Electrostatic Strip Oiler HVPS Ground

[BearB]

I have question about an Electrostatic Strip Oiler (ESO) used to coat oil on a steel continuous strip. The ESO has a High Voltage Power Supply for the top set of oil valves and High Voltage Power Supply (HVPS) for the Bottom set of oil valves. All has been operating OK until about 2 weeks ago the Bottom HVPS started reading about –67KV, .34ma on the display, should read about -67KV, 0ma. The set point was at 4ma that kicks the output out until it is manually reset. Increased the set point until problem can be corrected. Problem is not the HVPS or cable because swapped and still had problem. Something interesting is if the oiler is not being used to a period of time the HVPS reading “ma” signal gets up to about 5ma then lowers to about .34ma when strip gets moving but not to the 0ma as it should. Could not find a manual for this piece of equipment or not allot online to explain. I have never worked around this piece of equipment so I am learning about it as I go. I believe the oil is sprayed unto the steeI strip and is attracted to the steel strip (which is grounded through the equipment) via the high voltage. The problem is: “where the milliamp current going?”. Some are saying it is contaminated oil but it is the same oil used on the top and Bottom and the top has no issues. Others are saying it is the humidity because the outside temperatures are in the 90’sF. I am not sold on this because Operators that have worked there several hot summers said they do not remember this type of problem not can I explain how humidity could do this or if so a fix. Any ideas would be helpful.

 

[zappedagain]

63 KV / 0.34 mA = 185 Megohms (185,000,000 ohms).

That could be about anything. Did somebody lean a broom against the bottom set of valves? There is some 'leakage path' that this current is flowing through. Look for anything 'new' around or near the bottom valve assembly.

You stated 0.34 mA on the display, and a 4.0 mA limit; is that correct? If so, that seems like you still have good margin. That indicates the fault may be more of a pulsed mechanism (dynamic, or AC), so the display is only showing the average current (1A peak that lasts for 0.000034 seconds and repeats every 0.1 seconds would show 0.34 mA on the display - kind of like arcing). If that was supposed to be 3.4 mA, that is closer to the limit and indicates a constant fault (static, or DC), like the broom mentioned above.

John D

 

[BearB]

Thanks for the reply.
The limit is .4ma.
Yesterday on a Downturn we changed out the Pads that are located below the strip. The Pads are a neoprene type material that the strip touchs sometime. The HVPS readings this morning on the bottom are .02ma. Possible there were bits on metal imbed in the material and the steel strip being oil was contacting. Maybe if it was dark enough sparks would indicate, not sure. Learning about this as I go.

 

[zappedagain]

I'm glad you found it. The 0.02 mA could be vampires... I heard they sparkle in the daylight.