The handheld loop resistance tester is an important tool in the power system used for measuring the loop resistance of high-voltage equipment such as switches, circuit breakers, and busbars. Its core purpose is to check whether the conductive performance of the relevant connection points is good, and to identify problems such as increased resistance due to poor contact, oxidation, or loosening, thereby preventing overheating, damage to the equipment, and even safety accidents.
1. Core Functions and Principles
1. Core Function
It can achieve relatively accurate measurement of micro-ohm level (μΩ) direct current resistance, with typical measurement ranges covering 0.1 μΩ to several milliohms.
2. Measurement Principle
It uses the classic four-wire method (Kelvin bridge method) for the measurement process. The instrument outputs a constant large current (common specifications are 50A, 100A or higher), and simultaneously uses two independent measurement wires to precisely detect the voltage drop across the measured circuit terminals. According to the Ohm’s Law formula R=U/I
Calculate the resistance value. This method can effectively eliminate the interference of the test line’s own resistance and contact resistance on the measurement results, ensuring the high accuracy of the measurement data.
II. Application Scope
The handheld loop resistance tester is mainly used to evaluate the connection quality of current-carrying conductors. Its application scenarios cover almost all conductive circuits in medium and high-voltage power systems, including the following categories:
High-voltage switchgear type
This is the core application field of the handheld loop resistance tester, covering the detection work of various switch devices:
Breaker (oil, vacuum, SF₆ type): Measure the contact resistance of the main circuit moving and static contacts in the closed state. This indicator is the key basis for judging the conductive performance of the breaker.
Isolating switch (knife switch): Detect the contact resistance between the closed knife switch and the static contact. Due to the frequent operation of isolating switches and their exposure to the atmosphere, the contacts are prone to oxidation, so this test is particularly crucial.
Grounding switch: Check the conduction performance in the closed state.
Load switch: Test logic is basically the same as that of the breaker.
Busbars and connection systems
Suitable for the resistance detection of various busbars and electrical connection parts:
Busbar (copper busbar, aluminum busbar) connection points: Check the resistance values at bolted connections, welded or pressed points to determine if the connection process meets the standards.
Pipes and leads connection: For example, the connection parts of transformers and GIS equipment.
Cable joints and terminals: Evaluate the manufacturing and installation quality of medium and high-voltage cable intermediate joints and terminals.
Important bolts, line clamps, equipment line clamps in power plants and substations.
Other special applications
In addition to conventional equipment in the power system, it can also be applied in several special fields:
Rail transit: Measure the contact resistance between the locomotive pantograph and the contact network, as well as the connection resistance of the track.
Large motors / generators: Check the resistance conditions of the brushes, slip rings, and winding connection parts.
Lightning protection grounding: In the low-resistance test mode, it can be used to measure the conduction resistance at the connection points between the downlead and the grounding body.
Industrial smelting: Detect the connection parts resistance of large current equipment such as electrolytic cells and electric furnaces.
Core judgment logic: Any part that requires a large current and whose connection reliability will affect the safe operation, efficiency, or service life of the equipment is suitable for conducting tests using the handheld loop resistance tester.
Post time: Jan-14-2026