Copyright © MCEC and SEL 2014 Mitigation of Undesired Operation of Recloser Controls Due to Distribution Line Inrush Lee Ayers Mid-Carolina Electric Cooperative Larry Wright Schweitzer Engineering Laboratories, Inc.

53,000 active meters South Carolina counties ♦ Lexington ♦ Richland ♦ Newberry ♦ Saluda ♦ Aiken Mid-Carolina Electric Cooperative

MCEC Discussion Reasoning for changing recloser style Experience with tripping due to inrush Factors affecting inrush Solutions to tripping during inrush Future plans to address feeder circuit coordination

Example MCEC Distribution Circuit

Hydraulic Recloser Clearing Curves Two Fast A and Two Slow B Curves

Fast Curve Clears Temporary Faults Saves fuses Reduces outages

Historical Data 90% of faults clear on fast curve 5% of faults clear on slow curve 5% of faults proceed to lockout

Aging Recloser Fleet Reclosers were at least 20 years old One manufacturer was out of business Insufficient stock was available

Solid Dielectric Recloser With Microprocessor-Based Control

Reasons for Selecting New Reclosers Maintenance costs Coordination Safety Environmental concerns Testing Additional advantages

Hydraulic Maintenance Costs Maintenance required every 3 years Costs associated with maintenance – about $350 per recloser ♦ Parts and oil ♦ MCEC hours to change out recloser

Solid Dielectric Maintenance Costs No Regular Maintenance Required

Hydraulic Recloser Coordination Less reliable than expected Not repeatable Insufficient margin Prolonged outages due to poor selectivity

Solid Dielectric Recloser Coordination Microprocessor-based control Accurate and repeatable More curves available

Hydraulic Recloser Safety Hot stick is used for manual close and nonreclose Operator stands directly under recloser

Solid Dielectric Recloser Safety Operated remotely or on time delay No hot stick required (except yellow handle) Improved safety with hot-line tagging ♦ No closing ♦ More sensitive tripping

Hydraulic Environmental Concerns Mineral Oil Release Requires Cleanup Contaminated soil removal Decontamination Restoration

Solid Dielectric Environmental Concerns None

Hydraulic Testing Requires low-voltage, high-current test set Can only be done in shop

Solid Dielectric Testing Relay test set Recloser test set Soldering gun?

Additional Advantages of µP Control Forensic data Communications Self-monitoring and alarm Simpler-to-change settings

Initial Experience With µP Control More than 150 reclosers (35 A and 50 A) changed out Many event reports received Noticed unintended operations on fast curve when power restored

First Recloser Trip – Raw Event

Second Recloser Trip – Raw Event

µP Control Operate Curve

First Recloser Trip – Filtered Event

Second Recloser Trip – Filtered Event

Is This Normal? “There is an argument that a recloser rarely closes in and holds on second fast operations due to inrush current.” – McGraw Edison Power Systems Division, “Overcurrent Protection for Distribution Systems – Seminar Notes,” May 1984

Is This Acceptable? No. Why Unnecessarily Blink Customer Power?

Transformer Inrush

Inrush Current

Second Harmonic

One Method to Secure Relays Change Settings Change curve shape Raise pickup Raise time dial

Testing Other Fast Curves

Test Results CurveTrip 4No R N 17No 1Yes A (TD = 2)Yes

Disadvantages of Changing Settings Slows protection Is difficult to quantify distribution line inrush ♦ EMTP ♦ Real-time digital simulation

A Better, Easier Solution: Second-Harmonic Blocking

First Recloser Trip – Raw Event

First Recloser Trip Harmonics

Second Recloser Trip – Raw Event

Second Recloser Trip Harmonics

Second-Harmonic Blocking Logic

First Event With Second-Harmonic Blocking

Second Event With Second-Harmonic Blocking

Substation Recloser Inrush Event

Incorrect Second-Harmonic Blocking Step change in fundamental frequency ♦ Fourier transform ♦ Short-lived blocking (0.25 cycles) CT saturation ♦ Has low fault current and low X / R ratio ♦ Is backed up by slow curve

CT Excitation Curve

Path Forward Install three-phase 70 A reclosers with single-pole tripping Implement second-harmonic blocking on reclosers and feeder relays Perform coordination studies again

Transformer Fuse Coordination

Questions?