Experiencing overvoltage issues on a drive may indicate that the blowers are not starting simultaneously, resulting in one blower assisting the other during startup. This could trigger Regeneration (Regen) mode until both blowers reach the same speed. To address this issue, consider avoiding the use of 4 quadrant Regen mode on the VFD to prevent energy absorption for slowing down or syncing the blowers. Installing a Bus Loader or DB resistor could help eliminate overvoltage. It is crucial to set the current limit to no more than 125% to prevent equipment damage, as exceeding 200% poses a risk. When dealing with Flying Starts, it is essential to understand their operation thoroughly. Some videos start at the lowest frequency and gradually increase speed, while others begin at top speed and reduce frequency until motor synchronization is achieved. Consulting with drive engineers is recommended for a better understanding of these processes. Feel free to share your progress with us.
GaryS questioned the decision to set the current limit to 200%, noting that it should never exceed 125% to prevent equipment damage. However, it is permissible to temporarily increase the motor current above its nominal value. It is essential to ensure the motor is adequately protected, either through the motor model in the drive or by using a thermistor, especially for equipment controlled by a Variable Frequency Drive (VFD). (Please note that I do not have experience with flying start.)
Initiating large diameter centrifugal fans can be a challenging task due to the turbine's high inertia and energy accumulation. It demands significant torque, time, and a high current to reach the desired revolutions. Achieving an acceleration ramp of 1 second may seem unattainable, as some fans may take up to 20 seconds to start even with a higher power output of approximately 50kW. The key solution always lies in extending the acceleration ramps. Moreover, if the fan has a belt transmission system, the challenges intensify as attempting to accelerate too quickly can result in belt slippage, leading to a loud and unpleasant noise.
Thank you for all the responses! I will address the questions by bulleting as many answers as possible.- What is the purpose of a flying restart? *The need for a flying restart arises from the variably timed process. If a product does not arrive within 5 minutes, the blowers time out and shut down. Meanwhile, the Warehouse Management System (WMS) sends a request for a robot pick, requiring the blowers to spin back up immediately.- Is a 1-second ramp achievable? *It may seem impossible as timing a few starts resulted in around 4.5 seconds. I adjusted the acceleration ramp to 6 seconds on all Variable Frequency Drives (VFDs) to achieve the desired ramp, but experienced a fault this morning, indicating it may not solve the issue.- Why coast to stop? *Initially, the drives were set to ramp to stop. Testing revealed that the drives would fault when given a run command while still ramping down. I will try reverting a pair back to ramp deceleration to assess the results.- Concerns about drives not starting together. *Although both drives receive a run command simultaneously, they tend to fault together due to bus overvoltage. - Disabling 4 quad mode on drives to prevent energy absorption. *I am uncertain how to accomplish this on the Powerflex525.- The current limit for flying restart torque is 200%, while the actual Overload (OL) current limit is 125%.- The system may have been poorly engineered. All drives were auto-tuned to their respective motors. - Considering adjusting the carrier frequency and possibly installing a braking resistor.- Consultation with a distributor/Rockwell drive engineer is planned. Seeking advice before proceeding through initial drive support levels. - Exploring all programming options before considering additional hardware costs, such as a braking resistor.- The flying restart method involves ramping the drive to match the speed of the fan before accelerating to full speed, reducing the torque required. Further technical information on flying restart may be challenging to find. Any suggestions?
When ramping down too quickly without a sufficient brake resistor, you may encounter bus OV faults. After facing numerous obstacles, we upgraded to larger brake resistors and configured our drive with 2x Powerflex brake resistors to address OV and OL faults. Although our motor was unique (high slip NEMA design D), the autotune in SVC mode helped with OL faults but not OV. Ultimately, we resolved the issues by enabling flying restart, increasing the brake resistor size, and switching to a NEMA Design B motor. This setup has been running smoothly in V/Hz mode for months.
In a situation where the motor needs frequent restarts before coasting to a stop, adjusting the accel time and implementing a longer acceleration profile can improve performance. Despite some challenges, including analyzing trends and experimenting with different configurations, upgrading to a larger brake resistor and using a standard motor proved to be the most effective solution.
Additionally, in my experience with flying restart, the drive rapidly ramps up from 0 to max Hz with minimal current, likely analyzing voltage and current waveforms to determine the motor's position before starting the full-power ramp up at the configured rate. This method ensures a smooth transition to the desired speed within the specified accel time.
Let's start by exploring the concept of a 200% current limit, which means the motor is generating at least 200% torque on the motor shaft. However, it's important to note that the motor windings are constantly moving within the winding slots. The higher the torque, the more movement there will be, increasing the risk of winding failure. So, why take the chance of motor failure when it can be prevented?
The short 1-second ACC time is not sufficient for most fans to reach full speed. Each time the blower is started, the ACC time is determined by the current limit and the load, with a minimal difference between 100% and 200%, likely only about 1 or 2 seconds. Why put unnecessary strain on your equipment?
Now, let's consider the Flying Load, also known as Catch a Spinning Load. VFD manufacturers utilize the counter EMF of the motor to determine speed and direction, enabling them to control the motor effectively. However, if the motor is spinning in reverse when the VFD is instructed to start, it must first halt the motor's speed. This process requires the VFD to extract energy from the motor and redirect it to the VFD bus. Without proper management, the bus may trip due to overvoltage unless the energy is dissipated as heat in the bus loader. Alternatively, switching to line regeneration VFDs can recycle the energy for use by other VFDs.
When designing drive systems, numerous factors must be considered. To enhance the system, it is recommended to VPI (Vacuum Pressure Impregnate) all motors to secure and stabilize the windings, preventing movement in the motor slots and aiding in heat dissipation for prolonged motor life. Setting up VFDs in a common bus configuration can also allow energy collected during motor slowdown to be reused by other motors.
In today's focus on recycling and energy conservation, it's surprising that these practices are not more common, although they pose certain challenges. With so many aspects to consider, it can be difficult to cover everything comprehensively here.
Imagine trying to reach 60 mph in 5 seconds when your car's acceleration rate is actually 10 seconds. It's important to adjust the acceleration ramp to match the capabilities of the blower.
Joseph, I am exploring ways to identify emerging trends in the current situation. I have not had much success yet, but I believe further investigation may uncover something I have overlooked. I am aware of the challenges posed by ramping up too quickly, as the DC bus with a built-in resistor can only handle a limited amount of energy. I have encountered difficulties similar to what you described when trying to start the motor at different speeds with the ramp-to-stop feature enabled. Transitioning from a no run command to a run command often led to faults, but switching to coast mode helped alleviate the issue.
Gary, in case you missed it, I increased the acceleration time from 1 second to 6 seconds, which is within the capabilities of the drives. The Flying Restart feature is active, and the 200% torque refers to the Flying Restart Limit, not the Overload limit. The drives experience a higher fault rate when attempting to catch the load during a flying restart with a lower maximum torque %. It is perplexing, as it should require minimal torque to catch the load if the speed is being measured correctly. I have confirmed that the motors are not spinning in reverse during these situations, but are decelerating in the correct direction. While it would be beneficial to have a common bus setup and different motors, the existing hardware cannot be replaced without prior approval. I appreciate your suggestions and will take them into consideration.
Furthermore, I have extended the acceleration rate, as mentioned in my second post in this thread, but unfortunately, there are still unresolved issues.
It's impressive that you've reached out for assistance and advice on a problem. I always strive to offer my expertise without putting others down, unlike some. It seems that there may be a misunderstanding about VFD motor drive systems. When you mention a 200% current limit not being considered an overload, it's important to know that anything exceeding 100% of the motor's full load is indeed an overload. The duration and frequency of these overloads can accumulate and potentially lead to motor burnout.
Based on my experience, it appears that your motor may be operating in reverse due to air flow during startup, resulting in a bus overvoltage fault. Quickly stopping the motor when the VFD is activated is crucial, as exceeding the 200% overload can overwhelm the system. Proper VFD selection and configuration can address and resolve these issues, but a thorough understanding is key. Feel free to reach out for personalized assistance if needed.
GaryS stated that without a doubt, the motor will eventually burn out. Depending on the manufacturer of the Variable Frequency Drive (VFD), there may be a motor model in the VFD that calculates the thermal load of the motor dynamically. Users can typically adjust the response to a calculated thermal overload, often choosing to limit or reduce the speed. While the motor model may not be perfect, it is more effective than a standard overload relay.
It is highly recommended to protect a motor driven by a VFD, especially if it does not operate at a constant speed, with winding thermistors. All VFDs are equipped with thermistor inputs for this purpose. By implementing thermistor protection, users can adjust VFD settings without risking motor burnout.
GaryS believes that the motor may be running in reverse due to airflow during startup, resulting in a bus overvoltage fault. He suggests investigating the blower in the field. Although the motor shaft may not be visible in vacuum blowers, observing the fan end during startup can clarify if the blower is rotating in reverse.
Upon reviewing the initial post, it seems that the error situation may not be visibly apparent. JankyPLC mentioned observing the Output Frequency during startup, noting a brief flash of hz around 58-60 before settling to the normal 0-40hz range. Could the drive be configured for sensorless vector control or u/f mode? Perhaps opting for a simpler u/f setup would be more suitable. Additionally, adjusting the startup ramp from 1s to a more practical setting might prove beneficial, especially considering the necessity for the blower to start promptly.
JankyPLC noted in the forum discussion that the frequency (Hz) of drives faults is consistently in the 55-60Hz range, which is not within the typical operational range of the equipment. This could indicate a potential issue not related to electrical components, but rather with the pipe installations. In centrifugal fans, power consumption increases exponentially with the speed of the fan, which can lead to inefficiencies if the inlet and outlet openings are not properly configured. To optimize performance, valves are often installed at the inlet and/or outlet to adjust the operating point within the fan's pressure-flow characteristic curve. When the frequency reaches 55-60Hz, it suggests that the fan is consuming excessive power. Any insights or suggestions on this matter would be greatly appreciated.
@Ife, what you have is a regenerative vacuum blower, a powerful tool commonly used in industrial settings. When comparing regenerative vs. centrifugal blowers, it's important to understand the differences in their functionality. While both types are efficient at removing or pumping air, regenerative blowers offer unique advantages that make them stand out. To learn more about this topic, visit Becker Pumps' website for detailed information and comparisons.
Unlike traditional centrifugal fans that are heavier and slower to start, regenerative blowers like the one you have are known for their quick startup time. They are able to operate at different frequencies, with some variations in speed depending on the VFD settings. Visit the link provided for a visual representation of how a single-stage regenerative blower works.
Here's a new idea to consider. JankyPLC noticed something intriguing about the Output Frequency during startup, as it quickly flashes around 58-60 hz before settling into the usual range of 0-40hz. Could this indicate that the VFD is configured with a startup boost feature?
I previously installed regenerative fans, which require flow regulation using valves. The power of these fans also follows the rule that it varies with the cube of revolutions. Without proper restriction in the pipes, high revolutions lead to increased consumption and poor efficiency. Additionally, running without restrictions causes the fan to heat up the air significantly.
I believe it is essential to have a flow restriction mechanism in place. In the applications I have observed, valves are used to activate the vacuum as required. Therefore, the startup process involves keeping the valves closed until necessary.
In my experience, it is crucial to implement flow restrictions in the system. By adjusting the valves on each blower individually to achieve the desired flow and pressure at specific speeds, the system can operate efficiently. Another approach could be limiting the frequency to less than 55 Hz while keeping the valves open, which can result in a more energy-efficient solution. It is important for the installation designer to address potential energy losses caused by partially closed valves converting energy into heat. This method of controlling airflow is commonly known as regenerative fans, although I have always referred to them as Siemens ELMO type fans.
In our flywheel application that exhibited similar behavior to the original poster's, the spike in frequency indicated the drive was scanning to locate the motor's position. Once determined, it transitioned to "full power" mode and initiated a ramp-up. This behavior was part of the flying restart process in V/Hz and SVC modes. The counterclockwise trend did not provide much insight, as the sequence of events was inaccurate. The OV fault appeared before the bus swelled, followed by the frequency command dropping to 0, and finally the DC bus swelling after a brief delay. This misled me initially, prompting a reassessment. While trending data is valuable, it should be interpreted cautiously due to the short sample rate. Our distributor rep and Rockwell confirmed this inconsistency.
I persist in recommending a larger brake resistor. Using ProposalWorks, we sized it based on a 50% overhauling load (OHL). Since installation, the system has operated smoothly for several months, whereas previously it would only run for 8-10 minutes before encountering issues. This upgrade has proven essential for sustained performance.
Ensure your overload setting is at the recommended 125% and torque limiting is set to the maximum of 200% for optimal performance. When starting the fan with an across the line starter, expect a surge in current up to 600% FLA as it ramps up to full speed. It's essential to provide more than 100% torque to initiate the fan, even when using a VFD. If you're experiencing difficulties starting the fan with less than 200% torque limit, consider utilizing brake resistors to help manage the load.
In our flywheel application, we encountered a similar issue to what the original poster (OP) described. The sudden increase in frequency was due to the drive scanning to locate the motor's position before initiating a "full power" ramp. This behavior is commonly seen in flying restarts and happens in V/Hz and SVC modes. Is it inevitable that this behavior will lead to overvoltage if there is no brake resistor present? Can the system be adjusted to prevent this from happening?
The rapid increase to maximum frequency does not cause any problems. It simply helps the drive determine the starting point for its ramp during a flying restart. While this may delay the ramp's start by a few seconds, it is important to assess if a flying restart is necessary. If the high inertia load continues to spin during the start, a flying restart is likely needed to prevent an overload fault.
In our experience, we conducted extensive testing and made numerous parameter changes in V/Hz and SVC modes over the course of a week. By adjusting ramp times and even modifying them on the go, we saw improvements in the situation. However, the issue was only fully resolved after installing a larger brake resistor. This solution proved effective without the need for any complicated maneuvers.
With the appropriate resistor in place, the equipment now operates smoothly using simple V/Hz controls with a reasonable acceleration time of 5-10 seconds. Additionally, it can be stopped using either a ramp or coasting method. This adjustment has led to optimal performance in the presses.
Utilizing an encoder can help alleviate concerns when dealing with load winding issues. If the load is slowing down from a stop and needs to be restarted before coming to a complete rest, an encoder can provide crucial feedback and fill any gaps in the process. Encoders are valuable tools in optimizing operational efficiency and ensuring seamless motion control.
Apologies for the delay in updating everyone on this matter. In response to previous comments:
- The VFDs are currently set at 40 Hz instead of 60Hz, resulting in a reduced load.
- Schmalz advised running the blowers with vacuum bypass valves open for optimal cooling during idle periods. The bypass flow and suction pressure are controlled by a spring-loaded valve.
- I experimented with both V/Hz and SVC configurations to prevent faults without complete success. Currently, it is set as SVC.
- The acceleration ramp was extended from 1 sec to 6 sec to accommodate the loads.
- While an encoder may be beneficial, management does not view it as necessary for a basic blower operation.
- Despite suggestions of a braking resistor, management deemed it unnecessary due to the infrequency of the issue.
Thank you for all the insights provided. I will consider these factors for future projects.
Can your sedan car tow a trailer and accelerate to 50 miles per hour in just 3 seconds? This is the task at hand. I have experience working in a plant with 25 flywheel presses, each equipped with a 100 HP motor. These presses were able to start up in just 2 minutes without fault and stop in 1.5 minutes seamlessly.
For electric sedans, absolutely! The acceleration ramps on these drives are calibrated to prevent the blowers from reaching their maximum speed. While I can't recall the precise timings, with the ramp set at 0.1 seconds, the blowers can reach the reference speed in 3.4 seconds. Personally, I prefer a ramp set at 5 seconds. The drives are functioning efficiently without being overwhelmed.