A phase converter provides three-phase power from a single-phase source. Old-style mechanical converters use a hybrid motor/generator, while electronic converters use capacitors and other devices to simulate three-phase power.
The first image provides a look inside the cabinet of a Phase Technologies phase converter cabinet. Many of the electronic components are on the circuit boards on a metal panel in front of the capacitor bank. To replace the capacitors, this panel must be moved out of the way.
At first glance, it appears that the task of moving the panel will take hours and be very tedious. But the second image shows an easier solution that requires disconnecting a few cables at the bottom of the panel and gently swinging up the panel to reveal the capacitor bank. (I held the panel up with bungee cords and put some bubble wrap between it and the connectors behind it.)
Be sure to take pictures and draw a diagram listing all connections that were undone.
Making space for removal of the capacitor bank requires disconnecting one wire from a contactor lug and one other wire. Thankfully, the capacitors in this system are non-polarized. They are reconnected with one terminal to a grounding wire and the other to a numbered wire. (Note the bleeder resistors across the capacitor terminals.)
A few important notes about this task.
The most important step is to discharge the capacitors before beginning any work. According to the manufacturer, 30 minutes with the power source off before doing any work should be sufficient. I found that discharging required at least 30 minutes, then I used an alligator clip lead taped to the end of a dowel (the other end hooked to ground) to tap the connections and drain any remaining energy.
To do the job I also needed a long Phillips screwdriver to get to the panel mounting screws, a #20 Torx driver, a smallish adjustable wrench and a good tiny flashlight. Aside from a few zip ties, the reconnection of the wiring was straightforward.
Capacitors age while just sitting on the shelf, and their quality and testing can vary, as well as fakes being sold. Buy replacements from trusted vendors and test them yourself if possible.
Additional maintenance on these units includes testing the ventilation fans. They pull air from the bottom of the box and across the aluminum heat sinks, and blow it out the top. A thermal sensor on a heat sink starts the fans above a certain temperature. The sensor may take a few minutes to close. If the fans never start, check the voltage at the terminal strip. You can replace the fans if necessary.
Also check the contactor that closes when the converter is operational. Remove the cover to check the contacts for burning and pitting.
Phase converters add another layer of complexity to any facility. The newer generations require little maintenance and can run without problems for years. Keep spare fans and contacts to reduce potential downtime.
The Phase Technologies website provides support resources including the white paper “Phase Conversion Technology.” Find it here.
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