ABB Distribution Protection Unit 1500R
7-4
Records
9/99
website:www.abb.com/papd
Fault Locator
The DPU1500R fault algorithm is used to calculate estimated fault resistance and apparent distance to the fault. This
calculation is performed by comparing the prefault current and voltage to the fault current and voltage and by analyzing
the positive and zero sequence reactance per mile. Three to six of 6 cycles of fault current is needed to analyze the fault
values. The system parameters are used to estimate the source impedance (known impedance) and source voltage.
The fault values are used to estimate the load impedance (estimated impedance) and determine fault type. The known
impedance and estimated impedance are used to easily calculate the fault impedance. Once the fault impedance is
calculated, the distance to fault can be readily calculated using the fault impedance, the line impedance and the line
length.
The Fault algorithm was designed to be used on a homogenous radial distribution line. Therefore, the unit is not intended
to be used on a distribution line with many different types of conductors because the algorithm will not be as accurate.
Fault data may not be accurate for a close-into-fault condition where there is no prefault power flow. In the case of closing
into a fault during a reclose sequence, the apparent distance to the fault in miles for the first fault appears on the first line
of the LCD for the entire reclose sequence. The fault records also display the original fault distance in each record of that
reclose sequence. The algorithm for the fault locator is most applicable to a radial feeder.
Vs
Zs
ZI (m)
ZI (IÐm)
Rf
Zd
Vrly
Irly
Key: ZI = line impedance
Zs = source impedance
ZD = load impedance
Rf = fault resistance
M = distance