ABB RET670 Commissioning Manual page 213
Transformer protection
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Also See for RET670:
- Applications manual (1016 pages) ,
- Commissioning manual (318 pages) ,
- Installation and commissioning manual (240 pages)
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1MRK 504 165-UUS -
Transformer protection RET670 2.2 ANSI
Commissioning manual
used. A two phase short-circuit gives a negative sequence current of a magnitude:
magnitude = (1/√3) · fault current.
5.
Increase the injected current and note the value at which the step 1 of the function
operates. Pickup signal PU_ST1 must be activated when amplitude of the negative
sequence current lies slightly above the pickup level I2-1>. Corresponding trip
signals TRST1 and TRIP is activated after the pre-set time delay has expired.
Note: Block or disable operation of step 2 when testing step 1 if the injected current
activates the step 2.
6.
Decrease the current slowly and note the reset value.
7.
Connect a trip output contact to a timer.
8.
Set the current to 200 % of the pickup level of the step 1, switch on the current and
check the definite time delay for trip signals TRST1 and TRIP. Once the measured
negative sequence current exceeds the set pickup level I2-1>, the settable definite
timer t1 starts to count and trip signals is released after the set time delay has elapsed.
The same test must be carried out to check the accuracy of definite time delay for
ALARM signal.
Note: The output ALARM is operated by PICKUP signal.
9.
If inverse time is selected the trip signals TRST1 and TRIP operates after a time
corresponding to the formula:
This means that if current jumps from 0 to 2 times pickup and negative sequence
capability value of generator K1 is set to 10 sec and current pickup level I2-1> is set
to 10% of rated generator current, then TRST1 and TRIP signals operates at time
equal to 250 s ± tolerance.
10. Repeat the above-described tests for the step 2 of the function excluding the inverse
time testing.
11. Finally check that pickup and trip information is stored in the event menu.
Example
CTprim
CT
sec
The CT ratios
for all three phases is 1000 A, IBase is 1000 A, and the following
secondary currents are applied:
IA
IB
IC
Testing functionality by secondary injection
1
I
2 1
− >
100
[ ]
t s
=
(
Multiple of Pickup
Ampl = 1.1 A
Ampl = 0.6 A
Ampl = 1.3 A
Section 11
2
⋅ ⋅ K
2
)
Angl = 15 deg
Angl = 97 deg
Angl = -135 deg
207
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