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Old 01-10-2009, 02:07 PM   #1
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Flickering power...


This morning I hooked up a new circuit. Home run to the panel from small 500 watt 120V baseboard heater. 12/2. Neutral to neutral bus bar , ground to ground bus bar. Black to new breaker. Breaker is currently OFF. Waiting for some expanding foam to dry before I mount it, turn it on and try it out.

Went to run the microwave, and sometime into a 1 minute warm up, our power flickered like crazy on/off like 7 times. I am guessing this is the snow storm, ice/freezing whatever, as that is typically the only times we ever have power issues, but is there any chance something I did in the panel this morning could cause such a thing. I do not think I did anything incorrectly, however we do not typically have power issues, so it could be I messed anything up or pure coincidence?

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Old 01-10-2009, 02:42 PM   #2
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Flickering power...


You would have to have been messing with the feeders, is the microwave circuit on the lights circuit?

There are several possibilities, could be a loose wire in the panel, meter can, or street. Could even be a bad utility transformer.

It could be arcing downsteam on the kv poco lines.

Turn your main breaker(s) off and tighten all neutral and ground connections on the buses.

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Old 01-10-2009, 02:53 PM   #3
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Thanks I thought I will try tightening all of those. Microwave is on its own circuit, and the issue could not be duplicated.
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Old 01-10-2009, 03:39 PM   #4
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How many seconds apart were these flickers?

The reason I ask is almost all utilities have 'reclosers' on their big feeders.

This is an program built into a protective relay that works like this; the relay detects a fault, and trips the breaker open. A second or so later, it closes the breaker again. If the fault is still present, it'll trip open, if not, it stays closed. Most utilities set their reclosers to stay tripped after 3 tries, but sometimes more.

The reason for this scheme is because very frequently, a fault on an overhead line is temporary. Like a tree branch that shorts the lines out, then falls to the ground. Or wind that causes lines to hit each other.

7 times sounds like a lot though.

Rob
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Old 01-10-2009, 04:15 PM   #5
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Flickering power...


my wife said 3-4, i said 7, she is usually right
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Old 01-10-2009, 05:11 PM   #6
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Flickering power...


I agree with what rgsgww said. You could have disturbed a loose neutral (or hot) wire in the panel.
Maybe a loose breaker.
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Old 01-10-2009, 09:37 PM   #7
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Flickering power...


Quote:
Originally Posted by micromind View Post
How many seconds apart were these flickers?

The reason I ask is almost all utilities have 'reclosers' on their big feeders.

This is an program built into a protective relay that works like this; the relay detects a fault, and trips the breaker open. A second or so later, it closes the breaker again. If the fault is still present, it'll trip open, if not, it stays closed. Most utilities set their reclosers to stay tripped after 3 tries, but sometimes more.

The reason for this scheme is because very frequently, a fault on an overhead line is temporary. Like a tree branch that shorts the lines out, then falls to the ground. Or wind that causes lines to hit each other.

7 times sounds like a lot though.

Rob
Sometimes the fault may be seen as a load instead of a fault. Phase to phase maybe?
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Old 01-10-2009, 09:51 PM   #8
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Quite a few years ago, I hooked up a 15,000 HP pump, and the POCO had to be called every time before it could be started. The reason was because a load that size coming on all at once would be seen as a fault by the protective relays.

They would shunt out the relays, and as soon as they saw a huge spike of demand in the line feeding the pump, then they would put the relays back in to service.

Most POCOs have a limit on the HP of a motor that can be started across-the-lines, and they must approve any installation that's larger. Sometimes this is to not trip the relays, sometimes it's meant to not dim everyones lights.

Getting a relay dialed in just right is a real trick at times! It has to be set high enough to handle normal surges, but low enough to trip on an actual fault. Sometimes, the two are very close.

Rob
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Old 01-10-2009, 10:24 PM   #9
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Quote:
Originally Posted by micromind View Post
Quite a few years ago, I hooked up a 15,000 HP pump
What, oh what needs a 15,000 HP pump? That's over 11 MW! What was the voltage and what was it fed with?
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Old 01-10-2009, 10:27 PM   #10
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Quote:
Originally Posted by micromind View Post
Quite a few years ago, I hooked up a 15,000 HP pump, and the POCO had to be called every time before it could be started. The reason was because a load that size coming on all at once would be seen as a fault by the protective relays.

They would shunt out the relays, and as soon as they saw a huge spike of demand in the line feeding the pump, then they would put the relays back in to service.

Most POCOs have a limit on the HP of a motor that can be started across-the-lines, and they must approve any installation that's larger. Sometimes this is to not trip the relays, sometimes it's meant to not dim everyones lights.

Getting a relay dialed in just right is a real trick at times! It has to be set high enough to handle normal surges, but low enough to trip on an actual fault. Sometimes, the two are very close.

Rob
15,000hp?

What in the world needs that?
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Old 01-10-2009, 10:57 PM   #11
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Flickering power...


Sounds like a misplaced 0!
What would the HP rating of a pump in a water pumping station be?
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Old 01-10-2009, 11:49 PM   #12
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15,000 HP. It ran on 13,800 volts, I don't remember how many amps, but it had 6-15 KV 500 MCM copper wires from the starter to the motor. It started with a current-limiting reactor. Sort of a distant memory, but it was either a 34.5 KV, or a 60 KV POCO line that fed the transformer. The motor was about 9' in diameter, and about 12' tall, not counting the thrust bearing on top. The shaft was about 10" in diameter. It was a vertical solid-shaft motor coupled to a turbine pump.

A motor this size has a lot more things to connect than the power. There are winding heaters (to keep the windings dry when it's not running), usually 6 thermisters for winding temperature, and 2 more for each bearing. There are also vibration transducers. The bearings were pressure-lubricated, an oil pump and cooler was located nearby. The normal oil pump was 480 volt 3 phase, and there was also a 125 volt DC back-up pump that ran on batteries. This DC pump would run for a minute or so in case of a power failure, to keep the bearings lubed while the motor spun down to a stop.

It was part of an irrigation project, this was the head end. It pumped water from a river pond through a 72" (6') line, I don't know where the other end of the line was.

This was about 10 or 12 years ago, but something this big you'll never forget.

Rob
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Old 01-11-2009, 01:01 PM   #13
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Flickering power...


I'm not surprised it was a water pump. That was the only thing I could come up with for a 15,000 HP pump.

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