Variable speed drives are equipped with some degree of protection against ground faults generated on the load (output) side of the drive. This is intended to protect the drive in the event of a fault in the motor leads or the motor itself. Here we examine the causes and effects of these faults on drives, and ways of resolving them. 

Variable speed drive (VSD) ground faults are intended to trip the drive before its output power section is damaged. They are typically displayed as “GF” or an analogous code on the drive’s HMI. These faults may also be termed “earth leakage” in some drive manuals. When they occur, they usually indicate problems with the connected cabling or motor, and need to be addressed promptly. Let’s explore some basic causes and corrective measures.

The most common causes of drive ground faults are motor cables shorted to ground, or motor windings shorted to ground. As we have referenced in past articles, the characteristics of the synthesized AC output voltage and current from a pulse width modulated (PWM) variable frequency drive (VFD) can place additional stresses on cables, motor leads and windings. Particularly […]

Drive Overload faults can manifest themselves in response to rapidly changing load conditions or drive transistor over-temperature, among other causes. Below we discuss these faults, their causes and possible resolutions.

Variable speed drive (VSD) overload faults are intended to trip the drive before significant damage to internal components occurs. Various manufacturers have different means of monitoring drive loading and issuing faults when anomalies occur, depending on programming. Let’s examine what can trigger these faults, and how they can be corrected.

Overload faults can be generated in response to loading which exceeds the rated capacity of the VSD, or to user-programmed settings customized for the application. The first instance simply means that the rated current-carrying capacity of the VSD is being exceeded by a percentage and/or for a time greater than the specifications indicate, which can result in drive overheating and, ultimately, damage to internal components. Most drives are manufactured with a specific overload rating, in percent of rated output current and for a specific amount of time. For example, a VSD rated for what is termed “normal duty” might have an overload rating of 120% of rated output current for 60 […]

Today we examine the Output Phase Loss fault, as we continue with common Variable Speed Drive faults, their causes, and some ways to resolve them.

As noted in our previous articles, Variable Speed Drives (VSDs, a.k.a. Adjustable Speed Drives (ASDs) or, for AC motor control, Variable Frequency Drives (VFDs)) are equipped with a number of monitoring and control features, including extensive monitoring of power output to the load. One critical function monitored is the health of each phase of the VSD’s output; when a fault occurs there, it is termed an Output Phase Loss. Let’s examine what triggers this fault, and how to address it. Output Phase Loss is typically indicated on the drive’s HMI by some alpha or numeric designation, which varies depending on the drive. For purposes of this discussion, we’ll note it is indicated by “LF” (in the case of the Yaskawa GA800) (see Fig. 1) or a numerical code (on the ABB ACS880, “3381”).  This condition can result from a number of problems related to the output cabling, the connected motor, or the VSD’s output (inverter) section. One of the most common causes is a break in the connection to […]

Today we look at overvoltage faults, as we continue with some of the more common faults experienced by variable speed drives, their causes, and some ways to resolve them. Variable Speed Drives (VSDs, a.k.a. Adjustable Speed Drives (ASDs) or, for AC motor control, Variable Frequency Drives (VFDs)) are equipped with a number of monitoring and control features intended to protect the drive and its connected equipment from damage. Errors, Warnings, and Faults are logged in response to abnormal operating conditions and displayed on the drive’s HMI and/or sent to monitoring software in connected PCs or automation control systems. The drive’s response to the abnormal condition depends on the condition’s severity, and the potential it has to inflict damage. The faults we are discussing typically cause drive shutdown, and require that the fault be corrected and the drive reset or rebooted before it can operate normally.

Over the next few columns, we’ll examine some of the more common faults experienced by variable speed drives, their causes, and some ways to resolve them.

Modern variable speed drives (VSDs, a.k.a. VFDs or ASDs) are very reliable devices when installed and maintained properly. However, VSDs can experience faults, alarms, and errors from time to time, just as can any complex electronic component. It is helpful to know how to deal with such issues when they occur. Over the next few columns, we’ll discuss some of the more common faults that might be seen, and how to address them efficiently and with minimal wasted effort. I will be referencing troubleshooting methods recommended by a variety of VSD manufacturers we use, although many of these approaches will be suitable, with minor modifications, for any modern VSD.

Before we begin, let’s cover some general considerations applicable to any troubleshooting process. First, the manufacturer’s manual is usually your best source for determining the problem and what to do about it. Often the manual will have a decision tree or block diagram detailing the specific steps needed to troubleshoot each fault or alarm. This can […]

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Until relatively recently, flow control valves (FCVs; also sometimes referred to as throttling valves) were the most common means of regulating flow in a process line. Over the decades that FCVs have been in use, both control technology and mechanical construction have improved greatly, significantly reducing the process inefficiencies – hysteresis, lag, pressure drop, etc. – associated with these valves. And despite the sophisticated control systems often used to operate them, valves are relatively simple devices. With maintenance properly scheduled and performed they can last a very long time indeed.

Most people are aware that electrical and electronic components are heat-sensitive, and that their life expectancies can be reduced significantly if they are not kept within specified operating temperatures. Typical upper limits for specified operating temperatures are 40°C (104°F); occasionally 50°C (122°F). One common application challenge is maintaining temperature below these upper limits within a control enclosure. There are a number of variables which need to be considered when determining the cooling needed, including the size of the enclosure, its material and finish, its location (e.g. outdoors in shade or sun), and, in general, the variability of the ambient temperature during operating periods. Note that all of these factors are in addition to the the impacts of the internal components and their heat loads; i.e. the heat they give off during operation. Today we’ll examine these factors and look at one cost-effective means for addressing them – forced air cooling, also known as fan-forced air (FFA) or forced convective cooling.

First, let’s look at the formula to calculate the amount of forced air cooling needed. This formula […]

There is a good deal of knowledge, and more than a little misperception, about the use of variable speed drives (VSDs). The term “variable speed drive” encompasses both variable frequency drives (VFDs) used for controlling AC asynchronous and synchronous motors, and DC variable speed drives for controlling DC motors. In either case, determining if and when to use a drive will be much easier once the facts and myths about these controllers are clear. Let’s examine some of the more prevalent ones.

Myth: “My process flow application is already controlled by control valves, so I don’t need a VFD.”

Fact: In many cases, a VFD can more accurately control flow while reducing power consumed by the pump motor. If the flow control valves (FCVs) are being used mainly to throttle flow, you could instead use a VFD to reduce the speed of the motor, thus reducing the flow at the source. The reduced motor speed means less energy consumed by the system; per the Affinity Laws, power consumption (in watts) in a centrifugal pump application would be reduced by the cube of the reduction in speed (see formula below). You wouldn’t even need to remove the FCVs; simply open them fully and […]