NR Electric PCS-978, Instruction Manual

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3
Operation Theory
PCS-978 Transformer Relay 3-16
Date: 2013-01-16
0 20 40 60 80 100 120
-200
-100
0
100
200
Original Current
0 20 40 60 80 100 120
-100
-50
0
50
100
DPFC current
Figure 3.2-5 Waveform of original current and DPFC current
From above figures, it is concluded that DPFC can reflect the sudden change of fault current at the
initial stage of a fault and has a perfect performance of fault detection.
3.2.3.10.2 Operation Criterion
DPFC (Deviation of Power Frequency Component) biased differential protection reflects variation
of load condition to perform a sensitive protection for the transformer. Lab tests show that it is
more sensitive than the biased differential relay under the heavy load condition.
The operation criteria of DPFC biased differential are as follows:







       
     
    
 
pu I I I I
pu I I I
I I I
pu I
r e r d
r r d
dth dt d
d
2 3 . 0 75 . 0
2 6 . 0
25 . 1
2 . 0
} , , max{
1 1 1
  
  
    
m
k
ck
m
k
bk
m
k
ak r
I I I I
  
m d
I I I I
  
       
....
2 1
Equation 3.2-14
Where: