7Metering - Various Concepts

8/2/2019 7Metering - Various Concepts

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USAID / SOUTH ASIAREGIONAL INITIATIVE FOR ENERGY

(SARI/ENERGY)

23rdJuly to 7thAugust, 2010

CENTRAL INSTITUTE FOR RURAL ELECTRIFICATIONOF

RURAL ELECTRIFICATION CORPORATION

(A Govt. of India)

Hyderabad, Andhra Pradesh, India


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CAPACITY BUILDING

PROGRAM ONDISTRIBUTION LOSS

REDUCTIONFOR

AFGHANISTAN POWEREXECUTIVES


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METERING

Concepts & Basic Principles

CT metering

HT meteringMF calculation


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INTRODUCTION

Energy meter is a vital equipment in the Electrical Industry.Especially, in the present day context of conservation of energyand conservation of resources, the meter accuracy assumes a lotof importance.

When the energy measurement is looked at, it becomes clear thatmeter as such is a part of metering and the energy measurementtherefore depends not only on the accuracy of the meter but themetering system as a whole, which may comprise the associated

current and potential transformers and other wiring practices etc.,

When you think of an energy meter, we visualize an inductiondisc rotating from left to right and registering the energy by

pointers or a set of drum type registers. However, with the advent of electro static devices , especially the

microprocessor based devices entering the field of metering, theyare slowly revolutionizing the metering.


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Accuracy and proper functioning of energy meters and metering

equipment is of utmost importance, otherwise there may be heavyloss to the utilities. They should be accurate and maintain theaccuracy over long duration to register the consumption properly,so that the billing demand is correct.

Meters are to be selected according to the load characteristics.Before installing them at the consumers premises, they should betested. Connections should be proper and at the time of

commissioning, registration of meters should be checked on load.Periodical checking has to be conducted so that the completeequipment remains well maintained. This will ensure properfunctioning of the equipment over a long period.

Good quality of meters maintain high accuracy over a long periodof 15/20 years with varying load without recalibration ormaintenance, provided they are installed and commissioned

properly and protected from dust, vermins and mis-handling.However, test checks are to be applied from time to time.


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At present, most of the utilities continue to employ inductiondisc meters in LT supply system i.e. single phase and threephase. It is only recently i.e. about a decade back, theelectronic meters have entered the field of HT Trivector

metering with registering of historical MD Data, tamper dataetc.,

The microprocessor based metering is entering the field in a

big way, making the meter, in fact, a store house of data. Thedata is extractable with the help of electronic gadgets either bydirect contact or indirectly by a modem.


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FERRARI METERS

The classical meter is an induction disc meter where rotation isproportional to the energy being consumed.

Since the disc is rotating, friction is inevitable and reduction offriction by employing highly polished single jewel bearings,double jewel bearings or Magnetic suspension type arespecified in standards.

To cut the tendency to steal energy by reversing theconnections at terminal block, especially when such terminalsare available, some of the organizations have recently gone infor unidirectional meters, where the counter records always

forward, even when the disc is made to run in the reversedirection. Also meters with extended guarantee period can beordered and their performance can be kept under watch.


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Types of Meters:

The following types of meters are commonly used for consumers:

i. Single phase meters

ii. 3-phase 4 wire meters

iii. 3-phase 3 wire metersiv. 3-phase 4 wire meters with CT and MD

v. 3-phase 3 wire meters with Ct and MD

vi. Special meters :

3-phase 3 wire or 3-phase 4 wire Tri-vector meters

vii. Summation meters

i. Single-Phase Meters

Most of the lighting installations of domestic, commercial and smallpower consumers are connected on single phase. Similarly, streetlighting installations in rural and small townships are also connected onsingle phase. Single phase supply, otherwise, is not availed by othercategory of consumers except Railways who are given single phase HTsupply.


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i. Single-Phase Meters (Contd)

Single phase meters are rated for 240 volts A.C. supply, current rating2.5/5 amps. (maximum) or 10/20 amps. (maximum) and are for directconnection to the mains. The meters conform to respective standardsfor Electricity meters. It is claimed by manufacturers that the meters

are of robust design, with outstanding performance and characteristicsunder normal conditions. They are capable to take 400 percent overloadcontinuously and the load characteristics curve is extremely good overa measuring range of eight to one. They start registration with small

load of 3.5 and 7 watts and record up to 4400 watts.The outstanding feature of a single phase meter (induction type) is itssimplicity, compact and robust design so that relative positions of thesupporting parts remain unaltered. It comprises a potential coil and a

current coil. The potential coil, having large number of turns of finecopper wire, is fitted on the middle-limb of an E shaped Electro-magnetand connected across the supply main, producing some flux. Similarly,the current coil, consisting of a few turns of heavy gauge copper wire iswound on two limbs of a U- shaped electro-magnet. This is connected


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i. Single-Phase Meters (Contd)

in series with the load to be metered. When current passes throughit, the electromagnet is energised and this also produces some flux.The two fluxes so produced, set up a mechanical torque on the non-magnetic aluminium disc (which is located between the 2 coils)causing it to rotate. The rotating disc has to be of non-magneticmaterial. Otherwise, the disc will not be allowed to move by theelectro-magnets, as it gets attracted due to electromagnetic force.The rotating disc is mounted on a vertical spindle which is supportedby a sapphire cup contained in a bottom bearing screw. In order tocontrol the movement or rotation of the disc, set up by the twofluxes, a C-shaped brake magnet of of alloy-steel is provided. The

disc rotates through the narrow air gap of the C-shaped magnet andsets up eddy currents which brake the field and exert braking effect.


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ii. 3-Phase 4 Wire Meters

3 phase 4 wire meters (10, 30, 50 Amps) are used for agricultural andindustrial consumers. 3-phase supply is availed by these category ofconsumers either at H.T. or L.T. The meters are directly connected to thesupply, if load is up to 50 Amperes. If load is more than 50 Amperes, it is

preferable to provide C.Ts. They are rated for 415 volts.In a 3-phase 4 wire meter, 3 coils of each type i.e. potential coil and currentcoil are provided. In fact, a 3-phase 4 wire meter can be said to beequivalent to three numbers of single phase meters accommodated in oneframe, each element (i.e., potential and current coil) maintaining its ownidentity. A single common disc is there to record the consumption. It isnecessary that operation of each element is checked separately when it iscarrying load current to ensure that all elements are recording in positivedirection and that no negative torque is exerted by any element. In practice,

such cases of wrong connections have been noticed and detected. Hence,this point should be given special attention.

Each of the 3 elements of the meter produces equal torque i.e., 1/3 of thetotal torque under all conditions of varying power factor, with balanced

load.


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iii. 3-Phase 3 Wire Meters

A 3-phase 3 wire meter has 2 elements instead of 3 elements as inthe case of a 3-phase 4 wire meter. The basic principle of operationis the same as that for a 4 wire meter. The torque produced by 2elements is equal to each other, only when the power factor is unity.

At other power factors, the individual torques produced by 2elements are not equal and are of varying proportion.

B element produces more torque at lagging power factor, while theR element produces more torque at leading power factor. This

particular feature can be made use of to find out the P.F of the loadcurrent of the consumer, for the purpose of checking at site.

The table given below indicates the P.F. against the ratio of the timetaken by the B element for a fixed number of revolutions of the discto that of R element for the same number of revolutions. For suchrecording of time for each element through wrist watch or timer, theother element is to be made ineffective by removing its P.T. fuse and/or short circuiting the C.T. secondary.


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iii. 3-Phase 3 Wire Meters (Contd.)

The test will give correct results, only when the meter has beencorrectly connected and the phase rotation is in the order of RYBR.

Power factor lower than 0.5 will be indicated by the reverse runningof the meter with the R element only in operation.

Time Ratio App. P.F.

1.00

0.80

0.65

0.50

0.400.27

0.18

0.10

1.00

0.98

0.94

0.87

0.810.71

0.64

0.58


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iii. 3-Phase 3 Wire Meters (Contd)

Usually three-phase 3 wire meters are not used in recordingconsumption of L.T. power consumers for the simple reason that thelighting load (pilot lamp in case of Ag. Consumer) has to beproperly connected on one of the phases R or B. otherwise, if it isconnected on Y phase where no current coil is provided, the energy

consumption would not get recorded. The meters otherwise can beused if proper connections are made and checks are applied.


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iv. 3-Phase 4 Wire Meters with C.T. and M.D.

It is already mentioned that up to 50 amps, meters are available for

directly connecting to the supply. If the load is more than 50 amps,C.T. operated meters are to be used.

For example, a 70 kW load is to be supplied. Then, the load-current

at 0.8 P.F. would be :


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iv. 3-Phase 4 Wire Meters with C.T. and M.D. (Contd)

70 X 1000--------------------- = 126 Amperes.

3 X 400 X 0.8CTs are available in the ratio of 50, 100, 150, 200, 250, 300, 350,

400/5 Amps. Hence CTs with ratio of 150/5 amps. would be

required. The meter will have to be suitably calibrated so that it

records directly, the consumption with 150/5 amp. CTs. The ratio of

C.T. is also mentioned on the meter. The dial-factor would be oneand multiplying factor naturally will also be one. Suppose if we use

a meter calibrated for 100/5 CT ratio and if its dial-factor for this

C.T. ratio is one, then multiplying factor would be:

150/5M.F. = ----------- X D.F. = 1.5

100/5

Hence the recorded reading would be required to be multiplied by 1.5


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iv. 3-Phase 4 Wire Meters with C.T. and M.D. (Contd)

It is to be noted that CTs are to be properly selected for accuraterecording. Usually, rating of CTs should fall within 50 to 80 percentof the maximum load current of the consumer.

Sometimes, L.T. consumers opt for two part tariff and are requiredto be provided with metering having recording arrangement formaximum demand in kW as the tariff provides for kW demandcharges. The poly phase meters are provided with maximum demand(M.D.) indicators, which are nothing but additional mechanismattached to the meters to record the rate of consumption over a fixedperiod (usually half an hour) each time and then get reset with thehelp of a time-switch. A pointer indicating the highest ever rate of

consumption thus recorded by the M.D. indicator is left behind,which has to be manually reset, while taking down the reading everymonth.


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v. 3-Phase 3 Wire Meters with C.T. and M.D.

It is exactly like 3-phase 4 wire meter and work on the same

principle. It is also used in the same way and under the samecircumstances, as a 3-phase 4 wire meter.

However, while connecting, precaution has to be taken to connect itproperly. It also records M.D. in kW.


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vi. Special meters

(a) Bi-vector meters, and

(b) Tri-vector meters

Besides the energy charges and kW demand charges, the tariffprovides for kVA demand charges and also power factor surcharge.(If power factor is less than 90 percent, the consumer is penalized).For this purpose, special type of meters are required.


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vi. Special meters (Contd.)

c

I V I V

A B A

(a) (b)

There are two alternative methods of metering. In diagram (a) meter(A) is a watt-hour meter or cosine meter and measures the real

energy supplied, while meter (B) records the kVA hours. In diagram(b), A records the true-energy as in case of (a), while meter (C)records the wattless energy or kVA Sin energy, obviously.

(kVA Sin)2 + (kVA Cos)2 = (kVA)2


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vi. Special meters (Contd.)

If in diagram (a), B is fitted with a maximum demand indicator alsogiving kVA demand, then average P.F. of the load

Reading of meter A= -------------------------

Reading of meter B

The readings being, for corresponding periods of time. In case of (b)the average P.F.

Reading of meter A= -------------------------------------------------------------

((Reading of meter A)2 + (Reading of meter C)2)


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Installation and Commissioning of Meters

I. Apart from testing and calibrating the meters, they must beproperly installed, as per the connection diagram. After installation ofmeter, its performance should be checked at site also. If we take 100watt lamp (resistive load and constant of energy meter is 2400 rev/kWh), assuming normal supply voltage, the consumption in one hourwill be 100 watt hours. The meter disc should therefore rotate.

(2400 x 100) / 1000 = 240 rev. / hour

Therefore, time taken for one revolution is 60x60/240 =15 seconds

If the time taken is more, the meter is running slow and vice-versa, ifthe time is less. Suppose 16 seconds instead of 15 seconds are taken,then the meter is slow by (16-15) x 100/15 = 6.6%. It should,therefore, be adjusted.

For synchronous motors, power factor can be taken as unity. ForInduction motors, it is 0.7/0.8 and for welding transformer it is about0.6. The motors contribute inductive load in the system.


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Installation and Commissioning of Meters (Contd)

II.C.T, Operated MetersFor C.T. operated meters:

1. Ratio test by primary injection kit and

2. Polarity test should be carried out.

It should be borne in mind that C.T. Secondary terminals should not bekept open.

Following points must be kept in view, while installation of meters:

a) Position of meter should be such that reading is easily visible.

b) Mounting of meter should be on solid wall or D.P. structure or onpanel board.

c) For H.T. metering equipment, CTs should be right on the incomingside, before the point of isolation.

d) Meter should be fitted in a protected meter box, nowadaysprovided by the Utility. It should be installed at a place where rain-water cannot enter.

e) The meter box has facility of sealing from outside. It shouldtherefore be, sealed.

f) The meter-recording should be checked at site as explained.


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III. Meter Reading

(a) Registering or counting mechanism is to record continuously anumber. This recording is proportional to the revolutions made bythe moving system. The rotor shaft drives a series of five or sixpointers. These rotate on round-dial which are marked with tenequal divisions. There are two types of registration systems:

(i) Pointer type

(ii) Cyclometer type

Reading could be made from both the types of meters.


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III. Meter Reading (Contd)

(b) C.T. Type Meters

In case of C.T, operated meters, the multiplying factor should becalculated. It depends upon ratio, meter rating and dial factor. An

example is given below

(a) (i) Meter rating 100/5A; 400V

(ii) C.T.ratio:200/5A;400V

(iii) Dialfactor:48Overall M.F = [(C.T Ratio) / meter C.T rating] x Dial factor

= [(200 / 5 x 400 ) / 100 / 5 x 400 ] x 48 = 96


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The performance of the meter should be checked on load, afterinstallation and commissioning. It should be ensured for correctrecording, applying multiplying factor, which could be noted onpaper. This could be pasted in the meter box and one copy be kept infile/ledger. Many disputes have arisen due to this omission. If there is

delay by the consumer in connecting the load, the commissioning ofmeter could be deferred, till the consumer starts drawing power.

Repairs of Minor Defects in the Laboratory

Following main defects are generally found in meters :

1. Rotor shaft found bent.

2. Counting train found defective.

3. Rotor disc found bent.4. Pressure coil has discontinuity.

5. Meter excessive slow, fast even after an adjustment.


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6. Upper guide pin broken.7. Current coil short with body.

8. Wrong name plate meter constant as the revolutions of meter doesnot tally with constant

9. Demagnetized brake magnets.

10. Broken glass plates.

Out of new meters received from area Stores, defective ones are

replaced free of cost by supplier. Old defective meters are repairedat Meter Testing Laboratory and calibrated. It is very essential tocalibrate the meters, whenever components are replaced orelectromagnetic gaps are adjusted.

First apply the rated voltage to each element in turn for 3 ph. meterswithout any current in current circuit and adjust the low loadadjuster to a point where the rotor disc becomes stationary. If thisadjuster is moved in either direction, the disc should start to creep.


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The routine testing of meters could be once in 3/5 years. In addition,surprise checks on the consumers installation and meters should bemade from time to time. The important points to be paid attention,while checking are:

1)Connections of meter are proper.2) Seals are not tampered.

3) No loose or direct connection exists.

4) Meter is not damaged to record less.

5) CTs are properly connected. No reversal of any phase connectionexists. Multiplying factor is properly calculated and applied.

6) Meter is well-protected from rain, vermins and dust etc.

7) Links are connected.

8) Terminal block is not damaged.9) It may also be mentioned that with the help of load current of

known magnitude (preferably of resistive type) and a wrist watchhaving a seconds hand, one can off-hand check at site, the

performance of the meter and also its accuracy to some extent, asindicated below:


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Let the resistive load be a bulb of 40 Watts and the meter constant ofthe energy meter is 1200 Rev /kWh. Assuming normal supplyvoltage, the consumption in one hour is 40 watt hours. The meterdisc should therefore rotate

@ 1200 x 40 /1000 = 48 Rev/hour. Say for 1 Rev.the disc would take (60x60)/48=75 seconds,

If the time taken is more, it means the meter is running slow andvice-versa. In fact, the percentage error can also be calculated fromthe time it actually takes. In this particular case, if the time taken is78 sec, the meter is slow by

(78-75) / X 100 /75=4 %

If the load current is not resistive but inductive or capacitive, thepower factor of the current is to be assessed first, depending upon thenature of the load and then the energy consumption worked out. Forexample, a 10 HP flour mill drawing 10 Amps, current at 400 voltscan be presumed to be running at 0.8 power factor and having 3 x l0x 400 x 0.8 = 5.54 kW load, for the purpose of such checking.


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HT Metering

Low-Tension service connection is extended to a consumer by theutility when the demand is such that the technical parameters asprescribed under Electricity Rules can be met like stable & quality

supply, proper voltage regulation etc. Most of the utilities on theirexperience, therefore, restrict the extension of L.T. supply to theconsumer up to 50 H.P. or 100 H.P. (connected load). If theconnected load is such that the maximum demand of the consumer

is high, then supply at High-Tension is given. The supply voltagecould be from 11kV to 220kV depending upon the contracteddemand.


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H.T. Consumers Metering

Trivector MeterA well planned tariff covering an electricity service, takes intoaccount, both the energy consumed, maximum demand andrecording of power factor. Tariffs of this kind comprise:

1. Charge on energy consumed.

2. Charge on maximum demand on kVA

3. Charge on account of power factor, if it is below the specificlimit (0.90 lag).

A trivector meter is designed to record active, reactive and apparent

energy along with M.D. indicators on all. The trivector meter is acompact unit. It replaces a set of instruments which must otherwisebe installed and has the advantage of yielding full and more accuratedata.


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Trivector Meter (Contd)The trivector meter consists of three different recordingelement namely, kWh, kVAh and RkVAh. The recording

principle of kWh and kVARh elements is the same asdescribed in 3-phase meters, whereas kVAh elementrecords mechanically with the differential gearingarrangement. The TRIVECTOR is a brand name of M/s

Landis and Gyr., England. This meter is very reliable,robust and practically free of any adjustment even after along period of service.


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Proper Selection of Meters

For accurate metering it is necessary that meter normally operates atthe higher ranges, where its accuracy is better. To achieve this, theCT ratio is properly selected. It is recommended that the CTs usedare of single ratio, as far as possible.

It may be said as a guideline that while selecting CT ratio the sameshould be related to 80% of the ultimate contract demand that may beexpected in about a years time of the commissioning of theconsumer. As the current transformers are designed for 20%

overloading, the CT would be adequate where the load exceeds 80%of the contract demand. It may be prescribed that the CT ratio shouldbe checked in relation to the maximum demand once every year, orwhenever these is increase in the contract demand.

It may be added that whenever metering on L.T. side is provided forH.T. Consumer, 3 percent of the energy recorded is added for thetransformer losses. It is further to be ensured that a 3 phase 4 wiremeter is only installed.


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The H.T. Trivector meters of Electromagnetic type arecomplicated in that the measurement of KVAH, which isessential for the measurement of average M D in KVA requires

measurement of RKVAH.

General defects noticed in this type of meters are;

a) Meter bottom bearing defective

b) Meter top bearing defectivec) Meter PC. coil burnt or opened

d) Meter C.C. coil shorted.

e) Meter dial stuck up at 9th digit

f) The clutch coil openg) The M D needles stuck up or loose

h) The timer defective


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(i) Checking of Connection

The rotation of disc on element-wise, depends on the power factor ofthe installation. The above analysis is for the P.F. = 0.866.

S.No. Element kWh meter RkVAh meter

(i) If R element is connected to

the supply alone

Disc should rotate

in forward

direction

Disc should rotate

in forward

direction(ii) If B element is connected to

the supply alone

Disc should rotate

in forward

direction

Disc should stop

(iii) If both R, B elements are

connected to supply.

Disc should

rotated in forward

direction

Disc should

rotated in forward

direction


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(ii) Power Check

a. Energy can be calculated by line current, line voltage and P.F.multiplied by time.

b. Energy calculated under (a) should be equal to the recording by

kWh disc when P.T. fuses of both R and B phases are in circuit.

The above tests are to ensure that H.T. meters are properly installed

and tested. It is to ensure that the potential and current coilconnections are on the same phase; phase sequence of the meter iscorrect so as to give cumulative effect of loads on all three phases.

For C.T. and P.T. operated meters, it is preferred to use a test terminalblock (TTB) for C.T., P.T. and meter wiring. This TTB provides thefacilities of shorting CT secondaries for testing purpose without anyinterruption to the consumer.


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(ii) Power Check (Contd)

The P.T. leads should be connected through the fuses of proper rating.To eliminate the possibility of tampering with the fuses, the fusesshould be provided with protective cover and properly sealed.

Now a days pilfer box is provided for this type of meteringequipment. It should be used so that no outside agency can tamperwith the equipment. Since the meter records correctly in verticalposition, the box should be welded to the structure to avoid changing

of position.

(iii) Testing and Checking of H.T. Meters at Site

After installation and commissioning of meters or during routinetesting of H.T. meters, it must be ensured that same phase C.T. andP.T. are entering in one element of meter and phase sequence at themeter terminals is correct. Following checks are made after charging,on supply:

(iii) i d Ch ki f Si


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(iii) Testing and Checking of H.T. Meters at Site (Contd)

1. Voltage at meter terminals.2. Phase sequence at meter terminals.

3. Current on each phase should be approximately equal for threephase-load.

4. Element wise rotation of disc.5. Load test, it should tally with the connected load of consumers.

If results are satisfactory M.F., meter details, reading etc. should benoted and consumers signature should be taken on result sheet.

The meters of H.T. consumers may be tested at the following periodicity:

1. H.T. consumers having demand of more than 25 MW:- After every

3 months.2. H.T. consumers having demand between 5 and 25 MW:- After every

6 months

3. H.T. consumers below 5 MW:- After every one year.


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THE STATIC METERS


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THE STATIC METERS The static meters and meters based on micro processor are generally

designed for recording not only the energy by KWH but also otherparameters such as KVAH, RKVAH, average power factor,instantaneous values of current, voltage, KW, KVA etc.,

This is making the cost of meter high and probably that is why asingle phase or ordinary 3 phase meter could not come up to be usedextensively. By the comparable price of an electronic meter means,one has to look into the fact that a static meter need not be calibratedas frequently as is the case with an electro magnetic meter and this

reduces the number of rolling stock meters to be held by the utilityand administration and establishment charges of testing and replacingare reduced.

The present HT static meters are designed to record data ontampering also. It records reversal of currents, failure of a voltage etc.,It also records the frequency of tampering and total period underwhich the meter is kept tampered. All such data is helpful in assessingthe total energy lost.

Th St ti M t


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The Static Meters (Contd)

It records the present maximum demand, the integration timelapsed for the present and the corresponding demand and it alsostores and exhibits the historical data of the past 5 Maximumdemands, so that a reference to them can be made.

Static meters performance is generally found to be very good. Asan example, it can be mentioned that Static meter of L&G make(Imported) is installed in a Railway traction service which wasuntil then serviced by an electromagnetic meter of L&G make. The

railways complained that the new meter recorded low P.f., Ananalysis revealed that the static meter being sensitive to lowcurrents recorded lagging MVAR of the Power Transformer of theconsumer, which is in service continuously. The load for traction,

even though is nearly unity P.f., is incident on the secondary of thetransformer intermittently so that RKVAH recorded due to theinductive load of the transformer is comparable to the KWH loadrecorded by the meter. This could not be done by electro magneticmeter, as the meter cannot accurately record at very low loads.

The Static Meters (C d )


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The Static Meters (Contd)

Further, in low load conditions and no load conditions, theElectromagnetic type HT TVR meters have the tendency torecord average power factor of more than unity, which isobtained by dividing KWH by KVAH. Also, in some of the HTservices, the energy recorded at the HT meter point is less thanthat recorded by meters of the service at L.T. system. This isgenerally due to inaccuracies of meter at loads, less than 5%.Static meters on the other hand, are found to be recording theenergy even at such low loads as 0.5% and less.

The meters are now being specified to be compatible to be readwith a hand held meter reading instrument (M.R.I).

The manufacturers are now being asked to make available meterssuch that a universal M.R.I, can read different makes of meters.For this purpose, they have to make available, the necessarysoftware through which the M.R.I can extract the meter reading.


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Summation Meters


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Summation Meters

Summation meters are another special type of meters which are usedfor recording the total consumption of a consumer fed at more thanone point. The main purpose for connecting a summation meter is tofacilitate the correct recording of the total kVA demand, since

adding up of the MDs recorded by the individual meters,arithmetically, may not be correct because of the possible diversifyin their periods, even though the total unit consumption can beworked out arithmetically. There are a number of methods for

summing up the consumptions through one meter, some of whichare as indicated below:

1. Paralleling of the CT leads on the secondary side beforeconnecting them to the meter current coil.

2. To provide for each phase, one intermediate CT, known assummation CT, with a number of primary windings forconnections to the secondaries of individual CTs and only onesecondary winding to feed the meter current coil.

Summation Meters (Contd.)


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S a ( )

3. Use of multiple current coils in the same meter for directconnections to the individual CTs, the measuring elements beingcommon to all for the same phase.

4. To have independent elements for all CTs mounted on acommon shaft of the same meter so that the shaft gets the totaltorque and records total consumption thereby.

5. Separate elements to measure the consumption independently asin 4 above but having separate driving shafts connected to acommon one through differential gears to record the totalconsumption.

6. Separate meters, each fitted with an electrical impulsetransmitting device, to record the consumption at various pointsindependently and pass on the impulses simultaneously to acommon meter which then records the total consumption.

Electronic Meters


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Electronic tri-vector meters are now available for providing at theS/s or at the H.T. consumers premisis. The special features aredescribed below.

Special Technical Features of Electronic Tri-Vector Meters

Electro-mechanical meters used to record demand & energyutilisation by High Tension consumers have been noticed severaltimes to behave in an erratic way. Moreover, despite best efforts tostop tampering of meters by other agencies than that of the utility,

pilferage of energy in some way or the other, has been a commonfeature. Disputes on this account prolong for several years. It wastherefore thought to introduce electronic meters, which are nowavailable. Electronic meters, in the earlier stages, gave problems and

did not perform satisfactorily but modifications in display, recordingsystem of meters for (a) tampering, (b) error, (c) P.Ts utilized insummation system, (d) poor-battery output etc. have been carried outon the suggestions of the utilities. This has helped in overcoming

several problems.

Special Technical Features of Electronic Tri-Vector Meters (Contd)


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p

The display system of the meters, now consists ofi. Active Energy utilisation kWh/M

ii. Reactive Energy utilisation kVARh

iii. Apparent Energy utilisation kVAH

iv. Peak Maximum demand kVA

kW (with lagging PF)

v. a) Cumulative demand kVA

b) Billed MD for previous monthvi. Re-set counter

vii. Power factor

viii. Frequencyix. Occurrence of missing P.T. for supply of voltage

x. Time of the day metering

xi. Time-interval for time of the day metering

Special Technical Features of Electronic Tri-Vector Meters (Contd)


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p

xii. Energy-import/exportxiii. Tamper information

xiv. Raising demand with elapsed time

The meters could therefore be used at S/s ends or at the consumersend to have accurate data-base and utilisation of energy.

The meters meet with IEC 687 standard and are suitably designed to

record accurately with variation in voltage from +10 to -3% andfrequency 5. The meters are of 0.5 accuracy. The battery to meetvoltage demand of the circuit is of 3 volt lithium. The multiplyingfactor can be kept at unity, in order to avoid error due to use of

various ratings of CTs and PTs. Three seals are provided, one on thefront cover, one for terminal cover and one for M.D. and resetbutton. All other features are built-in to display the details describedabove. The meters are designed for C.T. ratio of 5 amps or 1 amp on

secondary side and PT. ratio of 110 volts.


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TAMPERPROOF ENERGYMETERS AND METER BOXES

TAMPERPROOF ENERGY METERS AND


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Energy Meters play the vital and important role of measuringthe energy consumed by various categories of consumers and

these are an important link in revenue collection of anyElectrical Utility / Electricity Board.

It is understood that energy meters currently available in the

market can be tampered with and some of the unethicalconsumers employ ingenious ways to tamper with calibrationof the meters, steal energy and do not pay for the energyconsumed by them. This results in loss of revenue, which is an

important factor, affecting the smooth and profitablefunctioning of any Electrical Utility.

METERBOXES

THE SALIENT FEATURES OF SUCH A TAMPER

PROOF ENERGY METER ARE


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PROOF ENERGY METER ARE1. The Energy Meter should meet the relevant standard

2. The Energy Meter meets the requirement of relevant AccuracyClass

3. The casing of the meter is fully transparent and made out of ultra-violet stabilized Polycarbonate material, resulting in:

a. fully transparent polycarbonate meter base.

b. fully transparent polycarbonate meter cover.

c. fully transparent polycarbonate terminal cover.

4. The meter cover and meter base have press fit arrangement, sothat the meter can be closed by simply pressing the meter cover onthe meter base i.e. the meter cover gets self locked to the meterbase. Additionally, the meter cover is ultrasonically welded to the

meter base so as to avoid insertion of any foreign material insidethe meter, with an intention of tampering with it.

5. The Terminal Block is made out ofGlass Filled, Fire RetardantEngineering Plastic material.

The Salient Features of such a Tamper Proof Energy Meter are(Contd )


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(Contd)

The fully transparent polycarbonate terminal cover also has selflocking / press fit arrangement with the terminal block. Afterinstallation of the meter at the consumers premises, the terminalcover is simply pressed and it gets self locked. Thus the connection

at the terminal block cannot be tampered with by the consumer.

With this arrangement, the self locked and ultrasonicallywelded meter can only be broken open.

6. As an additional precaution to avoid tampering, there isprovision for sealing the meters with lead wire seal.

7. The meter is provided with unidirectional counter so that the

meter reads only in the positive direction, even if the directionof rotation of the disc is reversed by reversing the connections.

8. in order to reduce the frictional losses and also the wear and tearof the moving parts, resulting into increased life of meter,Magnetic Suspension Bearing is provided in the meter.

The Salient Features of such a Tamper Proof Energy Meter are


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(Contd)

9. In order to reduce the apparent power loss, the burden of there-designed Potential Coil has been reduced from 6VA to4VA.

10. The Current Coil burden has also been reduced from 2.5VA to0.4VA

11. 100% meters are tested on computerized test benches withprintout facility, using Class 0.1 Electronic ReferenceStandards, in air-conditioned environment.

Certain utilities witnesses the testing of 100% meters at thetime of inspection.

12. Meters are guaranteed for 10 years satisfactory performance.

TAMPER PROOF METER BOXES


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It is widely known and has been reported that even the Tamper ProofEnergy Meters -both Static and Electro-mechanical, are prone to

tampering and can be tampered with by employing ingenious ways,

resulting in loss of revenue and endangering the smooth and

profitable working of any Power Utility. The solution lies in

installing the meters in a tamper proof enclosure at the consumers

premises.

CHOICE OF TAMPER PROOF METER BOXESIt is understood from the technical specifications of Meter Boxes

from various utilities, that the utilities are procuring three (3) types of

Meter Boxes :a. Fabricated Mild Steel Meter Boxes.

b. Deep Drawn Mild Steel Meter Boxes.

c. Moulded Engineering Plastic Meter Boxes.

SALIENT FEATURES OF TAMPER PROOF METER BOXES


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Various desired / implied anti-tamper features have been considered whiledesigning the tamper proof Meter Boxes and the salient features are asunder:

Tapered Roof, so that water does not stay at the top.

Toughened Glass / Transparent Engineering Plastic viewing window formeter reading.

Glass fixing from inside only with metal supporting clamps. Replacementpossible only on opening the door, after breaking the seals.

Cable entry & exit through cable glands, not accessible from outside. Two door hinges, fitted from inside and not approachable from outside.

For locking & sealing the cover with base, two nos. U-Shaped latchesprovided.

Provision for Padlock for additional sealing.

For ease of wiring, meter mounting portion raised by about 10 mm.

Provision for holding Meter Reading Card.

Customers special requirements can be complied with.


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FUTURE METERING The future for static meter appears to be very bright and


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The future for static meter appears to be very bright and

microprocessor based meters are probably going to dominate thefield.

Some of the features which are advocated in this area are:

a) Time of day meter

b) Multi Tariff meterc) Prepaid meter

d) Meters with historical data with a few MB memory to storevarious parameters

e) Meters to be read by hand held MRIs

f) Meters to be read by remote reading instruments.

The conservation of energy and load management systems demandartificially intelligent meters which switch off lights in an unusedroom or switch off the yard lightning automatically.

Also in future, meters may be designed to sense the frequency ofthe system and adopt load throw off concepts, built into them. Sayfor example, on occurrence of an under frequency, domestic meter

may sense it and switch off non priority loads.

CONCLUSION


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The Electro-magnetic meter will continue to be used for somemore time and general defects noticed in this meter are to betaken care of in their design.

The single phase and 3 phase energy meters of static typehave to be simple in design so that they compete with theElectro-magnetic meter.

Universal type of meter reading is to be developed by themanufacturers of static meters by coming to an understanding,in order to serve all the consumers.


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7Metering - Various Concepts

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