Selector Switchs and HV Switches Flashcards
1
Q
How would you handle setting an RSS during a routine bypass with standard busti electromechanical relays
A
- Information on the bus tie relays should be in the station instructions.
- The RSS and SSS for a bust I will be in the standby position when the relays are protecting the aux bus only.
- When performing a bypass the RSS and SSS will have changes made when the bus type PCB is in the open position prior to making or breaking parallel.
- The SSS is used to select the correct internal relay settings in order to protect the bypassed line.
- If there are too many positions then a RSS will be needed to select between the multiple sets of relays on the bus tie.
2
Q
How would you handle setting an RSS on a redundant set of SEL-121G relays
A
- The RSS on a redundant set of relays like the SEL 121g (and others) is used to cut out one set for maintenance and leave the other set in service.
- It is a 3 setting switch; SET 1- set one in service/set 2 off, SET 2- set 2 in-service/ set one off, OFF- both sets off.
- Coordinate with SPC to set the RSS to the correct setting for their work.
- Simply turn the switch to set that will remain in service
3
Q
How would you handle setting a RSS on a 500 KV position
A
RSS on a 500kV positions Works similar to lie to those for redundant sets of relays.
- There is typically one RSS for each set of relays to select the PCB to be tripped, including transfer trip.
- If the relays have transfer trip associated with them it will need to be cut out for the position that will be cut out.
- Usually this is done prior to making changes on the RSS but there are some exceptions be sure to check the station instructions for that position.
4
Q
How would you handle setting a RTS on a Transformer bank with redundant differential relays, phase overcurrent relays, and a neutral ground overcurrent relay
A
- RTS’s transfer the relay inputs from the line/Transformer PCB CT to the associated bus tie PCB CT.
- Always verify with prints to determine the inputs to various relays and zones of protection for relays associated with the bank.
- When bypassing the bank the differential relay may need to be cut out if one side’s CT inputs are from the CT on the PCB to be bypassed and the RTS does not transfer the relay inputs to the bus tie. In some cases the RTS will cut out the relay automatically when placed in the bus tie position but you may still need to cut out the relay manually because it will see a 100% differential and keep the coil energized the entire time which can cause damage to the relay, station instructions should give information on this as determined by SPC.
- Typically ground and phase overcurrent relays will remain in service because they usually transfer via the RTS
5
Q
What is a setting selector switch (SSS) and what does it do
A
- The use of the SSS gives the switchman the ability to make changes internal to a relay and is usually associated with a bustie PCB in order to properly adjust protection of a certain line or piece of equipment.
- Most substations have a SSS associated with SEL relays, which allows it to tap selectable setting groups that allow the relay to be able to protect lines and Transformers of different lengths and values that are to be carried by the bus tie breaker. As many as eight settings are available.
- If the PCB is energizing the Aux bus only the SSS should be left in the standby position if available (if no dedicated standby position then the shortest line is usually designated bie SPC as the standby)
6
Q
What is a relay transfer switch (RTS)
A
Most commonly associated with a line or Transformer position in order to transfer a transfer trip scheme from the normal PCB to the bus tie PCB.
- Can also be used to create a parallel path where both line PCB and bus tie PCBs are placed in the same transfer trip scheme.
- May be used to cut out Transformer differential relays
7
Q
What is a relay selector switch (RSS)
A
- Allows for Relay maintenance to be performed on redundant relay sets while still offering protection by isolating only one relay at a time.
- Has three settings: set 1 (with set 2 off) , normal (both sets in Service) , set 2 (with set 1 off).
- RSS associated with a bustie PCB allow the switchman to choose the protection that is adequately needed from a relay group or group of relays in order to protect a particular line or Transformer to be bypassed.
- If you have more line positions than SSS options, a RSS could be used to cut out a set of relays allowing the expansion into the other set.
- Example: you have 8 settings associated with set 1 and two settings associated with set to if you had 10 positions, the RSS would cut out that one allowing for the selection of the correct setting on the associated SSS for the set and service
8
Q
What is the purpose and general operation of arcing horns
A
- Arcing horns allow current to flow across the arcing horns during opening and closing operations so that the arc will happen across them instead of the main contact.
- Are the simplest additions to a disconnect switch consists of a stationary horn attached to the harp and immovable for an attached to the blade.
- Made of a material that can withstand arcing and are easier to replace if damaged.
- When added to a basic disconnect switch it allows it to interrupt limited charging current associated with the substation buses or very short transmission lines, and some parallel circuits within the substation
9
Q
What are the purpose of surge suppressing resistors
A
- Purpose is to reduce the effect of transients by adding resistance in series with the lump-sum Transformer or bus capacitance.
- Slowing down the frequency of the transients by increasing the RC time constant.
- These transients occur on 500 KV when switching long sections of bus or a Transformer and can apply unwanted high voltage has to Transformer insulation and induced voltages into control circuits.
- Consists of a number of stacked resistor modules in series.
10
Q
What is the purpose and general operation of a quick break attachment
A
Enhances the line droping capability of a disconnect.
-Two kinds blade and harp mounted. -Basically adds speed to the opening in order to extinguish the arc faster
11
Q
What is the purpose of General operation of auxiliary interrupters
A
- Used to improve the current interrupting capability of a disconnect.
- Primarily for Loop breaking but can also be used for line dropping if there are enough units.
- The arc is extinguished within the interrupting unit, which can be either SF6 insulated or a vacuum, across internal contacts causing there to be no external arc
12
Q
What is the purpose and general operation of a motor operated disconnect
A
- Uses an electric motor to rotate the vertical operating linkage of a disconnect. -It is contained in the cabinet at the base of the switch.
- Primarily used for 500 KV and some 230-kv disconnects.
- Can also be used on lower voltages as part of Auto sectionalizing schemes.
13
Q
Explain the purpose and general operation of hot stick operated disconnect links
A
- Used to isolate power system equipment, can also be used to isolate switchgear like circuit switchers.
- Not designed to break current including load, magnetizing, or charge being current.
- If current cannot be interrupted by means of a load break disconnect before opening a hot stick link than an outage must be taken.
- BPA uses 4 types: spring hinge, sliding hinge, telescoping, and line jumper
14
Q
Explain the purpose and general operation of hot stick operated disconnect switches
A
- Developed as an alternate to the hot stick link.
- Manually open and closed using a hot stick instead of an operating mechanism.
- A ring on the blade of the disconnect allows opening and closing of the device as well as rotating and locking the blade into the harp.
- A hot stick operated safety latch allows the operator to lock the switch in the open position as well as provide point for hanging tags.
- Not designed to break current including load magnetizing or charging current.
15
Q
What are some typical applications for the Relay selector switch
A
- Bustie positions to select a relay package (most often when the bus tie relays are electro-mechanical or there are too many line positions for one SSS).
- Redundant relay applications (two relays of the same type).
- 500kv relay applications with one RSS on each set of relays to select the power circuit breakers to be tripped, including transfer trip in some instances
