Large-Volume
E.L.F. Magnetic Field Compensation [LV-EMFC] Research Project
- Introduction -
In May, 1994,
Linear Research Associates of Trumansburg, NY entered into a research and
development contract with regional utility New York State Electric and
Gas Corporation to investigate methods for large-volume active-negative-feedback
a.c. magnetic field shielding. Research work outlined in the contract specification
was based on Linear Research Associates' commercial moderate-volume (to
10 m3) a.c. magnetic field mitigation
technology and also on background discussions with the sponsor's transmission
& distribution engineering personnel.
Midpoint goals
defined for this project included survey and source/feedback simulation
code research tools and survey instrumentation hardware. Project end-point
goals included final construction and in situ testing midpoint,
simulation work of sufficient quality and quantity to determine the feasibility
of cost-effective active shielding for protected volumes in the range of
at least 10,000 m3.
During the
period May, 1994 through June, 1995, a specialized magnetic field survey
system and proprietary, fully scripted large-volume active-feedback simulation
program were created, debugged and tested. Using the new survey instrumentation,
Beta Site magnetic field data were collected which could be utilized for
optimization runs. In May, 1995, Linear Research Associates demonstrated
the apparent feasibility of large-volume active-feedback a.c. magnetic
field [ACMF] cancellation over protected volumes up to 26,000 m3 (918,000
ft3).
In this interim
report we describe a generalized LV-EMFC active-negative feedback system
and specific Phase I survey and simulation tools developed for research
on its practical implementation. This report concludes with an examination
of Linear Research Associates' Phase I Beta Site simulation results.
1. Active-Negative-Feedback ACMF Shielding
Proposed Large-Volume [LV] active-negative-feedback
shielding technology.
Negative feedback is a classic engineering
principle which can be utilized for a.c. magnetic field [ACMF] reduction.
To implement this type of active shielding, a system of sensors, signal
processor/amplifiers and driven coils is placed in each axis (one protected
axis is depicted below). System operation is based on the physical principle
that an axial a.c. magnetic field component, Bi, through the
Protected Volume [PV] can be arbitrarily reduced in intensity by applying
fields of opposite phase. Such fields are here determined by axial
error components, Bi', at a specified number of sample points.
At each sampling sensor's location the magnetic field error component will
be equal to the difference between the incident (Bi) and compensating
fields. Analytically, the a.c. magnetic attenuation at each sensor reduces
to a constant factor independent of ambient variation. Compensation is
wideband, covering an instantaneous bandwidth which includes the fundamental
line frequency and all significant harmonics. Attenuation of the incident
field in each axis is gradient-dependent but may be improved as required
by subdividing the protected volume into an arbitrary number of sensor-coil
cells.
2. Simulation Program Example
Example simulation program command language compiler
input file, demonstrating how the transfer characteristic of a sensor may
be varied automatically.
An interpreter
allows input file parameters to be stepped over a series of optimization
runs and any specific output parameter function to be recorded for each
iteration.
#Define a three-phase parallel power line system
| SEGMENT |
-7.925 |
0. |
14.411 |
-7.925 |
10000. |
14.411 |
965.5 |
2.2943 |
| SEGMENT |
0. |
0. |
14.411 |
0. |
10000. |
14.411 |
965.5 |
4.18879 |
| SEGMENT |
7.925 |
0. |
14.411 |
7.925 |
10000. |
14.411 |
965.5 |
0. |
#Define a driven coil
DrivenCoil CoilX-one
{
| SEGMENT |
48.4 |
4994. |
10. |
48.4 |
5006. |
10. |
| SEGMENT |
48.4 |
5006. |
10. |
48.4 |
5006. |
0. |
| SEGMENT |
48.4 |
5006. |
0. |
48.4 |
4994. |
0. |
| SEGMENT |
48.4 |
4996. |
0. |
48.4 |
4994. |
10. |
}
#Define a sensor
| SENSOR |
SensorX-one |
48.4 |
5000. |
4. |
1. |
0. |
0. |
#Define a new variable which is the transfer characteristic
Variable t = (100.0e6, 200.0e6) %11
#Define a transfer element with variable characteristic "t"
Transfer SensorX-one CoilX-one t
| POINTBLOCK |
60. |
65. |
2 |
4098. |
5002. |
2 |
5. |
7. |
2 |
CalculationFormat
{
Loop t
{
| OutputFile |
<< "Sensor transfer Characteristic = " << t<< entl; |
| OutputFile |
<< "x" << tab << "y" << "tab" << "z"
<< "tab" |
|
<< "RMS" << endl; |
Loop x
{
Loop y
{
Loop Z
{
CalculateFields
outputFile << x << tab << y << tab << z <<
tab << RMS << endl;
}
}
}
OutputFile << endl;
}
}
Document
3. LV-EMFS Site Survey System
Unique features of this system are its ability
to record time-resolved d.c. and a.c. vector field data (while resolving
magnitude and relative a.c. phase for each axis), and its intrinsically
accurate axial alignment. Shown from left to right are the system 486DX2-40
portable computer, probe instrument, battery charger and UHF-FM remote
field reference monitor. For added survey height, extension sections up
to 6 meters in length may be fastened onto probe body.
Large-Volume E.L.F. Magnetic Field Compensation Site
System [LV-EMFS].
This page is Copyright 2002 Linear Research Associates.
Page designed and created by Stan
Borbat.
For more information contact Curt Dunnam