CHAPTER 08 final Rev 8.docx

CHAPTER 8 -- TABLE OF CONTENTS

List of Tables

List of Figures

Chapter 8 – Record of Revisions

8 Electrical Power Systems

8.1 Normal Electrical Power Systems

8.1.1 Design Basis

These systems are designed to supply all of the electrical power necessary to operate the NBSR during both normal and shutdown conditions. This includes all of the experiments, offices and other support spaces associated with the reactor. Electrical power is supplied to the NBSR by three independent, underground, 13.8 kV primary feeders. Each primary feeder is connected to a separate 13.8 kV/480V distribution transformer. The secondary of each transformer provides power to one of three specific sections of the main 480 V switchgear buss. A substation independent of the three feeders provides power to the equipment in the Secondary Coolant Pump Building (SCPB) and the cooling tower cell equipment. Other major components of the electrical distribution system include two independent electrical generators, battery power, two un-interruptible power supplies (UPS), two battery chargers, transformers, and associated distribution equipment.

The electrical generators are a source of emergency AC power and are independent of the NIST electrical distribution system, because a failure of the NIST system does not affect the reliability of the local generator as a power source. Battery power is provided by the station battery, described elsewhere in this chapter. The availability of multiple emergency power sources provides flexibility for operation of the facility in normal or emergency circumstances, but reactor safety requires only one operable backup power supply to prevent consequences from a single failure exceeding those from an accident analyzed in Chapter 13. Therefore, while equipment and power sources have redundancy, redundancy is neither present nor necessary in the normal configuration of the facility distribution system.

As described below, the electrical distribution system consists of three major sub-systems: the Facility (or Building Services) Distribution System, the Reactor Distribution System and the Emergency Distribution System.

8.1.2 System Description

8.1.2.1 High Voltage Input

The three 13.8 kV feeders supply the NBSR Electrical Distribution System from the NIST substation located near Gate D. FA-1, FB-1 and FC-1 enter Building 235 in the basement of the A-Wing. Load interrupter switchgear for each feeder serves as an isolation device. The supply voltage through the load interrupter switchgear is stepped down by a transformer to 480/277 V. A network protector and network disconnect switch are mounted on the load side of each transformer. Each network protector is a safety and isolation device, preventing reverse power flow through the associated transformer. The 480/277 V input switchgear supplies the various Motor Control Centers (MCCs), power panels and other loads through individual feeder breakers. The transformers, network protectors, and 480/277 V switchgear are located in the basement of the A-Wing.

8.1.2.1.1 Input Switchgear Busing Arrangement

The 480/277 V input switchgear is arranged in a linear configuration and is divided into three sections, designated Switchgear Bus FA-1, FB-1 and FC-1. While each section can be separately powered from its associated input transformer, the three sections are normally cross-connected via electrically operated tie-breakers in a closed “delta” configuration. This results in the total load being evenly split between the three input feeds. This arrangement also provides the capability to supply all of the loads needed to maintain the reactor facility in an operating condition from two of the three input feeds.

A simplified diagram of the High Voltage Input Switchgear bussing arrangement is shown in Figure 8.1.

8.1.2.1.2 Loads Supplied from Each Bus

Switchgear Busses FA-1and FB-1 of the 480/277 V input switchgear supply the loads associated with the reactor, experiments, and offices and support spaces located in the A-wing, B-wing, and C-wing. Important equipment necessary for both normal operation and shutdown of the reactor is duplicated. Equipment supplied by the Reactor MCC A-3 and the D-Wing MCC A-7 fed from FA-1 are duplicated by equipment supplied by the Reactor MCC B-4 and the D-Wing MCC B-8 fed from FB-1. Table 8.1A lists all of the loads on Switchgear Bus FA-1 while Table 8.1B lists all of the loads on Switchgear Bus FB-1.

Switchgear Bus FC-1 supplies the loads associated with the K and E-Wing offices and support spaces, the Guide Hall, the Compressor Building, and the South End Addition offices. It also supplies the Experimental UPS located in Room E-02 of the E-Wing basement. This UPS supplies all of the regulated power used by the experiments in both the Confinement Building and the Guide Hall. Table 8.1C lists all of the loads on Switchgear Bus FC-1.

All of the equipment (input transformers, network protectors and disconnect switches, input switchgear and associated busses) located in the high voltage cage was replaced in the fall of 2001. The new equipment met the requirements of the ANSI, NEMA and UL codes applicable at the time of manufacture and the requirements of the National Electrical Code (NEC) and local building codes applicable at the time of installation.

8.1.2.2 Facility Distribution System

The Facility Distribution System provides power to the offices and support spaces in the A-, B- and E-wings of the building as well as to the Guide Hall. Tables 8.1, 8.2A, and 8.2B list the loads. There are two motor control centers associated with this distribution system: MCCA-1 is located in the A-wing basement and MCCA-2 is located in B-200.

8.1.2.3 Reactor and D-Wing Distribution System

All of the electrical loads associated with the normal operation of the reactor and for emergencies are powered from two parallel sets of Motor Control Centers. Reactor MCCA-3 feeds Emergency Power MCCA-5. MCCB-4 feeds Emergency Power MCCB-6. Equipment necessary for the normal operation of the reactor is split between three sets of six Motor Control Centers (MCCA-3, A-5, and A-7), and (MCC B-4, B-6, and B-8). Equipment required for a shutdown reactor is split between Motor Control Centers MCC A-5 and MCC B-6. The Emergency Power MCCs are discussed in Section 8.1.2.4. MCCA-3 and MCCB-4 are located on the Basement level of the Confinement Building; MCC A-5 and MCC B-6 are located in Room C-01; and, MCC A-7 and MCC B-8 are located in D-200.

MCC A-3 MCC B-4 loads include: Main D2O Circulation Pumps and supply and exhaust fans. Miscellaneous Power Panel A-3, located on MCC A-3, supplies various minor electrical loads. MCC A-5 and B-6 loads include auxiliary D2O cooling system equipment, helium system equipment, and thermal shield cooling water system equipment.

MCC A-7 and B-8 power auxiliary secondary cooling pumps for cooling auxiliary D2O cooling system loads.

Off-site power provides AC power through the MAIN UPS to Critical Power Panel CP-1, which in turn supplies CP-2 and CP-3. The critical power panels supply power to the Reactor Control and Safety Systems. Normally, the STANDBY UPS is running and its output is directed to the main UPS reserve input.

Tables 8.4A, 8.4B and 8.4C list the loads on Critical Power Panels CP-1, CP-2 and CP-3, respectively.

Off-site power also provides AC power to maintain the lead-acid battery voltage and power to the DC loads on the 125 VDC Panel. Two battery chargers, one from MCCA-5 and one from MCCB-6, are load sharing devices and convert commercial AC power to DC power to provide a floating, or trickle, charge to the 125 VDC battery, and separately energize the 125 VDC panel. The battery chargers are designed to work with the battery, which prevents a large temporary voltage drop from occurring on the 125 VDC panel if a large DC load is energized.

The 125 VDC Distribution Panel supplies power to two other DC panels: MCC DC (Table 8.2I) which supplies Panel DCP-2; and Panel DCP-1. Tables 8.3A, 8.3B, and 8.3C list the loads on the 125 VDC Distribution Panel, DCP-1, and DCP-2, respectively. A simplified diagram of the Reactor Distribution System bussing arrangement is shown in Figure 8-2.

8.1.2.4 Emergency Distribution System

The two Emergency Power MCCs are tied together through a normally closed tie-breaker. The categorization of these motor control centers as emergency MCC is due to a single load, namely EF-5 on one MCC and EF-6 on the other MCC; both fan blowers also can be powered from the DC panel.

The normal distribution lineup has CB#1 closed and CB#4 open in stand-by. In this configuration, switchgear bus FA-1 supplies both MCC A-5 and B-6 via Reactor MCC A-3. Since EF-5 and EF-6 are considered to be necessary for an emergency response, provisions are made to automatically provide emergency power to the two loads. An under-voltage device monitors the voltage on MCC A-5 and through the closed tie breaker, MCC B-6. If this device senses a loss of voltage, it automatically trips open CB#1 and closes CB#4. This transfers the feed for MCC A-5 and MCC B-6 to Switchgear Bus FB-1 via Reactor MCC B-4.

If power is not restored to MCC A-5 and MCC B-6, this same under-voltage device trips open CB#4 and initiates the starting sequence of the emergency generators. Once a generator achieves the proper electrical parameters, its associated Feeder Breaker, CB#2 for Emergency Generator A or CB#3 for Emergency Generator B, closes to restore power to MCC A-5 and MCC B-6. The generators are discussed in Section 8.2.

Table 8.2E lists the loads supplied by MCC A-5 while Table 8.2F lists the loads supplied by MCC B-6.

The sequence of power transfers involving the UPS to maintain power without interruption to CP-1, starting with a normal reactor electrical distribution configuration, is as follows:

1. If AC power from MCC B-6 is lost to the input of the main UPS, then the battery bank for the main UPS would provide AC power to CP-1.

2. After the main UPS battery bank is depleted, the standby UPS provides AC power to CP-1 through the reserve input of the main UPS. If AC power is restored to MCC B-6 and the main UPS battery bank is not depleted and the main UPS has not tripped on a fault, then the main UPS would return to service automatically.

3. If AC power from MCC A-5 is lost to the standby UPS, then the battery bank for the standby bank would provide AC power to the main UPS reserve input. If AC power is restored to MCC A-5 and the main UPS battery bank is not depleted and the standby UPS has not tripped on a fault, then the standby UPS would return to service automatically and provide AC power to the reserve input of the main UPS.

4. After the standby UPS battery bank is depleted and after AC power is restored to MCC A-5, unfiltered AC power will be directed through the standby UPS to the reserve input of the main UPS.

If AC power is lost to the input of both battery chargers, the trickle charge to the sixty cell lead acid battery bank would cease and that battery bank would assume the loads on the 125 VDC panel for at least 4 hours. After AC power is restored, the primary battery charger resumes charging the battery bank.

CP-3 supplies power to Emergency Lighting Panel X-1 and CP-2 supplies power to Emergency Lighting Panel X-2. Transfer switches are no longer needed as power is supplied by the building UPS.

A simplified diagram of the Emergency Distribution System bussing arrangement is shown in Figure 8-2.

8.1.3 Electrical Power Capability

The normal electrical demand varies over the course of the year, with the summer months yielding the highest loads. The electrical loads for normal full power operation during the summer are approximately 2,700 amps at 480 VAC and 60 Hz. This equates to 2,250 kW (2,700 amps x 480 volts x 31/2) and 2,812 kVA at a 0.8 power factor (pf). The electrical loads for normal shutdown operations are approximately 1,700 amps at 480 volts AC and 60 Hz. This equates to 1,413 kW and 1,767 kVA at a 0.8 pf. The three input feeds that supply the facility are each capable of supplying 2,000 kVA (6,000 kVA total). While two input feeds are needed to support full power operation, only one input feed is needed to support the facility when in a normal shutdown condition.

8.1.4 Codes and Standards

The NBSR facility has undergone several major additions since it was first built in 1966. The distribution system in the A- and B-wings and in the Confinement Building conformed to the requirements of the 1965 Edition of the National Electrical Code (NEC). All additions/modifications to the distribution system were installed in accordance with the code requirements applicable at the time of the addition/modification.

8.1.5 Lightning Protection

The facility is furnished with a complete lightning protection system consisting of air terminals connected by copper conductors to the main grounding system. The air terminals are located at the top of the stack and at other high points around the building. The terminals are electrically connected together by means of bare copper cables that form a closed loop. Down conductors connect the closed loop to the copper conductors of the main grounding system. A separate lightning protection system is installed on the Cooling Tower.

8.1.6 Grounding

Two separate grounding systems are provided. All of the electrical equipment, switchgear, motor control centers, panel boards and motors, in addition to the building steel, are connected to the main grounding loop. The Reactor Console and Control Boards are connected to a separate insulated copper grounding system with its own separate ground rods. This grounding system is not looped and is insulated from the main grounding system.

8.2 Emergency Electrical Power Sources

8.2.1 Design Basis

Emergency electrical power is designed to provide power to the nuclear instruments and the emergency exhaust fans should a complete loss of off-site power occur. One of the two emergency generators is capable of supplying power to all necessary emergency equipment. Battery power is also capable of independently supplying the vital loads for a minimum of four hours. By requiring the operability of at least one emergency generator during reactor operation and requiring the availability of battery power during reactor operation, power sources will always be available for an emergency response.

8.2.2 System Description

This system consists of:

1. Two 150 kW diesel powered AC generators and associated support equipment. The four circuit breakers described in section 8.1.2.4 provide adequate automation to ensure the proper transfer of power supply from normal electrical power supply to diesel generator electrical power supply in case of an off-site electrical outage. The diesel generators share a common Diesel Fuel Oil Day Tank with a design capacity of 75 gallons and a Diesel Fuel Oil Supply Tank with a design capacity of 2,000 gallons. At full load the diesel consumes approximately12 gallons/hour of diesel fuel.

2. The station battery is composed of three battery banks, two of which would be in service in a loss of AC power scenario. One bank is made up of sixty, two volt, lead-acid type battery cells to produce a single output of 125 VDC with a capacity of 880 amp-hours. The other two banks comprise the emergency AC backup capability of the two UPS. One bank would be in-service, and the other bank would be in standby. Each bank is made up of valve-regulated lead-acid (VRLA) battery cells.

In case of a total loss of off-site power and emergency generator AC power, vital equipment would remain energized for at least four hours: EF-5 and EF-6 DC powered fans, controls, and associated valves; and nuclear instrumentation. Non-vital equipment on the critical power panels and the DC bus would remain powered for at least four hours, unless de-energized with individual controls, e.g. a local breaker. That equipment includes process instrumentation, AC and DC valve control power, effluent monitors, other critical power panel loads (see Chapter 7), and the reactor shim arm control.

The two diesel generators are located on the B2 level. A shared control panel is equipped with a PRIMARY/SECONDARY selector switch for each generator. Upon a loss of power to the emergency motor control center (MCC-A5 and MCC-B6) 480-volt bus, a control circuit will initiate the cranking cycle for the diesel in PRIMARY. This cycle is 5 seconds crank and 8 seconds pause.

After the third unsuccessful attempt the circuit will actuate the DIESEL "A" (B) FAILURE TO START annunciator in the Control Room. At that time it will call for the diesel in SECONDARY to start. After the diesel driven generator is ready to assume the MCC loads, the diesel output will automatically close the associated circuit breaker on the emergency motor control center to power the MCC.

Table 8.1A: Load List Switchgear Bus FA-1

Table 8.1B: Load List Switchgear Bus FB-1

Table 8.1C: Load List Switchgear Bus FC-1

Table 8.2A: Load List MCC A-1, Facility Service

Table 8.2B: Load List MCC A-2, Facility Service

Table 8.2C: Load List MCC A-3, Reactor

Table 8.2D: Load List MCC B-4, Reactor

Table 8.2E: Load List MCC A-5, Emergency Power

Battery Charger 2

Table 8.2F: Load List MCC B-6, Emergency Power

Table 8.2G: Load List MCC DC

Table 8.3A: Load List DC Distribution Panel See Chapter 7 Table 8.3B: Load List DC Power Panel 1 (DCP-1) See Chapter 7 Table 8.3C: Load List DC Power Panel 2 (DCP-2) See Chapter 7 Table 8.4A: Load List Critical Power Panel 1 (CP-1) See Chapter 7 Table 8.4B: Load List Critical Power Panel 2 (CP-2) See Chapter 7 Table 8.4C: Load List Critical Power Panel 3 (CP-3) See Chapter 7

Table 8.4D: Load List Power Panel P-9

8-18

Figure 8.1: Simplified Diagram – High Voltage Input Switchgear and Bussing Arrangement

Figure 8.2: Simplified One-Line Diagram for the Reactor and Emergency Power Distribution System (Normal/Preferred Lineup, Essential, and Vital Loads) image1.jpeg image2.jpeg