ATTACHMENT A - VFD Preventive Maintenace Checklist.docx

DEPARTMENT OF VETERANS AFFAIRS

Clement J. Zablocki VA Medical Center Facility Management, Bldg 70E 5000 W. National Avenue Milwaukee, WI 53295

Contractors must use the checklist below as a minimum standard for inspection and maintenance of Variable Frequency Drives (VFD). This form is to be turned in at the completion of each site visit and be signed by both the vendor and VA Contracting Officer Representative (COR).

C: Completed N/C: Not Completed

Visual Inspection & Cleaning

Technicians perform a complete visual inspection and cleaning. Broken or damaged parts are replaced as necessary. Drives are inspected for ambient temperature, dust, dirt, moisture, evidence of overheating, corrosion, integrity, etc. Capacitors are checked for leakage. Conductors and parts are checked for proper insulation. Drives are cleaned using vacuum or compressed air as required. Filters are cleaned or replaced. Power connections are re-torqued to manufacturer’s specifications. Check circulating fans for signs of bearing failure or foreign objects internally.

Cooling

Fans are energized and tested for airflow. Heat sinks and air passages are inspected to detect blockage or broken/cracked components. Fans are replaced as necessary. Air conditioners are checked for proper cooling.

Line Reactors, DC Link Reactors, Isolation Transformers

Reactors and transformers are inspected for wear, insulation breakdown, connections, and proper conduction. Transformer voltages are checked for proper amplitude and balance. Inspect DC bus capacitors for bulging and leakage.

Operator Interface

The keypad or other operator interface is checked for display, keypad, proper communication, and fault history log. Action is taken, as indicated, for fault indications.

Power-On Test

With power applied to the drive, the dc bus is checked for correct voltages and currents. Incoming AC voltages are checked for proper amplitude and balance. The dc bus is checked for voltage and excessive ripple voltage. Output voltages are checked for amplitude and balance. All values are compared with previous results to assess the rate of deterioration. Technicians look for evidence of unusual vibration or noise.

Harmonic Filters

Components are inspected for integrity, insulation breakdown, and connections. Line voltages and currents are verified for proper balance. Load voltages and currents are verified for balance and amplitude. Currents and voltages at the capacitors are also checked for balance and integrity. Capacitors are inspected for bulging, leakage, loose connections, etc. Current harmonics are measured and verified.

Converter Section

Each diode is isolated and tested for proper conduction and reverse voltage blocking capability. Connections are inspected for tightness and corrosion.

Inverter Section

Each transistor, or other switching device, is isolated and tested for proper conduction, commutation, and reverse voltage blocking capability.

Capacitors

Excessive ripple on the dc bus can cause erroneous operation and drive failure. Capacitors are isolated and tested to assure that they meet the manufacturer’s specifications. Defective capacitors can be replaced individually, or at your option, all capacitors can be replaced for extended operating life. Bleed-off resistors are also checked for continuity and integrity.

Parameter Settings

Programming parameters are checked, as required, to assure correct settings. Alarm and fault logs are viewed to find evidence of previous faults. Change logs are viewed to indicate any parameters, which have been inadvertently changed since the last maintenance visit.

Digital and Analog I/O

All inputs and outputs, digital and analog, are tested for calibration and correct operation.

Pre-Charge Circuit

The pre-charge circuit protects the capacitors and dc bus from damage. A faulty pre-charge circuit can lead to dc bus failure, and even explosions. The pre-charge resistor is tested for integrity and proper resistance. The bypass contactor (or solid-state bypass) is tested for correct operation and contact wear.

Firing Test

While the drive is running, an oscilloscope is used to verify correct waveform on each of the output phases. Control voltage is checked and verified.

Load Test

The drive is run under load (where practicable). Currents and Voltages are measured for proper balance and amplitude. Voltage and current readings are verified on the keypad.

Enclosures & Build-ups

Maintenance of enclosures and build-ups varies according to the application. Typical maintenance will include visual inspection, cleaning, fan inspection and/or replacement, replacing failed pilot lights, rotation verification and contact inspection on bypass contactors, calibration of analog transducers, tightening of electrical connections, damaged terminal blocks, etc.

Infrared Scan

An infrared heat scan will be done on the VFD’s and/or associated power equipment. The ThermaCAM report will include an infrared image of the VFD and/or associated equipment along with digital hot-spot temperature, color image showing temperature profile within the cabinet, and a problem report describing any abnormalities found.

Test Report

Trained technicians will provide a completed test report on each VFD.

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