CALCULATION FOR EARTHING CABLE OF TRANSFORMER

Earth Fault Current = Rated Current / Impedence
where Rated Current = Rated KVA / (Rated KV x 1.732)


Example : 1600KVA TX , 11/0.433KV, Impedence : 6


--> Earth Fault Current = [1600KVA / (0.433 x 1.732] / 6
= 355.57A

Note :
To refer to catalogue to choose which size of cable that can carry 355.57A

Study Report 1 : Upgrading of Electrical Supply

1. Introduction:

To check the effect of load increase due to the new equipment to be installed in the factory

2. Reference Document:

a. as built drawings

b. latest electrical bill

c. on-hands information by the client's representative

3. Current installation:

a. Single chamber sub-station with 1000KVA Transformer

b. Current size of ACB is 1000A TPN with 1600A Busbar

c. Current MD is 600A

4. New Installation:

a. New equipment (MD = 720A)

b. New a/c load (MD = 86A)

5. Maximum Demand Load Analysis:

a. Future MD (A) = Current MD + New MD

= 600A + 720A + 86A

= 1406A

b. Future MD (KW) = 860KW

c. Future MD (KVA) = 1012KVA

6. Conclusion:

a. New load cannot be catered by existing TNB sub-station

b. Application on new load / increasing of the current load need to be submitted to TNB

c. New MSB need to be installed to cater for future load / to upgrade the existing MSB (1000A TPN ACB to 1600A TPN ACB)

Forms of Assemblies - FORM 4 (Part 4)

Note:
The above Form Code have been tabulated based on IEC 439-1, Part 1, Clause 7.7 - FORUM

Forms of Assemblies - FORM 3 (Part 3)

Note:
The above Form Code have been tabulated based on the IEC 439-1 Part1, Clause 7.7 - FORUM

Forms of Assemblies - FORM 1 & 2 (Part 2)

Note :

The above Form Code have been tabulated based on the IEC 439-Part 1, Clause 7.7 - FORUM

Forms of Assemblies (Part 1)

According to IEC 439-1, Clause 7.7 Forms of Assemblies can be obtained by means of partitions or barriers (metallic or non-metallic) into separate compartments or barriered sub-section.

Why is Forms of Assemblies is very important?

1. to enable a functional unit to remains in service - to reduce the risk of making accidential contact with the live part or adjacent units of busbars

2. to reduce the risk of loose part, tools, or even debris falling into or otherwise passing into an adjacent compartment

3. to limit the probability that ionised gas created by the operation of a short-circuit protective device, could cause flash over accross adjacent equipments or busbars

4. protection against contact with live parts belonging to the adjacent functional units

Note :

The above are a summarisation of Form Code IEC 439-Part 1, Clause 7.7 - FORUM

VCB Mechanical Operation Checks - FAT

During FAT, there will be a Mechanical Operation Check to be done to ensure the mechanical operation and interlocking for the followings are in order :

1. VCB

a. the breaker can be racked in and out smoothly

b. when in the Connected Position : earth switch cannot be closed, control plug cannot be removed, when VCB closed - breaker cannot rack out, when VCB opened - breaker can rack out, VCB door cannot be opened

c. when in Intermediate Position : VCB cannot be closed and control plug cannot be removed

d. when in Disconnected Position : VCB door can be opened, earth switch can be closed and control plug can be removed

Note :

VCB cannot be connected when the VCB is closed, there is no control plug inserted, earth switch is closed and the door is opened.

2. EARTH SWITCH

a. it can be opened and closed smoothly

b. minimal rebounce on the blade

c. the padlock facility is provided

d. there is mechanical / electrcal interlock

3. SAFETY SHUTTER

a. smoothly open and close

b. the padlock facility is provided

c. latching facility provided

d. self-cancellation for latching facility in working condition

4. PT SHUTTER

a. smooth opening and closing

b. padlock facility provided

5. KEY INTERLOCKS

a. the key is released when breaker in disconnected position

b. VCB cannot rack in unless key is inserted

~ the above notes have been taken during my FAT at one of the well-known manufacturer of VCB in Malaysia