IEC TR 62068-2:2001 pdf download

IEC TR 62068-2:2001 pdf download.Electrical insulation systems (EIS) –
Electrical stresses produced by repetitive impulses – Part 2: State of the art.
3.3 Effect of frequency of pulse voltages
The frequency dependence of the failure time was examined. Above a threshold frequency. the degradation rate of the wire insulation increases. The result was explained with the dielectric heating in the insulation layer.
3.4 Surface charging
Using charge decay measurements on different dielectric materials, the role of the polarity of impulse is demonstrated (4).
3.5 Other Important effects
The effects of temperature, moisture and/or ambient atmosphere such as ozone on the
insulation life of the samples under repetitive impulse condition are reported.
4 RotatIng machines
4.1 General studies
The papers (5) (6) [7)18] (91 (101 (111 mainly describe the effect of feeding low-voltage rotating machines by Inverters. Different laws related to cables length, the role of the nature of the switch, and the need for standardization of testing are given. Reference 191 Indicates repair laws or specification for asynchronous machines.
4.2 Voltage (stress) Identification
IGBT drives can have rise times of 50 ns to 200 ne. Thus, a new study on electrical stress of insulation systems due to the non-linear voltage distribution of mush-wound motors when subjected to repetitive steep dV/dt square-pulse waveforms (rather than impulse wave testing) is presented. Magnitude and rise time of the repetitive ASD (Adjustable Speed Drive) surge-voltage transient induced on the machine terminals are reviewed, Papers 1121 [131 [141 (15) [181 (101 117) [18] present results (generally on equipped rotating machines) of voltage distribution both in the winding and at the motor terminal.
They also give rules for cable length determination or IGBT installation.
4.3 Modelling
4.3.1 Voltage distribution
Papers (191 (201 (211 (22) (23) 1241 (251 give or propose models able to explain voltage distribution and propagation in the winding acCording to different characteristics (type of winding, type of cable, type of enamel, wire gauge).
4.3.2 Multistress ageing
Papers [26] [27] aro a first attempt to approach the agoing of winding Insulating materials when fed by inverters. They are very general A recent one intends to summarize new developments in this field and to propose an evaluation of the impact of the different parameters [28].
4.5.2 On-hf. m.asur.m.nts
Reference [48) proposes a condihon monitoring based on the sum of line-to-neutral voltage. According to it, it would also be possib’e to detect semiconductor switch faults using this method. Reference (49] suggests that the space vector current is a good indicator of ageing.
Reference (50] proposes to. and has developed, a system able to count the number of surges and to detect PD during both off-line and on-line operations.
Reference [51) claims that it is possible to identify PD sources and location via their modelling.
4.5.3 Off-lIne measurements
References [52] (53) recommend and discuss surge withstand capability and test in surge as regards corona between turns
Reference [541 proposes a method to investigate the possibility of corona testing via surge test.
References (55] (56] propose a selection of power cable assuring a correct link between motor and inverter,
References (57] [58] (59] propose surge limitation.
References (60) (61] (62) propose and describe non-dissipative filters able to reduce overvoltage at the motor terminals.
5 Other electrical systems
5.1 Transformerslt
References (63] (641 describe studies of a.c. with lightning Impulses (1.2/50 s) for combination of oil and paper. The main conclusions are the following: no a.c. PD phenomena are triggered by lightning impulse voltage when the preapplled 50 Hz voltage Is less than 50 % of the r.m.s. value of the ac. PD Inception voltage for all combinations of polarities, and peak breakdown values of the superimposed voltage are reduced by 10 % to 19 % for a single applied lightning impulse with a low solid-to-liquid dielectric packing fraction (SLPF) for oil-impregnated paper in the intercooler model, but the difference In breakdown voltage between the superimposed voltage and a single lightning impulse is very small for a high SLPF for oil-impregnated paper. I.e. above about 30 %“.
Reference (651 demonstrates the role of the voltage distribution that can exceed (he peak value during propagation (such results are observed In rotating machines).