CH-ES 30-32.20 E
ABB Switzerland Ltd
02-07-02
1/3
DEMANDS ON MEASURING TRANSFORMERS FOR GENERATOR- Version 3.01
DIFFERENTIAL-PROTECTION FOR REG 316 / REG 316*4 / REG 216 and higher
Introduction
The operation of any generator differential protection is influenced by distortion in
the measuring quantities. The current to the protection will be heavily distorted
when the current transformer is saturated.In most cases it is not possible to avoid
current transformer saturation for all fault conditions, therefore measures are
taken in the generator differential protections to allow for current transformer
saturation with maintained proper operation. REG 316 / REG 316*4 / REG 216
can allow for heavy current transformer saturation but not an unlimited one.
For transformer differential protection see document CH-ES 30-32.10 E for
RET 316 / RET 316*4.
Requirements on current transformers
Choice of current transformers
The current transformer should be to type TPS,TPX or TPY with accuracy class
5P20 or better. The use of the linearized current transformer type TPZ leads only
to a small phase angle shift and they can be used without problems, if the same
type is on both sides of the generator. Possibly ABB Switzerland Ltd, Utility Auto-
mation
can be contacted for confirmation that the actual type can be used.
The current transformer ratio should be selected so, that the current to the
protection is larger than the minimum operating value for all faults that shall be
detected. Minimum operating current for the generator differential protection in
REG 316 / REG 316*4 / REG 216 is 10% of nominal current.
Conditions for the CT requirements
The requirements for REG 316 / REG 316*4 / REG 216 are a result of investigations
performed in our network simulation program. The tests have been performed with
a digital current transformer model.
The setting of the current transformer model was representative for current trans-
formers type TPX and TPY.
The performance of the generator differential protection was checked for internal
and external both symmetrical and fully asymmetrical fault currents. A source with
a time constant from 40 up to 300 milliseconds was used at the tests. The current
requirements below are thus applicable both
for symmetrical and asymmetrical fault
currents.
Both phase to ground, and three phase faults were tested.
Released: Department:
UTAST
Rev.: B
To Next Page
Loading...
