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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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Some Facts about overvoltage

Over voltage problems are the most frequent the most overlooked and neglected. Many times equipment failure, downtime, software and data corruption, are the result of a problematic supply of power.  There is also a common problem with describing power problems in a standard way. We have tried to list out some of the common facts about over voltage issues

  1. Overvoltage, and its destructive effects, are well known but are often not recognized or understood.
  2. Little is documented in terms of its magnitude and frequency.
  3. It is difficult to identify, due to its sporadic nature, and often comes and goes undetected.
  4. Because of all the above, its existence is sometimes denied.
  5. Equipment failures due to overvoltage are often misperceived as defective equipment.
  6.  Power companies do not deny its existence; but they do not publish or otherwise inform the users that it exists, or warn users of potential periods in which it may occur.
  7. Power fluctuations are also caused due to in–line equipment. Viz. Motor during its starting period draws heavy current due to which voltage drops causing imbalance and over voltage somewhere else.
  8. With very few exceptions, electrical power distribution systems are inadequate to provide voltage within acceptable limits to all users at all times.
  9. Power companies cannot prevent overvoltage because they can only react to its existence, usually in response to customer (user) complaints about failing appliances, etc.
  10. The time of response can vary widely (anywhere between one minute and weeks) depending on many variables in the distribution system.
  11. Overvoltage can occur at any time, due to many factors, but is most likely to occur during certain periods such as fast changing high load demands, as seen during severe cold weather periods.
  12. Power companies are mandated by law to provide service without overvoltage.
  13. Power companies are not held accountable by any regulation authority for overvoltage.
  14.  Power companies will sometimes reimburse damage costs due to overvoltage if proof is provided by the complainant.
  15.  Overvoltage can only be proved by the use of a voltage recorder.
  16.  Some power companies offer overvoltage insurance to users.
  17.  Over voltage events are misperceived to be equipment failures leading to their replacement with other brands that do not have overvoltage protection and essentially mask the effects of overvoltage which can lead to inevitable catastrophic failures.

Also see:

  1.  OVCD- Over Voltage Cut-off Device
  2. How does a Servo Controlled Voltage Stabilizer work?
  3. Product breakdown management
  4. Protect your Equipment from harmful power fluctuations..
  5. Give reliability to your UPS systems in high fluctuation areas. OVCD solves your servicing woes!!!
  6. Protect your electronics

Visit our website:

Our email us for more info at



OVCD- Over Voltage Cut-off Device

Only protection device for protection against neutral open and double phasing protection

DSCF 1046

Most of the equipments today are having power supply which can handle fluctuations between 170V to 270V.  Also a lot of equipments have built in over voltage protection. 

However there are accidental cases where trees fall on over head wires or accidentally neutral opens  and resulting fault causes voltage in single phase to shoot upto 440V. The in built over voltage protection of  any equipment is of no use , because they get damaged themselves. OVCD is protection device for protection against such problems of  neutral open or double phasing.

If you look at the pictures above you can see a typical distribution line problem. There is chance of wire sagging and over head wires touching each other . this can easily cause double phasing condition.

OVCD cuts off the supply to equipment whenever there is such a problem and connects the supply only when the voltage comes back to normal.

It effortlessly withstands voltage fluctuations up to 440 Volts and spikes up to 6000 Volts. It is programmed with a power-on delay of 3 seconds (configurable) for initial surges which are harmful to any other device.


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.

Cost to company if your product breaks down.

Man power cost Rs 800 Travelling and per day costof service person
Production down time Rs 1000 Could cost upward dependingthe type of machine
Part replacement Rs 500 Could cost upward
Equipment decay Yes Reduction of life of equipment
Goodwill lost Yes Incalculable
Customer’s loss Yes Significant
Disturbing to business focus Yes Significant( both to customersand vendor)
Replacement of product Product cost Capital Loss

All figures in Indian rupees

Costs projected are indicative and may vary for product and services


•Neutral open protection (Protection up to 440 volts)
•Withstands up to 6000V spikes
•Smart start
•Under/over voltage protection
•No wave form distortion
•Lightweight , transformer-less design
•Compact size.
How it works.

OVCD is connected at before the equipment in use.

Incoming current will first pass through OVCD then into the equipment. OVCD continuously monitors the line voltage.

Whenever the voltage is above or below the set voltage limits the OVCD simply cuts the voltage to the equipment thereby saving it from the line disturbance. It reacts within fraction of second to the disturbance. OVCD will withstand the voltage even as high as 440 Volts.It however does not stabilize the voltage as in the case of other devices in the same category like Stabilizer, CVTs.

When the voltage returns to normal , the OVCD resumes the supply to the equipment with short power-on delay of 3 seconds(configurable). This feature is called the Smart Start. It prevents the initial harmful transient that may damage the Equipment.


How is OVCD better than other power conditioning / protection products?

1.Superior protection
2.Occupies less space
4.Transformer less design
Feature comparison with other devices in the same category
FEATURES  OVCD Servos  Stabilizer CVT Spike buster
Protection up to 440V


No No No No
Under voltage / Over voltage protection Yes No No No No
Protection from spikes Yes
No No Yes Yes
Protection from over load Yes
No No Yes No
Line indication Yes
No No No Yes
EMI /RFI filters Yes
No No No No
Waveform distortion No
No No Yes No
IC technology Yes
No No Yes No

Customized to suit your requirements.

We can customize the OVCD in following ways.

1.Voltage Settings( higher cut off, Lower cutoff voltages)
2.Power on delay
3.Input and output terminations



End Use application

UPS AC drives Medical Equipments
Solar power plants Compressors CCTV system
Refrigeration equipments Control Panels Dish Satellite System


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