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What is WPP? Where is it used?
Worker Protection Practices (WPP) are the collective policy, rules, and requirements that apply to all work performed on equipment in Integrated Generation facilities for which hazardous sources of energy must be isolated and locked out for worker safety.
How are PSSP/WPP boundaries identified?
PSSP/WPP boundaries will be identified on the station one-line diagram with a dotted line and defined in a joint local operating order.
Who holds Operating Authority for the PSSP equipment at Integrated Generating Stations?
BCH T&D Control Center.
Who holds Operating Authority for the WPP equipment at Integrated Generating Stations?
Generation staff at site.
What is the procedure for establishing work protection for equipment identified on the station one-Line, located on the WPP side of the WPP/PSSP Boundary? Give an example.
the Operator at the Control Center will assign Operating Responsibility up to and including the appropriate one-line perimeter isolating devices
without directing the switching of the electrical isolating devices to an authorized category “D” worker on site.
- • On-site worker then assumes the role of PIC. The WPP PIC will open and lock the perimeter one-line isolating devices as required.
- • record in the official logs at both the Control Center and the Generating facility.
- • The Operator at the Control Center will tag each perimeter device “Operating Responsibility Assigned”.
- • Prior to returning Operating Responsibility, returning the equipment to service, or conducting on-line testing, the WPP PIC must consult with the Control Center Operator.
- • When returning Operating Responsibility, the on-site worker must inform the Operator of the status of each device in the assigned zone.
- • Perimeter isolating devices are to be returned in normal operating position if possible to do so.
- • Upon return of O/R, the official log will be updated
- - In the case of generating unit equipment, one-line perimeter isolating device is the unit isolating disconnect.
- - It is implied that all specific hydraulic or fuel control devices are included in the Operating Responsibility.
- - The Operating Responsibility will be described as the zone bounded by the one-line perimeter electrical isolating device.
Example: “RUS G3 UTAI 60DCB4” for work on Ruskin G3.
What are the two acceptable methods for work on equipment in the WPP area that requires isolation in the PSSP area? Give an example of each explaining when each would be used?
- Using GOI procedures:
- • The Control Centre PIC can issue a Guarantee of Isolation (GOI) to the WPP PIC on the PSSP area isolating device.
- Using Transfer of Operating Authority procedures:
- • If the PSSP isolation device is within the generation switchyard then the Operator at the Control Center can transfer Operating Authority up to and including the isolating device in the switchyard to a worker on site authorized to category “D” using the procedures in Appendix II of 1J-18. The on-site worker then assumes the role of the PIC and is responsible for establishing work protection according to WPP procedures.
Example: ALU 60WT2, “60WT2 UTAI 60D1 AND 60D28” would use a GOI since 60D28 is not within the WPP boundary.
CMS EG1, “EG1 UTAI 0_4D51 AND 2D3” would use a transfer of Operating Authority since 0_4D51 and 2D3 is within the WPP boundary.
What are the two acceptable methods for work on equipment in the PSSP area that requires isolation in the WPP area? Give an example of each explaining when each would be used?
- Using PSSP procedures:
- • The WPP PIC can issue a GOI to the Control Center PIC on the WPP area isolating devices, following receipt of Operating Responsibility. The work can then be done using PSSP procedures.
- Using WPP procedures:
- • If the PSSP isolation device is within the generation switchyard then the Operator at the Control Center can transfer Operating Authority to a worker on site using the procedures in 1J-18 Appendix II. The on-site worker will then assume the role of the PIC and is responsible for establishing work protection according to standard WPP procedures.
- • If a GOI is required on remote PSSP area isolating devices to perform this work then it can be issued by the Operator at the Control Centre using GOI procedures.
- Example: ABN 60CB1, “60CB1 UTAI 60DCB1 AND 60D1” would use a transfer of Operating Authority because the PSSP device (60CB1) is within the WPP boundary.
- SHU 25SA51, “25SA51 UTAI 25D251 AND 25D251” would use a GOI since the PSSP device (25SA51) is not within the WPP boundary.
Who retains Operating Authority for SPN NPRF facilities?
CBG (Columbia Basin Generation) has Operating Authority and Operating Responsibility for SPN NPRF.
Who retains Operating Authority for SEV NPRF facilities?
CBG (Columbia Basin Generation) has Operating Authority for SPN NRF. BCH T&D has Operating Responsibility for SEV NPRF.
What is the process for assigning Operating Responsibility to a category “D” authorized worker for SEV SPOG01?
- The Operator at the Control Centre will assign Operating Responsibility for SEV SPOG01 without directing the switching of the electrical isolating devices to an authorized category “D” worker on site.
- The on-site worker will then assume the role of PIC.
Who retains Operating Authority of station service facilities at BC Hydro integrated generating stations?
the generation region.
What is the procedure for assigning Operating Responsibility of station service facilities at generating stations?
Operator assigns Operating Responsibility UTAI the appropriate one-line perimeter isolating device to an authorized Cat D worker on site.
The on-site worker will then assume the role of PIC. The WPP PIC will open and lock the perimeter one-line isolating device as required.
What is the process for assigning Operating Responsibility to a category “D” authorized worker for work on JOR SS1?
The Control Center will assign Operating Responsibility of “SSI UTAI 25DSS1”. The on-site worker will then assume the role of PIC. The WPP PIC will open and lock the perimeter one-line isolating devices as required.
What is the purpose of protection?
- Protection does not prevent disturbances, rather it reacts to them after they have occurred.
- The purpose of protection is to detect faults and remove them from the system before they pull the entire system down. They do so by removing the smallest portion of the faulted system possible by clearing with fault removal devices (circuit breakers).
What is the difference between a protection system and a protection scheme?
- Protection System: Each individual protective arrangement which individually protects against a certain risk.
- Protection Scheme: Coordinated combination of protection systems.
With regards to protective relaying, what is meant by the term – Selectivity?
Selectivity: Only a minimum portion of the power system should be disconnected to isolate a fault.
With regards to protective relaying, what is meant by the term – Security?
Security: Schemes must be able to discriminate between signals which require action, and those that do not.
With regards to protective relaying, what is meant by the term – Reliability?
Reliability: Ability to operate without failure whenever a fault or abnormal condition exists.
With regards to protective relaying, what is meant by the term – Coordination?
Coordination: Schemes must relate to each other so they operate in the right order.
Provide two reasons why two sets of redundant protection are used on a piece of equipment. What are they named?
- Using two sets of redundant protection achieves:
- 1. Increased dependability
- 2. One protection may be removed from service for maintenance and the equipment will remain protected.
- They are called primary protection and standby protection.
Typically in a fault condition, current will __ while voltage ____.
current will rise while voltage falls
What are the two main reasons for utilizing instrument transformers?
- Instrument transformers
- 1. Provide useable quantities of voltage and current for metering and control.
- 2. Provide useable quantities of voltage and current for protection relays.
What is a VT? What purpose does it serve? What is its typical output?
- Voltage transformer (VT) provides relays, meters and control circuits with a low value of voltage proportional to system voltage.
- 120V is the typical standard secondary rating (output) of a VT.
What is a CT? What purpose does it serve? What is its typical output?
- Current transformer (CT) provides relays, meters and control circuits with a low value of current proportional to system current.
- 5A is the standard secondary rating (output) of a CT.
If a CT has a ratio of 2000:5, what is the primary current if the secondary current is 2.5 amps?
Primary current = 2.5A * 400 = 1000A
With respect to a CT, what is burden? How does exceeding the burden impact the operation of a CT?
- Burden (ohm) is the amount of load connected to the secondary of the CT.
- If the burden is exceeded, the CT saturates and can no longer accurately reflect system current.
With respect to a VT, can the secondaries be opened with the VT energized? Explain any consequences.
VT’s may have their secondaries open circuited (no burden on VT). The only consequence is for the protective relays utilizing the voltage reading from the VT.
With respect to a CT, can the secondaries be opened with the CT energized? Explain any consequences.
The secondaries of a CT must never be open circuited (no burden on CT). Extremely high open circuit secondary voltages may result.
What is a protection zone? How is it typically defined?
- A protection zone is the section of the power system that a particular protection covers.
- It is typically defined by the location of the CT’s.
What is a tripping zone? How is it typically defined?
A tripping zone is the section of the power system that is tripped by protection. It is determined by the circuit breaker locations.
With respect to protection, what is meant by the term overlap?
To prevent the possibility of unprotected area and to provide backup, protection zones are overlapped.
What is breaker fail protection?
Breaker fail protection operates to trip the adjacent zone if the circuit breaker protecting the faulted zone fails to open. Breaker fail protection initiates tripping if fault current is still flowing through the breaker after a time elapses following the protection zone operation.
What is the purpose of relay targets?
Relay targets are included in protective relay systems in order to provide a record of their operation.
They can be flags that must be reset or LEDs on the front of the replay.
What are symmetrical components? What is meant by positive sequence? What is meant by negative sequence? What is meant by zero sequence?
- Symmetrical components are commonly used for analysis of three-phase electrical power systems. If the phase quantities are expressed in phasor notation using complex numbers, a vector can be formed for the three phase quantities.
- Positive sequence means the current and voltage has a positive phase rotation (A,B,C). Each phase is equal in magnitude with a 120° angle between them. Under balanced conditions only positive sequence exists.
- Negative sequence may exist in addition to positive if conditions are unbalanced due to unbalanced loads or a fault. Unbalanced load or fault produces unbalanced currents which produces unbalanced voltages. Negative sequence voltages and currents are similar to positive except the rotation is negative (A,C,B).
- Zero sequence exists when conditions are unbalanced and there is a path to ground. Positive, negative, and zero sequences will exist. Zero sequences have phase quantities with equal magnitude and phase.
What two relays are used to detect stator phase to ground faults?
- Zero-sequence overvoltage relays
- Third harmonic voltage differential relays
What relay is used to detect stator phase to phase faults?
Differential relays (87) are used to detect phase to phase faults.
With respect to overspeed of an electrical generator, how is the unit protected?
Overspeed tripping (12) is provided by centrifugal speed switches or permanent magnet generator and initiates a trip of the generator to bring the unit to speed no load should the governor fail to limit the overspeed.
With respect to motoring of an electrical generator, how is the unit protected? Are there any exceptions?
A reverse power relay (32) is used to detect power flow into the generator and initiate tripping. This relay is blocked if the unit is running in synchronous condense mode.
Non-Lockout Partial Shutdown to SNL With Overspeed
Operates for conditions external to machine and will be removed once unit transformer is opened. Also operates when the transformer breaker may be accidentally tripped.
- The relay:
- Preforms non-lockout trip of breaker
- trip field breaker
- bring machine to SNL (unit is to be shut down)
- 5A is operated by:
- pole slip detector
- stator overvoltage
- negative sequence overcurrent
Non-Lockout Partial Shutdown to SNL Without Overspeed
Shuts down the unit but the unit transformer breaker is not locked out. Unit can be started and put back into service.
- The realy:
- Initiate 10-second gate closure
- Perform non-lockout trip of breaker when gates pass the SNL position
- Field shutdown by field gating when machine gates reach teh SNL position (field breaker does not trip)
- 5B is operated by:
- Incomplete starting sequence
- Electrical switch
Non-Lockout Unload Trip Without Overspeed
Intended for non-urgent tripping, which allows slow unloading of the machine to permit load transfer to other machines. The machine is separated from the system but not shut down. To bring the machine from full load to SNL requires ~30 seconds.
- The relay:
- slowly unloads the machine to SNL, and then trips the unit breaker (non-lockout)
- 5C is operated by:
- Stator over temperature device 42G
- Reverse power relay device 32G
Normal Lockout Shutdown
Protection tripping for conditions that require maintanence but do not require emergency shutdown.
- The relay
- Initiates 10-second gate closure
- Lock out trip when gates pass the SNL position
- Inhibit field gating (field breaker does not trip) upon tripping of the unit breaker
- 86N is operated by:
- Loss of field protection and timer
- Stator guard protection
- Field overtemperature
- Neutal resistor overtemperature
- Field ground protector
- Shaft vibration
- Intake gate drop
- Bearing overtemperature
- Turbing bearing oil level
- Governor sump tank oil level
- Governor pressure tank oil level
- Governor pressure tank oil pressure
- Actuator lock with overspeed
Generator Primary Lockout Shutdown
Initiates fastest possible shutdown of the machine. Operated only when the primary relay detects a major internal failure within the machine.
- The relay:
- Lockout trip breaker
- Trip the unit field breaker
- Initiate 10-second gate closure
- Initiate the fire protection (water spray) if fire detection equipment has operated
- 86G is operated by:
- Primary generator differential
- Split-phase protection
Generator Standby Lockout Shutdown
The same as 86G, except fire protection is not required.
- 86GS is operated by:
- Exciter transformer overcurrent
- Exciter transformer overtemperature
- Loss-of-field with undervoltage
- Breaker failure protection
- Control power failure
- Fire protection power failure
- Incomplete field flashing sequence
- Cooling fan failure
- Mechanical overspeed
- Emergency shutdown push-button