IEC 60885-3-2015 pdf download.Electrical test methods for electric cables – Part 3: Test methods for partial discharge measurements on lengths of extruded power cables.
This part of IEC 60885 specifies the test methods for partial discharge (PD) measurements on lengths of extruded power cable, but does not include measurements made on installed cable systems.
Reference is made to IEC 60270 which gives the techniques and considerations applicable to partial discharge measurements in general.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60270:2000, High-voltage test techniques – Partial discharge measurements
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60270 apply.
3.2 Symbols used in Figures 1 to 14
a 1 discharge magnitude measured with the calibrator at the end near to the detector
a 2 discharge magnitude measured with the calibrator at the end remote from the detector
C cal calibrator
C K coupling capacitor
C x power cable
D detector
I double pulse generator
l length of the power cable
M coaxial signal cable
Q discharge magnitude
R 1 R 2 matching resistors
RS reflection suppressor
v propagation velocity of partial discharge
V voltage indicator
W power supply
4 Overview
4.1 General
Partial discharge measurements shall be carried out using the test techniques specified in IEC 60270.
4.2 Object
The object of the test is to determine the discharge magnitude, or to check that the discharge magnitude does not exceed a specified value, at a specified voltage and a declared minimum sensitivity.
4.3 Problem of superposition of travelling waves for long lengths
Short lengths of cable behave in the same way as a single capacitor in that the discharge magnitude can be measured directly by considering the cable as a single capacitor. However longer cables behave like a transmission line and PD pulses travel away from their source in both directions along the cable, in the form of a wave. On reaching the remote end from the measuring equipment, the pulse will be reflected with the same polarity if the end is open circuit. The reflected pulse will then travel back along the length of cable and arrive at the detector at a time after the directly received pulse. If the time between the arrival of the two pulses is short (the time difference depending on the length of the cable) then the detection instrument may give a false response, indicating either a larger or smaller magnitude of discharge than was actually the case. The methods detailed in this standard allow correct measurement of partial discharges under these conditions.
Figures 1 to 4 illustrate the behaviour of travelling waves and possible superposition effects.IEC 60885-3 pdf download.