EN 50526-1 Railway Applications - Fixed Installations - DC Surge Arresters and Voltage Limiting Devices - Part 1: Surge Arresters

The European standard “ EN 50526-1 Railway applications - Fixed installations - DC surge arresters and voltage limiting devices - Part 1: Surge arresters” describes a procedure for spark-free, nonlinear metal oxide resistor type surge arresters designed to limit voltage fluctuations in DC systems with a nominal voltage of up to 3 kV.

For the purposes of this standard, the following terms and definitions apply:

• Nominal voltage refers to the specified value for a system.
• Maximum residual voltage refers to the maximum value of voltage that is likely to exist for an indefinite period of time.
• Maximum non-permanent voltage refers to the maximum value of voltage that is likely to exist for a limited period of time.
• Nominal insulation voltage refers to the direct current (DC) withstand voltage value assigned to the equipment or part of it by the manufacturer and characterizing the stated permanent (longer than five minutes) withstand capacity of its insulation.
• Nominal impulse withstand voltage refers to the impulse voltage value assigned to the equipment or a part of it by the manufacturer, characterizing the stated ability of its insulation to withstand transient overvoltages.
• Overvoltage refers to the voltage with a peak value exceeding the corresponding peak value of the highest non-permanent voltage.
• Transient overvoltage refers to the short-term overvoltage associated with the transient regime, with a duration of a few milliseconds (up to 20 ms) or less. Two special transient overvoltages are defined: switching overvoltage and lightning overvoltage.
• Switching overvoltage refers to the transient overvoltage at any point in the system due to a particular switching operation or fault.
• Lightning overvoltage refers to the temporary overvoltage at any point in the system due to lightning discharge.
• Surge protector refers to the device designed to limit transient overvoltages to a specified level.

Surge arresters are a protective device used to limit the voltage on equipment by discharging or bypassing surge current. They prevent the current from continuing to earth. However, surge arresters do not absorb or stop lightning. Surge arresters divert lightning, limit the voltage, and protect equipment installed in parallel. Surge arresters have many applications, from protecting a home to a power distribution station. They are installed on circuit breakers inside a residence, inside substation transformers, in pole-mounted transformers, in pole-mounted riser poles, and in transformer substations.

Surge arresters are used to protect high voltage equipment such as transformer substations, circuit breakers and bushings against the effects of lightning and switching surges. Surge arresters are connected in close proximity and in parallel with the equipment to be protected. Their purpose is to direct the surge energy safely to ground and to ensure that the resulting voltage across the terminals remains low enough that the insulation of associated devices will not be damaged by the effects of overvoltages.

Surge arresters and lightning arresters are functionally different. Surge arresters protect the installation from the inside, while lightning arresters protect the equipment from the outside. Surge arresters protect the system from lightning, switching, electrical faults and other transient voltages and surges, while lightning arresters are mainly used for lightning strikes and associated surges.

Insulation coordination is defined as the selection of the dielectric strength of the equipment according to the different types of overvoltages that may occur in the system. Surge arresters provide an indispensable aid to economical insulation coordination in electric power systems. Surge arresters play their role in the system by keeping the voltage below the equipment withstand voltage (the highest voltage that can be applied to an element without damaging it) with an adequate margin of protection within this range.

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