How to choose a medium voltage VFD:
Service network and reaction time
From end user’s perspective the uptime of the plant is crucial. The cost of loss of production quickly exceeds the equipment cost of the VFD. Therefore, you need a strong partner to support you with any kind of technical issue that might happen regardless if the drive is under warranty or not and regardless if the issue was triggered by the drive, by other system component or by external disturbance. A local service network with right level of competence is an assett that every user will appreciate during the lifetime of the VFD.
Remote support and local service network
Some issues (mostly the less severe ones) can be resolved by a service specialist remotely by using dedicated service and diagnostic tools and remote access. However, for severe cases it is usually necessary to have someone physically present at site. The person needs to make a thorough visual inspection. Maybe the root cause is not 100% clear from the trends / transient recorders / black box data and the technician at site shall help to figure out what actually happened. There is often the need to perform specific measurements and determine whether other components were damaged as well (besides those with clear signs of damage).
Reaction time / Mobilization
Whenever such thing happens the reaction time is crucial. The service specialist shall arrive on site as quickly as possible. The closer to the plant the service team is stationed the better response time can generally be achieved. Besides the physical distance it is important that the service team is adequately staffed. It does not help if you have a local service team nearby but the person is currently on another site and there is noone else to be mobilized (as a rule of thumb the experts are always busy and it won’t get any better).
Very dangerous situation is when the service personnel is located in another country and needs to apply for a visa before being able to start arranging the travel. Such process can easily take few days or weeks and may have fatal consequences for your business.
Besides the proximity of a service unit also the competence of the team is very important. It could happen that the local team can only handle “small issues” while for complex problems an expert team from abroad need to be involved. That may eventually be a threat for the reaction time and overall time to resolve the issue.
Checklist for drive services
Our general recommendation is:
- Make sure that there is a local service team is reasonable travel distance from your site.
- The service team shall have sufficient experience and skills (most manufacturers have several levels of service support and the basic level does not cover too much).
- The service team shall be properly staffed. There shall be persons available in standby mode for urgent matter.
- If the service person is sourced from another country there shall not be any visa obligation or the visa shall be fixed a priori.
- For critical applications the response time may be defined contractually. A service agreement is advisable option.
- The service technicians shall be trained and experienced with the type of VFD that you have installed or consider to purchase.
- For smaller issues and generally for faster processing of the intervention a remote connection is highly recommended.
Many of mentioned bullet points shall be checked before purchasing the VFD. After the purchase it may be too late. In most cases the user cannot expect the manufacturer to build up a new service centre close to the envisioned installation of the drives. Of course, if you are really large customer then you have a bit different position to get the manufacturer’s committment.
Cost and benefit of local service network
Maintaining a local team of skilled service technicians is a very costly thing. If there is a large installed base in the region it is quite easy to justify such investment. In other cases it might be more difficult. Especially for medium voltage drives the quantity of the products is not as high as in low voltage segment. Having such local presence is a valuable assett but it naturally comes with a price tag.
To put things in relation you can make a following simple consideration:
- Difference in purchase price of product A and B is xxx USD
- Cost of one day unplanned downtime of the drive system is yyy USD
If the difference in purchase price equals just 1-2 days of financial damages due to unavailability and the manufacturer of the more expensive product can guarantee a significantly better reaction time then it is probably a no brainer. With one single failure during the lifetime the premium in purchase price most likely pays off.
Life cycle management
Life cycle management is crucial as well. Finally, if the product is declared as obsolete, you can hardly expect any service support more. We have seen numerous replacement projects where the original drives could still serve their purpose for couple of years but the manufacturer wrote them off, declared them as obsolete and stopped providing spare parts. The customer as left alone… For most end users that is an unacceptable risk and they go for replacement although the installed equipment by far did not reach its design lifetime yet.
This topic deserves its own post.
Summary
The expectation on VFD lifetime is at least 20 years. To ensure a smooth operation and high availability throughout the equipment life a proper service and maintenance is essential. Do not underestimate the importance of local service network. Before purchasing the VFD make sure that an adequate service support is available in your region. Remote access for service specialists is highly recommended. However, it does not substitute the need for local service presence.
As a young drive engineer my interest was almost exclusively in the drive technology itself. The slides about service network at the end of a product presentation were quite boring for me. However, after couple of years in the business I have changed my mind. Looking more through the lens of the end user I must admit that a comptenent and dedicated service team that is near the customer (near for both physical distance and response time) is a huge benefit. Unfortunately, this factor is still largely understimated.
References
[1] How to choose a medium voltage VFD (series of articles), https://mb-drive-services.com/category/choose-mv-vfd/
