VFD Motor No-Load Operation: Acceptance Standards & Checklist

I. Electrical Performance Acceptance Criteria

1. Current Parameter Acceptance

• Three-phase current balance: The unbalance degree of the VFD’s output three-phase current shall be ≤10% (calculation formula: (Maximum current - Minimum current)/Average current × 100%), with no significant fluctuation (fluctuation range ≤5% of rated current).
• No-load current value: It shall comply with the motor technical manual, usually 20%~50% of the motor’s rated current (reference range for asynchronous motors; synchronous motors shall be adjusted according to specific models), without abnormal high or low values.
• No overcurrent alarm: During the entire operation process (including start-up, stable operation, and shutdown phases), the VFD shall have no “overcurrent” or “overload” alarms, and the current monitoring value shall not exceed 80% of the VFD’s overcurrent protection setting.

2. Voltage Parameter Acceptance

• Three-phase voltage symmetry: The difference between the VFD’s output three-phase voltages shall be ≤5% of the rated output voltage, with no obvious phase shift (the voltage waveform can be detected by an oscilloscope, which shall be close to a sine wave without severe distortion).
• DC bus voltage: The fluctuation range of the DC bus voltage during stable operation shall be ≤±5% of the rated value (e.g., for a VFD with 380V input, the DC bus voltage is usually 510~540V, and the fluctuation shall be controlled within 25V).
• No overvoltage/undervoltage alarm: When the input power voltage fluctuates within ±10% of the rated value, the VFD shall have no “overvoltage” or “undervoltage” alarms, and the output voltage shall change normally with frequency (voltage is proportional to frequency in V/F mode).

3. Frequency and Control Performance Acceptance

• Frequency stability: The deviation between the set frequency and the actual output frequency shall be ≤0.5Hz (e.g., when set to 50Hz, the actual frequency shall be in the range of 49.5~50.5Hz), with no frequency drift during operation (drift per hour ≤0.1Hz).
• Start-stop control: Smooth start-stop shall be achieved according to the set acceleration/deceleration time, with no current impact (peak current during start-up ≤1.5 times the motor’s rated current), and no voltage spike during shutdown (no over-threshold fluctuation of DC bus voltage).
• Control mode adaptability: For V/F mode, the voltage-frequency curve shall comply with the set value; for vector control mode, after no-load self-learning, the motor speed error shall be ≤1% of the rated speed, with no “loss of step” phenomenon.

II. Mechanical Status Acceptance Criteria

1. Speed and Rotation Direction Acceptance

• Speed accuracy: The deviation between the actual speed and the rated speed (corresponding to the set frequency) shall be ≤2% (e.g., for a 4-pole motor with 1500rpm corresponding to 50Hz, the actual speed shall be in the range of 1470~1530rpm), with no obvious speed fluctuation (fluctuation range ≤30rpm).
• Rotation direction correctness: The motor rotation direction shall be consistent with the design requirements (judged by equipment marks or load-end requirements), with no reverse rotation or unstable rotation direction.

2. Vibration and Noise Acceptance

• Vibration amplitude: It shall comply with the requirements of GB/T 10068 Mechanical Vibration of Electric Motors with Shaft Heights 56 mm and Above – Measurement, Evaluation and Limits of Vibration:
  • For motors with speed ≤3000rpm, the effective value of vibration velocity shall be ≤1.8mm/s (rigid mounting) and ≤2.8mm/s (elastic mounting);
  • There shall be no abnormal vibration during operation (such as periodic jitter, high-frequency vibration), and no sudden peak value detected by the vibration sensor.
• Noise limit: The motor operation noise shall be ≤85dB (A) (measured 1m away from the motor, with background noise deducted), with no abnormal sounds such as impact noise, whistling, or friction noise (judged by a sound level meter or manual hearing).

3. Temperature Acceptance

• Motor temperature:
  • The motor housing temperature shall be ≤ ambient temperature + 80℃ (or not exceed the “rated temperature rise” marked on the motor nameplate; usually, the temperature rise of Class B insulation motors is ≤80K);
  • The bearing temperature shall be ≤95℃ (rolling bearings) and ≤80℃ (sliding bearings), with no overheating phenomenon (measured by an infrared thermometer, recorded every 30 minutes, with no continuous temperature rise trend).
• VFD temperature:
  • The VFD module temperature shall be ≤60℃ (at an ambient temperature of 40℃), and the internal temperature of the cabinet shall be ≤50℃;
  • The cooling fan shall operate normally without stalling or abnormal noise, and there shall be no over-threshold temperature alarm (e.g., the VFD “overheating” alarm threshold is usually 70~85℃, and the operating temperature shall be more than 10℃ below the threshold).

III. Safety and Compliance Acceptance Criteria

1. Protection Function Verification

• Key protection tests:
  • Overcurrent protection: Simulate slight overcurrent (e.g., current reaches 1.2 times the set value), and the VFD shall trip within the set time;
  • Phase loss protection: Disconnect the wiring of any one phase of the motor, and the VFD shall alarm and shut down within 5 seconds;
  • Emergency stop function: Press the emergency stop button, the VFD shall immediately cut off the output, and the motor shall stop quickly (stop time ≤5 seconds, with no runaway phenomenon).
• Grounding compliance: The grounding resistance of the motor housing and VFD cabinet shall be ≤4Ω (measured by a grounding resistance tester), with no loose or virtual connection in the grounding line, and no grounding leakage during operation (leakage current ≤30mA, measured by a leakage detector).

2. Environmental Adaptability Acceptance

• Operating environment matching: The ambient temperature, humidity, and dust concentration during acceptance shall comply with equipment requirements (usually temperature 0~40℃, humidity 20%~90% without condensation, dust concentration ≤1mg/m³), and the equipment shall operate stably in this environment, with no performance degradation caused by environmental factors (e.g., no current limitation at high temperatures, no insulation degradation at high humidity).

IV. Document and Record Acceptance Criteria

1. Completeness of Acceptance Records

• The following records shall be provided with accurate and complete content:
  • No-Load Operation Parameter Record Form (including time, frequency, three-phase current/voltage, temperature, vibration value, etc., recorded every 10 minutes, with at least 3 sets of stable data);
  • Protection Function Test Record Form (including test items, test methods, test results, and abnormal handling measures);
  • Equipment Inspection Record Form (including pre-commissioning records such as wiring inspection, insulation resistance test, and bearing lubrication inspection).

2. Standard Compliance Certification

• The equipment operating parameters shall comply with:
  • No-load operation requirements in the motor and VFD manufacturer’s technical manuals;
  • Relevant national standards (e.g., GB/T 12668.3 Adjustable Speed Electrical Power Drive Systems – Part 3: EMC Requirements and Specific Test Methods for Products, GB/T 14811 On-Site Insulation Test Specification for Small and Medium-Sized Rotating Electrical Machines);
  • No-load acceptance indicators in the project design documents (e.g., speed accuracy, noise limit in specific scenarios).

V. Acceptance Judgment Rules

1. Qualified judgment: If all the above acceptance items meet the standard requirements, with no major abnormalities (such as overcurrent alarm, excessive vibration, over-temperature), and complete records, it can be judged as “qualified for no-load operation acceptance”, and the equipment is allowed to enter the load commissioning phase.
2. Rectification judgment: If there are minor abnormalities (e.g., current balance 8%~10%, noise 80~85dB (A)) that do not affect equipment safety, rectification shall be required (e.g., adjusting wiring, optimizing parameters), and re-acceptance shall be conducted after rectification until the standards are met.
3. Unqualified judgment: If any of the following situations occur, it shall be judged as “unqualified”, and the equipment shall be shut down for fault investigation:
   • Three-phase current unbalance >10% or no-load current >60% of rated current;
   • Motor bearing temperature >100℃ or VFD module temperature >70℃;
   • Effective vibration velocity >3.5mm/s or obvious abnormal noise;
   • Failure of protection functions (e.g., no alarm for phase loss, ineffective emergency stop).