The wiring for the air compressor temperature probe gauge is live! ! !
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This post was last edited by yeying34 on 2019-3-17 09:33. The radial bearing temperature of the air compressor (multi-axis type, driven by a turbine) is experiencing significant fluctuations. Tests using instruments showed that there was a voltage of several dozen volts in the wires coming from the sensors. There are two monitoring points for each radial bearing; one of these points had voltage, while the other did not. Even after grounding for discharge, there was still a voltage of several dozen volts, whereas none of the other temperature monitoring points in the same unit had any voltage. The measurement on the second day was only a few volts, so it’s still too risky to connect it to the system. Has anyone encountered a similar situation? How was it handled? What are the hazards?
Based on the description, it is possible that the insulation of the cable is damaged, or the insulation of cables laid in the same conduit is damaged, which causes abnormal voltage due to interference; one can use a megohmmeter to check whether the insulation resistance is within acceptable limits.
It should be induced electricity; just install an isolation diode
Today, the temperature of the other side of the same tile also experienced significant fluctuations; the AC voltage measured was 7–8 volts, while the DC voltage was around 40 volts. Even installing a isolation barrier didn’t solve the underlying problem! ! !
It could be due to damaged cable insulation, which led to contact with other live wires
It should be noted where voltage can be measured. 1. It is almost impossible to measure voltage at the junction box next to the machine on site, as the voltage comes from within the machine itself in the form of a resistance signal； 2. Voltage is detected when measured at the cabinet terminal panel; this is likely due to induced voltage resulting from the installation of the main cable and the power lines. It is necessary to carefully check the way cables are installed within the cabinets ；
This post was last edited by feng*aosa on 2019-3-18 at 18:51. I have encountered similar situations. The inspection result showed a grounding fault in the turbine unit. The anti-static device of the oil system has fallen off.
Our crew’s wiring was just connected; as for whether the grounding is effective or not, I’m not sure. When the instrument wiring was pulled out of the conduit, point A became uncharged, which is strange. Then the cable from point A was inserted into the conduit; point A still worked normally, while point B still had a voltage of 1-2 volts. The instrument suggests that it might be caused by worn or damaged cables, but given the source of interference and the unknown origin of the voltage, static electricity accumulation and discharge to ground cannot be the cause, as in such cases the voltage does not disappear.
Finding the source of interference is indeed troublesome, so I can only share some experience; I’m unable to give specific advice. 1. Hydraulic/lubricating oil is insulating in itself, and internal static electricity cannot be detected from the outside. One can only check along the oil pipes to see if there are wires for separate grounding (to the chassis), and determine whether everything is normal ； 2. Voltages that can be measured with digital meters but not with mechanical meters are definitely interference (induction). But what is measured by a mechanical watch could also be interference; however, the possibility of electric leakage is greater ； 3. Avoid shielding multi-point grounding; it is preferable for the sensor wires to be shielded wires with external insulation, and they should be placed inside metal tubes before entering the cabinet. And insulation damage outside the shield can only be detected by visual inspection ； 4. Sensors that are working properly cannot rule out the possibility of internal circuit encasement; if encasement occurs where it shouldn’t, the impact can be significant. Sometimes, working as usual can still affect other circuits.
The isolation barrier has already converted the resistance signal into a current signal; how is it possible that it won’t work?
Try to minimize the length of the wiring for three-wire thermistors. Then add a barrier; in my experience, that should solve the problem. Another point is: is the quality of the thermal resistance probe reliable? What is the insulation resistance of the motor? I wonder if you all have checked it.