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

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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

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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