CHAPTER 5: SETTINGS
GROUPED ELEMENTS
F35 MULTIPLE FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
5-249
5
The negative-sequence instantaneous overcurrent element can be used as an instantaneous function with no intentional
delay or as a definite time function. The element responds to the negative-sequence current fundamental frequency
phasor magnitude (calculated from the phase currents) and applies a positive-sequence restraint for better performance:
a small portion (12.5%) of the positive-sequence current magnitude is subtracted from the negative-sequence current
magnitude when forming the operating quantity.
I
op
= |I_2| - K x |I_1| where K = 1/8
Eq. 5-21
The positive-sequence restraint allows for more sensitive settings by counterbalancing spurious negative-sequence
currents resulting from
•
System unbalances under heavy load conditions
•
Transformation errors of current transformers (CTs) during three-phase faults
•
Fault inception and switch-off transients during three-phase faults
The positive-sequence restraint must be considered when testing for pickup accuracy and response time (multiple of
pickup). The operating quantity depends on how the test currents are injected into the relay (single-phase injection:
I
op
= 0.2917 x I
injected
; three-phase injection, opposite rotation: I
op
= I
injected
).
Figure 5-133: Negative sequence IOC1 logic
5.7.8 Voltage elements
5.7.8.1 Menu
SETTINGS
GROUPED ELEMENTS
SETTING GROUP 1(6)
VOLTAGE ELEMENTS
NEG SEQ IOC1
EVENTS: Disabled
Range: Disabled, Enabled
VOLTAGE ELEMENTS
PHASE
UNDERVOLTAGE1
See below
PHASE
UNDERVOLTAGE3
PHASE
OVERVOLTAGE1
PHASE
OVERVOLTAGE3
NEUTRAL OV1
