Transmission Line Protection
Fundamentals of
Distance Protection
GE Multilin
Outline
• Transmission line introduction
• What is distance protection?
• Non-pilot and pilot schemes
• Redundancy considerations
• Security for dual-breaker terminals • Out-of-step relaying
• Single-pole tripping
• Series-compensated lines
2/
GE /
December 7, 2014
Transmission Lines
A Vital Part of the Power System:
• Provide path to transfer power between generation and load
• Operate at voltage levels from 69kV to 765kV
• Deregulated markets, economic, environmental requirements have pushed utilities to operate transmission lines close to their limits.
3/
GE /
December 7, 2014
Transmission Lines
Classification of line length depends on:
Source-to-line Impedance Ratio (SIR), and Nominal voltage
Length considerations:
Short Lines: SIR > 4
Medium Lines: 0.5 < SIR < 4
Long Lines: SIR < 0.5
4/
GE /
December 7, 2014
Typical Protection Schemes
Short Lines
• Current differential
• Phase comparison
• Permissive Overreach Transfer Trip
(POTT)
• Directional Comparison Blocking (DCB)
5/
GE /
December 7, 2014
Typical Protection Schemes
Medium Lines
• Phase comparison
• Directional Comparison Blocking (DCB)
• Permissive Underreach Transfer Trip (PUTT)
• Permissive Overreach Transfer Trip (POTT)
• Unblocking
• Step Distance
• Step or coordinated overcurrent
• Inverse time overcurrent
• Current Differential
6/
GE /
December 7, 2014
Typical Protection Schemes
Long Lines
•
•
•
•
•
•
•
•
Phase comparison
Directional Comparison Blocking (DCB)
Permissive Underreach Transfer Trip (PUTT)
Permissive Overreach Transfer Trip (POTT)
Unblocking
Step Distance
Step or coordinated overcurrent
Current Differential
7/
GE /
December 7, 2014
What is distance protection?
Intended
REACH point
F1
Z
I*Z
V=I*ZF
I*Z V
RELAY (V,I)
For internal faults:
> IZ – V and V approximately in phase (mho)
> IZ – V and IZ approximately in phase (reactance)
8/
GE /
December 7, 2014
What is distance protection?
F2
Intended
REACH point
Distance Protection
GE Multilin
Outline
• Transmission line introduction
• What is distance protection?
• Non-pilot and pilot schemes
• Redundancy considerations
• Security for dual-breaker terminals • Out-of-step relaying
• Single-pole tripping
• Series-compensated lines
2/
GE /
December 7, 2014
Transmission Lines
A Vital Part of the Power System:
• Provide path to transfer power between generation and load
• Operate at voltage levels from 69kV to 765kV
• Deregulated markets, economic, environmental requirements have pushed utilities to operate transmission lines close to their limits.
3/
GE /
December 7, 2014
Transmission Lines
Classification of line length depends on:
Source-to-line Impedance Ratio (SIR), and Nominal voltage
Length considerations:
Short Lines: SIR > 4
Medium Lines: 0.5 < SIR < 4
Long Lines: SIR < 0.5
4/
GE /
December 7, 2014
Typical Protection Schemes
Short Lines
• Current differential
• Phase comparison
• Permissive Overreach Transfer Trip
(POTT)
• Directional Comparison Blocking (DCB)
5/
GE /
December 7, 2014
Typical Protection Schemes
Medium Lines
• Phase comparison
• Directional Comparison Blocking (DCB)
• Permissive Underreach Transfer Trip (PUTT)
• Permissive Overreach Transfer Trip (POTT)
• Unblocking
• Step Distance
• Step or coordinated overcurrent
• Inverse time overcurrent
• Current Differential
6/
GE /
December 7, 2014
Typical Protection Schemes
Long Lines
•
•
•
•
•
•
•
•
Phase comparison
Directional Comparison Blocking (DCB)
Permissive Underreach Transfer Trip (PUTT)
Permissive Overreach Transfer Trip (POTT)
Unblocking
Step Distance
Step or coordinated overcurrent
Current Differential
7/
GE /
December 7, 2014
What is distance protection?
Intended
REACH point
F1
Z
I*Z
V=I*ZF
I*Z V
RELAY (V,I)
For internal faults:
> IZ – V and V approximately in phase (mho)
> IZ – V and IZ approximately in phase (reactance)
8/
GE /
December 7, 2014
What is distance protection?
F2
Intended
REACH point