SHREE DATTA SHETKARI SAHAKARI KARKHANA LTD. CHARITABLE TRUST SHREE DATTA POLYTECHNIC COLLEGE, DATTANAGAR CLASS TEST-01

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1 SHREE DATTA SHETKARI SAHAKARI KARKHANA LTD. CHARITABLE TRUST SHREE DATTA POLYTECHNIC COLLEGE, DATTANAGAR CLASS TEST-01 Name of subject: Elect. & electronic Measurement Mark: 25 Institute Code: 1512 Subject Code Course Code: EE3G Time: 01:00 hr Q.1 Attempt any two of following 8 marks a) Draw the constructional diagram of PMMC instrument? Write down the equation for Td & Tc in case of PMMC meters? F=NBIL this force acts in opposite direction on two coil sides producing the deflecting torque it is given by formula =NBIL * 2r = (2r NBIL) I = * I AND * θ = cpring control constant

2 b) Compare PMMC & MI instrument? ANS= POINT MI POINT PMMC scale non- uniform uniform cost cheaper for same range higher cost for same range application used for ac and dc used for only dc measurements sensitivity less as compared to pmmc much sensitive than mi damping air friction is used eddy current damping is used c) A moving coil instrument giues full scale deflection of 24 ma when p. d. across it is 72 mv calculatea) Shunt resistance of full scale deflection of 120 amp b) The series resistance of full scale deflection of 600 volt c) Find power consumption in each case given: i=24ma=24* A V=72 mv = 72* V Ra= Rv=72/24=3 Ω a) I=120 A there for s=? * Ra = * 3 = 6 * Ω b) V=600 V Rm=? Rm= -Rv Rm = 3 = Ω =24.9 KΩ c) Is= I- I = = A Ps= S Watts = * (6* ) = 8.64 watt PRm= Rm watt = (24* ) * = watt

3 d)draw the connection diagrams of CT and PT and label their various connections? ans:- Q.2 Attempt any two of following 8 marks a) What is power factor? What is the p.f. value of pure capacitance? = power factor is the ratio of true power and apparent power Power factor= Substituting the expressions for P and S we get power factor= = cos θ value for pure capacitance= power factor = 0< p.f. +1 b)explain with neat diagram working principle of electro dynamometer type wattmeter and construction?

4 WORKING PRINCIPLE- current carrying moving coil is placed in the magnetic field produced by the two fixed coils hence force is exerted over the moving coil which is given as F=BILsin θ where F= force exerted on moving coil B= flux density in wb I = current in amps L = active length of conductor in m This force exerted dives the deflection of pointer proportional to the power consumption in load CONSTRUCTION- the construction of this meter is same as that off dynamometer type ammeter and voltmeter it consists of two identical fixed coils in the air gap between these fixed coils, moving coil is placed which is attach to spindle the fixed coil of meter is connected in series with the load and is known as current coil. its terminal are marked as M and L to living the current flowing through moving coil a high resistance is connected in series with the moving coil and its circuit is made pure resistive this coil is known as voltage coil or pressure coil and its terminals are marked as C and V this coil is connected parallel with load spring control is used to produce controlling torque b) Explain the term reactive power? Why the sometimes essential to measure reactive power of given circuit? Ans.The reactive power is defined as the product of v, I & sinǿ reactive power Q = VI sinǿ The reactive power is also called as imaginary power & it is expressed in VAR or KVAR. I sinǿ represents the quadrature component of I.it is 90 phase shifted with respect to the reference vector V. Reactive power is a part of total power which is not consumed by the load. Reactive power simply travels from source to load & back from load to source It is therefore the useless power & hence should be minimised. The energy meter installed to measure energy consumption.do not measure reactive power. With increase in reactive part of the load impeadence,the reactive power increases. Increases in reactive power causes the reduction in power factor there are several disadvantages of poor power factor.the supply utility system has decided to pay incentive on charge penalties if part of consumer increases or decreases beyond certain limits.therefore it is essential to measure the reactive power so that corrective measures can be taken accordingly to maintain systems power factor closest to the unity.

5 c) Draw neat circuit diagram and phasor diagram for measurement of power by two wattmeter methods in 3 phase star connected load and derive the relation of two wattmeter reading? =

Q.3 Attempt any three of following 9 marks a) Draw a neat circuit diagram and phasor diagram for measurement of reactive power in 3 phase balanced star

Ans-Multiplying Factor is the ratio of product of range of current coil & range of voltage coil to Maximum calibrated reading on scale.

6 Q.3 Attempt any three of following 9 marks a) Draw a neat circuit diagram and phasor diagram for measurement of reactive power in 3 phase balanced star connected load by one wattmeter? b) State multiplying factor of wattmeter? Ans-Multiplying Factor is the ratio of product of range of current coil & range of voltage coil to Maximum calibrated reading on scale. Multiplying Factor= range of current coil * range of voltage coil Maximum calibrated reading on scale. c) A single phase wattmeter rated for 500V,5A is having full scale deflection of 1000 watt what is the multiplying factor of the wattmeter?

Ans-Multiplying Factor= range of current coil * range of voltage coil Maximum calibrated reading on scale. = (500 * 5) / 1000 =2500/1000 Multiplying Factor = 2.

7 Ans-Multiplying Factor= range of current coil * range of voltage coil Maximum calibrated reading on scale. = (500 * 5) / 1000 =2500/1000 Multiplying Factor = 2.5 Ans d) State any four drawbacks of low power factor? Ans- Drawbacks of low power factor 1.Reactive power increase 2. Total current drawn by load increase 3.copper loss increase 4.High Maximum demand For same amount of power used. 5.Power handling capacity of system reduces. d) Draw a neat sketch of measurement of reactive power in 3 phase balanced load by two wattmeter method. State formula? The power factor in the two wattmeter method, W1-W2= V L I L SINɸ (1) Total reactive Volt-Ampere in a 3ɸ circuit is given by, Q = V L I L SINɸ (2)

8 But V L I L SINɸ = W1-W2 Therefore Q = (W1-W2) Thus we can obtain the reactive power by multiplying the difference between the reading of two wattmeter by Best Luck

Work, Energy and Power

1 Work, Energy and Power Work is an activity of force and movement in the direction of force (Joules) Energy is the capacity for doing work (Joules) Power is the rate of using energy (Watt) P = W / t,