EN 50388-2012 pdf download.Railway Applications -Power supply and rolling stock -Technical criteria for the coordination between power supply (substation) and rolling stock to achieve interoperability.
A large disturbance of the supply voltage is caused If the total impedance I admittance of power supply and existing vehicles have a negative real part and zero imaginary part at the feeding point for one specific frequency, called resonance frequency. This condition is sufficient from mathematical point of view. The imaginary part of the impedance can be created by the global power supply alone or by the resulting inductance of the supply line and substation transformer and the corresponding input capacitance of a four- quadrant converter vehicle with primary input filter, respectively. Important for the correct prediction of whether or not a complete system is unstable is the knowledge of the correct total damping factor at resonance frequency. The damping factor is negative at an instability. In principle, simultaneous oscillations at several frequencies could be possible.
C.2 Overvoltages caused by system instability
C.2.1 Compatibility criteria
Considering the traction unit as a single electrical entity (boundaries are pantograph(s) — wheels), the most suitable way is to formulate restrictions on the input admittance of the vehicle, including the effect of all controllers inside the vehicle. This can be done either by defining allowed regions for magnitude and phase, or better for real and imaginary part, the real part directly defining the damping and/or excitation contribution. This reflects that there are no instability sources but that instability is always a question of transfer behaviour. Requirements for low frequencies, where non-linear effects play an important role, will lead to additional requirements. Knowledge about these effects is still limited,
Defining requirements for the vehicle requires, as described above, that the internal stability criteria for the whole power supply system have to be defined first, and have been broken down correctly to the one-vehicle interface.
To avoid resonance instability, for frequencies greater than a given value (to be defined by the Infrastructure
Manager), the vehicle must be passive, i.e.: Re(Y(f))> 0. with a phase value of Y(f) in the range between –
90 and + 91Y.
C.2.2 Measurement and validation
On a one-vehicle level, tests can be clone by simulation, tests in the lab and on test tracks. Measurement of the vehicle input admittance versus frequency requires a power supply where a test voltage of a variable higher frequency can be superimposed on the fundamental supply voltage. In general this is practicable by means of different possible installations and has already been done before. The measurement of a nonlinear behaviour could be more difficult since it normally depends on the operation point of a vehicle.
Compatibility tests between one vehicle and the power supply can mainly show whether stability is maintained or not. Instabilities can be detected either by protective shutdowns or observation of unwanted oscillations. It is difficult to measure the distance towards the stability margin. Damping of transients can give an approximate figure for this.
C.3 Overvoltages caused by harmonics
C.3.1 Compatibility criteria
In principle the same is valid as for stability: since all power supply networks have both an input and a transfer behaviour, all network internal issues (such as amplification of harmonics between different locations in the network) have to be solved first.
For the compatibility check the manufacturer of rolling stock should get the following information from the infrastructure manager
Internal harmonic voltage source of the power supply. This includes the harmonics generated by the power supply itself (substations) as well as those generated by other vehicles. This can be done by definition of typically expected and maximum allowed voltage spectra at the pantograph of the vehicle;
Admittance versus frequency of the power supply, seen at the vehicle’s position. The admittance is provided for relevant conditions of the power supply network (including existing vehides). A link to the voltage spectrum source information has to be made (e.g. a certain source spectrum with high harmonic content could be relevant only In combination with a weak network admittance).
Traditionally the vehicle should not exceed certain limits of harmonic current versus frequency (harmonic envelope). The harmonic envelope is normally defined with respect to signalling equipment, a similar approach is possible with limitation of overvoltages. The more restrictive harmonic envelope should be applied.
C.3.2 Measurement and validation questions
Measurement of harmonic currents and voltages is state of the art. Simultaneous measurements at different locations allow some conclusions to be made. Also the transfer behaviour of the power supply network and the plausibility of the requirements put on the new vehicle can be quantified.
C.4 Examples
C.4.1 General
This section shows examples of voltage (and current) waveforms from experienced phenomena causing overvoltages. The phenomena are classified according to the description in the text in this annex and in Clause 10.
C.4.2 Overvoltages caused by system instability
a) Electrical resonance instability.EN 50388-2012 pdf download.