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What is the purpose of underground distribution lines?
- Feeder Cable:
- -To deliver electricity on the underground distribution system from the substation to industrial, commercial, residential customers
- Primary Cable:
- -To route the power to service transformers and secondary distribution cables
What is feeder cable?
- The underground portion of a feeder that delivers power from the substation pothead to the first switchable device in the field
- (usually pothead disconnect switch)
What are the basic classes of common cable
- PILC: Paper Insulated Lead Cable
- -all three phases ‘belted’ together in one lead sheath
- XLPE: Cross Linked Polyethylene (Plastic)
- -single conductor cable with larger diameter thermoplastic insulation
What is cable splicing and what are the general steps involved?
- -Cables must be connected and joined (usually in manholes) to provide a continuous power feed to reach the customer
- -General steps involve peeling back the layers of the cable, making the splice of the conductors, and rebuilding the cable layers back up to specifications
What is cable terminating and what functions must a termination perform?
- Installation of a device (elbow/ terminator/ pothead) at the end of a cable that allows
- connection to equipment on the system
- 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?
- Switches: provide incoming feed and capability of feeding through and continuing circuit
- Fuses: allow power to be tapped from switchgear to feed transformers and customer switchgear
How many compartments is the cabinet of a Mark II switching kiosk divided into to?
Four Separate Compartments
What Distribution Operating Order describes the operation of Vista switchgear?
Briefly describe some of the enhancements Vista switchgear provides over traditional Mark II switchgear.
- -Visual indication of switch position (closed, open, grounded)
- -SF6 gas as arc interrupting medium
- -Voltage indication and low voltage phasing
- -multiple switching configurations (up to 5 ways)
- -microprocessor based allows for fault detection, automatic transfers on loss of source
- -some Vistas are capable of supervisory control
Describe a fault interrupter way.
- The microprocessor based over-current control detects fault current on a specific ‘way’
- The ‘way’ can be automatically switched open
What is the purpose of a junction box?
- An underground distribution switching device that is in the form of a pad mounted kiosk or underground vault
- Used to tap off the primary and feed underground distribution transformers(single or three phase)
Describe load-break elbows.
Used to terminate primary cables and provide a connection that can be used to break current (200 Amps)
Describe a doghouse transformer.
- -Live-Front Free-Standing Transformer (1FS or3FS) with exposed primary connections
- -Basically, an overhead style transformer inside a metal enclosure
What is a dead-front transformer?
- -The primary connections are insulated (not exposed) and the outsides of the connections (elbows) are maintained at ground potential
- -LPTs and PMTs are dead front transformers
How do primary cables connect to dead-front transformers?
- -Load Break Elbows terminate the cables and are used to make the connections to the transformer bushings
- -Load break elbows can break current up to 200 Amps
What type of service is provided by a Low Profile Transformer?
Single phase service (designed to create underground loops)
What type of service is provided by a Pad Mount Transformer?
Three phase service (designed to connect radially or to create an underground loop)
Where in the province is the Dual Radial System unique to?
Downtown Vancouver (DGR, CSQ, MUR)
Briefly describe the Dual Radial System.
- -To reliably serve large customers, their vaults are provided with two feeds. One normal source, and one standby (normally open)
- -The Customer Vault essentially provides a loop path between two primary feeder sources.(same substation and in-phase)
What is a Double Dual Radial vault?
The Customer Vault is provided with two running circuits and one standby
What operating drawings are unique to the Dual Radial System?
- -Dual Radial Diagrams
- -Dual Radial Standby Drawings
- -Vault Drawings (Customer and Street Vaults)
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 is customer vault isolation accomplished on the Dual Radial System?
- -BCH retains O/A of running and standby disconnect switches
- -Standby disconnects are normally left locked open and tagged (T&W and GOI) to accommodate the numerous isolation points when issuing an SPG
- -Standby disconnects that are not normally locked open and tagged are listed in 7D-DRV-01 and noted on POCC (but will require locking open and tagging to support an SPG)
How are BC Hydro owned street vaults typically isolated on the Dual Radial System?
- Similar to isolating a Customer Vault, the isolation will include the circuit’s isolation points outside of the vault,
- -But will be completed by opening and tagging the load side-elbows of the disconnect switch (avoiding a customer outage)
How are switching instructions on the Dual Radial System issued to Power Line Technicians?
- The PIC uses Dual Radial Switching Cards to issue switching instructions
- -Every Dual Radial circuit has its own unique Switching Card template and Switching Card number
- -All the vaults and associated switches on the circuit are listed
What BC Hydro action is required following customer vault maintenance?
Field personnel must inspect the vault to ensure switches have been restored to proper operating status prior to issuing any SPGs which depend upon isolation in that vault
What is a Cable Transition Module?
- CTMs are points on the Dual Radial System designed to provide a means of tying standby cables from different substations together to facilitate emergency load transfer
- -Considered as permanent line cuts
- -SPG on both circuits required when connecting through a CTM
What two network system configurations are found in Victoria and what voltage levels do they operate at?
Integrated Network: 120/208 v ( approx.. 94 500 kVA transformers)
Spot Network: 347/600 v ( 6 Spot Networks – two 1500 kVA transformers each)
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
- Seven 12 kV primary feeders
What is the main advantage of a network system?
- -The system can sustain a primary fault without any disturbance or supply loss to customers
- -The fault is cleared by the substation breaker jointly with the network protectors
- -Parallel secondary runs have sufficient capacity to handle the extra load placed on them
Outside of Victoria, where in the province is the only other spot network located?
West End of Vancouver (very small 2 vault network)
What are the required isolation points for a network feeder cable?
- 1. The substation feeder disconnect switch
- 2. All associated network transformer high-voltage disconnect switches on that circuit
T or F – Network transformer high-voltage disconnect switches are capable of de-energizing network transformers.
What are the required isolation points for a network transformer?
- 1. The transformer high-voltage disconnect switch (Locked Open and tagged only after de-energizing the feeder cable)
- 2. The secondary breakers and associated fuses of a network transformer
Describe the function of a network protector.
- -An automatic device designed to protect and isolate the secondary network and prevent backfeed into the transformer and primary cable
- -Automatic electrically operated air circuit breaker with a tripping mechanism
- -The entire assembly is mounted on a roll-out unit, housed in a submersible enclosure
- -Isolation of the protector is achieved by removing the bottom solid links, and racking out the protector assembly
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