D I F F I C U L T I E S IN T E S T I N G E L E C T R I C I T Y M E T E R S

B. A. B l i z n y u k

Translated from Izmer i t e l ' naya Tekhnika, No. 12, pp. 52-53, December , 1961

There are over 650 three-phase and over 1500 s ingle-phase e lec t r ic i ty meters of various types at the Yuzhnyi

minera l concentrat ion plant. On the basis of the experience in their use we consider that Instruction 195-54 for testing e lec t r i c i ty meters comple t e ly meets the requirements for technica l and commerc ia l power consumption metering. In

fact, a l l users of e l ec t r i ca l power without exception work below the maximum load or, in ext reme cases, at nominal

loading, i .e . the e lec t r ic i ty meter current circuits never operate at more than 5 amp. The only except ion is provided by starting conditions; however, they are very short (the longest starting of 28 see is provided by the exhauster motors

Pn -- 2 ,oookw).

On the basis of what considerations does Instruction 195-60 specify the testing of e lec t r ic i ty meters at loads of

120, 150, 200 and even 400~ above the normal? It could possibly be expedient for e lec t r ic i ty meters used by con- sumers who, owing to the nature of their production process, have numerous and long starting periods or overloads.

Neither is it c lear why the checking of e lec t r ic i ty meters at 5% of the nominal load has been introduced, since at this lead the three-phase e lec t r i c i ty meters are diff icult to adjust, and the single-phase meters vir tual ly cannot be adjusted.

The fu l f i l lmentof the requirements specified by Instruction 195-60 presents the following difficult ies.

The raising of the load in order to check e lec t r i c i ty meters at 200-400% of their nominal value requires the reequipment of test racks, which leads to addi t ional expenditure and the withdrawal of the equipment from opera-

tion for a cer ta in t ime .

The extension of the adjustment ranges of the e lec t r i c i ty meters results in more t ime spent on testing the meters, i .e . i t leads to a larger number of operators or the disruption of the testing plan.

We consider, therefore, the requirements st ipulated in Instruction 195-60 to be incorrect; neither do we agree that e l ec t r i c i ty meters type IT Grades 1 and 2 should be withdrawn from use, since we have found them to possessex-

ce l len t qual i t ie r they can be easi ly adjusted and are re l iable in operation, whereas the new e lec t r i c i ty meters types 1-43 and 1-44 are diff icult to adjust.

Editorial Note. Electr ic i ty meters of t h e new design retain their grade of accuracy and can work for a long t ime over a wider range of loads (up to 300% and more) than meters of the old design.

Instruction 195-54 does not st ipulate the testing of e lec t r ic i ty meters at loads which are higher than the normal and are ca tered for in the design, thus providing a considerable loss to our nat ional economy. The users of e lec t r ic i ty

meters could not select them for new installations on the basis of their overload capac i ty , since the overload part of

the meter character is t ic was not tested after repairs. They selected meters with a nominal current equal to the max- imum load current instead of chosing meters with a maximum current,at which their grade of accuracy is not impai red ,

equal to the max imum load current. With such an incorrect choice the overload capac i ty of meters was not u t i l ized , thus lowering the accuracy in measuring smal l loads.

If the meter error at a load 200% of the nominal meets the GOST (All-Union State Standard) requirements stip- ulated for each grade, the me te r ' s nominal current can be half the maximum load current.

The choice of meters with a raised nominal current often leads to an underest imation of the consumed energy. Let us give an example . A 220 v, 10 amp meter is used to register the consumption of one 25 w bulb which produces

a load slightly in excess of 1%. Under such conditions the underest imation of the consumed energy may amount to tens of percent.

The accuracy of meters at smal l loads rises with a reduction in their nominal current for a given load. It is, therefore, necessary to select meters on the basis of their overload capaci ty .

The need to produce direct ly connected meters with a high overload capac i ty has been confirmed repeatedly by a wide c i rc le of e l ec t r i c i ty consumers when the standards for e lec t r ic i ty meters were discussed before their drafting (GOST 6570-53 and GOST 6570-60).

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Instruction 195- 60 does not require it but rather permits the checking of the new design e lec t r i c i ty meters at loads above 100% for s ingle-phase and above 120~ for three-phase meters. It concedes the right to test meters at suchhigh

loads and, therefore, the adjustment of meters after repairs must be as thorough as during their manufacture .

The difficult ies due to increasing the volume of work in checking meters were taken into account when Ins- truction 195-60 was drafted and i t st ipulates, therefore, only a min imum number of loads at which the meters which

are in service should be tested, namely , at three loads for cos ~ = 1 and at one or two loads (for three-phase meters) at cos ~ = 0.5. In issuing Instruction 195-60 an error has been made which which w i l l be corrected in the next normal reissue of the Instruction, by stipulating that, after repairs,tests should be carried out with loads specif ied for meters

which are in use and not with loads specified for manufactured meters. The agency which carries out the testing can,

on its own ini t ia t ive , chose loads at which a given mete r is to be tested.

Testing of meters at 200, 300, and even 400% of their normal load does not require a reequipment of the test racks as ind ica ted by B. A. Bliznyuk, since the racks are normal ly made for currents at least up to 50 amp.

The great shortcoming of Instruction 195-54 consists of its provision for an incomple te repair of meters. Thus, a meter manufactured with a smal l effect of the power factor on its readings could, after repairs, have any large ran- dom effect of cos cp on its readings, since the regulat ion did not insist on appropriate testing, and al lowed the meter to be s tamped as "checked for cos ~ = 1."

Discontinuation of the production of e lec t r i c i ty meters type IT requires no explanat ion, since they do not mee t the GOST requirements. As far as the diff icult of adjusting meters IT-43 and IT-44 is concerned, i t should be speci-

f i ca l ly stated which adjustment e lements are unsatisfactory, and whether it is diff icult to adjust by means of the mag- net, phase-shifter or the fr ict ion compensator. Such de ta i led statements wil l provide the possibili ty of raising the

question with the manufacturing plant.

M E T H O D FOR C H E C K I N G A N D M E A S U R I N G

N O I S E IN E L E C T R O N T U B E S

Z . V. M a g r a c h e v

Translated from Izmer i t e l ' naya Tekhnika, No. 12,

p. 53, December , 1961

M I C R O P H O N I C

Particular a t tent ion should be paid in designing amplifying devices with a sensit ivity of the order of 1 microvol t

to microphonic noise due to mechan ica l and acoust ica l effects on e lec t ron tubes. We have found that microphonic noise is present not only at low frequencies of the audio range, but also at frequencies of the order of 10-20 kc, de - pending on the structure of the tube and the technology of its manufacture. Tube noise varies between individual

samples and with the aging of tubes.

It is possible, as a rule, to e l imina te low-frequency microphonic noise by means of ef f ic ient damping and a

suitable structure of tubes. Microphonic noise of 100 cps and higher is, in the major i ty of cases, due to acoust ica l

vibrations whose screening is very diff icult (music, singing, speech, industrial noise).

Below we describe a method for checking and measuring such noise for the purpose of developing tubes accord- ing to their noise character is t ics and by their sensit ivity to acous t ica l interference. According to this method (see figure) the output of audio-osc i l l a tor 2 is measured on vol tmeter 1 and fed to loudspeaker 3 p laced at a set distance from tested tube 4,which serves as an input tube of a h ighly-sensi t ive ampl i f ier . The sockets for the tested input tubes are mounted on normal rubber or spring dampers in order to avoid the transmission of possible mechan ica l vibra-

tions.

The ampl i f i e r should provide, in the range of 100 cps-20 kc, measurement of signals with a vol tage not less than 10 pv in aper iodic ampl i f ica t ion , and not less than 1 pv in se lec t ive ampl i f i ca t ion with the possibili ty of feed-

ing the signal to the mi l l i vo l tme te r 5 or the oscil loscope 6.

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