The main purpose of a distribution substation is to bring the transmission voltage down to a distribution voltage and distribute it to the customers.
What factors affect the location of a distribution substation?
Possible objections from the public or private sector regarding noise, appearance or electrical effects, also atmospheric conditions, public safety and security.
What is the purpose of a substation ground grid?
To ensure and equipotential zone eliminating the risks from touch potential and step potential
What is the purpose of a transfer bus?
The transfer bus allows feeders to be paralleled, or run on another bus besides the main bus for maintenance, repairs or addition of new equipment in the field.
What is the main purpose of substation buildings?
The main purpose of substation buildings is to contain and give shelter to protection relays, control panels, auxiliaries, batteries, compressors, emergency generators, etc.
What is station service?
Station service is the power that the station requires to operate the equipment within it.
How is AC station service supplied?
AC station service may come from different sources including: transformers connected to the station buses, tertiary windings of the main transformers, line from another station and a diesel powered generator.
What are the limitations of AC station service?
AC energy can’t be stored
How is DC station service supplied?
DC station service is stored in DC battery banks and converted to AC when needed through a rectifier.
What is the purpose of DC station service?
The purpose of DC station service is to provide a backup to the AC station service. It can provide up to 8 hours of power to critical equipment in the station. Enough time to restore AC station service.
What are the standard AC and DC station service voltages?
AC is typically 120/208 V and 347/600 V, and DC can be 24 V, 48 V or 125 V
What is a station service auto transfer scheme?
In the event of a failure the station service auto transfer scheme will automatically transfer from one SS to the other upon failure.
Why is rigid bus usually hollow?
The rigid bus is usually hollow because of the “skin effect”, there is less useful conducting area with AC.
What type of conducting metal is used for outdoor rigid bus and why?
Aluminum is used because it is lighter than copper and the larger dimensions required to make up for the lower conductivity of aluminum actually helps lower the skin effect.
What are the reasons for using SF6 bus?
Safety, low maintenance, significant reduction in size, non-flammable, protection from atmospheric pollution and quiet operation.
What does CGIS stand for?
What SF6 gas qualities make it highly suited for use as the insulating medium in CGIS?
Good insulation properties and non-flammable
How is the dielectric strength of SF6 gas monitored?
It is monitored via a temperature compensated pressure switch
What are the most common distribution voltages?
4 kV, 12 kV & 25 kV
What is the purpose of a power transformer in a distribution substation?
To step down the transmission voltage to a usable distribution voltage
What are the basic components of a power transformer?
Tank, core & winding assembly and insulating/cooling medium
What is the purpose of a conservator tank and how does it function?
There are two main purposes for the conservator tank. One being that the tank can “breathe” or allow the oil to expand and contract with temperature changes and the second being that the oil in the main transformer tank never has contact with atmosphere.
What is the purpose of a silica gel breather?
The silica gel breather removes a good portion of the moisture from the air that is drawn into the tank during contraction of the oil as the temperature lowers.
What is the purpose of an explosion vent and how does it function?
The purpose of an explosion vent is to remove any high pressure in the tank, which could be caused by a fault in the transformer windings. The explosion vents whether mechanical or physical (glass, etc) will release the pressure once it gets beyond a sertain threshold
What is the purpose of transformer bushings? Why are the primary and secondary bushings different sizes?
Transformer bushings are used to create an oil-tight connection to the transformer. The primary and secondary bushings are different sizes because the voltages are different potential. The higher the potential more insulation is required, hence increasing the size.
How is oil circulation accomplished in oil-filled transformers?
The heated oil naturally moves to the top of the tank, as it cools it will sink to the bottom of the tank, natural convection or “thermosyphon effect”
What are the common methods used for cooling?
In oil-filled transformers the warm oil is passed over a cool surface via natural convection or forced pumps, or the warm oil is passed over surfaces cooled by water
In the case where no oil is used it would be cool air or gas in a sealed unit.
What are tap changers used for?
To keep voltage levels at a certain level.
How is an off-load tap changer adjusted?
It must be taken out of service to make tap adjustments
Why are load tap changers used?
They are used because they can change taps without having to be offloaded. These types of tap changers are used in areas where the load changes frequently
What three methods can be used to operate a load tap changer?
From a control switch, from a voltage relay, or from a hand crank
What are instrument transformers and what are they used for?
Instrument transformers are devices used to measure the voltage and current of primary lines.
What is the purpose of an instrument transformer’s polarity markers?
They are to indicate the direction of the primary and secondary currents.
How is the primary winding of a potential transformer connected?
It is connected in parallel with the line being measured
Why should the secondary winding of a potential transformer never be short circuited?
If you short circuit the secondary windings on a potential transformer you will quickly burn out the windings in the transformer
How is the primary winding of a current transformer connected?
The primary winding of a current transformer is connected in series with the line being measured
What is the standard rated secondary current of a current transformer?
Standard secondary current is 5 A
What is the burden of an instrument transformer?
The burden of an instrument transformer is the active and reactive power consumed by the load on the secondary winding.
What is the nominal current ratio of a current transformer?
The nominal current ratio of a current transformer is the inverse of the turns ratio.
Why must the secondary winding of a current transformer never be opened while the primary is energized?
It can cause extremely high voltages that can severely harm or kill the person opening them
What is the purpose of a circuit breaker?
To protect the equipment from electrical faults and to interrupt normal currents for maintenance purposes.
What are the four general categories of circuit breaker ratings?
1) Current interrupting requirements
2) Current carrying requirements
3) Operating voltage requirements
4) Operating speed requirements
What is an electric arc?
An electric arc is an electrical breakdown of a gas that produces an ongoing plasma discharge, resulting from a current through normally nonconductive media such as air.
What are the three basic methods used to increase the impedance of the arc path to extinguish an arc?
1) Increase the length of the arc
2) Decrease the cross sectional area of the arc path
3) Cooling the arc path and replacing ionized gas with a non-conducting material
Why is DC current more difficult to interrupt than AC current?
Direct current arcs are more difficult to interrupt than AC currents because AC
currents come to zero twice per cycle.
Briefly describe recovery voltage and re-strike.
Recovery voltage is the voltage that appears across the terminal after current interruption. A re-strike happens under certain conditions the breaker may open and the arc interrupted, but before the contacts have separated far enough the arc may be re-established.
Describe the two most common types of circuit breaker contact construction.
1) Bayonet type
2) Butt type
Describe the two types of oil circuit breakers.
1) Mineral insulating oil
2) Synthetic insulating oil
What are the advantages of air-blast circuit breakers over oil circuit breakers?
Air-blast breakers have reduced fire hazards by not having large amounts of oil, general maintenance is cheaper, less damage to the contacts themselves due to shorter arcing time and less chance of environmental incident due to oil spills.
Describe the operation of a puffer breaker.
When the contacts separate and the arc is formed, the blast valve moves and pressurized air shoots through the arc chutes to atmosphere. This cools and stretches the arc to help extinguish the arc.
What is the main advantage of vacuum circuit breakers? What is the main disadvantage?
The main advantage of vacuum circuit breakers is having a long and relatively maintenance free life. Main disadvantage is the loss of vacuum.
What is the purpose of a circuit breaker prime mover?
The prime mover is part of the operating mechanism that provides the mechanical force required to open and close the circuit breaker contacts.
What is the purpose of a circuit breaker control circuit?
The circuit breaker operating mechanism control circuits provide the necessary capability to operate the breaker safely. These controls enable the breaker to trip or close manually or automatically, as well as providing the stored energy to the prime mover for breaker operation.
How can motors be used in operating mechanisms?
Motors can be used to directly move the prime mover or store energy in springs, air etc. which is used to move the prime mover.
What is a trip-free operation?
If a breaker can trip automatically upon receiving a trip signal before the closing operation is complete, it is said to be “trip-free”.
What is the purpose of a circuit breaker control cabinet?
The purpose of the circuit breaker control cabinet is to house all of the control components and protect them from the elements.
How does metal-clad switchgear differ from cubicle switchgear?
The main difference is that cubicle switchgear does not have removable breakers with primary and secondary isolating devices.
What is the purpose of automatic shutters?
Automatic shutters which cover primary circuit elements when the removable element is in the disconnected, test, or removed position.
Why are feeder circuit breakers equipped with automatic reclosing?
To help prevent lengthy outages from transient faults.
What is the purpose of a substation disconnect switch?
They are primarily used to isolate equipment so field workers can work safely.
What is the advantage of a motor-operated disconnect switch?
They can be operated remotely or automatically
What is the purpose of a horn gap and how does it work?
Main purpose is for breaking light currents. They have arcing horns attached to the main contacts. When separated the arc forms across the arcing horns until broken reducing the wear arcing causes on the main contacts.
What is the purpose of a quick-break attachment and how does it work?
The purpose of the quick-break contact is to open the contacts quickly. The switch opens quickly due to spring action.
How can wind affect the arc control of an air-break switch?
The wind can blow the arc in any direction and cause a flashover.
Why is a load-interrupter device built as an auxiliary to an air-break switch?
For two reasons, the air-break provides the isolation after opening and the standard air-break switch provides economical foundation for the device.
What is the purpose of a circuit switcher?
It’s used for switching electrical currents. It interrupts the flow of current or closes the circuit at high voltage.
What are the components that make up a circuit switcher?
Interrupter with a disconnect accessory.
How does a circuit switcher differ from an interrupter switch?
The disconnect is in series with the interrupter in a circuit switcher.
How is a circuit switcher similar to an interrupter switch?
They both have a visible air gap
How is a circuit switcher similar to a circuit breaker?
A circuit switcher is able to interrupt current similar to a circuit breaker
What common application of the circuit switcher is most seen by the
It will be seen frequently on the high side of a power transformer.
What does a circuit switcher use as its interrupting medium?
What is the purpose of a voltage regulator and how are they applied in distribution substations?
Voltage regulators are used to maintain system voltage levels by bucking or boosting the input voltage. They are used to regulate individual feeders or to regulate substation buses.
What are the basic requirements of a voltage regulator?
Regulation must be automatic, changes in voltage must be in small quantities and load current must still flow during regulation
What is the most common type of voltage regulator used in distribution substations? Briefly describe their operation.
The step voltage regulator is most common due to lower costs. They adjust the voltage by changing the taps of the series winding.
What is load bonus?
Some 32 step regulators are designed to carry sustained load currents above their normal maximum, but only if the range of regulation is reduced.
Why are bridging wipers used?
They are used to allow a continuous supply
What is NCO?
Neutral Control Off
What is the primary purpose of a series reactor?
To limit the flow of current during fault conditions
What is the most common application of a series reactor?
A feeder reactor that is in series with the line feeding the load
Why are reactors installed in series with shunt capacitors?
To lower the required circuit breaker ratings, decrease the inrush currents and decrease the voltage transients.
What is percent reactance?
The “percent” reactance is the ratio of the voltage drop across the Reactor to the voltage between line and neutral on three-phase circuits, or the voltage between the lines on single-phase circuits.
What are shunt capacitors used for?
They are used to improve voltage conditions within the system.
Where is it best to locate shunt capacitors and why?
It is best to locate shunt capacitors as close to the load as possible to release generation, system and transformer capacity and reduce system losses and optimizes improvements to voltage regulation.
How does a capacitor store energy?
They store energy in their electric field
How does the applied voltage affect a capacitor’s output?
The electric field storage is a function of the voltage squared of the system.
What is the relationship between line loss and power factor?
The current. Improving the power factor will reduce the current.
How are substation shunt capacitor banks installed?
They are usually mounted in three tiers. One phase per tier.
What is a surge diverter?
A piece of equipment which acts as a safety valve to discharge electrical surges.
How does a surge diverter operate?
When it exceeds its conducting voltage
What can cause a voltage surge?
Lightning, switching, etc.
What is the difference between a spark gap and an arrester?
An arrester has a characteristic element and spark gap.
What is an arrester counter and why are they used?
An arrester counter keeps track of how many times they have functioned, or how many times lightning has hit a lightning arrestor.
Why are spark gaps sometimes used instead of arresters at substations?
Spark gaps are used in stations where lightning is not a common occurrence or where sky wires are installed. They are much cheaper than arresters.
How can the shape of a spark gap help extinguish an arc?
The shape can help in lengthening the arc making it easier to extinguish.
What is the purpose of overhead distribution lines?
To deliver electricity from the substation to the customers.
What is the difference between primary and secondary conductors?
Primary conductors carry primary voltages and secondary conductors carry lower secondary voltages to customer.
What is conductor sag and what are some of the factors affecting conductor sag?
Sag is the downward curve of a conductor between poles. Some factors that can affect sag distance between poles, age of conductor, weather, etc.
What vertical and horizontal forces are distribution poles subject to?
Vertical forces include the conductors, insulators, transformers and other equipment that is mounted to the pole. These forces can be greatly increased in cold weather if ice forms on them.
Horizontal forces include the service drops, unbalanced conductor tension at corners and horizontal weight of components if the pole isn’t completely vertical. There are also stress from wind, conductor breakage and failure of supporting guys.
What is guy wire used for?
A guy wire is used when there is a 5° to 45° bend in the primary line or at the end of a single phase primary. It helps compensate for the horizontal stress on the pole
What is a dead end?
A dead end is the end of a single phase primary line or at a 90° corner. Suspension insulators are used.
What is a double dead end used for?
This is a 1Ø double dead end structure, and is used to:
• Facilitate the extension of an existing 1Ø line
• Provide a 1Ø primary cut, or two different circuits back to back
• Reduce strain on conductors, as in a conductor-lifting or "uplift" situation
What is a dip?
A dip is a pole that moves overhead primary to underground.
What is a joint-use pole?
A joint-use pole is carrying telephone cable and access boxes as well as BC Hydro distribution lines.
What is the purpose of an overhead disconnect switch?
Overhead disconnects are used for switching and isolating feeder circuits.
What System Operating Order describes the capabilities and limitations of the various overhead switch types?
What is a pothead disconnect switch?
A pothead disconnect is where the primary underground feeder cables terminate and go from underground to overhead or a dip/reverse dip pole connection is located. These are single phase operated, but some locations do have gang operated.
What is required to operate an in-line disconnect switch?
Loadbuster tool and minimum 3-person crew.
What is a SCADA switch?
Supervisory Control and Data Acquisition switches are switches that can be remotely controlled from the main control center or FVO. They also have sensors that send information back to the control center.
What is a load-buster tool?
Load-buster tool has the capability to interrupt up to 600A on overhead circuits up to 34.5 kV
What is a recloser and what is its purpose?
A recloser is an automatic device that will coordinate with protection and open in fault conditions and then attempt a reclose after a set amount of time.
What Distribution Operating Order describes the various types of reclosers as well as the criteria for blocking automatic reclosing to facilitate Live Line Permits and Assurance of No Reclose Permits?
1D-03 (1D-51 and 1T-18 would cover these topics as well)
How does the sensing and operation of a hydraulic recloser differ from that of an electronic recloser?
A hydraulic recloser operates on hydraulic principles and has no control box. Electronic recolser operates via a control box.
What affect does enabling the HLT feature on an HLT recloser have?
It will remove the coordination and create a faster trip if a fault is detected.
What is a sectionalizer and what is its purpose?
A sectionalizer is used in areas where there may be regular faults due to trees, etc. It will sectionalize the line by removing the line past it to hopefully remove the portion of the line that has the fault. Removing the fault allows the rest of the line to be brought back by the recloser.
Describe how a sectionalizer works in conjunction with a recloser.
It is set to remove a portion of the line by opening prior to the recloser locking out. Usually set to operate on the last operation of the recloser prior to the recloser lockout.
What is the purpose of an overhead distribution transformer?
To step down transmission voltage to usable distribution voltage for customers.
What are the most common single-phase and three-phase secondary voltages?
Most common single-phase are 120 V and 240 V. Most common three-phase are 240 V delta, 120/208 V wye and 347/600 V wye.
How does BC Hydro protect its overhead transformers and what advantage does this method provide?
They are usually protected with a fused cutout. This makes it very easy for a PLT to visually see the blown fuse when patrolling a line and allowing quick restoration of the customers.
How can a three-phase transformer bank be modified to operate with one transformer out of service?
Emergency connections available are the open wye-delta, open delta-delta, open wye-wye, and open delta-wye banks. BC Hydro generally uses the open wye-delta and open wye-wye.
Where are field voltage regulators installed?
Field voltage regulators are installed in locations on the distribution lines where the feeder voltage falls below a minimum allowable value during heavy load hours.
What must be done prior to bypassing a voltage regulator?
It must be put to NCO
What is a bidirectional voltage regulator?
A bidirectional voltage regulator is able to sense the direction of the power flow and regulate voltage in either direction.
Why are shunt capacitors installed along feeders?
They are used to counter the inductive reactance created by motors, etc by adding capacitive reactance to the system.
How do field shunt capacitors help voltage?
They reduce the total current flow, which reduces voltage drop in the line
What are oil switches?
Oil switches are single-phase devices for use on distribution pole-mounted capacitor installations. An oil switch consists of a set of electrically operated main contacts, plus auxiliary equipment, immersed in a tank of oil.
What are the methods used to control field shunt capacitors?
Voltage controlled type, current controller type and VAR controlled type.
What is an Independent Power Producer?
IPP’s are independent electricity producers within a franchised utility area.
How are Distribution IPPs connected to the power system?
They are connected to the system through distribution feeders.
Why would a transmission line’s protection trip the feeder circuit breaker associated with an IPP?
They trip to ensure the IPPs don’t back feed the faulted transmission lines.
What provision is in place to prevent an out-of-sync close on a Distribution IPP?
The IPP designated feeders will have voltage transformers on the load side of the feeder circuit breaker to detect voltage on the feeder and will be used in the supervisory closing control of the feeder circuit breaker.
What is the purpose of underground distribution lines?
To deliver electricity on the distribution system from the substation to the customer
What is feeder cable?
The feeder cable is the underground portion of the feeder that connects the substation to the first switchable device outside the station fence.
What are the basic classes of common cable construction?
There are two basic classes: single-conductor and three-conductor
What is cable splicing and what are the general steps involved?
Cable splicing is joining the ends of two cables together to make one cable. The steps involved are cable preparation, connection and then re-insulation
What is cable terminating and what functions must a termination perform?
Cable terminating is defined as installing a device on the end of a cable that allows the cable to be connected to the equipment in the system. Terminations must perform four functions:
- Provide stress relief at the end of the terminated shield
- Protect against tracking or burning on the exposed surface of the termination
- Keep moisture out of the cable
- Protect against flashover
Mark II switchgear is outfitted with what two devices? What is the purpose of each device?
They contain gang-operated switches used for switching and fuses for protection
How many compartments is the cabinet of a Mark II switching kiosk divided into to?
What Distribution Operating Order describes the operation of Vista switchgear?
Briefly describe some of the enhancements Vista switchgear provides over traditional Mark II switchgear.
Vista switches can be remotely switched and also have automatic controls built in. They also provide readings for the control center. Some features include:
· Automatic controllers are programmed to transfer on loss of source, voltage unbalance, or any source-side open-phase condition.
· Over-current lockout is programmed to prevent automatic transfer operation from closing a source switch into a fault.
· Motor operators on source switch ways are installed to provide automatic switching between the sources.
· Three-phase current sensing is used.
· The voltage on ways 1 and 2 are monitored from voltage sensors installed in the bushings of ways 1 and 2.
Describe a fault interrupter way.
Is a way with load interrupter switches in series with vacuum fault interrupter
What is the purpose of a junction box?
Junction boxes are used in URD to tap off the primary and feed underground distribution transformers. They also work as switching points to allow for isolation of URD sections or re-routing of power.
Describe load-break elbows.
Load-break elbows act as terminators, connectors and switches. They can be used to break up to 200A of current.
What is a dead-break elbow?
Dead-break elbow is used in URD and can carry up to 600 A load, but can't be used for load breaking. Must be deenergized to operate.
Describe a doghouse transformer.
A doughouse transformer is what used to be an overhead transformer that is now set at ground level and on a pad.
What is a dead-front transformer?
With dead-front transformers, the primary connections in the operating compartment are insulated and the outside of the connections are maintained at ground potential. The sealed tank holds the transformer, primary bus, fuses, and switch.
How do primary cables connect to dead-front transformers?
They are connected through load-break elbows
What type of service is provided by a Low Profile Transformer?
What type of service is provided by a Pad Mount Transformer?
Where in the province is the Dual Radial System unique to? Briefly describe the Dual Radial System.
Dual Radial System is unique to Vancouver. Dual Radial System consists of a running circuit and a standby circuit.
What is a Double Dual Radial vault?
This vault contains two running circuits and one standby circuit.
What operating drawings are unique to the Dual Radial System?
Dual Radial Diagrams, Dual Radial Standby Drawings and Vault Drawings are used for the Dual Radial System.
What Distribution Operating Order describes the Dual Radial switching and isolation procedures?
What Distribution Operating Order describes the issues associated with feeder paralleling between substations through the Dual Radial System?
How are switching instructions on the Dual Radial System issued to Power Line Technicians?
They are issues on Dual Radial Switching Cards
What BC Hydro action is required following customer vault maintenance?
Per 7D-DRV-01: “The Control Centre will instruct field personnel to inspect each vault subsequent to customer work to ensure switches have been restored to proper operating status prior to issuing any SPG’s which depend upon isolation in that vault. The Control Centre will note which vaults have been worked upon and have not been checked by authorized personnel.”
What is a Cable Transition Module?
Cable Transition Modules are points on the Dual Radial System designed to provide a means of tying standby cables from different substations together in order to facilitate emergency load transfer.
How is customer vault isolation accomplished on the Dual Radial System?
A BC Hydro representative will isolate all potential sources to the Running circuit.
All vaults normally supplied from the Running circuit will be momentarily paralleled with the Standby circuit through the vault switches and then transferred to the Standby supply.
For vaults connected to the Running circuit but not scheduled for maintenance, Locks and both GOI and T&W tags will be removed from all of the closed customer vault Standby switches and placed on all of the open customer vault Running switches and on all other potential infeeds.
For the vault where switch maintenance will take place, the Running side disconnect switch to be maintained by the customer will be left open but will not be locked or tagged.
How are BC Hydro owned street vaults typically isolated on the Dual Radial System?
The switch that is being maintained will have the load break elbows opened and tagged Test & Work as a part of the isolation.
What two network system configurations are found in Victoria and what voltage levels do they operate at?
• The 120/208 volt Integrated Network
• The 347/600 volt Spot Network
What Distribution Operating Order describes the Victoria Underground Network?
What substation feeds the Victoria Underground Network and how many feeders does the network consist of?
Horsey substation has seven 12kV feeders for the Victoria Underground Network
Outside of Victoria, where in the province is the only other spot network located?
Vancouver’s West End
What are the required isolation points for a network feeder cable?
Isolation of feeder cables is accomplished by opening the substation feeder disconnect and all the associated network transformer high-voltage disconnect switches on that circuit.
What is the main advantage of a network system?
The main advantage is continuous power in the case of a single fault.
T or F – Network transformer high-voltage disconnect switches are capable of de-energizing network transformers.
Describe the function of a network protector.
The transformer network protector is an automatic device designed to protect and isolate the secondary network and prevent backfeed into the transformer and primary cable.
What are the required isolation points for a network transformer?
From 7D-HSY-01: To perform any work in this chamber, including changing the oil level for samples or filling, isolation is achieved by de-energizing and isolating the connected feeder cable and removing the connected transformer network protector breaker fuses.
When are LLP and ANRP permits to be in by?
All requests shall be submitted to the Control Centre not more than 5 days in advance nor later than 20:00 hours of the previous working day of the permit date.
What is proper work location description for LLP request from the field?
Station name, feeder name and location as follows:
a) Between switches 'X' and 'Y' or more switches listed if necessary; OR
b) From switch 'Y' to the end of the circuit; OR
c) For work on switch 'X';
d) For work on station XXX, feeder 25Fyyy or 12Fyyy if there is no field recloser on that feeder.
What is proper work location description for ANRP request from the field?
Station name, feeder name and
a) On "A" (St./Rd./Hwy) between device "X" and "Y"; OR
b) On "A" (St./Rd./Hwy) from device "Y" to the end of the circuit; OR
c) Accurate physical location (referenced to cross streets/compass bearing or on X Ave. between A & B street).
What should always be recorded by the person taking out an ANRP or LLP?
• equipment designation
• time the permit is issued or cancelled
• the PIC’s name
What should a Load Operator always reference prior to switching in a substation?
Load Operator should always reference the Stating Operating Order prior to switching in a substation
Describe the “5 R’s” of switching.
Readings: All associated readings on ccts being switched from the max demand sheets
Ratings: Ratings of all equipment involved
Recloser: Is there a recloser on the ccts being switched, is it auto
Reactors: Are there reactors on the ccts being switched, what is there impedance
Regulators: Are there voltage regulators on the ccts being switched, are the ccts same source or different source? Field parallel or station parallel for NCO rules
What is a low-side or low-voltage tie?
A low-voltage tie is when two transmission lines are tied together on the secondary side (or low side) of the station transformers instead of the primary side (or high side)
What are the two general types of isolation points? Give examples of each type.
The two types are:
Conventional: disconnect switches, circuit switchers, fuses, rack-out cct breakers, etc.
Line Cuts: Temporary line cuts like riser, a section of bus, a flying tap, a jumper between two dead-ends, a drop lead, etc.
What must be done to an isolation point in order for it to be used in support of a Safety Protection Guarantee?
The isolation point must be tagged in the field and on the PSSP MIMIC display
True or False – Voltage Transformer secondaries are Level 5 equipment and therefore, when located inside a Clearance zone, should be opened and tagged Self Protection to prevent backfeed prior to going to work.
Why are gas relays opened and tagged Caution when isolating a substation power transformer?
To make sure they don’t accidently operate while crews are working around or on transformers.
How is a transfer bus used to maintain service to a feeder position that is coming out of service?
The transfer bus allows two feeders to be paralleled together and then carry the feeder being taken out of service on the transfer bus by breaking the parallel
Describe how series reactors can affect load sharing when paralleling feeders.
The impedance of the reactors will determine how the current will flow once the parallel connection is made
Where is the criteria listed for D3 switching involving series reactors?
Define feeder cable.
Feeder cable is the underground portion of a feeder that delivers power from the substation to the first switchable device in the field.
Where is the isolation of a feeder cable typically mimicked?
Both AREVA and POCC
How do cablemen request for station risers to be removed in advance of planned feeder cable work?
They will add it to the comments section of the Outage Request Form in CROW
How is the removal of station risers mimicked?
It is mimicked in AREVA by toggling the appropriate station pothead symbol to “risers removed”
What is ferroresonance?
It is a phenomenon that can occur on electric circuits that contain a capacitance in series with a nonlinear saturable inductance. When ferroresonance occurs, it is typified by unpredictable nonlinear over voltages with high harmonic content and can lead to equipment damage and failure.
Where is the feeder cable switching procedure to be followed by Load Operators found?
What must be done prior to opening pothead sleeves on a feeder cable and why?
Prior to pulling the pothead sleeve, confirm current to be less than 2 amps. This procedure ensures that load will not be dropped or a parallel broken on the sleeve.
What is a standby circuit?
A standby circuit is a dedicated circuit that carries no load and that can parallel two feeders in the field via a NO switch
How can a standby and partial standby circuits be identified on AREVA and POCC?
A solid red box around the feeder text
How can maximum demand readings be used to help make operational decisions?
They will help in the calculations to make sure that equipment ratings or relay settings will not be exceeded
How can a feeder’s kVA report be used to help make operational decisions?
When sectionalizing and off-loading a feeder it will allow the operator to open and close switches with confidence that equipment ratings and relay settings will not be exceeded.
Name 6 criteria for LLP?
1 Before electrical journeypersons begin live line work or hazardous tree trimming near energized lines, they shall obtain a Live Line Permit from the PIC.
2 Only qualified electrical workers shall be
authorized to receive a Live Line Permit.
3 Before issuing a LLP PIC must ensure reclosing devices are off.
4 The PIC shall have a means of direct
communications with the permit holder.
5 In case of de-energization, the PIC shall
contact the permit holder before the circuit or equipment is re-energized, unless the circuit or equipment has been de-energized by other than its own protection or the cause is verified by a qualified person.
6 When a Live Line Permit is in effect, the
circuit involved shall not be paralleled without notifying the permit holder.
Name 4 criteria for ANRP?
1 An Assurance of No Reclose Permit is issued by the PIC to qualified electrical or nonelectrical workers for work near energized conductors or equipment when it is required that reclosing not occur if automatic tripping takes place.
2 Before issuing an Assurance of No Reclose Permit, the PIC shall make arrangements to prevent immediate re-energizing of the circuit or equipment (including any required Guarantees of No Reclose from other operating authorities), and shall retain Operating
3 The PIC shall have a means of direct
communications with the permit holder.
4 In case of de-energization, the PIC shall
contact the permit holder before the circuit or equipment is re-energized, unless the circuitor equipment has been de-energized by other than its own protection or the cause is verified by a qualified person.