tefc3

Variable	Symbol	Unit
Locked rotor current (Starting Current) Rated current No-load current	I_DI_N I_O	A
Locked rotor torque (Starting torque) Pull up torque Pull out torque Rated torque	M_D M_A M_M M_N	Nm
Rated speed Synchronous speed	N_N N_S	min^-1

Above classified torques are usually expressed as % of rated torque. ( M_N )
Full load torque is usually expressed in Kgm and can be calculated from the formula

Full Load Torque ( Rated Torque ) Kgm	=	Rated KW x 974
		-----------------------------
		Rated speed in RPM

Full load torque in Nm

Rated Torque in Kgm x 9.80665

Accelerating time of motor is derived by a formula

t_d	=	¶	N x Jn	Ma	=	M_D + 2M_A + 2M_M+ M_N	_	M_R
		---	-------			---------------------------------
		30	Ma			6

Where

Where M_R = Average Load Torque

t_d =   Starting time in seconds
N    =   Speed to be achieved
Jn   =   Moment of inertia in Kgm²
Ma =   Average torque developed by the Shaft
¶    =   3.142

From the above it is imperative that the starting time will be less if average torque developed by motor is more. Average torque developed will be more because of higher locked rotor and pull out torque.

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The Indian Electric Co.,Bharat Bhavan,
1360 Shukrawar Peth, Natu Baug,
Pune - 411 002 (India)
Phone No. : 020-4474303, 020-4473038
Fax No.: 020-4473037, 020-4470807
e-mail : iec@giaspn01.vsnl.net.in