4 Setting Up the MJ-5 Control Panel
Siemens Industry, Inc.
21
Many regulators are built with transformer turns ratios that
do not provide the exact basis voltage (115, 120, or 125 V)
to the controller. Previous generation controllers include a
tapped sensing transformer to correct the voltage. Instead of
using a sensing transformer, the MJ-5 corrects the voltage
mathematically, using the P2 PT turns ratio. The turn ratio
for a given regulator can be determined from the regulator’s
nameplate.
To define the turn ratio, you must first determine which
column in the nameplate describes the “P2” secondary for a
given primary voltage. P2 describes the pin on the
Polarized Disconnect Switch (PDS, or jack plug). The P2
pin is attached to the regulator Potential Transformer
secondary (if present), and is usually labeled Control Volts
on the nameplate. See Figures 4.1 to 4.4 for examples.
Note:
For an ANSI type B regulator, the utility winding
tap leads are labeled P3, P4, P5, ... and the P2 lead is
connected to the U2 terminal on the PDS.
View P2 PT. Then, specify the turn ratio exactly as it is
specified on the regulator nameplate (e.g., 7620:121). The
microprocessor will correct the reference voltage to the
basis voltage (115, 120, or 125 V). Default value is 120 V.
If an inverted (Type B) regulator has a source-side Potential
Transformer, the utility (tertiary) winding leads are labeled
P3, P4, etc., and the P2 lead is connected to the “U2”
terminal on the PDS. The source-side PT leads are now
labeled P12, P13, etc., and the P12 lead is connected to the
P2 terminal on the PDS in the control box.
Note also that no reverse power flow relay is required. The
microprocessor senses the reversal and applies the
appropriate polarity.
4.3.9 CTratio (Current Transformer Ratio)
The Current Transformer ratio defines scaling for current
measurements.
View CTratio: then specify the ratio exactly as specified on
the nameplate. See Figures 4.1 to 4.4 for examples.
The primary side of this ratio is also used by the control
program to define the CT primary rating. This rating and
the I Threshold % define a tap change deadband for use
during certain reverse power flow conditions. (I Threshold
% is described below.)
4.3.10 I Full Load
This item specifies the Full Load Current for use in
determining when an Overcurrent condition occurs.
Typically, the Full Load Current setting is the same as the
CT Primary (the first number of the CT Ratio screen),
though this is not always the case. Locate the regulator’s
Full Load Current specification on the upper right side of
the nameplate (just below the “Class” specification). The
regulator nameplate shows the Full Load Current as “XXX
Amps.” Enter the value for the Full Load Current setting
into the MJ-5. See Figures 4.1 to 4.4 for examples.
4.3.11 Power Flow Modes
The Power Flow Mode data item allows you to specify
which control program algorithm will be used under
reverse power flow conditions. Systems which experience
power flow reversals have unique control requirements.
The MJ-5 Control Panel senses the reversal and modifies its
operation based on the Power Flow Mode selected.
This section provides an introduction to each of the modes,
and describes how to select the desired mode. See Chapter
6 for a detailed discussion of the operational differences
between the modes.
Forward Locked Mode
This mode of operation (F LOCK) is intended for use in
systems where reverse power flow is not anticipated. Tap
changes are inhibited under reverse power flow conditions.
Reverse Locked Mode
This mode of operation (R LOCK) is intended for use in
systems where forward power flow is not anticipated. Tap
changes are inhibited under forward power flow conditions.
For this mode a Source-side Potential Transformer is no
longer required. See Sections 5.1 and 5.2.
Bi-directional Mode
This mode of operation (BI-DIR) is intended for use in
systems where reverse power flow is anticipated and
voltage regulation is desired under both forward and
reverse power flow conditions. For this mode a Source-side
Potential Transformer is no longer required. See Sections
5.1 and 5.2.
Idle Reverse Mode
This mode of operation (IDLE R) is intended for use in
systems where reverse power flow is to be treated as an
abnormal situation. When reverse power flow is
recognized, the regulator idles at the last tap position held
before the reversal.
Neutral Reverse Mode
This mode of operation (NEUT R) is intended for use in
systems where reverse power flow is to be treated as an
abnormal situation. When power flow reversal is
recognized, the regulator returns the tap changer to the
neutral tap position.
Co-Generation Mode
This mode of operation (CO-GEN) is for use in systems
where consumer-generated power may sometimes flow
from the consumer to the Utility. Under reverse current
flow conditions, forward regulation is allowed, using
reverse Line Drop Compensation settings.
4.3.12 Basis Volts
The Basis Volts data item defines whether the MJ-5 control
program is to convert the regulator transformer secondary
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