VFD layout options
Introduction
Default VFD layout is normally a straight lineup. The individual cabinets are installed side by side on a common base frame. However, specific site restrictions may require adaptations of the mechanical layout in order to fit into the available room. Thus, alternative layout options may better suit the mechanical integration of the VFD. The flexibility of drive layout depends on the specific product and the interface in between the individual cabinets. In this article we look at some variants of the VFD mechanical layout.
VFD layout options
Medium voltage VFD usually consists of several cabinets, also called units or modules (in case of modular design). Each unit has specific functionality. For example, one module is dedicated for the rectifier, another one for the dc link components, there is an inverter module, module for terminal connections, module accommodating the water cooling (if applicable), control unit etc.
Standard mechanical layout of the VFD has the modules arranged side by side on a base frame. This setup usually leads to most straight forward interfaces. The overall VFD layout is several meters long with a typical depth of 1.0…1.6 meters. In some cases, especially for high power rating or for a multidrive, the straight lineup may be too long making the installation difficult. Particularly for brownfield projects with existing electric room the VFD dimensions can be very restricted. Luckily, there are usually alternative layout options that can be used.
The feasibility of an alternative layout depends on the mechanical design. VFDs with modular design are more suitable for alternative arrangement than non-modular VFDs. The modules have clear interfaces and can be quite easily separated.
In this post following options are mentioned:
- Straight lineup
- Separation of certain modules (stand-alone)
- Back-to-back configuration
- Mirrored lineup
- L-shape lineup
- U-shape lineup
Straight lineup
Straight lineup is usually the default mechanical layout. The VFD modules are installed side by side on a base frame. With every new module the lineup is extended to the length while keeping minimum depth. The location of each module is given (for the sake of simplest interfaces), some modules can be swapped if required. Straight lineup fits for most projects. However, as the number of modules increases (e.g. high-power drive with several inverter units in parallel or a multidrive lineup), the VFD gets longer. Consequently, the mechanical integration may be challenging, especially in case of existing room. Thus, some alternative mechanical layouts may be used.
Stand-alone modules
Certain modules can be separated from the main lineup and placed as stand-alone. Such option provides more flexibility in case of limited space inside the room. Stand-alone modules are often the modules which are optional, resp. used only for certain configurations (e.g. excitation system, synchronization unit, bypass switch unit). However, also standard modules can be separated and installed as stand-alone (cooling unit, control cabinet).
The stand-alone modules are usually located close to the main VFD lineup. Nevertheless, in some cases they may be located in a different room. An example is the control unit which is sometimes separated because of personal safety (control cabinet is in a room that can be accessed while the VFD is in operation while other VFD modules are in a room not accessible during operation). Stand-alone modules can be also placed at another floor (below or above the main lineup).
Mirroring the lineup
First option is to keep a straight lineup but change the position of certain modules. Classical example is to mirror the lineup. The advantage is that the corresponding modules of two lineups are close to each other. It makes it easier for the interfaces such as inlet and outlet water pipes, power cables, auxiliary and control cables etc.
Back-to-back arrangement
Another option is back-to-back arrangement. It reduces the length of the lineup to approx. one half while doubling the depth of the VFD. Back-to-back is only possible when no back access is required for installation, service and maintenance. Thus, replacement of any internal component shall be doable using front access. It depends on product requirements whether the modules can be placed with their back sides touching or whether a small gap is needed (e.g. for cooling air circulation).
L-shape
In case of L-shape the lineup has one “90-degree bend”, i.e. it consists of two perpendicular sub-sections. Besides the functional modules, an additional corner module is often required. It helps to keep normal design for the standard modules while allowing connections in between the modules (e.g. water piping, busbars, power cables and control/signal cables.
U-shape
“U-shape” has three main sections of the lineup. The cabinet doors can be on the outside or inside. Outside variant seems more frequent (with just narrow corridor in between both arms for installation or maintenance access). U-shape typically contains two corner modules or an additional interconnecting module besides the standard modules. This option is suitable for very long lineups.
Summary
Majority of VFDs use a straight lineup as their default layout. However, the standard layout may not fit into the existing building or electric room. Especially brownfield projects may pose many restrictions with regards to the dimensions of the VFD. In such case, alternative layout options can be very useful. This article presents the most common variants: back-to-back arrangement, L-shape or U-shape. On top, some modules can be separated and placed stand-alone in the vicinity of the main lineup.
References
[1] Enclosure protection, MB Drive Services, January 2022, available online, https://mb-drive-services.com/enclosure-protection/
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