Page 38 - Basic PD Theory

On-line PD Tests

5.2.3 Triggered Data Collection
With the Guard systems, it is possible to set up scheduled, or triggered, data collection. Based on the installation options, these
triggers can be set based on operating parameters and time. For example, you can set the system to collect data at full-load hot
operating conditions at a frequency of once a month. Though the trigger definitions applicable to your situation will depend on
the condition of the winding, the type of winding, and the normal operating practice of the machine, the following are some
general recommendations for triggers:
 Full-load hot – once a month
 Full-load cold – once a month
 Reduced-load hot – once a month
 Reduced-load cold – once a month

5.3 Quality Flags or Flames
During testing, a flame will appear if a problem with the detected PD data occurs. Investigate the cause for this Quality flag or
flame by clicking on the flame. The reasons and recommended actions are as follows:
OVR: Over Magnitude – pulses with higher magnitudes than the test range. You need to increase the test range
magnitudes.
HNM: High Noise Magnitude – noise pulses with higher magnitudes than the test range. If the Unit PD is undetected, you
might want to lower the magnitudes of the test range to look for PD. Be careful if you are getting down into the 2-
32mV or 5-85mV range. DO NOT test at these lower ranges if the PD is above 1500mV.
HNPR: High Noise Pulse Rate – this just lets you know there were more noise pulses than the instrument could count. If
you raise the test magnitude, this should skip testing at the lower magnitudes where the high noise pulse rate occurs. It
does not affect the PD data.
POVRL: Pulse Count Overload – most likely more low magnitude pulses than the test instrument can count. Change to
higher test magnitudes and these pulses should no longer be detected. This flame is not a problem to the test
instrument.
UND: Under Magnitude – no pulses occurring within the selected test range, but pulses detected of lesser magnitude. You
need to decrease the test range magnitudes.

5.4 Errors
The message “Reference signal not 50Hz of 60Hz” indicates a problem with the voltage reference signal. For PDA and Bus
installs, the AC voltage between the center pin and the shield at the termination box of C1/Machine should be 100-600mV rms. If
this is not present, there is a problem with the sensor or the coaxial cable. For SSCs, the external voltage reference should have a
signal of at least 60mV rms.
If the computer cannot find the test instrument, you will get a “communications not established” message. The problem may be
that the network cards did not select the correct network port. Turn off the computer and the test instrument; reconnect the
network cable and then turn on the computer. You may also need to change the network protocols and adapters of the
computer; see the User’s Manual for more information about error messages.

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