Has anyone looked into electronic potentials products for reducing transients?

Merry Christmas

paulengr

Senior Member
It’s called a metal oxide varistor. It contains a disc made of metal oxides sintered together. The main component is zinc oxide but the blend of metal oxides and the sintering process are part of how it is made.

This is a voltage variable resistor. It is almost an open circuit below it’s design voltage. Above that point it quickly turns into nearly a dead short.

There are other devices that are similar but MOVs are so cheap you can buy a $10 power strip with one.

They are connected live to ground or sometimes line to line. Note that so-called “whole house” MOVs do not work as advertised. The MOV is a parallel device not serial. The voltage rises about 20 Volts per inch of cable length from the MOV. So it is ineffective even a few feet away. The NEC required protection is only there so that the AFCI manufacturers don’t have to incorporate one into their breakers. Your expensive electronics aren’t protected.

Everything else is a matter of filtering. Series inductors resist rapid changes in current while shunt capacitors short out rapid changes in voltage. Either one or both act to filter noise.
 
It’s called a metal oxide varistor. It contains a disc made of metal oxides sintered together. The main component is zinc oxide but the blend of metal oxides and the sintering process are part of how it is made.

This is a voltage variable resistor. It is almost an open circuit below it’s design voltage. Above that point it quickly turns into nearly a dead short.

There are other devices that are similar but MOVs are so cheap you can buy a $10 power strip with one.

They are connected live to ground or sometimes line to line. Note that so-called “whole house” MOVs do not work as advertised. The MOV is a parallel device not serial. The voltage rises about 20 Volts per inch of cable length from the MOV. So it is ineffective even a few feet away. The NEC required protection is only there so that the AFCI manufacturers don’t have to incorporate one into their breakers. Your expensive electronics aren’t protected.

Everything else is a matter of filtering. Series inductors resist rapid changes in current while shunt capacitors short out rapid changes in voltage. Either one or both act to filter noise.
This is all foreign too me haha sorry not very knowledgeable. Are you talking about the surge protection that is becoming required in a panel as an MOV or the device i linked? Those surge arrestors or whatever they are called everytime i see one they are dead and it has a red light saying "replace" seems like more planned obsolescence. But the other week i did have lightning strike so close to my house while at the computer the keyboard i was typing on felt like it had "static" or something felt weird. It just made my computer hiccup then everything was ok.

This seems an interesting thing to research i always wondered how noise could be such a big problem when we have devices like powerline adapters where u can send internet through a live circuit and it works just fine but somehow audio equipment can be influenced by transients.
 

paulengr

Senior Member
This is all foreign too me haha sorry not very knowledgeable. Are you talking about the surge protection that is becoming required in a panel as an MOV or the device i linked? Those surge arrestors or whatever they are called everytime i see one they are dead and it has a red light saying "replace" seems like more planned obsolescence. But the other week i did have lightning strike so close to my house while at the computer the keyboard i was typing on felt like it had "static" or something felt weird. It just made my computer hiccup then everything was ok.

This seems an interesting thing to research i always wondered how noise could be such a big problem when we have devices like powerline adapters where u can send internet through a live circuit and it works just fine but somehow audio equipment can be influenced by transients.

The original surge arresters were two sharpened metal studs adjusted very close together to form a spark gap. In the 1930s silicon carbide diodes came out. Two diodes placed back to back. Above a certain reverse voltage (the avalanche point) reverse bias diodes go into conduction. Larger (utility) systems used the exact same parts. For low voltage this is still used today with zener diodes (designed for this). Also for higher current a neon tube (has discharge tube) works excellent for say data lines. But in the 1970s metal oxide varistors came out. They are cheap, work at nearly any voltage over 100 V and below around 100 kV (combined with gaps above that point), and can be made arbitrarily big. On utility poles typically they are installed once every fifth pole. If you look up and see a jumper over to what looks like another small insulator next to the main line, that’s it. In fact those are so cheap (around $150 each) I bought 3 of them to protect a power factor correction capacitor in a 5 kV install yesterday instead of the “panel” style units. The surge arresters are attached at the top. This was replacing old failed power factor correction capacitors on a several thousand HP motor.

f4a4e5163ffd4c27f2229c9a3dbc08bc.jpg
 
The original surge arresters were two sharpened metal studs adjusted very close together to form a spark gap. In the 1930s silicon carbide diodes came out. Two diodes placed back to back. Above a certain reverse voltage (the avalanche point) reverse bias diodes go into conduction. Larger (utility) systems used the exact same parts. For low voltage this is still used today with zener diodes (designed for this). Also for higher current a neon tube (has discharge tube) works excellent for say data lines. But in the 1970s metal oxide varistors came out. They are cheap, work at nearly any voltage over 100 V and below around 100 kV (combined with gaps above that point), and can be made arbitrarily big. On utility poles typically they are installed once every fifth pole. If you look up and see a jumper over to what looks like another small insulator next to the main line, that’s it. In fact those are so cheap (around $150 each) I bought 3 of them to protect a power factor correction capacitor in a 5 kV install yesterday instead of the “panel” style units. The surge arresters are attached at the top. This was replacing old failed power factor correction capacitors on a several thousand HP motor.

f4a4e5163ffd4c27f2229c9a3dbc08bc.jpg
That looks like a fun install haha ive never seen an insulator in a cabinet.
 

paulengr

Senior Member
That looks like a fun install haha ive never seen an insulator in a cabinet.

That’s not an insulator. It’s a surge arrester.

IEC motors typically have insulated terminals. It’s just a ceramic or plastic block at low voltage. It is an insulator at medium voltage.

The original capacitors were about twice as high and the wiring was trimmed to fit. Even if I didn’t use the surge arresters my choices would be to replace all the wiring feeding this cabinet or install insulators as terminal blocks. The jumpers from the surge arresters to the capacitors are new.

Regardless at medium voltage switching transients are a serious problem. So it is very common to see surge arresters and/or surge capacitors mounted either in the peckerhead or right next to it.

As an example on older systems you often find both surge caps and SiC surge arresters. As an example of why the early vacuum contactors had notorious restriking problems. This was later corrected by using a “softer” material in the contact tips but early vacuum contractors were pretty rough. Also MV motors are often “close” to utility feeds and subject to transients from HV switches that need maintenance as well as lightning strikes. So practice is to always use surge arresters. This one didn’t have any. The surge cap is because there is a significant delay in terms of going into conduction with spark gaps and SiC arresters. So the cap delays the peak enough that it gives these older technologies time to start conducting. Newer MOVs don’t need surge caps because their response times are very short (microseconds) but old habits die hard.

In this case the motor is I think 2,000 or 3,000 HP. It tends to run idle a lot. With Dominion Power if your power factor is below 0.85 they “gross you up” to 0.85 on both demand and kwhr charges. So if you are only using say $1,000 in electricity a month but your power factor is 0.60 they will charge you $1,416! This one motor is the largest in the plant. Adding capacitors cancels about 90% of the vars which easily brings the plant close to 0.85. If they need a little more we can just put a couple caps on another large motor.

This is a lot of detail about medium voltage (1000-35,000 V) systems but something I work on all the time. Everything is made to order in MV so those of us in the field fabricate just about anything needed for the job.

One of the unfortunate things about MV is it’s less tolerant of surges. The typical spec is 200% of tge rated voltage plus 1,000 V. So for say 120 V wiring with THHN the wiring is rated 600 V so it is tested at 2200 V. NEMA has done a lot of testing and found most of it exceeds 2800 V. So a factor of over 2300%. On 4160 like this case the wiring is typically rated 5 kV. So surge testing and rating is 11 kV.or just 220%. So as you can see MV is a lot less forgiving when it comes to surges and surge arresters are added everywhere for good reason.
 
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