ABB REB670 Series - Page 180

I
ref
is the given reference load current


2
operate Bx ref Trip
III  
is the operate level heat content
I
Bx
is the selected base current based cooling system
ON / OFF
I
Trip
is the operate level load current
θ
n
is the current heat content
Consider that the given system has IBase of 1000 A and the cooling system is ON . The
following settings are used to calculate the operate time:
IRef 110%
IBase1 110% of IB
IBase2 120% of IB
Tau1 150 min
Tau2 90 min
IHighTau1 110% of IB1
Tau1High 125% of tC1
ILowTau1 90% of IB1
Tau1Low 75% of tC1
IHighTau2 110% of IB2
Tau2High 115% of tC2
ILowTau2 90% of IB2
Tau2Low 85% of tC2
ITrip 120% of IBx
ThetaInit 50%
ResLo 60% of Itr
As the cooling system is ON , IBase2 is selected as the base current and Tau2 setting is selected
as the time constant.
For example, the largest phase load current is taken as 1800 A, then:
2
1800
1.
2677685.95
1
final





2
(1.2 1000 1.1 1.2) 2509056
operate
   
Here
final n
Q > Q
At t=0
0.5 2509056 1254528
n init operate
ThetaInit

    
At next execution, θ
n-1
=1254528 and θ
n
=1254555.04.
Section 7 1MRK 505 370-UEN D
Current protection
174 Busbar protection REB670
Application manual