1. Conservative braking in winding drums.
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2. Brakes in winding drum can be of following types:
Friction Brakes.
Non-friction Brakes.

3. Friction Brakes:

4. Friction Brakes:

5. Friction Brakes:

6. Disadvantages of friction brakes:
Uses non-conservative forces to stop drum. Hence power is less efficiently utilized.
High heat generation. Hence requires high maintenance.

7. Non-Friction brakes:
Are the brakes, which use conservative forces to stop the drum.
Most of the kinetic energy is restored, so as to utilize it further at the time of acceleration.
The heat loss is comparably less.
Less prone to failure.

8. Types of non-friction brakes:
Mechanical
Air compressor brakes.
Vacuum brakes.
Electrical brakes.

9. Air compressor brakes:
As the off-centre drive shaft rotates, so does the vane housing, and the vanes slide in and out to maintain the contact with wall. Gas enters at largest opening and leaves at smallest opening.
From: dated 12th Aug, 2011.

10. Working of air compressor:

14. Advantages of Air compressor brakes:
Less heat loss in friction.
The heat generated in compression could also be used, as the heat is in the form of compressed air.
Less maintenance is required, as compared to friction brakes.

15. Non-friction vacuum brakes:

16. Advantages of non-friction vacuum brakes:
Doesn’t involve friction, so less loss of energy.
No compression occurs, hence no heat is generated.
The power could be efficiently used for regeneration of rotation in winding drums.
These brakes could be economically used.
These brakes require almost no maintenance.

17. Non-friction electrical brakes:
These are the counter current braking system, this is done by reversing the electric supply to the stator.
The amount of braking, in case of dc motors, could be controlled by installment of dc transformer.
In case of ac motors, braking is done by making a phase difference of 180, in the input current.

18. Disadvantages of electrical brakes:
It involves high line current, and cables to carry high line current has to be provided.
Just after the braking is done, high back emf is produced, leading to severe heat loss.
The voltage between the rotor and stator is doubled and the insulation of both should be adequate to prevent breakdown.

19. Conclusion:
It may be inferred that, the mechanical system of non-friction brakes are efficient and economical as compared to conventional system of friction brakes. Thus this system of braking could be known as conservative braking.

20. Reference:
Deshmukh D.J., Elements of Mining Technology, Vol III.