OPII Study Guide - Electrical Equipment

Disable ground trips/reclosing when making and breaking parallel opening /closing loop w/ d's (all reclosing devices ). Bypass regulators when making parallel or closing loop through them (both substation level and field regs) Disable VVO or IVVC prior to making parallel as well. (if Regulators or...

Disable ground trips/reclosing when making and breaking parallel opening /closing loop w/ d's (all reclosing devices ). Bypass regulators when making parallel or closing loop through them (both substation level and field regs) Disable VVO or IVVC prior to making parallel as well. (if Regulators or capacitors are to be moved to adjacent feeder) Make sure no issued contact tags prior to making parallel. **[Advance Dist. Equipment II]** What is Vista Switchgear? - Compact switch gear that is designed for building vaults. Utilizes a SF6 gas insulated bus to allow for close switch positions. Functionally, no different than a switching cabinet. Fully Submersible. Contain up to 6 ways. Gang or single-phase switching. Vista gear designation? - SH, SS, SC Vacuum Bottle Process? - Vacuum bottle opens (snuffing out the arc), switch opens, vacuum bottle closes. If it is a trip (fault) then the bottle opens and switch has to be opened to reset. VFI/VI? - Vacuum fault interrupter, vacuum interrupter (no relay set up, will not sense and interrupt faults) LPG Alarm/SF6? - Pressure gauge in ways 1 and 2. - Do not operate vista gear if there is a LPG alarm. - Gauge should be in green/green-yellow or 6-8 pounds per square inch. Clearance Point? - In Way\#, J-Switch (switch if not gang) on cables id'd is open mechanically blocked and tagged. AT? - Automatic transfer switch, has two feeds to the customer. Either a preferred source that is closed in and an alternate that is open and ready for service. Or, metal clad split bus, both sources serving the load with a normally open tie switch. Fault blocks, that keep the alternate source from closing in should there be a fault on the load side of the AT. GW is dead front, SC metal clad split bus and the micro AT are live front. Contact Tag load side of AT? - Verify source feeding the load, verify the alternate. Place on manual, install contact tag on source feeding the load. OH AT clearance points? - Same as recloser, bypass blades open and tagged N.O. and load/line side jumpers removed and tagged. Metal clad switchgear clearance? - open, decoupled and tagged. With bay number - PT Fuses need to be removed prior to hi potting. - Micro AT -- hi pot -- move input plug to shorting receptacle to avoid damage to voltage sensors (open, decoupled and tagged) **[Intro to Network Protectors ]** Network Protector? - Air break switch that connects/disconnects the transformer from the secondary network being served. Prevents reverse current from flowing from secondary to the primary Dedicated Network? - Feeders that supply network xfmrs only. Spot Network? - Feeder that serves network load as well as residential/commercial customer load. Viso Blocks? - Low profile disconnect, provides a visual airgap between the network protector and the network bus utilizes the kirk key system. Kirk Key? - Prevents the removal of the viso block rod prior to opening the network protector. NP is opened and key is obtained, which then is used to remove viso block. ARMS? - Arc reduction maintenance system, provides extra protection when crews are working in a vault that has this feature. Sense fault current in either direction Network? - Supplies customers with continuous load without interruption due to the secondaries being in parallel on the load side of the network protectors. Fault on Network feeder? - The breaker for the feeder opens, the network protectors associated with the feeder will open to prevent reverse current from flowing from the secondary to the primary. Send tmen to all network sites to verify other NP's on auto and closed, place on manual and verify open the affected NP's on the open feeder and remove LSL's and tag or VB's and tag. Then send to sub to establish clearance. (have switching order written for work) Secondary Fault? - Network protector is not designed to protect the secondary cable from overload or provide secondary fault isolation. If a secondary fault occurs, secondary z links, cable limiters or bus limiters will melt -- isolating the secondary fault from the network transformers/source. - Cable limiter is a fuse for disconnecting a faulted cable from the secondary network. Bus limiter disconnects a faulted bus from the secondary network NP,MN,UG,UV/SS, NVB,LSL,TSL? - Network protector, network xfmr without primary oil switch -has 600 amp deadbreak elbows, network xfmr with a primary oil switch, Vacuum Switch, Visoblock rods, load side links, transformer side links. High side Oil Switch? - Can be opened only after the network protector is opened. Cannot drop customer load, only xfmr load. Visual open for high side of xfmr. Can be in open, closed or grounded position. Network Transformer? - 3 phase padmount delta connected transformer. Cannot be energized or de-energized using single throw switches (Ferro Res.) unless using a loader or having customer load. Secondary Voltage is 277/480 Network Protector? - Airbreak switch that connects and disconnects the network transformer from the energized secondary bus. It will also open to prevent reverse current from flowing from the secondary to the primary should the breaker on the primary feeder open. 3 parts to a NP? - Consists of the enclosure, relay and operating mechanism. Submersible vs. Semi Dust? - Manhole and vault are submersible / semi dust for padmount. Relay for NP? - Close when transformer voltage and phase angle are met. (1.5 volts higher on secondary side of transformer than the network secondary bus. 0-degree phase angle) - Supervisory NP -- permissive has to be enabled to automatically close. Operating Mechanism NP? - Close -- do not use the hard-close function often -- bypasses the criteria for closing - Auto -- used when closing -- place on auto and let it close when criteria is met - Open -- operating handle in open position, np opens. Open in motor for closing circuit so it will not close automatically Sequence when protector opens? - Main contacts part, followed by secondary contacts, followed by arcing contacts. Arc Chute? - Once the arcing contacts open, arc chute provides a place to extinguish the arc TSL? - Transformer side link -- connects the secondary bus to the source side bus of the NP. LSL? - Load side link, connects the load side of the NP to the network bus. ARMS? - When it operates, all NP's for vault open. Sense and interrupt fault both ways -- primary or secondary. Light Stack Colors? - Blue -- enabled. Red -- closed. Green -- open. Yellow -- test mode. White -- connect position. Permissive Closing? - When the NP is open and the control handle is on auto, permissives are enabled -- the NP will close with the criteria is met (0 degree phase angle / 1.5 volts higher on transformer secondary than the network bus voltage). If permissives is disabled, will not close on auto -- even if all other criteria is met. Relax Close? - Allows for criteria to close to be widened by 10% - Pumping Lockout? - Should the NP operate more than 3 times within 1 minute, it will lock out for 60 minutes. - Can be reset remotely or in the field. - Will close in automatically when the criteria is met. If the issue still persists, it will open again as needed. **[Introduction to Circuit Reclosers]** G&W Viper? - OH reclosers that utilized vacuum interrupter bottles to interrupt fault current or drop load. Bi-directional -- does not matter where the source is coming from -- will operate as normal. Only has a yellow handle which will open the recloser, but when closed it will allow the recloser to be closed locally from the controls. - Vipers that are installed as substation breakers will open after 3 minutes if station power source is lost. Cooper Nova? - OH recloser that utilizes vacuum interrupters to open or close circuit/interrupt fault current. Can be in one of 3 modes: proception (recloser), switch or sectionalizing. - Has ground trips, reclosing, and hot line tag functions. Yellow manual trip handle per phase. Cooper Type W? - Oil encased j switch to open or close the circuit. Load break and fault interrupting capabilities. - Hydraulic reclosers -- yellow handle to open and close. Red to enable or disable reclosing. YFA? - Yukon Feeder Automation -- phoenix smart grid system within Gavilan Peak/Pioneer substations. Ability to sense outage, determine location, isolate fault and restore power without human interaction. - Bypass blades need to be updated in ADMS so YFA can make decisions based on switch positions. - Disable Feeder automation for contact tags or when work on feeder. Disable System Automation to turn YFA completely off. Low Impedance Fault? - Low resistance when going to ground, will have large fault current. High Impedance Fault? - Conductor makes contact with something that is not a good conductor and the fault is not easily taken to ground. Low fault current. May not be high enough to be detected by upstream protective device. Recloser Designations? - R, U, T, V and I for smart grid What is a recloser? - Protective device that minimizes an outage area and reduces exposure. It senses and interrupts fault current, then recloses a predetermined number of times until lockout. Disabling ground trips? - Device will not operate should it sense a phase imbalance that exceeds its MOC. **[Introduction to MOD's]** What is an MOD? - Motor Operated Device -- also known as an n switch. OH Supervisory Gang Operated Load Break Switch. Operated by ADMS, locally in field or manually in field. What supplies power to N Switch? - 12 volt battery supplies power to the switch motor and RTU's. Can go about 24 hours without charging power. Does Switch provide Volts or Amp readings? - No De-Couple? - Separate the motor operator from the switch. That way it can be operated without changing the switch position. CPSS? - Control power safety switches -- shall be off when setting up a clearance, controls power to the controls. Torsional? - Twisting or turning action Reciprocating? - Up and down motions of switch Standards for a MOD? - N or the GJ123S Remote operation of the switch needs what conditions met? - AC/DC fuses installed - Manual operating handle secured in clips - CPSS on - Switch on remote Local operations of switch? - AC/DC fuses installed - Manual operating handle in the clips - CPSS closed - In local Composite View? - Allows user to interact with the switch and can see in this view if it is on local **[Supervisory Control ADMS]** EMS? - Energy management system -- monitor and control transmission and dist. SCADA/DSCADA? - Supervisory control and data acquisition (Distribution) Analog point? - Provides numerical data such as amps or volts Status point? - Provides information about a status -- such as open or closed or enabled/disabled. RTU? Dual Port RTU? - Remote terminal unit -- converts sensor information into digital data -- which is related to DSCADA and can be viewed in ADMS. - Dual port -- allows it to be used in ADMS and EMS. Signals in ADMS? - Show status and analog information. Typical Sources of DSCADA information? - Monitor and control intelligent devices. Protective relays, device controllers and RTU's - Monitor stand alone sensors, CFI's - Monitor and control: 1. Network protectors 2. Vista gear 3. PME's 4. YFA/SMG 5. MOD's 6. Reclosers 7. Scadamates 8. Intellirupters 9. Monitor cap bank switch positions - When abnormal switch positions occur -- alarm information populates to alert the operator Single Circuit view? - Similar to composite but the conductors are colored and do show white with an outage. Usually seen for YFA/SMG and network sites or marina heights. - Both views will show incidents/ tags or notes installed on the device. - Also does not include some status/analog data that can be found in the signals window. Ways to access single circuit/composite? - Search device number, feeder name, network view, right click on device, or drag/drop device to new window Scan inhibit tag/stop processing tag? - When a SCADA device is sending the wrong status signal, a scan inhibit tag can be installed and the switch can be manually overwritten. **[Sectionalizing II]** Purpose of sectionalizing? - Safely restore power to as many customers as possible while utilizing sectionalizing devices with the safety of field personnel and the public as the top priority. Situational awareness checklist? - OH/UG, Feeder, Open air vs metal clad, CFI's/FI, direct buried/conduit, wire/cable size, outage area/boundary, residential customer, commercial, key accounts, medical monitoring, existing clearances, contact tags, crews in area, hazard calls, notes in map/other tags, temp cable, abnormal switch positions, contingency sources and wire/cable size of those sources, networks, PME, vista gear, AT's, YFA/SMG, Nova reclosers, intellirupters, Scadamate, reclosers, sectionalizers, cap banks, regulators, N-J-or K Switches, D's, Fused taps, switching cabinets, distributed generation, third party sources such as SRP, number of phases and grounding banks. Prior to making first test? - Mutual with ECC, verify in EMS - Notify SOCS - Notify supervisor - Verify no contact tags - Dispatch tmen/names on ticket - Check everyone in the clear and no hazards - Non supervisory, send to the substation 4 times we don't test feeders? - Contact Tag/DNO - Certain Key account customers - UG feeders - Dedicated networks Midpoint? - Good, better, best approach depending on the situation and calls. - Ideally an in and two outs and if it has a normal open, even better. Prior to using a normal open? - Put a DNO on the other feeder. Highpot? - Indication something was hit or when you reach 5 pieces of cable or less. No cause found? - Patrol, targets/reads, inspection of live front switching cabinets and check any networks that share the same bus as the feeder that tripped to verify all NP's are on auto and closed. Faulted energized cable? - Fault has blown a cable in the clear, energized up to the fault point and de-energized down stream. Open breaker (or recloser) prior to isolating that cable. Networks impact restoration efforts? - If a network needs to be isolated, have 3 phase delta connected Padmount xfmrs that cannot be energized or isolated using single throw switches. Unless using a loader or having customer load. Grounding Banks? - Do not energize or de-energize using single throw switches. Must be gang operated AT's? - Relay on the preferred source, timer of 90 minutes starts when that AT gets its preferred source back and will automatically switch back after that 90 minutes is up. If you are still sectionalizing, and lose the feeder -- customer could see multiple blinks. Best to place on manual and switch back at a later time. 1 **[Construction Release]** Release for operations? - Statement by one having complete authority over all parts of a new circuit or piece of equipment to a RSO that the installation of the circuit or equipment is complete. A construction release for operations guarantees all personnel are in the clear and the circuit or equipment may be safely placed into service. Operations release for removal? - Is a statement by a recognized system operator having complete authority over all parts of an electrical circuit or equipment, that said circuit or equipment is disconnected from all known sources and will remain in this condition during the 2 - course of the removal work. Operations release for removal is a transfer of control and responsibility over a circuit or piece of equipment from a RSO to the requesting group for the purpose of removing the circuit or piece of equipment from the system. Work release? - Is a statement by a recognized system operator having complete authority over all parts of an electrical circuit or equipment, allowing a piece of equipment to be taken offline to perform non electrical work, operational testing or inspection. A work release requires the workers to treat the equipment as energized normal operating voltages and use appropriate work practices for energized primary voltages. 7 things needed for a construction release? - Your name, the date, the crews name, times, partial/full, for operations or for removal, and a description of the work. Things to be down following release? - Job tag in the map, Sharepoint, TOA and equipment data base if applicable. **[Switching Orders]** DOC Jurisdiction? - Load side pad of the 43's. Operators job during switching orders? - Evaluate the steps, execute/distribute steps with field personnel, ecc or utilize supervisory devices. - Do not change a switching order without approval of Supervisor or DFP. Why is it important to know DOC jurisdiction? - Need to know boundaries and what steps are to be completed with ECC, for example -- opening and tagging 43's. Any actionable field action needs to be a step. Switching in a network following an issue needs a SO. Switching order life cycle? - Draft, submit, LMS approved, DOC approved, Complete, Archive. - Can change request when it needs to have changes made. Needs a unique and descriptive title? - Transfer load from x to y - End planned outage - Close/Open loop - Return load from y to x Switching steps should contain? - Role -- DOC or ECC - Item -- start planned outage, close loop, de-energize cable. - Switchman -- who is performing the step - Work location - Schedule date and time - Issued date and time - Operated date and time Things to consider when switching cabinet is changed out? - Phase out - Switch positions and elbow positions - Like for like? When to add a note for temp cable? - When size is different than 1/0 or 4/0 Permanent fuse change in switching order needs? - Documentation in the switching order and a data correction - Update the equipment data base if applicable. When do you need to enable/disable ground trips and reclosing? - Make or break parallel with single throw switches - Consider reclosers - Consider closing and opening loop if recloser is in the path Use a load break tool or device? - Break parallel, open loop, dropping load, de-energizing cable in accordance with chapter 14 of the APM. 5 W's of validation? - Who -- operator hits validate - What -- looking to validate to ensure steps work - Where -- in the SO - When -- prior to checking or working a SO - Why -- make sure your SO will work and no critical errors will be made When is change request initiated? - When there needs to be changes made to the switching order. Can be used in either LMS approved or DOC approved as needed. **[Smart Grid For Operators]** Intellirupter? - After clearing a fault, the Intellirupter will utilize pulse closing technology to test the line at a lower percentage to determine if there is a fault beyond it without subjecting the system or devices to high fault current again. - L switch provides the visual open / manually operated in the field after the Intellirupter is opened. - Controlled via ADMS or manual switch stick in the field. - Clearance on bypass blades and disconnect is opened and tagged. - Close Profile Protection (CP2) -- when enabled, disables pulse closing and allows for a hard close. Once close, will automatically disable. Scadamate? - Overhead, gang operated load break switch associated with flagstaff smart grid. - Sectionalizing device, cannot sense and interrupt fault current. Utilizes SF6 interrupter bottles to open and close the circuit. - Disconnect switch provides visual open and is the clearance point. Non load break, the Scadamate must be opened prior to opening the disconnect. PME? - Dead front switch gear that allows for automated switching within the SMG and YFA smart grids. - Used as supervisory switching cabinet outside of smart grid. - Clearance is open, decoupled and tagged. - 2 RTU's between the 2 6800 controllers Intellinode? - Provides the link to allow the substation breaker to interact with the teams to provide breaker status and loading data for SMG. Intelliteam II Software? - Smart grid software used to operate the Flagstaff SMG. Wait at least 10 minutes from last operation. - A switch can belong to more than 1 team - Restore up to 400 amps on a feeder in total (if a feeder has 250 amps on it, SMG can only put an additional 150 amps before it will stop restoring power using that source). **[Introduction to Intellirupter]** Pulse Closer? - Unique means for verifying the line is clear of a fault before initiating a close operations. Tests for a fault without creating high current surges that will put stress on the system. Sends a short, low current pulse down the line. - Unless CP2 is enabled, all close operations will Pulse Close first. CP2? - When enabled, it disables the pulse close technology and allows for a hard close. - Once close command is completed, CP2 is disabled and pulse closing is automatically enabled. Interrupter Housing? - Two current sensors and a voltage sensor. Provide voltage, current, power and var statuses. - Making and breaking capabilities and fault interruption. - Open and Close indication on the outside (green O and a Red I) Open/Close/Ready Lever? - Use of a manual switch stick. Pulling down on open results in opening of interrupters and blocks any ability to close. - Place in ready allows for a close operations and removes the blocking mech. - Close function utilizes the Close Profile Protection for a close operation and spring pops the manual operator to the ready position. Communication Module? - Allows for communication between the Intellirupter and its peers for the Intelliteam II software. - Loss of AC line voltage -- batteries will last a minimum of 2 hours. - If time elapses and battery is drained, once AC line voltage is back -- allow 15 minutes to operate remotely. Control Module? - Computer that controls the Intellirupter operations. Has a hotline light to indicate when it is enabled and a status light that flashes to notify everything is working. Hot Line Tag? - When enables, disables the reclosing abilities and changes the curve settings to open upon seeing fault current. - Can be enabled via ADMS or manual switch stick in the field. - Need to disable hot line tag prior to closing the Intellirupter. - Enabling this, disables the SMG on teams on either side of the device. Need to disable AR at feeder level for contact tag and verify all NO's AR are disabled. Ground Trip lever? - Manually enable or disable ground trips in the field or via ADMS. - If performing manual switching in the field on backbone, disable AR for feeders that apply AR? - Automatic restoration -- this device will be used by the SMG to restore customers following SMG operation. - When disabled, SMG will bypass the switch and any team that it is a part of. **[Introduction to Vista Gear]** Vista Way? - Vista gear has ways, not bays. Contains the bus work, vacuum bottle, switch blades. Because the ways are in close proximity, SF6 gas insulates the bus. Vacuum Bottle? - Vacuum bottle snuffs out the arc and allows for load interrupting capabilities and fault interrupting capabilities when the relay is set up (VI and VFI). - Vacuum bottle opens, switch opens, then vacuum bottle closes. LVE? - Houses the 6800 controller and the vista rack\\ Vista Rack? - Control boards/module for ways that have permanently installed motors. Vista Gear? - Compact switchgear that is designed for building vaults and utilizes a SF6 gas insulated bus to allow for switches for various ways to be in close proximity to one another. Functionally, it is no different than a switching cabinet. Completely submersible. Do not operate if there is a LPG alarm for low SF6. - Switches can have permanently installed motors and be operated via ADMS, locally in the field at the LVE/vista rack or external operator. Can also manually operate with tire iron on site / hook up motor with an umbilical cord. - Clearance: open, mechanically blocked, locked and tagged. The blocking lever will be in the close position, blocking key installed, locked and tagged. 1. Manhole Vista? - Barrel vista -- used in building vaults as a vacuum switch. UV or SS designation -- tied to a kill switch but not supervisory on its own. Reset the VFI following a trip? - Have to open the switch following a trip and then the vacuum interrupter will close. External Control Panel? - Found in some vista vault installations on the outside of the vault -- allows personnel to identify the status of the switchgear and control each way with a permanently installed motor. - The vista rack must not be in the local position. - Has a LPG indicator -- DO NOT operate if there is a LPG alarm. External Panel A? - Found outside of the vista switchgear enclosure -- enables or disables operation from the external control panel, vista rack, ADMS or the 6802 controller. - The Panel A has a toggle to dictate whether any motor operated switching can occur on any of the ways of a vista. Vault Kill Switch? - Located near the door - When pushed, vacuum bottle contacts will open but the switch blades will remain closed (Marina Heights). - Can be operated via ADMS Fire Suppression at Marina Heights? - Deploys FM200 -- works as a heat absorption to extinguish fires by creating a larger surface area. Will activate when it detects smoke - Have an alarm that will sound -- 30 seconds to get out until FM200 is deployed - Manual operation near vault door -- can also be disabled there as well. **[Introduction to Scadamate]** SF6? - Sulfur hexafluoride -- gas used to break arc when opening and closing the SF6 interrupter bottles AO? - Automatic Operation -- that the device will be used by the Intelliteam II software when sectionalizing -- following a fault/outage. AR? - Automatic restoration -- this device will act as part of the smart grid when enabled and in the restoration process following an outage. Scadamate Designation? - Y when part of a smart grid and N when not part of a smart grid. Scadamate? - Overhead, three phase, gang operated load break switch that uses SF6 interrupters to open and close the circuit. Does not have ability to sense and interrupt fault current. Scadamate must be open prior to operating the disconnect switch (which provides the visual open for clearance purposes). Controlled via ADMS, controls in the field and a manual switch stick. Manual open/close pull ring? - Manual switch stick to open or close the switch. If spring is charged, one pull on the pull ring will operate it. If not charged, 7 to 9 pulls. - Open close indicator -- green and red Disconnect open/close? - Manually switched in the field to provide normal open, only after opening the Scadamate. Current/Voltage Sensor? - Provide three phase monitoring. Voltage sensor also provides the battery charging power for the automatic switch control or communication/control unit, eliminating the need for a separate transformer. **[Introduction to PME's]** PME? - Pad mounted enclosure -- dead front switching cabinet that allows for supervisory switching and automated switch. 6800 controller w/ 2 RTU's. Current and voltage sensors for monitoring (voltage sensor provides battery charging power) LVE? - Low voltage enclosure -- houses the 6800 controller. PME switch operator? - Mounted on bays with switches that have supervisory controlled switches w/ permanently installed motors. Can operated the switches here on local, w/ a manual handle and can de-couple here. Local vs remote here will not show up in adms. De-Couple? - Separate switch from operator -- when decoupled -- motor can be operated without actually operating the switch. 6800 Controller? - Sophisticated automatic control schemes and RTU functionality. One controller can operate up to 3 switches, but APS uses two controllers to control 2 switches each. Clearance Point? - Jswitch on cables id'd is open, decoupled, and tagged. OC FAULT LIGHT? - Turns off after switch is closed, 3 phase line voltage sensed and 45 minutes has passed Or - Toggle local/remote, SCADA command, or restarting the control RTU Specific signals? - R1/R2 -- SCADA battery capabilities of RTU - cannot be relied on to operate via remote control when square is red. (normal is green) - OC Fault -- indicates that the switch saw overcurrent flow through it when the square is red. - Sectionalizing -- switch acts like a sectionalizer -- it will isolate a fault after it senses overcurrent and is de-energized a set number of times within a predetermined amount of time. Relies on the upstream recloser to open, the switch in the PME will open, then the upstream reclosing devices will close up to the PME. - Door Open Alarm - only one indicator per RTU/6800 controller. - Local/Remote alarm. -- only one indicator per RTU/6800 controller. - Only 1 controllable function in ADMS -- open or closing of the switch. **[Introduction to Communicating Fault Indicators]** Fault Indicator? - Indicates if a fault has passed through the conductor that it is installed on. Communicating fault indicator will relay this information so it can be viewed remotely. - CFI provides near real time voltage and loading data. / APS uses Pi Vision to display CFI data. CFI consists of? - Software, satellite clock, power inverter, power supply, pre fault memory, data recorder, local indication (LED panel), cellular modem and sim card and Bluetooth radio. - Green flash, okay. Red flash, fault passed through. - Will have a magenta outline in ADMS Ways to search for a CFI in ADMS? - Quick open tool - Advanced trace - Find tool - Fault target alarm - Equipment browser 4 Signals (3 will generate an Alarm)? - SustFaultDtct (fault lasting 5 minutes or longer) - MomFaultDtct (short fault condition that hasn't reset) - LossCurrDtct (loss of current) - RMSFltCurr (fault current magnitutde \*\*\*\*will not generate an alarm) **[Introduction to YFA]**