Selective Stator Ground Protection

1

• Selective Stator Ground Protection
• Expo Presentation

2
Team SyncGEN

• Sponsor Larry Gross
• Relay Application Innovation
• Advisors Dr. Brian Johnson Dr. Joe Law
• Webmaster / Client Contact John Trombetta
• Poster / Presentations Robert Schloss
• Documentation Manager Jason Panos

3
Acknowledgments

• Relay Application Innovation Larry Gross
• Idaho Power
• Schweitzer Engineering Laboratories
• University of Idaho - ECE Department
• Dr. Brian Johnson Dr. Joe Law

4
Background

• RAI customer has multiple machines on common high
  impedance grounded bus
• Using traditional overvoltage protection scheme
• Interested in a faster and more robust protection
  scheme for their system

5
Standard Protection

• Faults detected from neutral overvoltage

6
The Problem
Multiple machines on a common high impedance bus

• Faults seen on all machines
• Impossible to directly isolate the faulted
  machine from system measurements
• 3rd Harmonic protection cannot isolate faulted
  machine

7
The Problem

• Units must be sequentially tripped until the
  faulted machine is isolated
• Non-faulted machines must be restarted if tripped
  in the detection process
• Leads to large disturbances in the system

8
Proposed Protection

• Selective stator ground protection using
  microprocessor relay directional algorithms for
  ungrounded distribution systems
• Sensitive CTs in SEL-351 for detecting zero
  sequence current flow in the neutral
• Zero sequence current flows toward faulted
  machine

9
Proposed Protection

• Fast isolation of faulted units
• Selective stator ground protection in addition to
  standard overvoltage protection
• Standard sequential delays apply, but trip
  immediately when faulted unit is isolated

10
System Oneline
11
System Configuration
12
Protection Constraints

• Standard protection must be used in addition
• 32NF indicates unit is faulted
• 32NR indicates the unit is not faulted
• 32NF enables immediate tripping, bypassing
  standard delay

13
Testing Constraints

• Faults must be seen across the bus
• For bus faults, 32NR shows on all machines
• Fault isolation needed for faults down to lowest
  stator turn

14
Relay Elements

• SEL-351
• 50 Overcurrent
• 32 Directional
• SEL-300G
• 64G Overvoltage
• 59 Overvoltage
• Trip IN10164G1T (IN101 asserts for 32NF)

15
Event Report
16
Evaluation

• Method works for isolated machines down to lower
  5 of stator windings
• Passed our tests for isolated machines
• Worked intermittently for multiple machines due
  to issues with the model power system

17
Issues Encountered

• PTs of the model power system solidly grounded
  to neutral
• No CT in neutral line
• No neutral line from Avista
• System ground was floating
• Unable to elevate neutral impedance
• Model power system schematics were incomplete

18
Economic Analysis

• Setup Cost
• SEL-351 4,530
• Engineering design
• Additional hardware wiring
• Repair costs
• Stator rewinding 500,000
• Loss of Operation

19
Conclusions Recommendations

• Selective stator ground protection works in
  lower 5 of stator windings on isolated machines
• Address all issues with the model power system
• Test further to prove the method works for
  multiple machine configurations
• Use this method as supervisory protection with
  traditional overvoltage protection

20
Questions?
21
Generator Specifications
22
Lab Connections
23
Distribution Box
24
Sub-coils of Stator Windings