2. 16/03/2022 2
Partial Discharges in MV Motors
• Motor insulation systems are never perfect
• If the breakdown voltage of a material is exceeded, a partial discharge can occur
• Partial Dischage Monitoring is a proven tool to detect insulation defects, such as voids,
delaminations, inproper spacing, degradation…
• Every Motor on medium voltage has a PD footprint
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7. Ensure proper ground, through flat grounding
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Capacitors (IPDS) need to be grounded proper!
No isolating plates!
8. Below the IPDS the coaxial cable need to connected proper
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Conductor and Shield should not be switched!
Measure AC voltage at CH1, CH2, CH3 below Insulgard
e.g. 10kV Motor in Europe (50Hz) should deliver 400mV
9. Coaxial cabling check – allowed with running motor
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Unscrew the device – use Multimeter to measure
Measure AC voltage at channels 1-3
Typical issue: Cables swapped or screen touches Signal (shorting)
10. Sensitivity Check – Please note your values
10
Insulgard Channel Sensor Measurement [Ω] Expected Value Calibrator [nC] Insulgard [mW]
injected Signal visualized value
01 CCA ca. 3 kΩ
02 CCB ca. 3 kΩ
03 CCC ca. 3 kΩ
04 RTD01 < 2 Ω
05 RTD02 < 2 Ω
06 RTD03 < 2 Ω
07 RTD04 < 2 Ω
08 RTD05 < 2 Ω
09 RTD06 < 2 Ω
10 RTD07 < 2 Ω
11. 16/03/2022 Fußzeile 11
Sensitivity Check along Calibrator – Inject defined PD
Set Insulgard to Test mode, Power Freq. Cycles to 10, and turn off load threshold
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Sensitivity Check along Calibrator – Inject defined PD
Connect along USB or LAN to Insulgard, Send new settings to Device, Single Measurement
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Sensitivity Check along Calibrator – Inject defined PD
Connect Red to Phase and Black
to ground
Work with two people, one who
operates calibrator, one at the
instrument
Test each channel, if the time
allows with different amplitudes
Test RTD Board also
Create a table of the results and if
possible, a screenshot of all
pattern
14. 16/03/2022 Fußzeile 14
Sensitivity Checks - Qmax comparison
Calibrator pulse injected close to motor leads
Eisenhuettenstadt Gendorf
Oexelosund Trinec
Bremen OT5
Marl
15. Optional Coupler Termination Box CTB1A
15
- Protection for LV (sparc gap implemented)
- Offers connectivity to other PD devices
16. RTDs as PD sensors? Where are they located?
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Two RTDs per phase – near Slot Exit + Center of Winding
17. RTD wiring checks – ground correct?
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RTD Sensor Board allows PD Signal decoupling
If it is not, then the measured
PD level can be very low.
Screw and yellow
contact pad connected
to the motor ground?
The PD outputs (+ and - ) shown in the green oval
below are galvanically isolated from other board
circuits.
18. Please measure the following
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Below 2Ohm 10-15Ohm (copper RTD)
150Ohm (platinum RTD)
10-15Ohm (copper RTD)
150Ohm (platinum RTD)
Contact 1 to Contact 4 ~ 150kOhm
20. Motor Terminal Box - General Checks
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CTs should never be placed on MV cables without shield!
Use proper fixation of CT
Keep safety distance to other phases
Only qualified personnel is allowed to
work in the MV terminal box
