Modelling POM's Electricity Grid HV Power Line's Capacity (MW)
Here I am doing an exercise in modelling (using MS Excel) the POM Electrical Power Grid HV power line's power carrying capacity (in megawatts) by running various 'what if' scenarios. I am holding as a constant the 'Lemon' conductor out of the 16 possible other different conductors or power line types and varying the line voltage to get the various outputs. Three (3) scenarios of voltage supply: 132 kV, 66 kV and 11 kV, are varied to check the 'Lemon' conductor's power carrying capacity at these different line voltages against an established cyclic load.
Refer to this link below to see the presentation of the MS Excel model in an earlier post where I had initially asked for information to identify the exact Electricity Grid HV Conductor (Power Line) type for POM. Unfortunately, at the time of writing this, no information was forthcoming so I am making the assumption in this modelling that the conductor is 'Lemon'. It kind of makes sense too because this 'Lemon' conductor capacity suited the characteristics of the cyclic loading and load shedding schedule being experienced now in POM.
Here is what the summary one-pager output of the model will appear like.
On the 'Summary Output' page of the MS Excel model is a graph and the horizontal 'red line' is the inherent conductor design capacity in MW. It will move up or down along the vertical axis depending on the conductor type selected as well as the other variables input into the tab 'Input & Assumptions' of the model. The future power demand will also move up or down depending on 'Known Increases' and 'Potential Increases'. The 'Average Present Power Demand' for a typical daily load cycle is also shown on the 'Summary Output' page.
For this typical daily load cycle for the POM Grid, it can be seen that a night load of about 35 MW starts to increase each weekday at about 6 a.m. and reaches its maximum value of about 75 MW to 80 MW at about 10 a.m., a level that is sustained through a large part of the day. This is around the times that load sharing/shedding begins. At about 5 p.m., the load begins to fall to the night level, which is reached around midnight. This pattern is repeated on almost all weekdays of the year. I am using the weekdays load cycle in this modelling.
The below images are the conductors' electrical and mechanical data sheets that are referenced in the model.
The constant assumptions are these: industrial weathered, summer noon and still air; with a power factor of 0.8; and potential increase is based on 2027 forecast peak load for POM Grid which is 27.8 MW.
For the moment I have plugged into the model these variable inputs:
*Power Factor: 0.8
*Square Root 3: 1.7329
*Line Voltage: 132000 or 66000 or 11000
*Conductor Code: Lemon
*Conductor Operating Location: Rural Weathered
*Seasonal Temperature Extremes (Expected): Summer Noon
*Wind Speed: Still Air
*Conductor Safety Factor: 1
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*Potential Increases (2027 Forecast Peak Load for POM Grid): 27.8 MW
These variables appear in the tab 'Inputs & Assumptions' of the model as below.
The '2027 Forecast Peak Load for POM Grid' is given below (in MWH and converted to MW by dividing by 8760 Hrs/year).
How The MS Excel Model Works
This is how the model works. After entering the above values into the fields in the tab 'Inputs & Assumptions', the model goes to the tab 'Conductor Electrical Data' and looks up the values then return them to the tab 'Inputs & Assumptions'. These returned values are highlight in 'lime green' and are then fed/linked into the formula in tab 'Workings' to calculate the conductor capacity in MW. The formula is:
(Power Factor x Square Root 3 x Line Voltage x Conductor Current Rating x Conductor Safety Factor)/1000000
Data (i.e. 'Typical Daily Cycle' and '2027 Forecast Peak Load for POM Grid') for this modelling entered into the tab 'Input & Assumptions' comes from this source: Asian Development Bank's Technical Assistance Consultant's Report, Project No. 40174, Produced in April 2009 and titled "Papua New Guinea: Power Sector Development Plan" (Financed by the Japan Special Fund).
If I had the exact conductor type and specific line voltages, I will enter the respective voltage and then select from the drop down list in the tab 'Input & Assumptions' and this will help answer the question "Has The POM Inherent Power Line Capacity Been Exceeded?" which I had also posed and posted in this link here?https://lnkd.in/gmKnsgfY
Model Output For Lemon Conductor At 132 kV
Model Output For Lemon Conductor At 66 kV
Model Output For Lemon Conductor At 11 kV
Conclusion
While I do not have the exact conductor types of the POM Electricity Grid to model specifically per power line voltage, the 'Lemon' conductor offers the maximum MW capacity for the POM peak loads. But even at the maximum capacity offered by the 'Lemon' conductor and at 132 kV, this modelling shows that the HV power line capacity of the POM Power Grid may have now been already exceeded.
Furthermore to this is the load shedding that is now being frequently experienced and this now gives rise to this concluding poser: is load shedding/sharing (apart from the possibility of the generation capacity being exceeded) also a symptom of the power line capacity being exceeded?
Electrical Engineer/Energy Specialist/Mining Professional/Project Manager
1 年Good analysis and write up. As a rule of thumb, the substation (SS) feeder load readings are indicating the magnitude of current on the main conductor. Normally the SS breaker is sized firstly to protect the conductor. If current ampacity of the conductor is exceeded, the SS feeder will respond by tripping on over current. If breaker does not trip, the conductor copes, even at peak loads. To reduce the stress on conductors, plan to have double circuits on towers, larger conductor size capturing future load growth, redundancy line routes, and have additional substations where required. These options would help the conductor performance.
Mechanical Maintenance Engineer
1 年.Very interesting analysis work. I work at the power station so a little I see from my I'll share with you. Current loadshedding is presently based on managing the following parameters, the grid frequency (50Hz) and the system voltage (66kV for POM). Frequency begins to decline when the load increases on the system the dispatch in response call for the power stations to increase their output. if that cannot be done (power stations reach max output) distributition feeders are removed to keep the cycle around the 50Hz mark, loadshedding has commenced. A big system like Port moresby has a considerable amount of inductive load, these affects voltage levels. To regulate that we need to have sufficient compensator ( capacitors) equipment on the system to improve the power factor on the system. When the grid compensator are saturated the dispatch is forced to remove a distribution feeder I.e. loadshedding... Hope this helps improve your analysis work