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VIGNANS UNIVERSITY :: VADLAMUDI

EE216 - Electrical Measuremets ! Istrumetati" #EM!I$

UNIT % III

Measuremet "& '"(er a) Eer*+

MID-II

1Mar, uesti"s

1. Dynamometer type wattmeter used to measure---------------------

a. Ac power only b. Dc power only c. both Ac and DC power d .All of these

2. Scale of dynamometer type wattmeter is ---------------------------

a. non uniform b. uniform c. crowded in the beginning d. both b & c

3. n dynamometer type wattmeter! the mo"ing coil is connected-----------------------

a. n series with the fi#ed coil b. Across the supply

c. n series with the load d. Across the load

$. %he pressure coil of induction energy meter is ----------------------

a. highly resisti"e b. highly inducti"e c. highly capaciti"e d. highly inducti"e

& capaciti"e

. f an induction type energy meter runs fast! t can be slow down by ad'usting----------

a. disc b. (ra)ing magnet c. Shunt magnet d. series magnet

*. Damping pro"ided in dynamometer type instrument is -----------------

a. +ddy current b. ,luid friction c. Air friction d. none of the abo"e

. n the two wattmeter method of measuring 3-phase power. %he two wattmeters

indicate e/ual and opposite readings when the load power factor angle is

---------------lagging

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a. *0 deg b.0 deg c.0 deg d.30deg

. Creeping in a single phase induction type energy meter may be due to -------------------

. %ri"ector meter measures-----------

10. %he power in a 3-phase circuit is-----------------------

11. n a 3-phase power measurement by two wattmeter method! both the watt meters had

identical readings. %he power factor of the load was

a. unity b.0. lagging c 0. leading d. ero

12. 4hat is acti"e power5

13. 4hat is meant by reacti"e power5

1$. 4hat is meant by balanced system5

1. 4hat is meant by unbalanced system5

1*. 6ower factor cos7 for 3-phase wattmeter is -------------------------

1. 4hat is the other name for phantom loading -------------------------

1. Draw the circuit diagram for measuring reacti"e power in a 3 phase circuit using

single wattmeter.

1. Draw the circuit diagram for measuring reacti"e power in a 3 phase circuit using two

wattmeters.

20. Dri"ing tor/ue in electro dynamo meter type wattmeter is88888888888

2 Mar, uesti"s

1. 4hat is a meter constant5

2. 4hat is a creeping5

3. 4hat are the errors presented in the energy meters

$. 4hat are the errors in dynamometer type instruments5

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. 4hat is the phase error5

*. 4hat is the a"erage ma#imum demand formula5

. 4hich type of the brea)ing system is used in induction type energy meters5

. 4hat is the compensation used for temperature error5

. 4hat is the registering system5

10. 4hat is the wor)ing principle of dynamometer type wattmeter5

11. 9ention some ad"antages of the dynamometer type wattmeter5

12. 9ention some disad"antages of dynamometer type wattmeter5

. Mar, uesti"s

1. Describe in detail the wor)ing of a tri"ector meter5

2. n a dynamometer wattmeter the mo"ing coil has 00 turns of mean diameter 30

mm. +stimate the tor/ue if the a#is of the field and the mo"ing coils are at: i;

*00 ii; 00when the flu# density produced by field coils is 1 < 10 -3wb=m2! the

current in mo"ing coil is 0.0A and the power factor is 0.**.

3. 4hat is phantom loading5 +#plain with an e#ample how it is more ad"antages

than testing with direct loading.

$. +#plain how power can be measured in a 3 phase circuit with the help of two

wattmeter for a balanced star connected load5

. +#plain the wor)ing of electrodynamometer type wattmeter and also deri"e the

e#pression for deflecting tor/ue.

*. A wattmeter has a current coil of 0.03 > resistance and a pressure coil of *000>

resistance. Calculate the ?error if the watt meter is so connected that

i; %he current coil is on the load side!

ii; %he pressure coil is on the load side

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1. f the load ta)es 20 A at a "oltage of 220 @ and 0.* pf in each case

2. 4hat load current would gi"e e/ual errors with the two conditions.

. +#plain lag ad'ustment and creeping in case of single phase induction type

energy meter.

. +#plain o"erload compensation and temperature compensation in case of single

phase induction type energy meter.

. +#plain the wor)ing principle of single phase induction type energy meter.

10. +#plain the measurement of reacti"e power with single phase watt meters.

1/ Mar, uesti"s

1. a .+#plain the construction and wor)ing principle of single phase induction type energy

meter.

b. An energy meter is designed to ma)e 100 re"olutions of disc for one unit of energy.

Calculate the number of re"olutions made by it when connected to load carrying $0 A at

230@ and 0.$ power factor for an hour. f it actually ma)es 3*0 re"olutions! find the

percentage error.

2. a. +#plain 6, and B6, 4attmeters

b. n a balanced 3-7 system power is measured by %wo-wattmeter method and the

ratio of two wattmeter readings is 2:1. Determine the power factor of the system.

3. a. 4hy ordinary electrodynamometer wattmeter is not suitable for the measurement

of power in circuit with low power factor5 4hat special features are to be

incorporated so as to ma)e it suitable for the same5

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b. +#plain the following ad'ustments that are made in a single phase induction type

energy meter.

i; ag ad'ustment

ii; "erload compensation

iii; Creeping

i"; %emperature compensation

$. a. +#plain the dri"ing system! mo"ing system and bra)ing system in a 1- induction

type energy meter.

b. A 230@ single phase watt hour meter has a constant load of $A passing through it

for *hrs at unity power factor. f the meter disc ma)es 220 re"olutions during this

period! what is the meter constant in re"olutions per )ilowatt hour5 Calculate the

power factor if no. of re"olutions made by the meter are 1$2 when operating at

230" and A for $hrs.

. a +#plain how the measurement of power with wattmeter in con'unction with

instrument transformers can be used in single- phase ac circuits.

b. A 3- phase! $$0@ motor load has a power factor of 0.*. %wo wattmeters connected

to measure the power show the input to be 2 E4. ,ind the reading on each

instrument.

*. a. A 0 A! 230 @ energy meter in a full load test with unity power factor ma)es *1

re"olutions in 3 seconds. f the normal speed of the disc is 20 re"olutions=E4F!

Compute the percentage error

b. +#plain the measurement of 3-phase power with single phase watt meters.

. a. 4hy ma#imum demand meters are used5 +#plain with neat s)etch.

b. 4hat are the different errors occurred in energy meters5 Fow they are

compensated.

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. a; +#plain how a dynamometer G type wattmeter can be used to measure power in a

circuit ha"ing low power factor H6,;5

b; +#plain the design considerations in case of a 6, wattmeter and write short

notes on phantom loading.

a; +#plain the different errors in electrodynamometer watt meters

b; %he power to a 3-6h nduction 9otor was measured by %wo-wattmeter method

and the readings are 3$004 & -12004.calculate the power & power factor.

10. +#plain the different errors and compensation in energy meter.