System Operation
What a tester verifies
A rectifier converts AC to DC through a transformer with tapped primary windings and a rectifier bridge. The tester typically records rather than adjusts: tap position, DC voltage and current, AC input, fuse and breaker condition, cabinet grounding, and terminal tightness. Cabinet meters are often inaccurate; confirm output with a portable meter.
Reading the circuit
Circuit resistance follows Ohm's law: R = E/I. Rising voltage with falling current means resistance increased - a drying or gas-blocked anode bed, a broken header cable, or a corroded connection. Galvanic systems show declining output over their service life; check current with a shunt or clamp-on meter.
Interactions
Operation includes recognizing interference: bonds and diodes to foreign structures, DC transit stray current, HVDC ground electrodes, and cathodic protection on adjacent pipelines. Interruption cycles must be coordinated so the affected structures are interrupted in step.
Traps: comparing output to design without noting tap position; reading DC output on an AC range; assuming a rectifier is off when a fuse has blown; assuming zero current means zero voltage.
Worked example: a rectifier reads 14 V and 5 A, giving 2.8 Ω. Six months later, 14 V and 2 A gives 7 Ω. The current halved and resistance more than doubled, so the first suspect is the anode bed, not the DC supply.
Rule of thumb: when current falls and voltage holds, look at the groundbed circuit; when both fall, look at the supply.