Alstom SHPM 101 - Section 6. TECHNICAL DATA; 6.6 Accuracy of impedance measurement; 6.7 Current sensitivity of impedance measuring units.; 6.8 Returning ratio of impedance measuring units

SERVICE MANUAL R5888C
QUADRAMHO Chapter 2
Page 68 of 74
6.6 Accuracy of impedance measurement
The accuracy is unaffected by the Z
Ph
and Z
N
settings, the characteristic angle
setting or the dc supply (within the operative range).
The following accuracy claims apply under reference conditions:
Fine reach multipliers set to unity,
Ambient temperature 20°C
Nominal input frequency f
n
.
Zone 1 accuracy ±5% up to SIR = 30
Zone 1 accuracy ±10% SIR = 30 to SIR = 60
Zone 2 accuracy ±10% up to SIR = 60
Zone 3 accuracy ±10% up to SIR = 60
SIR is the system impedance ratio defined as the total source impedance divided
by the relay setting Z
Ph
+ Z
N
for earth faults or 2Z
Ph
for phase faults. At reference
settings and at a nominal source voltage of 110 phase-phase, SIR = 30
corresponds to 2.05V/0.213
I
n
for earth fault measurement and 3.55V/0.370I
n
for phase fault measurement and SIR = 60 corresponds to 1.04V/0.108I
n
for
earth fault measurement and 1.80V/0.188
I
n
for phase fault measurement.
The effective accuracy range at any setting has maximum limits of 1.2 times rated
voltage and 56 times rated current.
Transient overreach is less than 1%.
The additional error caused by a departure from reference conditions, within the
operative ranges, is not more than the error allowed at reference conditions.
6.7 Current sensitivity of impedance measuring units.
Determined by low set current level detectors. The sensitivity varies inversely with
coarse reach setting Z
Ph
and is nominally 5%I
n
at Z
Ph
= 4.8/I
n
Ω.
6.8 Returning ratio of impedance measuring units
Returning ratio is the impedance value at which the relay just returns to a reset
condition, divided by the impedance value at which the comparator just operates.
Returning ratio measured on the characteristic angle of the relay is less than 110%.
6.9 Characteristic angle setting ranges and accuracy
Characteristic angle settings
Z
Ph
Phase 85° to 45° in 5° steps
Z
N
Residual 85° to 45° in 5° steps
Accuracy of phase setting is ±2°, independent of relay reach setting.
The impedance reach accuracy does not vary with characteristic angle setting.
The characteristic angle switches have unused positions at the anti-clockwise end of
the switch knob rotation range. The relay characteristic angle is 45° if these
unused positions are selected.