Post by John on Feb 23, 2011 10:55:56 GMT -5
For guests not familiar with mining electrical equipment.
Intrinsically safe.
Low voltage electrical equipment, like signalling circuits, control circuits etc are required to undergo tests to make sure it is safe and meets the requirements of intrinsic safety, ie it will not produce an incendive spark that will ignite methane at a certain mix with air in normal or fault conditions.
Special transformers are used for signaling circuits, they comprise of a transformer mounted in a flameproof enclosure, and in series with the low voltage secondary is a none inductive resistor to limit fault current.
As coils on signal bells and relays generate a large back EMF which can cause a spark hot enough to ignite methane, they are required to have some means of "shorting" that EMF. One way to do that is to use DC as the supply current and to have a diode in "reverse" across the bell or relay coil.
Telephones also have to be designated I.S. in underground coal mines, so they use modern Zener barriers to short dangerous "spikes" that would otherwise be hazardous.
Flameproof/FLP/Explosion Proof.
An enclosure that will withstand an internal explosion of a methane and air mix, and will not rupture or allow an escape of hot gasses that will ignite a methane and air mix externally.
The enclosure doors/inspection hatches have machined flanges who's mating surfaces shall not exceed a maximum air gap, laid down by law. Usually 20 thousands of one inch for a flamepath of one inch, or 15 thousandths of one inch for a 3/4 inch flamepath.
Restrained Plug.
A plug on the end of a trailing cable, can be a bolted plug or a removable plug with a screwed retaining bolt having a clevis to unscrew the cable. Trailing cables come in various sizes and various voltage ratings up to 1100 volts down to 110 volts and are used for moving and portable machines from 110 volt rock/coal drills to shearers and continous miners.
Section Switches.
Usually isolators with protective circuits feeding electricity to a section, or district, normally 1100 volts maximum.
Can be high voltage high current, but in those cases more often called a circuit breaker.
Shaft Signals.
Electrical signalling equipment installed to instruct the winding engineman what he should be doing. A bell and rapper are installed at pit bottom and each inset in a shaft, and two or more bells are installed at the top of a shaft, (pit bank). Also two or more bells and indicators are installed in the winding enginemans cabin.
Signals are 1 to raise
2 to lower
3 Manriding
1 to stop while in motion.
4 to raise steadily.
5 to lower steadily
Then there are numerous signals sent for other functions, these being approved by the Manager of the mine.
GEB Gate End Box.
A piece of flameproof equipment that controls an electric motor or coal cutting machine, essentially a contactor and control circuits. It can be "banked" up to other gate end boxes to form a switchbank.
Usual voltages are 550 or 1100 voltage ranges.
Pilot Circuit.
More correctly "earth continuity circuit" A circuit used in conjunction with trailing cables to protect against open earthing cores of the cable. It also serves as a remote stop/start circuit.
The circuit runs at approx 7.5 volts and has a "polarized" relay at the GEB, the relay consists of "two" windings, one the normal wire winding, and the second is a copper sleeve. It's job is to act as a shorted turn if AC is applied to the relay and thus dropping it out. It also has an unwanted element, it causes the relay to have a slight delay in energizing.
At the remote end of the trailing cable, inside a motor or the machine the cable is coupled to, is a diode, and also if it's a machine a 30 ohm resistor. On starting the machine up, the start button shorts the resistor out and makes a circuit with just the diode, that energizes the pilot relay and brings the main contactor in powering the machine up. On release of the start button, the 30 ohm resistor is placed in series with the diode.
This acts as a safeguard should power fail and come back on. The resistance is enough to prevent the pilot relay energizing.
Ward-Leonard System.
A method of continuous variable speed for motor drives. It consists of a 3 phase motor mechanically coupled to a DC generator, the output of drives a DC motor.
Speed is controlled by variably controlling the field winding of the generator.
Uses are mainly confined to winding engines in coal mines.
Rarely used these days.
Intrinsically safe.
Low voltage electrical equipment, like signalling circuits, control circuits etc are required to undergo tests to make sure it is safe and meets the requirements of intrinsic safety, ie it will not produce an incendive spark that will ignite methane at a certain mix with air in normal or fault conditions.
Special transformers are used for signaling circuits, they comprise of a transformer mounted in a flameproof enclosure, and in series with the low voltage secondary is a none inductive resistor to limit fault current.
As coils on signal bells and relays generate a large back EMF which can cause a spark hot enough to ignite methane, they are required to have some means of "shorting" that EMF. One way to do that is to use DC as the supply current and to have a diode in "reverse" across the bell or relay coil.
Telephones also have to be designated I.S. in underground coal mines, so they use modern Zener barriers to short dangerous "spikes" that would otherwise be hazardous.
Flameproof/FLP/Explosion Proof.
An enclosure that will withstand an internal explosion of a methane and air mix, and will not rupture or allow an escape of hot gasses that will ignite a methane and air mix externally.
The enclosure doors/inspection hatches have machined flanges who's mating surfaces shall not exceed a maximum air gap, laid down by law. Usually 20 thousands of one inch for a flamepath of one inch, or 15 thousandths of one inch for a 3/4 inch flamepath.
Restrained Plug.
A plug on the end of a trailing cable, can be a bolted plug or a removable plug with a screwed retaining bolt having a clevis to unscrew the cable. Trailing cables come in various sizes and various voltage ratings up to 1100 volts down to 110 volts and are used for moving and portable machines from 110 volt rock/coal drills to shearers and continous miners.
Section Switches.
Usually isolators with protective circuits feeding electricity to a section, or district, normally 1100 volts maximum.
Can be high voltage high current, but in those cases more often called a circuit breaker.
Shaft Signals.
Electrical signalling equipment installed to instruct the winding engineman what he should be doing. A bell and rapper are installed at pit bottom and each inset in a shaft, and two or more bells are installed at the top of a shaft, (pit bank). Also two or more bells and indicators are installed in the winding enginemans cabin.
Signals are 1 to raise
2 to lower
3 Manriding
1 to stop while in motion.
4 to raise steadily.
5 to lower steadily
Then there are numerous signals sent for other functions, these being approved by the Manager of the mine.
GEB Gate End Box.
A piece of flameproof equipment that controls an electric motor or coal cutting machine, essentially a contactor and control circuits. It can be "banked" up to other gate end boxes to form a switchbank.
Usual voltages are 550 or 1100 voltage ranges.
Pilot Circuit.
More correctly "earth continuity circuit" A circuit used in conjunction with trailing cables to protect against open earthing cores of the cable. It also serves as a remote stop/start circuit.
The circuit runs at approx 7.5 volts and has a "polarized" relay at the GEB, the relay consists of "two" windings, one the normal wire winding, and the second is a copper sleeve. It's job is to act as a shorted turn if AC is applied to the relay and thus dropping it out. It also has an unwanted element, it causes the relay to have a slight delay in energizing.
At the remote end of the trailing cable, inside a motor or the machine the cable is coupled to, is a diode, and also if it's a machine a 30 ohm resistor. On starting the machine up, the start button shorts the resistor out and makes a circuit with just the diode, that energizes the pilot relay and brings the main contactor in powering the machine up. On release of the start button, the 30 ohm resistor is placed in series with the diode.
This acts as a safeguard should power fail and come back on. The resistance is enough to prevent the pilot relay energizing.
Ward-Leonard System.
A method of continuous variable speed for motor drives. It consists of a 3 phase motor mechanically coupled to a DC generator, the output of drives a DC motor.
Speed is controlled by variably controlling the field winding of the generator.
Uses are mainly confined to winding engines in coal mines.
Rarely used these days.
