Cold Weather Circuit Breaker Performance
Ken Benoit, Minnesota PowerKasey Borboa, Minnkota Power Cooperative
Minnesota Power System Overview
Number of SF6 Gas Breakers by Voltage
in MN
500 kV 1
230 kV 45
115 kV 162
Transmission Substations by Voltage
in MN
500 kV 1
345 kV 1
230 kV 16
138 kV 2
115 kV 60
Wholesale electric generation and transmission cooperative headquartered in Grand Forks, N.D.
11 member-owner cooperatives• 3 in ND, 8 in MN
12 municipals • Northern Municipal Power Agency
Serve 35,000 square miles
Substations• 40 Transmission• 212 Distribution
174 SF6 Breakers
Minnkota Power Cooperative System Overview
7-day weather outlook in International Falls
• Average Hi -8°F• Average Lo -31°F
Three daily records • 27th low -46°F• 30th hi -19°F• 31st low -45°F
Wind chill -60°F
20--
0 --
20--
40-
°F
Wind(MPH)
Jan-25 Jan-26 Jan-27 Jan-28 Jan-29 Jan-30 Jan-31
7-Day Lo/Hi
3.2 5.0 6.2 5.6 12.9 7.1 2.1
Polar Vortex
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0Te
mpe
ratu
re
I-FallsDuluthGrand Forks
January 29th
Hourly Temperatures
January 30th January 31th
Pressure vs Temperature of SF6 Gas at Constant Density
6
Alarms during the Polar Vortex Jan 25 to 31, 2018 SnapshotJan 30 00:53 78L FBS BLOCKED, normal at 11:43, then opened
Jan 30 02:05 1H CAN BLOCKED, normal at 09:56
Jan 30 02:34 16L ARD BLOCKED, normal at 11:21, then opened, BO HTR A Ph.
Jan 30 02:37 5T VRG BLOCKED, normal at 11:57
Jan 30 03:00 5L MLS BLOCKED, normal at 09:08
Jan 30 05:04 1L HYT BLOCKED, normal at 09:09
Jan 30 05:24 26L TMS BLOCKED, normal at 10:30, then opened
Jan 30 09:04 98L ARD BLOCKED, normal at 10:44
Jan 30 09:51 20K SQB BLOCKED, normal at 11:19
Jan 30 20:48 79L CAN Breaker opened, normal at 10:59 on Jan 31
Jan 30 23:21 78L FBS BLOCKED, normal at 11:16 on Jan 31
Jan 31 00:10 50R LFK BLOCKED
Jan 31 10:34 16L VRG NORMAL, repaired BO HTR A Ph.
Jan 31 04:32 94L SHA Blocked, normal at 10:45
345 kV Breakers –1 Low Gas Lockout (TRIP) 230 kV Breakers –
5 CB Low Gas Alarm 115 kV Breakers –
1 Low Gas Alarm 69 kV Breakers – 1 Low Gas Alarm,
1 Low Gas Lockout (TRIP) 13.8 kV Reactor Switcher –
1 Low Gas Alarm
Operational Experience
Operational ConcernsUsually open breakers before being blocked from trip or close
while keeping the system intact If can not open breaker, let the breakers ride through a block.
Usually breaker becomes operational next day when sun comes out Replaced failed heater blankets on 20 breakers in 2018When breakers are in blocked condition, trip coil monitors
alarms from relays are activated No alarming on failed breaker heaters, changed specification
on purchasing breakers to included a tank heater alarm
9
Annual breaker maintenance• Check tank and cabinet heaters
• Thermostat and contactor operation are verified
• Heater currents are measured and recorded, compared to previous results and nameplate
• Check SF6 gas levels• Inspect gas level and verify correct
pressure• Add gas as needed
MPC Maintenance and Operation
Operating conditions: -50°CTemperature compensated gaugesLocation of temperature probe
Insulated pipingLoss of AC alarmingTank heater failure alarming
Specification Considerations
Station service loading concerns when changing out Oil Circuit Breakers to SF6 Gas Breakers
500 kV 150A 240 VAC single phase
230 kV 33 to 38A 240 VAC single phase
115 kV 18 to 24A 240 VAC single phase
46 kV 13A 240 VAC single phase