Electrical Drive System

Electrical Drive System

The electrical drive system is an electromechanical system, which operates through the conversion of electrical energy into mechanical energy. During this process, the mechanical motion produced, impact motion on the device connected to it. However, all drive system has a prime mover which helps in the transmission of energy on the mechanical load. For an electrical drive system, the electric motor act as the prime mover. 

The electric motor helps in the electrical to mechanical energy conversion. Moreover, for any drive system with a prime mover, the prime can be an internal combustion engine( Diesel engine or petrol engine and the form of the engine used depends on the burning of fuel). Again, the prime movers could be a turbine, a steam engine or an electric motor. With this line of discussion, I will be talking on the electric motor.

Therefore, if a system is driven by an electric motor as its prime mover, that system is called an electrical drive system. In our world today, the electrical drive has a huge impact, with numerous advantages. Let’s see some of its advantages, as to why it’s important as a means of driving different machines for various kind of processes.

Advantages of an Electrical Drive System 

  • The control characteristics of this type of drive system are very flexible, this implies that changes can be made to suit the individual wants.
  • Unlike others, the electrical drive system has an easy starting and breaking medium 
  • Considering torque and speed, as we know, torque is the rotational force produced. For this type of drive system, the torque produced is more than the speed, having a wide range of torque to speed. For this reason, it can operate on any quadrant of the torque to speed plane.
  • The operational power of an electrical drive can be of several ratings. Its goes as low as a fraction of KW to a high power rating of more than 100KW.
  • It’s not affected by climate change, so it can literally operate at any environmental conditions, but this depends on its types.
  • Unlike drives that use an internal combustion engine as a means of drive. The electrical drive system doesn’t produce any form of exhaust gas, as such the system isn’t harmful to humans.
  • The point of starting and accelerating point of an electrical drive system is within a very short time. This implies that, when you start up any electrical drive machine, the point you start it and as to when it gains is the maximum speed, is within a very short time.

Factors affecting the choice of Electrical Drive System.

Choosing the electrical drive system over other forms of the drive system is factored on the following;

The reliability of the system: This reliability consideration is the probability of the system to be functional at a particular point in time but under stated conditions of the system.

The mode of power supply: Since the electrical drive system, needs electrical energy to be converted into mechanical electrical. This energy can either be a direct current source (DC) or alternating current source (AC). This mode of power supply depends on what you want and the system you need it to operate on. However, both have their individual advantages.

Cost: The cost of getting an electrical drive machine varies and it depends on the power rating of the system. Again, the cost of running and maintaining the system is something to lay consideration.

To torque to speed characteristics of the machine depends on the rotational force needed to execute the required function. The speed regulation, speed range and the efficiency of the drive system, is also to be considered.

Type of Electrical drive system 

There are several types of drive systems. However, these types of the drive system are classified based on the following;

  • Drilling mechanism 
  • Mode of supply 
  • Based on speed

So let’s talk more about the following classification.

According to the drilling mechanism 

Under this classification, a drive system can be seen as;

Individual drive: This form of system, implies that each machine that needs a rotational impact, has individual drive running it. In other words, they are not grouped or operated by one drive system. This’s the reason why it’s called an individual drive system. However, this type of system has a better flexibility control, as changes can be made without even altering other machines. Again during any form of fault in one system, and since they are not connected together, there will still be continuity in operation. Moreover, since each machine has its own drive, the initial cost(capital) will be very high. 

Group drive: From the name already, one that easily tells that the system is grouped together. Here, one prime mover drives a number of machines grouped together, through a common shaft. Moreover, since they are grouped together and operated by just one drive system, the initial cost is less compared with the individual drive system. Since all machines do not operate at the same time, the horsepower rating of the drive is lesser, compared to that of the individual sum of the machines. Most importantly, in a group drive system, the load capacity is high.

Limitations

However, in a group drive system, there are some limitations to it. These include speed control characteristics. Since they are grouped together, and let’s say you need one of the machines to run at a speed higher than the initial. Here, this can’t be achieved because of their grouping and as such the layout of this type of drive system isn’t flexible. Again, since they are all grouped, a fault or breakdown on the drive system will result in a total breakdown of operation. This will lead to a discontinuity of supply in the system. In addition to these limitations, the installation capacity of this type of drive is limited.

For cases where the stoppage of one operation, will lead to a stoppage of a sequence of operation, in such case, the group drive system is required. 

Multiple drives: This type of drive system, has both the individual drive system and group drive system combined together. Here each machine can either be driven by several drive systems in one unit. Here, both the advantages and disadvantages of the individual and grouped drive system are to be considered.

According to mode supply 

I said earlier that the electrical drive system has to convert electrical energy into mechanical energy. This electrical energy can be of different forms, which can either be Alternating current(AC) or Direct current(DC). However, both have different operating energy level.

AC drive system: Here, the prime mover is powered by an alternating current, which can be a single-phase AC or a three-phase system. This type of drive system includes; induction machines, synchronous machines or special machines. However, in most industries, the induction motor is commonly used and this is due to the fact that induction motors are cheap to acquire, almost indestructible and rugged.

DC Drive system: Here, the prime mover is powered by a direct current. However, no phase changes in this type of drive system. They can be gotten from batterie, which produces DC as its output. Also from rectifiers, this device converts alternating form of energy to a direct form of energy. The DC drive system includes; Compound motor, Series motor, and compound motor. However, some special kinds of machines can also be classified as a DC drive system.

According to speed 

The electrical drive system can be classified based on their speed, it can either be a constant speed or variable speed signal drive system. 

Constant speed: The operating speed of the drive is constant. This implies that the speed operates on a single speed and this speed is usually the machines rated speed level. Constant speed electrical drive system includes; induction motors and shunt DC motors.

Variable speed: The speed of this type of electrical system varies. They don’t operate on a single-speed, unlike the constant speed. This type of drive system includes; the DC motor and some special AC motors.

The element of an Electrical Drive System 

Block diagram of electrical drive system
Block diagram of a typical electrical drive system

The above diagram shows the block diagram of a typical electrical drive system. I will explain each block segment, their functions also. Back in school, we were asked as part of our exam question, to draw and explain the elements of an electrical drive system. So if probably you are asked in school, this will really be helpful.

Power source: A drive system needs a source to operate. However, for an electrical drive system, a power source will be required. This power source can either be a single-phase or three-phase, to power the system. It’s important to note that, without a power source in a drive system, the system will be as good as not working. So we can literally say that the power source in this type of drive, act as the main heart of the system.

Power modulator: This block segment, what it does is to take the output from the power source, and change the characteristics of the source to suit that of the drive system. This is needed because most at times, you might be having an AC power source and what your drive system needs are a DC power source. So the power modulator will help you convert the AC source to a DC source. The power modulator is more of a converter and they could be an inverter, voltage regulator, rectifier, DC chopper.

Explanation

Controller: One can deduce from its name that, the controller just helps to control the system. True though but what it simply does is that, it takes the system variable, monitors and compares if it suits that required by the system. It can as well adjust the output of the regulator to achieve the system desired performance.

Electric motor: This segment is our base of discussion, it simply converts the electrical energy to mechanical energy. However, the rotation produced by the motor could either be rotational or linear motion.

Mechanical load: This can be seen as the machine or mechanism and they include; pumps, fan, robots and many more. The mechanical load can be classified as active or passive loads. 

Active loads are loads that can’t drive the motor under equilibrium condition, and examples are pumps.

Passive loads are loads that can drive the motor under equilibrium condition, this process is more of a reverse process and they include; lifts, elevators and locomotive trains.

Component of the Torque produced in the electrical drive system.

  • Frictional torque: This torque produced is the sum of vicious friction, column friction and additional torque at stand still.
  • Mechanical or useful torque
  • Windage torque

However, the general torque equation is the summation of all the torques listed above.

Torque equation

mechanical load system
mechanical load system

From the diagram above, the motor is connected to the load through a shaft. The motor drives the load through a transmission system. The rotational motion of the motor can result in either a rotational or translational motion on the load. However, the torque produced by the motor can be represented by the equivalent sum of the torque exacted on the shaft and load. Most importantly, the motor load system can be represented as a rotational system.

Where;

J represents the moment of initial of the system 

{T}_{m} stands for the motor torque (Nm)

{T}_{L} represent the load torque 

The load torque and the moment of initial are referred to the rotor shaft. However, the following should be noted;

When the torque produced by the motor is greater than that produced by the load {T}_{m}> {T}_{L}. Then the angular change of speed with respect to time is greater than zero. At this condition, the electrical drive is accelerating.

For cases where the torque produced by the motor is less than that produced by the load {T}_{m}< {T}_{L}. Then the angular change of speed with respect to time is less than zero. This implies that the electrical drive is decelerating.

If the torque produced by the motor is equal to that produced by the load {T}_{m}< {T}_{L}. Then the angular change of speed with respect to time is zero. Therefore the motor is running at a constant speed. 

Electrical drive system impacts motion on the load through a transmission system. There are several types of drive transmission for which motion is being impacted on the load. The selection of a drive transmission system is based on consideration. 

Type of drive transmission 

  • Direct drive 
  • Belt drive 
  • Rope drive 
  • Gear drive
  • Chain drive 

Let’s discuss some!

Direct drive system: Here, the prime mover is directly connected to the driven member without any interposed gear in between. Therefore a universal joint is employed. This type of drive system of transmission has very high efficiency. Coupled with the fact that, the speed and drive mechanism is the same. In addition to its advantages, is that the direct-drive system is fairly Economical, occupies less space compared to others and has an accurate alignment.

Belt drive system: In this type of drive transmission, a belt is used to connect the drive member to the drive. Belts don’t cost much to purchase, so this type of drive transmission is also economical. Among its advantages, is that it has great applications in cases where the change speed of the drive can be altered. Moreover, the belt drive can either be a flat belt or a V-belt.

Advantages of Belt Drive Transmission

Most Drive system uses this type of drive transmission because of the following reasons:

  • It has great flexibility because let’s say the belt becomes faulty, it can be subjected to an easy change.
  • Under heavy load, it can protect the drive and the drive member from slipping.
  • The speed ratio can be altered to meet one’s desire. Let’s say you are running a machine whose speed is 1500rpm and what you desire is 3000rpm. With this very type of drive transmission, you can reduce the diameter where the belt rests on, to achieve your desired speed.
  • Although, despite its advantages, there are also some limitations to it. This type of drive transmission requires more space. Again the maximum power when using this type of drive transmission is limited to 150-220KW. So for a higher rating, this very type can’t be used.

However, the belt drive system is only economical for low-speed application. So for high-speed applications, you will have to spend more to get it. In addition to its limitations, the belt drive transmission system is not as efficient as the direct drive. This is because 3-4% (percentage)  of the transmission power is lost due to slip on the belt.

Rope drive: This type of drive system is way similar to the belt drive transmission system, just that it can take more power, even beyond that of the belt drive transmission system.

Application of Electrical Drive system 

This type of drive system has both domestic applications and as well as industrial applications.

Industrial applications;

  • Crusher
  • Conveyor 
  • Elevator
  • Escalator 
  • Traction 
  • Push 
  • Hoist e.t.c

Domestic applications;

  • Mixer
  • Microwave 
  • Fans
  • Electrical Blender
  • Washing machine 
  • CD player 
  • Fridge e.t.c

You can learn more on Electrical/Electronic Engineering, by checking our Electrical/Electronic Engineering category, you can find this under Academic page. Thanks for coming around.

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