Utilization of Electrical Energy

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This section covers the basic photometric quantities used in illumination engineering, the construction and working principle of common lamp types, and the design of indoor and outdoor lighting schemes.

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Basic Photometric Quantities Quantity Definition / Unit Luminous flux (Φ) Total light energy emitted by a source per unit time, as perceived by the human eye; unit: lumen (lm) Luminous intensity (I) Luminous flux emitted per unit solid angle in a given direction; unit: candela (cd) = lm/steradian Illuminance (E) Luminous flux received per unit area of a surface; unit: lux (lx) = lm/m² Luminous efficacy Luminous flux produced per unit electrical power input; unit: lumen per watt (lm/W) — a key figure of merit comparing lamp efficiency Lamp Types:

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Construction & Working Principle Lamp Type Construction & Principle Incandescent lamp A tungsten filament inside an evacuated/inert-gas-filled glass bulb; current heats the filament to incandescence (white-hot), emitting visible light; simple, low cost, very low luminous efficacy (~10–15 lm/W), most energy lost as heat Fluorescent lamp A glass tube containing low-pressure mercury vapor and inert gas, coated internally with phosphor; an electric discharge excites mercury vapor to emit UV radiation, which the phosphor coating converts to visible light; needs a ballast (to limit current) and starter; much higher efficacy than incandescent CFL (Compact Fluorescent Lamp) A miniaturized, folded/spiral fluorescent tube with integrated ballast, designed as a direct replacement for incandescent lamps; same discharge/phosphor principle as a standard fluorescent tube, but compact form factor LED (Light Emitting Diode) lamp A semiconductor p-n junction that emits light directly when forward biased (electroluminescence), as electrons and holes recombine and release energy as photons; highest luminous efficacy of common lamp types, very long life, low heat generation, instant-on with no warm-up Indoor & Outdoor Lighting Schemes Indoor lighting schemes (e.g. direct, semi-direct, indirect, semi-indirect, general diffusing) are classified by how much luminous flux is directed downward (toward the working plane) versus upward (toward the ceiling for reflected/diffused light), balancing glare control, uniformity, and shadow reduction.

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Outdoor lighting schemes (street lighting, floodlighting, area lighting) require luminaire placement, mounting height, and spacing chosen to achieve uniform illuminance on the target area while minimizing glare to road users and limiting stray/wasted light (light pollution).

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Lighting design for both indoor and outdoor applications considers the required illuminance level (lux) for the task, uniformity of illumination, glare control, and energy efficiency (favoring high-efficacy sources such as LED).

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This section covers electrical drawing conventions, the estimation and costing process for building and industrial electrical installations, and the relevant national codes and standards governing such work in Nepal.

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Electrical Drawing An electrical drawing (layout plan) shows the physical location of outlets, switches, distribution boards, wiring runs, and equipment on a building floor plan, using standardized symbols so the design can be interpreted consistently by installers and inspectors.

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Drawings typically include a single-line (schematic) diagram showing the electrical distribution hierarchy (incoming supply, main panel, sub-panels, circuits) separately from the physical layout, to clarify circuit protection, ratings, and connections.

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Estimation & Costing Estimation is the process of calculating, from the approved drawings, the quantities of materials (cable length, conductor size, switches, luminaires, distribution boards, conduit, accessories) and labor required to complete an electrical installation.

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Costing applies unit rates (material cost + labor cost, often from a standard schedule of rates) to the estimated quantities to arrive at the total project cost, which forms the basis for budgeting, tendering, and contractor payment.

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Estimation and costing must account for the load calculation (connected load, demand factor) driving conductor/protection sizing, as well as contingencies, overheads, and applicable taxes/duties.

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National Building Code & National Electricity Standards The National Building Code (NBC) of Nepal sets out minimum requirements for structural safety, fire safety, and building services (including electrical installations) that must be followed for buildings constructed in Nepal.

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National electricity standards and codes (covering wiring practices, earthing, protection, and installation safety) establish the minimum technical requirements that electrical designs, estimation, and installation work must comply with to ensure safety and reliability, and are referenced alongside the NBC during design approval and inspection.

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This section covers the types and structure of electricity tariffs, tariff schemes applied in Nepal, and the regulatory framework (Acts and Regulations) governing electricity supply and tariff-setting.

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Types of Tariffs Tariff Type Structure Flat rate tariff A single fixed rate per unit (kWh) consumed, regardless of time of use or demand — simple to administer but doesn't reflect the utility's actual cost structure Two-part tariff Combines a fixed charge (based on connected load/demand, covering fixed costs) with a running/energy charge (per kWh consumed, covering variable costs) — more accurately reflects the cost of supply Block (tiered/slab) tariff Energy charge per kWh increases (or decreases) in defined consumption blocks/slabs — commonly increasing-block tariffs are used to encourage conservation among higher- consumption residential customers Time-of-day (ToD) / Time-of-use (ToU) tariff Energy charge varies by time period (peak, off-peak, shoulder hours) to reflect the varying cost of supply and to incentivize shifting load away from system peak demand periods Demand tariff Charge based primarily on the customer's maximum demand (kW/kVA), typically applied to larger industrial/commercial consumers, often combined with an energy charge Tariff Schemes in Nepal Nepal's electricity tariff structure is generally organized by consumer category (domestic, industrial, commercial, irrigation/agricultural, and bulk/others), with domestic tariffs commonly structured as increasing-block (slab) rates to promote conservation among low-consumption households while moderating cost impact on essential use.

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Industrial and larger commercial consumers are typically billed on a two-part (demand + energy) tariff, reflecting both the capacity reserved for them and the energy actually consumed.

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Electricity tariffs in Nepal are set/approved by the sector regulator, with periodic review reflecting generation, transmission, and distribution cost changes.

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Nepal Electricity Regulations and Acts The legal and regulatory framework for Nepal's electricity sector includes the governing Electricity Act and associated Electricity Rules/Regulations, which establish licensing requirements for generation/transmission/distribution, safety and technical standards, and the basis for tariff regulation.

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A dedicated electricity regulatory body oversees tariff-setting, licensing, and enforcement of technical/safety standards, aiming to balance consumer protection with the financial viability of utilities and independent power producers.

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This section covers the classification of electric drives and the principles of motor sizing based on load power and torque requirements.

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Types of Electric Drives Drive Type Description Group drive A single motor drives multiple machines/loads via a common shaft and belts/pulleys; low cost but inflexible, one motor failure stops all connected machines, largely obsolete Individual drive A separate motor is dedicated to each machine/load; provides independent control and higher reliability (failure of one motor affects only its machine), the dominant modern approach Multi-motor drive Multiple motors are used within a single machine/process, each driving a different part/function (e.g. separate motors for different rolls in a rolling mill), allowing independent control of each part Electric drives can also be classified by control method: constant speed drives (fixed speed, e.g. simple induction motor drives) versus variable speed drives (speed adjustable via methods such as variable frequency drives/VFDs, providing energy savings and process flexibility).

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Power & Torque Calculation Motor power rating selection begins from the load's power requirement, accounting for the duty cycle (continuous, short-time, or intermittent duty) since a motor can often be rated lower for intermittent/short- time duty than for continuous duty at the same peak load.

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The fundamental relationship between mechanical power, torque, and speed is P = T × ω (P in watts, T in newton-metres, ω in rad/s), or equivalently P = 2πNT/60 with N in rpm — used to determine the required torque at the motor's rated speed for a given power demand, or vice versa.

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Motor selection must also verify adequate starting torque (to accelerate the load from rest, especially for high-inertia or high-starting-torque loads such as conveyors or compressors), acceptable starting current (to avoid excessive line disturbance/voltage dip), and suitability for the load's speed-torque characteristic (e.g. constant torque, constant power, or variable torque loads such as fans/pumps).

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A safety/service factor margin above the calculated running power requirement is typically applied when selecting the final motor rating, to accommodate load variation, voltage fluctuation, and aging.

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This section covers the principal types and applications of electric heating, along with general measures for electrical energy conservation.

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Types of Electric Heating & Application Heating Type Principle & Application Resistance heating Current passed through a resistive element (e.g. nichrome wire) generates heat (I²R loss); used in heaters, ovens, electric irons, water heaters — simple, low cost, widely used for domestic/general industrial heating Induction heating An alternating magnetic field induces eddy currents (and, for magnetic materials, hysteresis losses) directly within an electrically conductive workpiece, heating it internally without direct contact; used for melting metals, surface hardening, and industrial forging preheat Dielectric heating A high-frequency alternating electric field is applied across a non-conductive (dielectric) material, causing molecular friction/polarization losses that heat the material internally and uniformly; used for drying/curing non-metallic materials (wood, plastics, textiles, food) Arc heating Heat is generated by an electric arc struck between electrodes (or electrode and workpiece); used in arc welding and electric arc furnaces for melting metal (e.g. steel-making) Infrared heating Radiant infrared energy from a heated element or lamp directly heats the surface of the target material by radiation; used for paint drying, food processing, and surface curing Electrical Energy Conservation Measures Energy-efficient equipment: replacing inefficient devices (e.g. incandescent lamps with LEDs, standard motors with high-efficiency motors) reduces energy consumption for the same output/service level.

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Power factor correction (via capacitor banks) reduces reactive current drawn from the source, lowering I²R losses in supply conductors/transformers.

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Load management/scheduling: shifting non-critical loads away from peak demand periods reduces peak demand charges and overall system stress, while variable-speed drives match motor output to actual load requirement rather than running at fixed full speed.

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Improved insulation and heat recovery in heating/cooling applications reduces wasted energy, and regular maintenance (e.g. keeping motor bearings lubricated, avoiding voltage imbalance) sustains equipment efficiency over its service life.

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This final section of the chapter covers the types of electric traction systems, the motor types used, and the methods of starting and speed control applied to tramways, trolley buses, electric trains, and elevators.

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Types of Electric Traction System Description Tramway Rail-guided electric vehicles operating on city streets, typically powered from an overhead line via a trolley pole/pantograph, sharing the road with other traffic Trolley bus Rubber-tired electric bus drawing power from twin overhead wires via trolley poles, offering road flexibility (not rail-constrained) combined with electric traction's quiet, emission-free operation Electric train / railway traction Rail vehicles powered from an overhead catenary line or a third rail, used for suburban, mainline, and high-speed rail; may use DC or AC traction supply depending on the system Elevator (lift) traction A specialized vertical traction application using an electric motor (often with a counterweight system) to raise/lower a cab within a building shaft Motors Used for Electric Traction The DC series motor was traditionally favored for traction because of its high starting torque (torque roughly proportional to current squared at low speed) and its natural tendency to slow down as load/torque increases, well suited to the varying tractive-effort demands of starting, hill-climbing, and acceleration.

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Modern traction systems increasingly use three-phase induction motors (fed via variable-frequency inverter drives) or synchronous motors, offering higher efficiency, lower maintenance (no commutator/brushes), and precise electronic speed/torque control compared to traditional DC traction motors.

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Starting & Speed Control Traditional DC traction speed control methods include series-parallel control (reconfiguring motors between series and parallel connection to change the effective voltage per motor) and rheostatic (resistance) control (inserting/removing series resistance to vary motor terminal voltage/current), both largely superseded by modern power-electronic methods.

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Modern traction drives predominantly use chopper control (DC-DC converter varying the effective voltage applied to a DC traction motor by rapid switching) or variable-voltage variable-frequency (VVVF) inverter control (for induction/synchronous traction motors), both offering smoother, more efficient, and more precisely controllable starting and speed regulation than resistance-based methods, along with regenerative braking capability (returning braking energy to the supply).

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Elevator starting and speed control historically used DC motor drives or AC motors with mechanical gearing; modern elevators commonly use gearless permanent-magnet synchronous motors with VVVF drives, providing smooth acceleration/deceleration, precise floor-leveling, and energy-efficient operation.