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Transformer Health Analysis Using AMS Data
Presented by Steven Dennis and Charles Douglas III May 04, 2017 SWEDE 2017 Conference
~ 630 miles
~ 390 miles
Texas’ largest regulated transmission and distribution utility – 6th largest in the U.S.
117,000 miles of transmission and distribution lines
54,000 square miles of territory
3.4 million meters
Oncor Electric Delivery
Motivations For AMS Data Analysis
Electric utilities have recognized that analyzing voltage and loading data associated with transformers can help detect the likelihood of transformer failure. Analyzing Advanced Metering System (AMS) historical data allows us to develop insights into transformer health and, subsequently, to take proactive measures to plan the remedy instead of reacting to an outage after a failure.
AMS Data Analysis Use Cases
Identification of transformer winding damage issues • Proactive replacement • Employee safety e.g., daylight vs. dark in back yards • Scheduled replacement for added customer convenience • Improved service quality – reduced outage time Identification of overloaded transformers • Proactive load management • Labor load leveling • Employee safety e.g., daylight vs. dark in back yards • Scheduled replacement for added customer
convenience • Reduced environmental impact Identification of connectivity and phasing issues • Increase accuracy in system modeling for predictive
analysis
Data Sources Advanced Metering System (AMS) • KWH
• 15 minute data (5 year availability) • Instantaneous voltage
• 2 samples per day that are spaced to approximate the peak and valley of the daily load cycle
• Average voltage • 15 minute interval • About three million meters
Electrical Model
Proof of Concept for Shorted Coil Transformers - March 2016
Process • Sent out a spreadsheet to service centers with identified
locations • Issues were validated by field technicians and the
transformers were replaced • Verified that the voltage from AMS returned to a normal
range • Damaged transformers tested at the Oncor repair facility
• Transformer Turns Ratio (TTR) • Visual inspection • Arrester testing
• Break over voltage • Current leakage
Proof of Concept Results
205 transformers identified through the process and were validated
8 regulation-related issues addressed
• 84 transformers affected by the regulation issues
121 transformers tested and retired at the Oncor transformer shop Every transformer identified and tested had damaged coils
• Proof that the identification process works
Transformer Voltage Profiles
Coil Damage
Regulation
Connectivity Identification Example
Transformer A
Transformer B
Meter 1
Meter 3 Meter 2 Meter 1
Meter 3 Meter 2
Phasing Issue Identification
Lightning Analysis – Overvoltage Began Sept 24, 2016
Voltage Analysis Tool
Intranet Based Field Interface
Status Update for AMS Exceptions
This automated email is sent out to all service centers once a week
The top chart is all unresolved issues by service center
The bottom chart shows all work that was completed in the past week
Daily Targeted Email Notification
An automated email sent on a daily basis to the responsible service center anytime there is a new issue waiting for resolution in the interface
Project Results as of April 18th, 2017
Resolved Issues
Issue Year to Date Project to Date Damaged Winding Transformers 131 557 Regulation (Issue Count) 133 268
Benefit Realized
Customer Interruption Minutes (CIM) Avoided
112,360 399,885
Overloaded Transformer Analytics Using AMS Data
When a transformer is connected to a load that exceeds its KVA rating for a sustained period of time, excessive heat is generated in the windings.
Sustained overloading has an accumulative destructive effect on the integrity of the insulating fluid, winding and its insulation.
Once the insulating properties of the windings are compromised, the transformer will ultimately fail with an open or shorted coil.
Our goal here is to use AMS data to predict the end of life for a transformer and proactively address the overload condition before it fails.
Overload Project Target Selection Criteria
Single phase 120/240V secondary buses
Residential meters
Used daily kWh to select initial targets
Mean to peak kWh coefficient
Low-voltage correlation to overloaded transformers
Targets taken from 140-200% secondary bus kVA capacity
Low Voltage to Loading Correlation
Overload Project – March 2017
101 transformer buses were selected from the target population zone • Between 140 and 200% projected peak load
Intranet interface was developed and rolled out for communicating issues and receiving status feedback from the field • Transformer size validation • Meter connectivity validation • Connectivity corrective information (where applicable)
If the bus connectivity was valid (field matches the electrical model) the overload issue was proactively resolved • Upsized the transformer • Split up secondary bus and added an additional transformer
Typical Reactive Transformer Failure Rate by Month
6.49%
6.51%
8.02%
8.09%
10.60%
11.18%
11.99%
10.74%
8.07%
6.41%
5.48%
6.42%
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
Thre
e Ye
ar A
vera
ge
One Year Load Chart Using 15 Minute Load Data
Next Steps
Reduce connectivity issues sent to operations through the use of statistical voltage profile validation
Utilize historical 15-minute average kWh data to validate targets after the voltage profile analysis has validated the likelihood of correct model connectivity
Calculate top oil, hot spot temp., and transformer loss of life to further target near term failures • IEEE C57.91-2011 formula
Final Thoughts
Access to AMS data opens up a new window of opportunity for the discovery of efficiency improvements – most may not have even been envisioned at this point in time
The value of AMS is difficult to extract without connecting it with the electrical model to form a complete picture and this is where proficiency in data mining skills coupled with model knowledge is essential
Model connectivity errors is an industry-wide issue that is critical for the accurate analysis of AMS data but, ironically, AMS data also offers a solution for identifying connectivity issues
Questions?