BECKWITH ELECTRIC M-2601, Instruction Book

Page: 41 / 70

4–2
M-2601/02/03 Instruction Book
For example, with a condition of 5/8% taps (0.75 V)
(therefore 1 V bandwidth setting), if the bus voltage
varies more than 0.5 V (1/2 of bandwidth) from
the voltage setting, the regulator control will begin
timing towards an operation. The accumulating
timer has an operational threshold which is adapted
from the VRQF history and the VRQF setting. If
the history illustrates a VRQF less than the setting
(indicating a relatively stable bus voltage), the
threshold will be increased. This allows the natural
stability of the system to correct the voltage, and
in many cases to avoid the need for a tapchange.
If the history illustrates a VRQF higher than the
setting (indicating a relatively variable bus voltage),
the threshold will be decreased. This allows
tapchanges to occur sooner, and system voltage
variations to be minimized.
VAr Bias
Use of VAr Bias allows the Autodaptive
®
Regulator
Control (ARC) to coordinate its operation with the
M-2501A Autodaptive Capacitor Control (ACC)
devices on the distribution system in order to
minimize losses, subsequent voltage variations,
and equipment capacity requirements of
transmitting VArs.
The application of both the ARC and the ACCs
on a circuit provides for an interaction between
the devices that provides for faster response in
times of rapidly changing conditions on the
distribution system. This application combination
adds a “substation requirements” aspect to the
feeder requirements control of pole-top capacitor
banks.
For example, with one transformer, six feeders,
and 1200 KVAr pole-top feeder capacitor banks,
if each feeder is correctly compensated to within
400 KVAr, all feeder bank controls would be
operating correctly. However, the transformer would
be transforming 2400 KVAr (six feeders times 400
KVAr) from the transmission system. The ARC
on the transformer would detect this condition and
affect additional line capacitor operation by making
a temporary voltage level setting change. By
effectively delaying a voltage tap change for a
short time, a line capacitor bank control could be
biased into operation by the tapchanger control,
with reduced losses, better voltage profiles, and
fewer tap changes.
4.1 Measurements & Calculations
Voltage Measurements
Normal
The ARC accomplishes waveform sampling by
sampling a 60 Hz signal at a rate of four hundred
and eighty samples per cycle, or two hundred and
forty samples per half-cycle. This measurement
is repeated twenty times per second. Two
conditions terminate the sampling for one half-
cycle. They are:
1. The voltage being sampled crosses the
zero value line.
2. 240 voltage samples have been collected.
These samples are correlated with sine table entries
and processed to produce a voltage value. This
voltage is the fundamental component of the
voltage wave.
Bandcenter
In the ARC, Bandcenter is the value of voltage
selected by the customer as the desired value of
voltage for regulation. This value is the center
point for the selected bandwidth.
V
measured
V
measured
is the value of voltage which the control
measures for regulation.
Current Measurements
Line Current
Current is measured by its two components with
respect to the voltage signal, the in-phase or real
component (P) and the 90° or quadrature
component (Q). Values of P run from a positive
maximum to a negative maximum. Values of Q
run from a positive to a negative maximum, with
the negative values indicating a lagging power
factor on the load.
A vector sum of these current components is
displayed as secondary current.