QLDM-EA type Insulation Resistance Tester

The QLDM-EA Type Insulation Resistance Tester is specifically used for insulation test tests in laboratories or on-site. It contains a high-precision microcurrent measurement system and a digital boost system. Only one high-voltage wire and one signal wire are needed to connect the test sample for measurement. The measurement is carried out automatically, and the results are displayed on a large LCD screen and stored.

Main Features

1. Utilizes a 32-bit microcontroller for easy operation with an entirely Chinese user interface; automatic measurement is supported.
2. Automatically calculates and displays measurement parameters such as DAR, PI, and DD; displays measurement time, voltage, and resistance in real time.
3. Displays measurement data every 5 seconds, e.g., 5″, 10″, 15″, 20″, up to 600″, all displayed on the screen.
4. Dual display function: digital and analog pointer. Real-time display of tested voltage and resistance data.
5. Displays waveforms of insulation resistance versus test time.
6. High output current, short-circuit current ≥ 5mA. Strong anti-interference capability, meeting the requirements for on-site operation in ultra-high voltage substations.
7. Dedicated discharge circuit for rapid discharge of large capacitive samples. Automatic discharge upon completion of the test, with real-time display of the discharge voltage.
8. Automatic shutdown function: automatically shuts down 5 minutes (default) after operation stops to prevent power waste.
9. Includes a rechargeable battery and charger; a full charge provides 6-12 hours of continuous use.
10. Equipped with an RS232 serial port, enabling computer operation of the instrument.

Product Applications:

1. Measurement of insulation and winding insulation in cables, transformers, motors, generators, etc;
2. High resistance or high absorption testing;
3. Absorption ratio (DAR) and polarization index (PI) testing;
4. Multilayer insulated cable testing (DD);
5. Insulation resistance measurement of aging equipment and motors that have been in operation for a long time;
6. Preventive maintenance;
7. Testing of computer-controlled production lines;
8. Insulation resistance measurement by user-selected test voltage according to measurement requirements.

Main Technical Specifications

• Display Method: Dual display of digital and analog pointers. Temperature Measurement: -45℃～125℃
• Test Voltage Range: 250V, 0.5KV, 1KV, 2.5KV, 5KV, 10KV, Accuracy 10%±10V
• Short Circuit Current: ≥5mA Measurement Time: 1 minute～10 minutes (depending on measurement method)
• Charging Power Supply: 180～270VAC, 50Hz/60Hz±1% (Mainland power or generator power)
• Operating Environment: Temperature -10～40℃, Relative Humidity 20～80%.

Operating Component Functions

1. L Terminal: “L” is the high-voltage output terminal, also known as the line terminal. It is connected from the high-voltage cable to the terminal under test, such as a motor winding or cable core.

2. G Terminal: “G” is called the shield terminal. It is used for measuring the volume resistivity of insulation materials or cables using the three-electrode method. It is connected to the guard ring of the three electrodes.

3. E Terminal: “E” is called the ground terminal. It is connected to the ground or neutral terminal of the object under test. For example, the metal casing of a motor, the iron core of a transformer, or the shielding layer of a cable.

4. Precautions and Others: Please be careful! L is the high-voltage terminal! E is the ground terminal and must be connected to earth!

Instrument Function Selection

Press  the (Function Selection Key) to cycle through Insulation Resistance Test, view stored data, and adjust the date and time.

Introduction to Instrument Principles

Structure

Functions of Each Component:

• LCD Keyboard: Responsible for keyboard and display.
• CNC Voltage Regulator: Employs a PWM circuit to produce a 0-5V standard output efficiently.
• DC-DC 0-10kV: Utilizes a step-up transformer for efficient conversion, delivering a 0-10kV DC high-voltage output. Features short-circuit protection.
• Voltage Divider Circuit: Converts the 0-10kV high-voltage signal to 0-5V for easy ADC acquisition.
• Measurement Circuit: Responsible for data acquisition, current conversion, etc.
• Controller: Connects all the above modules to complete the measurement.

Main Factors Affecting Resistance or Resistivity Testing

• a. Ambient Temperature and Humidity: Generally, the resistance of a material decreases with increasing ambient temperature and humidity. Relatively speaking, surface resistivity is more sensitive to moisture, while bulk resistivity is more sensitive to temperature. Increased humidity increases surface leakage and bulk current. Increased temperature accelerates the movement of charge carriers, leading to a corresponding increase in the absorbed current and conduction current of the dielectric material. According to relevant reports, the dielectric resistance at 70°C is only 10% of that at 20°C. Therefore, when measuring the resistance of a material, the temperature and humidity at which the sample and environment reach equilibrium must be specified.
• b. Test Voltage (Electric Field Strength): The resistivity of a dielectric material generally cannot remain constant over a wide voltage range; that is, Ohm’s law does not apply to this. Under normal temperature conditions, at low voltages, the conduction current increases linearly with applied voltage, while the material’s resistance remains constant. Above a specific voltage, due to intensified ionization, the increase in conduction current is much faster than that in the test voltage, and the material’s resistance decreases rapidly. Therefore, the higher the applied test voltage, the lower the material’s resistance, leading to significant differences in resistance values ​​obtained under different voltages. It’s important to note that the determining factor for changes in material resistance is the electric field strength during testing, not the test voltage. For the same test voltage, different distances between the test electrodes yield different resistivity results; the smaller the distance between the positive and negative electrodes, the lower the measured value.
• c. Test Time: When a specific DC voltage is applied to the material under test, the current does not reach a stable value instantaneously but undergoes a decay process. A large charging current flows simultaneously with the application of voltage, followed by a relatively long period of slowly decreasing absorption current, finally reaching a relatively stable conduction current. The higher the resistance, the longer it takes to reach equilibrium. Therefore, to accurately read the resistance value, it should be measured after stabilization or after 1 minute of voltage application. Furthermore, the resistance value of highly insulating materials is also related to their charge history. To accurately evaluate the electrostatic properties of materials, before conducting resistivity tests, the materials should be destaticated and allowed to stand for 5 minutes before proceeding with the measurement procedure. Generally, for a single material, at least 3-5 samples should be randomly selected for testing, and the average value should be used as the test result.
• d. Leakage in testing equipment: During testing, wiring with low insulation resistance is often improperly connected in parallel with the test sample or sampling resistor, which can significantly affect the measurement results. Therefore: to reduce measurement errors, protective techniques should be employed, such as installing protective conductors on lines with high leakage current to essentially eliminate the influence of stray current on the test results; high-voltage lines have some leakage to ground due to surface ionization, so high-insulation, large-diameter high-voltage conductors should be used as high-voltage output lines, and the wiring should be shortened as much as possible, reducing sharp points and eliminating corona discharge; test benches and supports should be made of insulating materials such as polyethylene and polytetrafluoroethylene to avoid lower test values ​​due to these reasons.
• e. External Interference: When a DC voltage is applied to a highly insulating material, the current passing through the sample is minimal, making it highly susceptible to external interference and causing significant testing errors. The thermoelectric potential and contact potential are generally minimal and can be ignored; the electrolytic potential, mainly generated by contact between a damp sample and different metals, is only about 20 mV. Moreover, low relative humidity is required in electrostatic testing, and testing in a dry environment can eliminate the electrolytic potential. Therefore, external interference is mainly due to potential generated by stray-current coupling or electrostatic induction. When the test current is less than 10⁻¹⁰ A or the measured resistance exceeds 10¹¹ ohms, strict shielding measures should be taken for the test sample, test electrodes, and test system to eliminate the influence of external interference.

The compatibility of the instruments