Transcript 投影片 1

Shaft Generators
and Ship Electric Power Quality
軸電機與船舶電力品質
Chun-Lien Su
Power System Lab,
National Kaohsiung Marine University, Kaohsiung, TAIWAN
Department of Marine Engineering, National Kaohsiung Marine University
1
Outline









What is Shaft Generator?
What are some Shaft Generator Operation concerns?
What is Power Quality (PQ)?
What is Harmonic and what causes them?
What effects do Harmonics have on a building power system
and components?
How can Harmonics Issues be mitigated?
Power Quality evaluation process
R&D Recommendations for CSEC
Questions
Department of Marine Engineering, National Kaohsiung Marine University
2
What is Shaft Generator?
• Shaft generators are often used in combination with diesel
engines rotating the ship propeller for generating power on
ships.
• They can produce significant amounts of electric energy (for
instance in certain cases, one shaft generator can cover the
energy demands of the entire ship without associating with
generator sets) by using a part of the power produced by the
diesel engines.
• They can operate with non-expensive heavy fuel oil providing
huge amounts of energy, it is possible to reduce fuel and
operation costs.
Department of Marine Engineering, National Kaohsiung Marine University
3
What is main problem for Shaft
Generator ?
np
f 
120
E eff  4.44fnp 
• The main problem is that when the ship makes a voyage,
the speed of the diesel engine which is the main propulsion
engine can vary within a wide range, so the output
frequency of the shaft system is often not constant and
consequently the output voltage that significantly depends
on the frequency is also inconstant.
Department of Marine Engineering, National Kaohsiung Marine University
4
Shaft Generator Speed Control
• Fixed speed control (indirect driven)
– Gear box or pitch control is required
– Fixed-speed shaft generator system includes
• Asynchronous squirrel cage induction generator
• Capacitor bank for reactive power compensation
• Variable speed control (direct driven)
– Variable speed with partial scale frequency converter
• Doubly fed induction generator (DFIG) concept (WRIG)
• -40% to +30% of synchronous speed
• Partial scale frequency converter performs the reactive power
compensation
– Variable speed with full-scale frequency converter
• Wound rotor synchronous generator (WRSG) or WRIG or permanent
magnet synchronous generator (PMSG)
• No gear box or pitch control
• Multi-pole generator with a large diameter
• Frequency converter performs the reactive power compensation
Department of Marine Engineering, National Kaohsiung Marine University
5
Fixed Speed Shaft Generator
propeller
Gearbox
Squirrel
cage
induction
generator
MSB
US
IS
Compensating
capacitors
Department of Marine Engineering, National Kaohsiung Marine University
6
Variable Speed Shaft Generator (I)
Doubly fed
(wound rotor)
induction
generator
propeller
Gearbox
MSB
US
IS
Ur
Converter
Ir
Ic
Department of Marine Engineering, National Kaohsiung Marine University
7
Variable Speed Shaft Generator (II)
propeller
Direct-drive
synchronous
generator
US
IS Converter Uc
MSB
Ic
Department of Marine Engineering, National Kaohsiung Marine University
8
Shaft System Operation Concerns
• Voltage waveform distortion due to power electronics
– Harmonics
– Notching
• Voltage and frequency variations due to shaft system operation
(transient response)
–
–
–
–
Frequency converter system control
Reactive power and voltage controls with synchronous condenser
System starting and stopping controls
Power transfer between generators
Department of Marine Engineering, National Kaohsiung Marine University
9
Power Quality Overview
Department of Marine Engineering, National Kaohsiung Marine University
10
Categories and Characteristics of PQ
Power System
Electromagnetic
Phenomena (IEC)
Department of Marine Engineering, National Kaohsiung Marine University
11
Power Event Classification (IEEE 1159)
RMS Variations
Department of Marine Engineering, National Kaohsiung Marine University
12
Power Event Classification (IEEE 1159)
Waveform Distortions
Department of Marine Engineering, National Kaohsiung Marine University
13
Computer Equipment Disturbance Table
(Dranetz-BMI Field
handbook for PQ Analysis)
Department of Marine Engineering, National Kaohsiung Marine University
14
Current Shaft Generator System Scheme
Department of Marine Engineering, National Kaohsiung Marine University
15
Equivalent Circuit of the Shaft
Generator System
Department of Marine Engineering, National Kaohsiung Marine University
16
Output Voltage Waveform
for Shaft System
Department of Marine Engineering, National Kaohsiung Marine University
17
THD under Different Shaft Speeds
Department of Marine Engineering, National Kaohsiung Marine University
18
What is Harmonic?
• “A component frequency of a harmonic motion of
an electromagnetic wave that is an integral multiple
of the fundamental frequency”
• The fundamental frequency is 60 Hertz
– 3rd Harmonic is 3 x 60Hz or 180Hz
– 5th Harmonic is 5 x 60Hz or 300Hz, etc.
Department of Marine Engineering, National Kaohsiung Marine University
19
What Causes Harmonics?
Non-Linear Loads
– Current is not proportional to the applied
voltage
Department of Marine Engineering, National Kaohsiung Marine University
20
Linear Loads and Current Waveforms
Linear loads and current waveforms.
Pure resistance, inductance, and capacitance
are all linear.
What that means:
If a sine wave voltage of a certain magnitude
is placed across a circuit containing pure
resistance, the current in the circuit follows
Ohm's Law: I = E ÷ R.
So, for a specific value of ohms, the
relationship of volts and amperes is a straight
line. The current will always be a sine wave
of the same frequency.
Linear Loads include Incandescent lighting
and heating loads.
Department of Marine Engineering, National Kaohsiung Marine University
21
Non-linear Loads and Current Waveforms
Nonlinear loads and current waveforms.
Solid state electronics is based on the use of
semiconductors. These materials are totally
different in that their response to voltage is not
a straight line.
What this means:
With a nonlinear load, you cannot easily predict
the relationship between voltage and current —
unless you have an exact curve for each device.
With equipment containing many solid-state
devices, such an approach is impossible.
Nonlinear loads are switched on for only part of
the cycle, as in a thyristor-controlled circuit, or
pulsed, as in a controlled-rectifier circuit.
Non-linear loads with high harmonic pollution
E.g. drives, UPS’s, welders, PCs, luorescent
lighting systems, …
Department of Marine Engineering, National Kaohsiung Marine University
22
Effect of Harmonics on Waveform
180 Out
of Phase
In
Phase
When a waveform is identical from one waveform to the next, it can be represented as
a sum of pure sine waves in which the frequency of each sinusoid is an integer
multiple of the fundamental frequency of the distorted wave.
The sum of the sinusoids created by harmonics can be analyzed using the
Fourier series concept.
Department of Marine Engineering, National Kaohsiung Marine University
23
What do harmonics do?
•Increased losses in system (R.Irms2 = R . I12 + R . Ih2)
•Tripping of circuit breakers and other protective devices
-Increase of RMS Thermally
-Increase of peak Magnetically
•Motor problems
-Additional losses in windings & iron (RMS increase & skin effect)
-Perturbing torques on shaft (negative phase sequence harmonics)
Department of Marine Engineering, National Kaohsiung Marine University
24
What do harmonics do? (cont)
• Communication Problems
– If sharing common parallel path, potential for harmonics to have
inductive coupling effect on unshielded cabling
• Current Measurement Problems (distorted waveform)
• Unreliable Operation of Electronic Equipment
– Mis-operation of electronic equipment that measures frequency or
uses the zero crossing point of a sine wave.
• Control of Speed and Voltage Problems on Emergency
Generators (supplying power)
• Capacitor Bank Application Problems (heating)
• Computer (PC/CPU) data errors / data loss
– Affects power supplies and sensitive electronics
Department of Marine Engineering, National Kaohsiung Marine University
25
What do harmonics do? (cont)
• Excessive neutral current
– Mainly zero phase sequence harmonics (e.g. H3 phase-neutral)
• Distorted currents from harmonic-producing loads also distort
the voltage as they pass through the system impedance.
Therefore, a distorted voltage can be presented to other bus
bars on the system.
• Overall electrical system and power quality is affected by the
introduction of harmonics.
Department of Marine Engineering, National Kaohsiung Marine University
26
Sources of Harmonics
• Solid State Electronic Devices which contain a poor
power supply
– Computers (PCs/CPUs)
– Laser Printers
– Copy Machines
• Solid State UPS Units
• Solid State Devices (Fluorescent lighting ballasts)
• Rectifiers (AC-DC Converters  VFDs)
• Welding Units
• Arc Furnaces
Department of Marine Engineering, National Kaohsiung Marine University
27
Order of Typical Harmonics
Generated by Non-linear Loads
Department of Marine Engineering, National Kaohsiung Marine University
28
How can Harmonics be Reduced?
• Isolating harmonic loads on separate circuits (with
or without harmonic filters)
• Harmonic mitigating transformers
• Phase shifting (zig-zag) transformers
– Used to cancel out specific harmonics by making one
voltage circuit 180 degrees out-of-phase
• Filter capacitor backs
Department of Marine Engineering, National Kaohsiung Marine University
29
How can Harmonics be Reduced? (cont)
• For VFD and UPS specifically:
–
–
–
–
–
–
Line Reactors
K-Rated / Drive Isolation Transformers
Harmonic Mitigating / Phase Shifting Transformers
High order pulse Converters, e.g. 12, 18 or 24
Passive parallel / series tuned Filters
Active Filters
Department of Marine Engineering, National Kaohsiung Marine University
30
How can Harmonics be Reduced? (cont)
• Proper Grounding
– Neutral to ground conductor connection at one location;
at main panel or transformer secondary
• When neutral is connected to ground at multiple locations,
interference can occur with sensitive electronic devices.
– Run power and control conductors in separate raceways
– Sensitive loads should not share neutral and ground
conductors.
– Avoid using conduit as the ground return path, run
dedicated ground wire with circuit conductors
– Refer to IEEE Std 1100-1992 (Emerald Book)
Department of Marine Engineering, National Kaohsiung Marine University
31
Computer Equipment Grounding
TOP  Radial or “daisy
chain” grounding Although
Code compliant per NEC,
small
differences
in
potential
can
cause
unintended ground loops
BOTTOM  Best method
for grounding is via
dedicated
equipment
grounding
conductors
back to the source
Department of Marine Engineering, National Kaohsiung Marine University
32
IEEE Defined Harmonic Current Limits
Department of Marine Engineering, National Kaohsiung Marine University
33
Voltage Limit /Harmonics Evaluation
Procedure
Department of Marine Engineering, National Kaohsiung Marine University
34
Typical PQ Evaluation Process
Department of Marine Engineering, National Kaohsiung Marine University
35
R&D Recommendations for CSEC
•Power quality monitoring for ships with shaft generator
•Harmonics analysis and mitigation for CSEC ships
•Voltage spike analysis and mitigation for CSEC ships
•Optimal reactive power and voltage controls of ship power
system with shaft generator
•Others
Department of Marine Engineering, National Kaohsiung Marine University
36
Questions?
Thank You!
Power System Lab. at NKMU
Chun-Lien Su (蘇俊連)
07-8100888ext.5226 [email protected]
Department of Marine Engineering, National Kaohsiung Marine University
37