Power feeders for a new cooling tower require special design and installation considerations to be compatible with the existing power distribution system.
Tying a new 15kV feeder into an existing PILC (paper insulated, lead covered) cable system is just one of the important factors in the design and installation of a new cooling tower at AT&T Bell Labs in Holmdel, N.J. Other factors include the integrity of existing butyl rubber and PILC feeder cables and proper phasing within the existing primary selective distribution system. The design and installation details of this project provide some interesting perspectives.
As shown in Fig. 1, the incoming electrical service at the AT&T Bell Labs facility is 34.5kV, powering two 15 MVA transformers. From here, the voltage is stepped down to 13.2kV. The main switchgear is double-ended with a normally closed tie breaker and four feeder breakers on each side of the tie breaker. The main building is served by six 13.2kV feeders.
There are 40 other substations at the facility, ranging in size from 500kVA to 2500kVA. All are double-ended, primary selective.
Fig. 2 shows the existing 13.2kV site power distribution along with the new cooling tower power feeders. Providing electric service for the new cooling tower's 1500kVA substation required tapping existing HLC and butyl rubber feeders in an existing manhole. Specifically, existing Feeders A1 and B1 were tapped with Y-splices in existing Manhole 6. All building feeders are normally energized and pass through this manhole. No electrical shut-down was required for any phase of this work.
Splicing new cables to PILC cables
Feeder Al, installed over 30 years ago, is a 3-conductor, 500kcmil, oil-impregnated, paper insulated, lead-sheathed, PVC jacketed, 15kV power cable. Feeder Bl is newer and consists of three single-conductor, 500kcmil butyl rubber cables. The new cooling tower power feeders are single-conductor, 500kcmil, 15kV, 133% insulation level, EPR/PVC, shielded power cables. ([ILLUSTRATION FOR FIGURE 3 OMITTED] on page 68.)
The making of Y-splices to Feeders Al and B1 without interruption of power required good planning, skilled mechanics, partnering with AT&T's Plant Operations, and continuous effective communication among all parties involved. Feeder Al was the first feeder to be spliced and all substations affected were switched to Feeder B1.
The following is a step-by-step chronology of the splicing.
Step 1. With all loads transferred to B1, Feeder Al was taken out of service, locked out, and tagged. All four other feeders (A2, B2, A3, and B3), were still energized in Manhole 6 throughout the course of work.
Step 2. To ensure that Feeder Al was actually deenergized, the lead covering over the existing butt splice was melted off to reveal the singles so that a tic tracer would read any voltage. Once it was verified that Feeder Al was actually deenergized, preparations were made to cut the feeder and begin the splice.
Step 3. After Feeder Al was cut, each wire was identified to determine phasing at each ends. Cables in Feeders Al and B1 had to be tapped and terminated in proper phase relationship to permit momentary closure of both Al and B1 switches at the substations, as shown in Fig. 3.
Step 4. To make the required Y-splices, in-line transition splices from existing PILC singles to new EPR/PVC singles first had to be made; then the Y-splices could be made on the new EPR/PVC singles. As such, a loop of three EPR/PVC singles was added to the A1 Feeder.
The transition splices each required a butt joint. Because the copper conductors in the PILC were triangular shaped sectors, a compression coupler could not be used. Instead, a split tinned-solder coupler was used to couple the PILC sectors to the EPR/PVC round conductors.
After the inner portion of the splice was complete, a ground braid was attached with a spring clamp to the metallic tape shield of each EPR/PVC single. These three ground braids then were laid across the splice tubes and soldered to the lead sheath of the PILC cable. A shielding mesh was half lapped over the braids. A nonconductive sealing breakout was applied to the ends of the new singles and heat-shrinked in place. An overall wrap-around sleeve then was positioned and a channel clip installed. Finally, the entire assembly was heat-shrinked.
Each of the 6 transition splices required 41 steps to complete, with each finished splice 48-in. long. Since Manhole 6 is only 8-ft long by 8-ft wide, the transition splices had to be located one over the other.
Step 5. With the three single conductor EPR loops in place, the Y-splices could now be made. Half duplex solder connectors were used for the Y-joint. The Y-splices were completed, connecting each phase of Feeder A1 to the run of new EPR/PVC cables going to the cooling tower.
Little Silver Electric, Inc. was the electrical contractor, with Bud Flanagan foreman. Little Silver brought in certified high voltage splicers Dusty Rhoades and Robert Cushman to do the splices as well as the stress cone terminations.
Splicing new cables to existing Feeder B1
After the A1 circuit was proof-tested, it was put back in service. All loads were transferred to Feeder A1 and Feeder B1 then was deenergized.
As was done with Feeder A1, Feeder B1 was tested to verify that it was deenergized. Its conductors were cut, with each identified at all termination points to insure proper phasing.
Because Feeder B1 consisted of single conductor cables, the Y-splices were made directly on them.
Before hi-pot testing could begin, the cables had to be removed from the line side of switches in three different locations, as shown in Fig. 4 (see page 70). This eliminated the possibility of flashover across the switches since, with the load side energized at 13.2kV from Feeder B1, a potential of 36kV would develop across the switch, as shown in Fig. 5 (see page 72).
Feeder A1. Once the Y-splices were made in Manhole 6, each assembly was hi-potted at 18kV maximum for 15 min.
The existing PILC cable was hi-potted. before and after the making of the Y-splices. Hi-potting the old cable required removing all terminated ends. (It's a good practice to remove cables from an HV switch to ensure that hi-pot readings will not include bus work, instrument transformers, etc.)
Feeder B1. After making the Y-splices on this feeder, it was then hi-potted at 18kV maximum for 15 min. After all ends were terminated, the feeder was energized. A phasing stick was used at all locations where Feeders A1 and B1 terminate in adjoining switches to ensure proper phasing. The cables were then fire-wrapped and neatly racked in Manholes 6, 6A, and 6B.
New EPR/PVC cable. The new cable was hi-pot tested while still on reels after delivery to the site and was proof tested after installation between Manhole 6 and the cooling tower. This was done at 80% of the factory test level, or 65kV maximum for 15 min.
Mystery sound during testing
During the hi-pot testing of the 13.2kV feeders, a faint buzzing sound was heard at the rear of the main substation. An in-depth search for the origin of the sound was conducted, with cover plates for the horizontal bus in the main substation removed to aid in location. The sound was so faint that technicians weren't certain if it was real or imaginary.
The lights inside the main substation then were shut off, as a last test, to obtain a visual indication to the problem, if possible. A faint blue glow was seen around one of the horizontal busses, where it passed through an insulating barrier from the A1 circuit breaker to the A2 circuit breaker. The combination of buzzing sound and blue glow indicated that a high voltage corona condition existed and tracking was beginning to develop.
All loads then were transferred to the "B" feeders. The "A" side of the main substation was isolated and corrective action was taken. All horizontal busses were cleaned and retaped and the insulating barriers were replaced. As a precautionary measure, the same actions were taken on the "B" side of the main substation, after it was deenergized.
The lesson we learned: Be alert to your surroundings, expect the unexpected, and take appropriate action. The early detection of this problem and prompt response avoided a costly, unscheduled, and possibly long, out-age of the entire facility. The corrective action was done during normal working hours and transparent to the occupants of the facility.
Key interlocks and other tamper-proof systems prevent the accidental closing or opening of switches and switchgear out of sequence when used per system operating instructions. As with any other fail-safe systems, there are ways to override the intended use, which is to prevent the operation of the electrical system in the wrong sequence. This improper operating sequence could damage equipment and might prove personally dangerous to the operator. On this project, the normal sequence was not followed and the key interlock system was overridden to allow switching without any loss of power to the building.
Note: Interlocks for electrical equipment may not be used as a substitute for lockout and tagging procedures.
Lock out/tag out procedures
OSHA's lockout/ragout requirements are as follows.
* Locate and identify all sources of energy and control devices.
* Notify all affected employees of lockout.
* Isolate all energy sources, such as bleeding stored energy in hydraulic and pneumatic systems.
* Lockout and tag all switches in the OFF position.
* Test to ensure that equipment turned OFF are indeed deenergized.
* Perform the work required.
* After the work is complete, remove locks and tags from equipment. Be sure to notify all affected employees that the equipment is to be reenergized. Special note: only the person who installed the lock should remove the lock.
For this project, the switching procedures needed to be reviewed and revised by electricians from Little Silver Electric and AT&T Bell Labs facilities management to ensure employee safety was not compromised. This meant installing locks and tags on all of the 13.2kV switches that were being deenergized as well as going to the main switchyard and racking-out, locking-out, and tagging the feeder breaker in the main substation. This process was duplicated when splicing occurred on the second feeder. When the 13.2kV lines were opened for splicing or testing, the phasing was checked because the 13.2kV lines are sometimes paralleled to switch feeders without disruption to the building.
Construction procedures at AT&T Bell Labs
Operations personnel perform all switching and tagging of the electrical system under the direction of the operations supervisor. Formal procedures are followed to ensure safety and to avoid inadvertent shutdown of critical loads.
When there is a request to shut down an MV feeder, operations personnel go to each primary selective substation and switch the load from one feeder to the other paired feeder. The primary switches are key interlocked to prevent the closing of two primary switches simultaneously; however, procedures allow two of these switches to be closed together temporarily with permission from the operations supervisor. This is necessary to avoid interrupting power to critical loads during switching operations.
Project background information
The chilled water system has a capacity of 6000 tons and consists of five 1200-ton chillers. Until recently, the source of condenser water for the chillers was from a 6-million-gallon pond located at the front of the facility. Additional data processing and computer loads increased the demand for chilled water; thus the capacity of the front pond to provide adequate condenser water cooling for the chillers was eventually exceeded. The remedy to this problem was to construct a cooling tower to provide condenser water cooling.
The installation consists of five 25 x 25-ft fiberglass shelled, tile filled, modular cooling towers. Each tower has a 60-hp, 460V, 3-phase fan motor. The motors are powered from variable frequency drives, with contactor bypass.
The cooling towers are placed in a linear arrangement on top of a concrete basin. Condenser water is pumped via underground 30-in. diameter ductile-iron pipes from the cooling towers' location to the chiller plant, approximately 2500 ft away. The remote site for the cooling towers was chosen to eliminate noise and vapor in the vicinity of the main building.
Six 2-stage, vertical turbine condenser water pumps, driven by 200-hp, 460V, 3-phase, high-efficiency motors, are installed in the basin to meet the pumping requirements. Motor controllers for the pump motors are solid-state reduced voltage starters with bypass contactors.
The cooling tower is powered from a 1500kVA double-ended primary selective substation. The incoming power for the substation is 13.2kV and is connected to the existing primary distribution system. The tower itself is connected to the same feeders that feed the chilled water plant.
AT&T Bell Labs' facility electrical engineering group provided the conceptual design and acted as construction managers for the project. Black & Veatch, Fishkill, N.Y., furnished the detailed design services for the project. AT&T Bell Labs specified and prepurchased all major electrical equipment (substations, motor control centers, panels, cable, conduit, etc.), resulting in considerable savings.
At the AT&T Bell Labs facility in Holmdel, research is conducted primarily on data processing, software development, and computer-based communication systems. Accommodating this research requires a very large facility, which encompasses 2.5 million sq ft under one roof, with many complex systems.
This was a grass roots project, having minimal association with existing buildings and utilities, except for tie-ins. All contractors were instructed in AT&T safety practices. These included the use of hard hats for all personnel on the job site, ground fault protection of portable equipment, and OSHA requirements for maintaining a safe working environment.
Two critical safety issues were working in a confined Space and lockout/tagout procedures. Both of these issues were associated with the splicing of the 13.2kV feeders in Manhole 6.
Confined space according to OSHA's ruling is "a space in which an employee may enter and perform work." It is not a space intended for continuous occupancy and a person's entrance and exit is restricted. There are two basic types of these spaces, one being a permit required space in which there are hazards present in the area under normal conditions. These may include, but are not limited to, hazardous atmospheres containing methane gas or an oxygen deficient atmosphere, or hazards because of the configuration of the space, where a person entering may be trapped because of the shape of the space. This type of space must be considered permit-required confined space, requiring that special precautions be taken before entering the area so that a worker is protected.
The second type of space is the non-permit confined space. This area does not actually contain hazards that could cause death or bodily harm; nevertheless it still is a confined space. An example of an area like this could be a crawl space under a building. All employers were required to have surveyed their facilities by April 15, 1993, and identified the permit-required, confined areas, notifying all affected employees of their existence as well as those who would enter such spaces. Also, the permit-required spaces must be effectively guarded and identified as a restricted area to keep unauthorized personnel out. If the facility determined it has only non-permit spaces, nothing else would need to be done. However, good practice is to monitor these types of areas to assure that they remain a non-permit confined space.
The confined space issue requires contractors and owners to share information and work together in permit-required, confined spaces as noted here.
* Notify contractor why the area is a permit-required, confined space.
* Inform the contractor of any past experience with the area. In turn, the contractor must inform the owner of any hazards encountered while working in the permit area.
* Inform the contractor of the measures used to protect the employees who work near or in the permit-required, confined space. In turn, the contractor will inform the owner of what precautions that meet the standard will be used to protect the contractor's workers in or near the confined space.
* If both the contractor's and the owner's employees will be working in the confined space together, it is the owner's as well as the contractor's obligation to coordinate work operations to provide a safe work environment for all employees working in the area.
* The owner shall conduct an end-of-job meeting with the contractor to discuss any hazards found during work in the confined space.
This is a general industry standard and does not apply to construction, agriculture, or shipyard employment. There are state-run OSHA programs that cover places of employment that are not covered in the federal regulation. The states that run their own programs are California, Kentucky, Maryland, Michigan, and Virginia. In New Jersey, this is not the case. Most electricians are not familiar with this standard because it does not apply to construction. The conflict on a job like this one and others where there is a combination of new manholes (new construction) and existing manholes (general industry) is this: Where does the standard apply and what'S required? At this facility, we treat all manholes as permit-required, confined space areas and eliminated any possible safety concerns by taking the most stringent applications of the ruling. In our view, what's the difference if a hazard is on a new job or one already existing? NONE. Therefore, taking extra precautions is a small price to pay for employee safety.
Specialized equipment which may be needed for confined space entry may include the following.
* Air sampling instruments that measure for oxygen content, combustibles, toxic gases and vapors. A permit-required, confined space requires testing and monitoring to determine whether it is safe to enter, and remains safe for the job.
* Protective gear, which could include hard hats, rubber goods, barriers, etc.
* Ventilators/blowers, which may be used in instances where only atmospheric hazards exist. A simplified entry procedure may be used with continuously forced ventilation.
* Self-Contained Breathing Apparatus (SCBA), which would be needed for rescue operations or if the area could not be purged of the contaminant. This standard allows for rescue from the confined space by an onsite team or by outside help. Outside help is sometimes a problem because response time is critical in life saving efforts in a confined space. If an onsite team is used, one of the training requirements is that rescue team members be trained in basic first aid and cardiopulmonary resuscitation (CPR).
* Communication Equipment. Entrants must be able to communicate with attendants.
* Tripod and Winch, Lifeline, and Body Harness. The standard requires that a non-entry retrieval system, such as harness and rope, be used whenever an employee enters a permit-required, confined space. If the employee is deeper than 5 ft, then a mechanical type lifting device shall be available. The exception to the rule would be if these measures would not help in the rescue attempts or increase the hazards in the confined space.
James Canham is Facilities Engineering Operations and Maintenance Manager, Joseph Zec is Senior Facilities Engineer, and Jack E. Pullizzi is Assistant Facilities Engineer at AT&T Bell Labs, Holmdel, N.J. Mario Ciasulli is a Consulting Engineer for MMC Engineering, Inc.