NÔI DUNG CỦA PHẦN 1 BAO GỒM: • Definitions of Stability. • Types of Stability. • Angular Stability Analysis. • Operational Limits of Synchronous Operational Limits of Synchronous Machines.
Trang 1A Division of Global Power
POWER SYSTEM STABILITY CALCULATION TRAINING
D 1 B i P i i l Day 1 - Basic Principles
• July 4, 2013 Prepared by: Peter Anderson
Trang 2OUTLINE OUTLINE
• Definitions of Stability
• Types of Stability
• Angular Stability Analysis
• Operational Limits of Synchronous Operational Limits of Synchronous
Machines
Trang 3BASIC PRINCIPLES BASIC PRINCIPLES
Power System Stability:
What does it mean?
A power system at a given operating state is stable if following a given disturbance or a set of disturbances
following a given disturbance, or a set of disturbances, the system state stays within specified bounds and the system reaches a new stable equilibrium state within a
ifi d i d f ti specified period of time
Multi-faceted problem depending on:
Time Span of Interest p Nature & Size of the Disturbance Physical Nature of any resulting Instability
Trang 4BASIC PRINCIPLES
BASIC PRINCIPLES
Power System Stability:
IEEE/CIGRE Working Group
Power system stability is the ability of an electric power system, for a given initial operating condition, to regain a state of operating equilibrium after being subjected to a p g q g j physical disturbance, with most system variables bounded so that practically the entire system remains intact
It is not necessary that the system regains the same steady state
operating equilibrium as prior to the disturbance This would be the
case when e.g the disturbance has caused any power system
component (line, generator, etc.) to trip Voltages and power flows will
not be the same after the disturbance in such a case Most
disturbances that are considered in stability analyses incur a change
disturbances that are considered in stability analyses incur a change
in system topology or structure.
It is important that the final steady state operating equilibrium after the
fault is steady state acceptable Otherwise protections or control
actions could introduce new disturbances that might influence the
actions could introduce new disturbances that might influence the
stability of the system Acceptable operating conditions must be
clearly defined for the power system under study.
Trang 5TYPES OF STABILITY TYPES OF STABILITY
Power System Stability
Frequency Stability Angular Stability Voltage Stability
Small
Disturbances
Large Disturbances Short Term Long Term
Small Disturbances
Large Disturbances
Short Term Long Term Short Term
Trang 6TYPICAL TIME SPANS TYPICAL TIME SPANS
Harmonics Power Flow Fault Currents
Long‐Term Stability Short‐Term Stability
Stator Transients Resonance/Saturation Switching
Lightning
Time (s)
Trang 7ANGULAR STABILITY ANGULAR STABILITY
The ability of the Synchronous Machines
within a Power System to remain In
Synchronism following a disturbance
Large Disturbances (Transient Stability)
Small Disturbances (Small signal or Dynamic
Small Disturbances (Small-signal or Dynamic
Stability)
Trang 8FREQUENCY STABILITY
FREQUENCY STABILITY
The ability of the Synchronous Machines
within a Power System to restore the System
Frequency to within an acceptable range
following a disturbance
Short-Term (Governor action)
Long-Term (Turbines, Boilers, Nuclear Reactors)
Trang 9VOLTAGE STABILITY
VOLTAGE STABILITY
At every node in the system, the “Actual
Injected Reactive Power” is equal to the
Injected Reactive Power” is equal to the
“Desired Injected Reactive Power” required
to maintain the node voltage within
t bl li it acceptable limits
Local in nature since it is difficult to transport
Local in nature since it is difficult to transport
reactive power through the network (X>>R)
Short-Term (1-5 s Induction motors, Electronically
controlled loads, HVDC converters)
controlled loads, HVDC converters)
Long-Term (10s-5 m Tap changers,
Thermostatically controlled loads, Generation
current limiters))
Trang 10APPLICATION OF ANGULAR STABILITY
ANALYSIS
Disturbance Corrective
Actions
State-A: Power Flow
State-B: Power Flow
Transit from State-A to State-A’: Stability Analysis
Transit from State-A to State-A : Stability Analysis
Transit from State-A’ to State-B: Stability Analysis
Trang 12SYNCHRONOUS MACHINES SYNCHRONOUS MACHINES
Power-Angle Relationship g p
∂
sin X
0 4 0.6 0.8 1
0 30 60 90 120 150 180
Load Angle (deg)
Trang 13STEADY STATE OPERATIONAL LIMITS
STEADY-STATE OPERATIONAL LIMITS
Limiting Factors:
Stator Current Thermal Limit
•Rated Current (1 0 pu)
Field Current Thermal Limit
•Short Circuit Ratio (SCR≈1/Xd)
Rotor Angle Stability Limit
•Dependent on Exciter Speed of Response
Trang 14OPERATIONAL LIMITS FOR SYNCHRONOUS
Trang 15Stator Current Limit 1.25
Stator Current Limit
Trang 16OPERATIONAL LIMITS FOR SYNCHRONOUS
GENERATORS
Field Current Limit
IFrated = √{(SCR+sinθ)2 + cosθ2}
Trang 18OPERATIONAL LIMITS FOR SYNCHRONOUS
GENERATORS
Composite Operating Limits 1.25
Composite Operating Limits
Limits are reduced by:
Trang 20OPERATIONAL LIMITS FOR SYNCHRONOUS
GENERATORS
Case Study
/ / Rated MVA = 200 MVA/Xd = 1.5/Rated power factor = 0.9
220
180MW Generator/Slow-Acting Exciter
RATED MW
140 160 180 200 220
60 80 100 120 140
REACTIVE POWER (MVAR)
Trang 21Case Study
/ / Rated MVA = 200 MVA/Xd = 1.5/Rated power factor = 0.9
220
180MW Generator/Fast-Acting Exciter
RATED MW
140 160 180 200 220
60 80 100 120 140
REACTIVE POWER (MVAR)