Short Circuit & Temperature Rise Calculation

TEMPERATURE RISE & SHORT CIRCUIT CALCULATIONS

CUSTOMER NAME

PROJECT NAME

BOARD NAME

Temp. Rise

Short Circuit

Browse logo to print on report :

Inputs :

Data/Assumptions

Value/s

Unit of Measurement

Value Selected

Remark

MBB Rating

Bus bar material

MBB size/area

x x x

No.of bus bars per phase

No.of phases

Fault level

Fault level duration

Short Circuit Current Isc

Ambient temp.

Ambient temp. at installation site

Temp.rise

End temp

Temp rise at instant of fault

(Degree Of Protection) IP

MBB enclosure dim./area

MBB Insulation

MBB Ventilation

α₂₀ Al/Cu

k Al/Cu

Bus bar support material

Dist.betn.2 bus bar supports

Space betn. 2 phases

iconiclogo

currentdate

TEMPERATURE RISE CALCULATIONS

CUSTOMER NAME	txtClientName
PROJECT NAME	txtProjectName
BOARD NAME	txtBoardName
MBB RATING : txtMBBRating A	MBB SIZE : txtNosets x txt_rem_Space_betn_2 x txtMBBHeight x txtMBBT mm²	FAULT LEVEL : txtFault_level kA for txt_fduration sec.	TEMP.RISE : txtTemp_Rise ^oC

Inputs:

Data/Assumptions	Value Selected	Unit of Measurement	Remark
MBB Rating	txtMBBRating	A	txt_rem_MBBRating
Bus bar material	txtBusBarMaterial		txt_rem_BusBarMaterial
MBB size / area	t = txtMBBT & h = txtMBBHeight	mm²	txt_rem_MBBSA
No.of bus bars per phase	txt_Nbb		txt_rem_Nbb
No. of phases	txtNo_Of_Phase		txt_rem_No_Of_Phase
Fault level	txtFault_level	kA	txt_rem_Faultlevel
Ambient temp	txtAmbientTemp	^oC	txt_rem_AmbientTemp
Ambient temp at installation site	txtAmbient_Temp_at_installation_site	^oC	txt_rem_Ambient_Temp_at_installation_site
Temp. rise	txtTemp_Rise	^oC	txt_rem_Temp_Rise
End temp	txtEnd_Temp	^oC	txt_rem_End_Temp
(Degree Of Protection) IP	txtIP		txt_rem_IP
MBB enclosure dim./area	D = txtMBB_Enclosure_dim & H = txtMBB_Enclosure_area	mm²	txt_rem_MBBendimarea
MBB Insulation	txtMBB_sleeving		txt_rem_MBBsleeving
MBB Ventilation	txtMBB_ventilation		txt_rem_MBBventilation

A. The continuous current carrying capacity (i.e. value of DC current rating) for Bus bar having above details & temp. conditions is given by –

l_dc = 24.9 x A^0.5 x P^0.39 x O^0.61 = txtDC_Current_Rating A
√ sqrt( [1+{R x O} ] x S)

where A = cross sectional area of one bus bar in sq.cm.

P = Perimeter of one bus bar in cm.

O = Temperature Rise = difference between end temp. & ambient

R = Resistance temperature co-efficient at txtAmbientTemp ^oC ambient

S = Specific Resistance in micro ohms cm.

iconiclogo

currentdate

B. De-rating due to Skin Effect:

To obtain the A.C. rating, the D.C. rating is divided by a factor called ‘SKIN EFFECT RATIO’, as given below :

l_ac = l_dc / sqrt( R_ac/R_dc) = txtDC_Current_Rating / √sqrt( 1.11 ) = txtDe_Rating_Due_To_Skin A

where R_ac/R_dc is the Skin effect ratio

C. De-rating due to Temp factor :

Applying temp. correction factor to account for site amb. Temp condition, we get de-rating factor as -

[(T2) / (T1)]^1/1.7 = txtDe_Rating_Due_To_Temp

where T2 is the ambient temp. as per manufacturer in ^oC, & T1 is the installation site amb. temp. in ^oC

De-rated A.C current carrying capacity after the temp. correction factor = txtDe_Rating_Due_To_Skin x txtDe_Rating_Due_To_Temp = txtDe_Rating_At_Temp A

D. De-rating due to Enclosure :

Total Area of Bus bars / Total area of Enclosure = (txtNo_Of_Phase x txt_Nbb x txtMBBHeight x txtMBBT) / (txtMBB_Enclosure_area x txtMBB_Enclosure_dim) = txtderatingdata1 / txtderatingdata2 = txtDe_Rating_Due_To_Enclosure = txtDe_Rating_Due_To_EnclPer %

Thus, the A.C rating of the MBB after enclosure de-rating factor = txtDe_Rating_At_Temp x txtDe_Rating_For_DeRatting = txtDe_Rating_At_Encolsure A

E. De-rating due to proximity effect :

De-rating factor due to txt_Nbb no. of bus bars per phase = txtidratingproxy_E

The A.C rating of the MBB after proximity factor = txtDe_Rating_At_Encolsure x txtidratingproxy_E = txtDe_Rating_At_Proximity A

F. De-rating due to bus bar insulation :

De-rating factor due to bus bar insulation = txtidratingBB_insulation_F

The A.C rating of the MBB with selected insulation factor = txtDe_Rating_At_Proximity x txtidratingBB_insulation_F = txtDe_Rating_At_Insulation A

G. De-rating due to Ventilation of bus bar :

De-rating factor due to txtMBB_ventilation = txtidratingBB_ventilation_G

A.C rating of the MBB with txtMBB_ventilation = txtDe_Rating_At_Insulation x txtidratingBB_ventilation_G = txtDe_Rating_At_Ventilation A

H. Expected Temperature rise above the site ambient for the rated current is given by -

[(T1)/(T2)]^0.61 = (l1)/(l2)

Where I1 is the final de-rated current obtained, I2 is the rated current, T1 is the ambient temp. in ^oC,
and T2 is the temp. rise expected above the site installation ambient temp.

[txtMBBRating/txtDe_Rating_At_Ventilation]^1/0.61 x txtAmbient_Temp_at_installation_site = txtExp_Above_The_Amb ^oC

The calculated end temp.= txtFinalExpAbovesitetempforG ^oC, which tempIsorNot within the permissible temp.rise limit.

Thus, we conclude that the selected bus bar size tempIsorNot sufficient to carry the rated current.

iconiclogo

currentdate

SHORT CIRCUIT CALCULATIONS

CUSTOMER NAME	txtClientName
PROJECT NAME	txtProjectName
BOARD NAME	txtBoardName
MBB RATING : txtMBBRating A	MBB SIZE : txtNosets x txt_rem_Space_betn_2 x txtMBBHeight x txtMBBT mm²	FAULT LEVEL : txtFault_level kA for txt_fduration sec.	TEMP.RISE : txtTemp_Rise ^oC

Inputs :

Data/Assumptions	Value Selected	Unit of measurement	Remark
Bus bar material	txtBusBarMaterial		txt_rem_BusBarMaterial
MBB size/area	txtsetforshortC X txtRunsforshortC X txtMBBHeight X txtMBBT	mm²	txt_rem_MBBSA
No.of bus bars per phase	txt_Nbb		txt_rem_Nbb
Fault level	txtFault_level	kA	txt_rem_Faultlevel
Fault level duration	txt_fduration	Sec	txt_rem_FLduration
Short Circuit Current I_sc	txt_SCCIsc_val	A	txt_rem_SCCIsc_val
Ambient temp.	txtAmbientTemp	^oC	txt_rem_AmbientTemp
Ambient temp. at installation site	txtAmbient_Temp_at_installation_site	^oC	txt_rem_Ambient_Temp_at_installation_site
Temp.rise	txtTemp_Rise	^oC	txt_rem_Temp_Rise
End temp	txtEnd_Temp	^oC	txt_rem_End_Temp
a₂₀ Al/Cu	txtα20alcu_val	At 20^oC/^oC	txt_rem_Al_Cu
k Al/Cu	txt_kAlCu_val		txt_rem_KAlCu
Bus bar support material	txtBus_bar_support_material		txt_rem_Bus_bar_support_material
Dist.betn.2 bus bar supports	txtDist_betn_2_busbar_supports	mm	txt_rem_Dist_betn_2_busbar_supports
Space betn. 2 phases	txtSpace_betn_2_phases	mm	txt_rem_Space_betn_2_phases

txtimage1

1. To determine the min.size of conductor for a required fault level, I_scto account for the thermal effects, we use the following formula to

determine the min.size of conductor for any fault level

iconiclogo

currentdate

txtimgtheta_t = ( k/100 ) * (I_sc/A)² * [(1+ txtimgalpha α₂₀Ө txtimgtheta) t]

Where txtimgtheta_t = temp.rise ( in ^oC )

I_sc = symmetrical fault current r.m.s. ( in Amps )

A = cross-sectional area of the conductor ( in mm² )

txtimgalpha₂₀ = temp. coeff. Of resistance

txtimgtheta = operating temp. of the conductor at which the fault occurs ( in ^oC )

k = 1.166 for Al and 0.52 for Cu

t = duration of fault ( in seconds )

txtimgtheta Ө_t = txt_kAlCu_val/100 * (txt_SCCIsc_val/A)² * (1+ txtα20alcu_val x txt_End_Temp_val) . 1

A = Avalue mm²

This is the min. conductor size essential for this fault level. However, as per data input, for selected bus bar size, cross sectional area = txtcross_sectionalArea mm² which is symbolshort min.size required. Hence selected size chkISorNOt suitable for txtFault_level kA fault level.

isnotval1