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This paper evaluates the maximum potential rise on the traction earth (TE) conductor caused by stray currents in the Taipei Rail Transit Systems (TRTS). The stray current from the TRTS will flow into the earth due to the voltage difference along the running rails caused by the traction currents returning to the substations. The potential rise of 0.1 V is admitted in international recommendations as the maximum acceptable value for corrosion protection of utilities outside a dc railway system. Since TRTS is one of the dc-traction rail transit systems, it may cause corrosion or other effects by stray currents to the existing underground metallic structures. As a result, the purpose of this paper is to evaluate whether the maximum potential rise on the TE conductor caused by stray currents from IRTS is greater than the maximum permissible value 0.1 V or not. [ABSTRACT FROM AUTHOR]

Taipei Metro adopted the diode-grounded scheme for stray current collection in construction of its cross rail network. During operation of the network, a high rail-to-earth potential (Vrail) has been observed at the east end of the Blue Line (i.e., stations BL13-BL16). To find effective countermeasures, a series of field tests in a step-by-step development nature was conducted from 1999-2000, which led to the decision of disconnecting the impedance bond at Gil of the tie line so that the negative return current of the Blue Line cannot flow to the rails of the Red-Green Line, and vice versa (detailed in Sections 111-A and V-C). This decision was implemented through contract-out work in 2003. Since then, the Vrail has been lowered by almost half before disconnection. To gain the insight characteristic before the contract-out, numerical simulations were also conducted by simulating the multi-train and multisection features of the cross transportation network. The simulation results (for Vrail and stray current, or Istray) were consistent with the field-test results. This paper presents the design of these field tests and their test results in comparison with the simulation results, based on which the countermeasures for reducing Vrail and the present status after Vrail reduction at Taipei Metro are presented. [ABSTRACT FROM AUTHOR]

This paper presents a practical case for safety assessment of bulk supply substations (BSS) and traction supply substations (TSS) in Taipei Rail Transit Systems (TRTS). For a substation grounding system to be safe, the maximum touch-and-step voltages should not exceed postulated safety criteria. The safety criterion in IEEE Standard 80 is defined in terms of permissible body current. The permissible body current is then translated into the permissible touch-and-step voltages. Since the mesh voltage is usually the worst possible touch voltage inside the substation (excluding transferred potentials), the mesh voltage is used as the safety criteria. In other words, safety assessment of an ac substation grounding system in TRTS is referred to a procedure by which the mesh and step voltages are computed and compared to the maximum permissible (safe) touch-and-step voltages. Computation results for the orange line at 019 station are presented. [ABSTRACT FROM AUTHOR]