Pre Main Services Ltd. offers a preventive maintenance program that will reduce your costs and downtime. It will extend the life of your rectifiers and help control those unexpected rectifier failures. Our experience with all makes of rectifiers will make it easier to encounter any failures.

Each rectifier will receive a thorough vacuum cleaning and visual inspection for mechanical or heat wear.

I. Cleaning and Visual Inspection

This work must be done during down time, mainly on weekends.

Vacuum cleaning

Shut down and lock out unit.
Remove all panels.
Brush and vacuum complete rectifier thoroughly from top to bottom.
Each heatsink should be free of dirt.
Air ducts on transformers should be cleared for good air flow.

Visual inspection

Complete rectifier to be checked for loose or corroded wiring.
Diode cable to be checked for broken /burnt insulation.
Check for loose connections between diode cables and diode tails.
Check fan blade .( Loose or corroded)
Check fan motor. ( Spin fan blade to see if motor spins freely)
Check all stacks to see if they are corroded or blown. (Visual check)
Visually check transformer for any damage.

Any major problems or concerns are reported immediately.

II. Electrical

The rectifier is then checked under load. This test will be done while you are running regular production. It will not interfere with your production. Included in this load test are measurements of in-line voltage & currents, diode currents, main transformer output, meter readings, % ac ripple at the rectifier & tank etc. The voltage drop between rectifier and tank will be measured to check for proper bussbar connections.

Electrical Test Procedure Under Load

Remove panels
Do visual and audible inspection of rectifier and controls to check for obvious damage or trouble spots.
Check diode currents for balance.mark open or questionable ones for replacement.
Connect oscilloscope to output of rectifier to verify six clean pulses. If not,find why.
Check primary currents for balance.
Check gate voltages to find any questionable scr’s.
Check control transformer output.
Check main transformer outputs for balance.
Check that scr outputs are balanced and proportional to main transformer outputs.
Check output voltage and verify proportionality to feedback signals.
Check current feedback signal for continuity and proportionality.
Check panel or remote meters for accuracy relative to feedback signals .
Check that voltage at tank matches rectifier output voltage without unusual drops.

A typed report will be given for each unit, which will contain all above readings and summary of necessary repairs to be done. Also, a list of preventive maintenance for each unit.