Siemens MJ-XL Installation And Operation Manual page 29

VRC Mode
This data item defines the VRC mode of operation. Select
the desired mode, using the VRC Mode data item. Four
options are provided: OFF, LOCAL, REMOTE, and AUTO
(see Figure 4.4).
VRC Mode: OFF
Disables VRC function.
VRC Mode: LOCAL
When Local mode is selected, VRC activates immediately
to reduce output voltage by the amount specified in the
Local VRC % data item.
To enable VRC Local mode, view VRC Mode and select
LOCAL. View Local VRC % and define a reduction amount
between 0.0% and 10.0%.
VRC Mode: REMOTE (via Terminal Contacts)
When this mode is selected, VRC is conditioned to acti-
vate VRC upon closure of external contacts. These con-
tacts, which specify the reduction amount, are connected
to terminals (labeled VRC1 and VRC2) at the rear of the
controller. See Appendixes I and K.
Note that VRC Mode: Remote works differently than VRC
Mode: Local. When you enable VRC Mode: Local, voltage
reduction begins immediately. When you enable VRC
Mode: Remote, the microprocessor is only conditioned to
activate VRC. Voltage reduction does not occur until the
VRC contacts are activated.
To enable VRC Remote mode, view VRC Mode and select
REMOTE. Then to activate voltage reduction, you must
close the appropriate VRC contacts.
Remote mode is further subdivided into MJ-X
MJ-3A mode (compatible with the previous-generation
control). Both modes use the VRC terminal pairs; the dif-
ference is in the way the terminal pairs are used.
MJ-X Mode ("Static" Inputs)
In MJ-X mode, you can specify up to three Stages of volt-
age reduction— each with a different reduction value. View
VRC Remote and select MJ-X. Then view VRC Stage1,
VRC Stage2, and VRC Stage3 to set the VRC percentage
reduction values.
Two terminal pairs (VRC1 and VRC2) on the external termi-
nal block are used to trigger the three Stages (see Table
4.3).
Table 4.3 VRC Indicator Flashing Pattern for MJ-X Mode
Stage VRC Terminal
Pairs
Stage 1 VRC1 active;
VRC2 in-active
Stage 2 VRC1 in-active;
VRC2 active
Stage 3 VRC1 active;
VRC2 active
Siemens Power Transmission & Distribution, Inc.
4
Setting Up the MJ-XL Control Panel
MJ-3A Mode ("Pulsed" Input)
This mode simulates MJ-3A VRC; it uses only one exter-
nal contact(VRC1). MJ-3A VRC users can achieve compati-
bility with existing controllers using this mode.
To use MJ-3A mode, view VRC Remote and select MJ-3A.
Then select MJ-3A VRC% and specify the reduction value.
The single MJ-3A VRC% value defines a total reduction
value which control program logic subdivides into 33%,
67% and 100% steps.
To achieve a reduction equal to 100% of the MJ-3A VRC%
specification, activate the VRC1 contact for more than
three seconds ("latched"). To achieve partial voltage
reduction, "pulse" the VRC1 contact momentarily (a
"pulse" is 300 msec. to 3 seconds). See Table 4.4 below.
Table 4.4
Terminal Pair
For example, if you specify Fwd Volts=120 V, and MJ-3A
VRC% = 10%, the total reduction value is 12 V. This 12 V
L
mode, and
reduction value is further subdivided into thirds, so a sin-
gle pulse would result in a 4 V reduction; a second pulse
would produce an 8 V reduction, and a third pulse would
produce a total of 12 V reduction. Contact activation of
three seconds or longer is considered to be a "latched
condition" and would (in this example) produce a full 12 V
reduction.
Automatic Mode VRC with Remote Override
In Automatic mode, voltage reduction is activated auto-
matically whenever load current exceeds a predefined per-
centage.
There are two automatic VRC setpoints (AutoVRC1 and
AutoVRC2). When load current exceeds the percentage
specified in either of the AutoVRC %I data items, regula-
tor output voltage is reduced by the percentage specified
in the corresponding AutoVRCset data item.
VRC LED flashing
pattern
Only one set is active at a time; they are not additive.
long-short
AutoVRC remains active until the load current falls below a
value that is the lower of:
long-short-short
AutoVRCn%
long-short-short
or
MJ-3A Mode VRC Reduction
VRC1 VRC
Reduction
first pulse 33% of
specified value
second pulse 67% of
specified value
third pulse 100% of
specified value
fourth pulse 0%
latched 100% of
specified value
unlatched none
· ·
(1-2 AutoVRCsetn(%))
VRC LED flashing
pattern
long-short
long-short-short
long-short-short-short
not flashing
long-short-short-short
none
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