hi
i would like some help as i am trying to to use itmov in an 250 volt rms 50 Hz circuit my quiry are
1. what rating itmov should i connect between phase / line and neutral?
2. what rating itmov should i connect between ground and neutral?
3. The rateing on the mov (i.e vei 275) is the arresting voltage?
4. what rateing filters for input and output should i have to put for this
circuit?
5. i want to known the circuit and its components along with its rateing
for spike protection for the DTH?
6. i read on the net that there is a spike gaurd without a itmov/tmov/mov as the mov's are connected across the line and neutral, line and ground, etc by which the spike voltage/current is diverted through the ground or the neutral as both this wires are connected to the motherboard or the body of the equipmentand as such the equipment can get damage due to this spike. So they says their spike guard which does not have the mov is safe then the spike gaurd which has mov. so kindly through some light on this issue as to what is used instead of the mov's and how it works.
pl. give me the above details as i would like to do it myself.
Thanking you in advance

 

You want to do this yourself?

What types of amperage are you dealing with here?

 

are u online
to your first question is yes
to your second it is for a maximum of 150-200 watts at 250 volt 50 Hz rms. and for the cable connection which is connected to the STB from the dish of a Airtel DTH
also i want to put it for the cfl bulbs and electronic choke of tubelight the cfl bulbs are of 9w 14w and 18 watt and the choke is of 40 watt
thanks for replying.

 

Are you refering to the Littlefuse type MOV device with an integrated temperature sensitive switch?

Did you go to their website? Did you read the application notes for MOVs?

It would be helpful if you were to elaborate on why you want to use an itmov - on what power source you are using (we don't all know where you live) -and what equipment you want to protect - and why you don't want to use a commercial product that may do the that sort of protection?

Ciao, Tim

 

i think i have already mention the voltage and frequency and the load of my equipment if you want to know where i leave i leave in GOA INDIA as far as ready made spike suppressors we get only one mov in it but as far as itmov it gives the indication that is what i read in Littlefuse but i am confused as to which one to select regarding the arrest voltage and joules is concerned as i am not an electronic person but an electrician
please help if you are electronic person
thanks again.

 

thank you sir Tim. i have found out that you are a Electronic Engineer i am very greatfull to you for your attention
thanks once again

 

i request you to kindly check this site Brick Wall Surge Filters: Non Failure Surge Protection - Brickwall at www.brickwall.com/
also see the zero surge i.e total surge cancellantion (TSC) surge suppression - Computer Dictionary Definition at computer.yourdictionary.com/ surge-suppression and let me know as i have made a mention about it in my 6th point on my first post
thanks.

 

The proper application of MOVs is covered in the application notes. I strongly suggest that if you are unable to reasonably interpret the application notes then you shouldn't really be playing with the device. The whole topic of suppression of transients, and protection of equipment is huge - and many commercial products are dominated by marketing hyperbole - I suggest the brickwall product fits that bill well, because there is no mention of standards compliance and no references to peer reviewed technical papers, and they are pitching sales at those that may be aware of the topic but not aware enough to comprehend what is being offered.

Designing protection requires an understanding of the mains, and how it varies in the location - it could be quite constrained to 250 +/-10% with no probable reasons to be outside those limits, but not everyone is that lucky. The energy characteristic (Joule rating) also depends a lot on the environment and what you expect to be the source of transients.

Ciao, Tim

 

Thanks Tim.
I only want to know the techonology used by brickwall product is correct as an electrician the over voltage desipated by the mov through the Neutral / ground can hit the body / motherboard of the equipment as the Neutral and ground voltage should not be more then 2 to 5 volt in a unblance circuit.
Secondly as you said 250 +/-10% and to be more accurate as the distrubution transformer of the electricity dept. is just 300 meters away and as such the day time voltage is 256volt and on peak load time i.e 7pm to 9 pm the voltage is 237volt as i am worried as i will be purchasing a LED LCD tv which is quit expensive also the Dept. feeder is of over head line with many trees and coconut trees with leaves falling down on the lines and lately a coconut tree fell on this line which was carring all the three phases.
Also a year back two of mine cfl bulbs had fused off while switching only though they were rated for 100-300 volt in seperate incident and right now i myself has used 3 mov in parallel of @V14k VEI 275 and a 500mA fuse before the mov on the live wire inside the tv stablizer but there are two things first i will not know when this will be exausted and secondly it may bust into flames inside the stablizer as such i was planning to use the itmov but this too is not avalible in Goa and as such i am trying it in Mumbai
I would like to also bring to your knowledge that the local electronic repaires dont know any thing in this as one of my friend had taken his spike suppressor for repair and they told him that the small part is not available in the market and as such he has no other option but to purchase a new one but when i cut open the square box i found only a single mov in a 3 core cable socket strip and trust me this is what we get in Goa
so i request you to kindly help and give me the detail to do a some what good spike suppressor with line filters.
sorry for the long write up.
thank.

 

nel,

The issue for you is 'risk'. A MOV or line filter won't help you for some of the poor power quality issues you have raised, as those devices assist with low energy transients, not for long duration swells, or the odd HV line dropped on LV. A UPS may be more appropriate to operate 'expensive' equipment if the UPS has a proper charger/battery/inverter configuration - the charger of the UPS then get's it in the neck, so try and get a UPS with a large input voltage range (eg. rated to 265VAC max).

If you get lightning then you also need to do something about the antenna.

 

no Tim, i was not talking about the HV line it was the LT line with all the 3 phases along with neutral as you know that when 2 phases or a phase and neutral come together where the distrubution transformer having 200 Amps fuse on its secondary it take quit a long time to open the circuit by burning the 200Amps fuse wire by that time the phase voltage will pass through the neutral thus giving 2phase i.e 440volt to a 240volt equipment for atleast 30 sec.
thanks
nelson

 

30 SECONDS?

Wow. That is the SLOWEST fuse I have ever heard of.

There are power factor correction devices that are basically huge capacitors that can help with this problem. As for the peak cutoff problem, Do you have standard breakers on your lines?

There are devices that use heaters to trip lines when voltage is too high. You can easily add these devices to your breaker box.

It would seem for a complete solution, you need to move.

just kidding.

If these are not SPIKES but slow moving changes (By slow I mean it takes longer than half a second to go from 235 to 255) MOV's and filters will do nothing.

You really would need a UPS to buffer or stabilize the power.

Have you contacted the power company? They know of this problem?

 

HV on LV is not that uncommon, especially for aerial transmission.

In reality you won't get 440 - at most it's 415, and all the voltage drops will pull that down a lot.

 

From what I've read you have terrible power distribution in India, it's no wonder why we keep getting all the questions about building wind generators.

Jumping from 220V to 440V for anything more than a few pulses won't be controlled by an MOV of any type, they'll just burn up too.

If it really is that bad you need some sort of UPS that can accept a wide input range and output what you need. Economocally this presents a problem.