ABB 615 series Technical Manual page 853

1MAC059074-MB A
615 series ANSI
Technical Manual
Differential current monitoring
Differential current monitoring supervises the difference between the summed phase
currents I_A, I_B and I_C and the reference current I_REF.
The current operating characteristics can be selected with the Pickup value setting. When
the highest phase current is less than 1.0 × In, the differential current limit is defined with
Pickup value. When the highest phase current is more than 1.0 × In, the differential current
limit is calculated with the equation.
MAX I A I B I C ( _ , _ , _ ) × Pickup value
GUID-41E8DD52-0C7D-406D-9799-DA48A660D8E5-ANSI V1 EN
The differential current is limited to 1.0 × In.
I_DIFF
Max trip current
OPERATE
1.0 p.u.
Pickup value
GUID-D083BF22-574C-4603-971F-5F4371632A28 V2 EN
Figure 436: CCM operating characteristics
When the differential current I_DIFF is in the operating region, the FAIL output is
activated.
The function is internally blocked if any phase current is higher than the set Max trip
current. When the internal blocking activates, the FAIL output is deactivated
immediately. The internal blocking is used for avoiding false operation during a fault
situation when the current transformers are saturated due to high fault currents.
The value of the differential current is available in the monitored data view on the LHMI
or through other communication tools. The value is calculated with the equation.
27R
V_A_AB U_LO
V_B_BC
NON-OPERATE
V_C_CA
BLOCK
1.0 p.u. 2.0 p.u. 3.0 p.u.
Max(I_A , I_B , I_C)
Section 6
Supervision functions
(Equation 158)
4.0 p.u.
847