On a Rational Type of Explosion-Proof Magnetic Starter for Mobile Mining Machines
Abstract Generated abstract
This paper evaluates the deficiencies of PMV-type explosion-proof magnetic starters used for remote and automatic control of electric motors in underground mobile mining machines. It argues that persistent problems, including excessive size and weight, inconvenient housings and cable entries, unreliable protection, and operational difficulties, stem from the lack of clearly formulated design requirements. The author proposes a set of requirements covering starter size ranges, reversing and non-reversing versions, lightweight materials, removable plug-in panels, improved cover mechanisms, built-in instruments, comprehensive electrical protections, contact-position signaling, unrestricted remote-control distance, improved cable fittings, reduced control wiring, compatibility with high-frequency control circuits, and separate designs for stationary underground mechanisms. These recommendations are presented as a basis for developing safer, more reliable, and more practical explosion-proof starters for mining applications.
Full Text
On a Rational Type of Explosion-Proof Magnetic Starter for Mobile Mining Machines
I. G. Galeev
(Presented by the scientific seminar of the Department of Mining Electromechanics)
At present, the principal apparatus for remote and automatic control of electric motors of underground mechanisms is the PMV-type explosion-proof magnetic starter.
PMV-type magnetic starters have a number of substantial shortcomings, the main ones being: bulkiness, great weight, imperfection in the design of certain elements of the starter (housing, cable entries, contactor, etc.), lack of reliable protection for the surrounding environment, the electric motor, and the servicing personnel, and lack of complete reliability in operation of the starter. These shortcomings have repeatedly been mentioned in print, but they have not been eliminated in newly designed starters either.
The main reason for the long persistence of the above-mentioned shortcomings is the absence of more or less precisely formulated requirements for magnetic starters.
Explosion-proof magnetic starters for remote and automatic control of electric motors of mobile mining machines must satisfy the following requirements.
- They must be manufactured in two modifications: reversing and non-reversing.
| Non-reversing: 6 sizes | Non-reversing: 6 sizes | Reversing: 4 sizes | Reversing: 4 sizes |
|---|---|---|---|
| 1. | For operating currents 10–20 a | 1. | For operating currents 50–60 a |
| 2. | ” ” 30–40 a | 2. | ” ” 80–100 a |
| 3. | ” ” 50–60 a | 3. | ” ” 120–150 a |
| 4. | ” ” 80–100 a | 4. | ” ” 200–250 a |
| 5. | ” ” 120–150 a | ||
| 6. | ” ” 240–300 a |
The absence of magnetic starters for 10–20 and 30–40 a makes it difficult to convert to automatic control of winches, column drills, local-ventilation fans, tipper pushers, and other small mechanisms. At present, for these machines the more bulky and expensive PMV-1331 starters are used. As is known, our industry produces normal magnetic starters of these sizes.
Because of the absence of reversing starters for currents up to 250 a, two PMVI-1365 magnetic starters connected according to a reversing circuit are used for controlling mining combines.
- Starters must have low weight and small overall dimensions. Therefore, light alloys and plastics should be used for making the housings, and high-quality materials—permalloy, pressed powders, ferrites, etc.—for the magnetic cores.
Our industry produces DC contactors of types KM-200D and KM-400D for currents of 200 and 400 A respectively, weighing less than a kilogram and having overall dimensions tens of times smaller than those of the contactors used in explosion-proof magnetic starters. Applying this experience in the design of explosion-proof magnetic starters will make it possible to reduce weight and decrease overall dimensions.
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The circuit of the magnetic starter should be mounted on removable, interchangeable panels with plug-in connections. This will facilitate repair and simplify operation of the starter. In this connection it is necessary to make use of the experience of foreign apparatus engineering. English and French firms assemble the magnetic-starter circuit on sliding chassis.
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The pin-type cover lock must be abandoned and replaced by more convenient methods of closing covers, for example hinged ones. Very often, because dust and moisture get into the pin-type lock, it is impossible for one person to open the starter cover without using additional devices. Therefore, electricians are forced to use a sledgehammer, axe, chisel, etc., to open the starter cover, which leads to damage to the cover and to impairment of explosion safety.
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Starters must be equipped with a voltmeter and an ammeter. The presence of measuring instruments in magnetic starters will make it possible to organize the operation of electromechanical equipment more competently and will facilitate the conduct of research work connected with improving the electrical engineering facilities of mines. In foreign practice, some English and French firms equip explosion-proof magnetic starters with measuring instruments.
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Explosion-proof magnetic starters must have: maximum and zero protection, protection against excessive leakage currents, protection against short circuits in the control circuit, and monitoring of the serviceability of grounding.
Maximum protection must be provided by means of maximum relays. Plug fuses should be abandoned. This will improve protection of the electric motor and eliminate the possibility of operation on two phases.
The presence of protection against excessive current leakage in every magnetic starter will make it possible to raise significantly the safety of operation of electrical equipment in mines.
Protection against short circuits in the control circuit and monitoring of the serviceability of protective grounding will increase the safety of operation of electrical equipment.
Thermal protection of the electric motor must be provided by means of temperature relays built into the winding of the electric motor. This will make it possible to simplify the design of the starter and increase the reliability of the thermal protection of the electric motor.
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Magnetic starters must have signaling of the position of the contactor contacts. This will increase safety and facilitate remote control.
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The distance of remote control must not be limited by the design of the starter.
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The cable fittings must be convenient for connecting the cable. The cable fittings of modern starters are very cramped and inconvenient for installation.
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Control of the starter must be carried out with the smallest possible number of wires.
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In designing explosion-proof magnetic starters, it is necessary to take into account the possibility of using them in remote-control circuits with high-frequency currents.
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For controlling the electric motors of underground stationary mechanisms, it is necessary to design special magnetic starters adapted for stationary installation.
The implementation of these requirements should contribute to the creation of more advanced explosion-proof magnetic starters for remote and automatic control of underground mobile mechanisms.