IEC 60076-4:2002 pdf download
IEC 60076-4:2002 pdf download.Power transformers – Part 4: Guide to the lightning impulse and switching impulse testing – Power transformers and reactors.
The following parameters influence the Impulse waveshape:
a) the effective capacitance C1. and inductance of the test object, L1 C1 is constant for any given design and any given waveshape, L, is also a constant for any given design. The effective L1. however. may be influenced by the terminal treatment. It varies between the leakage inductance L, for short-circuited terminals and L0 for open-circuited terminals, More details in this respect are given in 7.1 and 7.3 and in annex A;
b) the generator capacitance C9
C) waveshaping components, both internal and external to the generator. R1, Ii,. R9, C1 (plus, where applicable, the impedance of a voltage divider ii):
d) the stray inductance and capacitance of the generator and the complete test circuit:
e) chopping equipment, where applicable.
The front time 1’1 is determined mainly by combination of the effective surge capacitance of the test object, including C1, and the generator internal and external series resistances.
The time to half-value F2 is, for lightning impulses, primarily determined by the generator capacitance, the inductance of the test object and the generator discharge resistance or any other parallel resistance, However, there are cases, for example, windings of extremely low inductance, where the series resistance will have a significant effect also on the wavetail, For switching impulses, other parameters apply: these are dealt with in clause 8.
The test equipment used in lightning and switching impulse applications is basically the same. Differences are in details only, such as values of resistors and capacitors (and the terminal connections of the test object).
To meet the dlffersnt requirements of the waveshape for lightning and switching impulses. due consideration has to be given to the selection of the impulse generator parameters, such as capacitance and series and discharge (parallel) resistances. For switching impulses, large values of series resistors andlor load capacitors may be necessary. which will result in significant reduction of the efficiency.
While the output voltage of the impulse generator is determined by the test levels of the windings with respect to their highest voltage for equipment t1m for the test object, the required energy storage capability is essentially dependent on the inherent impedances of the test object.
A brief explanation of the principles of waveshape control Is given In annex A.
The arrangement of the test plant, test object and the interconnecting cables. earthing strips, and other equipment is limited by the space in the test room and, particularly, the proximity effect of any structures, During impulse testing, zero potential cannot be assumed throughout the earthing systems due to the high values and rates of change of impulse currents and voltages and the finite impedances involved. Therefore, the selection of a proper reference earth is important.
