Altivar 312 Variable Speed Drives Page 44 Accessories and Options

44 Altivar 312 variable speed drives Accessories & Options Braking resistors The resistor enables the Altivar 312 drive to operate while braking to a standstill or during slowdown braking, by dissipating the braking energy. Two types of resistor are available: Enclosed model (IP 20 casing) designed to comply with the EMC standard and protected by a temperature-controlled switch or thermal overload relay. This model enables maximum transient braking torque. The resistors are designed to be mounted on the outside of the enclosure, but should not inhibit natural cooling. Air inlets and outlets must not be obstructed in any way. The air must be free of dust, corrosive gas and condensation. Non-protected model (IP 00) for lower power ratings only. For machines with high inertia, driving loads, and machines with fast cycles. Specifications Type of braking resistor VW3A7723 to VW3A7725 VW3A7701 to VW3A7705 Ambient air temperature around the device OperationF 140 F (40 C) 32 F to 122 F (0 C to 50 C) StorageF -13 F to 158 F (-25 C to +70 C) Degree of protection of the casing IP 00 IP 20 Thermal protection None Via temperature-controlled switch or via the drive Temperature controlled switch (1) Tripping temperatureF - 120 Max. voltage - max. current - 250 V a - 1 A Min. voltage - min. current - 24 V c - 0.1 A Maximum switch resistance m W 60 m W Operating factor for the dynamic brake transistors The average power that can be dissipated at 104 F (40 C) from the resistor into the casing is determined for a load factor during braking that corresponds to most common applications. The dynamic brake transistor is sized so that it can tolerate: The nominal motor power continuously 150% of the nominal motor power for 60 s (1) The switch must be connected in the sequence (use for signalling or in line contactor control). Load factor and determining the nominal power The average power that can be dissipated at 40C from the resistor into the casing is determined for a load factor during braking that corresponds to most common applications. This load factor is defined in the table above. For a specific application (example: handling), the nominal power of the resistor must be redefined incorporating the new load factor. Use chart 1 to determine coefficient K1 corresponding to a braking torque of 0.6 Tn and a load factor of 20%: K1 = 0.06 Chart 1 Graph of the average power as a function of the braking torque for a load factor Example: Motor power Pm = 4 kW Motor efficiency h = 0.85 Braking torque Tb = 0.6 Tn Braking time t = 10 s Cycle time T = 50 s Load factor fm = = 20% Chart 2 Permissible resistor overload as a function of time (characteristic curve) Use chart 2 to determine coefficient K2 corresponding to a braking time of 10 seconds. K2 = 7 The nominal power of the resistor (Pn) must be greater than: t T -- - Pn Pm K1 (1 1 K2 fm ---------------------) 4. = + 10 3 0,06 0,8 (1 1 7 0,2 -----------------) 350 W = + = 0 T t Speed Time Load factor: t: braking time in s T: cycle time in s t T -- - 0,1 0,01 0,001 0,1 0,06 1 0,6 0,5 1 1,5 K1 2% 20% 40% 60% 10% 5% Tb/Tn 0 10 1 100 1000 2 4 6 8 10 12 14 16 18 20 t (s) 7 K2 t T -- -

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