How do you maintenance a VFD? How actually need to perform maintenance a VFD? If you have been tasked with maintaining a Variable Frequency Drive (VFD), then you should be familiar with what it does and how to maintain it. VFDs are used for many applications of different scopes, including pulp, paper, and converting plants. They operate on a ‘variable speed’ principle which means that the frequency of signals sent through them is variable by direction to regulate the speed at which these machines run. Failure to maintain VFD properly can result in damaged motors or even motor failure. These machines are vital to the production and maintenance of many industrial processes. For example, if the VFD is damaged, then the machine it controls may stop working entirely due to unauthorized deceleration. Loss of a VFD can lead to serious problems associated with quality control and product safety, so it’s important that maintenance on these machines is carried out in an efficient way. The following article will show you why a VFD is important and how you should maintain it effectively.
VFDs run at varying speeds depending on what process they are regulating, for example, it may be fast on ‘1’, slow at ‘0’, and faster still at ‘-1’. This means that the frequency of the signal applied to them is variable by direction.
VFDs are used for many applications of different scopes, including pulp, paper, and converting plants. They run at varying speeds depending on what process they are regulating, for example, it may be fast on ‘1’, slow at ‘0’, and faster still at ‘-1’. This means that the frequency of the signal applied to them is variable by direction. Their operation relies on a system called pneumatic or electric creep control which ensures some safety and consistency within these machines. It prevents accidental deceleration or acceleration which would cause an accident and could cause serious damage to machinery and human life.
To prevent any adverse effects, the VFDs in a particular industrial installation will have been designed based on a maintenance plan that is tailored to the specific process. An example of an industrial maintenance plan would be one that was developed specifically for a pulp and paper production plant. This is because the frequency of VFD control signals determines in part how quickly chemicals are mixed, which is directly related to pulp consistency and quality. The frequency also controls chemical heating and cooling cycles in order to ensure product consistency.
A paper mill with a high level of chemical use can generate many harmful vapors, including hydrogen sulfide (H2S), sulfur dioxide (SO2), ammonia (NH3), formaldehyde, ketones, and phenol. These gases can be released into the air by VFDs. If left unchecked, these vapors can cause serious health problems and even be lethal. This is why the design of VFDs at a paper mill is highly complex, and often includes ‘wet heating’ to help neutralize some of these harmful vapors.
For larger plants, maintained by a knowledgeable maintenance team that includes engineers, plant managers, and technicians, it’s important that the necessary maintenance planning has been completed before any new installations are made. This allows for proper preventative maintenance to be carried out in addition to any scheduled service on machines. This kind of maintenance plan can be made more efficient if there is a tight relationship between the team members and the machines they are servicing.
Even with diligence on the part of the maintenance team, problems can still occur unexpectedly. The following section will outline some of the most common problems that arise with VFDs and how they should be treated.
There are numerous problems that can arise in a VFD installation and will depend on your individual machine and its control system. Problems vary depending on what kind of equipment is being controlled.
The following is a list of the most common problems that can occur in VFD installations:
- Frequent tripping of the field circuit breaker. This may be caused by improper or loose connections to the control signals. Another source of this problem could be interference in the form of pulses (called ‘noise’) from other equipment, which might cause a false signal to be detected by the driver. A shorted semiconductor device can also be a cause and will require attention by an expert in semiconductor electronics.
- Tripping of both power circuits simultaneously, including an overload tripping on the incoming power supply. When both power circuits trip at the same time, there may be a short in the motor. A shorted motor can often be isolated by removing the coils and checking them individually to see if they are shorted.
- The wrong speed set point is selected, resulting in an off-speed condition. This problem will cause an incorrect output of mechanical power and may decelerate or accelerate unexpectedly. The result of this can range from a momentary loss of load to the complete destruction of major components including valves, pumps, motors, and so on.
- Inefficient operation is due to the application of a constant voltage across the field terminals whereas normally a pulsed signal is applied. This problem can arise due to incorrect installation of the field terminals by an inexperienced technician.
- Malfunction or electrical arcing between the VFD and control circuitry due to inadequate shielding techniques.
- Relics of manufacturing defects left behind in a production line are no longer of concern but can cause problems in VFD installations. If this occurs, then it will require a customized solution for what appears as a failure in the original electronics equipment.
- Inadequate control and monitoring of the process condition, causing improper operation at all times. This is often the result of poor maintenance planning and prevention of VFD failures by unqualified technicians who are not familiar with their operation, proper use, or maintenance methods.
- A control or monitoring problem in the process prevents the proper operation of the VFD. This circumstance is often caused by an incorrect selection of process variables when designing the VFD installation.
- Over-voltage can be a big problem if not rectified immediately, and can lead to the destruction of many components such as relays, capacitors, fuses, and semiconductors. Any over-voltage in a VFD installation should be considered a serious situation and must be rectified by qualified personnel as quickly as possible. If failure is imminent due to over-voltage, there are some steps that you can take to avoid further damage:
Hopefully, now you have the answer to How do you maintenance a VFD effectively.
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