Learn Electrical Drive Online Free | VFD's for 3-Phase Motor

THEORY

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive, and inverter.

Frequency (or hertz) is directly related to the motor’s speed (RPMs).

 In other words, the faster the frequency, the faster the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement.

Working of Variable Frequency Drive

The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is comprised of six diodes, which are similar to check valves used in plumbing systems. They allow current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing systems) is more positive than B or C phase voltages, then that diode will open and allow current to flow. When B-phase becomes more positive than A-phase, then the B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the negative side of the bus. Thus, we get six current “pulses” as each diode opens and closes. This is called a “six-pulse VFD”, which is the standard configuration for current Variable Frequency Drives.AC Motor

The AC electric motor used in a VFD system is usually a three-phase induction motor. Some types of single-phase motors can be used, but three-phase motors are usually preferred. Various types of synchronous motors offer advantages in some situations, but three-phase induction motors are suitable for most purposes and are generally the most economical motor choice.

Let us assume that the drive is operating on a 480V power system. The 480V rating is “rms” or root-mean-squared. The peaks on a 480V system are 679V. As you can see, the VFD dc bus has a dc voltage with an AC ripple. The voltage runs between approximately 580V and 680V.

We can get rid of the AC ripple on the DC bus by adding a capacitor. A capacitor operates in a similar fashion to a reservoir or accumulator in a plumbing system. This capacitor absorbs the ac ripple and delivers a smooth dc voltage. The AC ripple on the DC bus is typically less than 3 Volts. Thus, the voltage on the DC bus becomes “approximately” 650VDC. The actual voltage will depend on the voltage level of the AC line feeding the drive, the level of voltage unbalance on the power system, the motor load, the impedance of the power system, and any reactors or harmonic filters on the drive.

The diode bridge converter that converts AC-to-DC, is sometimes just referred to as a converter. The converter that converts the dc back to ac is also a converter, but to distinguish it from the diode converter, it is usually referred to as an “inverter”. It has become common in the industry to refer to any DC-to-AC converter as an inverter.

When we close one of the top switches in the inverter, that phase of the motor is connected to the positive dc bus and the voltage on that phase becomes positive. When we close one of the bottom switches in the converter, that phase is connected to the negative dc bus and becomes negative. Thus, we can make any phase on the motor become positive or negative at will and can thus generate any frequency that we want. So, we can make any phase be positive, negative, or zero.

Notice that the output from the VFD is a “rectangular” wave form. VFD’s do not produce a sinusoidal output. This rectangular waveform would not be a good choice for a general purpose distribution system, but is perfectly adequate for a motor.

If we want to reduce the motor frequency to 30 Hz, then we simply switch the inverter output transistors more slowly. But, if we reduce the frequency to 30Hz, then we must also reduce the voltage to 240V in order to maintain the V/Hz ratio (see the VFD Motor Theory presentation for more on this). How are we going to reduce the voltage if the only voltage we have is 650VDC?

This is called Pulse Width Modulation or PWM. Imagine that we could control the pressure in a water line by turning the valve on and off at a high rate of speed. While this would not be practical for plumbing systems, it works very well for VFD’s. Notice that during the first half cycle, the voltage is ON half the time and OFF half the time. Thus, the average voltage is half of 480V or 240V. By pulsing the output, we can achieve any average voltage on the output of the VFD.

With the above theory a basic understanding of the Voltage Frequency Drive.

To get more into detail ,please see the youtube video of the actual trainer

Hope you like my vieos,dont forget to like and subscribe there are more than 19 videos on the different technologies of electrical drives

Learn Arduino Programming | Connecting LCD with Arduino

Arduino UNO Tutorial 10 - LCD 

We are now going to add an LCD display to our Arduino. The Arduino IDE comes with an example LCD sketch which uses an Hitachi HD44780 compatible LCD. We will use a similar LCD (Pololu 16x2 Character LCD 773 or 772)

We are going to use JHD162 LCD which is 16X 2 LCD. 

Link for the datasheet is

http://www.datasheetspdf.com/PDF/JHD162A/512991/1

The contrast pin on the LCD requires a fairly small voltage for ideal display conditions,here we have connected a fixed resistance. The lower the voltage the higher the contrast and vice versa. A voltage of approx 0.5V to 1V is about right, but depends on the ambient temperature. 

Here are the pinouts from the LCD and the corresponding pin connection on the Arduino

LCD Pin	Symbol	Function	Arduino Pin
1	Vss	ground (0 V)	ground (0 V)
2	Vdd	power (4.5 – 5.5 V)	+5V
3	Vo	contrast adjustment	9
4	RS	H/L register select signal	12
5	R/W	H/L read/write signal	ground (0 V)
6	E	H/L enable signal	11
11	DB4	H/L data bus for 4-bit mode	5
12	DB5	H/L data bus for 4--bit mode	4
13	DB6	H/L data bus for 4-bit mode	3
14	DB7	H/L data bus for 4-bit mode	2

And here is the Arduino Sketch. The PWM output to control the contrast is done in the setup routine, however, if you wanted to be able to control the contrast manually, then the addition of two push buttons and a bit more coding would allow you to increase and decrease the contrast in simple steps within the program.

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup() {
  // declare pin 9 to be an output:
  pinMode(9, OUTPUT);  
  analogWrite(9, 50);   
  // set up the LCD's number of columns and rows: 
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.print("  HobbyTronics");
}

void loop() {
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(0, 1);
  // print the number of seconds since reset:
  lcd.print(millis()/1000);
}

Hope you like it!

Step by Step Youtube Video coming up soon.

Learn Online | Electrical | Kit Kat Fuse Wire

Electrical Fuses : Their Types & Applications


The basic purpose of the fuse is to protect and is composed of an alloy which has a low melting point. A strip of this fuse is placed in series with the circuit. The working principle is that if the current is in excess then the strip would melt and break the circuit. There are different variants of fuse boxes available with different types of circuit breaking. For instance, in the case of slow blow fuses, a small overload is carried for some period without the circuit been broken.
Other fuse boxes are designed to break the circuit rapidly. The selection is based upon the kind of device and also the fluctuation level of the current.

Types
The main components of a standard fuse unit consist of the following items:
Metal fuse element
Set of contacts
Support body
The major two categories of fuses include:
Low Voltage Fuses
High Voltage Fuses
In order to understand Low voltage fuses better, we can further classify it further into:
Semi Enclosed or Rewireable Type
Totally enclosed or Cartridge Type


Rewireable Fuses

 
This kind of fuse is most commonly used in the case of domestic wiring and small scale usage. Another name for this type is the KIT-KAT type fuse. The main composition is of a porcelain base which holds the wires.
The fuse element is located inside a carrier that is also made out of porcelain. It is possible for you to remove the fuse carrier without any risk of electrical shock. Normally what happens is that when the fuse blows, you can replace it without having to change the complete thing.
The main metals or alloys used in making fuse wire include lead, tinned copper, aluminum or tin lead alloy.

Electrical Fuses Their Types and Applications 3
When there is an over surge that causes the fuse element to blow off, you can replace it. A new fuse carrier is inserted in the base.


The main advantage of this type of fuse is that it is easy to install and also replace without risking any electrical injury. But there are certain shortcomings associated with it too. For instance, with this fuse you would have an element of unreliability. There is a level of lack of discrimination and a small time lag, which may hinder its functionality.
With a slow speed of operation, you also get a low rupturing capacity.
Other types have current limiting features, and this one does not.
All this being said it is still a valuable fuse device for small scale usage.




How to check the fuses?



In order to check the fuse, a probe is used with readings from the terminals. The correct functioning would be when the value is 0V DC. The fuse should be checked with the voltage being supplied.

In cases, the value you are getting is higher than 0V DC, this means than there is a need to remove it.
Usage

The main usage of fuse is for the protection of the circuit. In a real term scenario, the current flowing through the wires may not be uniform at times. In such cases, your device could get overheated. There is also the chance of a fire if the fuse is not installed.

To learn this concept, we have a testing apparatus for fuses.

We are using a kit kat fuse here.The apparatus generates a current   upto 20A controlled by the variac in series with the fuse. 

The setup also trips the circuit,and automatically measures the time it takes to trip at a set current.

To learn more about working on the panel ,see the youtube video below

Three Phase Power Measurement by Two Wattmeter Method (theory and practical)

Two Wattmeter Method of Power Measurement

Two Wattmeter Method can be employed to measure the power in a 3 phase, 3 wire star or delta connected balanced or unbalanced load. In Two wattmeter method the current coils of the wattmeter are connected with any two lines, say R and Y and the potential coil of each wattmeter is joined across the same line, the third line i.e. B as shown below in the figure A.

The total instantaneous power absorbed by the three loads Z1, Z2 and Z3, are equal to the sum of the powers measured by the Two wattmeters, W1 and W2.

To explain the above concept practically,the youtube video shows a working panel in which there are Analog Wattmeters (lagging and leading ),resistive load with required ammeter and voltmeter.

The readings are taken by applying the load using switches and the reading are noted down in a table and results are compared theoretically and practically.

Happy Learning!

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