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Why TATA liebert ( Emerson network power) started using OVCD for protecting its UPS


The year was 1997 , when Tata liebert engineers visited us at an exhibition at world trade centre. They were looking for something that could protect their online UPS in harsh Indian conditions. Their attempts to use stabilizer has not resulted good results. The UPS was high frequency technology relatively new at that time and Tata leibert had ushered it to India from Chinese OEM in hopes to revolutionise the UPS industry with sleek models. The UPS was was more efficient in conversion of power as it had no transformer in it. All of this work was done with help of passive components.


However little did they know that they were in for a nasty surprise. the tolerance of these UPS was about 20% where as voltage fluctuations in India is more than 35%. At times trees would fall on overhead wire causing damage. Weak neutral or disconnection of neutral due to irregularities in distribution was very common. All this contributed to defect ratio of more than 26%. which would mean that 1 out of 4 UPS would come back for repair. This is bad statistic for any product. They were on verge of discontinuing the product line as it seriously dented the image of then no.2  company in online UPS.

DSCF 1046

This model was designed originally for TATA liebert.

After use of OVCD, their defect ratio went down from 26% to 6% which was a huge improvement. hence they decided to make it standard product for each UPS that would be sold in India.  

Many of distributors till date don’t know the exact use of OVCD, except for reason that it is supplied along with UPS and that it was mandatory to install it if they hoped for free servicing under warranty.

OVCD is protection device which safegaurds then equipment against damage caused by extreme overvotlage due to abnormal situations such as

1. neutral open condition

2. double phasing

Why should you consider using OVCD before your equipment?

1.No problems due to voltage fluctuation.
2.Zero downtime
3.Your equipment becomes more rugged
4.Less service calls = Increased profitability + Increased credibility.
5.Better perception of quality of your system in the minds of the customers
6.Increases the chances of repeat sales or referral sales.


Now you can install your equipment in the worst electrical conditions without being bothered about service calls.

We are looking for appointing dealers across India. If you are interested please drop us a email at

For bulk requirement we offer special rates

Visit our online store to purchase OVCDs online

The need for 400V protection in every premise

Whenever a building is designed all safety factors are taken in consideration. From electrical installations point of view safety factors to be considered are

  1. Short circuit
  2. Lightning
  3. Over voltage.

All of the above considerations are from worst case Scenario basis. All of the above factors, if not taken care of, can lead to #fires and loss of property and assets. there are also chances are of human tragedy.

Shortcircuit is normally taken care in all premises. Lightning protection is generally employed for high rise buildings . Both of these factors are from worst case scenario.

however voltage protection becomes the most neglected part. the worst case scenario in voltage is 440V in single phase and it can be caused by 2 reasons primarily

  1. Neutral open
  2. Double phasing caused by touching of overhead wires.

There is actually no safeguard designed to take care of this situation. We depend on our equipments to handle the overvoltage scenario. many equipment can handle this problem for short period of time only. Most electrical contractors consultants and architects do not offer a robust solution for such issues.

#MSS offers solution focusing on this very aspect of electrical problems. For details get in touch with us on


The need for double phasing and neutral open protection in Solar power plant design

Solar inv.jpg

Generally any equipment will get damaged due to 3 primary reasons.

  1. Short-circuit
  2. Lightning or surges
  3. Temporary over voltages.

First 2 reasons are taken care of in design and considered as per worst case scenario.

However safeguards for temporary over voltage are generally not taken, certainly not considered as per worst case scenario.

In secondary side of LT transformer , worst case scenario is 440V in single phase.

It happens more often than expected.

Reasons for 440V coming in your supply

  1. Neutral open condition
  2. Double phasing

Causes of neutral open.

  1. Uneven load distribution
  2. Loose wiring.
  3. Accidental breakage
  4. Maintenance work errors

neutral open

Causes of double phasing

  1. Trees falling on overhead wires
  2. Touching of overhead wires running through trees.

double phasing

Majority of projects are located outside of city limits due to roof space constraints and industry requirements. Such scenarios are very common

Not one of the available solar inverter can handle a continuous over voltage of the above nature and will get damaged resulting in down time.

There is strong need of safeguard against such issue in design stage itself so that such issues can be tackled with min losses.

To illustrate, if there is short circuit or lighting strike, the system is designed to handle it. However for continuous over voltage there is not a single solution that can be offered.

There is infact no solution incorporated for 440V in single phase. Most of integrators rely on the inverters capacity of handling voltage fluctuation, and they will definitely get damaged in such a situation.

This is where it is recommended to take cognizance of potential problem that can be taken care in design stage itself.

We specialise in this area i.e. Neutral open and double phasing protection.

You can see our website for details on how we can add value to solar field.

Lightning and surge protection

Surge protection

Surge Protection – a topic that has become increasingly important in recent years as got wide presence across industries. Costly electronic equipment, which is sensitive to voltage peaks on the supply, is no longer found only in offices and factories, but in our homes as well.

Nowadays, highly- sensitive data processing, telecommunication and computer networks form the back-bone of worldwide communications structures without which, no company can survive. Machines and production lines are monitored and controlled by electronic equipments programmed for specific purpose. Even many creative services are no longer conceivable without the aid of computers.
Common to all of them is their dependence on clean electrical energy, within tight tolerance limits and on a continuous supply of power around the clock.

Internal Lightning Protection according to IEC
Lightning current consists of a First stroke followed by a number of subsequent strokes. According to IEC 61024 and IEC 61312, wave shape of the first stroke is calculated to be 10/350 μSeconds.

lightning pulse

Approximately 25 to 30 % of failures in electrical/electronic equipments are because of surges created either by a Lightning or because of switching surges as per the data released by leading insurance companies

power survey

Lightning Peak Current and Frequency of strike:

The maximum value of Lightning current can go up to 200 KA as per IEC 61312 which is in the shape of 10/350 μ Seconds.

Lightning Current Distribution:

According to the standards IEC61024 and IEC 61312, during a lightning strike in a building having an external lightning protection, the lightning current reaches the earth termination. A part of Lightning current goes to earth and remaining part gets coupled into the building through conductive media like Steel reinforcement in Concrete, Earth Conductor Metal Parts connected to earth etc.

lightning distribution

The 100% of lightning energy breaks down as follows according to IEC61312:
–  50% of the lightning current will flow through the ground
–  50% of the lightning current will flow over the connected metal parts of the building (gets coupled into the building)
To protect electrical & electronic equipments inside the building, this 50 % of Lightning current which is entering into the building has to be diverted to the metal parts which is connected from outside. (Metal Water pipe, Metal Sewage pipe, Power lines, data lines etc)

Class B: (Class 1 according to IEC 61643 as well as Class C according to VDE0675)

is an arrester which is designed to carry a lightning current of 10/350 μ Sec duration. Important parameters to be taken care are Lightning Impulse current carrying capacity and Voltage Protection Level (Let through or limiting or clamp voltage)
Class C: (Class II according to IEC 61643 as well as Class C according to VDE0675)

is an arrester which is designed to carry a Surge current in the shape of 8/20 μ Sec. Important parameters to be taken care are Maximum or Nominal Discharge Current carrying capacity and Voltage Protection Level
Class D: (Class III according to IEC 61643 as well as Class D according to VDE0675)

is an arrester which is designed to carry a Surge current in the shape of 8/20 μ Sec as well as tested with a voltage impulse in the shape of 1.2/50 μ Sec. Important parameters to be taken care is Voltage Protection Level

connection diagram SPD

SPD’s are made with Spark Gaps, Metal Oxide Varistors(MOV) Silicon Avalanche Diodes(SAD), Gas Discharge Tubes(GDT) or a combination of these devices
Spark Gaps and GDT’s:

These are called as ‘voltage switching type’ SPD’s. The operating voltage can be determined by the distance between the electrodes. Spark gaps are arresters in which two or more electrodes in series are opposed to each other. The electrodes consist of incombustible material (e.g. carbon or tungsten-copper). Spark gap based arresters used in power line between Line and Neutral should be capable of interrupting the Short Circuit Current (also called as follow current)


Advantages – It can carry Very Large amount of Surge Current for a long Duration
Disadvantage – Need more time to react (about 100 nano sec), high follow Currents

(Metal Oxide Varistors) Varistors are ‘Voltage-dependent resistors’ with a highly non-linear V/I characteristic. Their electrical properties arise from a large number of micro-varistors connected in parallel and in series. The transitions between the micro-varistors can age under the influence of over voltages. Varistors are called as voltage clamping type SPD’s


Advantages – Faster than Spark Gap (approximately 25 nano sec). Limited current carrying Capacity
Disadvantage – Detoriation after every surge. Can create short circuit after a Maximum discharge current flow

Avalanche Diode:

Transzorb diodes (also known as suppressor diodes) are diodes that limit both positive and negative over voltages. Because of their very fast switching performance (in the picosecond’s region) they are well suited for use in precision and data line protection devices. These are also called as voltage clamping type surge arresters

Avalanche diode

Advantages – Very fast response to surges

Disadvantage – Very low surge current carrying capacity

By using Surge arresters at various zone boundaries, Transient over Voltages created due to a Lightning strike or switching surges can be limited below the Voltage Impulse with standing capacities of the equipments in respective zones.

SPD example

Write to us for more queries on queries@microsystemservices.

Also see

1. Does an AVR or surge (spike) suppressor really protect from voltage fluctuations???

2. How  does Servo Stabilizer work?


About the Author (Click on the image to visit his LinkedIn profile


Troubled by equipment breakdowns???

OVCD ad1

Does an AVR or surge (spike) suppressor really protect from voltage fluctuations???

AVR  means Automatic Voltage Regulation.

What it does is to regulate the mains voltage within a limited range. In the case of your UPS, it boost +12% when the incoming voltage is too low. Let’s say the incoming voltage is at 200 volts, the output then goes to 224Volts, +12% of 200 volts, which is still acceptable for most UPSs. When the UPS output reaches let’s say, 230V with the boost mode on, then the UPS sends a command to a component called relay so that the +12% compensation is turned off.

Basically the voltage regulation is a series of power transformers, it can either be step-up transformers or a step-down transformers  They basically do the same thing a 220V to 110V step-down transformer does, or a step-up transformer does, when it gets 110V and transforms to 220V. The UPS senses the incoming voltage and commands a series of relays  to select a different transformer output or “tap”, as they call it.

An automatic voltage regulator can only work within a limited range. Their “taps” are at a fixed rate lets say, +10volts. If the UPS have a 12% voltage trimming option and the incoming voltage reaches 270 Volts, it can only trim 12% of that, which will result in 237 Volts.

Voltage regulator transformer can have as many “taps” as its developer wants, but it makes the unit much heavier, it wastes more energy and generates more heat. It doesn’t matter if the AVR has four “taps” or sixteen taps, it is still slow for suppressing voltage surges
Surge suppression is basically made to protect against high energy and fast rising surges or spikes that can be caused by lightning, electric motors being turned on or turned off, etc. Surges are essentially fast rising spikes and voltage swells are slow rising and low energy in nature. Surge suppression can in some cases reduce voltage swells, but this is not its main purpose.
Surge protection is basically comprised of a component called MOV – Metal Oxide Varistor.

An MOV works at diverting surges to ground. When operating at its nominal voltage, or the mains voltage, the varistor acts like a resistor with its resistance tending to the infinite, so it does not conduct electricity to ground at this state. When there is a fast surge, it instantaneously reacts (in nanoseconds) by decreasing its internal resistance, allowing the excess energy to flow to ground.

The voltage regulator cannot act as fast as an MOV for suppressing high power and fast rising surges and would not be capable of that because of the nature of a power transformer. High energy surges must be diverted to ground and power transformers do not do that. Compared to the speed of an MOV, the voltage regulator is like a turtle.

There are some disadvantages regarding the use of MOVs for suppressing voltage swell. MOVs degrade very fast if frequent voltage swell are imposed to it, it gets too hot and it’s internal chemistry degrades. MOVs are made to react fast and come back to it’s initial state very quickly as well, which happens when a power surge occurs. That’s why manufactures of surge protective devices use an MOV that only triggers itself when the voltage is much higher than the mains voltage. If the MOV starts to conduct too early, it will degrade itself very quickly and on all power grids a relatively high number of fast duration swells, do happen

What an MOV doesn’t do…

An MOV does not provide equipment with complete power protection. In particular, a MOV device provides no protection for the connected equipment from sustained over-voltages that may result in damage to that equipment as well as to the protector device.

An  MOV provides no equipment protection from inrush current surges (during equipment start-up), from over current (created by a short circuit), or from voltage sags (also known as a brownout); it neither senses nor affects such events.

Susceptibility of electronic equipment to these other power disturbances is defined by other aspects of the system design, either inside the equipment itself or externally by means of  a circuit which typically consists of a voltage-sensing circuit and a relay for disconnecting the AC input when the voltage reaches a danger threshold. See OVCD).

In nut shell…

The AVR and the surge suppression solve two different problems. They’re complimentary technologies but do  not ensure total power protection.

The AVR can adjust the voltage of the line within a limited range to compensate for the voltage being too high or too low. However, the AVR does not respond quickly enough or have wide enough compensation to handle surges.

Surge protection is capable of putting huge surge voltages into ground very quickly, but won’t adjust the long-term voltage of the line as the AVR does.

Both however are ineffective against sustained high voltages. in neutral open condition , they themselves will need protection.

Please do give us your feedback

For more queries write to us on


Also see:

some facts about over voltage

Over Voltage cut off Device

How to protect your equipments from extreme power fluctuations



Loss to appliance manufacturers due to voltage fluctuation problems.

How often has this happen to you… You buy a brand new Plasma TV , Refrigerator, washing machine etc. just to find that it stops working with in the warranty period.

You call up the vendor and ask for replacement / repair of that equipment.  Have you considered that the quality of power at you house may be bad?  Even if you knew, would you acknowledge to the vendor?

Probably not!!! because you want a free service. Thats precisely what happens when any equipment fails. Equipment vendor is in a soup!!!

Power conditions are not good at all places. Voltage fluctuations are not something you can observe, not with out a voltage recorder definitely. But that wont be feasible at all times.

Effects of  voltage fluctuations are not understood until a very large catastrophe occurs and appliances are damaged.

Such a case has happen even in Metropolitan cities like Mumbai. There was a electrical fault at main distribution board of the house of very distinguished business person, wherein the neutral wire was burnt. This cause the voltage to shoot up to 440V ( this is called the neutral open condition).  At this voltage all the equipment in his house got damaged.  MCB/Fuse didnt react at all, and it will not. because MCB reacts to over current and not over voltage

He promptly called the appliance vendors and got the repairs done all free of cost as they were under warranty.

But here the manufacturer/ vendor had to bear the service cost. This includes salary for the day of the service technicians, changing of damaged components replacement of complete unit in some cases.

This cost is huge when you consider country-wide service.

We at MSS have developed , perfected and implemented device called OVCD for protection of equipments from power fluctuations.

We can help them reduce the events of such failures by more than 75%. This can improve the bottom line of the company.

Let us know in case of such problems at We will be glad to be of any assistance.

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