EngiMetric Arena / Engineering Trade-off
Choose a target power factor the capacitor bank can deliver
Competency Constraints and trade-offs primary Quantitative reasoning supporting
What you should take away: Relate a target power factor to the reactive compensation it requires, and choose a target inside a practical equipment limit.
The situation
What is happening
A 500 kW load runs at an existing power factor of 0.82. The project requires a target of at least 0.90, and the capacitor bank is limited to 160 kVAr. Specify a target power factor that the bank can achieve.
Given
| Quantity | Value | Unit | Note |
|---|---|---|---|
| Active power | 500 | kW | Plant load. |
| Existing power factor | 0.82 | - | Before correction. |
| Minimum target | 0.90 | - | Project requirement. |
| Maximum bank | 160 | kVAr | Installed compensation limit. |
Assumptions this challenge makes
- The load is steady at 500 kW and 0.82 power factor.
- The capacitor bank is rated at the system voltage and its output is not derated.
- Harmonic resonance and detuning are not modelled.
Limits this decision must satisfy
| Limit | Requirement | If it is breached |
|---|---|---|
| Required compensation | not more than 160 kVAr | Above the bank rating the specified power factor cannot be reached with the installed equipment. |
| Target power factor | not less than 0.9 - | Below 0.90 the design misses the project requirement even though the bank could reach it. |
Enter a target between 0.90 and the highest value the 160 kVAr bank can reach.
Your call
Your answer
Hints
- The reactive power to remove is the difference between the reactive demand at the existing and target power factors.
- Higher target power factor always needs more kVAr. Find where the 160 kVAr bank runs out.
- Stay above 0.90. Any target between the minimum and the bank limit is defensible.
Your answer Engine result
Where that comes from
Each limit, checked
Why
- At 0.82 the load draws about 349 kVAr. At 0.90 it needs about 242 kVAr, so the bank must supply about 107 kVAr.
- At 0.93 the requirement is about 151 kVAr, still inside the 160 kVAr bank. At 0.95 it rises to about 185 kVAr, which the bank cannot deliver.
- So the feasible target band is from 0.90 up to about 0.935. Every value inside it satisfies both the project minimum and the equipment limit.
- Choosing near 0.90 uses less compensation and leaves margin in the bank; choosing near the top reduces reactive current and losses but leaves little equipment margin. That is the trade-off.
- The calculation does not justify a single optimum. It defines the set of targets the installed equipment can actually achieve.
What this challenge does not establish
- The load is treated as steady at 500 kW and 0.82; real plant load varies and the target may need to be checked across the load profile.
- Capacitor output falls with voltage and temperature; no derating is applied.
- Harmonic resonance, detuning reactors and protection are not modelled.
- The bank rating is a project limit, not a verified manufacturer quotation.