In transformer maintenance, commissioning, and routine diagnostics, Winding Resistance Testing is instrumental in detecting potential hazards such as winding breakage, loose joints, and poor tap changer contact. Meanwhile, Transformer Turns Ratio (TTR) testing can effectively identify inter-turn short circuits, winding displacement, and off-nominal tap positions. Both tests serve as critical early warning mechanisms for faults. During Factory Acceptance Testing (FAT), they verify the compliance of winding configurations, conductor connections, and tap changer assemblies—timely eliminating manufacturing defects such as poor welding, incorrect turn connections, and turn deviations to guarantee product eligibility before shipment.
Consequently, these two tests are the most fundamental and vital among all transformer evaluation items, positioning them at the very top of the testing sequence. A failure in either Winding Resistance Testing or TTR indicates inherent physical defects at the manufacturing level (e.g., miscalculated turns or defective welding). This renders the transformer unqualified to proceed with subsequent high-voltage and performance tests.
Below is a curated list of the world's top 8 manufacturers of transformer Winding Resistance and TTR test equipment. Renowned for their exceptional measurement precision and long-term industrial reliability, these brands have become the benchmark choice for power utilities and transformer OEMs globally, delivering precise, code-compliant data to support your equipment commissioning, operation, and maintenance.
Founding Year: 1889
Current Development Status: Global industry pioneer and market leader.Headquartered in the UK, it has manufacturing facilities across Germany, Sweden, the US, and the UK, with an extensive sales network operating in over 130 countries.
Core Business Scope: High-voltage test equipment, cable fault location, protection relay testing, battery diagnostics, insulation testing, and transformer analytics.
Key Characteristics & Advantages: Unrivaled brand history; premium ruggedized field designs. Outstanding advanced software capabilities, multi-phase testing safety, and deep industry standard compliance.
Flagship Products:
Turns Ratio: TTR300 Series (Three-Phase Transformer turns ratio tester)
DC Winding Resistance: MTO300 Series (Automated Six-Winding Transformer Ohmmeter)
Website: https://www.megger.com
Official Email: sales@megger.com
Founding Year: 1984
Current Development Status: Top-tier global leader in power system testing and diagnostics. Headquartered in Klaus, Austria, it maintains 22 international offices and supports electrical grid utilities and manufacturers in over 170 countries.
Core Business Scope: Advanced testing and diagnostic solutions for primary and secondary substation assets, including power transformers, protection relays, circuit breakers, instrument transformers, and rotating machines.
Key Characteristics & Advantages: Industry gold standard for multi-functional, modular testing architecture. Exceptional software integration (Primary Test Manager), advanced automated tap-changer testing, built-in safety discharge features, and industry-leading partial discharge and insulation diagnosis.
Flagship Products:
Turns Ratio: TESTRANO 600 (Three-phase power transformer test system), CPC 100 + CP SB1 (Multi-functional test system with automated switch box)
DC Winding Resistance: TESTRANO 600 / CPC 100 (Features rapid three-phase simultaneous winding resistance measurement and automatic core demagnetization)
Website: https://www.omicronenergy.com
Official Email: info@omicronenergy.com
Founding Year: 2000
Current Development Status: Prominent European developer operated by IBEKO Power AB.Headquartered in Stockholm, Sweden, it supports power utilities and field service companies in over 100 countries.
Core Business Scope: Substation test solutions focusing on transformers, circuit breakers, and industrial battery testing.
Key Characteristics & Advantages: Renowned for inventing radically lightweight, portable, and mathematically advanced testing solutions using cutting-edge power electronics technology.3-year standard warranty.
Flagship Products:
Turns Ratio: TRT Series (TRT63A, TRT33A Three-Phase Ratiometers)
DC Winding Resistance: TWA Series (TWA40D, TWA25A Three-Phase Winding Ohmmeters)
Website: https://www.dv-power.com
Official Email: sales@dv-power.com
Founding Year: 1991 (Acquired by Doble Engineering Company in 2017)
Current Development Status: Operating as a specialized subsidiary under the Doble/ESCON Group brand. Based in Ontario, California, USA, serving international grid infrastructure operators.
Core Business Scope: Substation diagnostic equipment for circuit breakers, power transformers, and vacuum bottles.
Key Characteristics & Advantages: Known for producing highly reliable, automated instruments with massive integrated memory storage, quick graphic printouts, and robust field construction.
Flagship Products:
Turns Ratio: ATRT-03-S2, TRF250A (Multi-Phase Transformer turns ratio testers)
DC Winding Resistance: TRM403, TRM-20 (Transformer Winding Resistance Meters)
Website: https://www.doble.com
Official Email: customerservice@doble.com
Founding Year: 1976 (AEMC) / 1893 (Parent company Chauvin Arnoux Group)
Current Development Status: Key brand of the Chauvin Arnoux Group. Headquartered in Dover, New Hampshire, USA, acting as a major distributor across North and South American industrial markets.
Core Business Scope: Professional electrical power quality, ground resistance, insulation testers, data loggers, and micro-ohmmeters.
Key Characteristics & Advantages: Backed by French precision engineering. Excellent data management integration via proprietary DataView software; durable field enclosures.
Flagship Products:
Turns Ratio: DTR Model 8510 (Digital Transformer Ratiometer)
DC Winding Resistance: Model 6240 / 6255 (Rugged 10A micro-ohmmeters for winding tests)
Website: https://www.aemc.com
Official Email: sales@aemc.com
Founding Year: 1995
Current Development Status: Leading independent high-tech manufacturer based in Bremgarten, Switzerland, with an established international subsidiary network (Raytech USA).
Core Business Scope: High-accuracy automated test systems and single/multi-phase test instruments for the international power industry.
Key Characteristics & Advantages: 100% Swiss-engineered quality.Extraordinary high precision, sleek interface designs, modular software (T-Base), and dynamic resistance measurement capabilities.
Flagship Products:
Turns Ratio: TR-Mark III (Three-Phase Turns Ratio Meter), Mini-ATOS
DC Winding Resistance: WR50-12 / WR14 Series (Winding Resistance Meters up to 50A)
Website: https://www.raytech.ch
Official Email: welcome@raytech.ch
Founding Year: 2013
Current Development Status: Rapidly growing manufacturer based in Epsom, Surrey, United Kingdom, with a rising commercial presence across European and Latin American markets.
Core Business Scope: Substation test instrumentation, transformer analyzers, and circuit breaker diagnostic instruments.
Key Characteristics & Advantages: Focuses on highly competitive cost-to-performance instruments built according to strict international standards. Features intuitive touchscreen color graphical interfaces.
Flagship Products:
Turns Ratio: TURA-01, TURA-03 (Three-Phase Turns Ratio Testers)
DC Winding Resistance: WINRES-20, WINRES-50 (winding resistance testers with demagnetization)
Website: https://www.hightest.co.uk
Official Email: info@hightest.co.uk
Founding Year: 2009
Current Development Status: Kingrun is one of China's earliest manufacturers of transformer testing equipment; indeed, China's very first fully automatic DC winding resistance tester was developed by Kingrun. Leveraging its reputation for stable quality and exceptional cost-effectiveness, Kingrun currently commands nearly one-third of the Chinese market for DC resistance and turns ratio testers, and has established itself as a trusted, long-term supplier to Hitachi, Siemens, and ABB.
Core Business Scope: Specialized diagnostic tools for power transformers, distribution networks, and insulating oil testers.
Key Characteristics & Advantages: Exceptional manufacturing agility. Pioneer of handheld palm-sized 3-phase TTR testers with ultra-long battery runtimes. Highly competitive pricing, fast customization, and robust technical support.
Flagship Products:
Turns Ratio: JYT-A, Palm Turns Ratio Tester (1.6 kg portable unit)
DC Winding Resistance: JYR-10S, JYR-20S / 40S / 50S (Three-channel auto-magnetizing resistance testers)
Website: https://www.kritester.com
Official Email: info@kritester.com
