When it comes to resurfacing your collector rings and commutators, downtime is wasted time. So why take your unit off-line when Cutsforth Online Truing is more cost effective, less time consuming — and, in most cases, more accurate? Our online truing takes place at operational temperature and operational speed, so rings are ground in reference to the operational center, less material is removed, life expectancy is extended, and brush chatter and vibrations are reduced.
Our Cutsforth Online Truing Process restores your collector ring and commutator ring surfaces without an outage.
Caused by a compromised brush-to-ring connection. Brush box restrictions like carbon deposits, poor spring pressure and out-of-round rings are the most frequent culprits of visible arcing. Without proper maintenance, this arcing can escalate into a catastrophic ring fire causing equipment damage and a forced outage.
Any restrictions present in the brush box can restrict the brush moving freely in the box. Some examples:
Small, hardened carbon deposits (not carbon dust) that adhere to the brush box wall caused by the repetitive impact of the brush against the brush box in high-speed turbine generators.
Brush can become chipped when the collector ring becomes out-of-round causing the brush to move (or chatter) in the brush box. Chipping of brushes can occur when brush chatter reaches > 10–15 mls.
Brush catch mechanisms from some OEM and aftermarket brush holders can chip the brushes when they are not working properly. Brushes can also chip if they are not fully riding on the collector ring surface.
Selective action causes an overheating of shunts that lead to discoloring. A silvering of the shunt (see photo) can be an indicator that selective action is occurring — the brush is carrying too much current.
Also called imaging, footprinting, or ghosting, this is a common phenomenon where the brush-to-ring connection is compromised. The marks are signs of electrical erosion resulting in a compromised connection which affects the concentricity (or roundness) of the ring. The ring surface can be observed by using a strobe when the unit is in operation. Taking digital pictures can also capture photographing while the unit is running.
Contamination, rust, and dirty air can all negatively affect the surface of the collector ring. These conditions can cause rapid brush wear, affect the brush film (or patina) and cause problems with the transfer of current from the ring through the brushes.
Poorly designed and poorly maintained terminal connections can become trouble points for your brush holders. These connection points are difficult to maintain and are therefore not serviced regularly. The pictures show loose or burned connection points which can be trouble spots for arcing.
OEM and aftermarket brush holder spring designs do not allow for easy replacement. The spring is usually riveted to the spring clip or magazine type holder. Weakened or over-sprung springs compromise the brush-to-ring connection. Cutsforth brush holder’s spring is easily replaced. We provide a new spring with every brush eliminating this common problem.
Collector rings and commutators are grooved from mechanical and electrical brush wear. Unfiltered air and oil contamination can increase the ring wear as well. Cutsforth Online Truing Service can restore the ring surface without shutting down.
If any part of the spiral groove is worn below .035″ or is missing, the groove should be restored to prevent selective action related problems. Cutsforth Spiral Groove Restoration saves valuable outage time and maintenance dollars.
Flat or low spots on the collector ring or commutator from electrical erosion increases brush vibrations (or brush chatter) and vibration related brush holder problems. This out-of-roundness will not be noticeable to the naked eye. Cutsforth Online Truing Service addresses out-of-round collector rings and commutators since it is performed at operating speed and temperature.
When you experience excessive brush vibrations (> 6 Mils), arcing, grooving, or photographing (also called imaging, ghosting or footprinting) on your ring or commutator. One or more of these issues likely makes your collector rings a good candidate for online truing.
Our company has been performing our online truing process on rings and commutators since 1991.
We have safely performed truings on units around the world since 1991 and have never had a serious injury in any plant while truing.
The time varies from 2–10 hours depending on the condition of the collector rings or commutator.
Generally speaking, you do not need to reduce load. In rare instances of very high arcing or brush vibrations, a temporary drop in load may be required for the online truing to take place.
Our service techs measure the movement of the brush with a vibration analyzer in mils displacement. Basically, a round ring will register a low reading (generally < 2 mils) and an out of round ring will register high readings (> 6 mils is over the OEM recommended limit).
The process is often more accurate at creating a round surface because the work is performed on the generator while at normal operating speed and temperature. A round ring on turning gear does not always equal a round ring online.
We also true brand new rings after start-up due to the shift in operational center and the runout being high at speed/load.
As long as there is still a helical groove, it can be trued.
The biggest risk of tripping a unit comes from the ground detection system. Service techs will inspect and monitor the unit for oil contamination and the collection of particles to avoid alarming the ground detection system. In rare cases, if the oil film is severe enough, they may choose to not proceed with the process until the oil leak is resolved. Of the thousands of units that Cutsforth has performed online truing during the last 35+ years, <0.1% tripped during the process.
If you believe your unit is in an emergency state, we can usually respond within 24 hours for an expedited charge. If your unit can wait, we will work with your plant to schedule it in a timely manner.
All our field service technicians are experienced and capable of performing online truing at your plant.
No problem! If tolerances allow, Cutsforth can restore the spiral groove at your next scheduled outage. Most collector rings can be re-grooved once in their lifetime. The minimum recommended depth of a helical groove is 0.03 inches.
