Shaft current measurement
Shaft current measurement
(OP)
Sir,
How does the shaft current measurement is done in hydro machines? I know that the earthing brush is connected at turbine(driving) side and the guide bearings are not insulated to earth while the bearings at the other (nondriving) end is insulated to earth. My doubt is if the bearing near shaft earthing brush is not insulated how the current measurement will be accurate? The shaft current is found measuring through a ct which connected in series with earthing brush. I am referring about a hydromachine of 7.5MW capacity , horizontal shaft. Will the oil film during running make the insulation to earth in the driving end bearings? Or, is the driving end bearing is actually be insulated?
Two days ago, I saw that the shaft current values are found very low than which was flowing normally even though in the order of microamperes. When I meggered the shaft after removing the earthing brush I againg found meggervalue zero. That is why I thought that the driving end bearing would be earthed.
I request your valuable comments and advices.
with regards,
appunni
How does the shaft current measurement is done in hydro machines? I know that the earthing brush is connected at turbine(driving) side and the guide bearings are not insulated to earth while the bearings at the other (nondriving) end is insulated to earth. My doubt is if the bearing near shaft earthing brush is not insulated how the current measurement will be accurate? The shaft current is found measuring through a ct which connected in series with earthing brush. I am referring about a hydromachine of 7.5MW capacity , horizontal shaft. Will the oil film during running make the insulation to earth in the driving end bearings? Or, is the driving end bearing is actually be insulated?
Two days ago, I saw that the shaft current values are found very low than which was flowing normally even though in the order of microamperes. When I meggered the shaft after removing the earthing brush I againg found meggervalue zero. That is why I thought that the driving end bearing would be earthed.
I request your valuable comments and advices.
with regards,
appunni






RE: Shaft current measurement
http://www.memagazine.org/backissues/may00/features/jam/jam.html
for ceramic bearings
Also, there are different shaft currents in larger motors, one due to fast switching devices, IGBTs, IGCTs, etc. with their path directed to the ground. Another shaft currents circulate within the engine body, e.g. between the stator and rotor due to various motor physical asymmetries
RE: Shaft current measurement
Rich L.
RE: Shaft current measurement
RE: Shaft current measurement
RE: Shaft current measurement
Raymond Ong, J.H.Dymond, R.D.Findlay and B.Szabados, “Significance of Joints Due to Lamination
Segmentation on Shaft Current in Induction Machines,” Proceedings 1999 IEEE Biennial International
Electrical Machines and Drives Conference, Seattle Washington, 9-12 May, 1999.
R.Ong, J.H.Dymond, J.V.Kay, R.D.Findlay and B.Szabados, “Impact of Oil Lubrication on the
Magnitude of Shaft Current in a Large Oil Ring Lubricated Induction Machine,” Conference
Proceedings ICEM’98, Istanbul, Turkey, 2-4 September, 1998.
R.Ong, J.H.Dymond, R.D.Findlay, B.Szabados, "Shaft Current Measurement of a Large Induction
Machine Using the Rogowski Coil Method", IEEE International Symposium SDEMPED'97, Carry le
Rouet, conference proceedings pg 23-26, Sep 1997.
Raymond Ong, J.H.Dymond, R.D.Findlay, B.Szabados, “Shaft Current Phenomenon: Experimental
Testing and Analysis of a Large Induction Motor,” Proc. International Association of Science and
Technology for Development, International Conference on High Technology in the Power industry,
Orlando, Florida, Paper 262-025, pp 241-6, Oct., 27-30, 1997,.