Bus Bar Calculation for Main LT Panel

A. Bus Bar size calculation for 3200A Rating Panel: -

CONDITIONS

Rating Current: 3200Amp.

System: 415Vac, TPN, 50Hz.

Fault Level: 50KA. For 1 Sec.

Operation Temp: 40°C rise over 45°C ambient.

CONSIDERATION

Enclosure size: 1400mm. wide X 400mm. height

Bus bar Size: 2:200x10 per Ph., 1:200x10 for Neutral.

Bus bar material: Electrolytic gr. Al. (IS 63401/AA6101)

CALCULATION

1. AC Current rating for Dual Al. Flats 200x10mm considered = 4750Amp.

(As per Table – 8.4 as INDAL hand

book)

2. Ambient correction factor (k1) 45°C rise over 35°C (ambient) = .88

(As per Table – 5 as INDAL hand book)

If ambient Temp. 45°C instead of 35°C than De-rating Factor = 1-θ° C x α

θ = Temp difference = 45°C - 35°C = 10

α = Resistance-Temp. Coefficient for Al. Bus= 0.00403

k1A = 1-10 x 0.00403 = 0.96

3. Enclosure correction factor (k2) ratio of total conductor bus bar cross-

section to enclosure cross-section.

(3 x 2 x 200 x 10) x 100

--------------------------------- = 2%

1400 x 400

De-rating factor for enclosure = 0.82

(As per Table – 5 as INDAL hand book)

4. Correction factor (k3) for busbar material = 1

5. Up-rating factor (k4) for PVC Sleeving bus bar = 1

6. Total Combined De-Rating factor = k1xK1Axk2xk3xk4

= 0.88 x 0.96 x 0.82 x 1 x 1

= 0.693

So, actual rating of considered busbar = 4750 x 0.693 = 3291Amp.

Conclusion: -

It means 2:200x10mm Al. Bus Bar is much sufficient for

3200A Rating as per actual operating conditions.

B. Minimum Conductor size for Stand 50KA Fault : -

While considering short circuit condition, assuming a steady state average

temperature of 75°C and final temperature of 160°C then required bus

section:

CALCULATION: (As per table – 17)

Let θ f =Final conductor temp after the fault = 160°C.

θ I = Initial conductor temp before the fault = 75°C.

A = Cross sectional area of conductor (Sq. inch) =?

T = Duration of fault (sec.) = 1 Sec.

Isc = Short circuit current = 50KA.

A θ f + 258

Or Isc = 14 x 10 ------ log10 ----------------

T θ I + 258

Isc x T

Or A = ----------------------------------------------

θ f + 258

14 x 10 log10 ----------------

θ I + 258

50,000 x 1

Or A = ---------------------------------------------- = 0.93 in

160 + 258

14 x 10 log10 ----------------

75 + 258

Or A = 600 mm. Considered bus section = 2x200x10 = 4000mm.

Conclusion: -

It means 2:200x10mm Al. Bus Bar is much sufficient for

stand 50KA Fault Current for 1Sec.

C. TEMPERATURE RISE CALCULATION OF

CONDUCTORS : -

Max. Temperature at full Load condition: -

i.e. When 3200Amp. Flows thru steady state temperature of 45C.

Full Load Current

T max = Ambient X ------------------------------------------------------- X Allow T rise

Actual Current Rating of used Conductors

45 + (3200 / 3291) x 40 = 82.8C which is within the limit of 85C

[45+40].

Summary: Hence the designed bus bar for Main Panel

is OK & within the safe limit.

Reference: INDAL hand book

And IS: 8623 (Part – 1) of 1993.

Bus Bar Calculation for Bus Duct

A. Bus Bar size calculation for 3200A Rating Bus

Duct: -

CONDITIONS

Rating Current: 3200Amp.

System: 415Vac, TPN, 50Hz.

Fault Level: 50KA. For 1 Sec.

Operation Temp: 40°C rise over 45°C ambient.

CONSIDERATION

Enclosure size: 750mm. wide X 450mm. height

Bus bar Size: 2:200x10 per Ph., 1:200x10 for Neutral.

Bus bar material: Electrolytic gr. Al. (IS 63401/AA6101)

CALCULATION

1. AC Current rating for Dual Al. Flats 200x10mm considered = 4750Amp.

(As per Table – 8.4 as INDAL hand book)

2. Ambient correction factor (k1) 45°C rise over 35°C (ambient) = .88

(As per Table – 5 as INDAL hand book)

If ambient Temp. 45°C instead of 35°C than De-rating Factor = 1-θ° C x α

θ = Temp difference = 45°C - 35°C = 10

α = Resistance-Temp. Coefficient for Al. Bus= 0.00403

k1A = 1-10 x 0.00403 = 0.96

3. Enclosure correction factor (k2) ratio of total conductor bus bar cross-

section to enclosure cross-section.

(3 x 2 x 200 x 10) x 100

--------------------------------- = 3.5%

750 x 450

De-rating factor for enclosure = 0.78

(As per Table – 5 as INDAL hand book)

4. Correction factor (k3) for bus bar material = 1

5. Up-rating factor (k4) for Black Matt Painted bus bar = 1.2

6. Total Combined De-Rating factor = k1xK1Axk2xk3xk4

= 0.88 x 0.96 x 0.78 x 1 x 1.2

= 0.79

So, actual rating of considered bus bar = 4750 x 0.79 = 3752Amp.

Conclusion: -

It means 2:200x10mm Al. Bus Bar is much sufficient for

3200A Rating as per actual operating conditions.

Summary: Hence the designed bus bar for Bus Duct is

OK & within the safe limit.

Reference: INDAL hand book

And IS: 8623 (Part – 1) of 1993.

Bus Bar Calculation for Other Panels [Main Bus]

Sl.

No.

Used

Current

Rating in

Amp.

Used Bus Bar Size:

Current Rating

as per INDAL-

Hand Book

Table No. 8.4

in Amp.

Max.

[Approx]

Total De-

Rating

Factor

Actual

Current

Rating

1.0 1600Amp

.

2x100x10 – For

Ph.

1x100x10 – For N.

2650Amp. 0.7 1855Amp

2.0

800Amp.

100x10 – For Ph.

100x6 – For N.

1565Amp. 0.7 1095Amp

3.0

630Amp.

80x10 – For Ph.

80x6 – For N.

1250Amp. 0.7 875Amp