Hydropower generation converts mechanical energy from water-driven hydro-turbine rotation into electric energy by synchronous generators. Excitation systems function as the “control heart” of synchronous generators. They regulate DC currents inside excitation windings to control generator-terminal voltages and output reactive-power magnitudes. Operating-condition fluctuations are obvious in hydropower houses: variations of upstream water levels, load increase-decrease transitions and grid-side disturbances plus unit grid-connection and start-stop processes all bring drastic excitation-loop-load changes. Power-house workshops sustain year-round high-humidity and water-vapor-laden conditions; some underground workshops have limited ventilation and equipment readily suffers dew-condensation. Excitation systems adopt thyristor-rectifier schemes. Rectification processes generate massive harmonics and induce equipment-over-heating and current-ripple phenomena. Designed for steady-state power-frequency loads, general-purpose transformers and reactors cannot sustain short-term heavy-overload and large-current-ripple conditions of excitation systems. Under harmonic environments, additional losses surge and temperatures rise sharply. General-purpose products lack sufficient moisture-proof insulation and insulation performance degrades rapidly under water-vapor erosion inside power houses. Once supporting excitation-components fail, generators will suffer loss-of-excitation faults and voltage runaway, forcing units to be disconnected from grids and halting power-supply of hydropower houses. Custom-built for rectification-loop operating-conditions of hydro-turbine-unit excitation systems, special-purpose transformers and reactors for hydropower excitation deliver stable and reliable power-supply assurance for excitation-rectifier units, de-excitation loops and power-regulation units.

Application of Transformers and Reactors in Hydropower-excitation-system Scenarios

1.1 Excitation-specific Rectifier Transformer: Voltage Conversion, Galvanic Isolation and Rectification-excitation-loop Matching

Rectifier transformers for excitation serve as core front-end components of excitation-power units. They convert AC voltages from house-power-supply systems into AC voltages required by excitation-rectifier bridges and provide matched input power for thyristor-rectifier units. Galvanic isolation is realized between high-voltage house-power-supply loops and low-voltage excitation-power loops to block grid-side disturbances and surges from directly impacting excitation-rectifier modules and improve anti-interference capability of excitation systems. Transformer secondary sides mostly adopt multi-phase winding structures cooperating with rectifier bridges to reduce rectifier-output-current ripples and lower harmonic contents of excitation loops. Upon short-circuit faults of excitation loops, transformers possess short-circuit-current-limiting capability and prevent huge fault-currents from burning thyristor power devices directly. During unit grid-connection and sharp-load-rise-drop transitions, stable power is delivered continuously to rectifier units. Excitation-currents can follow changes rapidly to realize precise control of generator-terminal-voltage and reactive-power outputs and satisfy grid-side voltage-regulation requirements for hydropower-house units.

1.2 Excitation-system Input / Series Reactor: Suppress Switch-on Inrush-currents, Limit Short-circuit-currents and Filter Harmonics

Series reactors are deployed at front-ends of excitation-rectifier transformers or on AC sides of thyristors. At moments of unit excitation-initiation and excitation-switch-on, they suppress switch-on inrush-currents effectively and protect thyristor-rectifier components from breakdown by surge-currents. Large-quantity low-order harmonics generated during rectification flow backward into house-power-supply systems and cause house-transformer over-heating and abnormal-meter-measurement. Reactors attenuate harmonics, lower harmonic-distortion-rates of excitation systems and mitigate interference to other automatic-control and protective devices inside power houses. Upon short-circuit faults on excitation sides, reactors rely on inductive characteristics to limit fault-current-rise rates and peak magnitudes, win action time for excitation-protective devices and prevent fault-propagation-expansion. Under grid-voltage-fluctuation and sharp-unit-load-change conditions, they also damp excitation-loop-current oscillations, suppress low-frequency-oscillation risks of generators and improve stable-operation capability between units and power grids.

1.3 Excitation-smoothing Reactor: Smooth DC Excitation-currents, Reduce Current-ripples and Stabilize Excitation-outputs

Smoothing reactors are connected in series inside DC excitation loops after rectifier bridges. DC currents after rectification are not pure-DC but carry obvious ripple-wave components. Ripple-currents will cause excitation-winding over-heating of generators, increased electromagnetic noise and generator-terminal-voltage fluctuations. Relying on inductive energy-storage-release characteristics, smoothing reactors smooth DC excitation-currents greatly and reduce current-ripple-coefficient values, making DC currents flowing into generator-rotor-excitation windings more stable. Stabilized excitation-currents mitigate generator-terminal-voltage fluctuations and improve reactive-power-regulation precision of units. Meanwhile, they lower additional rotor losses induced by current-ripples and reduce temperature-rise of excitation windings. During unit-fault de-excitation processes, smoothing reactors cooperate with de-excitation resistors to suppress over-voltages on rotor loops and protect insulation of generator-rotor windings from breakdown.

Core Advantages of Hydropower-excitation Products versus General-purpose Industrial Products

2.1 Anti-magnetic-saturation Design under Heavy-current Conditions with Excellent Short-term-overload-resistance Performance

Hydropower-excitation systems feature short-term heavy-overload operating-conditions. Excitation-currents may rise sharply within short periods upon unit start-up and fault transient events. Optimized in core-air-gap and magnetic-circuit design, excitation-specific reactors resist magnetic-saturation under heavy-current shocks. Inductance-parameters remain stable and sustain current-limiting, smoothing and damping functions. General-purpose industrial reactors readily saturate under heavy-currents. Inductance decays rapidly and protective effects are lost.

2.2 Low-loss High-magnetic-conductivity Core-material Design Controls Long-term Temperature-rise

Excitation-system units run continuously year-round with strict temperature-rise-control requirements for equipment. Adopting high-grade low-loss silicon-steel sheets and optimized coil-winding layouts, products lower iron loss and copper loss. Temperature-rise remains controllable even under sustained harmonic action. General-purpose transformers and reactors feature large additional losses under harmonic environments and readily exceed temperature-rise thresholds under long-term operation, accelerating insulation aging.

2.3 Moisture-dew-condensation-resistant Insulation-process Adapted to High-humidity-conditions of Hydropower-house Workshops

Ground-floor and underground hydropower-house workshops feature heavy water-vapor and dew-condensation induced by day-night-temperature differences. Coils of products adopt VPI vacuum-pressure integral impregnation processes with moisture- and partial-discharge-resistant insulating materials. Matched with moisture-proof-coating and dew-condensation-resistant structural-design, they possess moisture-proof and mildew-proof capabilities and resist water-vapor erosion inside power houses. Lacking moisture-proof reinforcement, general-purpose industrial products suffer rapid insulation-performance degradation under long-term high-humidity-conditions inside power houses and bring risks of electric-leakage and breakdown.

2.4 Low-vibration Low-noise Structure for Long-term Continuous-operation inside Power-houses

Hydro-turbine operation brings sustained vibration to power-house foundations. Products adopt integral clamping-reinforced structures. Iron cores and coils are tightly fastened with shock-absorbing gaskets to lower electromagnetic-vibration and noise and prevent coil-loosening and insulation-abrasion induced by long-term vibration. Without anti-vibration reinforcement, general-purpose industrial products readily suffer internal-loosening and abnormal-noise faults under long-term vibration.

2.5 High-power-compact-customization Fits Layout Requirements of Excitation-cabinets / Excitation-power-cabinets

Single-unit power-ratings of hydropower-excitation-power-cabinets are high with limited internal cabinet-space. We customize outline-dimensions and winding-capacities according to cabinet drawings from excitation-complete-set OEMs. Volume-size is optimized under premises of guaranteeing electrical-performance indexes to facilitate complete-set-equipment integration and reduce redesign-workloads for excitation-cabinets.

Industry-specific Problems Solved and Application Values

3.1 Mitigate Risks of Large-excitation-rectification-loop-inrush-currents-induced Thyristor-component-damage

Inrush-currents generated upon excitation-switch-on and short-circuit-faults constitute main inducing factors for damage of thyristor power components. Combined solutions of rectifier transformers plus series-reactors limit surge-currents and short-circuit-currents, protect core power components and lower damage probabilities of excitation-power units and reduce power-house-shutdown-repair events. Hydropower-house-unit overhaul windows are precious; reducing fault-shutdown time increases power-generation durations of hydropower houses.

3.2 Resolve Problems of Large-excitation-current-ripple, Harmonic-caused Over-heating and Unit-voltage-oscillation

Rectification-induced harmonics and current-ripples cause excitation-winding over-heating and voltage-instability and may trigger low-frequency-oscillation between units and power grids in severe cases. Cooperatively optimized special-purpose excitation-transformers and smoothing-reactors smooth DC excitation-currents, suppress harmonics and oscillations, improve generator-voltage and reactive-power-regulation precision, guarantee stable unit grid-connection and satisfy power-grid-dispatching-requirements.

3.3 Address Early-stage-insulation-failure Problems of Components under High-humidity-conditions inside Hydropower-houses

General-purpose industrial components cannot adapt to high-humidity and dew-condensation environments inside hydropower houses and feature short insulation service-life. Moisture-proof-insulation-reinforcement techniques combined with anti-vibration structures greatly extend component service life, lower full-lifecycle operation-maintenance costs of excitation systems and guarantee non-stop safe power-generation of hydropower houses year-round.

Satisfying hydropower-excitation-industry standards, our series of special-purpose transformers and reactors for hydropower-excitation have passed temperature-rise tests, short-term-overload tests and vibration tests. They fit small-medium-sized and large-sized hydro-generator-unit excitation complete-set systems and have been widely applied in ground-floor and underground-workshop hydropower-house projects. They deliver reliable power-conversion and stability-governance solutions for excitation-control systems of hydro-power-house units.