12-06-2013, 03:01 PM
Power Quality Aspects of Electric Traction
Power Quality.ppt (Size: 107 KB / Downloads: 85)
Power Quality Definition
The term power quality is used to describe the extent of variation of the voltage, current and frequency on the power system. The variation of voltage and current can either be in terms of magnitude or waveform shape/distortion.
Power Quality Standards
IEEE 519, IEC 61000-3-2/4 for THD voltage and TDD i.e. current distortion limits at PCC for different power system voltages & fault levels and for different equipments respectively. IEEE 1159 describes Recommended practices for monitoring of power quality.
Performance standards like EN 50160 followed by EC, voltage un balance, harmonic distortion have been fixed for utilities. In UK for connection of non-linear equipments, ENA engineering guide G5/4-1 specifies harmonic limits.
For PCC > 33KV, to determine the distortion of the local network, system impedances data is used to construct a computer model, to show the effect of consumers’ network with local supply network.
Main features of electric traction
Traction load is nonlinear and prominent source of generation of odd current harmonics (16-20% THD).
Wide variation of load in short duration leading to voltage flickers and fluctuations (swell and sags in power quality terminology) and also resulting into poor voltage regulation.
Load is inductive resulting in poor power factor in the range of 0.7 to 0.8.
Essential nature, high level of reliability with minimum interruptions is desirable.
Statutory requirements for IR.
Indian Electricity act 2003 section 79 (i) Para (h) and (i) specifies obligation for transmission and distribution licensees to enforce the standards w.r.t. Quality, Continuity, and Reliability as mentioned in grid codes issued by regulatory commissions.
Bureau of energy efficiency constituted vide Energy conservation act 2001in its thrust area No.2 specifically mentions about demand side management.
Railways is mentioned at sr.no.10 of list of energy intensive industries.
Voltage unbalance
Railways take different phase to phase voltage in consecutive TSS to limit imbalance at PCC
Various regulatory commissions have fixed voltage unbalance limit for transmission licensee to 3% only
In European countries it is generally fixed at 1-2%
To maintain this limit transmission licensees may enforce Railways to deploy unbalance correction equipments by taking 3- phase supply at a nominated TSS.