FMS Publications

Power Quality Compatibility & Compliance

ABSTRACT:

An elevated EMF and magnetic field interference problem illustrates the interrelationship between Power Quality issues and unusual levels of EMF. Additionally, this case study illuminates the positive customer service changes taking place inside a major power utility in a deregulated environment.

1. THE PROBLEM:

Elevated EMF levels in a ground-floor space of a Class-A building in Westchester County, New York, had rendered the space unusable for most types of computer use. The building engineering staff concluded that the problem arose from the building electricity feeds.

At this point, when the issues of the consequences of elevated magnetic fields were assessed, and the decision to take corrective action was made, the participants did not know the complexity of the problem, much less that in the course of its solution, other, seemingly unrelated but far more potentially dangerous problems would be uncovered.

The building facilities engineering department contacted the Power Quality Group from ConEd (the local utility for Westchester) to verify field levels and to propose corrective strategies.

After review of the data, the building hired a Los Angeles-based EMF specialist, Field Management Services (FMS) to support the Power Quality Group.

It soon became clear that the fields were produced by a variety of sources, both common and uncommon. Some became visible only after the others were substantially eliminated and some were revealed as a consequence of the attempt to correct others.

2. OBJECTIVE:

The initial objective of the building's facilities engineering department was to lower the magnetic field levels emanating from the electricity feeds to a level that would allow computer operation in the affected area. The first general survey conducted by the ConEd Power Quality Group established an average field strength of 29.1 mG.

Throughout the course of the investigation, the full analysis revealed that the sources of the elevated magnetic field levels included:

1. Wiring errors in the upper floors of the building. These violations of Code were causing return current to travel on grounding conductors throughout the building.
2. High current conductors in the 460V Network Protector Vault at the edge of the building, below grade.
3. High current conductors in the building transformer vault and switchgear facility below the space.
4. Multiple ground paths in the 460V Network Protector and switchgear room were creating unusual field levels above the vault.
5. The neutral bus connection in the main distribution panel had been improperly and dangerously installed.

Although the fields from a high current conductor are fundamentally not distinguishable from those from a net-current wiring error, the available mitigation strategies are quite different. Therefore, as the investigation revealed the various sources, the corresponding mitigation strategies needed to be applied.

3. METHOD:

As is often the case, this project was amenable to a phased approach, starting with the more obvious or physically accessible sources and proceeding toward the more intractable and more complicated sources.

The place to start was with the wiring errors on the upper floors, beginning at the top floor and working down toward the vault. This is painstaking, time-consuming work. At the beginning of the work, the main distribution circuit had 140 amps of net-current. After corrections were made, a process which required several months to complete, the levels had been reduced to 11 amps.

Toward the end of this tedious work, a dangerous flaw was discovered. Following weeks of wiring problem resolution, the ConEd Power Quality Group was called on an emergency. On a routine inspection, the building engineer discovered that the bolts on the neutral bus inside the vault were cherry red and smoking. Now that the current was flowing on the neutral bus, as it should be, the bus was being overheated revealing that the bus connection had been improperly installed. Prior to the wiring corrections on the upper floors, a portion of the return current was flowing on the grounding conductors and a potentially dangerous installation error went undetected. The EMF investigation illuminated the danger. An emergency shunt was installed by the building engineer and ConEd Power Quality while a new bus bar was installed and the bus connections were corrected.

Average field strength after reducing the building net-currents: 35.2 mG. (The fields had actually increased.)

THE PROBLEM MOVES

The wiring corrections reduced the net-currents on the major circuits from the basement distribution equipment, reducing the fields on the upper floors, but the computer model had predicted much lower levels in the first floor space. These remaining fields appeared to be coming from the vault and switchgear rooms below the space. FMS created a map of the current flows inside the switchgear rooms. The model showed current flows producing high levels of magnetic fields from an alternate, parallel neutral current path between the ConEd transformer and network protection vault and the neutral-to-ground bond in the building's main distribution equipment. Approximately 40 amps of neutral current were flowing on building steel components, between the transformer/network protection vault ground point and the main distribution equipment neutral-to-ground point. This produced the fields of a net-current circuit condition in the street level tenant space which, like those produced from wiring errors on the upper floors, could not be mitigated or reduced by shielding measures.

The computer model suggested that the most efficient solution to this new problem would be to modify the existing grounding connections in such a way as to encourage the currents to flow on a single path and, in such as way as to maximize their capacity to self-cancel the currents normally in the vault and switchgear room. Inasmuch as these proposed changes impinged on substantial questions of safety and, consequently, ConEd transformer vault construction policies, it was essential that ConEd Distribution Engineering management could be made comfortable with these proposed changes. Accordingly a technical negotiation between the various parties (the building management and engineering, ConEd Power Quality, FMS and ConEd Distribution Engineering) resulted in a scheme which satisfied all of the participant's goals.

As a result of that agreement, the building engineering staff installed two additional grounds from the building switchgear to the building steel and an additional ground to the building cold water pipe. After these additional grounds were in place and verified by ConEd Distribution Engineering and the Power Quality Group, the original ground connection in the network protection room along with one of the original ground connections in the transformer vault were removed by ConEd. Measurements by ConEd Power Quality verified that the 40 amps originally running on the ground system had been reduced to 4 amps. More importantly, this reduction had been achieved without compromise to the integrity of the building electrical system design or to the principles of safety and reliability that were of concern to all participants.

The net-current circuit conditions were minimized and magnetic fields in the affected street level tenant area proportionately reduced.

Average field strength, after reduction of the vault net currents: 26.8 mG.

MAGNETIC FIELD SHIELDING

The net-currents in the building had now been sufficiently reduced to allow for the productive use of magnetic field shielding. FMS performed a detailed survey of the mechanical and electromagnetic characteristics of the space and developed a two-phase mitigation plan, which was guaranteed to reduce magnetic field strength levels in the affected area to a target range between 2 - 6 mG. The first phase involved a shield in the tenant space, and second, if necessary, a shield inside the vault.

4. RESULTS:

In the end, the residual field strength values from the first phase shielding were sufficient to the needs of the building and their prospective tenant and the second phase was deemed unnecessary.

Average Field Strength, After Shielding & Net Currents Reduced : 6.2 mG.

5. CONCLUSION:

Resolution of these problems required close coordination and a successful technical negotiation between the building management, ConEd Power Quality Group, FMS and, since the final resolution would require a change in grounding patterns, participation and agreement with ConEd Distribution Engineering.

Moreover, the resolution of this complex problem illustrates the relationship between unusual EMF levels and Power Quality issues and, as importantly, demonstrates the positive customer service changes taking place inside a major power utility in a deregulated environment.