Safety in Mines Research Advisory Committee Appendix D Measures to prevent overwinds A summary of by monkey6

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									Appendix D.
Measures to prevent overwinds
A summary of the findings and recommendations of the committee looking into measures to prevent overwinds is given below:

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Table D1

Summary of measures to prevent overwinds.

RECOMMENDATIONS

1
1.1

Conveyance
Damage to switch activation magnets by objects falling down shaft. Magnetic switch activators should be protected by ramps made of stout sections. Such ramps can be placed above the magnets.

Measures to prevent overwinds:
• 1.2 Protect magnets from damage. For man-riding cages, the cage should be suspended from the detaching hook by rope or chains of sufficient length to allow the cage to decelerate to rest under gravity without colliding with any beams above it. This would require longer jack-catch posts.

Attachments
Measures to prevent overwinds: • Insert flexible suspension element between hook and cage.

2 2.1

Shaft and headgear switches
Damage to switch by objects falling down shaft. Switches should be protected by ramps made of stout sections. Such ramps can be placed above switches to minimise the risk of damage due to falling objects. Use armour protected cables or other means such as running wires inside steel pipe or hydraulic hose.

Measures to prevent overwinds:

•
•

Protect switches from damage
Protect cables from damage

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RECOMMENDATIONS

3
3.1

Headgear
Overrun distance. Provide minimum of 7,5 m overrun distance from ultimate limit switch. No exemptions to above requirement. Move spectacle plate and jack-catches to a higher position where possible. Move ultimate limit switches to a lower position where these are higher than necessary.

Measures to prevent overwinds:
• • • • Provide minimum of 7,5 m overrun distance from ultimate limit switch. No exemptions to above requirement Move spectacle plate and jack-catches to a higher position where possible. Move ultimate limit switches to a lower position where these are higher than necessary.

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RECOMMENDATIONS

4
4.1

Brakes
Blockage in relief line. The brake design should be a fail safe duplicate system, utilising approved designs of valves, with oil filters and valve operation monitoring during normal winding cycle

Measures to prevent overwinds:
• • • • • 4.2 Fail safe design. Duplication of system. Correct valve selection (ball and seat not spool valve). Filtration of oil. Monitoring of valve operation during normal winding cycle.

Brake valve failure
As for 4.1 above.

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4.3

Error in set-up
Measures to prevent overwinds:
• • • Regular checking and testing. Work done by experienced competent persons trained on the specific winder. Checking and supervision of work performed by competent supervisor.

The brake system should be regularly checked and tested by experienced competent person trained on the specific winder. All work done on the braking systems should be supervised and checked by an experienced competent supervisor.

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4.4

Brake controller
Measures to prevent overwinds: • • • • • • • • Designed and set to stop conveyances safely. Note. Braking too fast is as dangerous as braking too slowly. Duplicate systems with separate inputs and cross checking. Fail safe design. Self-diagnostic systems. Regular static and dynamic testing and inspections by experienced competent persons. No work shall be done by other than competent persons and shall be overinspected by a competent supervisor. Brake lining excessive wear detection system should not cause a trip out but should provide an alarm and end of wind lock out. When the winder is tripped, controlled electrical retardation to low speed (creep speed) and then application of mechanical brakes should be used wherever possible.

The brake control system shall be designed to stop the winder safely under all conditions have a self-diagnostic system. The brake control system shall be a duplicate fail-safe system with cross checking and each system shall have separate independent input signals. Regular static and dynamic testing and inspections shall be carried out by experienced competent persons. No work shall be done by other than competent persons and shall be overinspected by a competent supervisor. Brake lining excessive wear detection system should not cause a trip out but should provide an alarm and end of wind lock out. When the winder is tripped, controlled electrical retardation to low speed (creep speed) and then application of mechanical brakes, should be used wherever possible.

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4.5

Brake safety circuits
Measures to prevent overwinds: • • • • Designed to operate in fail safe mode with duplicate safety contactors for each circuit. Reset circuit designed to prevent resetting if any one contactor has “welded” closed. Contactors shall be of selected for reliability eg “clapper” design. Multiple safety circuits where possible to be used for: a) Electrical retardation to slow (creep) speed and then application of brakes.

The brake safety circuits shall be designed to fail safe with multiple circuits where possible, each with duplicate contactors. The safety circuit reset circuit shall be designed to prevent reset if any one contactor has “welded” closed. Multiple safety circuits where possible to be used for: a) Electrical retardation to slow (creep) speed and then application of brakes.

b) Disconnection of electrical power to the motors and application of mechanical brakes. c) Lock out of winder at the end of wind when brakes are next applied to hold the winder.

b) Disconnection of electrical power to the motors and application of mechanical brakes. c) • Lock out of winder at the end of wind when brakes are next applied to hold the winder.

Regular testing and inspections shall be carried out by experienced competent persons.

Regular testing and inspections shall be carried out by experienced competent persons.

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5
5.1

Speed / distance protection
General Back up systems of different design, having different inputs, with cross checking to other systems and set to suit the type of winder control systemAccess is to the equipment is to be limited to authorised competent personnel (padlocked enclosures, passwords etc). The equipment and settings require regular inspection, testing and maintenance by experienced competent persons and the training of normal and relieving staff.

The committee recognised that this was the major means of preventing over and underwinds.
Measures to prevent overwinds: • • • • • • Back up systems of different design and having different inputs. Cross-checking of protection system to other systems. Set to suit the type of winder control system (eg An AC open loop winder speed increases when changing from power to dynamic braking). Access limited to authorised competent personnel (padlocked enclosures, passwords etc). Regular inspection, testing and maintenance by experienced competent persons. Training of normal and relieving staff.

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5.2

Mechanical speed / distance protection (Lilly type device)

The mechanical speed/ distance protection device (eg Lilly) must be correctly selected for the winder type. The drive shaft speed shall be correct for the device and broken shaft detection fitted where possible. An experienced competent person must correctly set the device.

Measures to prevent overwinds:
• • • • • 5.3 Correct selection of speed / distance protection device (eg duplex Lilly not suitable on low speed winders). Correct drive shaft speeds (eg Lilly designed for 90 rpm). Correctly set by an experienced competent person. Broken drive shaft detection system fitted where possible. Monitor acceleration relief system against sticking. A monitoring system to ensure that the acceleration relief device does not stick should be fitted.

Electro-mechanical speed / distance protection As 5.2 above.

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5.4

Electronic speed / distance protection Measures to prevent overwinds: • • • • • • • • Duplicate systems with cross checking. Fail safe design. Duplicate and separate inputs. Automatic synchronising to shaft switches at both top and bottom of shaft during each wind. Switching systems to automatically set-up the winder for false bank testing etc. Limited to slow speed after power outage until synchronising completed. Self-diagnostic systems. UPS systems.

The protection system should be of a fail-safe design and consist of duplicate systems with cross-checking and separate inputs. The system should automatically synchronise to shaft switches at both top and bottom of shaft during each wind. The unit should be self-diagnostic and have switching systems to automatically set-up the winder for false bank testing etc. The system should be designed to cater for power failures, have a UPS. In the event of a power failure the winder shall be limited to slow speed until synchronised to the shaft switches again.

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6
6.1

Normal winding operations
Control system Measures to prevent overwinds: • • • • • Duplicate systems with cross checking and cross checked to conveyance positions in the shaft. Duplicate and separate inputs into the control system and fail to safest winding situation. Designed to be resistant to and not cause electric and magnetic interference. Designed to prevent incorrect equipment cards and software being installed. Self-diagnostic systems. The control system should be a duplicate system with cross checking between them and with cross checking to actual shaft position of conveyances. Each control system should have separate inputs that fail to the safest winding situation. The control system shall be designed to be resistant to and not cause electric and magnetic interference, shall be self-diagnostic and designed to prevent incorrect equipment cards and software being installed.

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6.2

Clutching The committee recognised that clutching is one of the most hazardous operations undertaken during normal winding operations, as the out of balance load on each drum has to be held by the brakes of one drum only. Measures to prevent overwinds: • • • • Moving of winder should be at reduced speed only. There should be no load in the cages and skips. The braking systems should revert to “fast braking” mode. The brake engine back pressure on the unclutched drum must be drained to zero pressure ie maximum braking.

When a drum is unclutched the winder should be limited to moving at reduced speed only. Clutching should not be done with load in the cages and skips. The braking systems should revert to “fast braking” mode and the brake engine back- pressure on the unclutched drum must be drained to zero pressure ie maximum braking.

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7 7.1

Abnormal winding operations
Gravity winding Measures to prevent overwinds: • To be installed and operated in accordance with DME Directive C6. The test should be carried our regularly by and supervised by experienced competent persons in accordance with a standard written procedure for the specific winder. Whilst the control systems and speed / distance protection is out of service the winder shall be operated at slow creep speed only. After restoring the winder to normal condition after the test, the winder shall be operated at slow creep speed only until the winder controls, protection and position indication have been resynchronised with the actual shaft position by winding to the synchronising switch position or to a know shaft position such as the bank. If necessary personnel shall be stationed at the ends of wind to raise the alarm should an over or under wind appear possible. If necessary personnel shall be stationed at the ends of wind to raise the alarm should an over or under wind appear possible. The DME Directive C6 should be made a Regulation in terms of the Mines Health and Safety Act (Act 29 1996).

7.2

False bank testing The committee recognised that this test was an important test to prove that the speed / distance protection is correct but that it presented a major hazard that human error is possible in setting up the tests and restoring the winder to its normal condition. Measures to prevent overwinds: • The test should be carried our regularly by and supervised by experienced competent persons in accordance with a standard written procedure for the specific winder. Whilst the control systems and speed / distance protection is out of service the winder shall be operated at slow creep speed only. After restoring the winder to normal condition after the test, the winder shall be operated at slow creep speed only until the winder controls, protection and position indication have been resynchronised with the actual shaft position by winding to the synchronising switch position or to a know shaft position such as the bank. If necessary personnel shall be stationed at the ends of wind to raise the alarm should an over or under wind appear possible. If necessary personnel shall be stationed at the ends of wind to raise the alarm should an over or under wind appear possible.

• •

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7.3

Cutting ropes, replacing ropes, replacing conveyances Measures to prevent overwinds: • • • Carried out by trained and experienced personnel in accordance with a standard written procedure for the specific winder. Whilst the control systems and speed / distance protection is out of service the winder shall be operated at slow creep speed only. After restoring the winder to the normal condition, the winder shall be operated at slow creep speed only until the winder controls, protection and position indication have been resynchronised with the actual shaft position by winding to the synchronising switch position or to a know shaft position such as the bank. If necessary personnel shall be stationed at the ends of wind to raise the alarm should an over or under wind appear possible.

Carried out by trained and experienced personnel in accordance with a standard written procedure for the specific winder. Whilst the control systems and speed / distance protection is out of service the winder shall be operated at slow creep speed only. After restoring the winder to the normal condition, the winder shall be operated at slow creep speed only until the winder controls, protection and position indication have been resynchronised with the actual shaft position by winding to the synchronising switch position or to a know shaft position such as the bank. If necessary personnel shall be stationed at the ends of wind to raise the alarm should an over or under wind appear possible.

8

Power failures
Measures to prevent overwinds: • The winder controls, protection and indication systems shall be designed to fail safe under failure or voltage dip condition on any or all of the electrical circuits. UPS systems shall be installed wherever necessary. The winder depth indicators, control and protection systems shall remain synchronised to the drum and shaft during power supply trip outs of the winder and the winder coming to rest. Latching relays shall be used in critical circuits. eg directional switches on winders not designed to lower loads.

The winder controls, protection and indication systems shall be designed to fail safe under failure or voltage dip condition on any or all of the electrical circuits. UPS systems shall be installed wherever necessary. The winder depth indicators, control and protection systems shall remain synchronised to the drum and shaft during power supply trip outs of the winder and the winder coming to rest. Latching relays shall be used in critical circuits. eg directional switches on winders not designed to lower loads.

• •

•

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General
Some notes on general “good practice”: • • The ultimate trips on any winder should trip all winders in that shaft. Interlocking to prevent loaded conveyances going in downward direction at other than slow speed unless the winder is normally required to do this duty. Suppliers of winding systems should have ISO 9000 certification for design and manufacture and their designs should be reviewed by independent experts.

The ultimate trips on any winder should trip all winders in that shaft. Interlocking to prevent loaded conveyances going in downward direction at other than slow speed unless the winder is normally required to do this duty. Suppliers of winding systems should have ISO 9000 certification for design and manufacture and their designs should be reviewed by independent experts.

•

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