5.0 Reference: Application, Volume I, Chapter 5, Heritage Contract
1.5.30 Page 5-27: Provide a comprehensive explanation of the application of the Equipment Health Rating process to transformers and generators and provide examples of the output and how it has been used.
RESPONSE:
Equipment Health Rating (EHR) is an objective, repeatable equipment health evaluation system. EHR enables comparison of the health of BC Hydro generation assets. EHR has been developed to evaluate the following types of equipment: generators, exciters, turbines, governors, unit circuit breakers, unit transformers and coatings. Evaluation of the health criteria and test and inspection data is completed by a team of asset specialists.
The EHR system uses test and inspection data and other information to determine the condition or health of assets. The result is a technical evaluation of the asset resulting in a letter grade; Good, Fair, Poor, Unsatisfactory (G,F,P,U), as follows:
• Good no noticeable deterioration/defects;
• Fair some deterioration/defects exist (function not affected);
• Poor serious deterioration/defects exist in at least some portions
of the asset (function affected); and
• Unsatisfactory extensive deterioration/defects (no longer functions as
required).
In addition, the EHR process includes a "technical prescription" which is BC Hydro's asset specialists' recommendations on what needs to be done to restore the asset to “Good” condition, including a cost estimate and time period in which the work should be completed. This identifies future expenditures.
The technical prescription details the following:
• What? the intervention recommendation (e.g. replacement);
• When? the intervention timing (e.g. 2 to 5 years);
• Cost? a budget estimate of the intervention cost;
• How Long? an estimate of the time required to implement the intervention; and
The EHR results, along with economic, environmental and social risks are used to assess and prioritize investments. The Latent Risk Matrix shown below is used as a tool for investment prioritization.
The following examples illustrate the application of EHR for:
• GM Shrum unit transformers; and
• Mica generators.
Example 1. GM Shrum Unit Transformers
The EHR for assessing the condition of transformers includes the following criteria, and test and inspection data:
1. Age
2. Condition Index Tests and Inspections
• Gas in Oil Analysis
• Winding Insulation Megger Reading
• Winding Doble Power Factor Reading
• Furan Analysis
• Moisture Content.
• Bushing Doble Power Factor Test.
• Insulating Oil kV Breakdown
• Insulating Oil Power Factor (100 deg C)
• Insulating Oil Interfacial Tension
• Insulating Oil Moisture Content.
• Tank Surface Defects and Leaks
3. Known Problems
The results for GM Shrum T1 B-Phase Unit Transformer are as follows:
1. Age
The transformer is approximately 35 years old.
2. Condition Index Tests and Inspections
• The Gas in Oil Analysis indicates that the transformer paper insulation is overheating leading to premature failure.
• The Bushing Doble Power Factor Test indicates that the high voltage C1 bushing power factor is high indicating that insulation has deteriorated reducing the overall transformer performance.
• The Furan Analysis indicates that the paper insulation is ageing.
• The Moisture Content tests were not conclusive, indicating uncertainty with this particular test.
3. Known Problems
This transformer suffers from a severe known problem of low voltage lead overheating.
As a result, the most significant health measures indicated that the transformer is in "Unsatisfactory" condition and the technical prescription included a recommendation to replace the transformer. Replacement of the GM Shrum unit transformers rated "Unsatisfactory" is in progress.
Example 2. Mica Generators
The Equipment Health Rating for assessing the condition of generators includes the following criteria, and test and inspection data:
1. Forced Outages
2. Condition Index Tests and Inspections
• Stator Winding Insulation Resistance and Polarization Index Test
• Stator Winding High-Voltage Direct-Current Step Test
• Stator Winding Partial Discharge Test
• Rotor Winding Insulation Resistance and Polarization Index Test
• Rotor Pole Drop Test
• Stator Winding, Core and Support Inspection
• Rotor Winding, Core and Support Inspection 3. Trends of Condition Index Tests and Inspections 4. Age compared to industry life expectancy
5. Design
6. Spare Parts Availability 7. Technical Support 8. Safety
The results for Mica Unit 4 Generator are as follows:
1. Forced Outages
Mica Unit 4 has suffered four significant forced outages primarily due to core related problems. In particular, moving laminations cut into the stator winding insulation causing failures. On a number of occasions similar problems were discovered during inspections and were repaired prior to a failure occurring.
2. Condition Index Tests and Inspections
• Stator Winding High-Voltage Direct-Current Step Test results identify
weaknesses in the stator winding insulation system. The winding insulation system has failed during tests because of weakness caused by moving laminations.
• Stator Winding Partial Discharge tests show that the stator winding
continues to age at a faster than normal rate.
• Rotor tests show that the rotor is considered to be in acceptable and
expected condition for its age and operation.
• Inspection of the stator core studs since commissioning has revealed
core waves and lamination movement. A core stud was found to be broken during a routine maintenance inspection. Subsequent tests devised by Powertech Labs have identified and quantified core stud cracking. The stud cracking is a considered to be a significant problem and is caused by fatigue.
• Unit G4 also has a particular problem with the lower stator core
laminations migrating radially inward cutting into the winding insulation.
4. Age
The generator was commissioned in 1977.
5. Design
Stator core waves, lamination movement, and stud cracking are directly related to the generator design. This was verified by the Mica Stator Advisory Board Report dated 04 Dec 2003.
As a result, the most significant health measures indicated that the generator is in "Unsatisfactory" condition and the technical prescription included a recommendation to replace the generator stator.
The replacement of Mica Unit 4 Stator is listed in Chapter 11, Page 12, Table 11-4. Note that the reference in the table is incorrectly labelled as “Mica Units 1 to 4 Stator Replacement” instead of “Mica Unit 4 Stator Replacement”.
