Computerized Maintenance Management Systems (CMMS) allow you to track and trend equipment breakdowns through Failure Hierarchies.  Once a Failure Hierarchy has been entered into the CMMS for a specific type of equipment, maintenance personnel are able to identify the failure(s) they found during maintenance work, and how they fixed it.  A recurring set of similar failures, causes, or remedial actions can then be identified using the CMMS.  This information allows maintenance personnel to apply new preventive maintenance, adjust the frequency of existing preventive maintenance, or make other adjustments (for example, switching to a different type of grease) to address the trend.

The following is a matrix showing the terms I will use in this article, and the various Failure Hierarchy field names for some of the popular CMMS software packages.

To create the Failure Hierarchy for an indoor dry-type transformer, begin by identifying the "Class" and "Subclass" of the equipment.  Class identifies the component.  Example Classes include:  pump, circuit breaker, motor, transformer, etc.  The Class for this equipment is "transformer".  Subclass consists of an adjective(s) used to uniquely describe the component.  Example Subclasses for a transformer include:  dry, oil filled, etc.  The Subclass for this equipment is "dry".

Failure Hierarchies are typically created for each subclass.  The simplest way to create the Failure Hierarchy is from a Failure Modes and Effects Analysis (FMEA).  For instructions on how to perform an FMEA, refer to the article entitled "Performing a Failure Modes and Effects Analysis on a Dry-Type Transformer" in the June 2019 issue of Transformer Technology Magazine.  I will use the FMEA created in that article to write the Failure Hierarchy.  The pertinent fields from that FMEA are "Failure Mode" and "Cause" which are shown below.

For the Class/Subclass of Dry Transformer, I will now populate the remaining 3 Failure Hierarchy fields:

There can be multiple "Failures", multiple "Causes" for each "Failure", and multiple "Remedies" for each "Cause".  I will begin by using the Failure Modes from the FMEA to populate the "Failure" field in the Hierarchy.  The first 2 Failure Modes, "Loose Cable/Connections" and "Connection or Cable Failure", can be combined into a single Failure of "Transformer Cable/Connection Failure".  The remaining 3 Failure Modes can be entered as is, resulting in the following entries:

Next, I will use the FMEA Causes to write the Failure Hierarchy Causes.  For the Hierarchy Failure "Transformer Cable/Connection Failure", the applicable FMEA Causes are: 

Three FMEA Causes come directly over:

• Incorrect installation
• Dirt or other contaminant build-up
• Electrical or thermal overload

The remaining FMEA Causes are for "age" and "corrosion".  In the Failure Hierarchy, corrosion can be added as-is, but I list age related degradation as "damage".  Last, I will add a Cause for a "loose connection" as follows:

• Cable/Connection Corroded
• Cable/Connection Damaged
• Loose Connection

The complete list of Failure Hierarchy Causes for "Transformer Cable Connection Failure" then becomes:

I'm going to write the Causes for the Failure Mode "Transformer Forced Air Cooling Failure" next.  The applicable FMEA Causes are:

These FMEA Causes come directly over, with age related degradation listed as damage:

• Dirt/Contaminant Build-Up
• Insufficient Grease
• Fan Electronic Controls Failure
• Fan Damaged

Giving us:

Moving on to the next Failure Mode, "Transformer Insulation Failure", the applicable FMEA Causes are:

In the Failure Hierarchy, I express age related degradation as "damage".  These Causes then become:

• Electrical or Thermal Overload
• Insulation Physically Damaged

Giving us:

For the final Failure Mode "Transformer Windings Failure", the applicable FMEA Causes are:

In the Failure Hierarchy, these Causes become:

• Electrical or Thermal Overload
• Windings Physically Damaged

This completes the first 2 fields of our Failure Hierarchy:

Finally, I will write the "Remedies" for each Cause.  The Remedies are standard repair practices for dry-type transformers used by electrical maintenance crews, which the FMEA does not contain.  These are written in past tense because the electrician will select the Remedy implemented after the work has been completed, not before.  Examples of common Remedies include greasing a fan, cleaning a connection, replacing a cable, etc.

Beginning with the "Transformer Cable/Connection Failure", and first Cause "Cable/Connection Corroded", there are 2 possible Remedies:

For the same Failure, second Cause of "Cable/Connection Damaged", there is only one Remedy:

For the same Failure, third Cause of "Dirt or Contaminant Build-Up", there is only one Remedy:

For the same Failure, fourth Cause of "Electrical or Thermal Overload", there is also only one Remedy:

For the same Failure, fifth Cause of "Incorrect Installation", again, there is only one Remedy:

For the same Failure, sixth Cause of "Loose Connection", once again, there is only one Remedy:

Moving on to the "Transformer Forced Air Cooling Failure", for the first Cause "Dirt/Contaminant Build-Up", there is only one Remedy:

For the same Failure, second Cause of "Insufficient Grease", there is only one Remedy:

For the same Failure, third Cause of "Fan Electronic Controls Failure", there is only one Remedy:

For the same Failure, fourth Cause of "Fan Damaged", there are two Remedies:

Moving on to the "Transformer Insulation Failure", for the first Cause "Electrical or Thermal Overload", there are three possible Remedies:

For the same Failure, second Cause of "Insulation Physically Damaged", the same three possible Remedies exist:

Moving to the "Transformer Windings Failure", for the first Cause "Electrical or Thermal Overload", there are two possible Remedies:

For the same Failure, second Cause of "Windings Physically Damaged", the same two possible Remedies exist:

This completes the Failure Hierarchy:

It is ready to be entered into the CMMS and used to adjust your dry-type transformer maintenance strategy, making it more effective and resulting in better reliability.