Pumps 201
Pump System Troubleshooting Using Low Voltage Drive Information
Identifying the root cause of pump problems from data provided by an adjustable speed drive.
Jesus Vazquez | Toshiba International
| IMAGE 1: Monitor values from ASD software (Images courtesy of Toshiba International)
Pump failures can result from mechanical, electrical or hydraulic conditions that subject the system to excessive stress. When a pump fails, troubleshooting typically requires checking multiple components to identify the cause. The previous article, “Pump Protection Using Low Voltage Drives,” highlighted the potential protective features available when integrating an adjustable speed drive into a pump system, including monitoring and diagnostics. Modern adjustable speed drives (ASDs) provide real-time monitoring information such as voltage, frequency and current output from the drive to the motor. This information can offer valuable insight into pump failures by accessing the monitored values immediately before a fault occurs.
While ASDs help identify faults, diagnostics can help determine the root cause. This article focuses on using the monitoring and diagnostics features of an ASD to provide insight into pump and motor operation, leading to less reactive troubleshooting and more informed, proactive maintenance.
Understanding Diagnostics
It is important to understand the different values an ASD can monitor and what the diagnostics mean regarding the motor or pump. Common monitor values available on drives include output frequency, output voltage, motor current, torque, power, cumulative runtime and fault history. Although each parameter provides crucial insight into motor and pump performance under operating conditions, analyzing them simultaneously provides a more comprehensive assessment of the pump system.
For example, excessive current draw shown on the drive can indicate abnormal operating conditions. This information alone, however, may not be sufficient to identify the root cause. An increase in current draw may result from a pump operating outside the recommended range, harsh hydraulic conditions, a physical blockage within the pump or even motor-related issues. Evaluating multiple parameters at once can further support troubleshooting. As a result, technicians can better recognize abnormal operating patterns, pinpoint potential causes more efficiently and perform appropriate maintenance. The next step is recognizing these parameters and how they relate to specific faults displayed on the drive.
Fault Codes
One benefit of integrating an ASD into a pump system is fault detection based on monitored values. The different fault codes represent specific conditions within a pump system that exceed normal operating parameters. It is important to note that fault codes may vary depending on the specific manufacturer and model. Understanding the different fault codes and conditions eliminates the need to check areas that are outside the scope of possible causes.
Some common faults, such as undervoltage, are often associated with incoming power quality issues. An overvoltage fault can be caused by regenerative energy generated by the motor during rapid deceleration. Possible causes of an overcurrent fault include mechanical blockage within the pump, excessive load on the motor and issues within the motor or motor cables. A ground fault is another common fault that can indicate issues in the wiring or degradation of the motor insulation. Overall, the type of fault displayed helps identify where to begin troubleshooting. Once identified, it is important to investigate all areas that may have triggered the fault to ensure appropriate maintenance is performed.
| IMAGE 2: Overcurrent trip
Importance of Current, Torque & Speed
When analyzing data from an ASD, three key values to observe are the motor current, torque and speed. These parameters provide a deeper understanding of the pump system’s mechanical condition and can indicate issues before a fault occurs. Abnormalities in these motor characteristics often result from mechanical issues developing within the system, since the motor load depends on the demand of the driven equipment.
While a combination of high current and torque may point to mechanical blockage restricting operation or to the pump load exceeding normal operating conditions, the motor speed can further explain the issue. If high torque and current occur at slower speeds, the pump may be experiencing a physical blockage or restriction. The trend in which these characteristics change is also important. A sudden spike in current may suggest debris has entered the pump, causing unexpected resistance. A more gradual increase may result from mechanical deterioration of internal components. Deviations in these values can best be recognized by documenting the motor current, torque and speed and then comparing them with the expected values during normal operation. This can ultimately support a proactive approach to developing issues.
| IMAGE 3: Fault history example
Reading Fault History
Evaluating the fault history and data trends from an ASD may reveal recurring issues that would go undetected when looking at a single fault. Modern drives record a set number of past faults, including the fault type, when it occurred and the monitored parameters at the time of the fault. By analyzing this information, the technician can gain a better understanding of abnormal patterns and address them before they reach fault conditions.
For example, with a repeated overcurrent fault, the fault history may show that it consistently occurred at a specific output frequency. This information would allow maintenance personnel to investigate possible system changes occurring at that frequency. This includes identifying load fluctuations, physical restrictions on the equipment or mechanical resonance. Prioritizing possible causes and providing corrective measures will help prevent issues from developing into permanent equipment damage. Overall, monitoring the fault data along with the fault history will enable more effective troubleshooting and can help guide development of proactive maintenance procedures that will ultimately help improve system reliability.
Although adjustable speed drives are commonly known for protecting driven equipment from operating under abnormal conditions, they also provide valuable diagnostic information that can be used to gain a better understanding of system performance and further identify potential concerns. Analyzing information such as monitored parameters and fault data simultaneously can help identify whether a problem is mechanical, electrical or hydraulic. This helps diagnose the root cause more quickly and accurately, which reduces the likelihood of equipment failure. Ultimately, using the full diagnostic capabilities within an ASD allows authorized personnel to address issues more effectively while helping to increase system efficiency.
Jesus Vazquez is an application engineer for adjustable speed drives at Toshiba International Corporation. For more information, visit toshiba.com/tic.
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