GE P444 User Manual

Application Notes
P44x/EN AP/Hb
6
MiCOM P40 Agile P442, P444
(AP) 5-
41
On a line or on a cable, Z2 = Z1. It results:
(2) VA = Z1 (I1 + I2) + Z0I0
We can write also: IA = I1 + I2 + I0
(3) (I1 + I2) = IA – I0
If equation (3) is combined with equation (2), we obtain:
(4) VA = Z1 (IA – I0) + Z0I0
The physical fault current is IR = 3I0. The equation (4) becomes:
VA = Z1 [IA – IR/3 + Z0IR/3Z1] = Z1 [IA + IR (Z0–Z1)/3Z1]
With: (Z0 – Z1)/3Z1 = kZ0
(5) VA = Z1 [IA + kZ0 IR]
(6) Z1 = VA/(IA + kZ0 IR)
Special cases:
Resistive fault where:
Rfault = fault resistance (loop) (Rfault = Rloop )
Ifault: current crossing the fault resistance
(7) VA = Z1 [IA + kZ0 IR] + Rfault . Ifault
(8) Z1 = (VA – Rfault . Ifault) / (IA + kZ0 IR)
Open line (Ifault = IR = IA):
(9) VA = Z1 . IA (1 + kZ0) + Rfault . IA
(10) Z1 = (VA / IA – Rfault) / (1 + kZ0)
The detected impedance will be:
Z = Z1 (1 + kZ0) + Rfault
This is the form used for the result of Z measured with an injector providing U, I, ϕ
Separate compensation for each zone (KZ1, KZ2, KZ3/4, KZp and KZq) allows more
accurate earth fault reach control for elements which are set to overreach the protected line,
such that they cover other circuits that may have different zero sequence to positive
sequence impedance ratios (example: underground cable and overhead line in the protected
line).
3.1.2.3 Zone setting – Z
All phase or earth fault protection elements are quadrilateral shaped, and are directionalised
as follows:
• Zones 1, 2 and 3 - Directional forward zones, as used in conventional three zone
distance schemes. Note that Zone 1 can be extended to Zone 1X when required in
zone 1 extension schemes.
• Zone p and q - Programmable. Selectable (Distance scheme\Fault type) as a
directional forward or reverse zone.
• Zone 4 - Directional reverse zone. Note that zone 3 and zone 4 can be set with same
Rloop value to provide a general start of the relay.
Note: If any zone i presents an Rloop i greater than R3=R4, the limit of the start is
always given by R3. See also the "Commissioning Test" section.
3.1.2.4 Zone setting – Resistive reach calculation
3.1.2.4.1 Resistive reach calculation – Phase fault Element
Resistances are set per loop
The P442 and P444 relays have quadrilateral distance elements therefore the resistive reach
(RPh) is set independently of the impedance reach along the protected line/cable. RPh
defines the maximum amount of fault resistance additional to the line impedance for which a
distance zone will trip, regardless of the location of the fault within the zone. Therefore, the

GE P444 Specifications

General

Brand	GE
Model	P444
Category	Protection Device
Language	English