Devices 181 and 159 I&T, overfrequency and instantaneous and time overvoltage relays, respectively, are provided to protect the loads on the 25-kilovolt switchyard, including the 69-kilovolt switchyard, the 25-kilovolt lines, the grounding transformer KV2A, the station-service system, and the microwave station, from damage due to overfrequency or overvoltage resulting from load rejection on the 345- and 230-kilovolt lines. These relays are energized from the 25-kilovolt main bus potential transformers and operate to trip without initiating reclosing the 25-kilovolt breakers. The overvoltage relay 159 I&T is set to operate at a lower voltage than the generator overvoltage relay, device 59 1&T. (g) 345- and 230-Kilovolt West Buses and Unit Transformers.-Generator 1-2 unit transformer K1A is protected by a set of percentage-type differential relays. The protected zone includes from the 13.8-kilovolt generator side of the unit breakers 124 and 224, the unit transformer K1A, to the line side of breaker 1196, and to the unit transformer side of breaker 1292. Three winding differential relays are used to minimize tripping for system faults flowing through the switchyard. Generator 3-4 unit transformer K3A is protected by a set of percentage-type differential relays. The protected zone includes from the 13.8-kilovolt generator side of the unit breakers 324 and 424, the unit transformer K3A, to the line side of breaker 3396, and to the unit transformer side of breaker 3492. Generator 5-6 unit transformer K5A is protected by a set of percentage-type differential relays. The protected zone includes from the 13.8-kilovolt generator side of the unit breakers 524 and 624, the unit transformer K5A, the 345-kilovolt west bus, to the line side of breakers 1092 and 3292. Generator 7-8 unit transformer K7A is protected by a set of percentage-type differential relays. The protected zone includes from the 13.8-kilovolt generator side of the unit breakers 724 and 824, the unit transformer K7A, the 230-kilovolt west bus, to the line side of breakers 7386 and 8186. (h) 345- and 230-Kilovolt East Buses and Main Switchyard Transformer Bank KU5A.-The main switchyard transformer KU5A is protected by a set of percentage-type differential relays. One zone of protection includes from the unit transformer side of the 345-kilovolt breakers 1292 and 3492, the 345-kilovolt east bus, and from the line side of the 230-kilovolt breakers 7482 and 8282, the 230-kilovolt east bus, to the tertiary winding of the main switchyard transformer KU5A. (i) 25-Kilovolt Main Bus. --The 25-kilovolt main bus is protected by a set of percentage-type differential relays and a set of overcurrent relays. The zone of protection includes from the 25-kilovolt line or transfer bus side of breakers 4136, 4232, and 4632, across the regulator KV1A and reactor KV1B, to the tertiary winding of the main switchyard transformer KU5A. Although the regulator KV1A is included in the above protected zone, more adequate protection of the Closing of a trouble contact will light the red group lamp, light an annunciator window, and sound an alarm. The switchyard annunciators are connected to sound one bell in the switchyard section of the control board, while the generator and unit transformers and station-service annunciators will sound another bell in the generator section of the control board. The generator and unit transformer annunciator also sounds two horns located in the governor gallery and two horns on the generator floor (one at each end). The switchyard annunciator bell can be silenced and the red group lamp reset by pushing the alarm reset pushbutton. The generator and unit transformer annunciator bell and horns can be silenced and the red group lamp reset by pushing the alarm reset pushbuttons located in the control room or the governor gallery. The station-service annunciator uses the generator annunciator bell for alarm. The alarm can be silenced and the red group lamp reset by pushing the alarm reset pushbutton. Release of the alarm reset pushbuttons will not cause the audible alarm to sound or the red group lamp to light; however, there will be an audible alarm and the red group lamp will light when an additional trouble contact closes. The annunciator windows can be reset by pushing the lamp reset pushbuttons; however, if a trouble contact remains closed the associated annunciator window will remain lighted when the pushbutton is released. Each annunciator can be tested by pushing the test pushbutton. With this test, all annunciator windows of the annunciator group being tested should light. All related pushbuttons are located in the respective panels in which the annunciators are mounted. The annunciator systems are designed so that there will not be an annunciation under normal operating conditions. 95. GROUNDING SYSTEM. The grounding system consists of a ground mat under the powerhouse foundation connected to a loop under the dam consisting of two 500,000-circular-mil conductors running parallel approximately 160 feet apart and connected to a ground mat in the switchyard. The powerplant and switchyard ground mats are connected by two 500-circular-mil cables running through the control and power cable tunnel located between the powerplant and the switchyard. The grounding system was designed to provide a ground resistance of 1 ohm or lower. Actual powerplant ground resistance as measured in the field was 0.05 ohms. The exposed surfaces of all electrical equipment and practically all exposed metal objects are grounded. The risers (500,000 circular mils in area) are arranged two in parallel in a multiple riser system around the perimeter of the powerplant to be capable of withstanding the maximum sustained short-circuit current for at least 10 seconds. The ground mat at the transformers is designed for an 18,000-ampere line-to-ground fault. Fault currents on the low-voltage side of the main power transformer and generator switchgear which are calculated to be approximately 100,000 amperes are confined within the powerplant and do not enter the ground mat; accordingly the ground mat and risers are not designed for this magnitude of current as the current is confined to the isolated phase bus. 96. LOAD AND FREQUENCY CONTROL EQUIPMENT. The load and frequency control equipment is used to provide remote control of the output of the generators from the Montrose Power Operations Center located south of Montrose, Colo. The desired megawatt output for each unit is held within the setting of the high and low limits as set by the Montrose dispatcher. The limit settings are compared with the actual unit generation. The difference between "desired" and "actual" unit generation develops the megawatt requirement for each unit, or the unit control error. This is then used by a computer located at the Montrose Power Operations Center to develop raise-lower impulses which will bring the actual unit generation into balance with the desired unit generation. The impulses developed by the computer provide a mandatory raise-lower control signal to the generator. The raise-lower impulses are transmitted to the powerplant by Government microwave equipment. A unit controller turret has been provided at the powerplant. The unit controller turret is located on the operator's desk in the control room and provides manual "On-Off" load and frequency control of each unit. Remote control of the unit controller turret from the Montrose Power Operations Center has not been provided. The unit controller turret has the following control and indication features: (1) Lighted pushbuttons for "On-Off" control of each unit. The "On" pushbutton lights red when the unit is on load and frequency control and the "Off" pushbutton lights green when the unit is off load and frequency control. In addition "On-Off" control indication for each unit has been provided at the Montrose Power Operations Center. (2) Microwave signal failure white lamps indication for each unit. (3) A short time duration audible alarm. Unit load and frequency control for the individual units will be automatically tripped off and an audible alarm sounded for the following: A long-time pulse duration for raise or lower impulses to prevent misoperation of the generator due to faulty equipment or during extended periods of high noise level on the microwave channel Microwave channel signal failure Whenever any unit is taken off load and frequency control, the unit must be manually returned to load and frequency control at the powerplant. 97. SEQUENTIAL OPERATIONS RECORDER. A 400-point sequential operations recorder has been provided to minimize the logging by the operator. This equipment logs, in the proper sequence, the opening and closing of the generator switchyard, and station-service annunciator trouble contacts, and also the closing and tripping of the generator and switchyard power circuit breakers. The date and time at which any of the above events occur are also logged. The sequential operations recorder equipment is located in the control room and consists of an equipment board designated CCF, and a printer. The equipment board contains the scanner and input gate section, the timing section, the sequential memory, and the decoder and printer drive section. H. AUXILIARY ELECTRICAL EQUIPMENT AND INSTALLATION 98. ALTERNATING CURRENT STATION SERVICE SUPPLY SYSTEM. (a) General. -The alternating-current station-service supply system is supplied from two 3-phase, 3,750/4,687-kv.-a., 13,800 to 4,160-volt transformers. One transformer is connected to generators 3-4 common bus and the other transformer is connected to generators 5-6 common bus. A third emergency supply from the 25-kilovolt switchyard is available through a 3-phase, 3,750/4,687-kv.-a., 25,000 to 4,160-volt transformer. The two supplies from the two generator buses are normally used to carry the station-service loads with the switchyard feeder acting as a standby. Any one of these supplies will carry the entire station-service load, except that under some conditions nonessential loads may have to be curtailed (heating, lighting, machine shop, etc.). The 4,160-volt induction-type voltage regulators have plus and minus 10 percent voltage regulation capability and are used to regulate the generator supply sources to the station-service system. The entire station-service system is regulated, since the generator voltage varies approximately 20 percent from light to heavy load. The station-service supply system consists of a 4,160-volt, double-ended intermediate voltage switchgear; three 460-volt, double-ended secondary unit substations; five 208Y/120-volt single-ended lighting unit substations; and various quantities of power boards and power distribution panelboards. |