% of rated Voltage)Data for Time blocks of failure of VT supply on any phase has a star mark as prefix.
32Special Energy Meter (SEM) Each meter has an optical port to access data stored in its memory. Hand held data collection device (DCD) are used as an interface between the meters and the PCMeters can store 10 days data. Data downloaded in coded form (*.MRI, *.DAT) and is converted to Text file (*.NPC) through software SMARTGRID/ VINCOM.Each day data, is of the following formMeter no Watt hr Var – High Var – Low DateNP–4201–A –Meter no is of nine character starting with NP and A or B at the end indicates the type of CT used.Any voltage problem is indicated by a star “*” mark preceding the energy data.
33Testing of SEMs-general norms On-site functional checking and rough testing of accuracy are being carried out for all meters once a year by the CTUFull testing for accuracy for every meter is being carried out by the CTU at an accredited laboratory once every five (5) yrs. with meter of higher accuracy classThe constituents/agencies may depute one authorized representative to witness the tests.Normally no re-calibration is required.In case a meter is found to violate any of its accuracy , functional requirements during the above periodic accuracy checks, the same is replaced by CTU by a duly tested/certified meter, and the defective meter is sent back to the manufacturer for appropriate recalibration and re-certification
34Fictituous metersFictituous meters(FICTMTRS) are a combination of METERS treated as a single entity. e.g.(i) Total drawal of an SEB(ii) Total relief from a generating station(iii) Total transaction of energy between two regions.FICTMTRS used to simplify the calculation processEvery fictitious meter is basically summation of certain no of Real meters.E.g. (FK-92) = +(FK-08) +(FK-09) +(FK-10) +(FK-11)+(FK-12) +(FK-13) +(FK-17) +(FK-15) +(FK-16)i.e FK92 represents TOT FSTPP Gen = sum of all real main meters installed in all the outgoing feeders from FSTPPSuch FICTMTRS are incorporated vide a .cfg file where the above formulae are listed in format readable by the software code
36Pairs.Dat FileThis file gives the LOC-ID of main meter and standby meter and the permitted pair tolerance for each pair.Main meters are those which are connected on 400 kV side of ICT or generator side of power station or sending end of inter state linesThe standby/check meters are on the other endStandby meters are connected in reverse polarity so that sum of both MWh is zero in ideal condition. SupposeE.g. the power flow is from main meter to standby meter, the main meter gives a +ve value and standby meter gives a –ve value and vice versa. Tolerance value in MWh for a 15 min block in +ve direction & -ve direction is given in this PAIRS.DAT, depending upon transformer /Line losses & CT/PT errorsThe given tolerance value towards +ve side is called X value.The tolerance value towards –ve side is called Y value.
39Data Collecting Device (DCD) DCD is a hand held terminal, capable of communicating with SEM as also with PC. Both communication requires suitable software at both DCD and SEMFeatures:Battery operatedIt has a key board / padLCD display screenCommunication slot
40SEM data collection through DCD Conventional data collection method for past 12 years.DCD with Optical CordOptical port in SEM
41Data collection through RS-485 What is RS-485?Two wire connectivity (having ground) between meter and PC.Enables automatic data downloading from all the meters in a location to a local PC.No need of DCD
44Data processing of SEM data Raw data is sent to RLDCs every week by Tuesday noon from sites through .Raw data is converted to text files.All text files are appended to a single text file.Korba end SEM is used as master frequency meter.Actual energy is calculated by a software as per configured fictitious meter.Daily Output MWh pertaining to drawal/injection/IR exchange is created.Daily Regional output file for the week period is created.Regional loss is calculated after processing.RLDCs send processed SEM data to respective RPCs.
45Data checking & Validation Identification of any metering error can be done through three broad categories of checks.End1- End 2 (using pair check)Net bus check of Generators using Kirchhoff’slaw.Net bus check of substations using Kirchhoff’sChecks are also carried out to ascertain time drift in the meters with reference to Master meter.