Basic control operations
Set voltage
The set voltage is the voltage level to which the control
will regulate on the 120 V base. Since the control performs
ratio correction in the firmware, this value will normally be
set for 120.0 V, unless it is desired to operate at a voltage
level higher or lower than nominal. For proper operation, the
ratio-correcting transformer, located on the back panel of
the control enclosure, must also be set for the correct tap
as shown by the regulator nameplate.
Bandwidth
The bandwidth is defined as that total voltage range, around
the voltage setting, which the control will consider as a
satisfied condition. As an example, a 2 V bandwidth on a
120 V setting means the operational timer will not activate
until the voltage is below 119 V or above 121 V. When the
voltage is in-band, the band edge indicators are off and the
timer (time delay) is off. Selection of a small bandwidth will
cause more tap changes to occur, but will provide a more
tightly regulated line. Conversely, a larger bandwidth results
in fewer tap changes, but at the expense of better regula-
tion. Selection of the bandwidth and time-delay settings
should be made recognizing the interdependence of these
two parameters.
Time delay
The time delay is the period of time (in seconds) that the
control waits from when the voltage first goes out-of-band
to the time when a tap change is issued. If a rapid response
is required, a shorter setting should be used. If several
devices on the same line are to be coordinated (cascaded),
different time-delay settings will be required to allow
the proper devices to operate in the desired sequence.
Proceeding from the source, each device should have a
longer time delay than the preceding device. A minimum
15-second difference between regulators located on the
same phase on the same feeder is recommended. The
delay allows the upstream device to perform its operations
prior to the downstream device reacting. The time-delay
setting of a voltage-minimizing, activated capacitor control
should be set the same as a regulator control. Alternate
time delays are available with the voltage limiting feature.
Refer to the Voltage Limiting section of this manual.
Line compensation, resistance and reactance
settings
Quite often regulators are installed some distance from
the theoretical load center (the location at which the
voltage is to be regulated). This means the load will not
be served at the desired voltage level due to the losses
(voltage drop) on the line between the regulator and the
load. Furthermore, as the load increases, line losses also
increase, causing the lowest voltage condition to occur
during the time of heaviest loading.
To provide the regulator with the capability to regulate
at a projected load center, the control has line-drop
compensation elements within it. This circuitry usually
consists of a current source (CT), which produces a current
proportional to the load current, and resistive (R) and
reactive (X) elements through which this current flows. As
the load increases, the resulting CT current flowing through
these elements produces voltage drops, which simulate the
voltage drops on the primary line.
Within the control, the input current is sampled and is used
in a computer algorithm which calculates the respective
resistive and reactive voltage drops based upon the line-
drop compensation values programmed into the control at
FC 4 and FC 5 (or FC 54 and FC 55 for reverse power flow
conditions). This is an accurate and economical means of
developing the compensated voltage.
To select the proper R and X values, the user must know
several factors about the line being regulated.
Regulator configuration
The control is designed to operate on wye (star)-
connected and delta-connected regulators. Regulators
connected line-to-ground (wye) develop potentials and
currents suitable for direct implementation in the control.
Regulators connected line-to-line (delta) develop a potential-
to-current phase shift which is dependent upon whether
the regulator is defined as leading or lagging. The phase
shift must be known by the control to permit accurate
calculations for correct operation. This is accomplished by
entering the proper option at FC 41: Wye, Delta Lagging, or
Delta Leading.
Control operating modes
The CL-6 control supports three modes in which the control
responds to out-of-band conditions, permitting use of the
mode that best fits the application. The three modes are
Sequential, Time Integrating, and Voltage Averaging. The
mode setting can be selected by scrolling within FC 42 or
through Settings > Configuration in the menu structure.
Sequential mode
This is the standard mode of response. When the load
voltage goes out-of-band, the time-delay circuit is activated.
At the end of the time-out, a tap change is initiated. After
each tap change, a 2-second pause occurs to permit the
control to sample the voltage again. This sequence contin-
ues until the voltage is brought into band, at which time the
timing circuit is reset. Whenever the voltage goes in-band,
the timer is reset.
26
CL-6 SERIES CONTROL INSTALLATION, OPERATION, AND MAINTENANCE INSTRUCTIONS MN225016EN January 2016
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