SERVICE MANUAL R5888B
QUADRAMHO Chapter 1
Page 5 of 27
Section 11. CHOICE OF ASPECT RATIO (LENTICULAR ZONE 3 CHARACTERISTIC)
The Zone 3 aspect ratio of the type A (mho) relay will need to be adjusted when it
is envisaged that there will be load encroachment problems on the Zone 3, or
power swing blocking starter characteristic for a long line application. The Zone 3
aspect ratio
a
/
b
should be set so that with the required Zone 3 forward and reverse
reach settings, the Zone 3 characteristic or, if used, the power swing blocking
starter characteristic has a 10% safety margin separating it from the load
impedance region.
Section 12. CHOICE OF RELAY CHARACTERISTIC ANGLES
Maximum accuracy and sensitivity is obtained by setting the relay angle θPh equal
to, or to the nearest setting above the line positivie sequence angle
( Z
L1
)
and θN
equal to, or to the nearest value above
K
N
.Z
L1
where K
N
is the neutral
compensation vector (see worked examples).
Section 13. ZONE TIME DELAY SETTINGS
The time settings t
Z2
and t
Z3
determine the time delay from detection of a fault by
the relevant zone to the operation of the trip output device.
The relay operates for the majority of Zone 1 faults within 16 – 30ms. The Zone 2
time delay should be set to allow for the longest Zone 1 operating time, or if
applicable, the longest aided trip time and the circuit breaker operating times.
Generally a Zone 2 time delay setting of 0.2 – 0.3s is satisfactory, but longer times
may be required if the Zone 2 reach overlaps slower forms of protection.
Zone 3 is generally intended to provide back-up protection even if it is being used
as a reverse looking blocking element. It may be overlapping other forms of
protection such as inverse definite minimum time overcurrent relays. The Zone 3
time delay will depend on the system to which the relay is applied, but in any case
it will be longer than the Zone 2 time delay and will typically have a setting of 1s.
Section 14. SWITCH-ON-TO-FAULT TRIPPING FEATURE (SOTF)
This feature is enabled by the scheme logic when the line circuit breaker has been
open for a certain time. To determine whether the line circuit breaker is open, the
relay looks for an all poles dead condition (voltage and current level detectors
have reset on each phase). For the case where a busbar VT is used, pole dead
signals will not be produced, but a normally closed circuit breaker auxiliary
contact can be used via an opto-isolator input, to inform the relay that the circuit
breaker is open. For single pole tripping applications, the circuit breaker auxiliary
contacts of each breaker pole should be wired in series and connected to the
relay, so that the relay is only made aware that all three poles of the breaker are
open.
The SOTF feature becomes enabled 200ms or 110s after the relay detects that the
local circuit breaker has opened, depending on the setting of an option switch on
the front of the relay.
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