Transformer No-Load Loss, Load Loss, and Impedance Voltage Calculation Explained

Understanding transformer losses is essential for power utilities, industrial users, and electrical engineers aiming to improve energy efficiency and reduce operating costs. Transformer losses are mainly divided into no-load loss (iron loss) and load loss (copper loss).
Overview of Transformer Losses

Transformer losses consist of two primary components:

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No-load loss (Po): Also known as iron loss, caused by hysteresis and eddy currents in the transformer core. It remains nearly constant as long as voltage and frequency are stable.

*
Load loss (Pk or Pc): Mainly copper loss generated by winding resistance when load current flows. It varies with load and is proportional to the square of the current.

The total transformer loss is expressed as:

P = Po + Pc

Transformer Loss Calculation Formula

Transformer losses can be evaluated using the following standard formulas:

Active power loss:

P = Po + KT Pk

Reactive power loss:

Q = Qo + KT Qk

Comprehensive power loss:

Pz = P + KQ Q

Where:

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Po - No-load loss (kW)

*
Pk - Rated load loss (kW)

*
Qo - No-load reactive loss (kvar), Qo almost equal to Io% Sn

*
Qk - Rated load reactive power (kvar), Qk almost equal to Uk% Sn

*
Sn - Rated transformer capacity (kVA)

*
Uk% - Percentage short-circuit voltage

*
Io% - No-load current percentage

*
- Load factor

*
KT - Load fluctuation loss coefficient

*
KQ - Reactive economic equivalent (kW/kvar)

Recommended Parameter Selection

For practical engineering calculations, the following values are commonly used:

*
KT = 1.05

*
KQ = 0.1 kW/kvar (for 6kV-10kV urban and industrial power grids at minimum load)

*
Load factor ():

*
Agricultural transformers: 20%

*
Industrial transformers (three-shift operation): 75%

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Annual operating hours: 8760 h

*
Maximum load loss hours: 5500 h

Transformer-specific parameters such as Po, Pk, Io%, and Uk% should be obtained from manufacturer nameplates or factory test reports.

Calculation of Iron Loss and Copper Loss Energy

Iron loss energy consumption:

Iron loss (kWh) = Po (kW) times Operating time (h)

*
Continuous power supply users: 720 h per month

*
Intermittent supply: calculated based on actual energized hours

*
Users with accumulation clocks: based on recorded power supply time

Copper loss energy consumption:

*
When average load rate less than or equal to 40%: Copper loss = Monthly energy consumption times 2%

*
When average load rate > 40%: Copper loss = Monthly energy consumption times 3%

Load rate formula:

Load rate = Energy consumption / (Sn times T times cos)

Where T = 720 h and cos almost equal to 0.8.

Transformer Efficiency

Transformer efficiency is defined as:

= Pz / (Pz + P) times 100%

Where Pz is the transformer output power.

Typical transformer loss levels:

*
Copper loss: ~0.5%

*
Iron loss: ~5-7%

*
Dry-type transformers generally exhibit lower total losses than oil-immersed transformers.

No-Load Loss Measurement and Standards

No-load loss is measured by applying rated sinusoidal voltage to the primary winding with the secondary open-circuited. Accurate measurement requires:

*
Near-perfect sinusoidal voltage waveform

*
Difference between average and RMS voltage readings less than or equal to 3%

*
High-accuracy CTs, PTs, and wattmeters suitable for low power factor measurement

With modern low-loss core materials such as grain-oriented silicon steel and amorphous alloys, no-load power factors are extremely low, placing higher demands on test equipment accuracy.

Professional Transformer Testing Solution

For precise measurement of transformer no-load and load losses, the RDBK- Transformer Load and No-Load Tester [https://www.wrindu.com/product-search?key=RDBK-III] is a reliable and efficient solution.

The RDBK- integrates:

*
Advanced single-chip microcomputer technology

*
High-precision A/D synchronous AC sampling

*
Digital signal processing algorithms

This ensures accurate, stable, and repeatable test results, making it ideal for factory testing, site commissioning, and maintenance applications.

About Transformer Testing Solutions

Modern transformer testing plays a critical role in energy efficiency evaluation, condition assessment, and compliance with international standards. Selecting the right testing equipment helps utilities and industries reduce losses, improve system reliability, and achieve long-term cost savings.

For more information on transformer testing equipment or to request the latest quotation, please contact us [https://www.wrindu.com/contact] directly.

For more HV Testing Equipment, visit official website: www.wrindu.com / www.hvtesters.com

Media Contact
Company Name: Rui Du Mechanical and Electrical (Shanghai) Co., Ltd.
Contact Person: Wrindu
Email:Send Email [https://www.abnewswire.com/email_contact_us.php?pr=transformer-noload-loss-load-loss-and-impedance-voltage-calculation-explained]
Phone: 13661908522
Address:No.500 Jianyun Road, Pudong New Area
City: Shanghai
Country: China
Website: https://www.wrindu.com/

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