Page 7 - Industrial Technology EXTRA 20th July 2020

elevator doesn’t descend too quickly and cause Railway braking resistors operate in the same
harm. way as those on elevators. However, electrified
While a DBR may seem like a standard piece of railways also benefit from regenerative braking,
elevator equipment, its design demands a number where the power produced during braking is either
of variables in order to keep the lift safe and immediately reused by other locomotives or is stored
functioning. Key considerations include calculating for later use. This method is particularly beneficial
the energy per stop, the duty cycle and the ohmic for intensively used underground rail services, as the
value. Once these factors have been determined, generated power can be immediately fed back into
the resistor manufacturer can determine the the next approaching train.
required DBR peak and average power in order to Crowbar resistors, such as those supplied by
produce the right DBR for the job. Cressall, are another resistor type commonly found
track side. These resistors are used in traction
All aboard power supply circuits to deal with the effects of
Stopping a train also requires the dissipation of a transient or longer lasting over-voltage conditions. A
vast amount of energy. Conventional disc brakes soft crowbar pulses to dissipate transient over-
alone suffer a lot of wear, so dynamic braking is voltages, then if these persist or worsen the main
often used as an additional braking system to breakers are opened and the system is short
absorb the high amounts of energy generated by circuited using a hard crowbar to absorb the stored
stopping electric trains. energy.

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