IEEE 1627-2019 pdf free download – IEEE Standard for Transient Overvoltage Protection of DC Electrification Systems by Application of DC Surge Arresters.
5. Surge environment- DC transit electrifcation system Using an OCS as an example, it is evident from de ectrification systems that there are two paths for the surges to impact substution equipment: one from the OCS side and the other fom the incoming ac primary power supply system. The expected upper limit of the surge without the de surge arester that could propagate through the ocS will be equal to the dry fushover value of the oCS, which is typically 35 kV peak for 750-V de systems (Paul, 2004 [B18]). Incoming ac primary voltage to TPSS8 is genenally medium-volage (MV)and design practie is to apply properly rated ac surge aresteres on the primary side of the retifier tansformer. This will reduce the surge voltage magnitude on the sccondary side of the rectfer transformer, and then application of capacitors in prallel with diodes leaves al remote possibility of lightning surge getting into the dc switchgear. impedance.
The intensity of the incoming surge will be rlated to distribution system parameters and the magnitude of the incoming sunge and system impedance parameters. Intermal switching surges and surges at the OCS will be related to any of the system operational causes listed in4.1.2.
Due to the proximity of the oCS positive wire, and the running rails or negative wire in case of an elecrie trolley bus (ETB) systems, there are equal chances that the lighting may strike both positive and negative wires simultaneously Any surge voltage striking the OCS wire is free to propagate towurd the de switchgear, as well as to the vehicle via the current ollector. The associated surge current will divide according to the surge impedance paths and will experience some attenuation before reaching the equipment if there are n加o surge aresters between the strike location and equipment.
A discussion of surge environment is provided here for the OCS; however, similar discussion applies to other de transit etficatin systems. For de applications, the same nonlinear resistors that are used in ac surge arrester assemblies are used in the de arster housing but tested difrentnlr The busic requirements of a de surge arester include the fllowing,
a) At highest working volage, the device shall be esetially non-conducting with a minimal leakage curent. Surge current conduction only occurs when transient voltage becomes higher than sunge anester MCOV rating.
b) At overvoltuge moderately above the working voluge, the device while conducting shall permit only small increases in its own terminal voltage.
c) A device shall have suficient energy absorption capability to handle the stored enengy in the de system.
d) Upon suppressing the system transient overvolage, the device shall quickly iteterupt the normal de volage fllowcurrent.
e) A device shall be suitable for outdoor and indoor application and subjected to harsh atmospherie conditions without degnudation in performance. Outdoor arresters shall be tested for pollution to assure the surge arester housing does not show signs of tracking across the arester assembly due to pollution and contamination of metallic dlust in the traosit track areas.
f) The residua voltage at the OCS at maximum expected surge curent mugnitude shall be less than the damaging volage of the equipment to be protected. Residual voltage is ffected by the lead length’s inductance and rate-of-rise of sunge current.IEEE 1627 pdf download.