Did You Know

Advantages of VVVF Drive

SOME OF THE ADVANTAGES OF STEPLESS SPEED CONTROL USING VVVF DRIVES ARE AS LISTED BELOW.

Ø ALL MOTIONS CAN BE OPERATED FROM 10% TO 100% OF THE SPEED.

Ø ALL MOTOR PROTECTIONS ARE PROVIDED IN THE DRIVE.SOME OF THE PROTECTIONS ARE AS LISTED BELOW.

§ OVER LOAD OR OVER CURRENT PROTECTION

§ SINGLE PHASING PROTECTION.(CURRENT SENSING)

§ OVER TORQUE PROTECTION

§ PHASE SEQUENCE PROTECTION.

Ø MINIMIZED LOAD SWING.

Ø EXCELLENT LOAD HANDLING CAPABILITIES.

Ø NO CRANE SKEW.

Ø OPTIMISED LOAD CURRENT DEPENDING ON THE LOAD BEING HANDLED.

Ø SOFT START AND SOFT STOP REDUCING STRESSES ON CRANE MECHANICALS, MOTORS AND BRAKES.

Ø ENHANCED MECH BRAKE LIFE AS IT IS ONLY USED TO HOLD THE LOAD, STOPPING IS DONE ELECTRICALLY.

Ø ALMOST UNITY POWER FACTOR.

11.09.17

motor pole and torque

motor poles and torque

it is well known that motor horse power is

hp = TxRPM/5250

where T stands for torque and RPM is the motor RPM

So this means that for a given hp, lesser is the RPM more will be the torque. i.e which means that 6 pole motor shall have more torque compared to a 4 pole motor of the same horse power.

so then why do we use 4 pole motors instead of 6 pole motors?

07.09.17

motor rpm and poles

The synchronous speed for an electric induction motor is determined by the power supply frequency and the number of poles in the motor winding and can be expressed as:

n = f (2 / p) 60 (1)

where

n = shaft rotation speed (rev/min, rpm)

f = frequency (Hz, cycles/sec, 1/s)

p = number of poles

Example - Speed of Electric Motor with Two Poles

A motor with two poles is supplied with power with frequency 50 Hz (1/s). The rotation speed can be calculated as

n = (50 1/s) (2 / 2) (60 s/min)

= 3000 rpm (1/min)

06.09.17

Hoist control panel mountings

What are the different types of control panel mountings for a hoist ?

there are 2 places where a control panel for a hoist can be mounted

1) on the Hoist itself -- better known as Hoist mounted panel

2) Near the operating floor level - also known as Wall mounted control panel, structure mounted control panel

Hoist mounted control panel is more common compared to the other option. It is much cheaper because then only 4 core cable/shrouded bus bar is required for the power supply to the hoist control panel.

Wall mounted control panel is expensive in a way that all the power and control cabled then need to travel from the control to the hoist, hence the ultimate cost of the DSL increases not only by cables but also by the DSL trolley size.

in this case shrouded bus bar cannot be used, as the no of cores increases and in shrouded bus bar only 4 cores/lengths are there.

normally when wall mounted type control panel is used the DSL is mounted on the same beam as that of the hoist.

NTPC normally opts for this type of control panel mounting.

advantages of wall mounted type control panel :

1) the advantages of wall mounted type control panel is that of maintenance, any issue on the panel can be easily resolved by standing at the floor level itself, one does not need to climb up to the hoist for maintenance of the panels.

2) In case the dusty/heat environment one would require the panel to be not subjected to adverse conditions hence this type of arrangement is chosen.

Disadvantages of Wall mounted type control panel :

1) Expensive

2) No of cables increases

3) in case of curved path with wall mounted type control panel , the travel of DSL becomes more cumbersome.

Care :

While calculating the DSL cost, the cables length should be 1.25x travel length + height from monorail beam till operating floor level.

While costing care should be taken that the prices of the cables is taken upto the operating floor level and not the entire lift of the hoist.

05.09.17

What is True Vertical Lift

What is True Vertical Lift ?

True Vertical Lift is when weight carried moves in true vertical center line. i.e the weight carried does not move laterally. i.e it does not change the position when at the top or when at the bottom in the horizontal plane.

Pros:

a) The weight handled always maintains the center line and hence usefull in case where the load is being moved in shafts ;applications like gates

b) The Load is evenly distributed on both the ends/ on the wheels

c) The runway beam/structures sizes can be reduced

Cons

a) the crane/hoist with the true vertical lift is expensive than the single reeving arrangement equipment.

b) the gearbox reduction is double in case case true vertical lift and the toruqe requirement is also double

How to Achieve true vertical lift:

True vertical lift is achieved by having wire rope drums grooved both left hand and right hand. The wire rope ends are anchored to both the ends of the drum and hence there are 2 leads of the wire rope which are coming out of the drum.

Figure attached shows the 2/4 fall reeving arrangement true vertical lift example.

In single reeving arrangement the grooving on the drum is either left or right hand. The wire rope is wound on the drum and there is only one lead of the wire which comes out of the drum.

04.09.17

IP (Ingress Protection)

Ingress Protection (IP) and what it means

The IP Code (Ingress Protection Rating) consists of the letters IP followed by two digits and an optional letter. As defined in international standard IEC 60529, it classifies the degrees of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water in electrical enclosures.

First Digit: Solids

The first digit indicates the level of protection that the enclosure provides against access to hazardous parts (e.g., electrical conductors, moving parts) and the ingress of solid foreign objects.

Second Digit: Liquids

Protection of the equipment inside the enclosure against harmful ingress of water.

Reva Beam Rotator

Introducing Reva Beam Rotator. Use: 1) The long girders, beams or other assymetric peices can be lifted and rotated. 2) Suitable for welding lines. or individual welding on long beams. 3) Avoids use of overhead cranes, there by increasing overall efficiency of the plant 4) Allows welder to quickly and securely turn the work piece. 5) Height adjustment of the work piece according to workers desire/comfort. Specifications: 1) available from 2T till 30T 2) Length can be adjusted by keeping the two separate coloumns near or apart. 3) rotation speed customizable recommended 3 rpm

30.08.17

EOT Cranes Nomenclature

29.08.17

Difference between Chain Hoist and Wire Rope Hoist

Electric Chain Hoist and Electric Wire Rope hoist are both electrically powered used for lifting and transferring material.

Difference lies in the mechanism used for lifting, Chain Hoists as the name suggests uses chains as lifting medium, whereas Wire rope hoists uses wire rope as the medium for lifting.

The wire ropes are wound on the Drum and only single layer of wire rope is allowed to be wrapped on the drum, whereas in chain hoist, the chain is deposited in a container.

Also the diameter of the sprocket is very less compared to that of wire rope drum, because the chain can bend much more than that of the wire rope, hence minimum drum diameter is recommended based on the wire rope dia in the standards.

The above two difference makes the wire rope hoist much more expensive than chain hoist.

chain hoist's are also compact and occupy less space compared to electric wire rope hoists.

However while working wire rope hoists are considered more rugged, since chain if breaks will break in one go, whereas wire rope if break will break strand by strand.

Also chain hoists are suitable only for capacities upto 5t, above which electric wire rope hoists are only preferred,

so inference:

Chain hoists are cheaper than electric wire rope hoists but electric wire rope hoists are much more rugged and versatile in comparisions

28.08.17

HOW TO SELECT CLASS OF DUTY OF HOIST

Hoists are designed for min 20 yrs operation considering that hoist will work 250days per year for class1, 300 days per yr for cl2 and 333 days per yr for class3 &4.

Also per day working is defined in IS3938 table 1. Which states for class 2 will run 1.5hrs per day. Cl3 will work 3 hrs per day and cls4 will work over 6 hrs per day.

Total working hrs of a hoist based on class is also defined in IS3938.

26.08.17

values of headroom of hoist

The above pic shows headroom we can achieve in straight path, curved path and low head room hoists.

Tip: Using the sub-page listing gadget

What is headroom of a hoist?

Head room of hoist is distance from the beam (on which the hoist is hanged) bottom to the saddle of the bottom block hook!

24.08.17