Transformer milliohmmeter UHV-40A

digitalportable

Overview
Compact, lightweight DC winding resistance tester for transformer windings and high-power inductive equipment. Intuitive menu operation and rapid, repeatable measurements with laboratory-grade accuracy (±0.2% FS ±2 digits) and 0.1 μΩ resolution.

Product parameters
Designed for transformer handover, overhaul and tap-changer maintenance. Multiple test currents, internal data storage and portable form factor to support field and workshop diagnostics.

Technical parameters
Test currents: 2.5 A, 5 A, 10 A, 20 A, 40 A
Measurement ranges: 2.5 A: 10 mΩ–8 Ω; 5 A: 1 mΩ–4 Ω; 10 A: 1 mΩ–2 Ω; 20 A: 1 mΩ–1 Ω; 40 A: 1 mΩ–500 mΩ
Accuracy: ±(0.2% full scale ±2 digits)
Data storage: 255 records
Display: LCD, 4½-digit resistance display
Resolution: 0.1 μΩ
Power supply: AC 220 V ±22 V, 50 Hz ±2 Hz (fuse 10 A)
Max power consumption: 1200 W (at 40 A)
Operating environment: 0 °C to 40 °C; relative humidity ≤ 80%
Dimensions: 440 × 230 × 490 mm
Weight: 20 kg (without accessories)

Features

• Compact and lightweight for site and workshop use.
• Clear menu operation for straightforward testing.
• Fast measurement cycle with stable, repeatable readings.
• Automatic discharge and discharge-indication functions to reduce operator error and improve safety.

Precautions

• After measuring inductive loads, do not remove test leads immediately; wait for the instrument discharge indicator to complete to avoid inductive discharge hazards.
• Do not switch no-load tap-changers during measurement.
• If power is lost during a measurement, the instrument will start automatic discharge; wait at least 30 seconds before removing wiring.
• Do not short-circuit other untested windings to ground during measurement to avoid slowing magnetization and prolonging stabilization time.
• Check supply voltage before startup: AC 220 V ±10% 50 Hz.
• Confirm tested equipment is de-energized and disconnected from other live circuits before testing.
• Ensure the instrument casing is reliably grounded during tests.
• Do not place unrelated objects on or around the equipment panel during testing.
• When replacing fuses or accessories, use the same model as specified for the instrument.
• Protect the instrument from moisture and oil.

Characteristics / technical specifications

• Model: UHV-40A
• Available test currents: 2.5 A, 5 A, 10 A, 20 A, 40 A
• Resistance ranges by current: 2.5 A (10 mΩ–8 Ω); 5 A (1 mΩ–4 Ω); 10 A (1 mΩ–2 Ω); 20 A (1 mΩ–1 Ω); 40 A (1 mΩ–500 mΩ)
• Accuracy: ±(0.2% full scale ±2 digits)
• Resolution: 0.1 μΩ
• Display: LCD, 4½ digits
• Data memory: 255 records
• Power: AC 220 V ±22 V, 50 Hz ±2 Hz (fuse 10 A)
• Max consumption: 1200 W (at 40 A)
• Operating temperature: 0 °C to 40 °C; relative humidity ≤ 80%
• Dimensions: 440 × 230 × 490 mm
• Net weight: 20 kg (without accessories)

Application field
DC resistance tester is widely used in multiple industries, mainly for testing the DC
resistance of electrical equipment and components. Here are its core uses:

• Equipment testing in the power industry. In the power industry, resistance testing of equipment such as transformers, switches, and terminal blocks is crucial. The DC resistance tester can measure the resistance value of equipment, helping to detect whether the contact resistance of the equipment is too high, thereby preventing energy loss or failure caused by abnormal resistance of the equipment.
• Maintenance of motors and generators. In the maintenance process of motors and generators, measuring the resistance of motor windings is very important. The DC resistance tester can effectively detect the health status of motor windings, identify early signals of motor faults, and ensure the stability of equipment operation.
• Quality control of electronic components. In the production and testing of electronic components, DC resistance testers can efficiently detect the quality of resistance components, ensuring that the electrical performance of the product meets the requirements. Accurate resistance measurement is the key to quality control for various components such as resistors and capacitors.
• Inspection and maintenance of cable lines. Cables are important components for power transmission, and their resistance value can reflect their degree of aging and damage. The DC resistance tester can be used for regular inspection of cable lines, helping maintenance personnel to detect potential electrical hazards in a timely manner and reduce the risk of accidents.