Thermal Elements - GE 845 Instruction Manual

CHAPTER 6: METERING

Thermal Elements

Tap Changer
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
Where:
I = (I + I + I )/3 is the actual average phase current (W(1/2) Average Ph Current) for the
avg a b c
corresponding winding.
I , I , I are magnitudes of the corresponding actual phase currents of the winding.
a b c
V is the rated phase to phase nameplate voltage for the corresponding winding.
rated
S is the rated nameplate apparent power for the transformer.
rated
For three winding transformer the winding load and winding average phase current are
calculated as:
W(1/2/3) Load (% of rated) = √3 x I
Where:
I = (I + I + I )/3 is the actual average phase current (W(1/2/3) Average Ph Current) for
avg a b c
the corresponding winding.
I , I , I are magnitudes of the corresponding actual phase currents of the winding.
a b c
V is the rated phase to phase nameplate voltage for the corresponding winding.
rated
S is the rated nameplate apparent power for the transformer.
rated
Path:
Metering > Transformer > Thermal Elements
The calculation of all "Thermal Elements" actual values starts at the time the relay is first
powered up. Therefore, the Daily Rate Loss of Life starts accumulating in the next 24 hour
period. All records can be cleared either from the relay's keypad, or from the EnerVista 8
Series Setup PC program using the Clear Loss of Life command from the menu Records/
Clear Records.
Path:
Metering > Transformer > Tap Changer
Tap Position
Range: -19 to 39 in steps of 1, Invalid, Not Set
Ohms In 1
Range: 0 to 5100 ohms in steps of 1
Winding Voltage
Range: 0.00 to 1200000.00 kV in steps of 0.01
Delta V Above Min Tap V
Range: 0.00 to 1200000.00 kV in steps of 0.01
"Invalid" Tap Detection
An "Invalid" tap position is displayed under one of the following conditions:
• The measured analog input value is one tap step lower than the analog value
corresponding to minimum tap.
• The measured analog input value is one tap step higher than the analog value
corresponding to maximum tap.
• The detected BCD combination corresponds to a tap which is either below the
minimum, or above the maximum tap programmed in Tap Changer setup menu.
• Sudden change from valid BCD combination corresponding to a valid tap position to
another valid BCD combination corresponding to a non-sequential tap position.
(1/2/3) x V (1/2/3) x 100% / S
avg rated
TRANSFORMER
(1/2/3)
Wrated
6–7