Advertisement
Settings
The setting values are displayed with the three
rightmost digits of the display. The setting
value presented on the display is indicated by
an illuminated indicator under the relevant
setting knob.
p
s
I
1
I
2
The matching of the vector group of the
protected transformer is done with switches
1...6 of switchgroup SG1. The vector groups
to be matched, the corresponding switch
settings and the related checksums are shown
in Table 1 and 2. Table 1 shows the matching
selection, when the HV side of the power
transformer is star connected and Table 2
shows the matching selection when the HV
side is delta connected. The checksum of
switchgroup SG1 can be read on the display,
when the indicator under the switchgroup on
the front panel is lit. By comparing this
checksum with the values of Tables 1 and 2,
the correctness of the switch settings can be
verified. Note! Switches 7 and 8 of switchgroup
SG1 with the weighting factors 64 and 128
resp. must also be included in the calculation
of the checksum. The shaded areas of the
tables show the most common transformer
vector groups and their corresponding
recommended relay settings.
By means of switch SG1/7 the latching function
of the tripping signal is selected. Switch position
0 = no latching, 1 = latching. With switch SG1/
8 the blocking mode is selected. Switch position
0 = the harmonics blocking is enabled only
during a connection inrush situation, i.e. the
blocking is inhibited, when the relay detects
load current on both the HV and the LV side of
the transformer, switch position 1 = the
harmonics blocking is permanently allowed,
see Fig. 1. When, at rated load, the secondary
currents of the current transformers stay below
the rated current of the relay (as a minimum
50% of the rated current), the secondary cur-
rents can be amplified by means of the electro-
nics of the relay to correspond to the rated
current. The amplification is set with the trans-
forming ratio correction potentiometers I
and I
forming ratio are also taken into account in the
values shown on the display of the module.
Basic starting value, setting range
20...50 % of the relay rated current I
Starting ratio, setting range 10...50 %.
/I
Transforming ratio correction of the HV
n
side current transformers, setting range
0.50...1.00.
/I
Transforming ratio correction of the LV
n
side current transformers, setting range
0.50...1.00.
/I
. These settings for correcting the trans-
2
n
Example 1.
Protected object: 110 kV/ 10.5 kV power trans-
former with the rated power S
The high-voltage side and low-voltage side
rated load currents I
I
= S
/(√3 x U
) =
1n
n
1n
.
= 40 MVA/(√3 x 110 kV) = 210 A
n
I
= S
/(√3 x U
) =
2n
n
2n
= 40 MVA/(√3 x 10.5 kV) = 2199 A
Standard current transformers are selected,
i.e. 300 A/1 A for the high-voltage side and
2500 A/5A for the low-voltage side.
The secondary currents I
I
= 210 A/300 A/1 A = 0.70 A
1
I
= 2199 A/2500 A/5 A = 4.40 A
2
Thus, the current correction values I
I
/I
to be set on the relay will be:
2
n
I
/I
= 0.70 A/1 A = 0.70
1
n
I
/I
= 4.40 A/5 A = 0.88
2
n
If the selection of the matching of the vector
group has been properly done, the load currents
on either side of the protected object should be
the same and the differential current thus zero,
when the secondary currents of the current
transformers have been corrected. If the vector
group matching and ratio corrections fail to
achieve the zero differential current, the vector
group has obviously been incorrectly selected
or the wiring of the measuring transformers is
improper.
In addition to the previously mentioned poten-
tiometer settings the relay is provided with two
so called soft settings, the restraint limit
percentage I
and the high-set differential
hr
current setting I
>>. These settings are found
d
in the submenus of switchgroup SG1, the
restraint limit setting in submenu 4 and the
high-set stage starting current setting in
submenu 8. The restraint threshold can be set
within the range 10...20 % of the differential
current, default value 15 %. The high-set stage
starting current can be set within the range
20...30 x I
, default value 25 x I
n
stage operates if the momentaneous value of
the differential current during two consecutive
samples exceeds the set starting level. When
the differential current exceeds the starting
level of the high-set stage the load current
through the protected object no longer has any
stabilizing effect on the function of the high-set
/I
stage. When the stabilizing current falls below
1
n
about 33 % of the differential current, the
actual starting value (submenu 7 of switch-
group SG1) is automatically halved, while in a
situation like this a fault must exist inside the
protected area.
= 40 MVA.
n
and I
are:
1n
2n
and I
will then be:
1
2
/I
and
1
n
. The high-set
n
C
5
Advertisement
