Helpful Tips to Help You Specify an Online DGA Monitor
Once you’ve decided to install an online DGA monitor on your power transformer, correctly specifying the device is critical to ensure you get the best return on your investment.
To give you a better idea of what it takes to create an effective specification, I’ve grouped the kinds of requests we typically receive from customers into three distinct levels.
Level 1 specifications are the most basic and can sometimes be as short as a single sentence. Something like, “Please quote 7 gases + moisture online DGA system for 200 MVA power transformer”. In most cases, however, it goes into a bit more detail than this to include:
- the exact parameters to be measured
- communication methods (i.e. how to access information from the device)
- environmental conditions
- safety requirements
Unfortunately, level 1 specifications leave too much room for interpretation. To fulfill these requirements a vendor could build a very simple device that requires constant attention from the user during its two-year lifetime – hardly the ideal outcome.
Level 2 specifications are more complete, and typically include information on:
- the purpose of the system
- general requirements like standards and ambient conditions
- preferred measurement technology
- measured parameters with range and accuracy requirements
- sampling method and rate
- communication methods
While this is a great improvement, too many factors are still left open and some critical elements are missing, including the role of consumables, the expected device lifetime, and expected total costs.
Creating an effective specification
To give you an idea of the level of detail needed, the typical specification for a power transformer is a good place to start. You should begin by looking at what DGA monitoring technologies are available to make sure you understand the pros and cons of each one. Online DGA equipment also varies in terms of ease of operation, maintenance needs, and maintenance costs.
You also need to address the big question: “Is this device maintenance free, and what does that actually mean?” Based on discussions I’ve had with disappointed end users, claiming that a device is maintenance free when actually it’s nothing of the sort is something that many manufacturers seem to be guilty of. To help determine the maintenance needs of a device, it’s worth asking questions like:
- Does the system use wear components or consumables?
- Can the supplier clearly demonstrate that a device is maintenance free?
- Will there be commercial penalties if this is not the case?
In practice, this means that a level 3 specification should include the main points from level 2 with the following additions:
- expected lifetime of the online DGA monitor
- required warranty period and available options for extended warranty
- details of consumables or other operational costs during lifetime, if any
spare parts required during lifetime, if any
- calibration requirements and methods
- software fees or licenses
- details of installation and associated costs
By including lifetime costs, a level 3 specification makes a total cost of ownership (TCO) evaluation possible and helps to move the conversation away from empty words toward concrete measurable values, helping you to choose the solution that gives you maximum return on your investment.
Example of TCO comparison enabled by level 3 specification: