Why does this breaker pop?

Guest
I run my shop from a rotary phase converter and this setup has been
trouble free for years. Then a couple years ago I bought a machine
that runs on 480 volts that came with a transformer to boost 240 volts
to 480 volts. Most of the time when I turn on the breaker that
energizes the transformer nothing happens. But once in a while, maybe
2% of the time, the breaker pops when I turn it on. The breaker is
sized properly for the wires connected to it so it can't be replaced
with one with a higher rating. I also don't think it is faulty because
It is new. I replaced the old breaker after it had popped a few times
when being turned on. The new breaker acts the way the old one did.
When the breaker pops I wait only a few seconds before turning it on
again and it never pops the second time it gets turned on. And it
never pops while the machine is running, only when it is turned on.
Could it be that the breaker is just on the edge of popping every time
because of the inrush current when the transformer is energized?
Thanks,
Eric
 
On Friday, September 4, 2015 at 2:08:31 PM UTC-4, et...@whidbey.com wrote:
I run my shop from a rotary phase converter and this setup has been
trouble free for years. Then a couple years ago I bought a machine
that runs on 480 volts that came with a transformer to boost 240 volts
to 480 volts. Most of the time when I turn on the breaker that
energizes the transformer nothing happens. But once in a while, maybe
2% of the time, the breaker pops when I turn it on. The breaker is
sized properly for the wires connected to it so it can't be replaced
with one with a higher rating. I also don't think it is faulty because
It is new. I replaced the old breaker after it had popped a few times
when being turned on. The new breaker acts the way the old one did.
When the breaker pops I wait only a few seconds before turning it on
again and it never pops the second time it gets turned on. And it
never pops while the machine is running, only when it is turned on.
Could it be that the breaker is just on the edge of popping every time
because of the inrush current when the transformer is energized?
Thanks,
Eric
Click to expand...

Yeah (knowing nothing of AC power stuff) I would guess some sort of inrush current.
(as you suggest). I usually think about inrush current charging
up some capacitor (w/ DC voltage) perhaps the same type of thing
can happen with a transformer. And if you switch it on during the
wrong part of the phase, it pops.

George H.
 
On 09/04/2015 02:11 PM, etpm@whidbey.com wrote:
I run my shop from a rotary phase converter and this setup has been
trouble free for years. Then a couple years ago I bought a machine
that runs on 480 volts that came with a transformer to boost 240
volts to 480 volts. Most of the time when I turn on the breaker that
energizes the transformer nothing happens. But once in a while,
maybe 2% of the time, the breaker pops when I turn it on. The breaker
is sized properly for the wires connected to it so it can't be
replaced with one with a higher rating. I also don't think it is
faulty because It is new. I replaced the old breaker after it had
popped a few times when being turned on. The new breaker acts the way
the old one did. When the breaker pops I wait only a few seconds
before turning it on again and it never pops the second time it gets
turned on. And it never pops while the machine is running, only when
it is turned on. Could it be that the breaker is just on the edge of
popping every time because of the inrush current when the transformer
is energized? Thanks, Eric
Click to expand...

That's a bit of a FAQ on sci.electronics.repair.

If the transformer is turned _off_ near the zero crossing, the core has
some remanent magnetization. When you turn it back on, there's a 50:50
chance that the first half cycle is in the same direction. The
magnetized core saturates more easily in that direction, so you get a
huge current spike when that happens.

How often the breaker blows depends on things like the line voltage and
the safety factor built into the transformer--which is usually not a
huge number.

People use various soft-start methods, e.g. a resistor and a time delay
relay, or an NTC thermistor.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net
 
On Fri, 04 Sep 2015 15:45:32 -0400, Phil Hobbs wrote:

On 09/04/2015 02:11 PM, etpm@whidbey.com wrote:
I run my shop from a rotary phase converter and this setup has been
trouble free for years. Then a couple years ago I bought a machine that
runs on 480 volts that came with a transformer to boost 240 volts to
480 volts. Most of the time when I turn on the breaker that energizes
the transformer nothing happens. But once in a while, maybe 2% of the
time, the breaker pops when I turn it on. The breaker is sized properly
for the wires connected to it so it can't be replaced with one with a
higher rating. I also don't think it is faulty because It is new. I
replaced the old breaker after it had popped a few times when being
turned on. The new breaker acts the way the old one did. When the
breaker pops I wait only a few seconds before turning it on again and
it never pops the second time it gets turned on. And it never pops
while the machine is running, only when it is turned on. Could it be
that the breaker is just on the edge of popping every time because of
the inrush current when the transformer is energized? Thanks, Eric


That's a bit of a FAQ on sci.electronics.repair.

If the transformer is turned _off_ near the zero crossing, the core has
some remanent magnetization. When you turn it back on, there's a 50:50
chance that the first half cycle is in the same direction. The
magnetized core saturates more easily in that direction, so you get a
huge current spike when that happens.

How often the breaker blows depends on things like the line voltage and
the safety factor built into the transformer--which is usually not a
huge number.

People use various soft-start methods, e.g. a resistor and a time delay
relay, or an NTC thermistor.

Cheers

Phil Hobbs
Click to expand...

Inneresting. Who woulda thunk it?

Do you know if there are commercial starters that'll do this (like from
Grangers), or is it something you have to roll your own?

--
www.wescottdesign.com
 
Here in the UK the std/usual breaker is a Type B.
There are Type C & then Type D that have time/current curves double of the
Type B with the same current breaking capacity.
These allow the inrush current to drop before tripping. Motors would
usually be on Type C.
Of course there are other factors to consider to remain in spec of the
circuit.

I presume the USA has something similar.

HTH
Mitch

--
Terminal_Crazy

Mitch - 1995 Z28 LT1 M6 terminal_crazy@sand-hill.freeserve.co.uk
Lancashire England http://www.sand-hill.freeserve.co.uk/terminal_crazy/
 
On 9/5/2015 3:06 PM, Tim Wescott wrote:
On Fri, 04 Sep 2015 15:45:32 -0400, Phil Hobbs wrote:

On 09/04/2015 02:11 PM, etpm@whidbey.com wrote:
I run my shop from a rotary phase converter and this setup has been
trouble free for years. Then a couple years ago I bought a machine that
runs on 480 volts that came with a transformer to boost 240 volts to
480 volts. Most of the time when I turn on the breaker that energizes
the transformer nothing happens. But once in a while, maybe 2% of the
time, the breaker pops when I turn it on. The breaker is sized properly
for the wires connected to it so it can't be replaced with one with a
higher rating. I also don't think it is faulty because It is new. I
replaced the old breaker after it had popped a few times when being
turned on. The new breaker acts the way the old one did. When the
breaker pops I wait only a few seconds before turning it on again and
it never pops the second time it gets turned on. And it never pops
while the machine is running, only when it is turned on. Could it be
that the breaker is just on the edge of popping every time because of
the inrush current when the transformer is energized? Thanks, Eric


That's a bit of a FAQ on sci.electronics.repair.

If the transformer is turned _off_ near the zero crossing, the core has
some remanent magnetization. When you turn it back on, there's a 50:50
chance that the first half cycle is in the same direction. The
magnetized core saturates more easily in that direction, so you get a
huge current spike when that happens.

How often the breaker blows depends on things like the line voltage and
the safety factor built into the transformer--which is usually not a
huge number.

People use various soft-start methods, e.g. a resistor and a time delay
relay, or an NTC thermistor.

Cheers

Phil Hobbs

Inneresting. Who woulda thunk it?

Do you know if there are commercial starters that'll do this (like from
Grangers), or is it something you have to roll your own?
Click to expand...

They have about 200 choices. Found that after about 4.4 seconds of looking.
 
In article <nmnjuahtq0h12eu8ghcll2arb1tujbppus@4ax.com>,
etpm@whidbey.com says...
I run my shop from a rotary phase converter and this setup has been
trouble free for years. Then a couple years ago I bought a machine
that runs on 480 volts that came with a transformer to boost 240 volts
to 480 volts. Most of the time when I turn on the breaker that
energizes the transformer nothing happens. But once in a while, maybe
2% of the time, the breaker pops when I turn it on. The breaker is
sized properly for the wires connected to it so it can't be replaced
with one with a higher rating. I also don't think it is faulty because
It is new. I replaced the old breaker after it had popped a few times
when being turned on. The new breaker acts the way the old one did.
When the breaker pops I wait only a few seconds before turning it on
again and it never pops the second time it gets turned on. And it
never pops while the machine is running, only when it is turned on.
Could it be that the breaker is just on the edge of popping every time
because of the inrush current when the transformer is energized?
Thanks,
Eric
Click to expand...

You are using the wrong type of breaker..

Transformers can create back EMF at the worst time when
applying power, depending where the phase angle is at the time
of contact.

Get youreself a motor starter relay that comes with overloads,
they are normally designed to stand off up to 8x the holding current
when an event like this happens.

Drive the tansformer with it or use a fused disconnect with FRS type
fises, assuming that range fits your needs.


Jamie
 
On Sat, 5 Sep 2015 22:28:43 -0400, M Philbrook
<jamie_ka1lpa@charter.net> wrote:

In article <nmnjuahtq0h12eu8ghcll2arb1tujbppus@4ax.com>,
etpm@whidbey.com says...

I run my shop from a rotary phase converter and this setup has been
trouble free for years. Then a couple years ago I bought a machine
that runs on 480 volts that came with a transformer to boost 240 volts
to 480 volts. Most of the time when I turn on the breaker that
energizes the transformer nothing happens. But once in a while, maybe
2% of the time, the breaker pops when I turn it on. The breaker is
sized properly for the wires connected to it so it can't be replaced
with one with a higher rating. I also don't think it is faulty because
It is new. I replaced the old breaker after it had popped a few times
when being turned on. The new breaker acts the way the old one did.
When the breaker pops I wait only a few seconds before turning it on
again and it never pops the second time it gets turned on. And it
never pops while the machine is running, only when it is turned on.
Could it be that the breaker is just on the edge of popping every time
because of the inrush current when the transformer is energized?
Thanks,
Eric

You are using the wrong type of breaker..

Transformers can create back EMF at the worst time when
applying power, depending where the phase angle is at the time
of contact.

Get youreself a motor starter relay that comes with overloads,
they are normally designed to stand off up to 8x the holding current
when an event like this happens.

Drive the tansformer with it or use a fused disconnect with FRS type
fises, assuming that range fits your needs.


Jamie
Click to expand...
Thanks eveybody for the replies. I have been away from the internet
for a few days so I couldn't reply sooner. I'll get myself a motor
starter. How should it be rated? It is a three phase transformer rated
at 15KVA. Do I just look for a motor starter rated for 15KVA?
Thanks,
Eric
 
In article <ls7uuah9dn7dd09o1qu2dpeijno3ifvqp7@4ax.com>,
etpm@whidbey.com says...
On Sat, 5 Sep 2015 22:28:43 -0400, M Philbrook
jamie_ka1lpa@charter.net> wrote:

In article <nmnjuahtq0h12eu8ghcll2arb1tujbppus@4ax.com>,
etpm@whidbey.com says...

I run my shop from a rotary phase converter and this setup has been
trouble free for years. Then a couple years ago I bought a machine
that runs on 480 volts that came with a transformer to boost 240 volts
to 480 volts. Most of the time when I turn on the breaker that
energizes the transformer nothing happens. But once in a while, maybe
2% of the time, the breaker pops when I turn it on. The breaker is
sized properly for the wires connected to it so it can't be replaced
with one with a higher rating. I also don't think it is faulty because
It is new. I replaced the old breaker after it had popped a few times
when being turned on. The new breaker acts the way the old one did.
When the breaker pops I wait only a few seconds before turning it on
again and it never pops the second time it gets turned on. And it
never pops while the machine is running, only when it is turned on.
Could it be that the breaker is just on the edge of popping every time
because of the inrush current when the transformer is energized?
Thanks,
Eric

You are using the wrong type of breaker..

Transformers can create back EMF at the worst time when
applying power, depending where the phase angle is at the time
of contact.

Get youreself a motor starter relay that comes with overloads,
they are normally designed to stand off up to 8x the holding current
when an event like this happens.

Drive the tansformer with it or use a fused disconnect with FRS type
fises, assuming that range fits your needs.


Jamie
Thanks eveybody for the replies. I have been away from the internet
for a few days so I couldn't reply sooner. I'll get myself a motor
starter. How should it be rated? It is a three phase transformer rated
at 15KVA. Do I just look for a motor starter rated for 15KVA?
Thanks,
Eric
Click to expand...

Yes, a 35 amp version would most likely work for you just fine..
 
"M Philbrook" <jamie_ka1lpa@charter.net> wrote in message
news:MPG.30556ee29969aa0f989ce3@news.eternal-september.org...
You are using the wrong type of breaker..

Transformers can create back EMF at the worst time when
applying power, depending where the phase angle is at the time
of contact.

Get youreself a motor starter relay that comes with overloads,
they are normally designed to stand off up to 8x the holding current
when an event like this happens.

Drive the tansformer with it or use a fused disconnect with FRS type
fises, assuming that range fits your needs.
Click to expand...

Motor starters come after fuses or breakers. Unless that is changed first ,
the starter will not do any good.
 
In article <Y-adnaZci_eYim_InZ2dnUU7-KednZ2d@earthlink.com>,
rmowery28146@earthlink.net says...
"M Philbrook" <jamie_ka1lpa@charter.net> wrote in message
news:MPG.30556ee29969aa0f989ce3@news.eternal-september.org...

You are using the wrong type of breaker..

Transformers can create back EMF at the worst time when
applying power, depending where the phase angle is at the time
of contact.

Get youreself a motor starter relay that comes with overloads,
they are normally designed to stand off up to 8x the holding current
when an event like this happens.

Drive the tansformer with it or use a fused disconnect with FRS type
fises, assuming that range fits your needs.



Motor starters come after fuses or breakers. Unless that is changed first ,
the starter will not do any good.
Click to expand...

It would be obvious there is a higher amp protection somewhere before
the starter and the starter comes with overload protection that is
interlocked to the coil.

Jamie
 
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