system operation

what are the requirements for paralleling ?

1) line to ground and phase to phase voltages must be the same 2)the angular displacement of the transformer banks must be identical 3)the phases must always match each other across the paralleling point 4)the frequency of each system must be the same desirable to have impedances of transformers and circuits the same but this is not always possible

what are the reasons to parallel circuits?

1) transfer load from one circuit to another to distribute load as needed 2)clear a piece of equipment in a substation 3)transfer load from one circuit to another in conjunction with clearing a section of line

what are the procedures for looping?

1)block all line regulators that are in the path of the loop from moving by turning the control to manual off 2)disable the ground tripping function of any line reclosers in the path of the parallel some utilities also disable the reclosing function

with transmission lines with long lines needing to go to load if there is a low voltage condition what should be done?

1)disconnect shunt reactors 2)connect shunt capacitor banks 3)energize open lines to provide var support 4)raise load tap changer set points 5 raise set points on generator regulators 6 let big customers know to curtail their load use shed firm loads

what are the procedures to getting a clearance?

1)identify plan and confirm clearance details 2)request clearance in writing 3)Approve clearance 4)isolate lock and tag all potential sources of energy 5)establish and issue clearance 6)test and apply personal grounds 7)releasing the clearance 8)returning the system to normal

what are the procedures when testing a transformer bank?

1)inspect the bus and transformer closely to see if there are any obvious indicators of a fault 2)disconnect all load from the transformer 3)clear the transformer and perform any investigative tests such as ttr gas analysis 4)always test the transformer with the load disconnected 5)test the transformer with high side protection 6)verify the proper output voltage before connecting the load 7) leave all protection features enabled

what are the following procedures when testing/energizing a bus?

1)inspect the bus closely and confirm the source of power 2) make sure all protection features such and ground trip are enabled 3)disable the reclosing feature on the source breaker in case a fault occurs

how would you clear a line regulator ?

1)place on manual postition 2)adjust to neutral 3)verify neutral 4)control to off 5)close in disconnects bypassing regulator 6) open switches on load side of regulator and tag for yourself 7)open switches on source side of regular and tag for yourself 8)confirm clearance point with dispatch 9)clearance is issued

how should you operate disconnects?

1)when closing close in a continuous smooth motion do not use excessive force 2)when opening disconnects open by cracking them gradually cracking them open gives the operator an opportunity to close them back if an unexpected arc should occur 3) do not use standard disconnects to de energize equipment such as capacitor banks transformers reactors or regulators 4) always confirm the proper rack or bay position before operating the disconnects 5) understand what each disconnect operation will accomplish before it is performed

electric arcs can reach what temps?

5000 to 25000 degrees c

what is a standard clearance?

This clearance is a condition in which all potential sources of energy are isolated by opening devices in the path of the potential flow of power. these devices are opened checked open locked if possible and tagged grounds are typically applied under the direction of the system operator or under the direction of the employee in charge

what is an overcurrent relay?

a relay which controls how a breaker reacts during a fault this relay can be preset to allow the breaker to open and reclose for a set number of times it can also be disabled to prevent any reclosing if desired

what is a reclosing relay

a relay which controls how breaker reacts during a fault this relay can be preset to allow the breaker to open and reclose for set number of times it can also be disabled to prevent any reclosing if desired

what is an oscillograph ?

an instrument that can record one or more rapidly varying electrical quantities such as voltage or current

when paralleling circuits should the ground relays with enabled or disabled and explain why

as a switch or disconnect is closed making the parallel there is a change that one phase may close before another. this is obvious with single hook disconnects but can also occur with gang operated switches where one phase can hang up or switch is out of adjustment in this case an unbalanced condition can occur which can result in excessive neutral current that can trip a breaker or line recloser by ground over current (as soon as parallel is separated ground tripping is restored to all breakers and line reclosers)

whats the major factor considered when de energizing transmission lines? when de energizing a line with load connected what will be experienced ?

capacitance that is present high voltage and high amperage when de energizing a load with no load experience will be high voltage low amperage

fault sensing can be combined with the automation of _ _ and _

capacitor banks and switches

with transmission lines capacitance is present when de energizing or energizing long sections of line as a general rule the longer the line the greater the capacitance each line or line section has different characteristics such as length clearances between phases and ground and impedance. this capacitance effect with long unloaded transmission lines is commonly referred to as _ _

charging current

which equipment is substations is routinely cleared for maintenance ? explain the purpose of the transfer or auxiliary bus in a substation?

circuit breakers given the large number of them in substations breakers are typically cleared by rerouting the flow of power through an other breaker or bus if a breaker is used if a breaker is used it is important that it is not overloaded some utilities will keep one side of disconnects closed to confirm proper working operation on the bus

open jumpers are utilized as _ points on both primary and secondary circuits

clearance

list 6 items that might be logged by a system operator in the operations center log?

clearances that were issued or release power interchanges load transfers system outages abnormal conditions such as low system voltage equipment failures visitors to the centers

what should be done with high voltage conditions?

connect shunt reactors disconnect shunt capacitors operate generator voltage regulators in a buck mode lower set points on load tap changers close open ended lines to reduce capacitance take certain transmission lines out of service to remove their charging current and to place more load on adjacent lines

during loop switching on transmission lines when a switch is opened line to _ voltage exists on each side of switch

ground

when would you likely refer to a single line diagram in a substation?

it is critical to understand the the operation of any substation this diagram helps the operator better understand

what should you consider loop switching?

it is important to understand that it is easier for a device to connect a loop then to separate a loop. a loop that requires a load break disconnect to interrupt the flower of power may only require a basic switch or disconnect to connect the loop. it is important to assure that a device designed for loop switching has the capability for interrupting the flow of power

when testing a circuit with a potential fault what is a good practice?

observe the ammeter when the circuit breaker is closed. if any of the ammeters peg the scale it is an indication that fault is present on the phase or phases which peg the ammeter if the circuit relays out again the relay targets can be checked to confirm the type and magnitude of the fault

what is restrike?

one of the phenomena that can occur when an arc is being interrupted is termed restrike as the switch contacts are being opened and the arc is interrupted at the current zero a high level of voltage tries to continue to force power across the gap if the level of this voltage is greater than the strength of the dielectric between the contacts the arc can be reestablished (restrike)

with metal clad switch gears before any breaker is racked out it must be in the _ position

open

what energy sources are considered when clearing lines and equipment ?

power flow from same circuit or line power flow from a different circuit or line power flow from a foreign generator

what is load transfer/load shift?

refers to the operation of the system which takes a portion or all of the load being supplied by a given circuit or system and transfers it to another circuit or system by opening and closing circuit breakers or switches

an other key factor with the tie design is that load can be _ and balanced between circuits and substations

shifted

when parallels are made or separated that load is not picked up or dropped but is _ from one source to another

shifted

what is single pole relaying?

some of the higher voltage circuits utilize single pole relaying to clear temporary faults this concept is to clear only the phase that is affected and has relayed allowing power to continue being carried on the other phases

what is paralleling ?

term confirming an operation in which two separate circuits emanating form the same or different transformer source are physically connected together so that there is a current flow from each source that meets at some point along the path of flow

what is looping?

term to paralleling that is typically used to define an operation where two branches of the same circuit are connected together

what is the ferranti effect

the capacitance that can result in a large voltage rise occurring when a long transmission line is opened at one end and no load is on the line

what should you verify immediately after operating a switch?

the contact position of each phase to verify it open or closed completely

when bypassing an electronic line recloser with non gang related disconnects what should you disable ?

the ground tripping function

locking

the locking of a device refers to the task of physically installing a padlock through a locking mechanism in a manner which prevents the device from being operated

what does nerc stand for

the north american electric reliability corporations certification

tagging

the physical attachment of an approved visible tag to or near the device that has been opened and will be utilized as a clearance point

what is non reclose condition?

the temporary disabling of a reclosing feature of a circuit breaker or recloser

what is a clearance?

the word clearance means a formally recognized condition of line, line section or equipment that has been de energized from all potential sources of energy by opening devices in the path or the potential flow of power

what is a RTU

this refers to a remote terminal unit which provides a centralized point to send and receive date and commands to monitor and operate the system typically a metal enclosure with electronic equipment inside typically mounted on poles substations and in underground enclosures

what is a clearance point?

this term refers to any device, connector, or open that is utilized to isolate the line or piece of equipment from a potential source of energy

what is cold load/inrush?

this term refers to the amount of load that be connected when the system or portions of the system are energized after being out of service for extended amount of time it can be as high as ten times the normal system load

what is a safety clearance?

this type of clearance is used as much as the standard clearance however it is not utilized by some companies this clearance is where the main source of energy is opened de energizing the line or piece of equipment however no visual opening is confirmed nor are personal protective grounds installed

what is loop switching

this type of switching involves the connecting and disconnecting of transmission lines supplied from different sources of power when a loop is opened the open points interrupts the path of flow of power

what are the 3 major rules for clearing lines and equipment

to assure the safety of the employees who are working on lines and equipment to minimize the impact to reliability and capacity of the system that will occur as a result of the clearing of the line or piece of equipment minimize number of customers out

list some key responsibilities of the operators

transfer load as needed monitor system conditions maintain proper flow of power with proper voltage levels var flow frequency restore lines and equipment to service direct switching for planned unplanned and forced outage conditions

what are the procedures for paralleling?

utilize a gang operated device such as an air switch line recloser or circuit breaker to make and separate parallel 1)disable the ground tripping function of any station breakers or line reclosers in the path of the parallel 2)match the voltages of the 2 circuits as closely as possible at the point of separation by setting the load tap changers or regulators that are in the path of the parallel to neutral or the same step 3)take load readings at each station on the circuits being paralleled before during and after the paralleled some utilities also disable the reclosing function

what is var flow?

var is short for volt ampere reactive which is a term defining the reactive flow or non working flow of power in a system this term goes hand and hand with the voltage of the system

explain how system operators utilize wall maps?

wall maps can be used to operate the substations and main feeder portions of the circuits

what is the null point?

when 2 circuits are tied together in parallel the flow of power is from the source of each circuit out to a point where no current is flowing this point is the null point

what is inrush current

when energizing circuits or portions of circuits that have been out for some time heavy initial currents can occur which can trip fault indicators most manufacturers offer inrush restraint feature which prevents the indicator from tripping on inrush

dc arcs are much more difficult to interrupt since the voltage and current never drop to _

zero