Adjustable high-voltage digital megohmmeter

　　1、 Product Overview and Definition

Adjustable high-voltage digital megohmmeter is a high-precision electronic measuring instrument specifically used to measure the insulation resistance of electrical equipment such as transformers, motors, cables, etc. As an important tool in the field of modern power detection, it accurately measures the resistance value of insulation materials by applying adjustable DC high voltage, thereby evaluating the insulation performance and safety status of electrical equipment.

This instrument represents a significant technological upgrade from traditional hand cranked megohmmeters, integrating advanced features such as digital display, automatic calculation, wide range measurement, and anti-interference ability. Its core value lies in the ability to measure high-voltage electrical equipment without disconnecting wires in strong electromagnetic interference environments, greatly improving detection efficiency and accuracy.

　　2、 Working principle and technical principle

1. Basic Measurement Principles

The working principle is based on Ohm's law (R=U/I). The high-voltage generator inside the instrument generates adjustable DC test voltage, which is output through the E-pole (ground terminal) and reaches the L-pole (line terminal) through the insulation layer of the tested object, forming a measurement circuit.

The generated small leakage current is converted through an I/V (current/voltage) conversion circuit, and then processed by a divider to display the insulation resistance value in digital form directly on the LCD screen. The entire process is controlled by a built-in embedded industrial microcontroller and real-time operating system, achieving fully automated measurement.

2. Key technological breakthroughs

High voltage generation technology: The instrument adopts DC/DC conversion technology to convert the low voltage DC power of the battery into the required high voltage DC power. The test voltage can be selected from multiple levels such as 0.25kV, 0.5kV, 1kV, 2.5kV, 5kV, 10kV, 15kV, and even smoothly adjusted from 0V to the desired voltage.

Anti interference design: For strong electromagnetic environments such as substations, the instrument adopts equipotential protection rings and fourth-order active low-pass filter technology to effectively shield external power frequency and strong electromagnetic field interference.

Intelligent measurement algorithm: The instrument can automatically calculate the absorption ratio (DAR) and polarization index (PI), two key insulation performance indicators. The absorption ratio is the ratio of insulation resistance values at 60 seconds to 15 seconds, and the polarization index is the ratio of insulation resistance values at 10 minutes to 1 minute. These parameters are of great significance for determining the moisture level and aging state of insulation materials.

　　3、 Core functional characteristics

Automatic range conversion: The instrument can automatically switch the range based on the measured resistance value, without the need for manual adjustment, greatly simplifying the operation process.

Timing and alarm function: Built in stopwatch function, with a cycle of 20 minutes. It has a sound alarm function, which emits a prompt sound at 15 seconds, 60 seconds, and every minute, making it convenient to record absorption ratio and polarization index measurement data.

Data storage and transmission: Supports continuous storage of measurement results for more than 9 times, with anti power failure protection function. Some models support USB or Bluetooth data transfer, and test data can be uploaded to a PC for analysis and archiving.

　　3.2 Security Protection Mechanism

Automatic discharge protection: After the test is completed, the instrument automatically monitors and releases residual high-voltage charges on the tested equipment to prevent electric shock to the operator.

Short circuit protection: When the output terminal is short circuited, the instrument automatically stops testing and alarms to avoid equipment damage.

Grounding status indication: Equipped with a safety grounding indicator light, allowing the operator to easily confirm that the instrument is properly grounded, ensuring personal safety.

Overvoltage and overcurrent protection: When the external voltage exceeds 50V, the test will automatically stop and an alarm will be issued.

　　3.3 Multi mode testing capability

Modern adjustable high-voltage digital megohmmeters support multiple testing modes to meet different diagnostic needs:

IR test: Basic insulation resistance test, quickly determine the overall insulation performance

DAR/PI testing: Absorption ratio and polarization index testing to evaluate the state of insulation materials

SV test: Step voltage test, locating local defects through segmented pressurization

DD test: dielectric discharge rate test, detecting multi-layer insulation moisture penetration

　　4、 Application Fields and Scenarios

4.1 Power System

Power plant: used to test the insulation condition of generator stator, rotor winding, excitation system, high-voltage switch, busbar, etc.

Substation: Especially suitable for 500kV and above ultra-high voltage substations, it can measure the insulation resistance parameters of large transformers without disconnecting the wires. It is known that this instrument can adapt to the strong interference environment of a 500000 volt substation site.

Transmission and distribution lines: Test the insulation resistance of high voltage, medium voltage, and low voltage cables, and investigate issues such as moisture, aging, and damage. It is particularly suitable for testing in special environments such as remote ultra-high voltage power grids spanning thousands of kilometers, railway engineering power grids at altitudes of 5000 meters, power cables or buried cables, underwater cables, etc.

4.2 Maintenance of Industrial Equipment

Motor and generator: Regularly check the insulation condition of the motor and generator windings to prevent burning accidents caused by insulation degradation. For high voltage motors of 6kV and above, a test voltage of 5000V and above is required.

Electrical control cabinet: Check the insulation between components such as busbar, circuit breaker, contactor, relay, terminal block, and ground inside the cabinet.

Chemical equipment: In industries such as petroleum, chemical, and metallurgy, the insulation performance of electrical equipment is more easily affected due to the presence of corrosive gases, high temperatures, humidity, and other harsh conditions, requiring frequent use of insulation resistance testers for testing.

4.3 New Energy Sector

Photovoltaic power station: Test the insulation resistance of 1500V DC system, inspect the insulation condition of photovoltaic modules to ground, DC combiner box, inverter, and AC grid connected lines.

Wind farm: Test the insulation of the internal windings of wind turbines, cables inside towers, and box type transformers.

Electric vehicles: Testing the insulation resistance of high-voltage battery packs, motor controllers, drive motors, and high-voltage wiring harnesses is the core testing item for high-voltage safety and must comply with standards such as GB/T 18485.1-2015.

4.4 Architecture and Infrastructure

Building electrical system: After electrical installation or regular maintenance, test the insulation resistance of lighting circuits, power circuits, and socket circuits to ensure compliance with safety regulations such as IEC, NEC, GB, etc., and prevent leakage and fire risks.

Rail transit: testing the insulation of traction motors, auxiliary power supplies, and control lines for locomotives, high-speed trains, and subway vehicles.

Elevator system: Test the insulation of elevator control cabinets, motors, and cables.

　　5、 Operation and usage guide

5.1 Preparation before Testing

1. Safety confirmation: Ensure that the tested equipment has been powered off and use a dedicated discharge rod to discharge capacitive loads (such as cables) for more than 2 minutes.

2. Cleaning treatment: Wipe the surface of the tested object with a specialized cleaning agent to eliminate surface leakage current caused by oil, dust, or moisture.

3. Instrument inspection: Check the battery level of the instrument, confirm that the test line is intact and the instrument is reliably grounded.

5.2 Wiring method

Correct wiring is the key to ensuring accurate measurement:

1. E end (ground end): Connect the red test wire, and the other end is connected to the grounding point or shell of the test sample.

2. L end (line end): Connect the white core wire of the black shielded wire, and the other end is connected to the conductive part of the test sample that is insulated from the ground.

3. G-end (protective end): When necessary, connect the black core wire of the black shielded wire to the G-end, and connect the other end to the shielded or non measured part of the test sample to eliminate the influence of surface leakage current.

5.3 Measurement steps

1. Power on settings: Turn on the power switch "ON" and select the desired voltage level. The instrument usually defaults to 500V, and the corresponding gear can be selected according to the voltage level of the tested device.

2. Start test: Press the high-voltage "start stop" button lightly, the high-voltage indicator light will turn on, and the instrument will start outputting the test voltage.

3. Reading record: The stable display value on the LCD screen is the measured insulation resistance value. Note that due to the polarization phenomenon of the insulation material, there may be slight drift or jumping in the reading, which is a normal phenomenon.

4. Absorption ratio/polarization index measurement: The instrument has an automatic timing function, which can automatically record resistance values at time points such as 15 seconds, 60 seconds, and 10 minutes, and calculate DAR and PI values.

5. Test completed: Press the high-voltage "start stop" button to turn off the high-voltage output, and the instrument will automatically discharge the tested equipment. Finally, turn off the power of the entire machine.

　　6、 Safety precautions

6.1 Operational Safety Standards

1. High voltage warning: During the testing process, the instrument may generate high voltage. Keep a safe distance and do not touch the exposed parts of the testing line or the tested equipment.

2. Grounding requirements: Before testing, it is necessary to ensure that the instrument and the test object are reliably grounded to prevent the accumulation of static electricity and the risk of electric shock.

3. Environmental conditions: Avoid testing in flammable and explosive places, as sparks may cause explosions. Do not operate the instrument when the surface is damp or when the operator's hands are wet.

4. Equipment status: If the instrument is damaged or has exposed metal parts, it should be immediately stopped from use.

6.2 Special Precautions

1. Capacitive equipment: After testing capacitive equipment such as cables and capacitors, it is necessary to wait for the instrument to automatically discharge or use a dedicated discharge rod for manual discharge to prevent residual charges from causing electric shock.

2. Low resistance measurement: When the measured resistance is below 10M Ω, continuous measurement should not exceed 10 seconds to prevent instrument overheating and damage.

3. Harsh environment: When used in environments with an altitude exceeding 2000 meters or a temperature below 0 ℃, special requirements in the instrument technical manual should be referred to.

4. Regular calibration: It is recommended to perform professional calibration on the instrument every 12 months or after 1000 uses to ensure measurement accuracy.