BoatEletrician
New User
- Location
- Miami FL
- Occupation
- Boat Electrician
The following thread may be useful to help to resolve this case :
[/URL]
forums.mikeholt….com
/threads/multiple-generators-with-common-neutral.101753/
On Feb 16 2013
===========================
On a marine application, a yacht using two generators ( not connected in parallel), to feed 7 separate circuit panels, separated disconnects but common neutral.
Both generators have their neutral connected to their own frame, and to the whole yacht common neutral; also frames are interconnected by the grounding system of the vessel.
Would be comparable to two generators running on different houses between two neighbors, as grounds ( but no directly neutrals) are connected by earth grounding bars.
——-
On the yacht the air conditioning system, is composed by 3 chillers and 12 remote fans, each fan has its own independent temperature controls for its cooling zone. (regulating the motor speed through ballasts); fans and chillers are feed from different panels.
Somehow on panel #4 (which can be manually switched to be feed by generator#1 or generator #2 ) there are on the same circuit, two fans with one single-phase motor each; those motors stall, and cannot re-start, they get blocked, cogging (not been able to begin rotating with a buzzing sound).
I don’t know why would motors stall ( except that the temperature regulators pauses them, or reduces speed to low).
Single-phase motors cannot re-start if there is :
1. Low voltage or high frequency ( the two generators may have up to 1 hz difference), as the starting torque is proportional to Volt/Frequency.
2. Start capacitor failure; but this two capacitor is in good working conditions).
Randomly those two single-phase motors work well.
Above situation ONLY occurs when both generators are working; It doesn’t happen with only one generator is working; also it doesn’t happens when the yacht is connected to shore power (utility from the dock).
I haven’t tried with some panels connected to one generator, and other panels connected to the utility at the dock.
Other fan motors connected to separate panels are not showing same problem.
This SIMULTANEOUS cogging happens only in this two fans, on the same circuit, from the same panel, from any of the two generators, and only when the two generators are working.
Would this situation ( low starting voltage & cogging) be caused by different potential between the two generator’ neutrals ?.
These generators are not paralleled, so even if they are not rotating synchronically, and having different phase angle, the electrons sharing the same neutral conductors shall seek only its own source generator, and not circulate through the other generator.
Or could it be a harmonics or frequency caused problem… but only on those two motors, from the same panel out of 12 fans connected to different panels ?
=====================
Rarely, On 3-phase motors, cogging or crawling ( low starting torque) could be caused by the harmonics 5th or 7th, producing a Counter-Torque, and consequent stalling.
But i DON’T KNOW, if this could alSO happen on single-phase motors 208 VAC, 60 Hz; I read that on single-phase motors, the 3rd harmonics are relevant, but I DON’T KNOW, relevant for what? .
|
forums.mikeholt….com
/threads/multiple-generators-with-common-neutral.101753/
On Feb 16 2013
===========================
On a marine application, a yacht using two generators ( not connected in parallel), to feed 7 separate circuit panels, separated disconnects but common neutral.
Both generators have their neutral connected to their own frame, and to the whole yacht common neutral; also frames are interconnected by the grounding system of the vessel.
Would be comparable to two generators running on different houses between two neighbors, as grounds ( but no directly neutrals) are connected by earth grounding bars.
——-
On the yacht the air conditioning system, is composed by 3 chillers and 12 remote fans, each fan has its own independent temperature controls for its cooling zone. (regulating the motor speed through ballasts); fans and chillers are feed from different panels.
Somehow on panel #4 (which can be manually switched to be feed by generator#1 or generator #2 ) there are on the same circuit, two fans with one single-phase motor each; those motors stall, and cannot re-start, they get blocked, cogging (not been able to begin rotating with a buzzing sound).
I don’t know why would motors stall ( except that the temperature regulators pauses them, or reduces speed to low).
Single-phase motors cannot re-start if there is :
1. Low voltage or high frequency ( the two generators may have up to 1 hz difference), as the starting torque is proportional to Volt/Frequency.
2. Start capacitor failure; but this two capacitor is in good working conditions).
Randomly those two single-phase motors work well.
Above situation ONLY occurs when both generators are working; It doesn’t happen with only one generator is working; also it doesn’t happens when the yacht is connected to shore power (utility from the dock).
I haven’t tried with some panels connected to one generator, and other panels connected to the utility at the dock.
Other fan motors connected to separate panels are not showing same problem.
This SIMULTANEOUS cogging happens only in this two fans, on the same circuit, from the same panel, from any of the two generators, and only when the two generators are working.
Would this situation ( low starting voltage & cogging) be caused by different potential between the two generator’ neutrals ?.
These generators are not paralleled, so even if they are not rotating synchronically, and having different phase angle, the electrons sharing the same neutral conductors shall seek only its own source generator, and not circulate through the other generator.
Or could it be a harmonics or frequency caused problem… but only on those two motors, from the same panel out of 12 fans connected to different panels ?
=====================
Rarely, On 3-phase motors, cogging or crawling ( low starting torque) could be caused by the harmonics 5th or 7th, producing a Counter-Torque, and consequent stalling.
But i DON’T KNOW, if this could alSO happen on single-phase motors 208 VAC, 60 Hz; I read that on single-phase motors, the 3rd harmonics are relevant, but I DON’T KNOW, relevant for what? .
