We thank you for the courtesy extended to  me and our SBS Power and Earthing Solution team ,

The major points that were discussed  are summarized below ;

 A .The GRID  SYSTEM  OF EARTHING  :

It is very important to use this method when specifically LOW EARTH  RESISTANCE –OHMIC VALUES  are required for very  SPCIALISED  APPLICATIONS .In this case the EARTHING SYSTEMS are   CONNECTE D IN FOLLOWING MANNERS ;

TWO EARTHING – LONGITUDINAL –STRAIGHT LINE

 THREE EARTHING —TRANGULAR   SHAPE 

FOUR AND   ABOVE –RECTANGULAR _PENTAGON _HEXAGON  AND SO ON IN GEOMETRIC   SHAPES.

THE FORMULA USED  IS AS UNDER  :

1/R ====1/r1 + 1/r2+1/r3 +1/r4  and so on 

THE NET REWSISTAANCE IS INVERSELY  PROPOTIONAL . SUPPOSE YOUR AVERAGE VALUE IS EXPECTED IS    2 ohms , connecting 4 earthings in GRID will GIVE YOU VALUE OF 0.5 ohms  . 

PRECAUTIONS ; 

1THE EARTHING SHOULD BE FIXED AWAY FROM WALL –MINIMUM 1,5 meter .TO avoid  DRYNESS OF SOIL

1.The EARTHING SHOULD BE AWAY  FROM DARINAGE  SYSTEM   OR FLOWING WATERS .it  IS VERY IMPORTANT  BECAUSE THE CHEMI CAL UESD WILL GET WASHED AWAY . THE EARTHING WILL FAIL.

2.ALL  INTERCONNECTIONS   MUST BE BE WITH STAINLESS STEEL NUTS AND BOLTS  WITH  DOUBLE SPRING WASHERS  TO AVOID  LOSSENING OF JOINTS .ALL JOINTS  WITH EARTHING AND EQUIPMENTS MUST BE “ NO FAIURE JOINTS “

 

B.NEUTRAL  EARTH VOLTAGES –(NEV ) AND  ISOLATION TRANSFORMERS 

Today  NEV PLAYS VERY IMPORTANT ROLE  TO PROTECT DAMAGING OF PCB OF ELECTRNIC EQUIPMENTS .

As the name suggest this voltage between the STAR POINT _NEUTRAL POINT OF SUPPLY  AND WITH THE EARTH..

STAR  POINT VOLTAGE IS ZERO and  THE VOLTAGE (POTENTIAL DIFFERENCE)   OF EARTH IS  ZERO  

THE  IDEAL NEV SHOULD BE ZERO . BUT IT IS NOT POSSIBLE because ELECTRICITY IS POLLUTED BECAUSE OF FOLLOWIND LOADS AND THE LOADS ARE  NOT BALANCED  EQUALY IN THREE PHASES 

 Electricity is  Polluted today(OVER STRESED)  . The pollution is due to the following main reasons 

1. Transients

2. Interruptions

3. Neutral Earth Voltages and floating Neutralcurents

4. Sag / Undervoltage

5. Swell / Overvoltage

6. Waveform distortion

7. Voltage fluctuations

8. Frequency variations

 

These are controllable by the user by distribution of load, ProperEarthing//Grounding of the equipment to maintain low earth resistance values.The subjects of Neutral Earth Voltages popularly known as NEV  are  discussed in details here under 

LET  US EXPLAIN IN DETAILS

1.The protection against floating neutral voltages :

Let’s explain what NEV (Neutral to earth voltage) is?

It is voltage b/w neutral and earth which should be theoretically zero. In electrical Engineering it is a well known fact that Earth is at zero potential and so is the neutral point of the star connected supply line.

2.When you connect a voltmeter b/w Earth and Neutral point it should be zero. 

NE

 

 

3.Neutral voltages are today known as Floating neutral voltages as the voltage change with the change of load condition in the existing plant or in the neighboring plant. The voltages keep on changing during various times of the day and even week or in a month as the parameters of balance load will change.

4.Neutral currents are calculated as per the following formula:

I= {(A²+B²+C²)-(AB+BC+AC) }½

Let’s put the values in the above formula,

              A=10,B=10,C=10

Then value of neutral current comes,

              I=0A

Other example is, A=9,B=8, C=7

Then value of neutral current comes,

I=1.73 A because of load unbalanced

V=IR

R=2 ohms ohmic value of Earth resistance, then V= 1.73×2= 3.46 V

When R=3 ohms, V= 1.73x 3= 5.1 V

When the load is unbalanced the Phase angle of the star point is changed as per the following calculations :

 Voltage b/w phase A & B is 415 V

Angle B/w two phases 120 degree 

Therefore the change of voltage per degree of change of phase angle 415/120= 3.45 degree

                                                A B

120

415 vN

 

 

C

In the above examples when the load current varies b/w 9, 8 & 7 A the phase angle get changes nearly 1 degree which is reflected in the calculation given above. This is nearly 3.51 volts.

Conclusion: as you will observe from the data given above that the following factors are not in control of Earthing systems.

A.The load current will vary throughout during the day and will also differ substantially during the various periods of the month or in a year.

B.Electricity travels always from An easier path and therefore it will travel from the neighboring industries or installations which will get reflected from the star point and therefore the NEV is always known as Floating Neutral Voltage and this voltage cannot be controlled by Earthing systems.

C.Following suggestions are given:

i.Balance the loads periodically to ensure that the floating Neutral voltages are under control. Checking of neutral point and outgoing connections time to time.

ii.The most of the PCB cards are designed for operations of 9 v-18 V and the small neutral voltages up to 9 volts are not likely to damage the PCB. It will of course the manufacturers of molding machines of such equipments are abundantly over cautious on insisting upon the clients to maintain the low neutral voltage at the time of commissioning the equipment. The technical executives of machinery manufacturers also have knowledge that the neutral voltages will float in higher level without their knowledge depending on the condition of load when they leave the installation after commissioning.

iii.The apprehension of the neutral voltages floating to higher levels makes the manufacturers unnecessarily very very over cautious and insist upon the user low neutral voltage rather than persisting the customer to do the electrical audit time to time and balance the loads which in their per view.

iv.Electrically speaking it is none of the business of the user to run an industry and electrical equipments on the unbalance loads. The Electricity rules as a user guideline doesn’t permit in any way to unbalance the loads. If they do it they do it at their risk and cost.

 

The safest way to ensure the neutral   Earth voltages down come into picture and you want to play 100% safe please don’t use supply neutral at all but use an Isolation Transformer of Delta- Delta combination with 1:0.95 i.e. is the final and last positive solution if you don’t want to take risk.

 

USE OF ISOLATION TRANSFORMERS  –THE ONLY FOOL PROOF SOLUTION   

   

ISOLATION OF NEUTRALS  EXPLAINED  BELOW 

 

The electrical system would be fine if the interconnection of the primary and secondary Neutrals were removed. This would eliminate any voltage entering from the primary neutral. But this is not permitted, since it would allow a potentially dangerous situation’s

Since a normally configured and properly wired distribution system almost never has neutral-to-earth voltages in excess of 6/8 volts, it can be blocked by virtually creating open circuit 

, “blocking” the neutral-to-earth voltage from entering a customer’s

Service. If the neutral-to-earth voltage is over 11 volts, either a fault or other failure has occurred and it  acts as a short circuit, connecting the neutral

For safety with the impedance in  “shorted” mode.

 

ADDITIONAL EARTHING OF LITTLE HELP:

 

A typical response when encountering –off-site stray voltage is to drive an additional earthing   on the premises. Please consider the numerous earth stations along the multi-grounded distribution system; the addition of even a few additional grounds is not likely to materially reduce the voltage. In actuality, if the entire grounding complex were duplicated the voltage would only be reduced by a magnitude of one-half.

The equipotential plane has been used in industries or other loads for protection within a small confined area. It does nothing to eliminate source and corrects nothing in the connected loads etc.

 

SOLUTION TO NEUTRAL TO EARTH  VOLTAGE:

 

 Neutral sources can be safely guarded against by installation of  ISOLATION TRANSFORMERS .This will cost much less than a single problem which  can occur when  costly computerized equipment can be damaged.The  use of ISOLATION TRANSFORMER  is very sound choice for a cost

–effective device which retains system safety and reliability while eliminating troublesome neutral-to-earth “Stray Voltage”.

 

FINAL CONCLUSION 

The safest way to ensure the neutral   Earth voltages down come into picture and you want to play 100% safe please don’t use supply neutral at all but use an Isolation Transformer of Delta- Delta combination with 1:0.95 i.e. is the final and last positive solution if you don’t want to take risk.

C ELECTROSTATC DISCHARGE

Electrostatic Discharge (or ESD

When you walk across a carpet and touch a metal door knob, you experience a slight shock on your fingers. If the same ESD occurs in If the same ESD occurs in data networking equipment, the equipment can be damaged or destroyed.

In summary, ESD damage occurs due to the following:

1. Direct electrostatic discharge to the device

2. Electrostatic discharge from the device

3. Field-induced discharges

4. ESD damage can be unknowingly caused when inspecting, sorting, or installing the ESD-sensitive device

PRECAUTIONS TO BE FOLLOWED 

Permanent / metallic wrist straps

Use permanent or metallic wrist straps instead of disposable ones as metallic wrist straps have better connectivity to the skin of the operator, and are less prone to failure when compared to disposable wrist straps, which are made of inexpensive and not very resistant material.

ESD shoes Anti-ESD SHOES 

In all the installation sites that have conductive floors . encourage wearing ESD shoes that have metallic elements, so that the static electricity gets discharged when the shoes come in contact with the ESD flooring.

However, we recommend that with ESD shoes, users should also wear a wrist strap when handling sensitive components. This is essential for users working at a bench where they can rest their feet on a table bar and lose contact with the floor.

ESD mat

Use an ESD mat  that is grounded to the rack when performing a card swap. In fact, if it is not possible to immediately store the replaced or damaged cards in an anti-static bag, the ESD mat offers a surface to temporarily keep the electronic equipment and prevent ESD damage.

Kindly follow all the pre  cautions 

We have made quite detailed  presentation on thee topics . Kindly clarify  any pints 

 

SBS POWR======