9/24/2014
U
I Time Overcurrent Relays
ECE525
Lecture 14
More or less
approximates
thermal fuse
Allow
coordination
with fuses
Time Dial
Setting
Direction
of
Current
Induced
Torque
Restraining
Spring
Reset
Position
Disk
Time Overcurrent Relays
U
I
Fall 2014
ECE525
Basic equation
Operating torque
Restraining Torque
I 2
T s 1 K d
I
t
p
s = restraining spring
Time Overcurrent Relays
Lecture 14
torque
I = applied current
Ip = pick up current
Kd = disk damping
factor
= angle of disk
rotation (proportional
to Time Dial Setting
(TDS)
Fall 2014
9/24/2014
U
I
ECE525
Relay Response
Lecture 14
2. Integrate w.r.t. Time
1. Operating torque = Restraining Torque
I 2
1 t t
2 1
2 1
K d I p
I 2
s 1 K d
I
t
3. TDS (setting angle),
where triptime = t2 -t1
I 2
1 trip time
TDS
K d I p
Time Overcurrent Relays
U
I
Fall 2014
ECE525
Relay Response
Lecture 14
4. Finding trip time
Kd
trip time TDS
Where:
I 2
1
I
TDS
A
1
M = I/Ip
A = Kd/ts
Time Overcurrent Relays
Fall 2014
9/24/2014
U
I
Standard Curves -standard formats
Reset Time (M < 1)
ECE525
Lecture 14
C
tr TDS
2
1 M
Trip time (M 1)
B
tt TDS p
M 1
Some manufacturers include disk inertia in B
Time Overcurrent Relays
U
I
Fall 2014
US and IEC curve
parameters
Curve
U.S. Moderately inverse (U1)
U.S. Inverse (U2)
U.S. Very inverse (U3)
U.S. Extremely inverse (U4)
U.S. Short-time inverse (U5)
I.E.C. Class A - Standard inverse (C1)
I.E.C. Class B Very inverse (C2)
I.E.C. Class C Extremely inverse (C3)
I.E.C Long-time inverse (C4)
I.E.C Short-time inverse (C5)
Time Overcurrent Relays
A
0.0104
5.95
3.88
5.67
0.00342
0.14
13.5
80.0
120.0
0.05
B
0.2256
0.180
0.0963
0352
0.00262
0.0
0.0
0.0
0.0
0.0
ECE525
Lecture 14
C
1.08
5.95
3.88
5.67
0.323
13.5
47.3
80.0
120.0
4.85
P
0.02
2.00
2.00
2.00
0.02
0.02
2.00
2.00
2.00
0.04
Fall 2014
9/24/2014
U
I
US Inverse (U2)
Characteristic
Time Overcurrent Relays
U
I
ECE525
Lecture 14
Fall 2014
ECE525
Comparison of curves
Time Overcurrent Relays
Lecture 14
Fall 2014
9/24/2014
U Extremely Inverse Curve
I
and 50E fuse
Time Overcurrent Relays
ECE525
Lecture 14
Fall 2014
U
I
ECE525
Example
Bus
#1
Local
Load
Bus
#2
Local
Load
Lecture 14
Bus
#3
Source
Vs
Local
Load
Z1
Z2
Z3
Faulted
Line
Z4
R2
R3
R4
It is desirable for the relay on the faulted line, R4, to be the only
relay to trip
Max and min fault current (based on ends of faulted line)
1
Time Overcurrent Relays
Fall 2014
9/24/2014
U
I
ECE525
Example continued
Lecture 14
The desired coordination can be accomplished by increasing
the time dial settings as one proceeds toward the source.
If relay R2 is expected to provide backup protection for
relay R4,
Then R4, the relay with the greatest source impedance, would
be set with the lowest time dial setting
If IMIN is defined as the minimum fault current,
Then the pickup current must be set at least as low as the
current but above maximum load current.
For relays R2 and R3, the TDS must be set to trip no
faster then the next downstream device when the fault
current is maximum for an out of zone fault
Time Overcurrent Relays
Fall 2014
U
I EMTP relay simulation
ECE525
Lecture 14
R Bus
S Bus
Source
Impedance
Gen
Load
Xfmr
Breaker
Breaker
69KV
230KV
25
52
52
Load
Fault #2
C-G
225
Fault #1
C-G
250 resistive fault is initiated at 8.3 ms and progresses to a 25 fault at 62 ms
as can occur by a tree branch coming in contact with the wire.
Time Overcurrent Relays
Fall 2014
9/24/2014
U
I
ECE525
Example with a trip
Time Overcurrent Relays
Comparing relay
U
I coordination (light load)
Time Overcurrent Relays
Lecture 14
Fall 2014
ECE525
Lecture 14
Fall 2014
9/24/2014
Comparing relay
U
I coordination (heavy load)
ECE525
Lecture 14
Time Overcurrent Relays
Fall 2014
Directional Control vs
Direction Supervision
U
I
ECE525
Lecture 14
DC Bus +
Reference
Signal
Phase
Current
Directional
Element
(32)
Reference
Signal
32
32
Directional
Element
(32)
Phase
Current
32
DC Bus +
Phase
Current
Overcurrent
Element
(50 or 51)
50/
51
50/51
Phase
Current
52
a. Directional Supervision
Time Overcurrent Relays
32
Overcurrent
Element
(50 or 51)
AC Circuit
Breaker
DC Bus -
50/
51
50/51
52
b. Directional Control
AC Circuit
Breaker
DC Bus -
Fall 2014
9/24/2014
U Directional Step-Time
I Overcurrent (ANSI 67)
ECE525
Lecture 14
The directional overcurrent relay can be perceived as a
type 50 instantaneous element controlled by a type 32
directional element
If the type 67 relay element is to provide backup protection,
they use definite time delay for downstream coordination
The 67 element requires more attention to detail for
coordination than do type 51 relays
The advantage that the stepped time has over the 51 is that
the time steps are independently set.
The disadvantage is that overreach errors have a more
pronounced affect that often proves difficult to
coordinate
Time Overcurrent Relays
Fall 2014
U Directional Step-Time
I Overcurrent (ANSI 67)
51
Bus S
Load 5
F1
Load
1
Time Overcurrent Relays
Lecture 14
Increasing
time
67
ECE525
F2
Load
2
F3
Load
3
F4
Load
4
Fall 2014
