o. mÄkinen fi session 3 block 3 barcelona 12-15 may 2003 1 what is an intermittent earth fault...
TRANSCRIPT
1O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
What is an intermittent earth fault (IE/F)?
InsulationConductor
Screen
Insulationbreak-down
• Characterised as series of cable insulation break-downs
• Originates from insulation deterioration
• Extinguishes itself when fault current crosses zero
In spite of complicated deterioration processes the resulting fault pattern is usually very same alike !
2O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
Residual current I0 and voltage U0
FEEDER FEEDER MEAS.
INCOMER
COMP. COIL
I0j I0v U0
FaultPoint
KRe
RfUtres
ICtot
50 100 150 200 250 300 350-0.4
-0.3
-0.2
-0.1
0
0.1
50 100 150 200 250 300 350-0.4
-0.3
-0.2
-0.1
0
0.1
Res
idu
al C
urr
ent
(kA
)R
esid
ual
Vo
ltag
e x
102
(kV
)
I0j
(Faulty Feeder)
I0v
(Healthy Feeder)
U0Pulse width400 – 800 s
Pulse interval5-300 ms
Peak value~0.1 ... 5 kA
3O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
Residual current and faulty phase voltage UPR
FEEDER FEEDER MEAS.
INCOMER
COMP. COIL
I0j I0v
FaultPoint
KRe
RfUtres
50 100 150 200 250 300 350-0.4
-0.3
-0.2
-0.1
0
0.1
Res
idu
al C
urr
ent
(kA
)R
eco
very
Vo
ltag
e x
102
(kV
)
I0j
(Faulty Feeder)
I0v
(Healthy Feeder)
Utres
50 100 150 200 250 300 350-0.4
-0.3
-0.2
-0.1
0
0.1
Utres UPR
Varying breakdownvoltage Utres at fault point
Resistor Re and K determines the increaseof recovery voltage UPR
UPR
4O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
Selectivity problems between feeder DE/F relay and station RO/V relay
FEEDER FEEDER FEEDER
COMP. COIL
INCOMER
I >0 I >0 I >0 U >0
MEAS.
DE/F RO/V
1
1. Intermittent E/F occurs• No detection (or delayed operation) by the DE/F relay• RO/V relay starts normally
trip
2. RO/V relay trips incoming CB according to set operatingtime-> unselective operation resulting to unnecessary outage
2
5O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
Why conventional relaying does not work properly during IE/F fault ?
• IE/F detection in numerical relays depends mostly on:
0.015 0.02 0.025 0.03-0.1
0
0.1
0.2
0.3
0.4
0.5
Actual waveform
Filtered & sampled waveform
• Input filtering & sampling frequency
U0
I0 j
Start delay0
0Start signal
• Length of the starting delay
6O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
Why conventional relaying does not work properly during IE/F fault ?
• IE/F detection in numerical relays depends mostly on:
Problems to perform satisfactorily most likely to be faced !!
• Shape of the operating sector
U0
I0J
Operating sector,type 1
Operating sector,type 2
U0
I0J
I0V
• Behaviour of I0 and U0 in respect to the operating sector
Area for faulty feeder I0
Area for healthyfeeder I0
7O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
New Detection Methods for IE/F (1)
U0
I0 j
I0v
spike detection_v
spike detection_j
max_count_j
max_count_vdrop-off time_j
operate time delay_j
start signal_j
0
0
0
0
counter_pos
counter_neg
• Spike Detection Method
• Based on detection of I0-spikes of appropriate polarity
• Counter functions to minimise the risk of false operation
• Settable drop-off timer to prevent resetting between fault pulses
8O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
• Operating criteria: - phase angle between U0
and I0 between certain limits - amplitudes of I0 and U0
above set values
• Settable drop-off timer to prevent resetting between fault pulses
-120
60120
0-60
drop-off time_j
operate time delay_j
start signal_j (internal)
0
0
0
j
v
extended operating sector
start signal_j 0
New Detection Methods for IE/F (2)
• Phase Angle Criterion
9O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
IE/F field testing procedure in general
U >0
trip trip trip
FAULTYFEEDER
COMP. COIL
INCOMER
trip
I >0 I >0
R1
I >0 I >0
R2
I >0 I >0
R1
I >0 I >0
R2
I >0 I >0
R1
I >0 I >0
R2
Analog and digital signals
Oscilloscope
HEALTHYFEEDER . . .
HEALTHYFEEDER
• Different relay types in use in each feeder (R1 and R2)
• Fault point was arranged by drilling a hole through the cable insulation
• The hole was filled with water
• Energisation of the faulty feeder initiates the intermittent fault
• Relevant analog and digital signal were recorded
10 kV
10O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
Network parameters varied during IE/F tests
• Capacitive earth fault current 60 – 140 A
• Degree of compensation 0.5 – 1.3
• Current rating of the earthing resistor in parallel of the coil 2, 10 or 20 A
• Fault distance from the station 20 – 400 m
• The variation of the network parameters on the relay response
and on the fault characteristics were investigated
11O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
Results from IE/F field testing
0 0.2 0.4 0.6 0.8
R2 start R2 trip R1 start R1 trip CB
Time [msec]
0 0.2 0.4 0.6 0.8-150-100-50050100150
U0 (t
) [%
]
0 0.2 0.4 0.6 0.8-3-2-10 123
I 0j (t
)[k
A]
0 0.2 0.4 0.6 0.8-0.6-0.4-0.20
0.20.40.6
I 0v(t
)[k
A]
• In the faulty feeder both detection methods gave out the trip signals correctly
• A few false starts occurred in the healthy feeder
• False starts occurred when the network was heavily under or overcompensated and the feeder in question had a high capacitive current contribution
• Detection algorithms still need some improvements to prevent false starts
12O. MÄKINEN FI Session 3 Block 3
Barcelona 12-15 May 2003
IE/F Conclusions
• Intermittent earth faults have been investigated by theoretical studies, simulations and field tests
• Field test results have been used to verify simulation models and actual relay response, and results seem to be very promising although some improvements are still needed
• Simulation models to be used more in further algorithm development work
• Conventional feeder DE/F relays have difficulties to detect this fault type• Dedicated protection functionality is needed
• New detection methods have been developed and implemented in new numerical feeder terminals