1. IEEE Guide for Protective Relay Applications to Transmission Lines
What’s New in C
IEEE Guide for Protective Relay Applications to Transmission Lines
Georgia Tech Protective Relaying Conference 2018

2. Background
Revision of C
Application of relays and protection systems to protect transmission lines
D19 Working Group of IEEE Power System Relaying and Control (PSRC) Committee
31 working group members
Approved on December 5, 2015

3. C37.113-2015 (D19 WG) members Don Lukach - Chair
Jeffrey Barsch – Vice Chair
Martin Best
Gustavo Brunello
David Circa
Stephen Conrad
Randall Cunico
Alla Deronja
Normann Fischer
Dom Fontana
Gary Kobet
Walter McCannon
Alexis Mezco
Dean Miller
John Miller
Joe Mooney
James O’Brien
Dean Ouellette
Claire Patti
Elmo Price
Sam Sambasivan
Mohindar Sachdev
Phil Tatro
Richard Taylor
Michael Thompson
Ian Tualla
Demetrios Tziouvaras
Jun Verzosa
Solveig Ward
Roger Whittaker
Zhiying Zhang

4. Table of Contents Definitions, abbreviations, acronyms Fundamentals
Impact of system configuration on selection of protection schemes
Relay schemes
Annex and extensive bibliography
Fundamentals: zones of protection, relay selection, effects of load
Impact of system configuration: line design considerations, number of line terminals, weak systems, lines with distribution station taps, parallel lines, terminal configuration and mutual coupling considerations
Relay schemes: non-pilot, pilot, problems with multi-terminal lines, distance relay considerations, series-compensated lines, short line applications, system transients

5. What’s New Communication systems Redundancy Autoreclosing
Ground overcurrent protection
Line length considerations
Lines terminated into transformers
Current differential applications
Ground path configurations
Effects of high grounding resistance

6. What’s New (continued)
Transfer and stub bus configurations
Relay elements used in step distance schemes
Polarization methods
Specially shaped characteristics
Single-phase tripping and reclosing
Fault and system studies

7. Communications Communications allows for include high-speed clearing
Considerations when choosing a communication-based scheme
High-speed clearing can help with: generator stability, limit fault current damage, allow HSR, limit voltage sag, better fault clearing for multi-terminal or weak infeed terminals
Considerations: number of systems required, type (analog or digital) and medium (pilot wire, fiber optic, carrier), need for alternative paths, operational and maintenance issues

8. Redundancy and Backup Considerations
Main 1: differential protection system
Main 2: Permissive overreaching transfer trip (POTT) system
The two systems are functionally equivalent and do not share any components => they are redundant.
Main 1 and main 2 systems for protecting a transmission line

9. Remote backup protection of a transmission line
All lines shown are protected with step-distance systems with no breaker failure protection.
Fault F should be cleared by breakers B3 and D3.
Distance relays at circuit breakers A1, C2, E1, E2, and F4 may detect this fault and provide backup clearing.
Drawback of remote backup: results in complete loss of supply to the affected substations.

10. Line length considerations and SIR
SIR > 4 ; short line
0.5 <= SIR <= 4 ; medium line
SIR < 0.5 ; long line
Short lines pose challenge for line protection
Distance element: higher SIR means lower restraining voltage at the relay for an out-of-zone fault, and a very low voltage can be more susceptible to measurement errors and transients - > this can result in undesired overreach of an underreaching element
Overcurrent relay: difference between fault current magnitude for in-zone and out-of-zone faults can be smaller than the typical margins used for setting the pickup

11. Line length considerations and SIR
A suggested method to calculate the source impedance for the purpose of classifying line lengths is to place a short circuit at the remote bus and calculate the source impedance as the voltage drop from the source to the relay location divided by the fault current.
This figure shows a transmission system that has been reduced to its two-source equivalent with the line and transfer impedance branches. The transfer impedance branch that represents the complex transmission system network can have a significant effect on the voltage at the relay.
ZS = (VDROP_SOURCE) / (IRELAY) , then SIR = ZS / ZLine

12. Considerations for Line Distance Applications
Line Terminated into a Transformer
Reach of a distance relay is measured from the location of the VTs.
Fault direction is sensed by the location and connections of the CTs.
Transformer and line zones of protection are easily discriminated with this approach.
Preferred scheme
Use VH and IH

13. Considerations for Line Distance Applications
Impedance reach is measured from low-side VTs and should include the transformer impedance ZT
Disadvantage for Relay A: reach of line protection is limited when ZT is large compared to ZL
For wye-delta transformers, zero-sequence currents on line cannot be measured by the low-side CTs. This impacts ground distance, zero-sequence directional, and ground overcurrent relays. [These same issues exist on the prior example using VH and IL .]
Relay uses VL and IL

14. Transfer bus and stub bus configurations
Transfer bus configuration: The bus coupler circuit breaker allows a circuit to be connected to the station bus when either CB2 or CB3 are removed from service.
Two options: (1) Connect CTs, status, and trip circuits of the bus coupler breaker to the relays which protect the transferred circuit. This requires the use of auxiliary switches to transfer the physical relay connections. (2) Use relays dedicated to the bus coupler breaker – these relays would be set to protect any of the circuits terminated at the station. Use of multiple setting groups may be used. This option is complicated if communications-based protection schemes are used on any of the circuits.
Stub bus configuration: A transmission line may have a disconnect switch in a breaker-and-a-half or ring bus configuration such that the line can be separated from the main bus. If relay potentials are on the line side of the disconnect switch, then distance and directional relays will be unable to operate. Line current diff relays will also operate incorrectly.
Transfer bus configuration

15. Specially shaped characteristics
Impedance as seen by the relay moves along the load line toward the origin as load increases.
Distance relays with mho and quadrilateral characteristics will misoperate if load impedance reaches points L or K, respectively.
Quadrilateral characteristic achieves good fault resistance coverage with higher immunity to load as compared to the mho characteristic.
Numerical relays use specially shaped load blinders or load encroachment to allow more resistance coverage for faults and less resistance coverage for loads.

16. Load blinders and lenticular characteristic
Both of these characteristics can impact fault coverage and should be reviewed for all aspects of their intended functions.

17. Cone-type load blinder
The full mho characteristic can be allowed to operate during faults.
Load encroachment blocking element can be bypassed during faults by detecting current imbalance (e.g., I2/I1) or phase undervoltage.

18. Effects of high grounding resistance on operation of line protection
Example shown is for a 500kV transmission line.
Limit is based on assumption that total fault current is limited only by the fault resistance (system and line impedances are negligible).
The limit of 300 ohms is calculated from the total fault current being approx. 962 amps [500kV / (sqrt(3) * 300].
At the midline location, 50% of the current (481 A) comes from each terminal, and 600/1 CT’s are used.
With a ground overcurrent relay setting of 0.5 amps and allowing for a dependability factor of 1.5 (the fault current being at least 150% of the pickup setting of the relay), the limit is about 300 ohms for a midline fault.
Fault-resistance coverage limit increases as the fault location moves toward the line terminals.
For a 600-ohm fault near Bus A, terminal A trips => current in the fault resistance decreases => voltage drop in the fault resistance decreases => ground fault contribution from Bus B increases => relay at B detects fault and initiates a trip.

19. Sensitive ground OC fault protection
High impedance faults pose challenge for distance relays
Directional ground OC relays must balance sensitivity and security
Considerations when using OC relays
Coordination requirements
Due to increased focus on sensitivity, we must consider: maximum ground current due to system imbalance during heavy loads, the system model, mutual coupling, CT inaccuracies, single-phase tripping, and contingencies
System model should include: specific cable types, series compensation, structure type, earth resistivity; under-built distribution lines may need to be considered for mutual coupling
Coordination requirements: ground OC relays should coordinate with ground distance relays and other ground OC relays

20. Role of directional ground OC relays with ground distance relays
Directional ground OC can provide sensitive protection for ground faults
Directional comparison pilot schemes
Load and system imbalance
A secure approach is to coordinate all ground elements with each other
In directional comparison pilot schemes, zero-sequence instantaneous units provide excellent sensitivity without having to be concerned with seeing faults beyond the protected line.
Ground OC settings should take into account the various causes for zero-sequence current flow.
Coordination should consider:
(1.) OC elements at local terminal vs. distance elements at remote, (2.) OC elements vs. OC elements, (3.) distance elements vs. distance elements, and (4.) distance elements vs. OC elements.

21. Directional ground overcurrent relay polarization methods
Various methods are discussed
Importance of using matching polarizing methods
Various methods are discussed, including zero-sequence voltage, zero-sequence current, negative-sequence (uses V2 and I2), dual, and others.
In a directional comparison pilot scheme, it’s very important to use similar directional polarizing methods at each terminal!
In this example, relay RA uses zero-sequence current for directional polarization, whereas relay RB uses negative sequence current and voltage for direction. This mismatch can lead to a misoperation for an external fault such as the one shown because each terminal may see the fault in the forward direction. This would not occur if the line and system negative- and zero-sequence impedances were identical, but they are not.

22. Autoreclosing methods
IEEE Std C37.104
Discusses criteria used for selecting autoreclosing schemes
High-speed and time-delayed are discussed
Typical criteria used for selection: voltage level, customer requirements, stability considerations, proximity of generation
Benefits of HSR: fast restoration of power to customers, improved system stability, immediate restoration of system capacity and reliability

23. Single-phase tripping and reclosing – Special considerations
Faulted phase selection
Arc deionization
Automatic reclosing considerations
Pole disagreement
Effects of unbalances currents
Extra requirements for circuit breakers and relays
Phase segregated line current differential and phase comparison schemes are inherently phase selective and do not generally require additional phase selection logic.
Capacitive coupling of the two energized phases with the faulted phase makes the arc more difficult to extinguish.
Special logic must be designed to handle when a pole is open.
Breaker failure and open-phase detection functions need to work on a per-phase basis. LOP detectors may require blocking from open-phase detection.
Single-phase autoreclosing typically uses elaborate sequences depending on the fault type and shot count.

24. Something did not change
The design of a line-protection system may fail to recognize one of the more important design factors: simplicity. ………………………”.
The problems caused by incorrect or incomplete implementation of overly complex protection systems may create more serious consequences than not providing solutions for special situations. Protection engineers should carefully weigh the consequences and probability of each problem to determine if they justify using the complex special solutions that might be available or could be developed.

25. Existing PSRC D Subcommittee Guides
C pages
C pages
C – 141 pages
C – 76 pages
C – 72 pages

26. Standard can be purchased from the IEEE Standard Association