1、 Clearly define the test object and scenario

The insulation characteristics and testing standards of different electrical equipment are different, and instruments need to be selected according to the type, voltage level, and usage environment of the tested equipment:

Low voltage equipment (such as household appliances, low-voltage motors, lighting circuits, etc.) typically requires a test voltage of 500V or below, with a measurement range covering 0~1000M Ω.

Medium and high voltage equipment (such as transformers, cables, high voltage motors, insulators, etc.): require higher testing voltages (2500V, 5000V, or even 10000V), with a measurement range of 10000M Ω (10G Ω) or more to meet the testing requirements of high voltage insulation.

Special scenarios: such as outdoor humid environments and explosion-proof places (such as coal mines and chemical areas), instruments with waterproof and dustproof (IP65 or above) or explosion-proof certification should be selected; When there is no power supply on site, priority should be given to portable devices with strong battery life.

2、 Focus on core performance indicators

1. Test voltage range

The core of insulation resistance testing is to measure leakage current under a specified voltage and calculate insulation resistance (R=U/I). The voltage level needs to match the rated voltage of the tested equipment

Equipment with rated voltage<500V: select 250V and 500V levels;

Equipment with a rated voltage of 500~3000V: select 1000V and 2500V levels;

Equipment with a rated voltage greater than 3000V: choose 2500V, 5000V, 10000V levels (such as transformers with 110kV and above requiring 5000V and above).

Prioritize selecting instruments with adjustable multiple voltage levels to meet the testing needs of different devices and improve versatility.

2. Measurement range and accuracy

Measurement range: It is necessary to cover the possible values of insulation resistance of the tested equipment. For example, the insulation resistance of new cables can reach thousands of M Ω, while old equipment may drop to several M Ω. The instrument range should include these ranges (such as 0.1M Ω~100000M Ω).

Accuracy: According to industry standards such as DL/T 596 "Preventive Test Code for Power Equipment", the measurement error of insulation resistance should be ≤± 10% (at room temperature). When selecting, it is necessary to confirm whether the accuracy of the instrument within the commonly used range meets the standard, in order to avoid misjudgment caused by excessive errors.

3、 Functional requirement matching

Select necessary functions according to the testing purpose to avoid functional redundancy or insufficiency:

Basic function: Insulation resistance (R) measurement is the core, ensuring stable readings and rapid response.

Extended functions:

Absorption ratio (K1=R60s/R15s) and polarization index (K2=R10min/R1min): used to determine the insulation moisture or aging status of large capacity equipment (such as transformers and cables). It is recommended to prioritize instruments with this function for high-voltage equipment testing.

Automatic discharge: After testing, the instrument can automatically release the residual charge of the tested equipment to avoid electric shock to the operator, which is particularly important for capacitive equipment such as cables and capacitors.

Data storage and transmission: When multiple sets of test data need to be recorded (such as comparisons between different times and devices), choose instruments that support large capacity storage (≥ 1000 sets), USB export, and Bluetooth transmission for convenient data management and report generation.

Waveform display: Some high-end instruments can display voltage and current waveforms to assist in analyzing anomalies at the moment of insulation breakdown (such as intermittent discharge).

4、 Operation and portability

Convenience of operation: For on-site testing, it is necessary to quickly get started, and priority should be given to instruments with large Chinese display screens, simple menus, and one click testing; Supports backlit display and adapts to operating in dim environments.

Portability: For on-site mobile testing (such as outdoor cables, tower insulators), weight (recommended<3kg) and volume should be considered, and a portable or backpack design should be chosen; Battery powered instruments should pay attention to battery life (can complete ≥ 50 tests on full charge) and support fast charging.

5、 Anti interference and safety

Anti interference capability: There is electromagnetic interference in industrial sites (such as stray magnetic fields during the operation of motors and transformers), and instruments with digital filtering technology should be selected to ensure stable readings under strong interference (such as fluctuations within ± 2%).

Safety protection: The instrument needs to pass the withstand voltage certification (such as AC 2kV/1min), with overvoltage protection, overload protection (automatic power-off when the test line is mistakenly connected to high voltage), and short circuit protection (no damage to the instrument when the tested equipment breaks down), to ensure the safety of personnel and equipment.