Page 36 - Basic PD Theory

On-line PD Tests

5
Chapter

5 On-line Periodic Tests

Overview of on-line testing with portable instruments

5.1 Periodic Testing
Purpose: To periodically observe the PD that occurs in a machine during normal operations
This requires an Iris instrument and a laptop computer running PDLitePro. This PD test requires the prior installation of PD
sensors within the stator winding. The permanently mounted PD sensors block the AC power signal, but pass the high
frequency PD pulses (see Section 3). During normal operation, an Iris instrument connected to the sensors separates noise and
properly classifies the PD. The type of sensor installation and test instrument depends on the machine or equipment being
monitored (see Section 3.2).
To collect PD data, the Portable instrument is temporarily connected to the termination box via coaxial cable generally using
BNC connectors for EMC installations and SMA connectors for SSC installations. A laptop computer controls the Portable
instrument as shown in Figure 23. The continuous systems, Figure 24, are permanently mounted and can be configured to
trigger based on operating conditions, activate alarms and provide output signals based on the PD levels.
5.1.1 Safety Precautions

The shield of the coaxial cable should be hard grounded at the termination box. The 50/60Hz AC  Assets > 6kV –
voltage between the center pin and the shield of PDA and Bus installs should be 100-600mVAC. If Semi-annual testing
the ground is disconnected, it is possible that this voltage may float to a higher value, so always check
before connecting cables. SSCs and RFCTs are not electrically connected to the HV, so there is no  Assets ≤ 6kV –
steady 50/60Hz signal available; however, you should verify both the presence and the magnitude of Continuous monitoring
the external reference voltage.

5.1.2 Test Setup & Procedures
We recommend tests be done semi-annually in order to provide maintenance personnel with advanced warning should problems
develop. As PD development is normally a slow process, Iris recommends tests be done semi-annually to provide maintenance
personnel with advanced warning should problems develop. For assets rated less than 6kV, continuous monitoring is
recommended. You should first perform an instrument check to make sure the computer and instrument are properly
communicating

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