Crane Duty Motors

APPLICATION :

Prabal series 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 equipments, and cranes of all types. These motors can serve as auxiliary motors in rolling mills or wherever intermittent duty 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 torquelrotor inertia ratio.

TYPICAL APPLICATIONS :

Crane duty motors are used for following applications in majority: Cranes & hoists: long travel drive, cross travel drive, main hoist, auxiliary hoist. Material handling equipments: various conveyors Lifts Rolling mills

RANGE :

Manufacturing range for cast iron slip ring crane duty motors is from 112 to 400 frame. The same for squirrel cage motors in cast iron enclosure is from 80-400 & in aluminium enclosure is from 63-160.

MOUNTING :

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

POWER SUPPLY :

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 50 Hz or 60 Hz. The rotor voltage is committed for stator supply of 415 V, 50 HZ.For other supply conditions, Rv to be confirmed from CG.

AMBIENT TEMPERATURE :

The motors are rated at 45°C ambient temperature. For temperatures, other than 45°C, a deration factor has to be applied as indicated below.

ALTITUDE

The motors are suitable for altitude upto 1000 m above mean sea level. For altitudes more than this, deration factor shall be as per below

STANDARD OPERATING CONDITIONS

Power supply : 415 volts, 3 phase, 50 Hz
Voltage variation : ± 10%
Frequency variation : ± 10% (absolute sum)
Ambient temperature : 45°C
Altitude : upto 1000m.

STANDARD SPECIFICATIONS
PERFORMANCE AND FIXING DIMENSIONS

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:60034-1

IS: 807

Motors with following steel plant specifications also can be

supplied on request:

IPSS: 1-03-003 IPSS:1-03-004

For detail dimensions, please refer drawings on page 31-37 in this publication.

CONSTRUCTIONAL FEATURES: (MECHANICAL)
STATOR FRAME AND ENDSHIELDS

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.

STATOR AND ROTOR CORES

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.

ENCLOSURE AND COOLING

Standard crane duty motors have IP55 degree of protection as per IS:4691. IP 56 & 66 can be provided on request. The cooling code of motor is IC 411 as per IS:6362.

SHAFTS AND BEARINGS

The shaft is of high grade steel and of appropriate diameter to withstand the bending and torsional stresses. All shafts are ultrasonically tested for any minor flaw in the material. Shafts are machined to extreme fine limits to ensure fit and interchangeability of bearings. The motors are provided with single shaft extension.

Special shafl extensions like:

1) change in diameter and length,

2) taper shaft, with threaded end, and with hexagonal nut and lock washer.

3) double shaft extensions, (cylindrical & taper) are available on request.

Motors are provided with deep groove ball bearings. They are mounted with extreme care in dust proof housing. (Refer bearing size table for details). Sealed bearings are provided for motors upto frame 225M. Grease lubricated bearings are used on frames 250 and above. The correct amount of grease is filled in the bearings during manufacturing. On line greasing facility is provided for 250 frame & above to facilitate greasing of bearings without dismantling the motor. For provision of insulated bearings, please refer to CG.

PRABAL 'E' SERIES MOTORS

PRABAL SERIES MOTORS:
(Bearing references for single shaft extension)

TERMINAL BOX

Terminal box is provided with IP55 degree of protection. The box can be turned through 3600 in steps of 900 to give cable entry from anyone of four positions. The terminal boxes are suitable for BS screwed conduit. However, fittings like double compression type cable glands are available on request.

Terminal box position can be provided as per table below:

SLiPRING AND BRUSH GEAR

All sliprings are made of cupro-nickel. The slip ring unit is having high insul~tion resistance ensuring minimum wear and breakdown. The brush holders are assembled as a complete unit which can be easily replaced. The slipring enclosure is dustproof & has a cover with accessibility for inspection. The slip rings are epoxy moulded / fabricated type as per requirement.

MOTOR GO. SQ.

For large no. of starts, it is necessary that the accelerating time of the system should be as small as possible. For this purpose, total inertia of the system (motor GO sq. + Load GO sq.) should be minimum. Motor GO sq. value and permissible load GO sq. are indicated in the tables.

INTERCHANGEABILITY AND SPARES

All Prabal series crane duty motors are built to standardised designs and all spare parts are interchangeable.

CONSTRUCTIONAL FEATURES (ELECTRICAL)

Class of Insulation:

Stator: Class F insulation with temperature rise limited to class B

Rotor: Class H insulation with temperature rise limited to class F

Prabal series crane duty motors with higher class for stator insulation (class H) can also be offered on request.

WINDINGS STATOR WINDINGS

Stator winding (and rotor winding in case of slipring motors) consists of enamelled copper wire impregnated with superior quality class F varnish which is rigid at all working temperatures. Stators in motors with frame 280 & above are manufactured with vacuum pressure impregnation process as a standard. All rotors irrespective of frame size are processed with vacuum pressure impregnation. This gives added electrical & mechanical strength to the winding for high number of starts. The varnish has a high insulation resistance and excellent resistance to moisture, saline atmosphere, acidic/ alkaline fumes, and also to oil and grease. The insulation gives complete reliability under all atmospheric conditions, including humid tropical climates. Stator and rotor wound packs are subjected to surge test before impregnation.

ROTOR WINDINGS

Stator winding (and rotor winding in case of slipring motors) consists of enamelled copper wire impregnated with superior quality class F varnish which is rigid at all working temperatures. Stators in motors with frame 280 & above are manufactured with vacuum pressure impregnation process as a standard. All rotors irrespective of frame size are processed with vacuum pressure impregnation. This gives added electrical & mechanical strength to the winding for high number of starts. The varnish has a high insulation resistance and excellent resistance to moisture, saline atmosphere, acidic/ alkaline fumes, and also to oil and grease. The insulation gives complete reliability under all atmospheric conditions, including humid tropical climates. Stator and rotor wound packs are subjected to surge test before impregnation.

1. Wound rotor

Rotors of slip ring motors are wound and impregnated similar to stator windings. In addition, rotor windings are braced with resiglass banding. This gives protection against centrifugal forces experienced by overhang during overs peed and frequent reversals. Gelcoat is provided on the winding overhang for better consolidation and protection from vibration. Strip wound rotors are provided on frames 355 and above.

2. Cage rotor

Rotors are of pressure diecast aluminium upto 355 frame. They are designed for high starting torque, suitable for high number of starts. Cooling fins cast integrally with the rotor cage, improve the cooling action within the motor. All rotors (cage and wound) are dynamically balanced to comply with the requirements of IS: 12075

TERMINAL ARRANGEMENT

The terminals are mounted on a moulded base and are enclosed in a box having an inspection cover. In case of slip ring motors, three terminals for stator and three terminals for rotor are terminated in terminal box with adequate creepage and clearance. The rotor terminals are in the same box as those of the stator. Separate terminal box for rotor terminals is provided for NDW355LX & NDW400LX frames. This simplifies wiring and maintenance.

EARTHING

One earthing terminal is provided in the terminal box and two terminals on mounting feet.

ACCESSORIES:

Crane duty motors can be provided with various accessories as per table below:

Space heating for anti condensation:

Space heaters are used for avoiding accumulation of moisture/water in humid atmospheres. In motors upto 200 frame size, motor windings can be heated up to keep winding temperature above ambient by 5 to 10 degrees, by giving low supply voltage upto 10% of rated voltage. Supply voltage is to be adjusted by keeping 20-25% rated current. Thermal protection: Stator windings can be provided with PTC thermisters for alarm/trip or PT 100 type resistance temperature detectors according to the accessories table provided. Bearings can be provided with PT100 type resistance temperature detectors as per enclosed table 6.

ROTOR VOLTAGE

The rotor voltage of the motor is kept such that the insulation of the rotor and of the associated switchgear is not unduly stressed during rapid plugging when rotor voltage can rise to 2 to 3 times the rated value. Rotor voltage for slip ring motors is as per performance tables enclosed. Special rotor voltage can be offered for wire wound rotors with confirmation from CG.

PULL OUT TORQUE

The pull out torque value at rated voltage is indicated in the respective tables. Since available torque varies as the square of the supply voltage at motor terminals, an allowance for voltage drop in long cables, live rails and collectors must be considered. These voltage drops are significant when motor is operated at pull out point, since current at this point is much higher than the rated current. Pull out torque is maximum for 300 starts/hour class. This high pullout torque ensures rapid acceleration irrespective of drop in effective torque due to stepped rotor resistance. However, care to be taken that gears and other drive transmission equipments can withstand this peak torque.

OVERLOAD CAPACITY

The motors can withstand 1.5 times the rated current for 2 minutes without suffering damage. This feature makes the motor suitable for severe duties experienced on the crane or similar applications.

LIFE OF THE MOTOR

Crompton Greaves crane duty motors are designed and manufactured with carefully selected and tested insulating materials to ensure long services. The life of the motor mostly depends upon the life of the insulating materials since bearings, brush gears, slip rings etc. can be replaced easily during normal maintenance.

MAXIMUM PERMISSIBLE OPERATING SPEED

All 4, 6, 8, and 10 pole motors are designed for withstanding an over speed of 2.5 times rated synchronous speed or 2000 rpm whichever is less.

VFD CRANE DUTY MOTORS ( Cast Iron)

Crane duty squirrel cage motors when used with inverter drives give better current control, speed control & improved operation. Current control is similar or better than slip ring motors & maintenance cost /efforts are less than equivalent slip ring motors. Current control of VFD driven motors is better than standard squirrel cage motors.

Prabal series Inverter duty motors are provided with special insulation system suitable to withstand voltage spikes when fed from inverters. The motors are provided with following features:

⇒ Vacuum pressure impregnation of stator winding, this gives less voids & stronger winding.

⇒ Strengthened insulation system for withstanding voltage stresses.

Standard features:

Base Voltage: 220 volts to 650 volts Base frequency: 50 or 60 Hz Insulation class: Class "F' or 'H' as required (temp rise limited to class B) CG make motors are suitable for the following IGBT drive output

⇒ High frequency in the range of 3kHZ - 6 kHZ. Voltage rise time> 0.1 sec.

⇒ Voltage spikes up to 1600V and rise time of 0.1 sec.

⇒ Voltage spikes up to 1600V and rise time of 0.1 sec.

⇒ THD < 3%

Mode of operation: Modes of operation of inverter driven motors are classified according to type of load & speed range. They are:

⇒ Variable torque

⇒ Constant torque

⇒ Constant power.

In case of cranes/hoists, the mode of operation is constant torque. The typical speed range is from 10% to 100% of synchronous speed. The speed during lowering cranes in unloaded conditions may be more. The limiting speed should not exceed 2.5 times of rated synchronous speed or 2000 rpm whichever is less.

The selection of frame size for various duty type & starts shall be as per table enclosed.

For higher cable length from drive to motor, use suitable dv/dt filters & a lower switching frequency.

Use of insulated bearing at non driving is recommended for frame size above 315 to reduce bearing failure due to shaft currents.

Use of thermisters for frames upto 250 & resistance temperature detectors for frame 280 & above is recommended.

Additional losses & temperature rise:

Harmonics of voltage & current in a cage induction motor supplied from a converter cause additional iron & winding losses in the stator & the rotor.

There is no simple method to calculate the additional losses & no general statement can be made about their value.

When the motor is tested with converter supply at rated load, base voltage & base frequency, the permissible temperature rise will be within the limits of the insulation system used. For example when a motor havinf class F insulation system is tested with sinusoidal supply at rated voltage , rated frequency & rated load, may have temperature rise within class B limits. However, when the same motor is tested with converter supply under same test conditions, the temperature rise will be within class F limits. It is assumed that, while testing with converter supply, the HVF factor of converter output supply, is maximum 3%.

Hence the outputs of crane duty inverter driven motors are as listed in the table on page 28-30.

GENERAL REQUIREMENT:

All additional general requirements like accessories, paint shade, insulation class, degree of protection, voltage and frequency variation shall be available at extra cost. The cost structure of extra features is same as that for standard motors.

DEFINITIONS

The terms used frequently in intermittent duly drive and hoisting are as bellow:

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.

INTERMITIENT DUTY TYPE RATINGS.

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 energized, (CDF)

iii) The number and type of cycle per hour, (duty class)

iv) and the inertia of the motor and the load.

CLASSIFICATION OF STARTING:

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.

Squirrel cage motors:

4 jogs or inchings 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 inchings or jerks = 1 start

1 plug bra~ng = 0.8 starts

1 plug reversal = 1.8 starts

DUTY TYPE :

Crane duty applications can be classified into duty types S2 to S10. The duty types are as per table 4 below:

The duty types S2 to S5 are explained in detail as per below:

Short time duty (duty type S2) :

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 2°C of the coolant. (See figure 1) The recommended values for the short time duty are 10, 30 and 90 minutes.

Intermittent periodic duty (duty type S3) :

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. (See Fig. 2) 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 inutes. The recommended values for the CDF are 15, 25, 40 and 60 percent.

Intermittent periodic duty with starting (duty type S4) :

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 too short to attain thermal equilibrium during one duty cycle. (See Figure 3) 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 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 at constant load, a period of rapid electric braking and rest and de-energised period. The operating cihd rest and de-energised periods being too short, to attain thermal equilibrium during one duty cycle. (See Fig. 4) 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.

Selection of motors for hoist motions:

For hoisting motor, the power required shall not be less than that computed from the following:

Where, derating factor will be taken as 12%,

Kw = one hour power rating for dc motors & power rating at (8 - 40%) cyclic duration factor for ac motors.

M = mass of rated load on hook plus weight of hook block & wire ropes in tones

V = specified hoisting speed in M/min

E = combined efficiency of gears & sheaves

= (0.93)n x (0.98)m for sleeve bearings

= (0.95)n x (0.99)m for antifriction bearings

= (0.985)n x (0.99)m for hardened profile ground & oil splashed lubricator, where

n = number of pairs of gears

m = total number rotating sheaves passed over by each part of the moving rope attached to the drum

Cv = service factor for vertical motion depending on type of motors,

= 0.67 for ac motors,

= 0.5 for dc motors

Cdf = duty factor

Camb = Derating factor for ambient temperature as per table 1.

For an ac hoist motor, the specified full load hoist speed must be obtained at not more than rated torque, therefore, the calculated full load kw must be multiplied by :

Where sufficient information is not available values given in table 9 below for duty cycles, cyclic duration factor & starting class corresponding to mechanism class shall be used. The values given are based on the following formula: