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Sub Operations Step 4 > BFRs > Flashcards

BFRs Flashcards

1
Q

Explain the theory of operation for different types of BFRs used in your district (OTM 3.3-13)

A

The purpose of a breaker failure relay (BFR) is to deft if a breaker has failed to interrupt fault current, and then to trip other PCBs in order to isolate the fault and the failed PCB
There are several ways in which a PCB can fail such as:
Failure in the trip circuit
Burned out trip coil
Mechanical failure
Only partial opinion of one or more heads

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2
Q

Describe the conditions that must be met for an electromechanical BFR to operate. (OTM 3.12-8)

A

the PCB must be closed
A fault must be decked by the line relays and the BFR
The PCB fails to operate clearing the fault
The BFR time delay times out tripping a lockout auxiliary relay clearing the fault and failed PCB

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3
Q

Explain the types of equipment failure that can cause an electromechanical BFR to operate (OTM 3.3-13)

A

Failure in the trip circuit (wire from protective relay? Blocking diode failure?)
Burned out trip coil
Mechanical failure
Only partial opening of one or more heads

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4
Q

What is the purpose of a BFR?

A

Breaker failure relays are used to provide local back-up protection against failure of a PCB to properly trip open when its protective relays detect a fault

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5
Q

How do we clear a faulted PCB when we use a BFR?

A

To eliminate all the possible fault paths/sources to the faulty PCB. We must eliminate all the possible sources by operating the other PCBs. This is an important concept that applies to any type of bus arrangement

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6
Q

Which side of the PCB provides the CT input for a BFR?

A

The main bus side CT. Through the PCB and out onto the line.

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7
Q

Which trip coil receives the retrip?

A

Trip Coil #1 receives the retrip. Protective relays trip to trip coil #2.

This is true for all operations in the SEL-BFR. The SEL-BFR retrip function sends an external retrip to trip coil #1 for a protective relay trip. It also sends an instantaneous retrip to trip coil #1 for a control switch trip or supervisory control trip

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8
Q

What are the two types of Lockout relay schemes for a BFR operation on a ring bus or breaker and 1/2?

A

Line LOR and PCB LOR

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9
Q

What relays use auto isolation?

A

SEL-BFR and the SEL-352

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10
Q

What is auto Isolation in a SEL-BFR?

A

The SEL-BFR has the capability to confirm that a PCB has been de-energized and then open the MODs on both sides of the fail PCB. This process is known as “auto-isolation.”

The advantage of auto isolation is that the time required by DISP to restore the power system to service is greatly reduced. Any buses or transmission line that were cleared to isolate the failed PCB can be restored to service in minutes. Without this capability, outages could last for hours until a substation operator can reach the substation and open the disconnects to the failed PCB.

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11
Q

How does the Auto Isolation Scheme work on a SEL-BFR?

A

BFR isolation logic (auto isolation scheme). The BFR relay provides a trip command to open the isolating MOD’s if a dead line is detected (no current detected through the breaker) it then allows the BFR LOR’s to reset.
MOD operate current: this setting is the overcurrent element that is used to supervise the tripping of the MOD’s if the current through he breaker is less that “50MD” then the MOD trip logic is enabled (this value should be set as Lowe as possible to prevent opening MOD’s under load. Setting: 50MD =0.1A)

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12
Q

What are the 4 uses for pending failure on the SEL-BFR?

A
  1. Fail to trip for load or line charging current
  2. Flashover protection of the PCB, current through an open breaker
  3. Current unbalance on close, fail to close (phase discordance)
  4. Thermal protection (closing resistors remain inserted), undesired current flow through a closing resistor
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13
Q

What re some common output for the A1-A5 programmable output of the SEL-BFR?

A
  1. Pending failure trip and alarm
  2. MOD trip
  3. LOR reset
  4. BFR failure alarm
  5. Failure to isolate alarm
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14
Q

What is the SEL-BFR MCS?

A

It is the Maintenance Cutout Switch

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15
Q

Types of breaker differential installation

A

SEL-587 with SEL-BFR on 500KV
•SEL-587 acts as diff only
•both trip in parallel directly to the LOR
•Independant tripping, no redundancy

SEL-587 with SEL-352 on 500KV
•SEL-587 acts as diff only
•SEL-587 trips to the SEL-352 which then trips to the LOR
•no independent trip so when 352 is c/o both are

SEL-787 with SEL-352 on 500KV
•SEL-787 is diff and backup BFR
•B/U function only enabled when 352 is disabled
•787 BFR function is basic, 3-pole only no staggered/PoW operation
•both trip in parallel direct to LOR

SEL-787 on 230KV
•acts as both differential and BFR
•Both functions are always enabled if in service
•no redundancy for either function

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16
Q

Does the BE1-50BF have a retrip?

A

Yes, if the PCB has two trip coils. The retrip will occur anytime the contact sensing input is activated.

17
Q

What doe the BE1-50BF targets stand for?

A

BF1, BF2, Inst.
The INST indicate a retrip has occurred. The BF1 and BF2 are trip outputs. We usually only have 1 trip output on BF1 but if there is an output to 2 separate LORs then you would have a target for BF1 and BF2.
An example would be the failure of a bus sectionaling breaker where we would need to trip 2 LOR’s to isolate a faulty PCB.

18
Q

What are the advanced functions of the SEL-BFR?

A

Ability to operate for load current. After a control switch trip or supervisory trip, the SEL-BFR will send an instantaneous external retrip to the opposite trip coil. It will also start timing. If the PCB does not open after 6 (OTC)/ 8 cycles the SEL-BFR will send a pending failure trip. After 16 cycles a BFR operation will occur. We can give the PCB extra time since we have load and not fault current.

19
Q

What are the additional capabilities of the SEL BFR and the SEL 352 relays over conventional BFRs

A
  • Operate for a PCB trip command from SCADA or control switch provided that line turn charging or load current is flowing through the PCB, it is not necessary to have fault current and a line reel a pickup.
  • Operate for PCB close command from SCADA or control switch provided that line charging or load current is flowing through at least one phase, no fault current is necessary.
  • Provides for automatic isolation of a failed PCB by opening the MODs adjacent to the PCB.
  • Will initiate Re-trip to PCB with two trip coils, Re-trip is sent to the opposite trip coil(TC1) from the line protective relays(TC2).
  • Will initiate re trip for single pole.
  • An added feature includes re-trip for all trip commands to the associated PCB via external relay components
20
Q

Describe the auto isolation sequence associated with an SEL BRF

A

Once the BFR LORs are tripped, fault detectors(UV relays) monitoring the station bus voltage, or voltage through the failed PCB for ring and breaker and a 1/2, see 0 volts around the PCB, close contacts that are supervising the MOD trip circuit will shut. After the MODs are open, contacts driven by the MOD operating linkage will close enabling the reset circuit on the BFR LORs

21
Q

Describe the term pending failure as it applies to SEL BFRs

A
  • An abnormal condition in the PCB that is not bad enough to warrant immediate BFR action (clearing the bus).
  • Examples; retrial, Low levels of flash overcurrent while PCB is open, Phase discordance, and undesired current flow through a closing resistor.
  • In all of these pending failure conditions, there is some time allowable before the PCB must be isolated.
  • It makes sense then to try to open this PCB first before initiating a BFR LOR trip and the energizing more circuits than necessary
22
Q

Describe the term re-trip as it applies to SEL BFRs

A

A tripping scheme that is used to re-trip a second trip coil (TC 1) in a PCB, to prevent full-blown BFR operation in the event of the original trip signals not making it to the trip coil (TC 2) .

23
Q

Describe the difference between an SEL bfr and a basilar bfr

A

The Basler BE1-50BF is a solid state relay while the SEL BFR is a microprocessor relay. Both are capable of initiating re-trip actions however the SEL BFR offers more protection than just failure to trip for fault current in the form of pending fail

24
Q

What are the inputs and outputs for the SEL BFR

A
  • Inputs; mod status, potential from PTs, current from CTs, PCB status, protective relay inputs, closed-circuit inputs from SCADA, control switch, and reclosing.
  • outputs: retail, alarm, BFR trip to lockout relay, A1-A5 programmable outputs

Sub Operations Step 4 (7 decks)

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