Transmission Switching Procedures (115kV)

Line Testing

Where possible, 115kV line testing for new construction or energizing new or rebuilt station transformers should be accomplished by testing from a “clean” line (that is, a line with no stations or load) with that line on Hot Line Hold.

District Types and Ratings of 115kV Switches

“A” SWITCHES

SWITCH TYPE
“A” Disconnect Switch with Standard Arcing Horns

LOAD DROPPING CAPABILITIES ARE:

  • Disconnecting circuit breaker(s).
  • Breaking one transformer’s magnetizing current.
  • Breaking charging currents on sections of line up to 2 miles.

LOAD PICKUP CAPABILITIES ARE:

  • Energize circuit breakers.
  • Energize one unloaded transformer.
  • Energize unloaded sections of line up to 2 miles.

“B” SWITCHES

SWITCH TYPE
“B” High Speed Arc Restrictor Switch

LOAD DROPPING CAPABILITIES ARE:

  • Breaking one transformer’s magnetizing current.
  • Breaking charging current of lines up to 20 miles in length.

LOAD PICKUP CAPABILITIES ARE:

  • Crank Handle—Line and/or one unloaded transformer making parallel between two energized lines.
  • Swing Handle—Load up to the rating of the switch but no more than 100MW or making parallel between two energized lines.
  • Motor Operator—Load up to the rating of the switch or making parallel between two energized lines.

“C” SWITCHES

SWITCH TYPE
“C” Loop Breaking Interrupter Switch

LOAD DROPPING CAPABILITIES ARE:

  • Breaking loop current in loop feeds but not for load dropping.

LOAD PICKUP CAPABILITIES ARE:

  • Crank Handle—Line and/or one unloaded transformer making parallel between two energized lines.
  • Swing Handle—Load up to the rating of the switch but no more than 100MW or making parallel between two energized lines.
  • Motor Operator—Load up to the rating of the switch or making parallel between two energized lines.

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“D” SWITCHES

SWITCH TYPE
“D” Load Interrupter Switch

LOAD DROPPING CAPABILITIES ARE:

  • Breaking transformer magnetizing currents and transformer load current.
  • Breaking line charging currents.
  • Breaking loop feeds or radially-fed loaded lines up to the rating of the switch.

Note: When used for transformer protection, the switch will have a fault interrupting rating.

LOAD PICKUP CAPABILITIES ARE:

  • Crank Handle (S&C switches or Siemens Allis Switches)—Load up to the rating of the switch, but not more than 100MW or making parallel between two or more energized lines.
  • Crank Handle (All other switches)—Line and/or one unloaded transformer or making parallel between two energized lines. (Not commonly found)
  • Swing Handle—Load up to the rating of the switch but no more than 100MW or making parallel between two energized lines. (Not commonly found)
  • Motor Operator—Load up to the rating of the switch or making parallel between energized lines.

“CIRCUIT BREAKER”

SWITCH TYPE
“CIRCUIT BREAKER” Oil and SF6 Circuit Breakers

LOAD DROPPING CAPABILITIES ARE:

  • Breaking any load up to the rating of the switch.

LOAD PICKUP CAPABILITIES ARE:

  • Any pick-up conditions up to the rating of the circuit breaker.

To Clear a Motor-Operated Switch

The following procedures describe basic switching orders for the overhead and underground distribution systems. These procedures can be modified to fit particular circumstances.

A clearance shall not be issued on any line that has a motor-operated switch on any SCADA terminal until the following switching has been done. These switches are cleared for two basic reasons:

  • Used for a clearance point.
  • Cleared for maintenance.

Follow these procedures to clear a motor-operated switch.

Step 1: Employee

  • Submits a completed Switching Request to the Energy Control Center (See Section A)

Step 2: System Operator

  • Reviews the Switching Request and verifies the exact location.
  • Verifies the electric system configuration to accommodate the request.
  • Remotely opens the switch via SCADA (if applicable) or orders switch to be manually opened.
  • Verify the switch is open, orders switch to be de-coupled, and the motor operator locked and tagged with a Master Safety Card.
    Note: The employee will have the authority to open the DC supply to the motor operator. The employee will notify ECC prior to proceeding as an alarm may be received via SCADA.

Step 3: Employee

  • Verifies the switch(es) to be open, de-couples the motor operator, locks the switch open, and tags the device with a Master Safety Card.
    Note: The employee will have the authority to open the DC supply to the motor operator. The employee will notify ECC prior to opening the DC power as an alarm may be received via SCADA.
  • Check for SF6 gas targets. (If it is a circuit switcher)
  • Verifies with ECC that the switch has been opened, locked, decoupled, and tagged.

Step 4: System Operator

  • Proceeds with the Switching Order and issues the clearance.

Step 5: Employee

  • Receives clearance and proceeds to Verify, Test and Ground, if applicable.
  • Completes repairs and makes the switch ready for service.
  • Releases the clearance and notifies the System Operator that they removed their personal grounds, and all personnel and equipment are in the clear.

Step 6: System Operator

  • Orders all cards removed on the open switch.
  • Orders switch to be unlocked, recoupled and closed.

Step 7: Employee

  • Verifies the switch to be open and removes all cards.
  • Unlocks and re-couples the motor operator. (DC power restored) Notifies ECC.
  • Verifies that the switch is closed via SCADA or manually closes the switch.
  • Verifies to ECC that the switch is back to normal.

Automatic Sectionalizing Scheme

Automatic switching is installed to quickly sectionalize and restore sections of high voltage lines, and to improve service reliability to distribution substation loads. When used in conjunction with SCADA, automatic switching should assist the System Operator in determining which section(s) of line is faulted, enabling faster customer restoration.

Automatic switching is any circuit breaker, load-break, or disconnect switch that will open or close automatically in response to loss of potential (voltage) or re-energization of potential.