A Low-Cost Online Health Assessment System for Oil-Immersed Service Transformers Using Real-Time Grid Energy Monitoring
- A step-up transformer: the generated energy in power plants has low voltage and high current value. The step-up transformers are usually used in all generating plants to support stepping up the voltage supply from a low level to a higher level for efficient electricity transmission .
- A step-down transformer or distribution substation is used to convert the high voltage level of the transmission lines to a lower voltage level and adapt it to the distribution grid.
- A service transformer is the final voltage transmission step in the distribution grid. This type of transformer is applied to convert the voltage of the distribution grid level to home level. The nominal power of this type of transformers is usually below 1 MVA.
- Investigate the importance of transformers’ components and then select the most effect indicators to assess the condition of service transformers.
- Propose an online assessment system using the Fuzzy logic evaluation model that responds quickly to the variations of inputs to monitor service transformer health using real measurements without adding expensive sensors and interrupting transformer operation.
2. Structure of an Oil-Immersed Service Transformer and Selection of Monitoring Indicators
- The transformer tank is the physical component which is used to protect the transformer core and windings. It is also an oil container to cool down the transformer.
- Insulating oil is an insulation for core and windings.
- Bushing is applied to provide insulation when the terminals are routing through the tank to connect the transformer with the electric network.
- The tap changer is applied to adjust the transformer’s output voltage. For low-voltage service transformers, it is impossible to change the when the transformers are energized; the change could be implemented after the transformer is isolated from the grid.
3. Assessment Indicators for Service Transformers
3.1. Top Oil Temperature Estimation
- Δθoil is is the rise of the top oil temperature at the current conditions, °C
- Δθoil,R is the rise of the top oil temperature at the rated conditions, °C
- Set R represents the ratio of the core’s heat generation to the winding’s heat generation at rated load
- K represents the load factor
- τTO is the time constant, hour
3.2. Vibration Estimation
3.3. Transformer Loading
4. The Online Monitoring System for Service Transformers
5. Simulation Results and Discussion
- Scenario 1: Evaluate the transformer health using 1-day data to evaluate the sensitivity of the monitoring program to the abnormal changes in the transformer. The electrical parameters were aggregated using an energy monitoring device on 1 November 2019. Three sub-cases were implemented in this scenario to compare the results.
- Scenario 2: Evaluate the transformer health using 2-week data. Basically, the assessment of transformer condition requires long-term observation to assess the actual condition of the transformer and not just based on temporary and unstable evaluation results. This is important in making the final decision as to whether to repair or replace the transformer. The electrical conditions on the transformer were measured in December of 2019.
5.1. Evaluate the Transformer Health Using 1-Day Data
- Case 1: The transformer works at normal condition. The peak transformer load is mostly changing in the range from about 40% to 80% rated capacity of the transformer.
- In case 2 and case 3, the transformer’s load profile is modified to check how the output health index will change in new conditions:
- Case 2: Transformer is assumed to be in “Fair” operating condition. The peak transformer load is simulated to change in the range from about 50% to 150% rated capacity from 12:00 pm to 1:30 pm. The overload doesn’t happen continuously, but it is “on”, “off” in some period of time.
- Case 3: Transformer is assumed to be in “Poor” operating condition. It is worse than case 2 and is worst-case, which could happen to any old transformer. The peak transformer load is simulated to change in the range from about 100% to 150% rated capacity in a longer period of time from 9:00 am to 1:30 pm, equivalent to the operating data of an old transformer.
5.2. Evaluate the Transformer Health Using 2-Week Data
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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|Limit Ranges||Fuzzy Membership|
|TL ≤ 80%||Good|
|80% ≤ TL ≤ 100%||Needs caution|
|TL ≥ 100%||Poor|
|Top oil temperature|
|θtop oil ≤ 80 °C||Good|
|100 °C ≤ θtop oil ≤ 115 °C||Poor|
|θtop oil ≥ 115 °C||Very poor|
|100 °C ≤ θtop oil ≤ 115 °C||Poor|
|0 ≤ νtank ≤ 40 dB||Good|
|40 dB ≤ νtank ≤ 55 dB||Needs caution|
|55 dB ≤ νtank ≤ 60 dB||Poor|
|νtank ≥ 60 dB||Very poor|
|7.5 ≤ Health index ≤ 10||Good||Maintenance as normal|
|5 ≤ Health index ≤ 7.5||Fair||Needs more |
|3.0 ≤ Health index ≤ 5.0||Poor||Planning |
|Health index ≤ 3.0||Very poor||Immediate |
|1||Top oil-temp = Very poor||HI = Very poor|
|2||Vibration = Very poor||HI = Very poor|
|3||Top oil-temp = Very poor and Vibration = Poor and Transformer loading = Poor||HI = Very poor|
|4||Top oil-temp = Very poor and Vibration = Need caution and Transformer loading = Poor||HI = Very poor|
|5||Top oil-temp = Poor||HI = Poor|
|6||Top oil-temp = Good and Vibration = Poor||HI = Poor|
|7||Top oil-temp = Need caution and Vibration = Poor||HI = Poor|
|8||Top oil-temp = Need caution and Vibration = Need caution||HI = Fair|
|9||Top oil-temp = Need caution and Vibration = Good||HI = Fair|
|10||Top oil-temp = Good and Vibration = Good and Transformer loading = Poor||HI = Fair|
|11||Top oil-temp = Good and Vibration = Need caution||HI = Fair|
|12||Top oil-temp = Good and Vibration = Good||HI = Good|
|Case 1||Case 2||Case 3|
|Top oil temperature|
|STT||Style||Installation Year||Voltage (KV)||Rated Power (KVA)||Top Oil Temperature |
|Transformer Loading |
|Fuzzy Logic Health Index||Health Index Given By CGC|
|Comparison Results||Proposed Method Evaluation|
|Good||Fair||Poor and Very Poor||Total|
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Tran, Q.T.; Roose, L.; Doan Van, B.; Nguyen, Q.N. A Low-Cost Online Health Assessment System for Oil-Immersed Service Transformers Using Real-Time Grid Energy Monitoring. Energies 2022, 15, 5932. https://doi.org/10.3390/en15165932
Tran QT, Roose L, Doan Van B, Nguyen QN. A Low-Cost Online Health Assessment System for Oil-Immersed Service Transformers Using Real-Time Grid Energy Monitoring. Energies. 2022; 15(16):5932. https://doi.org/10.3390/en15165932Chicago/Turabian Style
Tran, Quynh T., Leon Roose, Binh Doan Van, and Quang Ninh Nguyen. 2022. "A Low-Cost Online Health Assessment System for Oil-Immersed Service Transformers Using Real-Time Grid Energy Monitoring" Energies 15, no. 16: 5932. https://doi.org/10.3390/en15165932