Paper 3 –Set A Solutions

Regn No: ______

Name: ______

(To be written by the candidates)

NATIONAL CERTIFICATION EXAMINATION 2006

FOR

ENERGY MANAGERS & ENERGY AUDITORS

PAPER – 3: Energy Efficiency in Electrical Utilities
Date: 23.04.2006 Timings: 0930-1230 HRS Duration: 3 HRS Max. Marks: 150

General instructions:

o  Please check that this question paper contains 9 printed pages

o  Please check that this question paper contains 65 questions

o  The question paper is divided into three sections

o  All questions in all three sections are compulsory

o  All parts of a question should be answered at one place

Section – I: OBJECTIVE TYPE Marks: 50 x 1 = 50

(i) Answer all 50 questions

(ii) Each question carries one mark

(iii) Put a (Ö) tick mark in the appropriate box in the answer book

1. / Select the incorrect statement:
In system distribution loss optimization, the various options available include
a) re-routing and re-conducting such feeders and lines where the voltage drops are
higher
b) power factor improvement
c) optimum loading of transformers in the system
d) selection of Aluminium Cored Steel Reinforced (ACSR) lines instead of All Aluminium
Alloy Conductors (AAAC)
2. / A pure capacitive load in an alternating current (AC) circuit draws
a) lagging reactive power b) active power
c) leading reactive power d) none of the above
3. / Select the incorrect statement:
a) harmonics occur as spikes at intervals which are multiples of the supply frequency
b) harmonics are multiples of the fundamental frequency
c) devices that draw sinusoidal currents when a sinusoidal voltage is applied create
harmonics
d) transformers operating near saturation level create harmonics
4. / In a 11 kV feeder, if the voltage is raised from 11 kV to 22 kV for the same loading conditions, the voltage drop in the same feeder system would be lower by a factor of
a) 1/4 b) 1/2 c) 1/3 d) none of the above
5. / A 10 kVAr, 415 V rated power factor capacitor was found to be having terminal supply voltage of 370 V. The capacity of the power factor capacitor at the operating supply voltage would be approximately
a) 10 kVAr b) 9 kVAr c) 8 kVAr d) none of the above
6. / The actual speed of a 2 pole induction motor operating at 49.8 Hz and at a slip of 1.5 % is given by
a) 2955 RPM b) 2980 RPM c) 2943 RPM d) none of the above
7. / Power factor is the ratio of
a) kW/ (kW2+kVAr2)1/2 b) (kW2+kVAr2)1/2/kW
c) kVAr/kW d) kVAr/ (kW2+kVAr2)1/2
8. / The nearest kVAr compensation required for improving the power factor of a 1000 kW load from 0.8 lagging power factor to unity power factor is
a) 500 kVAr b) 750 kVAr c) 1000 kVAr d) none of the above
9. / The approximate size of the capacitor selected for the PF improvement and its installation at the induction motor terminals may be equal to
a) No-load kVAr of motor b) 90% of no-load kVAr of motor
c) full load kVAr of motor d) none of the above
10. / A 7.5 kW, 415 V, 14.5 A, 1460 RPM, 3 phase rated induction motor with full load efficiency of 88% draws 10.1 A and 5.1 kW of input power. The percentage loading of the motor is about
a) 60 % b) 70 % c) 50% d) none of the above
11. / Select the wrong statement:
a) for every 4°C rise in the air inlet temperature of an air compressor, the power
consumption will normally increase by one percentage points for the same output.
b) after-coolers remove the moisture in the air before it enters the next stage of
compressor to reduce the work of compression
c) for every 250 mm WC pressure drop increase across the suction path due to
choked filters etc., the compressor power consumption increases by about 2 percent
for the same output
d) centrifugal compressors are better suited for applications requiring very high
capacities, typically above 12,000 cfm
12. / The reciprocating air compressor efficiency does not depend on
a) discharge pressure b) flow rate
c) suction pressure d) system air leakages
13. / The leak test results show load time of 10 seconds and unload time of 20 seconds in a load-unload reciprocating compressor. If the compressor capacity is 256 cfm, then the approximate leakage would be
a) 85 cfm b) 170 cfm c) 256 cfm d) 128 cfm
14. / Dynamic air compressors are mainly of the following type
a) two stage reciprocating compressors b) centrifugal compressors
c) two stage screw compressors d) none of the above
15. / The flow output of which of the following changes with the discharge pressure
a) screw compressor b) centrifugal compressor
c) reciprocating compressor d) none of the above
16. / Higher chiller COP can be achieved with
a) higher evaporator temperature and lower condensing temperature
b) lower evaporator temperature and higher condensing temperature
c) lower evaporator temperature and lower condensing temperature
d) none of the above
17. / In water cooled refrigeration systems, condenser cooling water temperature should be closest to
a) ambient dry bulb temperature b) ambient wet bulb temperature
c) dew-point temperature d) none of the above
18. / The refrigeration load in TR when 20 m3/hr of water is cooled from a 13 o C to 8 o C is about
a) 33 b) 80.3 c) 39.6 d) none of the above
19. / One ton of refrigeration (TR) is equal to
a) 50.4 kcal/min b) 3516 W c) 200 BTU/min d) all of the above
20. / In a vapour compression refrigeration system, the component where the refrigerant fluid experiences no heat loss or gain is
a) compressor b) condenser c) expansion valve d) evaporator
21. / A fan with 25 cm pulley diameter is driven by a 1470 rpm motor through a v-belt system. If the motor pulley is reduced from 20 cm to 15 cm at the same motor rpm and fan pulley diameter, the fan speed will reduce by
a) 1176 rpm b) 882 rpm c) 294 rpm d) none of the above
22. / For centrifugal fans, the relation between Power (kW) and Speed (N) is given by
a) = b) = c) = d) none of the above
23. / The pressure flow characteristic curve of a centrifugal fan changes with the following flow control method
a) inlet guide vane b) inlet damper c) outlet damper d) none of the above
24. / The hydraulic power of a motor pump set is 6.9 kW. If the power drawn by the motor is 14.0 kW at a 88% efficiency, the pump efficiency is given by
a) 43.4% b) 49.3% c) 56% d) none of the above
25. / Which of the following is not true of air receivers?
a) smoothen pulsating air output b) storage of large volumes of air
c) a source for draining of moisture d) increases the pressure of air
26. / If inlet and outlet water temperatures of a cooling tower are 42oC and 36oC respectively and atmospheric DBT and WBT are 39 oC and 32 oC respectively, then the effectiveness of cooling tower is
a) 85.7% b) 60% c) 75% d) none of the above
27. / The efficiency of forward curved fans compared to backward-inclined fans is__
a) higher b) lower
c) same d) none of the above
28. / The motor efficiency is 0.9 and pump efficiency is 0.6. The power transmitted to the water is 15.11 kW. The input power to the motor driving the pump is about
a) 28.0 kW b) 16.8 kW c) 25.2 kW d) none of the above
29. / What is the impact on flow and head when the impeller of a pump is trimmed?
a) both flow and pump head increases b) both head and flow decreases
c) flow decreases and pump head increases d) none of the above
30. / In a pumping system the static head is 10 m and the dynamic head is 15 m. If the pump speed is doubled, then the total head will be
a) 50 m b) 70 m c) 40 m d) none of the above
31. / Lowering the Cycles of Concentration (C.O.C) in circulating water in a cooling tower, the blow down quantity will
a) increase b) decrease c) not change d) none of the above
32. / A water pump is delivering 200 cubic metres per hour at ambient conditions. The impeller diameter is trimmed by 10%. The water flow at the changed condition is given by
a) 180 m3/hr b) 160 m3/hr c) 140 m3/hr d) none of the above
33. / Which of the following ambient conditions will evaporate maximum amount of water in a cooling tower
a) 40oC DBT and 37oC WBT b) 38 oC DBT and 37 oC WBT
c) 35 oC DBT and 29 oC WBT d) 35 oC DBT and 30 oC WBT
34. / The L/G ratio of a cooling tower does not depend on
a) range b) enthalpy of inlet air
c) outlet wet bulb temperature d) dry bulb temperature
35. / The lowest theoretical temperature to which water can be cooled in a cooling tower is
a) average DBT and WBT of the atmospheric air
b) WBT of the atmospheric air
c) DBT of the atmospheric air
d) difference between DBT and WBT of the atmospheric air
36. / The unit of lux is
a) 1000 lumens per square feet b) 10 lumen per square metre
c) one lumen per square metre d) one lumen per square feet
37. / If voltage is reduced for gas discharge lamps to its optimum value, it will result in
a) reduced power consumption
b) increased power consumption
c) increased light levels
d) no change in power consumption
38. / Which is the most energy efficient lamp?
a) LPSV b) HPMV c) FTL d) GLS
39. / The ratio of luminous flux emitted by a lamp to the power consumed by the lamp is ___.
a) Illuminance b) Lux
c) Luminous Efficacy d) Colour Rendering Index
40. / Which of the following is the best definition of illuminance?
a) time rate of flow of light energy
b) luminous flux incident on an object per unit area
c) flux density emitted from an object without regard for direction
d) flux density emitted from an object in a given direction
41. / Typical exit flue gas temperature of a 5 MW DG set operating above 80% load is in the range of
a) 340 to 370 deg C b) 250 to 280 deg C
c) 200 to 230 deg C d) none of the above
42. / In a DG set, the generator is consuming 150 litre per hour diesel oil. If the specific fuel consumption of this DG set is 0.25 litres/ kWh at that load, then what is the kVA loading of the set at 0.6 PF?
a) 300 kVA b) 600 kVA c) 1000 kVA d) none of the above
43. / The factors affecting Waste Heat Recovery from exhaust flue gases of DG set are:
a) DG set loading
b) Temperature of exhaust flue gases after turbo charger
c) Back pressure on the DG set d) all of the above
44. / The jacket cooling water in a diesel engine flows at 12.9 m3/hr with a range of 10oC and accounts for 30% of the engine input energy. The power output of the engine will be
a) 430 kW b) 500 kW c) 387 kW d) none of the above
45. / The maximum back pressure drop (mmWC) allowed in a DG set is
a) 100-150 b) 150-200 c) 250-300 d) none of the above
46. / The electronic ballast in lighting application does not have one of the following characteristics
a) lower operational losses than conventional ballasts
b) tuned circuit to deliver power at 28-32 KHz
c) requiring a mechanical switch (starter)
d) low temperature rise
47. / Energy savings potential of variable torque applications in comparison to constant torque application is:
a) higher b) lower c) equal d) none of the above
48. / The function of soft starter includes
a) delivers a controlled release of power to the motor
b) provides smooth, stepless acceleration and deceleration.
c) extension of motor life
d) all of the above
49. / The occupancy sensors in a lighting installation are best suited for
a) large production shops/hangars
b) conference halls
c) street lighting
d) entrances of offices/buildings
50. / The blowdown quantity required in cooling towers is given by
a) evaporation loss/ (cycle of concentration –1)
b) (cycle of concentration –1)/ evaporation loss
c) evaporation loss/ (1 - cycle of concentration)
d) evaporation loss/ (cycle of concentration +1)

……. End of Section – I …….

Section – II: SHORT DESCRIPTIVE QUESTIONS Marks: 10 x 5 = 50

(i) Answer all Ten questions

(ii) Each question carries Five marks

S-1 Calculate the transformer total losses for a 100 kVA transformer for an average loading of 40%. Assume no load and full load losses as 1.70 kW and 10.50 kW respectively.

Ans:

Transformer losses = No load losses + (% loading)2 x Full load losses

= 1.70+ (0.4)2 x 10.5

= 3.38 kW

S-2 Fill in the blanks

a)  Slip ring induction motors are normally less efficient than squirrel cage induction motors

b)  Low speed Squirrel cage induction motors are normally less efficient than high speed Squirrel cage induction motors

c)  The capacitor requirement for PF improvement at induction motor terminal increases with decrease in rated speed of the induction motor

d)  Induction motor efficiency increases with increase in its rated capacity