Modern Design for Variable Speed Motor-Generators: Asynchronous and Synchronous Electric Machinery Options for Pumped Storage Power Plants SHF - Enhancing Hydropower plants Grenoble, April 9-11, 2014 1
Shaft Power over Speed P shaft Maximum shaft power depending on rotational speed Limitation by stator / rotor / converter currents, voltages (-> field weakening range), torque, transformer power n min ( n sync ) n max 2
Overview Electric Machinery FixSpeed VarSpeed Synchronous Machine with Salient Poles (SYM) as Generators & Motor- Generators Double Fed Induction Machine Stator Fed Synchronous Machine (2 Speed -> Pole Switching Synchronous Machine) 3
Rotor of Synchronous Machine Rotor of Double Fed Induction Machine Variable Speed Motor-Generators Overview Electric Machinery Only Visual Comparison - Not to Scale 4
Overview Electric Machinery Machine: Rotor Pole Synchronous Machine: Salient Pole - Salient Poles - DC Field Winding - Damper Winding - Stacked Pole Body with Solid Endplates Machine: Rotor Pole Pitch Induction Machine: Pole Pitch - No Salient Poles - 3-phase AC Winding - No Damper Winding - Stacked Rotor Body (Silicon Steel Laminates) 5
Synchronous Machine Double Fed Induction Machine Variable Speed Motor-Generators 2D-FEM Calculation Magnetic Induction 6
Overview Electric Machinery Converter Fed Synchronous Machine: P mech S stator S stator-side conv P.F. * S grid-side conv P.F. * S transformer High Voltage Grid Block Transformer Additional transformer may be required for retrofit or special applications DC-Excitation Full Power Converter ~ = DC-Link = ~ Pump- Turbine Grid-Side Converter Unit Stator-Side Converter Unit Synchronous M-G 7
Overview Electric Machinery Sum of stator and rotor branch: - Active Power and - Reactive Power High Voltage Grid Block Transformer AC-Excitation Transformer ~ AC-Excitation System = Grid-Side Converter Unit - Failure Currents - Harmonics (Voltage Waveform) DC-Link = ~ Rotor-Side Converter Unit DFIM Pump- Turbine 8
Example THD Harmonic Distortion THD of the stator voltage at 1.5 Hz rotor fundamental: THD < 0.8% with converter fed rotor for comparison: THD < 0.5% for sinusoidal rotor voltage Rotor (Converter) Voltage Spectrum Stator Voltage Spectrum Rotor fed by converter (clocked voltage source) 9
Major influence on components Double Fed Induction Machine: Grid code requirements rotor-side converter Power factor converter & rotor & stator Time for mode changes rotor & converter voltage Black start capability converter Converter Fed Synchronous Machine: Bypass required? motor-generator Moment of inertia (limiting hydraulic overpressure) motor-generator (number of pole pairs) 10
Efficiency Synchronous Machine with Full Power Converter DF Induction Machine with AC-Excitation System Operation mode : 428.6rpm; 102MW; Total 110MVA, p.f. 0.90; Stator 101MVA, p.f. 1.0 428.6rpm; 102MW; Total 111MVA, p.f. 0.90; Stator 110MVA, p.f. 0.92 Friction losses 480 kw 580 kw No-load losses 210 kw 200 kw Stator I2R losses 210 kw 250 kw ( 98.8 %) ( 98.3 %) Rotor I2R losses 110 kw 390 kw Additional losses 160 kw 300 kw Excit. system losses 20 kw 380 kw (incl. AC-Excitation) Converter losses 1510 kw ( 98.5 %) - Total losses / efficiency 2700 kw / 97.3 % 2100 kw / 97.9 % 11
Ventilation Concept SYM: Axial intake into pole gaps, or radial-radial air-flow DFIM: Radial-radial air-flow Synchronous Machine: Ventilation axial-radial Induction Machine: Ventilation radial-radial 12
Ventilation Concept Verification by CFD Analysis: Air-flow distribution Cooling air velocity Verification of ventilation losses Estimation of heat transfer 13
Ventilation Concept Closed air circulation Self ventilated sliprings plus shaft mounted radial fan Filter and air-water heat exchangers on top Open ventilation concept Self ventilated sliprings Combined system for heated air and carbon dust extraction Air intake Manifold 14
Challenges for the Winding System Clocked voltage with high du/dt C r R _Fe(f) L i(f), L a R (DC) R (f) R _Fe(f) L i(f), L a R (DC) R (f) Additional loading for the corona protection system Capacitive current through the main insulation (-> bearing currents) The standard equivalent circuits do not represent the reaction on high frequency events, such as voltage peaks with high du/dt. 15
Overview Electric Machinery SYM with Converter DF-IM (+) Synchronous machine (-) DF-IM as more complex machine (-) Converter cost for full stator power (+) Converter for rotor power only (-) Efficiency drop due to converter losses (+) Higher efficiency (-) Additional converter power required for power factor regulation (+) Separate active and reactive power control (+) By-pass operation possible (-) Practically converter always in operation (+) Very flexible operation, incl. e.g. high speed power shifts and mode changes. (o) Flexible operation, incl. e.g. high speed power shifts (but limited by the speed range) (+) Very quick startup (pump in water) (-) Startup of pump with runner in air (+) Black-start capability (o) Additional provisions for black-start (+) Retrofit opportunity to speed variable units (-) Complete new rotor plus converter 16
Contact: Ludger Koedding Tel. +49 7321 37-2915 ludger.koedding@voith.com 17
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