Thyristors in Railway Traction How can their effects be measured?

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4 Waveform recording of 25 kV 50 Hz thyristor locomotive primary current at approximately 90° advance on second rectifier bridge (1 div. - 24 Amps). Second bridge is indicated by the fact that the two 'steps' in the cycle are staggered by about 220 Amps. It can be deduced that the armature current is approximately 110 Amps, multiplied by the transformer turns ratio (referred to one secondary), divided by the number of armatures in parallel. Quite a lot can therefore be determined even from one waveform o_^_^-.\-. -y-ys jK o_^_^-.\-. -y-ys ~' B jK ~' B • ___ ___...____...______._______ ___________ _^_ j , m - p«^^«_ - ^^^_ - _ - ^^^^ , _ - _ - _ - _ - _ - ^^^^^^^_ - ^^^^^^^^^^^^^^^^^^^^^^^^_ - ^^^^^^^^ , ^^-r --- ^^ I pw-'-'q , q , ^-r'iw^ , f , pw_ l _ - f^^ , _ - _ - r^^^^_ - _ - _ - ^^^_ - ^^^^^_ - ^^^^^_ - ^^^^_ - ^^^^_ - _ - ^^^^_ - _ - ^^^^^H ■■■-■-■■ L "-"- - __C'! j ■■■-■-■■ _^_^_t ^__^__J^__^__H^_P__^__^B__^__i __^__^__H^__^__H^_I^__H^_^_K *_B L "-"- - __C'! j _^_^_t ^__^H^__^__H^_P__^__^B__^__i __^__^__H^__^__H^_I^__H^_^_K ■T -■H^B-. ^>». ^-^». :■>■>.- :■>■>, ■9B3EH K_3_E3_E_i_l K__^E_H_^H ■ W BBBfl B-B-BB I ___■. ._■ \ \\ . ^ X -^- V v . ^^^MBM* ^^^Mgmj » - ^-> ^P«^^^W^^ffW^ mtm am, ^- v- — ■—— — - «u «ti • .%... ♦ #? #F » # Waveform recording (left) of thyristor locomotive primary voltage (upper trace) and current {lower trace), made with B & K Type 6302 portable two-channel Waveform Retriever (above) and Type 2309 Portable Two- Channel Level Recorder (p.16). The Waveform Retriever is an instrument for enabling accurate chart recordings to be made of repetitive waveforms with frequency components up to 10 kHz, even when the wanted signal is buried in noise. In this recording 1 division = 7,5 kV and 24 Amps vertically and 2,8 ms horizontally. The current waveform shows that the locomotive has about 80° of advance on one rectifier bridge. This can be deduced from the fact that the current lingers at zero amps for two significant parts of the cycle. Furthermore the marked ringing on the voltage waveform occurs just after each voltage peak. Note that commutation from thyristors to diodes (at the trailing edge of each current peak) causes almost no perturbation on the voltage waveform. The waveforms are recorded in their correct time-relationship with this arrangement of instruments, and the lagging power factor is easily observed
Psophometric n o i s e T h e p *°? h ?T- T Y voltage ^ r a n g e s (at 10dB intervals, i.e., * if! telephone C i r C U i t S 3 , 1 6 increments of sensitivity) from 100/A/ to 30V RMS full scale def- On AC systems the h a r m o n i c s l e c t i o n , and a built-in calibration produced by thyristor control e q u i p - s o u r c e which may be used without ments tend to lie at lower audio f r e - d i s t u r b i n g the range setting, and quencies than on DC s y s t e m s , w h i c h also permits subsequent inmainly within the restricted b a n d - s t r u m e n t a t i o n (such as a level recorwidth used for telephone c i r c u i t s . d e r ) to be calibrated at the same Furthermore, the lengths of t h e s e t i m e . circuits are longer on inter-city routes (which are usually AC e l e c t r i - A versatile selection of outputs is fied) than on commuter r o u t e s , a v a i l a b l e for recording and monitor- (which are generally DC electrified), ing purposes. There is an AC output increasing the coupling between Type 2429 Psophometer (on a BNC socket) providing 3,16 V cables. Telephone interference is RMS out from a low impedance at therefore more of a problem when full scale deflection, with a peak thyristors are introduced on AC sys- sured with it as psophometric capability of 14 V. There is a DC outtems, than on DC systems. It is also noise. put (also on a BNC socket) with less worse generally on the newer indus- than 50O source impedance, trial-frequency electrifications (50 The Bruel & Kjaer Type 2429 pso- + 3,16V DC at full scale deflection and 60 Hz) than the older "railway" phometer conforms to the require- and a peak capability of + 14 V. Linfrequency systems (16-2/3 and ments of CCITT P53 and DIN earity of this signal against input 25 Hz) because the predominant 45 405 for telephone circuit noise RMS level is better than ±2,3% of harmonics from the latter lie at measurement. It may be used at the level between 25% and 78% of melower frequencies, outside the tele- site of the trials, powered from a ter full scale deflection, and better phone bandwidth (usually 200Hz to pair of external batteries (18 to than ±6% of level between 8% and 3 kHz) and there is less excitation of 25V), or in the laboratory (to mea- 245% of meter full scale deflection. transmission line resonances. Be- sure the signal recorded on tape). There is a headphone outlet on a cause the quality of telephone powered from 50 to 400 Hz, 100 to pair of screw terminals capable of speech is not usually higher than it 250V mains. Connection to a tele- accepting bare wires or banana needs to be for intelligibility, for^ rea- phone circuit is made using a 3-pin plugs. Finally there is a 7-pin DIN sons of economics, some interfer- plug to DIN 41 628 (B & K part no. socket carrying both AC and DC outence from electric traction units is JP 0316). The input includes a puts, battery inputs, and a line for generally tolerated, and the levei of transformer providing symmetry and an external capacitor which may be immunisation on telephone circuits a high level of isolation from poten- connected to increase the averaging is chosen to provide the best com- tially hazardous voltages which may time of the RMS detector. promise between cost and intelligi- be induced in the telephone circuit bility. However, when a new elec- from the traction supply. trie traction unit is introduced to an existing system and generates a different pattern of interference, its effect on intelligibility must be measured. Intelligibility is a subjective matter. Different frequencies interfere more or less with speech, and the annoyance level of a given frequency is also dependant on the bandwidth of the wanted speech signal. Consequently, to measure noise objectively in a telephone circuit one needs both a measuring amplifier and a weighting filter to weight the different frequencies according to the results of statistical experiments on human subjects. The weighting filter used for this purpose is known as a pSOphome- Response curves for Telephone Weighting and Unweighted characteristics of the Type 2429 trie filter and the COmDlete instru- Psophometer. Note that both the amplitude and frequency axes of this graph are logarithmic, in , . ,x . , contrast to the spectra on pages 7 to 14. A logarithmic frequency scale is useful for frequency ment is a psophometer. It is also . . ,+ . . *i . . .. . +. . . ,. . ' . ^ , . . K K analysis of transmission paths (of which the ear and an electrical network are two examples), al- COmmon to refer to the noise mea- though over a range of less than two decades of frequency, either linear or logarithmic scales may be used 5
Page 1: 18-060
Page 4 and 5: TflnP RPCOrH thfi a " the ' n f° r
Page 8 and 9: This external capacitor facility is
Page 10 and 11: On AC electrified railways the sign
Page 12 and 13: The next possibility to consider wo
Page 14 and 15: To prevent aliasing (spurious sampl
Page 16 and 17: An ideal method of predicting relia
Page 18 and 19: Type 2307 Level Recorder Type 2307:
Page 20 and 21: SnPPIril nrnhlpm^ erase-head, it ca
Page 22: different choke cores to minimise a

Thyristors in Railway Traction How can their effects be measured?

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