SSE-N NEGATIVE FIELD FORCING SHUNT STATIC EXCITER/REGULATOR SYSTEM Control Chassis 6 SCR Power Chassis APPLICATION The SSE-N Negative Field Forcing Exciter/Regulator is used for both new and old installations (replacing the rotating brush-type exciter) to apply a variable dc voltage into the field of the synchronous generator. The SSE-N Shunt Static Exciter/Regulator offers the best response to voltage control. During system disturbances, the SSE-N can apply both positive and negative voltage into the field of the synchronous machine. Having this ability speeds generator voltage recovery time and stabilizes the system voltage faster. Negative field forcing is particularly important in applications (i.e. hydroturbine generator) to reduce generator overvoltage that can occur due to a prime mover overspeed at load rejection. The SSE-N is widely adaptable to various system conditions and machine characteristics to provide optimum unit performance. FEATURES and APPLICATIONS this page DESIGN FEATURES Pages 2 and 3 FEATURES 6 SCR power rectifier bridge High operating efficiency Optional redundant rectifier bridge & crowbar Redundant fans included on forced air cooled bridges Crowbar field discharge Soft start generator voltage build-up Automatic voltage regulator and backup manual voltage control Voltage regulation better than ±½% High initial response per IEEE 421.2 Voltage limited Volts/Hertz compensation for field and stator overheating protection Selectable single and three phase voltage sensing Paralleling provisions for reactive var sharing control Plug-in circuit boards Wide selection of accessories adaptable to specific system requirements Modular design Field voltages up to 375 Vdc Field currents up to 3600A SPECIFICATIONS Pages 4 and 5 SELECTION TABLE Page 5 ACCESSORIES AND ORDERING INFORMATION Pages 6 and 7 INTERCONNECTION Page 8 P. O. BOX 269 HIGHLAND, ILLINOIS, U.S.A. 62249 PHONE 618-654-2341 FAX 618-654-2351 TBY-1 9-93
DESCRIPTION The SSE-N is a shunt static exciter designed to work directly into the exciter field or main field of a synchronous generator. The SSE-N provides both positive and negative voltage for field forcing to optimize generator voltage recovery time. The SSE-N is compatible with NEMA field voltage ratings up to 375 Vdc. Continuous current ratings are available up to 3,600 Amperes. The SSE-N static exciter regulator consists of three basic components: a control chassis, power rectifier chassis and power potential transformer. The following is a description of each component and associated features utilized in the excitation system. CONTROL CHASSIS: The control chassis consists of plug-in circuit boards that provide easy user access. Screw-type terminal blocks are provided for external connections. The control chassis includes the following features: Power Supply The power supply for the SSE-N is designed for dual power input, ac and dc. It ensures continuity of power during interruption of a single source. When ac supply voltage is available, there is no load on the dc power source. Voltage Buildup/Field Flash Circuit When static exciter power is derived from the generator bus, an external dc power source, contactors and resistors are used to build generator voltage. Field flashing is de-energized when approximately 50% generator output voltage is sensed. For the field protection, should the generator not build voltage within 20 seconds, the dc battery source will be automatically removed and the excitation system will be tripped off (see Excitation Accessories, page 6). When the static exciter is externally powered, a current input from the PPT is used to detect field current buildup. Soft-Start Voltage Build-up The voltage regulator and manual voltage control are designed to provide soft-start generator voltage buildup. Soft-start eliminates voltage overshoot as the generator builds terminal voltage to the desired setpoint. An adjustment is provided for optimizing the excitation system to the generator characteristics. DESIGN FEATURES Voltage Regulator A 1% voltage regulator is provided to maintain fast and accurate voltage regulation at the generator output. Voltage droop is provided for reactive var sharing between generators and the utility bus. The voltage regulator is also equipped with an adjustable stability control to vary the generator voltage response for best system performance. Underfrequency Compensation A voltage limited Volts/Hertz circuit is standard. It is used to reduce generator voltage as a function of prime mover speed. A user-selectable 1 P.U. or 2 P.U. Volts/Hertz circuit is available to prevent generator field and stator heating caused by low prime mover speed. An LED is provided for indication during underfrequency operation. Null Meter Output Signal for Bumpless Transfer A signal is provided for external monitoring between the automatic voltage regulator and manual voltage control. A zero reading output signal at the null meter indicates a balance between the automatic voltage regulator and manual voltage control setpoints. Manual Voltage Control Standby manual voltage control is provided for an alternate control to the automatic voltage regulator. Manual provides for reliable backup to the automatic voltage regulator. 2
DESIGN FEATURES, continued POWER RECTIFIER BRIDGE CHASSIS: The power rectifier chassis consists of plug-in circuit boards that provide easy disconnect for the user. Bolton terminals are provided for power connections. The rectifier chassis includes the following features: *Three phase full-converter bridge using 6 SCR Power SCR Power SCRs are used to convert ac to dc for controlling the excitation into the field of the exciter or generator. A two quadrant controllable power rectifier bridge is provided. It can produce positive, as well as negative, output voltage into the field. Parallel 6-SCR bridges are available in current ranges up to 3,600A and compatible with NEMA field voltage ratings up to 375 Vdc and forcing voltages up to 540 Vdc. All power bridges are fuse protected for field short circuit or extended field overload. Crowbar Circuit 6 SCR bridges with current ratings above 36 Amperes have a crowbar circuit to quickly dissipate the field energy. The crowbar consists of two power SCRs (connected in antiparallel) with a series discharge resistor that is connected across the generator field. A polarity sensitive voltage detector circuit senses voltage induced at the generator field and triggers the power SCR of correct polarity to discharge the field energy during abnormal operating conditions. The crowbar provides excellent protection for transients induced during pole slip or generator short circuit. 6 SCR bridges, 36 Amperes and below, are supplied with a thyrite for field protection. Cooling 6 SCR bridges rated 36 Amperes and below are convection cooled. Rectifier bridges rated above 36 Amperes are forced air cooled with redundant fans. The primary fan is user selectable. Power Semiconductor Redundancy Where necessary, power semiconductor redundancy can be provided to maintain 100% power to the field in the event of a primary bridge failure. The redundant bridge includes redundant crowbar circuits for maximum reliability. *Alarms The following user alarms are provided for annunciation: A. Power semiconductor failure B. Fail to build generator voltage The following alarms are provided on systems greater than 36 Amperes: A. Bridge high temperature B. Crowbar trip C. Backup fan on D. Loss of Pulse (redundant rectifier system) POWER POTENTIAL TRANSFORMER: A power potential transformer is provided to step down generator voltage or bus supply voltage to levels required by the power rectifier bridge. Power transformers are all copper wound, open coil core construction with varnish impregnation with standard and optional BIL levels as shown in table 1. Primary 208-480 VAC 2400-4800 6600-7500 10,500-15,500 AC Supply Voltage 600 VAC VAC VAC VAC Transformer Standard 10KV 25 KV 35Kv 50Kv BIL Ratings Optional 25 KV 60KV 75 Kv 95KV and 110KV Table 1 - Power Potential Transformer Supply Voltages and BIL Ratings 3
SPECIFICATIONS Voltage Regulator Underfrequency Compensation Parameters: See Figure 1, adjustable frequency roll-off for 50 and 60 Hz systems. Field selectable slope: 1.0 pu V/Hz, 2.0 pu V/Hz Manual Voltage Control Range: 25% to 120% of rated field voltage. Voltage Sensing: Customer Selectable: 1Ø or 3Ø 60 Hz, 120-1 39, 208-240. 416-480, 520-600, ±10% 50 Hz, 100-1 19, 220-240, 360-415, ±10% Maximum Burden per Phase: 10VA Reactive Droop Compensation: Voltage Burden Input Droop Power Sensing Current Factor 120 25VA 3-5A 0-10% & 20% 0.8 240 25VA 3-5A 0-10% 0.8 480,600 25VA 3-5A 0-5% 0.8 Regulator Response: Less than 50 milliseconds Figure 1 - Voltage versus Frequency Roll-Off Characteristic Regulation: *Voltage regulator ±1% from no load to full load *Manual voltage control regulates 4% for 20% AC power input voltage change. Generator Soft Start Voltage Buildup: Ramp duration adjustable from 1 to 20 seconds. Auto/Manual Null Balance Signal: ±0.1 ma or ±10 Vdc. Power Supply: AC: 90 vac 132 vac. DC: 60 Vdc - 150 Vdc (250 Vdc available upon request) Voltage Buildup/Field Flash Circuit: Exciter, powered by generator: Adjustable from <10% to 100% of nominal ac voltage. Exciter externally powered: Power potential transformer current adjustable from <0.5A to >3A @ AUX CT input (CT sold separately; consult factory) Voltage Regulator Adjust Range: ±10% nominal voltage Exciter Field Forcing: Standard: Positive field forcing 144% of nominal. Negative field forcing 130% of nominal. Note: For higher field forcing, consult factory. Field Crowbar Trip: Exciter Voltage Field Voltage Discharge Level 125 VDC 375V 250 VDC 750V 375 VDC 1150V Annunciation: LED ALARM Volts/Hertz Power Semi-conductor fail (maintain) Operation Fail to build generator voltage (momentary) Systems greater than 36 Amperes Crowbar Bridge High Temperature (maintain) Failed SCR Crowbar Trip (momentary) Rectifier Bridge Backup Fan On (maintain) Enable Loss of Pulse (Redundance Rectifier System) (momentary) Temperature Coefficient: Better than 1% for a 50 C ambient temperature change Ambient Operating Temperatures: -25 C to +50 C (-13 F to +122 F) Storage Temperature: -40 C to +85 C (-40 F to +185 F) 4
SPECIFICATIONS, continued Table 2 - Shunt Exciters Selection Table 5
EXCITATION ACCESSORY OPTIONS Enclosure The excitation system can be mounted in steel enclosures designed for special environmental considerations. The cubicle is rigid and self-supporting with full length doors in the low voltage compartment. Easy access is provided to all necessary controls and terminal points to make installation easy. The cabinet design is NEMA 1, ventilated, with options for other NEMA types also available. When requested, the cabinet may also include interior lighting with switch, convenience outlet, thermostatically controlled space heaters. The power potential transformer is mounted in a separate enclosure with current limiting fuses when specified. For other special cubicle requirements, consult factory. Metering - ac and dc All meters are switchboard type with 1% accuracy and 250 dial scale. Metering may include ac voltmeter, field voltmeter, dc field ammeter, and/or Auto/Manual nullmeter for bumpless transfer from automatic voltage regulator to manual voltage control and position setpoint meters. Other special metering requirements can also be provided. AC Shutdown and Field Flash Contactors External contactors can be supplied on all SSE-N models. The ac contactor or breaker removes ac input power to the exciter to remove field excitation. The contactor or breaker is controlled from remote contacts. A field flashing contactor is used to permit positive generator voltage build-up from a battery. Minimum/Maximum Excitation Limiter The excitation limiter can be provided to perform two functions when used with the SSE-N. As a maximum excitation limiter, it senses the field current output of the SSE-N and limits the field current to prevent overheating of the field. As a minimum excitation limiter, it senses the leading var output of the generator. It limits the excitation to prevent loss of synchronization and end-iron overheating due to too little field excitation for large kw loads during parallel operation. The limiter is adjustable to the machine s specific requirements. See Figure 2. Var/Power Factor Controller This device is used for parallel operation with the utility to maintain the generator s Power Factor or reactive power at a desired level without operator action. RA-70 Microprocessor-based Reference Adjuster The RA-70 can be provided to remotely control the operation of the automatic voltage regulator, manual voltage control, or the var/pf setpoint from two or more locations. Autotracking Follower Autotracking is used to have manual voltage control automatically follow the output of the automatic voltage regulator for bumpless transfer. It requires no operator action for nulling. Protective Relays A wide variety of protective relays can be provided with the static excitation system. These include Field Ground Detection Relay, Voltage Phase Balance Relay, Underexcitation Relay with time delay, Overexcitation Relay with time delay, Loss of Sensing, Loss of Field, and Overvoltage relay. Figure 2 - Minimum/Maximum Excitation Limiter Power System Stabilizer A power system stabilizer is used with the voltage regulator to resolve power oscillations that can occur in the system. A signal of power, representative of the oscillation, is directed into the voltage regulator to reduce and suppress the power oscillation. 6
EXCITATION ACCESSORY OPTIONS, continued This list reflects some of the commonly requested accessories. The SSE-N system is a highly adaptable system, able to accommodate virtually any custom-designed control scheme. Send in your specifications for a design customized to your needs. Table 3 - Accessories Selection Chart ORDERING EXAMPLE GENERATOR DATA I) Voltage (L-L) kw Frequency Power Factor 4160 5250 60 0.8 Prime Mover RPM Hydro-Turbine 120 II) Generator Field Data at Rated Load and Power Factor Generator Field Voltage = 200 Vdc Generator Field Resistance =.659 Ohms Ill) Determining SSE-N voltage and kilowatt size: 1) Select the SSE-N voltage (125 or 250) that equals or is greater than the field voltage at full load = 250 2) Calculate the kilowatt size by squaring the SSE-N voltage divided by the generator field resistance. Generator SSE-N Voltage Field Resistance 250 2 1.695 95 = Kilowatts 3) From Table I select SSE-N 250-100 Ensure that the static exciter minimum resistance is equal to or less than the resistance of the generator field. 4) Specify the nominal voltage rating for the excitation power transformer. 4160 Volts (Usually the same as the generator voltage rating.) 7
INTERCONNECTION Figure 3 - Typical Interconnection of SSE-N Static Exciter ROUTE 143, BOX 269, HIGHLAND, ILLINOIS U.S.A. 62249 P.A.E. Les Pins, 67319 Wasselonne Cedex FRANCE PHONE 618-654-2341 FAX 618-654-2351 PHONE (33-3-88) 87-1010 FAX (33-3-88) 87-0808 http://www.basler.com, info@basler.com