Modern Design for Variable Speed Motor-Generators · 7 Converter Fed Synchronous Machine: P mech...

1 Modern Design for Variable Speed Motor Generators | SHF 2014 | Ludger Koedding | 2014-04-10

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


|Pshaft|

( nsync ) nmax nmin

• Maximum shaft

power depending

on rotational speed

• Limitation by stator

/ rotor / converter

currents, voltages

(-> field weakening

range), torque,

transformer power

Variable Speed Motor-Generators

Shaft Power over Speed


FixSpeed

• Synchronous Machine

with Salient Poles (SYM)

as Generators & Motor-

Generators

• (2 Speed -> Pole Switching

Synchronous Machine)

• Stator Fed Synchronous

Machine

• Double Fed Induction

Machine

VarSpeed


Overview Electric Machinery


Only Visual Comparison - Not to Scale

Ro

tor

of S

yn

ch

ron

ou

s M

ach

ine

Ro

tor

of D

ou

ble

Fe

d In

du

ctio

n

Ma

ch

ine




Synchronous Machine: Rotor Pole

- Salient Poles

- DC Field Winding

- Damper Winding

- Stacked Pole Body with Solid Endplates

Induction Machine: Rotor Pole Pitch

- No Salient Poles

- 3-phase AC Winding

- No Damper Winding

- Stacked Rotor Body (Silicon Steel Laminates)

Synchronous Machine: Salient Pole Induction Machine: Pole Pitch




Synchro

nous M

achin

e

Double

Fed I

nduction M

achin

e


2D-FEM Calculation Magnetic Induction

7

Converter Fed Synchronous Machine:

Pmech ≈ Sstator ≈ Sstator-side conv ≈ P.F. * Sgrid-side conv ≈ P.F. * Stransformer

Modern Design for Variable Speed Motor Generators | SHF 2014 | Ludger Koedding | 2014-04-10

Synchronous

M-G

~

= DC-Link

Stator-Side Converter

Unit Grid-Side Converter

Unit

Block Transformer

High Voltage Grid

~

=

Full Power Converter

Pump-

Turbine

DC-Excitation

Additional transformer may

be required for retrofit or

special applications



8

DFIM

Pump-

Turbine

AC-Excitation System Block Transformer

High Voltage Grid

~

= DC-Link

Rotor-Side

Converter Unit Grid-Side

Converter Unit

~

=

AC-Excitation

Transformer


Sum of stator and rotor branch: - Active Power and

- Reactive Power

- Failure Currents

- Harmonics (Voltage Waveform)




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)


Example THD


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)


Major influence on components


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

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 %

(≈ 98.8 %) (≈ 98.3 %)


Efficiency

12 Synchronous Machine: Ventilation axial-radial

• axial air intake into the pole gaps

or radial-radial possible.

Induction Machine: Ventilation radial-radial

• air intake into the rotor hub.

SYM: Axial intake into pole gaps, or

radial-radial air-flow DFIM: Radial-radial air-flow


Ventilation Concept



Verification by CFD Analysis:

• Air-flow distribution

• Cooling air velocity

• Verification of ventilation losses

• Estimation of heat transfer


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


Ventilation Concept


• Clocked voltage with high dU/dt

• 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.

R‘(f)

R‘(DC)

L‘i(f), L‘a

R‘_Fe(f)

C‘r

R‘(DC)

R‘(f)

L‘i(f), L‘a

R‘_Fe(f)


Challenges for the Winding System


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




Contact:

Ludger Koedding

Tel. +49 7321 37-2915

[email protected]


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Modern Design for Variable Speed Motor-Generators · 7 Converter Fed Synchronous Machine: P mech...

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