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"Power Plant Protection and Control
Strategies for Blackout Avoidance"
by Charles Mozina
Technical paper covering the following topics:
- Coordination of generator protection with the AVR (limiters
and controls)
- Explore generator protection tactics to provide security against
stable swings and load encroachment
- Explore generator protection tactics to provide reliability
for tripping on unstable swings and local area undervoltage depression
brought about by VAr deficit caused by a generator
- Discuss modern AVR limiter and control functions compared to
older legacy systems (advantages), role of power system stabilizer
(PSS) and positive/negative field forcing to help maintain generator
and system stability
- Describe effects of voltage depression on AVR control and limiters
- Response of small versus large machines using field forcing
to support voltage during system faults
- Response of small versus large machines using PSS to maintain
stability during system upset
- Review wide area generator interaction for system voltage support
and stability during system upset
"Upgrade of Generator Protection
to Comply with IEEE Guides"
by Thomas Beckwith
Tutorial covering the following topics:
- Latest developments reflected in:
- Std. 242: Buff Book
- C37.102: IEEE Guide for Generator Protection
- C37.101: IEEE Guide for AC Generator Ground Protection
- C37.106: IEEE Guide for Abnormal Frequency Protection for
Power Generating Plants
- Improved sensitivity
- Negative sequence
- 100% stator ground fault
- Field ground fault
- Loss of Field
- Dual Mho Element to ride through system swings
- Voltage supervision for fast trip release
- Overexcitation
- Reverse power
- Improved Security
- Distance Element Enhancements
- Load encroachment blinding
- Power swing blocking (for stable swings)
- New protections
- Inadvertent energizing
- VT fuse loss (integrated)
- Special applications unique to generators
- Generator breaker failure
- Pole flashover (prior to syncing)
"Motor Bus Transfer: Considerations
and Methods"
by Clark Shaughnessy
Technical paper covering the following topics:
Addresses the types of motor bus transfer (MBT), technical challenges
and analyzes the thought process for proper setting creation that
is involved when implementing a MBT system for power plant spinning
motor auxiliary buses or industrial plant spinning motor buses.
Classic approaches are described and conditions are explored that
make these transfers proper or improper. Advanced implementations
of MBT methodology are explored that use high speed sensing, decision
making and breaker control to account for the dynamic conditions
in and about the plant, such as, motor dispatch and loading, new
source conditions and faults.
Describes an automatic high-speed system to transfer loads from
the interrupted bus section to the alternate bus with no interruption
of service to the transferred bus section loads. The system has
been successfully used at a number of power plant and industrial
facilities. Operating experience at these facilities will be discussed
in the paper. The system is designed to provide a high-speed fast
transfer immediately after separation. A unique feature of the system
is that if the initial fast transfer is unsuccessful a second in-phase
transfer attempt is made at the first phase coincidence (first zero
degree crossing). The paper describes the measurement technique
that is used to predict phase angle, slip frequency and voltage
decay at the time of closure to the alternate source. It also addresses
the setting and application requirements to avoid motor damage due
to shaft torque and inrush current. The transfer system is also
equipped with a residual voltage transfer backup scheme to address
the case where a severe fault near the plant disrupts the voltage
on bus being transferred to the point where high-speed transfer
and in-phase transfer attempts are unsuccessful.
"Advanced Concepts in Transformer
Protection"
by Clark Shaughnessy
Tutorial covering the following topics:
- Review Protection Objectives for Transformers
- Phase Faults
- Ground Faults
- System Short Circuit Back Up Protection
- Buses and Lines
- Phase Faults
- Ground Faults
- Abnormal Operating Conditions
- Open circuits
- Overexcitation
- Abnormal Frequency
- Abnormal Voltage
- Breaker Failure
- Overload
- Geo-magnetically induced currents (GIC)
- Review Connection and Grounding
- What Makes Transformer Differential Protection a Challenge?
- CT Ratio, Saturation, Remnance and Tolerance
- Polarity, Winding Arrangement and Angular Displacement
- Transformation and LTC-caused Mismatch
- Zero Sequence Current Elimination
- Inrush Phenomena
- Harmonic Content Availability
- Overexcitation Pnenomena
- Internal Ground Fault Sensitivity
- Switch Onto Fault Considerations
- Advanced Transformer Protection Concepts and Element Design
- Advanced Installation and Commissioning Tools
- Commissioning Lab
"How to Nuisance Trip Distributed
Generation"
by Charles Mozina
Technical paper covering the following topics:
The protection system at the DG interconnection must provide security
to allow the DG to be connected to the utility grid, as well as
reliably disconnect the DG from the utility grid for a variety of
reasons: loss of utility supply to the feeder (anti-islanding),
shunt faults on the utility system, abnormal operation conditions
and power import/export restrictions.
Most protection systems are set to trip the DG offline in less
than one second, and often much quicker (10-30 cycles). Events can
occur on the system and within the DG facility, however, that may
lead to undesired trips. These trips occur due to protection elements
being set with very close tolerances and the interplay of events
that include power surges from cycling of loads within a DG facility,
faults within the DG facility that should be cleared by other means,
and misapplication of protective elements.
We will various scenarios that can lead to nuisance tripping of
DGs that result from: a) power protection sensitivity and directionality
with fluctuating DG site load; b) sensitivity and directionality
issues for phase fault protection; c) DG facility protection and
DG interconnection protection coordination.
We will highlight a feature of modern protective systems that is
a event analysis aid, waveform capture, applied at the point of
common coupling at the DG facility and the utility. By examining
the captured waveforms for the various scenarios-including pre-event
currents, voltages and power flows-conclusions can be made as to
where the event originated (in the DG facility or on the utility
grid), and if the trip decision was correct. If the trip is deemed
a nuisance trip, the captured waveforms can help determine a remedial
course of action: setting adjustment (pick up and time delay), use
of protective elements (directionalizing, use of voltage control)
and plant operations modifications (adjustment of generator bias,
schemes to stagger tripping of large blocks of load).
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