Page 66 - Basic PD Theory

Zone of Coverage

• Noise – all pulses detected that do not exhibit PD characteristics
Note that the Zone of coverage for a single-ended installation will include everything; so if further investigations are warranted due
to high PD, they should always start at the terminals.

PDA Test Method (PDA-IV, HydroGuard, GuardII, HydroTrac and HydroTracII)
During normal machine operation, either the PDA-IV is temporarily connected, or the HydroGuard or GuardII, or HydroTrac
or HydroTracII is continuously connected to the previously installed couplers in each phase. If there is an internal circuit ring
of sufficient length, the best installation is a differential mode; otherwise, a directional mode is required.
Two or more couplers per phase are installed near the junction of the circuit ring and the high voltage coils of different parallels
per phase [4]. These Iris instruments separate PD from System disturbances based on simultaneous time-of-arrival and pulse
characteristics, while measuring the number, magnitude and AC phase position of the PD pulses. This configuration can
reliably account for System activity and ensure there is no negative impact on unit PD measurements. It is a reliable means of
monitoring the PD activity in a hydro generator where internal machine disturbance is not generally a problem.
The PDA-IV, HydroGuard, GuardII, HydroTrac and HydroTracII are capable of separating pulses into three categories:
• C1 – narrow pulses originating near the C1 circuit
• C2 – narrow pulses originating near the C2 circuit
• System Activity – narrow pulses that arrive simultaneously at the two coupler outputs
Note that the Zone of coverage for each pair of couplers, C1 or C2, will include the portion of the circuit ring from where the
coupler is connected back to where the circuit ring splits; so if further investigations are warranted due to high PD, they should
always start at the junction of the circuit ring.

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