What is the purpose of underground distribution lines?
Underground distribution cables deliver electricity on the distribution system from the substation to the many industrial, commercial, and residential customers.
What is feeder cable?
Feeder cable is the underground portion of a feeder that delivers power from the substation (from the substation pothead) to the first switchable device in the field.
What are the basic classes of common cable construction?
The basic classes of common cable construction are: single-conductor and three-conductor.
What is cable splicing and what are the general steps involved?
Splicing is the joining and connecting of cable.
Generally, various layers of the two cables being spliced are removed until the conductor is exposed, then the conductors are joined, and the layers are rebuilt using various tapes and tubes. There are very precise measurements and dimensions involved in building a successful and quality splice.
What is cable terminating and what functions must a termination perform?
Cable terminating is 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?
Mark II switchgear is outfitted with a combination of switches and fuses.
The switches on one side provide incoming feed and the capability of feeding through and continuing the circuit. Or, if only one switch, just an incoming feed.
The fuses on the other side allow power to be tapped from the switchgear to feed transformers and customer switchgear.
How many compartments is the cabinet of a Mark II switching kiosk divided into to?
The Mark II switching kiosk is divided into 4 compartments for fuses and one for switch(es).
What Distribution Operating Order describes the operation of Vista switchgear?
1D-08 Vista Underground Distribution Switchgear Operation.
Briefly describe some of the enhancements Vista switchgear provides over traditional Mark II switchgear.
• Vista switchgear have load-interrupter switches “switches” and load-interrupter switches in series for vacuum fault interrupters “fault interrupter ways/load taps”.
• Visible indication of switch positions
• Voltage indication and low-voltage phasing
• SF6 gas
• Fault interrupter ways are controlled a microprocessor
Describe a fault interrupter way.
A fault interrupter way is the switchgear in a vista switch that is a load-interrupter switch in series with a vacuum fault interrupter. They are known as “fault interrupter ways” or “load taps”. Fault interrupter ways have 200 amp load-break bushings for their cable connects.
Fault interrupter ways are controlled by a microprocessor based over-current control which can be programmed to emulate various fuse curves as well as several IEC curves.
What is the purpose of a junction box
Junction boxes are used on underground residential distribution (URD) to tap off the primary and feed underground distribution transformers. They also work as switching points to allow the isolation of URD sections or the re-routing of power.
Describe load-break elbows.
Load-break elbows are used to terminate primary cables and provide a connection that can be used to break current, typically up to 200A. Both the junction kiosks and vaults contain junction bars into which load-break elbows are inserted, providing load-break switching.
Load break elbows have two white bands on the body of the elbow.
Describe a doghouse transformer.
“doghouse” or live-front transformers is an overhead-style transformer inside a metal enclosure set at ground level on a pad.
What is a dead-front transformer?
A dead-front transformer has the primary connections in the operating compartment insulated and the outside of the connections are maintained at ground potential.
The transformer is tapped off the internal bus (energized from either primary bushing). The transformer fuse is connected between the internal primary bus and the transformer so when an internal fuse blows, the primary bus inside the transformer is still energized and only the transformer primary coil has been interrupted.
How do primary cables connect to dead-front transformers?
Primary cables connect to dead-front transformers through load-break elbows. Load-break elbows are used to terminate primary cables and provide a connected that can break current (typically 200A). These elbows can be used for switching and isolation of the primary circuit.
What type of service is provided by a Low Profile Transformer?
Single phase service
What type of service is provided by a Pad Mount Transformer?
Where in the province is the Dual Radial System unique to?
The Dual Radial System is unique to Vancouver.
Briefly describe the Dual Radial System.
A Dual Radial System consists of a running circuit and a standby circuit. Each customer provides a loop path between two primary feeder sources. The customer’s main tap supply is located between two primary disconnect switches, one of which is NO. Through switching, the customer supply can be changed from the normal to the alternate supply.
What is a Double Dual Radial vault?
Double Dual Radial vaults have two running circuits and one standby circuit.
What operating drawings are unique to the Dual Radial System?
Dual Radial Diagrams and Dual Radial Standby Drawings are used to represent the Dual Radial System.Vault drawings represent the numerous customer and street vaults sourced from the Dual Radial System.
What Distribution Operating Order describes the Dual Radial switching and isolation procedures?
7D-DRV-01 (Dual or Double Dual Radial Vaults) 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?
7T-CSQ_MUR_DGR-01 (Cathedral Square, Murrin, and Dal Grauer Feeder Paralleling Issues) 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?
Customers will contact BC Hydro Control Centre prior to commencing any switching that impacts the normal operation of the vault switches. Customers working on their own equipment shall apply their own locks and tags in accordance with Work Safe BC OHS Regulations.
For performing line-end disconnect switch maintenance the customer will require a Guarantee of Isolation (GOI) from the BC Hydro PIC prior to isolating the equipment.
How are BC Hydro owned street vaults typically isolated on the Dual Radial System?
For entrance switch maintenance in a street vault, switching will be done the same as any other vault with the exception that street vaults have load break elbows located on the load side of the entrance disconnects which are used in the isolation of the switch. The switch that is being maintained will have the load break elbows opened and tagged Test & Work as a part of the isolation. Generally no outage has to be taken to the vault while undergoing switch maintenance.
How are switching instructions on the Dual Radial System issued to Power Line Technicians?
Switching instructions on the Dual Radial System are issued to Power Line Technicians with a Switching Card.
A Switching Card lists all the vaults and associated switches on the circuit with each switch listen as either a “Running Circuit” or a “Standby Circuit”.
Switching Cards are issued and returned in a similar manner as a Switching Order, except the switching steps are not individually defined.
What BC Hydro action is required following customer vault maintenance?
The Control Centre will note which vaults have been worked upon and instruct field personnel to inspect the vault to ensure that the switches have been restored to proper operating status prior to issuing any SPG's which depend upon isolation in that vault.
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 (DGR & CSQ) in order to facilitate emergency load transfer. They are normally considered to be permanent line cuts and not required as isolation points. In order to connect two cables together through a CTM, a SPG with an isolation zone encompassing both standby cables is required.
What two network system configurations are found in Victoria and what voltage levels do they operate at?
Integrated Network: 120/208V
Spot Network 347/600V
What Distribution Operating Order describes the Victoria Underground Network?
7D-HSY-01 describes the Victoria Underground Network
What substation feeds the Victoria Underground Network and how many feeders does the network consist of?
Horsey (HSY) substation consists of seven 12kV feeders and feeds the Victoria Underground Network.
What is the main advantage of a network system?
The main advantage of a network system is that single failures can occur in the primary system, transformers, or individual secondary cables without interrupting the power flow to customers.
Outside of Victoria, where in the province is the only other spot network located?
The only other spot a Network system is located is a small spot network in 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.
T or F – Network transformer high-voltage disconnect switches are capable of de-energizing network transformers
False, the disconnect switch is not rated to interrupt the magnetizing current of the transformer. It must not be switched from closed to open or ground unless the network transformer is de-energized.
What are the required isolation points for a network transformer?
Isolating a network transformer requires de-energizing the feeder cable, and then opening the associated transformer high-voltage disconnect switch and removing the network protector breaker fuses.
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.
A network protector is a large reverse-current sensing circuit breaker.