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What should a Load Operator always reference prior to switching in a substation?
The associated Substation Operating Order.
Describe the “5 R’s” of switching.
- Reclosing - All associated reclosing must be turned off prior to commencement of switching.
- Reactors - The impedance of reactors affect how they share current. This must be taken into consideration to plan the order in which switching can be done if it can be done at all with the available switches’ ratings.
- Regulators - Voltage Regulators must be placed in NCO prior to switching.
- Readings - Readings are required in order to know what currents will be flowing during switching.
- Ratings - Rating of equipment must be adequate to support the currents that will flow during and after switching.
What is a low-side or low-voltage tie?
A low-side or low-voltage tie is when high-voltage circuits that are normally tied together directly, are tied together through low-voltage ties as a result of switching.
What are the two general types of isolation points? Give examples of each type.
Two general types of isolation points are conventional and temporary line cuts. Examples of conventional isolation points used by a PIC to establish a Safety Protection Guarantee are: a cutout a disconnect switch a circuit switcher a racked-out circuit breaker On the high voltage electric system a temporary line cut is normally a fixed, non-operable component such as a riser, a section of bus, a flying tap, a jumper between two dead-ends, a drop lead, etc., that has been removed or securely tied back to provide visible separation between conductive elements.
What must be done to an isolation point in order for it to be used in support of a Safety Protection Guarantee?
It must be enforced by hanging the appropriate “Do Not Operate” tag.
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.
False – As per 1T-03 “The isolation point must be tagged with a Safety Protection Guarantee (T&W or CL) Tag. Use of a Self Protection Tag is not acceptable. The PIC must not issue the SPG until this isolation has been completed“.
Why are gas relays opened and tagged Caution when isolating a substation power transformer?
Gas relays are a form of non-electrical protection. These relays are opened and tagged “Caution” so that they do not inadvertently operate while work is being performed on the equipment.
How is a transfer bus used to maintain service to a feeder position that is coming out of service?
A transfer bus is an alternate or standby bus that can be used to tie feeders together within the substation or off-load a feeder position onto the transfer bus itself. The transfer bus is tied to each feeder position via the D3’s. When a feeder position is coming out of service, it can be paralleled with the transfer bus through the feeder position’s D3 prior to being switched out. This will maintain continuity of service to the customers being supplied by the OOS feeder position. Parallel can be made by closing the D3 if it is rated to do so. If the D3 is unable to make parallel, a transfer bus carrying no load can be de-energized via the t-bus CB, re-energized via the feeder position’s D3, and then a parallel can be made between the t-bus and feeder position using the t-bus CB again (this is the preferred method as CB’s are made to handle opening and closing onto high current levels).
Describe how series reactors can affect load sharing when paralleling feeders.
If two series reactors with different impedances are in parallel, current will flow according to ohm’s law. The lower impedance reactor will carry more of the shared current while the higher impedance reactor will carry less.
When two reactors of the same impedance are in parallel, they will share the current equally.
Where is the criteria listed for D3 switching involving series reactors?