Power Plants Engineering

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This section covers the classification and layout of hydroelectric power plants, site selection criteria, the major types of water turbines and their applications, turbine governing, and the auxiliary systems that support hydro- plant operation.

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Classification & Layout Classification Basis Types Head available Low head (<30 m, high flow, e.g.

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Kaplan turbines), medium head (30-300 m, e.g.

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Francis), high head (>300 m, e.g.

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Pelton) Water flow/storage Run-of-river (little/no storage, depends on natural river flow), storage (reservoir) type (dam impounds water for regulated release), pumped storage (water pumped back to upper reservoir during off-peak for later regeneration) Load served Base load plants (continuous, steady output) and peak load plants (quick-starting, meet demand peaks, often pondage/pumped-storage type) A typical layout comprises: intake → headrace (canal/tunnel carrying water to the forebay) → forebay/surge tank (absorbs pressure surges from load changes) → penstock (pressure pipe delivering water to the turbine) → powerhouse (turbine-generator units) → tailrace (returns water to the river downstream).

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Site Selection Key considerations: adequate and dependable water supply/head, suitable geology/foundation conditions for dam and powerhouse, minimal environmental/social/resettlement impact, reasonable access for construction and transmission, and economic proximity to load centers.

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Water Turbines Turbine Type & Application Pelton wheel Impulse turbine; used for high head (>300 m), low flow sites; water strikes spoon-shaped buckets via one or more jets at atmospheric pressure Francis turbine Reaction turbine; used for medium head (30-300 m), medium-high flow sites; most widely used turbine type worldwide, water flows radially inward through guide vanes onto the runner Kaplan turbine Reaction turbine (propeller-type with adjustable blades); used for low head (<30 m), high flow sites; blade pitch can be varied for efficiency across a range of flows Governing & Hydro-Plant Auxiliaries Governing of water turbines: a governor automatically regulates water flow to the turbine (via guide vanes/needle valves) to maintain constant speed (and hence frequency) as electrical load varies, preventing over-speed on sudden load rejection.

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Hydro-plant auxiliaries include: cooling water systems, drainage and dewatering pumps, compressed air systems (for braking/governor operation), lubrication systems, cranes for maintenance, and protection/control equipment.

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This section covers site selection criteria for diesel electric power plants and the essential elements/layout of a diesel plant.

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Site Selection Key considerations include: proximity to the load center (to minimize transmission cost, since diesel plants are often used for standby/peaking/isolated supply), availability of fuel supply and access for transportation/storage, availability of water for cooling, adequate space for plant and fuel storage, and environmental considerations (noise, exhaust emissions).

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Elements of a Diesel Plant & Layout Element Function Diesel engine The prime mover; converts the chemical energy of fuel into mechanical (rotational) energy via internal combustion Fuel supply system Storage tanks, fuel transfer pumps, filters, and day tank supplying clean fuel to the engine Air intake & exhaust system Supplies filtered combustion air to the engine and safely discharges exhaust gases (often via a silencer/muffler) Cooling system Removes heat from the engine (water-cooled with radiator/cooling tower, or air-cooled for smaller units) to prevent overheating Lubrication system Supplies oil to reduce friction/wear between moving engine parts and assists in cooling and cleaning Starting system Starts the engine (compressed air, electric starter motor, or hydraulic starting, depending on engine size) Governor Regulates fuel injection to maintain constant engine speed as electrical load varies Generator Coupled to the diesel engine shaft; converts the mechanical rotational energy into electrical energy Diesel plants are relatively quick to start and have low capital cost per kW for small capacities, but have relatively high running (fuel) cost, making them suited to standby, peaking, or isolated/off-grid supply rather than continuous base-load generation.

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This section covers the principles and key components of solar and wind power generation, two of the most widely deployed non-conventional (renewable) power generation technologies.

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Solar Power Generation Technology Principle Solar Photovoltaic (PV) Converts sunlight directly into DC electricity via the photovoltaic effect in semiconductor (typically silicon) solar cells;

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DC output is converted to AC via an inverter for grid connection or AC loads Solar thermal (Concentrated Solar Power, CSP) Uses mirrors/lenses to concentrate sunlight to heat a working fluid, producing steam that drives a conventional turbine-generator Key PV system components: solar panel/array (PV cells), charge controller (regulates charging of batteries in off-grid systems, prevents overcharge/deep discharge), inverter (DC to AC conversion), and (for off-grid/hybrid systems) a battery bank for storage.

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Solar output is intermittent (dependent on sunlight/weather/time of day) and requires either storage or backup/grid support for continuous supply; output is characterized by capacity factor typically lower than conventional thermal/hydro plants.

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Wind Power Generation A wind turbine converts the kinetic energy of moving air into mechanical rotational energy via aerodynamic blades, which drives a generator (directly or through a gearbox) to produce electricity.

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Wind power output is proportional to the cube of wind speed (P∝v³), making site selection (consistent, adequate wind speed) critical to economic viability.

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Like solar, wind generation is intermittent/variable, requiring grid flexibility, storage, or backup generation to maintain reliable supply; a pitch control and/or yaw control mechanism optimizes blade angle and orientation relative to wind direction for maximum/safe energy capture.

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This section covers major grid-scale energy storage technologies: pumped storage plants, battery energy storage, compressed air energy storage, and flywheel storage.

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Energy Storage Technologies Technology Principle & Characteristics Pumped Storage Plants (PSP) Water is pumped from a lower to an upper reservoir during off-peak/low-cost periods, then released through turbines to generate electricity during peak demand; large capacity, long duration, mature and widely deployed technology, but requires suitable topography (two reservoirs at different elevations) Battery Energy Storage System (BESS) Stores electrical energy electrochemically (e.g. lithium-ion, lead-acid, flow batteries); fast response (near-instantaneous), modular and scalable, siting-flexible, increasingly used for grid frequency regulation and renewable integration; duration/capacity limited by battery size and cost Compressed Air Energy Storage (CAES) Uses off-peak/surplus electricity to compress and store air (e.g. in underground caverns); air is later released, heated, and expanded through a turbine to generate electricity; suitable for large-scale, long-duration storage but requires suitable geological formations Flywheel Storage Stores energy as kinetic energy in a rapidly rotating mass; very fast response and high power density, but relatively short storage duration — suited to short-term applications like frequency regulation and power quality support rather than long-duration bulk storage Comparative Notes Storage technologies are generally compared on: response time (how quickly they can deliver/absorb power), energy vs power density (how much energy vs how much instantaneous power they can provide), storage duration (how long they can sustain output), and round-trip efficiency (ratio of energy delivered to energy input).

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Pumped storage and CAES suit large-scale, long-duration bulk energy storage; batteries suit medium- scale, fast-response applications and renewable integration; flywheels suit very fast, short-duration power quality/frequency regulation applications.

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This section covers the excitation systems used to supply DC field current to synchronous generators in power stations, and the construction and operation of the Automatic Voltage Regulator (AVR) that controls them.

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Types of Excitation Systems Excitation Type Description DC excitation system A separate DC generator (exciter), often mounted on the same shaft as the main generator, supplies field current via slip rings and brushes; simple but limited response speed and requires brush maintenance AC excitation system An AC exciter (a small alternator) generates AC, which is rectified (via diodes/rotating rectifiers) to DC before being supplied to the main field winding Static excitation system Field current is derived directly from the generator's own output terminals (or an auxiliary source), rectified by static (thyristor-based) power electronic converters, and fed to the field winding via slip rings; offers fast response and precise control Brushless excitation system A rotating AC exciter armature (on the same shaft as the main rotor) and a rotating rectifier assembly supply DC directly to the field winding, eliminating slip rings and brushes entirely — reduces maintenance and eliminates brush-related faults Automatic Voltage Regulator (AVR) Construction: an AVR comprises a voltage sensing/measuring circuit (compares actual generator terminal voltage to a reference setpoint), an error amplifier/comparator, and a control output stage that adjusts the exciter's field current (and hence the main generator's field current and terminal voltage).

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Operation: the AVR continuously monitors generator terminal voltage; if it deviates from the setpoint (due to load changes), the AVR adjusts the exciter output to increase or decrease the main field current, restoring terminal voltage to the desired level — a closed-loop (negative feedback) control system.

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AVRs also typically incorporate protective/limiting functions, such as over-excitation limiting (protects the field winding from thermal damage) and under-excitation limiting (prevents loss of synchronism/instability from insufficient excitation).

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This final section of the chapter covers the prerequisites for starting generators in hydro and diesel power stations, and the concept and role of black start units in power system restoration.

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Prerequisites for Starting Generators Station Type Key Starting Prerequisites Hydro station Adequate water availability/head; governor and control systems operational; cooling/lubrication systems ready; unit isolated/de-energized checks complete; excitation system ready; protection relays in service; auxiliary power supply available (for gates, controls, lubrication pumps) Diesel station Adequate fuel supply and correct fuel quality; lubrication oil at correct level/pressure; cooling system ready; battery/starting system charged and functional; auxiliary systems (air intake, exhaust) clear; governor and protection systems operational In both cases, after the prime mover reaches rated speed and the AVR brings terminal voltage to rated value, the generator must be synchronized (matching voltage, frequency, phase sequence, and phase angle) before being connected to the grid/bus.

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Black Start Units A black start is the process of restoring a power station/grid to operation after a total shutdown (blackout) without relying on the external transmission network for initial power — since a normal station typically needs grid power for its own auxiliaries (pumps, controls, lubrication) to start up.

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A black start unit is a generating unit capable of starting independently, without external electrical supply (e.g. using its own battery/diesel-generator-based auxiliary power, or a small hydro unit with gravity-fed systems), and is then used to energize the auxiliary systems of larger units and progressively restore the grid.

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Common black start units include small diesel generators, gas turbines (which can start on their own battery/air-start systems), and certain hydro units with minimal auxiliary power requirements; they play a critical role in power system restoration strategies following a major blackout.