NEMA TP1 Energy Efficiency Standard

Single Phase and Three Phase

NEMA TP1 Energy Efficiency Standard
NEMA TP1 Energy Efficiency Standard

Most commercial and industrial facilities require several low-voltage transformers to decrease the voltage received from the utility to the voltages used by various loads such as lighting, computers and other electrically operated equipment. Standard transformers convert approximately 95% of the electricity received into usable output voltage.

Since these transformers are energized continually, even a small improvement in efficiency can provide significant energy savings.

These energy efficient transformers are specifically designed to help save money on utility bills and reduce energy waste. Depending on the size of the transformer, a “NEMA TP1 compliant” transformer can save $100-300 each year at an electricity rate of $0.075 cents per kWh.

A typical large commercial facility will have 6-10 low voltage transformers, and thus can save between $600 and $3,000 per year.

Basic Design Characteristics

The TP1 designs include the use of higher grade electrical steel and other features designed to lower flux density and reduce losses especially at average 35% loading where the TP1 measurements apply.

To meet TP1 the design engineer must consider both the “I square R” losses and the core or iron loses. Simple de-rating from a higher kVA will not satisfy the TP1 standards as the efficiency level is dependent on the combination of core (no-load) losses and I2R (winding) losses. The core construction employs the use of high quality non-aging electrical grade grain-oriented silicon steel with high permeability, low hysteresis and low eddy current losses. These characteristics are required to achieve the TP1 efficiency levels.

Core laminations must be tightly assembled enabling magnetic flux densities to be kept well below the saturation point. The core and coil designs must be low loss type with minimum efficiencies per NEMA TP1 when operated at 35% of full load capacity. Efficiency shall be tested in accordance with NEMA TP2 (Standard test method for measuring the energy consumption of distribution transformers).

The efficiency levels must meet the following minimums.

TP1- Energy Efficient transformers

Single PhaseThree Phase

New Super Energy Efficient Transformers:


TP1S transformer designs surpass the NEMA TP1 standards for efficiency. These units are designed not to exceed 115°C temperature rise above a 40°C ambient under full linear load and not to exceed 150°C rise under a non-linear load level of K13 (K20 for HMT units).

Standard features of the TP1S, HM1S, HM2S units include:

  • Higher efficiency level with Linear Load Efficiency: 25% less loss than NEMA TP-1 from 35% to 65% load @ 75°C for sizes 15-750KVA
  • TP1S units are TP1 Rated efficiency under non-linear loads with a load profile of K13 at 50% loads @ 75°C
  • Noise levels are 3 dB lower than NEMA ST-20
  • Standard 200% neutral
  • K13 rating on nameplate (K20 for HMT units)
  • Electrostatic shield
  • Ten year pro-rated warranty with standard liability limitations same as Sentron Harmonic Mitigation units

SOURCE: Siemens Power Distribution and Control

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About Author //


Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry fascilities. Professional in AutoCAD programming. Present on

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