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Maintenance and cleaning of inverters are crucial for ensuring long-term stable operation of the equipment. Below are detailed maintenance and cleaning procedures along with important precautions:

Daily Cleaning and Maintenance Steps
1. Safety Preparations
After shutdown, first disconnect the main power supply at the high-voltage switchgear and close the earthing switch.
Disconnect the VFD's control power supply and UPS power source.
Wait at least 15 minutes to ensure capacitors within the power units are fully discharged before opening cabinet doors to prevent electric shock hazards.
2. Cleaning Dust Filters
In high-dust environments, weekly cleaning of intake air filters is recommended.
After cleaning, use a vacuum cleaner to thoroughly remove accumulated dust from the cabinet interior.
3. Cabinet Interior Cleaning and Inspection
Carefully remove dust from the surfaces of power units, control boards, and other components using a vacuum cleaner, taking care to avoid damaging precision electronic components and fibre optic connectors.
Inspect the fibre optic plugs on each power unit for any signs of looseness, ensuring all connections are secure.
5. Tightening Inspection
Within the first month of inverter operation, it is advisable to retighten all incoming/outgoing cables and control terminal connections.
Thereafter, conduct regular inspections and retightening every six months, covering all power and control cables.
6. Resuming Operation
Upon completing cleaning and inspection, ensure no tools or foreign objects remain inside the cabinet before closing all electrical cabinet doors.
Restore power supply and document the details of this maintenance inspection.

Key Considerations
Cooling System Inspection: During routine patrols, verify the normal operation of cooling fans. A simple test involves placing an A4 sheet at the cabinet's air intake; the paper should adhere firmly to the filter screen, indicating adequate air pressure.
Environmental Requirements: Maintain cleanliness within the VFD room, ensuring ambient temperatures do not exceed 40°C and adequate ventilation is provided.
Standby Unit Maintenance: For standby power units, it is recommended to power them up and run them once every six months to ensure they remain in good working order. Additionally, ensure the fibre optic socket plugs on standby units are securely inserted to prevent contamination.

To verify the operational status of the S terminal (multifunctional input terminal), the following methods may be employed:

Measure terminal voltage
Using a multimeter set to the DC voltage range, measure the voltage between the S terminal under test (e.g., S1) and the COM-1 terminal:
·   Normal state: When an external contact closes to activate the S terminal, the voltage should be approximately 24V; when the terminal is open-circuited or the contact is broken, the voltage should be 0V.

Check digital input functionality
This is the most direct method. Apply a valid switch signal to the S terminal and observe the system response:
1.  Configure the S terminal under test to a specific function (e.g., ‘Run Signal’ or ‘Fault Reset’) via function codes (e.g., P05.00-P05.11).
2.  Close the external contact corresponding to that S terminal.
3.  Observe whether the VFD or iSVG system executes the set function (e.g., starts or resets a fault). A normal response indicates the S terminal function is operational.

Observing Indicator Light Status
Some equipment control boards may feature indicator lights corresponding to digital input states. When the S terminal is active, the relevant indicator light should illuminate, aiding verification that the terminal has correctly received the signal.

Precautions
·   The S terminal input voltage must utilise the system's built-in 24V power supply; external power sources must not be connected.
·   An unconnected terminal is interpreted by the system as being in a disconnected state.
·   Should significant on-site interference occur, appropriately increase the value of function code P05.13 (Digital Input Filter Frequency) to prevent false triggering.

By following the above steps, you can effectively verify the operational status of the S terminal. Should the function test fail to respond or voltage measurements prove abnormal, it may be necessary to inspect external wiring, terminal connections, or the control board itself.

The VFD outputs a Pulse Width Modulation (PWM) waveform, not a utility-frequency sinusoidal wave. It consists of a series of high-frequency voltage pulses (typically in the range of several kHz to tens of kHz), whose fundamental frequency is the motor operating frequency you set (e.g., 50Hz). Ordinary AC clamp meters (especially non-"True RMS" types) are designed and calibrated to measure pure 50/60Hz sine waves. They cannot accurately measure the true RMS value of non-sinusoidal waves like PWM, which are rich in harmonics, and this typically results in significantly lower readings.

You can use the same clamp meter to measure the current on the input side (R/S/T terminals) of the VFD. If the clamp meter reading for the input current is also much lower than the output current displayed by the VFD (for example, only around 7-8A on the input side), this provides strong evidence that your clamp meter is not suitable for measuring the VFD output. Only if the input side current reading is close to the output side displayed value (11.9A) should you suspect an issue with the VFD's internal detection circuit.

For on-site measurement verification, be sure to purchase or borrow a "True RMS" clamp meter

The VFD outputs a pulse width modulation (PWM) waveform rather than a utility frequency sine wave. It consists of a series of high-frequency voltage pulses (typically ranging from several kHz to tens of kHz), with its fundamental frequency being the motor operating frequency you set (e.g., 50 Hz). Standard AC clamp meters (especially non-RMS types) are designed and calibrated to measure pure 50/60Hz sine waves. They cannot accurately measure the true RMS value of non-sinusoidal waves like PWM (which are rich in harmonics), often resulting in significantly low readings. For field verification measurements, always use an RMS clamp meter.

To enable the inverter to start directly from a specific frequency, configure the settings as follows:
Start-up Mode Configuration:
· Select the ‘Direct Start’ mode in function code P01.01 (set to 0)
· Set function code P01.02 (Direct Start Start Frequency) to the desired specific frequency
Frequency Command Configuration:
· Select the frequency command source via function code P00.06, configurable as Function Code Setting (0) or Analogue Setting (1-4)
· If Function Code Setting is selected, set the operating frequency to the specific value via P00.13
Control Mode Verification:
· Ensure the operating command channel (P00.01) is set to the correct control mode (e.g., Local Control, Communication Control)
· Upon receiving the run command, the drive will start directly from the specified frequency
This start method is suitable for applications requiring rapid attainment of a specific rotational speed. The drive will commence output directly from the set frequency without accelerating from 0Hz.

1. Check the fault history and current alarms. Review the historical fault records on the HMI, as they may reveal the root cause of the POFF condition.

2. Verify control and auxiliary power supplies. Ensure all low-voltage circuit breakers and switches in the control cabinet are closed. If a UPS is present, check its operational status. Alternatively, open the VFD control cabinet door and observe whether indicator lights for all power modules (e.g., PLC power supply, trigger power supply, drive board power supply) are lit normally (typically green indicates normal operation).

3. Verify all interlock and safety signals. An unclosed safety interlock circuit will force the system into POFF. Check external safety interlock signals on user terminals—including emergency stop, remote/local switch, fan fault, and transformer overtemperature signals—to ensure they are in normal state (typically normally open or normally closed contacts). Simultaneously confirm all cabinet doors (switchgear, transformer, control) are fully closed.

This frequency jump from 0 to a specific value is typically a parameter setting issue rather than a fault. Reset the parameters and restart to see if it resolves. Typically, parameter P01.01 sets the initial frequency during inverter startup, causing the inverter to start at the frequency specified in P01.01. Alternatively, parameters P08.08 and P08.09 may be configured to bypass undesired frequency levels and jump directly to the target frequency. These parameters can all cause the inverter frequency to jump abruptly.

If it operates normally without the motor, an under-voltage fault with the motor connected usually indicates the relay is not functioning. Power on and listen for the relay clicking into place. The relay operates on internal 24V power. If no sound is heard, disconnect the fan power cable at the top, then power on again and check for the relay clicking sound. If still absent, this indicates no internal 24V power. Replace the relay or the internal power board.

When configuring parameter P4.03, if you find that a low baud rate connects successfully but 56700 fails, this may indicate a switching frequency issue. Check P9.53. If its current value is 4k, change it to 8k before attempting connection again (P9.53 requires developer permissions; contact INVT engineers in advance if needed).