SERVICE MANUAL R5888C
QUADRAMHO Chapter 2
Page 52 of 74
approximately 6°. This action expands the right hand portion of the mho polar
characteristic without affecting the reach at the characteristic angle.
5.16.20 Self testing
Periodic self testing of all relay comparators is done automatically every 2 weeks
or on demand, by pressing and releasing the pushbutton on the front of the relay.
In the event of a comparator failure, diagnostic information is stored in the relay
and may be read by a test option facility (See Section 4.9.46) to simplify fault
finding. In order for a self check to be performed, all voltage level detectors must
be operated (ie. picked up) to ensure that the comparators are receiving signals on
their inputs. The microcontroller first issues a reset pulse and then a signal (SC)
instructing the comparators to ignore their inhibit inputs (See Section 5.1 and
Figure 34).
A short time later (40ms) the microcontroller reads the comparator outputs and
stores this information. The microcontroller then issues a further signal (MRI) which
in conjunction with the previous signal (SC) forces the comparators to reverse their
state (i.e. those in restrain move to operate, and those operated move to restrain).
A short time later (40ms) the microcontroller again reads the status of the
comparator outputs and this information is “Exclusive OR”ed with the previous
state of the comparator, to ensure that all comparators can operate and are not
operated for both conditions. Should any comparator output not meet these
requirements it is considered to be faulty. If a faulty comparator is detected, then
the “Relay Available” LED is extinguished and an alarm given by closing the
“Relay Inoperative” contact. The self check routine takes approximately 85ms.
Once the self check routine has been completed the SC signal is removed just
before the MRI signal. This has the effect of resetting all comparators before the
relay is returned to normal operation. The SC signal is also used to change the
polarising of the quadrilateral ground fault comparators to a signal which only
requires voltages (as described in Section 4.4) since there may not be sufficient
current to correctly polarise the quadrilateral ground fault comparators.
The self testing feature is selectable by means of switch SW5 set to the right to
enable and set to the left to disable self checking.
5.16.21 Operation of standard schemes and input/output interfaces
The arrangement of the auxiliary relay trip outputs differs slightly depending on
whether the relay is to be used in a single- and three-pole tripping mode, or in a
three-pole only tripping mode. The standard external connection diagram for the
former case is given by Figure 67, Appendix A.
In addition to the standard schemes, special scheme logic software may be
designed to meet the requirements of individual customers. The functions of the
relay input and output interfaces may differ if these special schemes are in use and
the standard diagrams then no longer apply. Details of special schemes will be
given as an appendix to this manual, if applicable.
5.16.22 Standard scheme options
Five standard scheme options are offered by the scheme logic of Quadramho.
The options are based on a permissive underreaching scheme (PUR), a permissive
overreaching scheme (POR), a blocking scheme (BLOCK) and a Zone 1 extension
scheme (Z1EXT). A basic scheme (BASIC) controlling the normal Zone 1, time
delayed Zone 2 and Zone 3 and SOTF action, is common to all options and may
also be selected as a scheme in its own right. A choice of single phase tripping for
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