Modern VSDs use sophisticated electronics for control and communication. They will operate in extreme conditions and are very reliable and effective. However avoiding inverter drive failures involves regular review and maintenance.

Despite being serviceable, drives are often forgotten after installation. Recognising this, manufacturers have made developments to improve their reliability. They invest significant time and resources to ensure product reliability.

ABB optimises performance using accelerated life testing to stress devices and assemblies. These demonstrate that their new variable speed drives will fulfil the reliability requirements. In these tests, drives operate at temperatures almost twice the specification limits. As a result, it enables them to simulate ten years of real application stresses in four to six months.

According to ABB, there are only two reasons why products fail: overstress and wear-out. If the stress exceeds its strength the product will fail, and the result is an overstress failure. Wear-out failure happens when the cumulative stress exceeds the product’s durability.

Areas of potential weakness are the primary cooling fans and main capacitors. As a result, in modern ABB drives these components have a minimum design life of ten years.

Avoiding inverter drive failures

In use there are three main reasons for inverter drive failure: poor installation; poor maintenance, and adverse loading.

Installation

A common cause of initial problems and tripping is poor installation, but this is the easiest to resolve.

The inverter installation should be dust and moisture free to prevent corrosion. Intense heat and cold, vibration, corrosive atmospheres and general misuse affect VSD performance and should be avoided. Where appropriate, high IP rated enclosures are available.

Avoiding high operating temperatures by ensuring a good airflow across the drive is important. Further, excessive operating temperatures reduce the lifecycle of the onboard electronics, and increase tripping.

Avoid long cable runs between the VSD and motor as they can cause short-time overvoltages that may damage the cable and the motor windings.

Preventative maintenance

Planned maintenance reduces the cost of failure. The good news is the maintenance requirements for inverter drives are generally straightforward. The first step is to follow the manufacturers maintenance routing in the manual

Checking the connections are tight (not overtightened) will reduce damage to the terminals from arcing, and transients. As stated earlier, excessive heat reduces the life of electronic devices.

It is important to regularly blow-through the main heat sink, filters and cooling fans with dry compressed air. Where the control board have fans installed they these too need inspection. Furthermore, manufacturers like ABB recommend replacement intervals in their service information.

The long-life cooling fans in ABB drives are due for replacement every nine years. The main capacitors are also serviceable parts, requiring replacement every nine years. For larger drives, ABB offers preventative maintenance kits to ensure reliable operation.

Adverse loading

When installed inverters and motor are usually matched to one another. If there is a mismatch, the drive may run over its capacity. This will cause stress and damage the drive. Furthermore, it may be also possible for operators to over-ride the controls to run over capacity and damage the drive.

The result of these precautions helps in avoiding inverter drive failures: it requires work and planning, but it is not difficult.

Over time, electronics device makers cease production and spares are more difficult to find. This means a product becomes uneconomic to repair. If replacement is necessary, the manufacturer can also help. Replacement drives from the same manufacturer often have the same footprint. In addition, often have offer help with conversion kits.

Finally, there are many advantage to replacing drives. Newer drives will be more efficient, offering improved energy management. They will have more functionality and connectivity for networking,  and IIoT enabled drives will improve the plant and machine operation.

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