Harmonic Mitigating Transformers (HMTs) are specialized electrical devices designed to reduce energy wastage by minimizing losses caused by harmonic distortions. They achieve this through several mechanisms:
1. Triplen Harmonic Cancellation: By cancelling out zero phase sequence harmonic fluxes, HMTs prevent triplen harmonic currents from circulating in the primary windings. This results in a decrease in primary side I2R and eddy current losses.
2. Balanced Harmonic Reduction: HMTs equipped with multiple outputs are capable of cancelling the balanced components of higher order harmonics like the 5th and 7th within their secondary windings. Only the unbalanced residual harmonics reach the primary windings, leading to a reduction in losses.
3. High Efficiency at Both Fundamental and Harmonic Frequencies: Certain HMT designs maintain high efficiency not just at the standard 60Hz but also at harmonic frequencies. Models that comply with Energy Star standards meet NEMA TP-1 efficiency minimums at 35% loading, achieving this by lowering core losses to boost efficiency under light loads. Mirus' Energy Star compliant Harmony™ Series HMTs are engineered to meet NEMA TP-1 minimum efficiencies across the full operational range from 35% to 65% loading.
Figure 1 :75 kVA Transformer losses at various loading conditions with non-linear K-9 load profile.
Energy Savings Demonstrated:
An example provided in Figure above showcases the potential savings achieved by using HMTs instead of conventional or K-rated transformers. A 75 kVA transformer was analyzed under different load conditions with a non-linear K-9 load profile, typical of environments with heavy computer equipment usage (Ithd = 83%). The graph compares losses between a conventional delta-wye transformer (Conv), a K-13 rated delta-wye transformer, and a Harmony-1E™ single output Energy Star compliant HMT.
Figure 2 : Energy Efficiencies for various types of 75 kVA transformers supplying linear (K-1) loads and non-linear (K-9) loads under varying load conditions.
Impact of Non-Linear Loading on Efficiency:
This Figure further illustrates how non-linear loading affects transformer efficiency. It contrasts the performance of different transformers under both linear (K-1) and non-linear (K-9) loading conditions. Efficiency drops significantly for conventional and K-13 transformers under non-linear loading, particularly at higher loads.
Estimating Energy Savings:
To quantify energy savings from reduced harmonic losses, one must consider the electric utility rate and the load's operating profile. These factors can vary widely based on location and application. Table 1 demonstrates the energy savings when comparing a 75 kVA HMT to a K-13 transformer in an office setting with extensive computer equipment.
HMT energy savings and payback estimate comparing a 75 kVA HMT to a K-13 transformer in a typical office environment with a high concentration of computer equipment
Calculation of Annual Savings:
Assuming operation for 12 hours per day, 260 days a year, with an average utility rate of $0.07 per kWh, and accounting for additional cooling energy needed to dissipate transformer-generated heat (estimated at 30%-40% of the loss power), the annual savings can be calculated as follows:
Annual Consumption = (Total losses in kW) x (hrs/day) x (days/yr) + (NL loss in kW) x (24 – hrs/day) x (365 – days/yr)) $/yr Savings = (H1E Annual Consumption – K13 Annual Consumption) x 1.35 x (rate in $/kWhr)
Payback Analysis:
Based on transformer costs and assuming a lifespan of 30 to 40 years, the premium paid for a Harmony-1E HMT can be recovered many times over through energy savings alone. Payback periods are typically 1 to 4 years for loading in the 50% to 65% range.
Additional Example:
Table 2 presents a scenario for a broadcasting facility or data center with lower harmonic content (K4 load profile), operating 24 hours a day, 365 days a year. With the transformer in an air-conditioned area, the payback period becomes even shorter, making the investment in HMTs particularly attractive in such applications.
Table 2: HMT energy savings and payback estimate comparing a 75 kVA HMT to a K-13 transformer in a typical Broadcasting Facility or Data Center
In conclusion, the intrinsic capability of HMTs to cancel out harmonic currents within their windings translates into measurable energy savings when compared to the higher losses incurred with conventional or K-rated transformers. If we consider the average premium cost of HMT relative to K-13 transformers, the typical payback period for energy savings is 1 to 4 years when the load is expected to be in the range of 50% to 65%.
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