Page 32 - contactors_motor_protection_for_rolling_stock_application

DOL and reversing starters protected by overload relays

With AF..B contactors - Open type version in kit form
Switching frequency diagrams

General
Overload relays cannot be operated at any arbitrary switching frequency in order to avoid tripping. Applications involving up to 15 operations per
hour are acceptable. Higher switching frequencies are permitted if the duty ratio and the motor starting time are allowed for and if the motor's
making current does not appreciably exceed 6 times the rated operating current. Please refer to the adjacent diagram for guideline values for the
2 permitted switching frequency.

Thermal overload relay
Intermittent periodic duty Example:
140
Switching frequency (ops/h) 120 t = 0.5 s Starting time of the motor: 1 second - Duty ratio: 40 % means a permitted
switching frequency of max. 60 operating cycles per hour.
100
a
80
60
a
a
40 t = 3 s t = 1 s
a
t = 1.5 s
20 t = 5 s
a
0
0 20 40 60 80 100
Duty ratio (%)
ta: motor starting time

1SBC100259S0201

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