Vanguard TRM-20 Transformer Winding Resistance Tester | Selectable 1–25 A, 1 µΩ–2,000 Ω, dual channel, automatic discharge and demagnetization, LTC testing

Vanguard TRM-20 Transformer Winding Resistance Tester: 25 A, Dual Channel

Overview

The TRM-20 is a third-generation transformer winding resistance tester from Vanguard Instruments, used to measure the DC resistance of transformers, rotating machine windings and other inductive equipment. Two resistance measurement channels measure the primary and secondary windings simultaneously, and a 60 Vdc source speeds up magnetization stabilization on large transformers. After measurement it automatically discharges and demagnetizes the device under test, and it can also perform dynamic on-load tap changer (LTC) testing. Because it measures down to 1 µΩ, it can also serve as a micro-ohmmeter for contact resistance of EHV circuit breakers. The TRM-40 in the same series offers 1–40 A test current (range up to 500 Ω); please inquire separately.

Key Specifications

• Test current: 1–25 A, in 1 A steps
• Measurement range: 1 µΩ–2,000 Ω
• Accuracy: 1–19,999 µΩ: ±0.5% ±1 count; 20–999 mΩ: ±1% ±1 count; 1–2,000 Ω: ±1.5% ±1 count
• Test voltage: Magnetization 60 Vdc; up to 18 Vdc during measurement
• Channels: Dual static resistance measurement channels
• Printing and storage: Built-in 2.5-inch thermal printer; 256 static records (up to 111 readings each) and 120 dynamic records internally; up to 999 records on USB flash drive
• Interfaces: RS-232C, USB, Bluetooth
• Power and environment: 100–240 Vac, 50/60 Hz; operating temperature -10 to 50 ℃
• Dimensions and weight: 53 × 43 × 24 cm; 15.4 kg

Applications

• DC winding resistance and tap changer testing of power transformers.
• Rotating machine winding and circuit breaker contact resistance measurement.

Specifications per the specification tables on the Vanguard TRM-20 and TRM-40 product pages (doble.com, retrieved 2026-10-23).