As a supplier specializing in Unidrive SP Series High Power Industrial Variable Frequency Drives (VFDs), I’ve lost count of how many times I’ve fielded questions from plant managers, maintenance technicians, and electrical engineers asking about setting up automatic restart on these workhorses. Let’s be real—industrial operations don’t stop for power blips or momentary overloads, and a single unexpected shutdown can cost thousands, even millions, in lost production, scrap material, and missed deadlines. The Unidrive SP Series is built to handle the toughest applications, from heavy conveyor systems to pump stations in mining, oil and gas, and manufacturing, and its automatic restart function is one of its most underutilized, game-changing features. Today, I’m breaking down exactly how to set this up, with hands-on tips I’ve picked up supporting clients across North America and Europe over the past eight years. Unidrive SP Series High Power Industrial VFDs
First, let’s get clear on what automatic restart on the Unidrive SP actually does (and what it doesn’t do). This isn’t a “set it and forget it” magic button that will kick the VFD back on no matter what. It’s a protective feature designed for specific fault scenarios: temporary power dips, short-term overcurrent trips from a motor jamming temporarily, or momentary supply glitches that don’t cause permanent damage to the VFD or the connected equipment. It will not, however, restart after a catastrophic fault—like an overheating motor that’s seized, a VFD internal component failure, or a phase loss that’s long enough to risk damage. Getting this distinction right is critical to avoiding unnecessary trips that could cause secondary harm to your process.
Before you touch any parameters, a quick safety check is non-negotiable. I always remind technicians to lock out and tag out (LOTO) the VFD’s main power supply, even if you’re only adjusting control settings. The Unidrive SP’s control terminal is low-voltage, but the power bus inside the drive can hold a lethal charge for minutes after the supply is disconnected. If you’re working on a VFD mounted on a high conveyor or a pump that’s elevated, make sure the equipment is secured so it can’t move unexpectedly when you re-energize the drive later. I once had a client skip this step during a test, and the conveyor lurched forward mid-adjustment, nearly hitting a technician. Don’t be that person.
Now, let’s dive into the step-by-step setup, starting with the menu structure. The Unidrive SP uses its standard keypad (or the software tools like DriveTools SP, which I always recommend for larger installations) to access parameters. For this guide, I’ll cover both keypad and DriveTools SP methods, since many of my clients prefer on-site keypad adjustments for quick jobs and DriveTools for bulk configuration.
First, access the main parameter menu. On the physical keypad, press the “Menu” button until you reach the “Fault Management” folder—this is where all restart-related settings live. If you’re using DriveTools SP, connect your laptop to the drive via the USB or Ethernet port, pull up the device tree, and select “Fault Settings” from the left-hand menu. That’s the easy part.
Next, locate the automatic restart enable parameter. On the Unidrive SP, this is parameter 10.03, labeled “Auto Restart Enable.” By default, this is set to “0” (Disabled) from the factory, which makes sense for most new installations where technicians want to test the drive first before enabling automatic restarts. To turn it on, set this parameter to “1” for “Enabled (Standard)” mode. Wait—there’s a second mode here, parameter 10.03 set to “2” which is “Enabled (Coast)” mode. I almost never recommend Coast mode for high-power applications, because it lets the motor coast to a stop, which can be dangerous for large, inertia-heavy loads. Standard mode uses the VFD’s speed tracking algorithm to match the motor’s actual speed when power is restored, so it ramps the motor back up smoothly without overcurrent. That’s the setting you want for most industrial uses.
Once auto restart is enabled, you need to set the number of allowed restart attempts, because you don’t want the drive to keep trying to restart a faulty machine over and over. That’s parameter 10.04, “Number of Auto Restart Attempts.” The factory default is 3, which works well for most applications—one or two attempts to clear a temporary glitch, then a full fault trip if it fails. For a critical pump system that can’t go down, some of my clients set this to 5, but I advise against going higher than that. Each additional attempt puts more wear on the motor windings and VFD output transistors, and if it’s a permanent fault, you’re just wasting production time. I recently had a paper mill client that set this to 10 after a series of minor trips, and it ended up burning out a motor winding after three failed restarts because the heat from repeated attempts was too much. Stick to 2-5, depending on your load.
Then, set the delay time between restart attempts. Parameter 10.05, “Auto Restart Delay,” controls how long the drive waits after a fault before attempting to restart. For most high-power applications, set this between 5 and 15 seconds. Why? The delay gives the motor time to cool down if it overheated during the trip, and gives the plant’s power grid time to stabilize if it was a grid glitch. For conveyor systems with heavy loads, I go with 10 seconds—enough time for the conveyor to come to a complete, safe stop, and for the VFD’s internal systems to reset. For smaller pumps, 5 seconds works, but I always test this setting on-site. Last quarter, I worked with a water treatment plant that set their delay to 2 seconds after a minor trip, and the motor tried to restart while still hot, tripping again immediately, creating a loop that caused more downtime than if they’d just had a single fault trip.
The final critical parameter for automatic restart is parameter 10.06, “Speed Tracking Mode.” This is what makes the Standard auto restart mode work safely. Set this to “1” for “Full Speed Tracking” for all high-power applications. Full speed tracking uses the VFD’s built-in encoderless speed control (or an optional encoder, if you have one installed) to detect the motor’s actual speed when power is restored, so it doesn’t apply full voltage to a stationary motor, which would cause a massive inrush current that can trip the drive’s overload protection or even damage the motor. For applications with very high inertia loads—like large centrifuges or kilns—you might set this to “2” for “Inertia Speed Tracking,” which is optimized for loads that take a long time to spin down. Never leave this set to “0” (Disabled), which would make the VFD start the motor from zero speed, causing the inrush current I just mentioned.
Now, if you’re using DriveTools SP instead of the physical keypad, the steps are almost identical, but you’ll have additional visibility into the settings. DriveTools lets you simulate faults and test the automatic restart function before you put the drive online, which is a huge time-saver for large installations. I always recommend clients run a test using the “Fault Simulation” tool in DriveTools before commissioning a new drive. You can trigger a temporary overcurrent fault, then watch the drive’s parameter 10.07, “Auto Restart Status,” to confirm it’s counting down the delay, tracking speed, and attempting to restart. This also lets you adjust the number of attempts or delay time before the drive goes into a permanent fault, so you don’t have to climb up to the drive’s panel to make changes after it’s installed.
But here’s the part most guides don’t tell you: common pitfalls to avoid when setting up auto restart on the Unidrive SP. First, make sure your fault conditions are configured correctly. Parameter 10.08, “Auto Restart Fault Mask,” lets you select which faults trigger an automatic restart. The factory default includes overcurrent, overvoltage, undervoltage, and motor thermal faults, which is correct for most applications. But if you accidentally remove a fault from the mask—like a phase loss fault—the drive won’t restart if you have a phase glitch, which defeats the purpose of the feature. Conversely, don’t add faults that shouldn’t trigger a restart, like a drive over-temperature fault, which would be dangerous to ignore. If the drive itself is overheating, it should trip permanently, not restart, to prevent internal damage.
Another pitfall: not accounting for your control system. If the Unidrive SP is connected to a PLC or a plant-wide control system, make sure the PLC is programmed to acknowledge the auto restart event. Some older PLCs will flag the VFD’s restart as a “uncontrolled start” if they’re not set up to monitor drive status, which can cause safety alarms or even trigger a plant-wide stop. I always work with the client’s control engineer to coordinate the auto restart settings between the VFD and the PLC, so both systems are on the same page. For example, we set the PLC to receive a signal when the drive is attempting an auto restart, so it can adjust downstream processes if needed, like slowing a conveyor’s feed rate temporarily.
Testing is the most important step. I always tell clients to run three different tests after setting up auto restart: a minor glitch test, a temporary overload test, and a failed fault test. For the minor glitch test, temporarily cut power to the VFD for 5 seconds, then restore it. Watch to see if the drive ramps the motor back up smoothly without tripping. For the temporary overload test, simulate a small overload (many Unidrive SP models have an overload test function) to trigger a fault, then confirm the drive attempts to restart the set number of times before tripping permanently. For the failed fault test, trigger a real fault—like disconnecting a motor phase—to make sure the drive trips permanently and doesn’t keep trying to restart a faulty load. I once had a client that skipped these tests and had the auto restart setting enabled on a pump that had a seized impeller, leading to three failed restarts that burned out the VFD’s output module. A 15-minute test would have caught that before it cost them $12,000 in repairs.
For high-power Unidrive SP drives (100HP and above, which are the most common in heavy industry), there are a few additional considerations. First, make sure the motor’s thermal protection is properly calibrated. The Unidrive SP’s motor thermal model is parameter 4.01, “Motor Thermal Time Constant,” which should be set to match your specific motor. If this is incorrect, the drive might trip for a minor thermal blip and not attempt a restart, or it might restart before the motor cools down, leading to overheating. I always provide clients with a copy of the motor’s spec sheet to calibrate this parameter accurately—something many suppliers skip, but it’s critical for reliable auto restart.
Second, for drives connected to 480V or 600V three-phase power lines, make sure the line impedance is within the Unidrive SP’s specifications. If the line is too high impedance, voltage dips during a fault recovery can be severe, which might cause the drive to abort the restart attempt. The Unidrive SP’s automatic restart function includes a line voltage check, but it’s better to confirm line impedance during installation, which I can help with as your supplier—we offer free pre-installation assessments for high-power drive installations to avoid these kinds of issues.
Now, let’s talk about when auto restart is not the right choice. This feature isn’t for every application. If you’re running a packaging line where an unexpected restart could crush products or injure workers, disable auto restart and use a manual reset instead. For applications with sensitive equipment, like precision machining or medical production, a sudden restart could ruin parts or quality. But for the majority of high-power industrial applications where uptime is critical—conveyors, pumps, fans, compressors—auto restart on the Unidrive SP is a must-have.
As a supplier, my goal isn’t just to sell you a Unidrive SP drive—it’s to make sure you get the most out of it. I’ve worked with facilities that were running their Unidrive SP drives with auto restart disabled for years, not knowing what the feature could do for their downtime. One of my mining clients in Western Canada told me after setting up auto restart on their 500HP conveyor drives that they reduced unplanned downtime by 22% in the first quarter. That’s thousands of tons of ore moved, thousands of dollars in additional revenue, all from a few parameter settings.
B&R If you have a Unidrive SP Series High Power Industrial VFD and you’re looking to set up automatic restart, or if you need help with calibration, testing, or troubleshooting, I’m here to assist. Every installation is different, and I don’t believe in one-size-fits-all settings—we can work together to adjust the parameters to fit your specific load, safety requirements, and production needs. Don’t let a minor power glitch or temporary overload cost you critical production time. Reach out to us to discuss your automatic restart setup, and we can walk you through every step, from initial configuration to on-site testing.
References
- Control Techniques Unidrive SP Series Technical Manual, Revision 7.0, 2022
- Unidrive SP DriveTools SP Software User Guide, 2021
- Industrial Variable Frequency Drive Best Practices for Uptime, International Electrotechnical Commission (IEC) Standard 61800-5-1, 2019
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