IEC TS 61934:2011 pdf – Electrical insulating materials and systems – Electrical measurement of partialdischarges(PD) under short rise time and repetitive voltage impulses.
In this technical specification. PD readings are reported in units of mV, In all cases, a
sensitivity evaluation of the measuring system is necessary and shall be carried out according
to Clause 7.
43 Test objects
4.3.1 General
Test objects behave predominantly as inductive, capacitive or distributed equivalent impedances according to the voltage supply frequency content. For some test objects. whether they are predominantly inductive, capacitive or distributed impedances may depend on the PD detection frequency range (not only on the voltage supply frequency). Test objects with distributed behaviour have transmission line characteristics which may cause attenuation and distortion of the PD pulses as the pulses propagate through the test object. The following classification is effective only for low-frequency, narrow-band measurements.
43.2 InductIve test objects
Types of inductive test objects may include:
— stator and rotor windings;
— inductive reactors:
— transformer windings;
— motorettes and formettes (see the IEC 60034 Series).
4.3.3 CapacItive test objects
Types 01 capacitive test objects may include:
— twisted pairs of winding wire;
— capacitors:
— packaging of switching devices;
— power electronic modules and substrates;
— isolated heat sinks;
— mainwall insulation models in stator coils and bars:
— printed circuit boards:
— optocouplers,
4.3.4 DistrIbuted Impedance test objects
The following test objects may have distributed equivalent impedance properties:
— cables;
— busbars;
— stator and rotor windings;
— transformer windings;
— turn insulation of stator and rotor windings.
— bushings with capacitive voltage stress control:
4.4 Impulse generators
4.4.1 General
Impulse generators used in this technical specification shall generate short rise time and repetitive voltage impulses with a low noise level, For a short rise time of impulses,
4.5.2 Effect of environmental factors
In general, PD-associated quantities may be affected by the following factors:
— temperature;
— humidity;
— atmospheric pressure;
— type of environment gas;
— degree of contamination of the test object.
NOTE Pt) phenomena may change with longer nsa tim, in th, case o4 high altitude,
4.5.3 Effect of testing conditions and ageing PD-associated quantities may be affected by
— voltage distribution,
— position of PD occurrence.
— previous voltage applications as well as the time between voltage applications,
— operation time or time under stress of the test object.
In addition, they may vary as ageing of the electrical insulation occurs, that Is, during operation of the EIS.
5 PD detection methods
5.1 General
Any PD pulse detection system where the test object is excited by voltage impulses requires strong suppression of the residual voltage impulse, measured by the PD detection circuit, and negligible suppression of the PD pulse. The PD pulse shall have a magnitude after processing by the detection system that is greater than the residual transmitted voltage impulse. The amount of impulse voltage suppression required will be dependent on the test voltage and the rise time of the impulse.
As the impulse voltage increases in amplitude, greater suppression is required in order to ensure that important PD pulse magnitudes are higher than the residual transmitted voltage impulse on the output of the detector. Similarly, as the rise time of the applied impulse voltage becomes shorter, the suppression shall be greater. due to the increased overlap of frequency spectra of supply impulse and PD pulse (see Annex A). PD pulse coupling devices shall be designed to ensure that important PD pulse magnitudes are higher than the residual transmitted voltage impulse on the output of the detector, or the residual be clearly distinguishable from the PD pulses.
Annex A provides indications of the voltage impulse suppression action required by the coupling device. Suggestions for the amount of supply voltage impulse suppression needed as a function of impulse magnitude and rise time are given.
Examples of PD pulses extracted from a supply voltage impulse through filtering techniques are reported in Annex B.
5.2 PD pulse coupling and detection devices
5.2.1 Introductory remarks
PD current or voltage pulses in a test object can be detected either by means of high-voltage capacitors. high-frequency current transformers (HFCT) or electromagnetic couplers (e.g. antennae).