# Electrical loss reduction: Science and thermodynamics

Why tiny percentages of loss add up to huge totals

Source page: https://www.materialinsights.org/energy/e_electrical_recovery/rc-sci/

What this tab covers The thermodynamics: the grade (temperature or pressure) of the energy being recovered, energy versus exergy efficiency, and how harsh the waste stream is on equipment.

Electrical losses are small as a percentage but huge in total, because motors and transformers handle most of the world's electricity. Most of the value lies in avoiding the loss; reusing the low-grade heat it creates usually needs a heat pump.

#### Grade of energy
Mixed

Losses in transformers and motors end up as low-grade heat in oil, windings and cooling air. A UK study found transformer oil leaving at only about 33 to 43 C at 40 to 60% load, so the heat needs a heat pump to feed a district heating network at 75 C. Reactive power and harmonics are different. They are not lost energy as such, but they carry extra current that heats cables and transformers. Regenerative inverters deal with the highest-grade stream, braking energy in a motor drive, which goes straight back into grid-quality electricity. Electric motor systems used about 53% of global electricity, 13,462 TWh in 2023. US transmission and distribution losses averaged about 5% in 2018 to 2022.^[1](https://www.iea-4e.org/wp-content/uploads/2025/12/4E-Policy-Brief-EMSA-9-20251218.pdf)^[5](https://www.eia.gov/tools/faqs/faq.php?id=105)^[12](https://doi.org/10.1016/j.egyr.2023.09.074)
 Transformer oil outlet temperature about 33-43 C at 40-60% load^[12](https://doi.org/10.1016/j.egyr.2023.09.074) Motor systems' share of global electricity 53% (13,462 TWh, 2023)^[1](https://www.iea-4e.org/wp-content/uploads/2025/12/4E-Policy-Brief-EMSA-9-20251218.pdf) US T&D losses about 5% (2018-2022)^[5](https://www.eia.gov/tools/faqs/faq.php?id=105)

#### Exergy versus energy efficiency
Mixed

Transformers are typically more than 99% efficient. ABB's 2,500 kVA example loses 2.78 kW with no load and 23.7 kW at full load, about 98.95% efficiency at full load and unity power factor (calculated). The UK study models losses at about 0.7% of rating at full load (calculated from its loss formula). Heat quantity is small and exergy is low, but heat pumps lift it efficiently: the study's transformer heat pump reached a seasonal COP (heat out per unit of electricity in) of 3.40, against 2.68 for air-source heat pumps. Motor losses split between stator copper (25 to 40% in older standard motors), rotor copper, iron core, friction and stray losses. Regenerative drives return high-exergy electricity. Otis and Danfoss quote harmonic current distortion of about 5% for their regenerative units (vendor claims).^[2](https://www.energy.gov/sites/prod/files/2014/04/f15/amo_motors_handbook_web.pdf)^[3](https://library.e.abb.com/public/929bc703922d49069e6920d5ce6ab9c1/53-57%202m522_EN_72dpi.pdf)^[6](https://www.otis.com/documents/256045/6552829/Regen_Drive_UK.pdf)^[12](https://doi.org/10.1016/j.egyr.2023.09.074)^[14](https://files.danfoss.com/test/Drives/DKDDPFP402A322_Active_Front_End.pdf)
 2,500 kVA transformer losses (vendor case) 2.782 kW no-load, 23.682 kW load^[3](https://library.e.abb.com/public/929bc703922d49069e6920d5ce6ab9c1/53-57%202m522_EN_72dpi.pdf) Transformer heat pump seasonal COP 3.40 (air-source 2.68)^[12](https://doi.org/10.1016/j.egyr.2023.09.074) Stator I2R share of motor losses 25-40% (older standard motors)^[2](https://www.energy.gov/sites/prod/files/2014/04/f15/amo_motors_handbook_web.pdf) Regenerative drive THD (vendor) 5% or less^[6](https://www.otis.com/documents/256045/6552829/Regen_Drive_UK.pdf)^[14](https://files.danfoss.com/test/Drives/DKDDPFP402A322_Active_Front_End.pdf)

#### Media compatibility and corrosiveness
Favourable

The media are clean: insulating oil, air and electricity. The engineering risks are electrical. A poorly applied passive filter or capacitor bank can resonate with the network and amplify harmonics. Passive filters suit stable loads with known harmonics. Active filters, which inject cancelling current in real time, suit variable loads such as drives. Compliance is judged against IEEE 519 at the point where the plant connects to the utility. Transformer heat recovery needs an oil-to-water exchanger that cannot leak water into the transformer.^[11](https://www.ecmweb.com/power-quality-reliability/harmonics/article/55396601/harmonics-what-electrical-contractors-need-to-know-part-2)

#### Variants compared^[3](https://library.e.abb.com/public/929bc703922d49069e6920d5ce6ab9c1/53-57%202m522_EN_72dpi.pdf)^[4](https://www.energy.gov/node/4839605)^[6](https://www.otis.com/documents/256045/6552829/Regen_Drive_UK.pdf)^[7](https://www.alstom.com/press-releases-news/2025/6/capturing-wasted-energy-our-cities)^[9](https://www.mahadiscom.in/consumer/wp-content/uploads/2019/03/KVAh-FAQs.pdf)^[10](https://www.mahadiscom.in:443/consumer/wp-content/uploads/2019/03/Methodology-PF-Penalty-Incentive.pdf)^[11](https://www.ecmweb.com/power-quality-reliability/harmonics/article/55396601/harmonics-what-electrical-contractors-need-to-know-part-2)^[12](https://doi.org/10.1016/j.egyr.2023.09.074)^[13](https://innovation.ukpowernetworks.co.uk/projects/full-circle)^[14](https://files.danfoss.com/test/Drives/DKDDPFP402A322_Active_Front_End.pdf)^[21](https://www.mahadiscom.in/consumer/wp-content/uploads/2020/04/Commercial_Circular_for_MYT_Order-3.pdf)

| Variant | What it recovers or avoids | Typical gain | Evidence in this pass |
|---|---|---|---|
| **Power factor correction** | Reactive current; tariff penalties | kVAh billing for HT consumers since 2020 makes low PF costly (Maharashtra); earlier penalty below 0.90 | MSEDCL and MERC documents |
| **Harmonic filters** | Harmonic heating, trips, resonance | Not quantified | EC&M (qualitative) |
| **Low-loss transformers** | Core and winding losses | No-load loss 2.78 to 1.75 kW in ABB example | ABB, US DOE |
| **Transformer heat recovery with heat pump** | Warm oil at 33-43 C | 56-81% of available heat reused (modelled UK case) | LSBU study, UKPN Full Circle |
| **Regenerative and bidirectional inverters** | Braking energy from drives | Lifts up to 75% (vendor); metros 99% of recoverable | Otis, Alstom, Danfoss |

#### Sources

1. [Electric motor systems: why are they important? Energy Efficiency Policy Brief EMSA 9](https://www.iea-4e.org/wp-content/uploads/2025/12/4E-Policy-Brief-EMSA-9-20251218.pdf) IEA 4E Electric Motor Systems Annex (EMSA), 2025
2. [Premium Efficiency Motor Selection and Application Guide: A Handbook for Industry](https://www.energy.gov/sites/prod/files/2014/04/f15/amo_motors_handbook_web.pdf) US Department of Energy, Advanced Manufacturing Office, 2014
3. [Transforming revenue: ABB's technology cuts transformer losses (ABB Review 2/2015; vendor case)](https://library.e.abb.com/public/929bc703922d49069e6920d5ce6ab9c1/53-57%202m522_EN_72dpi.pdf) ABB, 2015
4. [DOE finalizes energy efficiency standards for distribution transformers (press release, 4 April 2024)](https://www.energy.gov/node/4839605) US Department of Energy, 2024
5. [How much electricity is lost in electricity transmission and distribution in the United States?](https://www.eia.gov/tools/faqs/faq.php?id=105) US Energy Information Administration, 2023
6. [ReGen drive (product brochure, UK; vendor claims)](https://www.otis.com/documents/256045/6552829/Regen_Drive_UK.pdf) Otis
7. [Capturing wasted energy in our cities (Hesop reversible substations; company press release)](https://www.alstom.com/press-releases-news/2025/6/capturing-wasted-energy-our-cities) Alstom, 2025
8. [kVAh billing: frequently asked questions](https://www.mahadiscom.in/consumer/wp-content/uploads/2019/03/KVAh-FAQs.pdf) Maharashtra State Electricity Distribution Co. (MSEDCL), 2019
9. [Methodology for power factor penalty and incentive (MERC order in Case 195 of 2017)](https://www.mahadiscom.in:443/consumer/wp-content/uploads/2019/03/Methodology-PF-Penalty-Incentive.pdf) Maharashtra State Electricity Distribution Co. (MSEDCL), 2019
10. [Harmonics: what electrical contractors need to know, Part 2 (R. Ignall)](https://www.ecmweb.com/power-quality-reliability/harmonics/article/55396601/harmonics-what-electrical-contractors-need-to-know-part-2) EC&M, 2026
11. [Heat recovery opportunities from electrical substation transformers (Lagoeiro, Davies, Marques and Maidment), Energy Reports 10, 2931-2943 (open access)](https://doi.org/10.1016/j.egyr.2023.09.074) Elsevier, 2023
12. [Full Circle (transformer heat recovery project)](https://innovation.ukpowernetworks.co.uk/projects/full-circle) UK Power Networks, Strategic Innovation Fund, 2024
13. [VLT Active Front End drive (product sheet; vendor claims)](https://files.danfoss.com/test/Drives/DKDDPFP402A322_Active_Front_End.pdf) Danfoss, 2014
14. [Commercial Circular No. 323: implementation of MERC MYT order in Case 322 of 2019 (kVAh billing)](https://www.mahadiscom.in/consumer/wp-content/uploads/2020/04/Commercial_Circular_for_MYT_Order-3.pdf) Maharashtra State Electricity Distribution Co. (MSEDCL), 2020

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_electrical_recovery/index.md)
- [Overview](https://www.materialinsights.org/energy/e_electrical_recovery/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_electrical_recovery/correlation/index.md)
- [Engineering and integration](https://www.materialinsights.org/energy/e_electrical_recovery/rc-eng/index.md)
- [Economics and contracts](https://www.materialinsights.org/energy/e_electrical_recovery/rc-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_electrical_recovery/rc-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_electrical_recovery/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_electrical_recovery/links/index.md)