Has anyone ever heard of using a "AC curve test" to set neutral on a DC machine. We have a client who has requested this procedure to set the neutral on (2) 1500 HP DC main propulsion motors that power a research vessel. They have been experiencing sparking on the commutator at full load on the starboard motor that is eliminated after the comm has been stoned but recurs after approximately a month in service. We suspect loose commutator bars (it's an overhung 3 segment glass band comm) but they suspect the armature may be set off neutral. They are returning to port on Monday and would like us to perform this test. Any thoughts?
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AC curve test to set neutral in DC machines
- Thread starter accordlx
- Start date
Skogsgurra
Electrical
It is quite common over here. Just connect an AC source - mains voltage is OK because the impedance of the excitation winding is quite high. Then measure the induced voltage picked up by the brushes.
Make a diagram where the voltage vs brush position (degrees or mm or whatever) is plotted. Then set the brushes where the line you draw between the different points crosses zero volts.
There are other ways of doing this. Run the rotor at exactly the same speed in both directions and adjust brush position until voltage is equal when running CW and CCW. ABB used to do this, but never done it myself. I always use the AC method.
Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
Make a diagram where the voltage vs brush position (degrees or mm or whatever) is plotted. Then set the brushes where the line you draw between the different points crosses zero volts.
There are other ways of doing this. Run the rotor at exactly the same speed in both directions and adjust brush position until voltage is equal when running CW and CCW. ABB used to do this, but never done it myself. I always use the AC method.
Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
It's always a good idea to check the neutral setting on a D.C. machine during the troubleshooting process.
What you're describing as sparking on the commutator at full load would continue even after stoning the bars.
If the brush neutral position was/is indeed off, it would be immediately obvious with continued arching under load.
Your suspicion of loose commutator bars is valid. High mica is a common issue related to arching as well if the motor
has not been serviced in a while.
Enjoying the forum,
John
What you're describing as sparking on the commutator at full load would continue even after stoning the bars.
If the brush neutral position was/is indeed off, it would be immediately obvious with continued arching under load.
Your suspicion of loose commutator bars is valid. High mica is a common issue related to arching as well if the motor
has not been serviced in a while.
Enjoying the forum,
John
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