Transcript WG A1.38 Tutorial

STUDY COMMITTEE A1- ROTATING ELECTRICAL MACHINES
WG A1.38 - Guide for Generator On-Line Over and Under
Excitation Operation Issues
Rodica Zlatanovici (Romania), Convener
xxxxx. Paris xxxx
WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
AGENDA
1. INTRODUCTION
2. GENERATOR CAPABILITY CHART (PQ DIAGRAM)
3. ELECTROMAGNETIC PHENOMENA AT FRONTAL
ZONE OF GENERATORS
4. GENERATOR OPERATION IN OVER AND UNDER
EXCITED REGIMES
5. CONCLUSIONS
AGENDA
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
1- INTRODUCTION
- EXTENSION OF WG A1.01.22 – GUIDE FOR THE PREVENTION
OF OVERFLUXING OF GENERATORS ( 2011 ) – during the run-up
- TERMS OF REFERENCE:
GOAL:
To present the mode of utilization of the electric generators
for voltage control in the electrical grid where they are
connected .
CONTENT OF THE REPORT:
Includes information gained from responses to a
Questionnaire on this topic sent out to the National
Committees of CIGRE in 2013, and to all members and
experts SCA1.
REPORT UTILITY:
Practical and theoretical aspects of operation in
inductive and capacitive regimes.
1 - INTRODUCTION
MEMBERS 14
(10 countries)
Pinto Cajetan
IN
Remi Tremblay
CA
Wang Bo
CN
Pu Jun
CN
Juergen Weidner
DE
Martin Stronge
EI
Jun Matsumoto
JP
Kenji Tanaka
JP
Dan Zlatanovici
RO
Cristinel Cicirone
RO
Rodica Zlatanovici
RO
Aalvik Geir
NO
Oscar Martinez
SP
Jim Edmonds
US
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
2 - GENERATOR CAPABILITY CHART (PQ DIAGRAM)
The PQ active – reactive power diagram of the synchronous generators is
a synthetic diagram that delimits the admissible operational field of the generators,
based on considerations related to the heating of the active parts and on the static
stability considerations.
2.1. Theoretical PQ Diagram is valid for the rated values of the:
 active power,
 voltage at the generator terminals,
 stator current,
 field current,
 frequency and
 parameters of the cooling agent (temperature, pressure).
The modification of one of these parameters leads to the modification of the PQ
diagram, by increasing or diminishing the admissible operational field.
2 - GENERATOR CAPABILITY CHART (PQ DIAGRAM)
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
Theoretical PQ diagram for turbo-generators
Theoretical PQ diagram for hydro-generators
In the Annex there are detailed:
 the significance of all curves
 the equations of all significant curves
 the mode of construction of the theoretical PQ Diagram
2 - GENERATOR CAPABILITY CHART (PQ DIAGRAM)
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
2.2. The Actual PQ Diagram
It is, in fact, a thermal diagram where the main theoretical curves represent
isotherms of maximum admissible temperatures of different active parts of
the Generator in over and under excited regimes.
But not only: other limitations, not necessarily related to the operation in over and under
excited regimes, could be represented on the PQ Diagram,
due to (for example):
 increased vibrations
 overheating of the brushes, scintillation etc,
Actual PQ diagram with limitation
of the field current; in the shaded zones
of the diagram the generator can not operate
2 - GENERATOR CAPABILITY CHART (PQ DIAGRAM)
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
2.3. The On-line PQ Diagram
It is the PQ diagram where all the defining parameters are
directly acquired from the process and the current position of the
operation point in each moment of time is shown.
This PQ diagram modifies its configuration in real time, according to
the variation of the parameters from the process.
Other influences on the diagram limits can be added.
2 - GENERATOR CAPABILITY CHART (PQ DIAGRAM)
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
On-line PQ diagram with rated
condition (1) and three different
limitations of current operation
condition (2) - (4)
1
2
3
4
rated operation condition: voltage Un, frequency fn , hydrogen cooling gas temperature tn H2
reduced terminal voltage 0.95 Un
increased cooling gas temperature, 1.1 tn H2
increased stator cooling water temperature 1.1 tn water due to clogged hollow copper strands
2 - GENERATOR CAPABILITY CHART (PQ DIAGRAM)
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
3 - ELECTROMAGNETIC PHENOMENA AT FRONTAL ZONE OF GENERATORS
Axial magnetic field components at stator core of a generator in over excited regime:
low resultant magnetic field leads to a cold end zone.
3 - ELECTROMAGNETIC PHENOMENA AT FRONTAL
ZONE OF GENERATORS
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
Axial magnetic field components at stator core of a generator in under excited regime:
high resultant magnetic field leads to a hot end zone.
3 - ELECTROMAGNETIC PHENOMENA AT FRONTAL
ZONE OF GENERATORS
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
Axial magnetic field distribution at frontal stator core teeth:
the highest magnetic edge field at opposite flank of tooth next to phase split.
3 - ELECTROMAGNETIC PHENOMENA AT FRONTAL
ZONE OF GENERATORS
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
Resultant flux density on the upper tooth flat and distribution of the over temperature
due to eddy current losses at core laminations.
3 - ELECTROMAGNETIC PHENOMENA AT FRONTAL
ZONE OF GENERATORS
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
4 - GENERATOR OPERATION IN OVER AND UNDER EXCITED REGIMES
4.1. Characteristics of the generators used for voltage control
- Turbo-generators
- Hydro-generators
- Output powers > 5 MW
- Nuclear
- Voltage: 1 – 24 kV ± 10% or 5%
- Wind generators
4.2. Generators capability to operate continuously in over and under excited regimes
Type of generator
cos φ leading - cos φ lagging
Hydro generators
0.86 lead - 0.85 lag
Turbo generators in thermo power plants
0.85 lead – 0.85 lag
Turbo generators in nuclear power plants
0.95 lead - 0.85-0.9 lag
Wind generators
0.95 lead – 0.95 lag
4 - GENERATOR OPERATION IN OVER AND UNDER EXCITED REGIMES
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
4.3. Use of generators for voltage support on the transmission system
The generators operate mainly with:
 voltage set-point in the majority of the countries;
 reactive power set-point in several countries;
 power factor set-point.
Operation in over and under excited regimes has as consequence a greater heating of some
elements of the generator.
In comparison with operation at Q  0:
 when operating at P = Pn in over excited regime with Q = Qmax lag, and
 when operating at P = Pn in under excited regime with Q = Qmax lead
the stator winding, rotor winding and stator core heating increases by less than 10 deg.C
in the majority of the cases, but there are cases where the heating increases by more
than 15 deg.C.
4 - GENERATOR OPERATION IN OVER AND UNDER EXCITED REGIMES
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
4.4. Long-term, on-line operation in over and under excited regimes
can cause damage to generators
During the long-term operation of a generator, both in over and in under excited regimes,
some undesirable phenomena can occur, such as:
 Premature aging of the stator insulation
 Premature aging of the rotor insulation
 Occurrence of short-circuited turns in the rotor
 Increased vibrations of the stator core
 Increased vibrations of the rotor
 Deterioration of the slip rings or brush system
 Exciter diode fault
 Heating on overhang of end bent winding.
In addition, in under excited regime other possible damages could appear:
 Deterioration of the insulation between sheets in the frontal teeth
 Deterioration of the insulation of the stator bars at the exit from slots
 Excitation loss and asynchronous operation.
4 - GENERATOR OPERATION IN OVER AND UNDER EXCITED REGIMES
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
Example of Actual PQ Diagram with restrictive limits
Limitation of the field current in extreme over excited regime due to rotor vibrations and rotor winding
overheating. Limitation of the reactive power in extreme under excited regime
due to the overheating of the frontal stator core teeth
1 - rated power of the turbine; 2 - stator current limit; 3 - field current limit; 4 - minimum field
current limit; 5 - thermal limit of the frontal stator core teeth; 6 - natural static stability limit with
10% reserve; 7 - minimum output power of the turbine; 8 - reduced field current; 9 - limit due
to rotor vibrations; 10 - reduced field current limit due to rotor overheating.
4 - GENERATOR OPERATION IN OVER AND UNDER EXCITED REGIMES
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
4.5. Economic implications of over and under excited operation
Additional costs for operating in over and under excited regimes consist of:
 additional costs in operation;
 additional costs for maintenance / repairs because of premature ageing of the generator
 implications on the generator design and size and, consequently, on the cost.
4.6. Implications of over and under excited operation in generators design
In the frontal zone of the stator core the following measures are implemented:
 frontal teeth with steps;
 frontal teeth with slots;
 slits in the sheets of the frontal teeth;
 additional measures for the improvement of the frontal zone cooling.
4 - GENERATOR OPERATION IN OVER AND UNDER EXCITED REGIMES
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
5 - CONCLUSIONS
• All the power plants are required to participate in voltage control in the power
grids where they are connected and, consequently, the generators operate in over
excited regime (inductive, with generated reactive power), or under excited regime
(capacitive, with absorption of reactive power).
• In order to achieve the voltage control, the excitation system of the generator
operates with a reactive power set-point, or with a voltage set-point, or with a
power factor set-point.
• The maximum amounts of produced / absorbed reactive power at different levels
of the output power at the generator terminals is revealed by the Capability Chart
of the generator, or so called PQ Diagram, comprising mainly the limits for: output
power, stator current, field current, reactive power and static stability curve in PQ
coordinates.
• The PQ Diagram can be determined and used in three modes: the theoretical PQ
Diagram determined by computation in the generator design phase, the actual PQ
Diagram determined experimentally and reflecting the actual state of the generator
and the On-line PQ Diagram calculated continuously with the actual values
acquired directly from process data.
5 - CONCLUSIONS
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
• Operation in an inductive regime is conditioned by the field current limit
and the stator current limit determined from the condition of notsurpassing the admissible temperatures.
• Operation in a capacitive regime is conditioned by the supplementary
electrical losses in the frontal zone of the stator, the stator teeth
specifically. The capacitive limit is also determined by the natural static
stability curve (the dP/d criterion) of the generator, and by the limit of
the minimum field current.
• Operation in over and under excited regimes has as consequence a
greater heating of some elements of the generator in comparison with
the operation with Q  0: stator and rotor windings overheating, end
zone of the stator core overheating, etc.
• During the long-term operation of a generator, both in over and in under
excited regimes, some undesirable phenomena can occur, such as:
premature aging of the stator and rotor insulation, occurrence of shortcircuited turns in the rotor, increased vibrations of the rotor and stator
core.
5 - CONCLUSIONS
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
In addition, in under excited regime other possible damages could appear
such as:
deterioration of the insulation between sheets because of
excessive heating of the frontal teeth,
deterioration of the insulation of the stator bars at the exit
from slots because of excessive heating of the frontal teeth,
excitation loss and asynchronous operation.
•The monitoring of the generators operating in over and under excited
regimes is achieved by means of the already classical devices or
equipment, used with less or more extent.
•The economic implications of the operation in under and over excited
regimes are expressed only qualitatively.
5 - CONCLUSIONS
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WG A1.38 GUIDE FOR GENERATOR ON-LINE OVER AND UNDER
EXCITATION OPERATION ISSUES
SCA1 – ROTATING ELECTRICAL MACHINES
TUTORIAL
THANK YOU
Rodica Zlatanovici
WG A1.38 Convener
[email protected]
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