6kv and above, indicated by the red area on GD meter
Ungrounded phase to ground voltage
2.77kv
BØ shows zero, AØ/CØ shows 4.8kv
Conventional Ground
AØ shows 1kv, BØ/CØ shows 4kv
Partial AØ Ground - AØ conductor is connected to Ground through some impedance
True/False
I High Voltage Ground may have more than one phase at 6kv or above
True
With a High Voltage Ground, the grounded phase or phases cannot always be determined by .
metering
BØ phase GD reads zero, AØ and CØ GD reads 2.77kv
Blown BØ GD fuse
True/False
If the GDs on all three phases read zero, than the fuses on all three phases are blown
False - could also be a High Voltage Ground or Unusually High voltage Ground and needs to be investigated
True/False
In Package Style Stations, Reset the ground alarm at the banks when the GD meters read normal to clear old alarms
True
In Package Style Stations, the is blocked on all units with grounded circuits
automatic transfer switch (ATS)
In Package Style Stations, what prevents the feeder circuit breakers (CB) from reclosing
Blocking the ATS
In Package Style Stations, the auto reclosers (AR) are blocked on all units with , if available
grounded circuits
True/False
In Package Style Stations, the bank load ratio controllers (LRC) are blocked on neutral on both banks in the position (one bank is the grounded bank, and one bank is ungrounded)
True
Paralleling banks during a ground condition will sometimes change conventional grounds into or grounds
high voltage, unusually hazardous high voltage
True/False
During a Conventional Ground Search in a Non-Package Station, Auto Reclosers (AR) are to be blocked on all feeder circuits
True
During a Conventional Ground in a Non-Package Station, test only those circuits being supplied from the affected
for grounds
4.8-kV bus
What equipment cannot be tested in a 4.8kv ground search
4.8kv Ground Detectors, 4.8kv cables, Banks
What do you do is the Bank is suspected of being grounded
Notify the LD and obtain a Work Authority for testing and analysis of equipment.
Contact the ACO so the ESM may be advised of the suspected grounded equipment.
What do you do if Station Service is grounded
Contact the LD
Contact the ACO to have ESM begin repairs and/or supply a portable generator so critical Station service load may be supplied
True/False
An intermittent conventional ground is not searched
True
True/False
Intermittent and High Voltage and Unusually High Voltage grounds are searched as though they are not intermittent if the ground indications are stable enough to draw conclusion from switching
True
True/False
A multiple ground condition may be indicated when, after a circuit is dropped, a ground is still indicated, but with different voltage reads
True
What do you do if multiple grounds exist
Stop the ground search and notify the Load Dispatcher and Electric Trouble Dispatcher (ETD).
True/False
Do not parallel banks if multiple grounds exist, whether on the same phase or not. If the grounds are on different phases, paralleling the banks will usually cause a short circuit
True
What is the basic insulation level (BIL) for 4.8-kV equipment
7.2-kV for older equipment, or 15-kV for newer equipment
What is the biggest safety risk regarding High Voltages grounds
Phase-to-ground voltages may exceed the voltage rating of insulators and bushings, which presents an extreme safety risk
because a flashover may occur at the weakest point of insulation
What should you do upon identifying a High Voltage Ground
Notify the Electric Trouble Dispatcher (ETD) as soon as possible, in order to alert the field crews about the hazardous condition
True/Fasle
During a high voltage ground search, leave de-energized any feeder that reduces or eliminates the ground condition. These feeders are tested only on the orders of the LD
True
If upon de-energizing a feeder, the high voltage ground
becomes a , the high voltage ground
search is continued until all grounds have cleared
conventional ground
What should be reported and to whom during a High Voltage Ground Search
ETD and the LD
Report which feeders cleared or reduced the high voltage
ground indication
Report the results of the testing of feeder positions
True/False
In an Usually High Voltage Ground situation, if there are more feeders that caused a conventional ground than there are separate, ungrounded sources, contact the LD for restoration instructions
True
During a conventional ground search, why must the time in which the Banks are in // be minimized as much as possible
Because of increased fault capacity
The ground condition may be worsened by paralleling banks
True/False
The Load Dispatcher (LO), ETD and the Operator must agree prior to performing any bank switching during ground searches
True
True/False
Overloads are permissible while performing a ground search using the Transfer method, but should be minimized as much as possible
True
If there was a ground on a GD or the fuse may have blown
potential transformer
A bank showing a ground on its GD meters, but the transformer itself is not grounded
Grounded Bank
A bank showing normal GD reads
Ungrounded Bank
During a conventional Ground search, If all load is transferred off the 4.8-kV bus, and the location of the ground has not been determined, what steps are necessary to determine the location of the ground
Verify that any 4.8-kV bus connected capacitors are off.
Supply the bus or bus section with the load transferred off from an ungrounded source.
If the previously ungrounded bank becomes grounded, then the ground is on the 4.8-kV bus or bus section
What is one of the issues with an ungrounded system
A high-voltage condition. This can be caused by the traditional theory on ferroresonance, or by a DC offset transient overvoltage due to re-striking (arcing grounds) or intermittent ground faults
When the inductive impedance (such as in the Distribution Bank) equals the capacitive impedance of the system (feeders).
ferroresonance
An arcing ground on the system.
DC offset high voltage condition
The persistence of the arc due to the flow of capacitive current causes a condition known as "" in which cyclic charging and discharging of the system capacitance though
the fault results in high frequency oscillations being superimposed on the whole system and a buildup of very
high voltages can occur.
arcing ground
voltages are practically unchanged whereas are dramatically affected due to shifting of the ungrounded neutral with respect to ground
Phase-to-phase, phase-to-ground voltages
One phase connected to ground does not cause the circuit to relay because of the Department's closed delta system
ungrounded
A ground where the meter for the grounded phase
reads zero or close to zero, and the meters for the other two phases read between 4.8-kV and 6.0-kV, usually close to 4.8-kV
conventional ground
SAS
Substation Automation System (SAS).
What are causes a false ground alarm
Blown Fuses
Bank carrying little to no load
Nature of Field Load (stations with ungrounded feeders
What may be the cause of a Partial Grd
A partial ground may be caused by the grounded phase having a high resistance to ground
A partial ground may be caused by more than one ground on the same phase, one of which is a partial ground
A ground that moves from one phase to another phase.
Intermittent grounds
True/False
Any ground condition can appear as an intermittent ground
True
What can casue conventional grounds to turn into high voltage grounds
3.11.3.1. Ferroresonance or DC transient overvoltage conditions.
3.11.3.2. Trouble in the station and/or field.
3.11.3.3. Station and or field switching
Unusual station conditions that identify an unusually hazardous high voltage ground are indicated by one or more GD meters reading over 6-kV and one or more of the following conditions
3.11.3.1. Ferroresonance or DC transient overvoltage conditions (arcing grounds).
3.11.3.2. Trouble in the station and/or field.
3.11.3.3. Station and or field switching
True/False
The Operator may isolate the failed equipment before notifying
the LD and requesting a Work Authority
True
True/False
Any Power System employee can declare an emergency and
request a feeder to be de-energized immediately
True
Why are capacitors taken off during a 5kv ground search
The capacitors are taken off to reduce ferroresonance and high voltage conditions
True/False
Separate banks that are in parallel, such as in Gas Co. style stations, or stations where two banks normally supply one 4.8-kV bus
