GE Distance Relay Calculations
For The Latta 230 kV Line
Brunswick 230 kV
Fayetteville 230 kV
Laurinburg 230 kV
CTR: 1200/5 PTR 2000/1
We desire for the zone 1 distance relay to operate for faults up to 90% of the length of the line as seen from Weatherspoon
We must now convert the Z primary value to an impedance that the protective relay sees which is Z secondary. We do this by entering the CT & PT ratios into the equation
Weatherspoon 230 kVLatta 230 kV
FLO 230 kV
Marion 230 kV
Total Impedance of the line in rectangle form then to polar form.This is at 230 kV and is referred to as Z primary.
Dillon Maple St. Distribution Substation
Latta 230 kVWeatherspoon 230 kV
The zone 1 relay is a General Electric 12CEY 15A3A. The relay has a range of 2-20 ohms and an angle of maximum torque of 60° (from the nameplate of the relay). We must choose what percentage of the relay restraint winding we need to use to protect 90% of the line.
Relay minimum ohm range angle of the line relay angle of maximum torque
Z secondary impedance The % of the restraint winding we need to use
The closest tap to what we need is 70% so this is what we set the relay for.
21-1: 12CEY15A3A 2-20 Ohms @ 60° MTA
Z Primary: 21.8 Ohms @ 83.7° Z Secondary: 2.61
Ohms @ 83.7°
Set: 70 % Z Minimum = 2 Ohms @ 60°
T10 On: 60 And T2 On 10
These Are Settings Given To The Relay Technician
Now we must calibrate the relay to match the setting we have installed and to insure the relay characteristic is correct.
We will test the relay at the angle of maximum torque (60°) to confirm the relay reach and at two other angles (90 ° and 30 ° ) to ensure the characteristic is a circle.
Relay minimum ohm range Relay angle of maximum torque Test angle
Restraint Tap Setting
2 Z relay at 90° = 4.952 Z relay at 60° = 5.712 Z relay at 30° = 4.95
2 Z relay at 30° = 4.952 Z relay at 60° = 5.712 Z relay at 90° = 4.95
Relay Test voltage values are chosen to keep the current in a manageable range
Fault Test Angle
Test Voltage Selected
Calculated Pickup Current
2 Z Relay
30° 40 8.08 amps 4.95
60° 40 7.0 amps 5.71
90° 40 8.08 amps 4.95
Calculate using ohms law
Three Pickup Points Plotted On A Polar Diagram
Relay Test voltage values are chosen to keep the current in a manageable range
Fault Test Angle
Test Voltage Selected
Calculated Pickup Current
2 Z Relay
30° 40 8.08 amps 4.95
60° 40 7.0 amps 5.71
90° 40 8.08 amps 4.95
0°
15°
45°
75°
105°
120°
135°
Calculate using ohms law
Pickup Points Plotted On Polar Diagram
Directional Blocking Scheme
• Purpose is to speed up the tripping of faults.
• One of the most popular.
• A communication channel between relay terminals must be provided.
• Local distance relay zone 2 delay timer
• Local relay will trip the local breaker unless it
• receives block key from the remote relay (zone 3 or ground current in the reverse direction both would mean external fault).
R
𝑋𝐿
Relay Zone III Mho
Characteristic
Relay Zone III
Reach Setting
Looking Forward
θRelay MTA
Z3Z2
Z1
Zone 1 = 0TD
Zone 2 = 30 Hz TD
Zone 3 = 90 Hz TD
Directional Comparison Scheme No Communication Channel
R
𝑋𝐿
Relay Zone III Mho
CharacteristicRelay Zone III
Reach Setting
Looking Reversed
θRelay MTA
Z3
Z2Z1
Zone 1 = 0TD
Zone 2 = 30 Hz TD
Zone 3 = 90 Hz TD
Carrier = 0 TD
Directional Comparison Scheme With Communication Channel
Relay Zone II &
Carrier Characteristic
is The Same
R
𝑋𝐿
Relay Zone III Mho
Characteristic
Relay Zone III
Reach Setting
Looking Reversed
θRelay MTA
Z3
Z2Z1
Zone 1 = 0TD
Zone 2 = 30 Hz TD
Zone 3 = 90 Hz TD
Carrier = 0 TD
Directional Comparison Scheme With Communication Channel
Relay Zone II &
Carrier Characteristic
is The Same
Zone Three Has Offset Does Not Pass Through The Origin