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MCQ on Active Energy Efficiency Using Speed Control Course | energy university schenider electric


What is the main alternative to variable speed control in fan and pump applications?


  • Changing to an interruptable tariff
  • Reducing the operating hours of the equipment
  • Using a valve or damper to adjust the flow
  • None of the above


Electronic Variable Speed Drives


  • Make starting and stopping operations smooth and controlled
  • Minimize inrush currents
  • Convert mains AC supply into a tunable frequency and voltage
  • All of the above


Which of the following is the most common motor starting method available on the market under 10kW (15Hp)?


  • Direct-on-line
  • Star/delta
  • Soft starting
  • None of the above


This starting method progressively increases the motor voltage so that the motor becomes strong enough to accelerate the load to rated speed without causing torque or current peaks.


  • Direct-on-line
  • Star/delta
  • Soft starting
  • None of the above


Which of the following drive and has very accurate speed and torque control?


  • Gear box
  • Frequency converter
  • Eddy current
  • Damper


Which of the following is an advantage of variable speed control?


  • Controlled start and stop
  • Accuracy
  • Mechanical protection
  • All of the above


Chokes, passive filters and C-less drives are used in conjunction with variable speed drives to reduce the effects of what?


  • Harmonics
  • Belts
  • Linear loads
  • Input shafts


Using variable speed drives, the highest potential energy savings can be found on


  • C-less drives, DC chokes, and passive filters
  • AC chokes, multi-pulse drives, and active filters
  • Pumps, fans and compressors
  • Hoisting, Conveyors, generators


Which of the following conditions have the potential to negate the value of a variable speed drive?


  • Energy is very cheap
  • Valves or dampers are normally set in a fully open position
  • Payback period or internal rate of return that does not meet company financial criteria
  • All of the above


An energy saving opportunity is identified on a fan installation. The flow from the fan can be reduced from 100% of nominal output to 75%. According to the affinity laws, how much power will be saved at this output, compared to the power used to supply 100% of the flow?"


  • 25%
  • 40%
  • 58%
  • 75%


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Active Energy Efficiency Using Speed Control Course


At the completion of the  Active Energy Efficiency Using Speed Control Course , you will be able to: 
  • Identify main motor starting methods 
  • Recognize the frequency converter principle and its advantages 
  • Realize substantial energy savings using speed control 
  • Reduce harmonic distortion generated by frequency converters 
  • Calculate the payback of an investment in a variable speed drive 


Many motors only have two settings: on and off. They operate at constant speed. If a motor turning at constant speed is driving a device or process that requires less output, adjustments are required to achieve the desired output level. This adjustment is often achieved by letting the motor run at full speed, while using downstream devices to block part of the output.

Active Energy Efficiency Using Speed Control Course MCQ Answers | energy university schenider electric

For fan applications, we have motors generating a full flow of air, and we use dampers to partially block and reduce the flow. For pump applications, we have motors generating a full flow of fluid, and we use dampers to partially block and reduce the flow. Energy is used to generate the output and then it is immediately thrown away.

This is like driving your car by having one foot fully depressing the accelerator pedal, and the other on the brake to constantly control the speed. It sounds absurd, but this is still one of the most common control methods. An estimated 60% of motors are not speed controlled.

The focus of this course is to explore the different ways we can control motor speed efficiently and with minimal physical stress on equipment. In addition, we'll discuss other advantages such as controlled starting and regulated torque.

Summary of Active Energy Efficiency Using Speed Control


Many types of equipment can benefit from proper speed control - from pumps and fans to compressors and other machines.

Due to associated costs, traditional direct-on-line starting is the most common starting method on the market today. There are many compelling reasons to consider other starting options, however.

These include benefits such as smooth starting and stopping, minimized inrush currents, and electrical efficiency. While soft starters avoid the mechanical stress associated with direct-on-line starting, nothing enables mastery of torque and speed the way variable speed drives do.

Despite all the advantages of variable speed drives, at least 60% of all motors are still not speed controlled.

For Pumping systems, a variable speed drive can save 20% to 50% depending on the operating cycle and average flow.

Applying variable speed drives to ventilation systems creates 20% to 70% in energy savings! In fact, a variable speed drive generally pays for itself in 1 to 2.5 years.

 If dampers are fixed and air or water flow rarely needs to change, it will be difficult to justify investment in a variable speed drive - A VSDs advantage lies in its ability to operate the motor at a varying rates.

Variable speed drives are non-linear loads and can therefore create harmonic distortion. Harmonics can overload the rectifier bridge and drive capacitors.

As a result filters are often embedded within the drive or connected externally in order to mitigate the damage harmonics can cause.

The construction, cost, and effectiveness of harmonics mitigating equipment can vary. Harmonic filtering effectiveness is expressed in terms of THDi rating.

The savings associated with variable speed drives is as dramatic as upgrading to new generation lighting.

Speed control savings are ready to be realized. Using tools such as Schneider Electric’s Energy Consumption Simulator and ECO2 Energy Calculator can quantify VSD savings before any investments are made.

معلومات ومصطلحات مهمة لفهم كورس كفاءة الطاقة الفعالة باستخدام التحكم في السرعة
  • ما هو Chokes : هو صمام خانق وأحد مكونات الPassive filter
  • معني Conveyor system: هو نظام نقل للمعدات والادوات مثل سير نقل المعدات والمنتجات في المصانع
  • ما هو actuator مشغل : الة تستخدم لتحريك جزء صغير او محرك صغير
  • شرح VAV box : نوع من انظمة التبريد والتدفئة وعند درجة حرارة معينة يختلف تدفق الهواء باختلاف انظمة التبريد الاخري
  • معني damper خانق الهواء  : هو صمام او شبكة تنظم تدفق الهواء داخل قنوات التبريد والتكيف
  • ما هو throttling : هو خنق نطاق معين بغرض تقليل سرعته مثلا   



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