Industrial Systems

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This section covers hydraulic and pneumatic circuits — their fundamentals, elements, design and selection — and the working principle and application of the different types of compressor.

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Fundamentals of Fluid Power • Fluid power transmits force and motion through a fluid: hydraulics uses almost incompressible oil at high pressure (typically 70–350 bar) and pneumatics uses compressed air (typically 6–10 bar).

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Both work on Pascal's law — pressure applied to a confined fluid is transmitted undiminished in all directions. • Key relations:

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Force F = p × A; actuator speed v = Q/A; hydraulic power P = p × Q (kW = bar × L/min ÷ 600); torque of a motor T = p·Dm/2π; cylinder retract force uses the annulus area (Apiston − Arod), so the retract stroke is faster but weaker. • Advantages of fluid power: very high force/torque from a small unit, infinitely variable speed, easy reversal, overload protection by the relief valve, and simple linear motion; limitations: leakage and contamination, fluid cost and disposal, noise, lower efficiency than direct electric drive, and (for air) poor stiffness and position control.

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Feature Hydraulic Pneumatic Electric drive Working pressure 70–350 bar 6–10 bar — Force capability Very high Moderate/low Moderate Speed/response Moderate, well controlled Very fast, less controllable Fast, precise Stiffness/positionin g High (oil nearly incompressible) Poor (air compressible) Excellent Leakage Messy, fire risk with mineral oil Harmless — Cost of energy Moderate High (compressed air is expensive) Lowest Typical use Presses, injection moulding, excavators, lifts Clamping, ejecting, packaging, hand tools, robotics grippers Conveyors, machine feeds Elements of a Hydraulic System Element Function / types Reservoir (tank) Stores oil, dissipates heat, settles contaminants and releases air; with baffle, strainer, breather, level gauge Pump Converts mechanical to hydraulic power: gear (cheap, robust, fixed displacement), vane, piston (axial/radial) — high pressure, often variable displacement (pressure-compensated) for energy saving Pressure-control valves Relief valve (limits maximum pressure — essential safety element), pressure-reducing, sequence, counterbalance and unloading valves Direction-control valves Spool or poppet valves designated by ports/positions (2/2, 3/2, 4/2, 4/3);

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4/3 centre types — open, closed, tandem and float centre; actuated manually, mechanically, by solenoid or pilot pressure Flow-control valves Throttle/needle and pressure-compensated valves; meter-in (controls oil into the cylinder — for opposing loads), meter-out (controls oil leaving — for over-running loads, e.g., lowering), bleed-off (diverts part of the flow — efficient but less accurate) Actuators Single- and double-acting cylinders (also telescopic, tandem), hydraulic motors (gear, vane, piston) for continuous rotation, rotary actuators Accessories Filters (suction, pressure, return;

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ISO 4406 cleanliness), accumulator (bladder/piston — stores energy, absorbs shock, emergency supply), heat exchanger, pressure gauge, hoses and fittings, seals; fluid = mineral oil (or fire-resistant/biodegradable types) • Common circuits: pressure-relief, unloading and pump-unloading circuits, regenerative circuit (rod-side oil fed to the cap side for a fast approach stroke), sequencing circuit (clamp then feed), meter-in/meter-out speed control, counterbalance for vertical loads, synchronising circuits, accumulator circuits, and hydro-pneumatic (air-over-oil) circuits.

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Circuits are drawn with ISO 1219 symbols. • Design and selection procedure: define the load, stroke and cycle time → size the cylinder from F = pA at the selected working pressure → compute the required flow Q = A·v → select the pump (displacement × speed) and prime mover power (P = pQ/η) → choose valves for the flow and pressure → size pipes for recommended velocities (suction ≈ 0.6–1.2 m/s, pressure ≈ 3–6 m/s, return ≈ 1.5–3 m/s) → check reservoir volume (≈ 3–5 times pump flow per minute) and cooling → specify filtration and safety devices.

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Pneumatic Systems • Layout: compressor → after-cooler and air dryer (refrigerant or desiccant) → receiver → distribution main (sloped, with drain legs) → FRL service unit (filter, pressure regulator, lubricator) → direction-control valves → cylinders, air motors, grippers or vacuum devices; silencers on exhaust ports. • Merits: clean, safe in hazardous/explosive areas, fast acting, simple and cheap components, overload-proof, air is freely available and exhaust needs no return line.

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Demerits: compressibility gives poor speed/position control (unless with servo-pneumatics), low force per size, high energy cost, noise, and the need for dry clean air. • Typical industrial applications: clamping and ejecting, packaging and bottling machines, pick-and-place units, air tools, blow moulding, conveying (air knives), spray painting, braking of vehicles, and process control (I/P converters, pneumatic actuators for control valves).

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Compressors Type Working principle and application Reciprocating (piston) Positive displacement; piston in a cylinder with suction and delivery valves; single- or multi-stage with intercooling for high pressure; intermittent, pulsating delivery; small to medium flow, pressures up to hundreds of bar — workshops, PET blowing, air brakes Rotary screw Two meshing helical rotors compress air continuously; oil-flooded or oil-free; steady flow, low noise, good for continuous plant air at 7–13 bar — the standard industrial machine Rotary vane Slotted rotor with sliding vanes in an eccentric casing; compact, steady flow, moderate pressure Scroll / diaphragm Oil-free, quiet, small capacity — laboratories, medical and food use Centrifugal (dynamic) Impeller raises velocity, diffuser converts it to pressure; very large flows at moderate pressure; used in big plants, turbochargers, process gas service Axial (dynamic) Rows of rotating and fixed blades; very high flow, low pressure ratio per stage — gas turbines, blast furnaces • Performance terms: free air delivered (FAD), volumetric efficiency (falls with clearance volume and pressure ratio), isothermal/adiabatic efficiency, specific power (kW per m³/min ≈ 6–7 for a good 7-bar screw machine). • Selection is by required pressure, flow (FAD with diversity and future allowance), duty cycle, air quality (oil-free or lubricated) and energy cost; multiple smaller machines with a sequencer are more efficient at part load, and variable-speed drive (VSD) compressors save energy where demand varies.

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Energy-saving measures were given in Chapter 2.6.

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This section covers the construction and working of transformers including operation on load, voltage regulation, losses and efficiency; the construction and working of the DC generator, DC motor, three-phase induction motor and three-phase synchronous motor; and industrial and domestic electrical supply systems.

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Transformer • A transformer transfers electrical energy between circuits at different voltages by mutual induction, at constant frequency and (ideally) constant power; it has no rotating part. • Construction: laminated cold-rolled grain-oriented (CRGO) silicon steel core (laminations reduce eddy-current loss) in core type or shell type form; primary and secondary windings (copper, insulated); for power transformers — tank with transformer oil (insulation + cooling), conservator, breather with silica gel, Buchholz relay, radiators/fins, bushings, explosion vent, and a tap changer (off-load or on-load) for voltage adjustment. • EMF equation:

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E = 4.44 f N Φm; turns ratio V1/V2 = N1/N2 = I2/I1 (ideal).

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On no load the transformer draws a small magnetising current at a very low power factor; on load the secondary current sets up an mmf that is balanced by an additional primary current, so the flux stays nearly constant. • Losses: core (iron) losses — hysteresis (∝ f B1.6) and eddy current (∝ f²B²t²) — practically constant at all loads; copper (I²R) losses — vary with the square of the load.

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Efficiency η = output/(output + iron loss + copper loss); maximum efficiency occurs when copper loss = iron loss, i.e. at a load fraction √(Pi/Pcu,fl).

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All-day efficiency (energy basis) is used for distribution transformers, which are energised all day but loaded only part of it. • Voltage regulation = (Vno-load − Vfull-load)/Vfull-load × 100 — smaller is better; it depends on load current, impedance and power factor (it can even be negative at leading power factor). • Tests: open-circuit (no-load) test on the LV side gives the iron loss and magnetising branch; short-circuit test on the HV side gives the full-load copper loss and equivalent impedance; polarity, ratio and insulation tests.

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ONAN, ONAF, OFAF for oil-filled; dry type (cast resin) indoors.

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Three-phase connections: star-delta (Dy11 common for distribution), delta-delta, star-star, with auto-transformers for small ratios.

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DC Generator and DC Motor • Construction (common to both): yoke (frame), field poles with field windings, armature core with slots and lap or wave winding, commutator and carbon brushes, shaft and bearings, interpoles/compensating winding. • DC generator works on Faraday's law (Fleming's right-hand rule) — the commutator rectifies the alternating armature emf.

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EMF equation E = PΦZN/60A (A = 2 for wave, A = P for lap winding).

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Types: separately excited, and self-excited shunt, series and compound (long/short, cumulative/differential).

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Characteristics: shunt — nearly constant voltage; series — rising then falling; compound — level or over-compounded.

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Armature reaction distorts and weakens the field (corrected by interpoles and compensating windings), and commutation problems cause sparking. • DC motor works on the force on a current-carrying conductor in a magnetic field (Fleming's left-hand rule).

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Back emf Eb = V − IaRa (it regulates the current drawn); torque T ∝ Φ Ia; speed N ∝ Eb/Φ. • Types and uses: series motor — very high starting torque, speed varies widely, must never run unloaded (traction, cranes, hoists); shunt motor — almost constant speed (lathes, fans, pumps); compound motor — high starting torque with limited no-load speed (presses, shears, rolling mills).

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Starters (3-point, 4-point) limit the heavy starting current because Eb = 0 at rest.

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Speed control: armature-voltage (below base speed, Ward-Leonard or thyristor drives), field-flux (above base speed) and armature-resistance control.

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DC drives have largely been replaced by AC drives with VFDs in modern industry.

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Three-Phase Induction Motor • Construction: laminated stator with a three-phase winding, and a rotor — squirrel cage (bars short-circuited by end rings; rugged, cheap, maintenance-free — over 90% of industrial motors) or slip-ring (wound) rotor with three-phase winding brought out through slip rings for external resistance. • Principle: the three-phase stator current produces a rotating magnetic field at synchronous speed Ns = 120f/P; it induces emf and current in the rotor (transformer action), and the interaction produces torque (Lenz's law) — the rotor always runs a little slower, so the motor is called asynchronous. • Slip s = (Ns − N)/Ns — typically 3–5% at full load; rotor frequency = sf; rotor copper loss = s × rotor input; torque-slip curve shows starting torque, maximum (pull-out) torque at s ≈ R2/X2, and a stable operating region at low slip; torque ∝ V² so it falls badly with low voltage. • Starting: direct-on-line (DOL) draws 5–7 times full-load current (used for small motors); star-delta starting reduces starting current and torque to one-third; auto-transformer starter; rotor-resistance starter (slip-ring motors — high starting torque); modern soft starters and variable-frequency drives (VFD) (which also give speed control at constant V/f). • Speed control: frequency (VFD — the standard method), pole changing, voltage control, rotor resistance (slip-ring).

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Applications: pumps, fans, compressors, conveyors, machine tools, crushers — practically all constant-speed industrial drives.

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Three-Phase Synchronous Motor • Construction: three-phase stator (armature) as in an induction motor, and a rotor with DC-excited field poles (salient pole for low speed, cylindrical for high speed) fed through slip rings or a brushless exciter, plus a damper (amortisseur) winding. • Principle: the rotor locks into step with the rotating field and runs exactly at synchronous speed Ns = 120f/P at all loads; increasing load increases the torque (load) angle δ, not the speed; beyond the pull-out torque the motor loses synchronism. • Not self-starting — it is started as an induction motor using the damper winding (or by a pony motor/VFD), and the DC excitation is then applied. • Excitation and power factor:

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V-curves show that an over-excited synchronous motor draws a leading current, so it can supply reactive power — an over-excited machine running on no load is a synchronous condenser used for power-factor improvement and voltage support in plants.

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Under-excited machines draw lagging current. • Applications: large constant-speed drives (compressors, crushers, mills, pumps) in cement, steel and chemical plants, and power-factor correction; disadvantages — higher cost, DC excitation needed, not self-starting, hunting under sudden load changes.

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Industrial and Domestic Supply Systems • Chain: generation (in Nepal mostly hydropower) → step-up transformer → transmission at 400/220/132 kV → sub-transmission 66/33 kV → distribution at 11 kV → distribution transformer → 400 V three-phase, four-wire / 230 V single-phase, 50 Hz to consumers (the Integrated Nepal Power System operated by NEA). • Industrial supply: three-phase (400 V LT, or 11 kV/33 kV HT for large loads with the consumer's own substation), with metering of energy (kWh) and maximum demand (kVA), power-factor measurement, HT/LT switchgear, capacitor banks, standby generator with changeover, and distribution boards feeding motors through starters/VFDs.

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Domestic supply: single-phase 230 V through a service cable, energy meter, main switch, MCBs/RCCB and final circuits (lighting, sockets, water heater). • Protection and safety: fuses and MCBs (overload/short circuit), MCCB and relays for larger circuits, earthing of all metal enclosures (earth pits, earth electrodes, earth continuity), ELCB/RCCB for earth-leakage protection, surge protection and lightning arresters, isolation and lock-out/tag-out before maintenance, correct cable sizing and voltage-drop limits, and periodic insulation-resistance testing. • Tariff and energy management (see 8.5): energy charge, demand charge, time-of-day rates, power-factor penalty/rebate; load management, capacitor banks, efficient motors and VFDs.

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This section covers the working principle and applications of boilers and furnaces, operating strategies for cogeneration plants, the types of fuel used in furnaces, general fuel-economy measures in furnaces, boiler performance assessment and boiler safety.

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Boilers • A boiler (steam generator) converts the chemical energy of fuel into the enthalpy of steam for process heating, drying, sterilising, power generation and cogeneration. • Classification: fire-tube (hot gases inside tubes surrounded by water — Cochran, Lancashire, locomotive, packaged boilers; simple, cheap, large water volume, limited to ≈ 20 bar and moderate capacity) and water-tube (water inside tubes, gases outside — Babcock and Wilcox, La Mont, Benson; high pressure and capacity, quick steaming, used in power plants); also natural vs forced circulation, internally/externally fired, stationary/mobile, low/high pressure, and fuel type (coal, oil, gas, biomass, husk, electric). • Mountings (for safety and control, fitted on the boiler): two safety valves, two water-level indicators, pressure gauge, steam stop valve, feed check valve, blow-off cock, fusible plug and manhole.

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Accessories (to improve efficiency): economiser (heats feed water with flue gas), air pre-heater, superheater, feed pump, injector, steam separator and steam trap. • Water treatment: softening/demineralisation, deaeration and dosing prevent scale (an insulator that wastes fuel and overheats tubes), corrosion and carry-over; blowdown controls dissolved solids: blowdown % = feed-water TDS × 100/(maximum permissible boiler TDS) of the feed rate; heat can be recovered from blowdown.

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Boiler Performance Assessment • Equivalent evaporation = ms(h − hf1)/2257 kg of steam per hour from and at 100 °C; evaporation ratio = kg steam per kg fuel (typical ≈ 6 for coal, 13–14 for oil/gas). • Direct (input-output) method: η = ms(hsteam − hfeed)/(mf × GCV) × 100 — quick, but shows nothing about where losses occur. • Indirect (heat-loss) method: η = 100 − (dry flue-gas loss + loss due to hydrogen in fuel + loss due to moisture in fuel and air + CO/incomplete combustion loss + radiation/convection and unaccounted losses); requires flue-gas analysis (O2, CO2, CO), temperatures and fuel analysis. • Key operating indicators: excess air (from flue-gas O2: too little → CO and soot, too much → stack loss; typical 15–25% for oil/gas), flue-gas exit temperature (every ≈ 22 °C rise ≈ 1% efficiency loss), steam pressure and load factor, condensate recovery percentage, TDS and blowdown rate, and boiler loading (best near 70–90% of rating). • Typical efficiencies: modern oil/gas packaged boilers ≈ 85–90%, coal/biomass boilers ≈ 65–80%.

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Boiler Safety • Hazards: overpressure, low water level and overheating (the commonest cause of serious accidents), furnace explosion from accumulated unburnt fuel, scale-induced tube failure, and water hammer. • Safety devices and practice: two spring-loaded safety valves set above working pressure, low-water cut-off and high/low alarms with two independent level controls, pressure switches and modulating controls, flame monitoring (photocell/ionisation) with automatic fuel cut-off, purging of the furnace before ignition, interlocks on burner start-up, water-level gauge blow-down testing every shift, feed-water treatment and testing, regular blowdown, operator training and licensing, safe start-up/shut-down procedures, and periodic statutory inspection and hydraulic testing of the pressure vessel.

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Furnaces • A furnace heats materials above ambient temperature for melting, forging, heat treatment, rolling, drying, calcining or firing.

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Classification: by heat source — fuel-fired (solid/liquid/gaseous) or electric (resistance, induction, arc); by mode — batch (box, pit, bogie-hearth, bell, muffle) or continuous (pusher, walking-beam, rotary-hearth, roller-hearth, tunnel); by heat transfer (direct/indirect fired, recuperative/regenerative); by application — melting (cupola, crucible, induction, arc), reheating, forging, annealing/hardening, cement and brick kilns. • Fuels used: solid — coal, coke, charcoal, wood, rice husk, briquettes (cheap but ash, handling and pollution problems); liquid — furnace oil, LDO, diesel (needs preheating and atomisation for furnace oil; easy control); gaseous — natural gas, LPG, producer gas, biogas (cleanest, best control, no ash, highest cost); electricity — precise, clean, no flue gas at the point of use, but expensive per unit of heat. • Furnace efficiency = heat actually taken up by the stock ÷ heat supplied by fuel; typical values are low (batch furnaces ≈ 20–40%, good continuous furnaces ≈ 50–70%).

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Losses: flue-gas (sensible heat — the largest), wall/structure conduction, opening (radiation) losses through doors and peep holes, skin and cooling-water losses, heat in scale and in the conveying fixtures, and unburnt fuel/air infiltration. • General fuel-economy measures in furnaces: complete combustion with minimum excess air (control by flue-gas O2), correct burner setting and atomisation; preheating of combustion air by recuperators or regenerators (every 100 °C of air preheat saves ≈ 2% fuel) and preheating of stock with waste heat; good insulation and ceramic-fibre linings (low thermal mass — big saving in batch operation); minimum opening of doors and proper door sealing; maintaining slightly positive/neutral furnace pressure to stop cold-air infiltration; correct charging, loading and scheduling (avoid idling and partially loaded furnaces); automatic temperature and fuel-air ratio control; avoiding excessive soaking time and over-heating (which also causes scale loss); regular maintenance of burners, refractories, insulation and instruments; and waste-heat recovery to generate steam or heat process water.

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Cogeneration Operating Strategies • Cogeneration (CHP) produces electricity and useful heat from the same fuel, raising total utilisation to ≈ 70–85% (Chapter 2).

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Topping cycles generate power first and use the rejected heat (back-pressure steam turbine, extraction-condensing turbine, gas turbine with a heat-recovery steam generator, reciprocating engine with jacket and exhaust heat recovery); bottoming cycles generate power from high-temperature process waste heat (cement, glass, steel). • The key design parameter is the heat-to-power ratio of the plant, which must suit the site's demand; sizing and operating strategy are chosen accordingly:

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Operating strategy Description Base thermal load matching The CHP unit is sized for the minimum (base) process heat demand and runs fully loaded; extra heat from boilers, extra power imported from the grid — the safest option Base electrical load matching Sized for the minimum site electrical load; additional power imported, and heat supplemented or wasted Thermal load following Output modulated to follow the heat demand; surplus power exported or deficit imported — needs an export agreement Electrical load following Output follows the site's electrical demand; excess heat dumped or supplemented — suitable where power is costly or supply unreliable Mixed / peak-lopping (stand-alone) Unit run to shave peak demand charges or during grid outages; island operation in isolated plants • Selection depends on the relative cost of fuel and grid power, the demand charge, reliability of supply, ability to export, the heat-to-power ratio and part-load efficiency — evaluated by NPV/IRR and payback (Chapter 10.2).

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This section covers the factors in material-handling problems, the principles of material handling, reduction in time and handling, maintenance and repair, material-handling equipment and its selection, and the unit-load principle.

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Material Handling — Meaning and Objectives • Material handling is the movement, storage, protection and control of materials throughout manufacturing, warehousing, distribution and disposal.

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It adds cost but no value to the product, yet typically accounts for 20–50% of manufacturing cost and a large share of factory accidents — so minimising it is a classic industrial-engineering objective. • Objectives: deliver the right material, in the right quantity and condition, to the right place, at the right time, in the right sequence and position, at the right cost, by the right method.

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Practical aims: lower handling cost and damage, higher productivity and machine utilisation, shorter throughput time and less WIP, better space utilisation, improved safety and working conditions, and better control of material. • Signs of poor handling: crowded aisles, long or crossing material flows, manual lifting, back-tracking, idle machines waiting for material, high damage and scrap, overflowing WIP and repeated rehandling.

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Factors in Material-Handling Problems Factor What must be considered Material characteristics Type (solid, liquid, bulk, unit), size, shape, weight, quantity, fragility, temperature, hazard, value Move (flow) characteristics Source and destination, distance, route, frequency, throughput rate, speed required, vertical/horizontal movement, continuous or intermittent Method Manual, mechanised or automated; unit load or bulk; equipment and manpower available Building and layout Floor load capacity, headroom, aisle width, column spacing, floor condition, doorways, levels and lifts; layout type (process, product, cellular, fixed position) Cost Capital cost, operating and maintenance cost, labour saved, space saved, payback/return on investment Safety and environment Operator safety, ergonomics (manual handling limits), fire and explosion risk, noise, dust, contamination Flexibility and future needs Product mix changes, volume growth, layout changes, obsolescence Principles of Material Handling • The ten modern principles (Material Handling Institute): planning, standardisation, work (minimise handling work = flow × distance), ergonomic, unit load, space utilisation, system (integrate handling with production, storage, shipping and information flow), automation, environmental and life-cycle cost principles. • Classic rules that follow from them: eliminate handling wherever possible; move in the shortest, straightest path; use gravity where practicable; keep material moving (avoid interim storage and rehandling); move in bulk or large unit loads; use mechanical aids rather than muscles; combine handling with processing or inspection; maintain a clear and safe aisle; keep equipment utilisation high; and standardise equipment to simplify spares and training. • Reduction in time and handling is achieved by: better plant layout (process → cellular/product layout reduces travel), balanced lines, combining operations, point-of-use storage, smaller batches with continuous flow (lean), containerisation, pre-positioning material at the correct height, mechanisation and automation (conveyors, AGVs), bar code/RFID tracking to avoid searching, and by analysis tools — flow process chart, from-to (travel) chart, string diagram, flow diagram, distance-intensity analysis and systematic handling analysis.

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Unit Load Principle • A unit load is a number of items arranged so that they can be picked up and moved as one — on a pallet, in a container, tote pan, bin, skid, cage or wrapped stack.

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Standard pallets (e.g., 1200 × 1000 mm and 1200 × 800 mm) allow standard racks, trucks and containers. • Advantages: fewer trips and less handling time and labour, faster loading/unloading, less product damage and pilferage, easier counting and stock control, better use of cubic space and transport, and simpler mechanisation.

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Disadvantages: cost of pallets/containers and of the handling equipment, tare weight and space of the container, the need to return empty pallets, and less flexibility for irregular or very large items. • Unit loads should be as large as the equipment, aisles, storage and safety permit, and are usually secured by strapping, stretch or shrink wrapping.

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Material-Handling Equipment and Selection Class Examples Conveyors (fixed path, continuous) Belt, roller (gravity and powered), chain, slat, screw, bucket elevator, overhead trolley/power-and-free, pneumatic conveying — high volume over a fixed route, low unit cost, but inflexible and they occupy floor space Industrial trucks (variable path) Hand trucks, pallet (hydraulic) trucks, forklift trucks (counterbalance, reach), platform trucks, tractors-trailers, AGVs/AMRs — flexible routing, need aisles and operators Cranes and hoists (variable path, limited area) Jib crane, overhead travelling (EOT) crane, gantry crane, monorail, chain and wire-rope hoists, mobile cranes — heavy and awkward loads, vertical movement, free floor space Positioning equipment Lift tables, tilters, turntables, manipulators, balancers, industrial robots — handle the load at the workplace, reduce ergonomic risk Unit-load formation Pallets, skids, containers, tote pans, strapping and stretch/shrink wrapping machines, palletisers Storage equipment Selective and drive-in racking, shelving, stacking frames, mezzanines, carousels, AS/RS (automated storage and retrieval), silos and tanks Identification and control Bar codes, RFID, voice picking, weighing systems, WMS software linking handling with inventory records • Selection procedure: analyse the material, the move and the method (the 'MMM' approach) → list feasible equipment → compare on capacity and throughput, flexibility, investment and operating cost, space and building constraints, safety and ergonomics, maintenance and spares, and integration with existing systems → evaluate economically (cost per tonne moved, payback, NPV) → select, install, train and measure. • Useful rules: use fixed-path equipment (conveyors) for steady high-volume flows on fixed routes; use variable-path equipment (trucks, AGVs) where routes and volumes vary; use cranes for very heavy or bulky items; use gravity wherever possible; avoid over-mechanising a low-volume, variable operation. • Maintenance and repair: material-handling equipment failure stops production, so it gets planned preventive maintenance — daily operator checks, lubrication, inspection of wire ropes, chains, hooks and slings, brakes and limit switches; periodic load testing and statutory inspection of cranes and lifting tackle; spare parts for critical items; battery care for electric trucks; safe operating procedures, marked safe working load (SWL), operator licensing/training, and accident investigation.

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This section covers types of energy, energy conversion and conservation, energy and the environment, the types, characteristics, basic elements and calculations of power systems, energy policies and the national and international energy scenario, financial and economic analysis of energy projects, and energy pricing and tariff selection.

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Types of Energy and Conversion • Primary energy occurs in nature (coal, oil, gas, uranium, hydro, solar, wind, biomass); secondary energy is converted (electricity, petrol, hydrogen).

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Renewable (hydro, solar, wind, biomass, geothermal) vs non-renewable (fossil, nuclear); commercial (electricity, petroleum, coal) vs traditional/non-commercial (fuelwood, agricultural residue, dung — still a large share of Nepal's total energy use). • Forms: mechanical, thermal, electrical, chemical, radiant and nuclear.

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Conversion devices: boiler and turbine (chemical → thermal → mechanical), generator (mechanical → electrical), motor (electrical → mechanical), PV cell (radiant → electrical), fuel cell (chemical → electrical), battery (chemical ↔ electrical). • Every conversion has losses; the overall efficiency of a chain is the product of the stage efficiencies (e.g., fuel → electricity ≈ 35% in a thermal plant, then motor and drive losses at the user's end), which is why saving one unit at the point of use saves several units of primary energy. • Energy conservation: energy audit, efficient equipment (motors, boilers, lighting), waste-heat recovery, insulation, power-factor and load management, process changes, and an energy management system (ISO 50001) with monitoring and targeting.

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Conservation is usually cheaper per unit saved than new generation ('negawatts').

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Energy and the Environment • Fossil-fuel use produces CO2 and other greenhouse gases, SO2, NOx and particulates (acid rain, smog, health effects); biomass burning indoors causes serious indoor air pollution in rural Nepal; hydropower has land, river-flow, sediment and resettlement impacts; all projects require IEE/EIA under the Environment Protection Act 2076 (Chapter 6.2). • Mitigation: renewables, efficiency, fuel switching (to electricity/clean cooking), emission control, carbon markets and climate commitments (Paris Agreement, Nepal's Nationally Determined Contributions and its long-term net-zero target — verify current commitments).

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Electrification of cooking, transport and industry is Nepal's main strategy because its electricity is hydro-based.

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Power Systems — Elements, Characteristics and Calculations • Basic elements of any power system: generation (hydro, thermal, solar, wind, diesel), transformation and transmission (step-up transformers, EHV lines, substations), distribution (11 kV feeders, distribution transformers, LV network) and the load, together with protection, control (SCADA/load dispatch) and metering. • Types of hydropower plants: run-of-river (RoR), peaking run-of-river (PRoR), storage/reservoir and pumped storage; micro/mini/small/large classification; thermal (steam, diesel, gas turbine), solar PV, wind and hybrid systems with battery storage. • Load characteristics: load curve (load vs time) and load duration curve; connected load; maximum demand; base, intermediate and peak load plants.

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Factor Definition Demand factor Maximum demand ÷ connected load (< 1) Load factor Average load ÷ maximum demand (over a period) — a high load factor means efficient use of installed capacity and lower unit cost Diversity factor Sum of individual maximum demands ÷ maximum demand of the system (> 1) Plant capacity factor Actual energy generated ÷ (installed capacity × period);

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Nepal's run-of-river plants ≈ 50–60% annually, solar PV ≈ 15–20% Factor Definition Plant use factor Energy generated ÷ (capacity × hours the plant was actually in operation) Utilisation factor Maximum demand ÷ rated capacity of the plant/equipment • Example: a factory with a maximum demand of 500 kVA consuming 1 80 000 kWh in a 30-day month at 0.9 pf has an average load of 180 000/720 = 250 kW; with maximum demand ≈ 450 kW, the load factor = 250/450 ≈ 0.56. • Other calculations met in practice: energy = power × time; three-phase power P = √3 V I cos φ; kVA = kW/cos φ; capacitor kVAr required = kW(tan φ1 − tan φ2); transmission loss ≈ I²R; and the sizing of generators, cables and transformers.

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Energy Scenario and Policies • Nepal: theoretical hydropower potential ≈ 83 000 MW with roughly 42 000 MW considered economically feasible; installed capacity has grown rapidly in recent years (a few thousand MW, mostly run-of-river, with seasonal surplus in the wet season and import from India in the dry season); national grid access now covers most households; nevertheless traditional biomass still supplies a large share of total energy and all petroleum products are imported, dominating the import bill.

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(Figures change every year — verify with NEA's annual report, the Water and Energy Commission Secretariat and the Economic Survey.) • Institutions:

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Ministry of Energy, Water Resources and Irrigation;

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Nepal Electricity Authority (NEA) (generation, transmission, distribution and bulk supply);

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Electricity Regulatory Commission (tariff and licensing);

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Alternative Energy Promotion Centre (AEPC) (renewable/rural energy);

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Water and Energy Commission Secretariat;

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Independent Power Producers selling through power purchase agreements (PPA); the Investment Board for large projects. • Policies and laws (verify current versions):

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Electricity Act 2049 and its regulations (a new Electricity Bill has been under consideration), Hydropower Development Policy 2058 (2001), Rural Energy Policy 2063, Renewable Energy Subsidy Policy, National Energy Efficiency Strategy, Nepal's periodic plans and White Paper targets for generation, domestic consumption and electric cooking/transport, and the NDC and net-zero commitments under the Paris Agreement. • International: global primary energy is still dominated by fossil fuels, but renewables (especially solar and wind) are the fastest-growing sources; agencies — IEA, IRENA; drivers — energy security, climate policy, falling renewable costs, electrification and storage.

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Financial and Economic Analysis of Energy Projects • Financial analysis (from the investor's view) uses market prices: capital cost per kW, capacity factor, O&M cost, fuel cost, debt/equity and interest, taxes and depreciation; criteria — NPV, IRR, benefit-cost ratio, payback and discounted payback (Chapter 10.2). • Levelised cost of energy (LCOE) = present value of all lifetime costs ÷ present value of energy generated (Rs/kWh) — the standard way to compare a hydropower, solar, diesel or efficiency option; it is sensitive to the discount rate, capacity factor and plant life. • Economic analysis (from society's view) uses shadow/economic prices, excludes taxes and subsidies (transfers) and includes externalities such as emissions, health and displacement; used for public projects and donor appraisal. • Selection between options: compare LCOE/NPV over the same period with sensitivity and risk analysis (hydrology, demand, fuel price, exchange rate, construction delay); energy-conservation projects are evaluated on the same basis, usually with much shorter paybacks.

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Energy Pricing and Tariff Selection • The cost of supply has fixed components (capital, interest, depreciation, fixed O&M) and variable components (fuel, energy purchase, variable O&M), so tariffs generally have two parts. • Tariff types: flat/uniform rate, block (slab) rate (domestic — rate changes with consumption), two-part tariff = demand (kVA/kW) charge + energy (kWh) charge (industrial), maximum-demand tariff, time-of-day (TOD) tariff with peak, off-peak and normal rates, seasonal (wet/dry) tariffs and power-factor penalty/rebate; bulk/HT tariffs for large industrial consumers with their own substations. • Tariff selection for an industry: compare the options at the plant's actual load factor and demand pattern; a plant with a high load factor benefits from a demand-based two-part tariff, while a plant with peaky demand should reduce maximum demand (load staggering and shifting, load limiters, avoiding simultaneous starting of large motors) or shift work to off-peak hours under a TOD tariff; improving power factor with capacitors avoids penalties and lowers the kVA demand; captive generation is compared with grid tariffs on a cost-per-kWh basis. • Related concepts: subsidies and cross-subsidy between consumer categories, PPA rates for IPPs (different wet- and dry-season rates in Nepal), net metering for rooftop solar, and the regulator's role in tariff setting.

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This section covers control systems and automatic control, open- and closed-loop control, path and speed control, standard input signals, adaptive control and servo systems, position and other sensors including encoders and resolvers, electromagnetic actuators and programmed control, and basic CNC systems and microcontrollers.

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Automation and Control Systems • Automation is the use of control systems and information technology to operate equipment with reduced human intervention.

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Types: fixed (hard) automation (high volume, dedicated — transfer lines), programmable automation (batch production — CNC machines, robots) and flexible automation (FMS — variety with no changeover time).

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Reasons: productivity, quality and consistency, cost, safety in hazardous work, reduced lead time and the ability to make complex parts; limitations: capital cost, skilled maintenance, inflexibility of fixed systems and social/employment issues. • A control system consists of a reference input (set point), a controller, an actuator (final control element), the plant/process and — in feedback systems — a sensor and an error detector (comparator).

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Open-loop control Closed-loop (feedback) control No feedback; output is not measured or compared with the set point Output is measured and compared; the error drives the controller Simple, cheap, stable, easy to build More complex and costly; can become unstable if badly tuned Cannot correct for disturbances or parameter changes; accuracy depends on calibration Automatically corrects for disturbances, load changes and drift; high accuracy Examples: a stepper-motor drive without feedback, a washing-machine timer, a simple conveyor Examples:

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CNC axis with an encoder, temperature control with a thermocouple, servo drive, cruise control Control Modes, Standard Signals and Advanced Control • Control modes: on-off (two-position) — simple, causes oscillation around the set point (thermostats); proportional (P) — output ∝ error, leaves an offset; proportional-integral (PI) — integral action removes the offset;

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PID — derivative action anticipates the rate of change and improves the transient response.

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Tuning by Ziegler-Nichols or auto-tuning. • Standard test signals used to study system response: step (sudden change — gives rise time, peak overshoot, settling time and steady-state error), ramp (constant rate — position tracking), parabolic (constant acceleration), impulse and sinusoidal (frequency response, Bode/Nyquist analysis, gain and phase margins for stability). • Feedforward control acts on a measured disturbance before it affects the output; cascade control uses an inner fast loop inside an outer loop. • Adaptive control automatically adjusts the controller parameters as the process changes — gain scheduling, self-tuning regulators and model-reference adaptive control; in machining, adaptive control varies feed or speed in real time from measured force, power or vibration to protect the tool and maximise removal rate. • Servo systems are closed-loop position/velocity control systems (servo motor + encoder/resolver + drive + controller) — used for CNC axes, robots, packaging machines and positioning tables.

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Path control may be point-to-point (only the end points matter — drilling, spot welding) or continuous path/contouring (the whole trajectory is controlled by interpolation — milling, arc welding, painting); speed control of drives is by VFD (AC) or armature-voltage control (DC).

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Sensors and Feedback Devices Sensor Principle and use Potentiometer Resistive track gives an analog voltage proportional to position — simple, limited life LVDT Linear variable differential transformer — non-contact, very accurate displacement measurement, AC output proportional to core movement Incremental encoder Disc with slots gives a train of pulses (A, B quadrature + Z index); measures relative movement and direction; counts are lost on power failure, so a home/reference return is needed at start-up Absolute encoder Coded disc (often Gray code) gives a unique digital word for every position — position is known immediately at power-on; more expensive Resolver / synchro Rotary transformer giving sine/cosine outputs of shaft angle — rugged, suitable for heat, vibration and dirty environments; needs a resolver-to-digital converter Proximity sensors Inductive (metals), capacitive (any material), photoelectric/optical (through-beam, retro-reflective, diffuse), ultrasonic, magnetic reed — non-contact detection of presence Limit switches Mechanical contacts operated by a moving part — end-of-travel and safety interlocks Pneumatic limit valves and back-pressure (air-jet) sensors A 3/2 valve operated by the workpiece, or an air jet whose back pressure rises when the nozzle is blocked/approached — used in pneumatic logic and in explosive or wet environments where electrical sensors are unsuitable Pressure switches Diaphragm/bellows operating a micro-switch at a set pressure — pump and compressor control, safety interlocks Velocity sensors Tachogenerator (DC voltage ∝ speed), encoder pulse frequency, magnetic pick-up Other process sensors Thermocouples and RTDs (temperature), load cells and strain gauges (force/weight), flow meters, level sensors, machine-vision cameras • Decoders and signal conditioning: quadrature decoders convert encoder A/B pulses into counts and direction;

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Gray-to-binary decoders, resolver-to-digital converters, amplifiers, filters and A/D converters prepare signals for the controller; standard industrial signals are 4–20 mA and 0–10 V.

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Actuators and Programmed Control • Electromagnetic actuators: solenoids (short linear stroke — valves, clamps, locks), relays and contactors (switching power circuits), DC and AC motors, stepper motors (rotate a fixed angle per pulse, e.g., 1.8°/step = 200 steps/rev; simple open-loop positioning, but can lose steps under overload) and servo motors (closed-loop with encoder feedback — accurate and powerful); linear motors and voice coils; also hydraulic and pneumatic cylinders and proportional/servo valves. • Programmable Logic Controller (PLC): an industrial computer with a CPU, memory, input and output modules (digital and analog), power supply and communication ports, programmed in ladder logic (also function block, structured text).

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It works on a repeating scan cycle — read inputs → execute the program → update outputs (plus housekeeping).

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Features: timers, counters, maths, PID blocks, rugged construction, easy modification.

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Used for machine and process sequencing, interlocks and safety. • Microcontrollers: a single chip with CPU, RAM/flash, timers, counters, ADC, PWM and digital I/O (8051, PIC, AVR/Arduino, ARM) — embedded control of instruments, small machines, appliances and IoT devices; cheaper but less rugged and less standardised than a PLC. • Supervisory systems:

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SCADA and DCS with HMI screens, alarms, trending and data logging; industrial networks and fieldbuses (Modbus, Profibus, Profinet, Ethernet/IP, CAN, IO-Link); and, in Industry 4.0, IoT sensors, cloud analytics and digital twins.

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Basic CNC System • A CNC machine is a closed-loop programmable positioning system: the part program (G and M codes, from manual programming or CAM) is read by the machine control unit (MCU), which performs interpolation and sends commands to the axis servo drives; encoders/linear scales feed the actual position back for comparison (a simple open-loop CNC uses stepper motors without feedback). • Elements: ball screws with preloaded nuts (no backlash), linear guideways, spindle drive, automatic tool changer, coolant system, limit and home switches, and safety interlocks.

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Control types: point-to-point vs contouring;

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2, 2½, 3 and 5-axis machines;

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DNC and machining centres; adaptive control options. • Advantages and limitations, G/M codes and industrial robotics were covered in Chapter 5.4 — the same control principles apply to robots, CMMs, EDM and laser cutting machines.