Hello fellow technicians, today we will be discussing a crucial topic in the world of PLC programming - the empirical formula for judging the direct start of a motor. As professionals, we know how important it is to have a smooth and efficient start for our motors. A direct start, also known as a full voltage start, is when the motor is started at its full rated voltage. It may seem simple, but judging the direct start of a motor requires a bit of calculation and knowledge. Let's dive in and explore this formula in detail.
What is an empirical formula?
Before we dive into the specific formula for judging direct start, let's first understand what an empirical formula is. In simple terms, it is a formula based on observation and experience, rather than theory. In the case of PLC programming, it is a formula that has been tried and tested and has proven to be effective in judging the direct start of a motor.
The formula
Now, let's get to the formula itself. The empirical formula for judging the direct start of a motor is as follows:
Voltage Drop Percentage = (Inrush current - Rated current) / Rated current x 100
This may seem like a mouthful, but let's break it down step by step.
Step 1: Determine the inrush current
The first step is to determine the inrush current of the motor. Inrush current is the initial surge of current that flows through the motor when it is first started. It is important to note that the inrush current is always higher than the rated current of the motor. This is because the motor requires an extra burst of energy to overcome inertia and start moving.
Step 2: Determine the rated current
The next step is to determine the rated current of the motor. This can be found on the motor nameplate or in the motor specifications provided by the manufacturer. The rated current is the maximum continuous current that the motor can safely handle without overheating or damaging itself.
Step 3: Calculate the voltage drop percentage
Now, with the inrush current and rated current in hand, we can calculate the voltage drop percentage using the formula mentioned above. The resulting number will give us an indication of how much voltage drop is happening during the direct start of the motor.
Interpreting the results
The final step is to interpret the results of the formula. The general rule is that a voltage drop percentage of less than 10% is acceptable for most motors. However, for larger motors and those that require precise control, a voltage drop percentage of less than 5% is recommended. If the percentage is higher than 10%, it means that the motor is experiencing a significant voltage drop, which can affect its performance and may eventually lead to motor failure.
Application of the formula
Now that we have an understanding of the formula, let's see how it can be applied in real-life scenarios. For example, let's say we have a motor with an inrush current of 20 amps and a rated current of 15 amps. Plugging these numbers into the formula, we get a voltage drop percentage of (20-15)/15 x 100 = 33%. This is a significant voltage drop, which indicates that the motor may experience performance issues and may require additional measures such as a soft start or a motor starter to alleviate the voltage drop.
Conclusion
In conclusion, the empirical formula for judging the direct start of a motor is a valuable tool for ensuring smooth and efficient motor operations. By determining the voltage drop percentage, we can identify potential issues and take necessary actions to prevent motor failure. As professional technicians, it is our responsibility to use this formula and other tools at our disposal to ensure the proper functioning of our systems. I hope this article has provided you with a better understanding of the formula and its application. Happy programming!