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Thread: Average voltage regulator (AVR)

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    Average voltage regulator (AVR)

    We are experiencing problems with "sensitive" electronic equipment.

    I read an article the other day which indicates that an over voltage can reduce the lifespan of a piece of equipment by as much as 50 %... Eskom decided many years ago to increase the voltage in SA from 380/220 - 230 400... i have never thought much of it ... until it is time to replace fault LED lights etc... suddenly that 50 000 hours they offer does not apply to SA.

    Then we loose a power supply feeding a VSD in a machine and the "technician" indicates a replacement cost of around R80 000 ...now you have my attention... the machine technician is telling my customer that all his drives and power supplies are only going to last around 5 years ...' (some of the machines are already 10 years old ands til working fine) because the factory voltage is sitting at over 400 VAC... I indicated that the machine should be able to tolerate at least a 10 % fluctuation in the voltage ...lets say the machine is old and has a 380/220 transformer... the voltage should be able to vary from 380 to around 341 - 418 max.

    First question ...how bad is the 230 VAC compared to 220 VAC?

    I see products being offered to consumers to extend the life of their equipment by offering a stable 220 volts supply via a device used to "stabilize" the power.

    The second question ...is it the 230 VAC causing the problem with the equipment or the unstable power supply we have in SA... I am yet to see a stable 230 VAC supply on my fluke 435 ...more dips to as low as 135 VAC than a stable 230 VAC ... some recordings vary for 230 down to 190 up to 250.

    A site in Durban we have had to bypass the trip connect because the unstable voltage keeps dropping the contactor out (below 180 volts) yes we have had the electricity department arrive with a duspol tester and indicate the power is on... in that situation i did just smile and walk away.

    The third question...who is responsible for equipment required to create a stable power supply... if you buy your electricity supply from a property management company (who bills you every month) are they responsible for the power or as they indicate ...they just manage the account ...or is it Durban electricity department... when we start having equipment fail at a huge cost ...who pays the repair bill?
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Diamond Member Justloadit's Avatar
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    Modern electronic equipment, including motor inverters, are designed to work at much higher voltages than what is supplied by the mains. Equipment is designed to work in USA at 110V and the rest of the world at 230/250V. Effectively there is one fits all. I know difficult to accept. Effectively single phase equipment is rated to work from 85V to 285V AC.

    What kills electronics is "Spikes" caused by what is known as brown outs.
    Brown outs occur under 3 typical conditions
    1. When the load on the supply transformer exceeds the transformer rating, the causes the transformer to saturate, and the output voltage dips for the duration of this overload. The overload is not severe enough to cause the breakers to trip, and in many occasions occurs for a short period.
    This is typical of a almost fully loaded transformer, and a DOL starter is used to start very large motors. One of the reasons for Star-Delta Starters, and Reduced voltage Starters, and in inverter drives, the slow start function. In some instances the reduced voltage starting may not be possible, such as compressors, electrical guillotines, hot stamping, and punching operations where fly wheels and mechanical controls may not be suitable. This also typically occurs when long incorrectly sized supply cables are used to power heavy loads. The cable causes a voltage drop due to the cable resistance caused by the in rush current.
    The problem however, is that when the voltage dips, all inductive loads tend to cause what is known as a back E.M.F.. This back E.M.F. can cause a voltage spike many times higher than the supply, and is what causes the failure of electronic equipment. Interestingly the effect of the back E.M.F. is effectively used in many electronic supplies, such as Flyback Transformer and Flyback SMPS.
    2. When one of the high voltage supply to the primary transformer is lost for what ever reason, that instant loss acts similarly to the brown out, with similar symptoms.
    3. Which I have been noting in recent years, when a local grid is switched from one power station to another, there seems to be an out of phase symptom. Not sure what it is but it is similar to switching from a generator supply to the mains, with out allowing the load to synchronise to the mains supply, and the load when switched over could be 180 degrees out of phase, causing the lights to flicker, and motors to 'step a beat', because it is like starting the motor from standstill.

    Many of the cheap LED lighting use what we call an 'RC' circuit. To save money, the reactance of a capacitor is used to create an impedance, or a series resistance to reduce the amount of current to the LED. Using the Reactance of the capacitor, practically no heat loses are experienced as opposed to using resistors, and reduces foot print.
    The reactance of a capacitor is calculated as follows
    XC = 1/(2 x pi x F x C) pi = 3.14, F = 50Hz, C the capacitor value.

    The problem with this method, is that the reactance is based on the frequency, however this is not entirely true. The frequency is based on the time domain where the voltage rises from 0 to peak, which in the case of 50Hz is 10 milli seconds, however, in the case of a spike, the rise time from 0 to peak, which can be several hundred volts above the supply, can occur in the micro seconds range, so effectively, the charge rate in the capacitor is not a 50Hz supply, but experiences a instant supply of several hundred kilo Hertz, and as per the formulae, the reactance value reduces by the rate of the rise of the spike. SO effectively the current the LED is exposed to, may be 10 times what it expects, and causes the silicon in the LED to deteriorate. If this occurs many times, then the accumulation of the damage cause the LEDs to fail, become dim and change colour, and in some cases to flicker.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar and LED lighting solutions - www.microsolve.co.za

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    Justloadit... as i read your reply ...many things come to mind ...but the one that stands out the most is load shedding... (brown outs) as we are all aware load shedding could create this situation ...in reality we should be billing eskom for all the long term damage they are causing to the expensive equipment... for many customers who can make use of a generator... that couple of seconds in many cases where there is a change over to the generator is causing damage that will only be noticed in months or years to come.

    In this particular incident i mentioned above ...recently (less than 2 weeks ago) we had 2 power outages... a couple of days apart ...on both occasions it caused issues with the CNC lathes ...components had to be reset on the first ...but the second actually damaged the CNC's... (there is no generator connected)

    I have connected the fluke 435 at the main DB ...but instead of just plugging it into a socket outlet ...i have plugged the 435 power supply into the inverter ...so that we can record when it switches off and when it switches back on... unfortunately the outages last so long that the 435 battery would go flat and i would lose the startup.

    I dont believe the technicians theory is correct ... that the slight over voltage is damaging the equipment ... i believe it is load shedding and power outages which are destroying the equipment... fortunately we have all the computers .. servers ...screens and other essential equipment connected to a pure sine wave inverter...which lasts around 12 hours... we have had a total shutdown ...twice since the inverter was installed.

    I have recording dating back to 2018 ... one of the things i have noticed ...not a flat spot but more a dent in the top right on the sine wave on every cycle and on all 3 phases... something i need to investigate.

    The other issue we have is the power switches off then back on again ...but this time feed from the other side of the ring main... we have tried changing the transformer tappings from 2-3 and back to 2 ...but when supply changes over ...so does the voltage ...either increases or decreases... we are fighting a losing battle.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Diamond Member Justloadit's Avatar
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    What I have done in the past, but does cost some money.
    However depending on the value of the equipment, is to place a suitably rated constant voltage transformer also known as a CVT, between the equipment and the supply, whether from the mains, generator or inverter.
    The nature of the design of the transformer, removes spikes, noise and other nonsense which comes down the supply line.

    If the cost is too high for the complete equipment, then separate the electronics side of the equipment, and place a smaller CVT only for this part of the equipment.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar and LED lighting solutions - www.microsolve.co.za

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    Quote Originally Posted by Justloadit View Post
    What I have done in the past, but does cost some money.
    However depending on the value of the equipment, is to place a suitably rated constant voltage transformer also known as a CVT, between the equipment and the supply, whether from the mains, generator or inverter.
    The nature of the design of the transformer, removes spikes, noise and other nonsense which comes down the supply line.

    If the cost is too high for the complete equipment, then separate the electronics side of the equipment, and place a smaller CVT only for this part of the equipment.

    Each CNC lathes is fed from a 380/230 volt 3 phase transformer ...my thoughts are to fit some sort of electronics at the transformer on the CNC lathe ... if i do it at the main supply i will need a massive CVT ... the old lathes and milling machines dont need protection ...it would be a waste.

    I have been in contact with Nick from Sollatek.

    https://www.crown.co.za/sparks-elect...energy-savings
    Comments are based on opinion...not always facts....that's why people use an alias.

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