Metropolitan Electricity Authority, MEA Cloud Server
Remark: sorted by health index (HI), lowest first. Edge colour: green normal, yellow caution, red alarm. How HI is calculated
Sensor dots: green normal, yellow caution (slow blink), red alarm (fast blink), grey not trended. Hover for the reading, select to open the chart. or .
Each transformer starts at 100 points. Points are deducted for every monitored parameter whose present value is at caution or alarm level:
Ncaution is the number of parameters at caution level and Nalarm is the number at alarm level. Each parameter counts once, using its worst phase, and the result is kept between 0 and 100. Ambient temperature and tap position are shown for information and do not affect the score.
| Parameter counted | Caution level | Alarm level | Status now |
|---|
Good 85 to 100
Fair 60 to 84
Poor 0 to 59
The weights (12 and 30 points) and the caution and alarm levels are placeholders for design review. They should be replaced with values agreed under MEA asset management criteria, for example a weighted scoring method per parameter group.
| Substation and transformer | PD sensor (magnitude, PRPD) | DGA sensor (H₂) | Bushing sensor (C1, tan δ) | PD zone |
|---|
X means the sensor reports an abnormal reading, --- means normal. Select a row to open that transformer.
Slope = change of the reading per 100 A of load, from a straight-line fit. It is worked out for each day of the 30-day record, then the first 7 days (baseline) are compared with the last 7 days (recent).
Slope = change of the reading per 100 A of load, from a straight-line fit. It is worked out for each day of the 30-day record, then the first 7 days (baseline) are compared with the last 7 days (recent).
Paper insulation ages faster as the winding hot spot gets hotter. The hot spot is calculated every 10 minutes from the measured top oil temperature and load current (IEC 60076-7):
K is the load factor (highest phase current ÷ rated current), H = 1.3 is the hot-spot factor, gr = 26 K is the rated winding-to-oil gradient and y = 1.3 is the winding exponent. The ageing rate V for thermally upgraded paper then compares the insulation ageing with rated conditions (V = 1 at 110 °C):
Heat is not the only thing that ages paper. Water and oxygen in the insulation speed it up several times, which the temperature formula alone does not capture. The ageing rate is therefore multiplied by an environment factor:
Loss of life is added up over the selected period (24 h, 7 days or 30 days). Life consumed since commissioning = years in service × 8,760 h × the 30-day average of V × fenv × 0.85, where 0.85 allows for lighter loading in earlier years.
At the light loading typical of distribution transformers, insulation ageing alone gives very long lives, so the 50-year design life usually governs. A furan analysis or degree-of-polymerisation (DP) result from an oil or paper sample gives the actual paper condition and should replace this estimate when available.
| Hot spot | V | Life used per day |
|---|---|---|
| 80 °C | 0.036 | 0.86 h |
| 90 °C | 0.116 | 2.77 h |
| 98 °C | 0.282 | 6.76 h |
| 104 °C | 0.536 | 12.87 h |
| 110 °C | 1.000 | 24.00 h |
| 116 °C | 1.830 | 43.91 h |
| 120 °C | 2.709 | 65.01 h |
| 130 °C | 6.984 | 167.62 h |
| 140 °C | 17.199 | 412.79 h |
Normal ageing average V up to 1
Accelerated ageing average V above 1 up to 2
High ageing average V above 2
Every tap change wears the diverter switch contacts. Wear rises with the current being switched, but even a change at low current causes some arcing and mechanical wear. Wear is added up for each of the six contacts (main and transition contacts on phases R, Y and B):
Isw is the load current at the moment of the tap change and Ir the rated current, so a change at rated current counts as 1. The fixed part (0.2) is the minimum wear of any operation. ktype is 1.0 for transition contacts and 0.55 for main contacts, which carry less arcing duty. kphase is (phase current ÷ average current)², so the more heavily loaded phase wears faster.
300,000 is the rated electrical life in operations at rated current. Operations before the monitoring record are estimated with the average wear per operation of the recorded operations.
800,000 is the mechanical life of the tap changer. At light loading the mechanical life, not contact wear, is usually the limit. Remaining operations are also shown as years at the 30-day average operation rate; above 40 years the dashboard states that the service interval governs.
Service is due at 60,000 operations or 7 years after the last service, whichever comes first:
Operations per day is the average over the selected period (24 h, 7 days or 30 days), so the forecast date moves with the period you choose. Status turns caution within 90 days of the due date and alarm once service is overdue.
Healthy below 75% used
Plan replacement 75 to 89%
Replace 90% or more
Same limits apply to mechanical life used.
The 50-year design life, the environment factor (2.0 and 0.1 per ppm) and the 0.85 history factor are placeholders; set them from MEA asset policy and DP or furan results. Rated contact and mechanical life, the minimum wear (0.2), the exponent (1.5), wear factors and the service interval are placeholders for design review. Replace them with values from the tap-changer manufacturer for each OLTC model.
Selected transformer Caution Alarm ▲ Highest in fleet
Each cell is the maximum over the selected period. The bottom row shows where the selected transformer stands, for example 2nd of 10 means only one transformer has a higher value; bars compare it with the highest value in the fleet. Hover a cell for the phase and time. Rows are sorted by health index, lowest first. Select a column heading to sort by that value (again to reverse, a third time to return to HI order), or a row to switch transformer. Load current also shows % of rated, because units differ in rating.
Abnormal readings on this transformer with no active work order. Related readings count as covered, for example a bushing work order covers tan δ, C1 and a PD zone 2 result. Select Create to fill in the form.
| Work order | Work required | Linked reading now | Priority | Status | Assigned to | Due | Age |
|---|
Select a row to open the work order.
| Substation and transformer | HI | Active | Overdue | Awaiting verification | Needs a work order | Closed, last 30 days | Oldest open work |
|---|
Sorted by health index, lowest first. Select a row to switch to that transformer and follow its work.
Work orders are stored in this browser for the design review, with sample orders to start. In service they would be kept on the MEA server and shared by all users.
All values are simulated for design review. Caution and alarm limits are placeholders to be set against MEA asset management criteria. Data points every 10 minutes; present values refresh every 5 seconds.