Electrical Systems

The new facilities shown in the master plan reflect the university's development program through the year 2030, but the specific areas and uses of each building will be adjusted during the development of the building's program. The recommendations made in the electrical report are conceptually based upon this development program. Designers of new facilities should re-evaluate these recommendations based upon the building program for the new facility and the actual as-built size and use of other buildings or facilities that have been constructed since the completion of this master plan.

Sources of Electrical Power

Source 1: The 1604 campus is provided electrical power from two 138 kV City Public Service (CPS) overhead transmission lines to the CPS substation located at the north end of the campus at Loop 1604. Within the CPS substation, power is transformed from 138 kV to 13.8 kV, metered, and delivered via two underground circuits to the UTSA main distribution switchgear located just east of the CPS substation.

Source 2: A combination diesel/natural gas-fired engine-generator rated at 3500kW/4250 kVA, 4160Y/2400-volt, three-phase, four-wire is located at the Thermal Energy Plant. This generator is used primarily for providing electrical power to a 3000-ton, 3000 HP centrifugal chiller located at the Thermal Energy Plant. The generator is connected, however, in such a way as to permit back feeding of 480-volt systems (a 1000-ton chiller and Motor Control Center "MCC3") within the Thermal Energy Plant in the event of loss of normal utility service. Use of this generator greatly reduces the amount of electrical energy that UTSA would otherwise have to purchase from CPS. At the present time, it is not possible to serve electrical power from the generator to loads beyond the Thermal Energy Plant.

Existing Campus Distribution

Power is provided from the CPS substation to the UTSA campus via two 13.8kV, 800-amp underground circuits that terminate in the existing UTSA main distribution switchgear. The main bus of the switchgear is arranged in a main-tie-main fashion to allow maintenance of either of the two services to be undertaken without loss of power to the campus. With recent modifications to the CPS substation and these two underground circuits, the capacity of the service to the UTSA campus has been increased to 20 MVA.

13.8-kV distribution throughout the 1604 Campus is accomplished by twelve distribution circuit breakers in the UTSA main distribution switchgear. These twelve breakers are connected in sets of two to each end of six loops serving the campus. All of these breakers are rated at 1200 amps/15kV with protective relays at various settings which can be easily field adjusted or modified to permit trip settings up to the rating of the cable being protected (240 amps). The 240-amp rating of the cable used allows each circuit breaker to deliver as much as 5736 kVA, however, to allow redundancy, only 5736 kVA is permitted per pair of breakers forming a loop. Each loop has a normally open switch located within the campus that divides the loop into two radial circuits. This main-tie-main arrangement on the distribution loops provides UTSA maintenance the same advantages as are available on the main bus. It also prevents a single fault from taking off-line more than about half of the load on any given loop.

Existing Campus Loads

Since completion of the most recent campus master plan in 2001, the following loads have been added or are in the process of being added to the existing campus electrical distribution system:

• Recreation/Wellness Center (2002)
• Child Care Center (2002)
• Student Housing Phase I (2004)
• Student Housing Phase I(a) (2004)
• Dining Hall (2004)
• Facilities Services Building (2004)
• Main Building (2004)
• BSE 1(2005)

The campus load flow study that was completed in August 2002 was recently updated in March 2004. This updated load flow study provides the estimated peak load on the existing UTSA distribution system and the estimated loop loading after the completion of all buildings listed above. Summary results of the March 2004 study are provided in the table. As shown in that figure, the present UTSA electrical distribution system has no spare capacity for any future loads and will have to be modified to accommodate any additional loads. The data in the figure was used as the starting point for this update to the campus master plan.

Projected Campus Loads

The projected campus load has been estimated for each new proposed facility and a summary list of all new proposed buildings and/or facilities is shown in the accompanying table. Based on the calculations shown in that figure, the estimated added load is 79,461 kVA (80 MVA). A diversity factor of 0.7 was used for sizing the main substation equipment, which results in an estimated peak load of 55,628 kVA (56 MVA). This means that the existing system capacity must be increased by 55,628 kVA (56 MVA) to support the projected load on campus.

Several approximations were used to estimate the added load for each new building and facility. For expansions to existing buildings, a load ratio based on building square footage and actual peak load has been calculated for various buildings on campus. A summary of these calculations is shown in the figure to the right. For new buildings a VA/SF value based on 2004 Means data has been used. A summary of new building VA/SF estimates is shown in the figure below.

Campus Building Load Ratios

A calculation of the existing campus load ratio as of 2003 is shown in Figure 3. This load ratio assumes that all central plant loads are being fed from the CPS power grid and not from the central plant generator. The load ratio calculated for the existing campus is 8.82. A similar load ratio for all of the proposed new buildings and facilities has been calculated and shown in Figure 13. The load ratio calculated for the proposed new buildings and facilities is 13.4. The increase in load ratio is attributed to the fact that many of the new facilities are research facilities that have higher power demands mainly due to large outside air requirements that result in higher HVAC power demands. In addition, all new thermal plant loads have been assumed to be fed from the CPS utility grid and not from power generated on site.

New Campus Distribution

In the existing CPS substation, two distribution system voltages are available (13.8 kV and 35 kV). In discussions with UTSA personnel, they stated that they would like to stay with the 13.8 kV distribution system for the entire campus. In discussions with CPS personnel, they would like to supply all power to the UTSA campus at 35 kV. The following is a list of advantages and disadvantages for each system.

13.8 kV Advantages

• Symmetry of system, all equipment the same.
• Familiarity of UTSA operations personnel with 13.8 kV system.
• This system can be modified in a more timely manner than going to a new 35 kV system. This works well with the schedule of ongoing projects.
• Allows loads to be transferred between loops as necessary to react to system outages.
• Can be implemented in phases to grow as the load on campus grows.

13.8 kV Disadvantages

• Requires larger duct banks and more feeder loops to distribute the required amounts of power.
• Limitations on CPS transformer size will result in two metering points for the campus.
• Limitations on CPS transformer size will limit service capacity expansion to 60 MVA.

35 kV Advantages

• Can utilize smaller duct banks and fewer feeder loops to distribute the required amounts of power.
• Could result in a single point metering for the campus.
• Service capacity expansion is not limited to 60 MVA.

35 kV Disadvantages

• Requires larger footprint for installation of equipment.
• UTSA personnel are not familiar with the operation of a 35 kV system.
• Results in a mixed system on campus.
• UTSA would have to purchase and maintain two large substation type transformers to backfeed old 13.8 kV system.
• Would make system on existing campus less flexible (i.e. cannot use 35 kV loops to back up 13.8 kV loops).

In developing the different options listed in this master plan update, both distribution system voltages have been considered. A total of four options have been developed and are listed below.

Option 1

Keep entire campus distribution system at 13.8 kV. This option involves two phases as follows.

Phase A

CPS will install a new/separate 13.8 kV service to the UTSA campus. This new separate service will include the following CPS provided equipment:

• New 40 MVA, 138 kV-13.8 kV transformer and 13.8 kV distribution switchgear lineup will be installed in the open bay next to the existing 100 MVA, 138 kV-35 kV transformer inside the CPS substation.
• Two new underground feeders from the new CPS 13.8 kV switchgear will be installed to a new UTSA 13.8 kV distribution switchgear lineup to be located next to the existing UTSA 13.8 kV distribution switchgear lineup.

UTSA will provide the following equipment for connection and distribution of this new CPS 13.8 kV service:

• New 13.8 kV distribution switchgear lineup with an ultimate configuration of 20 breakers for a total of 10 new loops. Available funding will determine how this new 13.8 kV switchgear is installed. This will increase the system capacity by 40 MVA.

CPS will also modify the existing 13.8 kV service as follows:

• Upgrade the two existing feeders to the existing UTSA 13.8 kV switchgear lineup from 800 amps to 1200 amp.

This will increase the system capacity by 5 MVA, which will result in a total Phase A system capacity increase of (40 + 5) 45 MVA.

Phase B

CPS will modify and increase the capacity of the existing 13.8 kV service to the UTSA campus. These modifications will include the following CPS-provided equipment:

• CPS will replace the existing 25 MVA, 138 kV-13.8 kV transformer feeding the existing UTSA 13.8 kV distribution switchgear lineup with a new 40 MVA, 138 kV-13.8 kV transformer to match the transformer installed in Phase A.
• CPS will replace their existing 13.8 kV distribution switchgear lineup on the secondary of the existing 25 MVA transformer with switchgear sized for the new 40 MVA transformer.
• CPS will upgrade the two existing feeders to the existing UTSA 13.8 kV switchgear lineup from 1200 amp to 2000 amp.

UTSA will provide the following equipment to upgrade their system to accommodate the increased capacity from the CPS system:

• The existing UTSA 13.8 kV distribution switchgear lineup will be replaced with a lineup to match the lineup installed in Phase A.

These modifications will increase the existing system capacity from 25 MVA to 40 MVA resulting in a total Phase B system capacity increase of (40 -25) 15 MVA. The resulting total Option 1 system capacity increase is (45 + 15) = 60 MVA. See figures 16 and 17 for one line diagrams.

Option 2

Continue to feed existing buildings and loads from the existing 13.8 kV system and feed all new buildings and loads from a new 35 kV system.

CPS will install a new, separate 35 kV service to the UTSA campus. This new service will include the following CPS provided equipment:

• New 100 MVA, 138 kV-35 kV transformer and 35 kV distribution switchgear lineup in the open bay next to the existing 100 MVA, 138 kV-35 kV transformer inside the CPS substation.
• Two new underground feeders from the new CPS 35 kV switchgear will be installed to a new UTSA 35 kV distribution switchgear lineup to be located next to the existing UTSA 13.8 kV distribution switchgear lineup.

UTSA will provide the following equipment for connection and distribution of this new CPS 35 kV service:

• New 35 kV distribution switchgear lineup with an ultimate configuration of 10 breakers for a total of five new loops. Available funding will determine how this new 35 kV switchgear is installed. This will increase the system capacity by 100 MVA.

CPS will also modify the existing 13.8 kV service as follows:

• Upgrade the two existing feeders to the existing UTSA 13.8 kV switchgear lineup from 800 amps to 1200 amp.

This will increase the system capacity by 5 MVA, which will result in a total Option 2 system capacity increase of (100 + 5) 105 MVA.

Option 2A

Same as Option 2 but with both 35 kV feeds originating from the existing CPS, 35 kV service transformer.

Option 3

Provide new 35 kV service to feed the entire campus, back feed existing 13.8 kV distribution switchgear from the new 35 kV system, continue to feed existing buildings and loads from the existing 13.8 kV switchgear, and feed all new buildings and loads from a new 35 kV system.

CPS will install a new/separate 35 kV service to the UTSA campus. This new separate service will include the following CPS provided equipment:

• A new 100 MVA, 138 kV-35 kV transformer and 35 kV distribution switchgear lineup in the open bay next to the existing 100 MVA, 138 kV-35 kV transformer inside the CPS substation.
• Two new underground feeders from the new CPS 35 kV switchgear will be installed to a new UTSA 35 kV distribution switchgear lineup to be located next to the existing UTSA 13.8 kV distribution switchgear lineup.

UTSA will provide the following equipment for connection and distribution of this new CPS 35 kV service:

• A new 35 kV distribution switchgear lineup with an ultimate configuration of 12 breakers for a total of 5 new loops. Available funding will determine how this new 35 kV switchgear is installed.

This will increase system capacity by 100 MVA.

CPS will also remove the existing 13.8 kV service feeders to the existing UTSA 13.8 kV distribution switchgear. This will require UTSA to provide the following equipment for connection of the existing 13.8 kV system to the new CPS 35 kV service:

• Two new 25 MVA, 35 kV - 13.8 kV transformers and underground duct banks to connect the existing 13.8 kV switchgear lineup to the new 35 kV switchgear lineup.

This will increase the system capacity by 5 MVA, which will result in a total Option 3 system capacity increase of (100 + 5) 105 MVA. See figures 20 and 21 for one line diagrams.

Option 3A

Same as Option 3 but with both 35 kV feeds originating from the existing CPS 35 kV service transformer.

Option 4

Replace and upgrade existing 13.8 kV switchgear, feed all existing and new buildings/loads within the existing campus from the 13.8 kV system, and install a new 35 kV system to feed all new buildings/loads constructed on the new East Campus.

CPS will install a new/separate 35 kV service to the UTSA campus. This new separate service will include the following CPS provided equipment:

• A new 100 MVA, 138 kV-35 kV transformer and 35 kV distribution switchgear lineup in the open bay next to the existing 100 MVA, 138 kV-35 kV transformer inside the CPS substation.
• Two new underground feeders from the new CPS 35 kV switchgear will be installed to a new UTSA 35 kV distribution switchgear lineup to be located next to the existing UTSA 13.8 kV distribution switchgear lineup.

UTSA will provide the following equipment for connection and distribution of this new CPS 35 kV service:

• A new 35 kV distribution switchgear lineup with an ultimate configuration of 6 breakers for a total of 3 new loops.

This will increase the system capacity by 100 MVA.

CPS will modify and increase the capacity of the existing 13.8 kV service to the UTSA campus. These modifications will include the following CPS provided equipment:

• CPS will replace the existing 25 MVA, 138 kV-13.8 kV transformer feeding the existing UTSA 13.8 kV distribution switchgear lineup with a new 40 MVA, 138 kV-13.8 kV transformer.
• CPS will replace their existing 13.8 kV distribution switchgear lineup on the secondary of the existing 25 MVA transformer with switchgear sized for the new 40 MVA transformer.
• CPS will upgrade the two existing feeders to the existing UTSA 13.8 kV switchgear lineup from 1200 amp to 2000 amp.

UTSA will provide the following equipment to upgrade their system to accommodate the increased capacity from the CPS system.

• The existing UTSA 13.8 kV distribution switchgear lineup will be replaced with a new 13.8 kV distribution switchgear lineup with an ultimate configuration of 24 breakers for a total of 12 loops.

Available funding will determine how this new 13.8 kV switchgear is installed.

These modifications will increase the existing system capacity from 25 MVA to 40 MVA resulting in a total Option 4 system capacity increase of (100 + 15) 115 MVA.

Option 4A

Same as Option 4 but with both 35 kV feeds originating from the existing CPS 35 kV service transformer.

Although each option has advantages and disadvantages, the design team recommends Option 1 as the best short- and long-term solution for electrical distribution.

New Duct Bank Configuration

Regardless of the system voltage used, it is recommended that all new duct banks be constructed with six-inch conduit and 750 kcmil cables to maximize the amount of load that can be connected to each new loop. Utilizing 750-kcmil cables will result in a capacity of 300 amps for each loop, which will allow the following load to be connected to each loop:

13.8 kV: 7,170 kVA
35 kV: 18,186 kVA

The rating of each circuit in the duct bank must be calculated based on the actual configuration of the duct bank installed. Calculations should be based on the ultimate configuration of the duct bank and not on the initial cabling installed.

Present configurations of duct banks include (9 to 12) four-inch conduits for communications located below the power conduits. All new duct banks should include communication ducts below the power ducts. Size and quantity should be verified with UTSA personnel.

New Duct Bank Location

Figure 25 shows the existing campus duct bank layout and the proposed new duct bank layout. Two new major duct banks are proposed as shown in the figure. The first duct bank will feed all of the new loads located in the center core of the existing campus and will contain new loops (7 through 11). The second duct bank will feed all of the new loads located on the new east campus and will contain new loops (13 through 20). The existing duct bank feeding the west campus currently has spare ducts for installing a new loop 12 to provide power to new facilities located on the west campus. The West Campus duct bank system will be extended as shown to provide power for the new facilities located on the West Campus. To feed new the new parking garage on the north side of campus, the existing duct bank system is proposed to be extended from manhole #9 as shown.

Loop Summary

The following figures show the proposed loop connections and associated loop loading for all new proposed buildings and facilities.

Figure 24: Summary of New Electrical Loads (Expansions and Additions on Existing Campus Connected to Existing Loops)

Figure 25: Campus plan showing existing and new duct banks

Figure 26: Modified Existing Electrical Distribution System Loading (Substation and Loops) With Additional Loads Per 2004 Master Plan Update

Figure 27: Summary of New Electrical Loads (Expansions and Additions on Existing Campus Connected to New Loops)

Figure 28: New Existing Electrical Distribution System Loading (New Substation and Loops) Existing Campus Only

Figure 29: Summary of New Electrical Loads (East Campus)

Figure 30: New Existing Electrical Distribution System Loading (New Substation and Loops) East Campus Only

In all four options, it is recommended that the existing UTSA main distribution switchgear feeders be upgraded to carry 25 MVA of load. This will allow maximum utilization of the existing UTSA distribution switchgear and loops.

Figure 25 shows the connection of all expansions to existing buildings to the loop that is currently feeding the building. It is assumed that the switchgear in each building that is being expanded has adequate space and capacity to feed the small expansions to each building. Figure 25 also shows the connection of two small parking garages (2 and 26) and the Chaparral Village expansion (52) to existing loops on campus. Addition of these loads to the existing loops will utilize the existing system to its maximum capacity. (See Figure 26 for resulting system and loop loading).

Figure 27 shows proposed loops for all new buildings and facilities to be built on the existing campus. A total of six loops to provide power for these loads is recommended. (See Figure 28 for system and loop loading).

Figure 29 shows proposed loops for all new buildings and facilities to be built on the east campus. A total of eight loops to provide power for these loads is recommended. See Figure 30 for system and loop loading)

Communications

Existing communications ducts should be extended to provide service for buildings built on the existing campus. Communication service for the east campus will be provided from a new duct bank system currently under construction. This new duct bank system consists of manholes 13C through 20C as shown on Figure 25.

Metering

The only metering currently installed on the UTSA campus consists of CPS totalizing metering at the UTSA main substation and various KW meters installed on the 480-volt switchgear throughout the campus. These various meters have been used to approximate the actual loading of the main substation and the existing six distribution loops feeding the campus. It is recommended that new metering be installed on each main and feeder breaker in the proposed new substation switchgear. If funding becomes available it is also recommended that metering of the existing UTSA substation mains and feeder breakers be installed. With metering installed on all mains and feeder loop breakers, the actual peak load of each substation and feeder can be obtained. This information would allow the system to be utilized to its full capacity. This more accurate metering data would allow UTSA personnel to balance the load on each loop and give them a better understanding of how and what loads could be connected to back up loops in response to system and feeder abnormalities.