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Crane Duty Motors

   Crane Duty Motors

Crompton Greaves squirrel cage! slip ring crane duty motors are specially designed for service on cranes and hoists. They can also be used for similar applications such as material handling, weirs and sluices, and lifts of all types. These motors can serve as auxiliary motors in rolling mills or wherever intermittent drives are required.
These are duty type rated motors developing high starting torque with low starting current. The motors are suitable for frequent starts/stops and reversals. Also rapid acceleration is achieved by high pull out torque/rotor inertia ratio.

Tables on page nos. 6 to 18 indicate the frame v/s output relationship for slip ring crane duty motors. Tables on page nos. 19 to 27 indicate the frame v/s output relationship for squirrel cage crane duty motors.


Squirrel cage crane duty motors are supplied with horizontal foot-mounting. However, motors suitable for vertical foot / flange / face-mounting or any combination of these can be offered when required. Slip ring motors are normally available with foot mounting. Flange mounting can be supplied on specific request.

Crane duty motors are suitable for 3 phase supply and can be wound for any single voltage from 220 to 650 volts and frequencies from 40 hz to 60 hz.

The motors are rated at 400C ambient temperature. For temperatures other than 400C, a duration factor has to be applied as indicated below.

Power supply: 415 volts, 3 phase, 50z
Voltage variation: + 10%
Frequency variation: + 5%
Combined voltage and frequency variation: + 10 %(absolute sum) .
Ambient temperature: 400 C
Altitude: upto 1000 m

The motors are manufactured with standard metric frame sizes, and they comply with the following standards (latest versions).
IS: 325 IS :4722      IS : 1231 IS :2223      IS :3177 IEC:34-1

The motors also comply with the following steel plant specifications..
IPSS 1-03-003 IPSS: 1-03-004 ,
For detail dimensions, refer drawings in this Publication.

The terms used frequently in intermittent duty drive and hoisting are as below:
1. Duty : Operation of the motor at load including no load and de-energised period to which the motor is subjected, including the sequence and duration.
2. Cyclic duration factor : (CDF) : The ratio between the period of loading including starting and electric braking and the duration of the duty-cycle expressed as percentage.
3. Starting : The process of energizing a motor to bring it upto rated speed from rest.
4. Jogging or inching : This is an incomplete start during which the motor does not attain more than 25% of the rated speed.
5. Electric braking : A system in which a braking action is applied to an electric motor by causing it to act as a generator.
6. D.C. Injection braking : A form of braking of an induction motor in which a separate dc supply is used to magnetise the motor.
7. Plug braking : A form of electric braking of an induction motor obtained by reversing the phase sequence of its any two lines.
8. Regenerative braking : A system of electric braking in which energy is returned to the supply system.

The basis of the ratings is that of thermal capability, taking into account,
i) frequency of starting (starting class).
ii) percentage of time during each operating cycle the motor is energised, (CDF),
iii) the number and type of cycle per hour, (duty class,)
iv) and the inertia of the motor and the load.

The starting classification for a motor indicates the maximum permissible number of starts per specified inertia, taking into account complete starting, jogging or inching and electric braking. Rating for the commonly used starting i.e. 6, 150 and 300 starts/hour class, are listed in this publication. However, following factors can be used to calculate output rating for different number of starts and CDFs.
Slarts/hour 40% CDF 60% CDF
600 0.7 0.67
500 0.8 0.74
400 0.9 0.80
300 1.0 listed
200 1.1 0.96
150 listed 1.0
100 1.21 1.05
50 1.28 1.1

When calculating for the duty, allowance should be made for inching and reverse current braking on the following basis:

Squirrel cage motors : 
4 jogs or inching or jerks = 1 start 1 plug braking = 3 starts          1 dc injection braking = 2 starts 1 plug reversal = 4 starts
Slip ring motors :
4 jogs or inching or jerks = 1 start 1 plug braking = 0.8 start        1 plug reversal = 1.8 starts


Crane duty applications can be classified into duty types S2 to S5

Short time duty (duty type 52) : Operation at constant load during a given time, less than that required to reach thermal equilibrium, followed by a rest and de-energised period of sufficient duration to re-establish machine temperatures within 2C of the coolant.
The recommended values for the short time duty are 10,30,60 and 90 minutes.

Intermittent periodic duty (duty type 53): A sequence of identical duty cycle, each including a period of operation at constant load and a rest and de-energised period. These periods being too short to attain thermal equilibrium during one duty cycle. In this duty type, the
starting current dose not significantly affect the temperature rise. Unless otherwise specified, the duration of the duty cycle is 10 minutes. The recommended values for the CDF are 15, 25,40 and 60 percent.

Intermittent periodic duty with starting (duty type 54): A sequence of identical duty cycles, each cycle including a significant period of starting, a period of operation at constant load and a rest and de-energised period. These periods being 100 short to attain thermal equilibrium during one duty cycle
In this duty, the stopping of the motor is obtained either by natural deceleration after disconnection of the supply or by means of braking such as a mechanical brake which does not cause additional heating of the windings.

Intermittent periodic duty with starting and braking (duty type S5) : A sequence of identical duty cycles, each cycle consisting of a period of starting, a period .of operation al constant load, a period of rapid electric braking and rest and de-energised period. The operating and rest and de-energised periods being too short, to attain thermal equilibrium during one duty cycle.

Note: In all above types of duties, the loading period and rest period of the cycle are so short that the steady state temperature is not reached. While working on these identical cycles continuously, the motor temperature rise must not exceed the permissible values for a given class of insulation.

Made of high quality cast iron conforming to IS : 210, ribbed externally to ensure maximum heat dissipation. All components are machined on CNC machines ensuring concentricity and correct alignment. The windings and working parts are completely enclosed and air is forced over the stator body by fan, mounted on the shaft and protected by a cowl. The feet are integrally cast with the body. This ensures sturdiness and resistance to vibrations.

Both the stator and rotor cores consist of low loss and high permeability steel stampings which are assembled under
pressure and rigidly secured by end plates.

Standard crane duty motors have IP55 degree of protection as per IS : 4691. The cooling code of motor is IC 411 as per IS : 6362.


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